© Author(s) 2021. CC Atribution 4.0 License The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) Sesljanski prelom in sesljanska upogibna cona Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC Geološki zavod Slovenije, Dimičeva ul. 14, SI-1000 Ljubljana, Slovenija; e-mail: ladislav.placer@telemach.net; petra.jamsek-rupnik@geo-zs.si; Prejeto / Received 27. 9. 2021; Sprejeto / Accepted 24.11. 2021; Objavljeno na spletu / Published online 28. 12. 2021 Key words: Sistiana Fault, Sistiana Bending Zone, adjusting fault, Adria Microplate, Gulf of Trieste Ključne besede: Sesljanski prelom, sesljanska upogibna cona, izravnalni prelom, Jadranska mikroplošča, Tržaški zaliv Abstract The Sistiana Fault is an alleged disjunctive deformation of Microadria in the sea bottom of the Gulf of Trieste. Onshore, it is visible only in the Sistiana Bay, but towards the northeast it soon pinches-out, in structural- geometric terms it diminishes soon after the crossing of the thrust boundary of the Dinarides, or the Istrian- Friuli Underthrustig Zone, respectively. Further to the northeast, only the bending zone is developed in the External Dinarides, which stretches all the way from the Sistiana Bay to the Idrija-Žiri area. We named it the Sistiana Bending Zone. Its direction can be determined based on geological maps and is around 60°, so we conclude that the Sistiana Fault should extend approximately in this direction. In the bending zone, the Trieste-Komen Anticlinorium, the Vipava Synclinorium, the Trnovo Nappe opposite to the Hrušica Nappe and the Raša and Idrija Faults are laterally bent. The size of the bend is the largest in the Sistiana Bay, and in the east-northeast direction it decreases linearly. The general geological circumstances suggest that the Sistiana Fault has not been recently active. Izvleček Sesljanski prelom je domnevna disjunktivna deformacija Mikroadrije v podmorju Tržaškega zaliva. Na površju je viden le v Sesljanskem zalivu, vendar se proti severovzhodu kmalu izklini, v strukturno-geometrijskem smislu izzveni kmalu zatem, ko preseka narivno mejo Dinaridov, oziroma istrsko-furlansko podrivno cono. Naprej proti severovzhodu je v Zunanjih Dinaridih razvita le še upogibna cona, ki se vleče vse od Sesljanskega zaliva do idrijsko-žirovskega ozemlja. Imenujemo jo sesljanska upogibna cona. Njena smer je določljiva na podlagi podatkov geoloških kart in znaša okoli 60°, zato sklepamo, da naj bi Sesljanski prelom potekal približno v tej smeri. V upogibni coni so bočno upognjeni Tržaško-Komenski antiklinorij, Vipavski sinklinorij, Trnovski pokrov nasproti Hrušiškemu pokrovu ter Raški in Idrijski prelom. Velikost upogiba je največja v Sesljanskem zalivu, proti vzhodu-severovzhodu pa se linearno manjša. Iz splošne geološke slike izhaja domneva, da Sesljanski prelom recentno ni aktiven. GEOLOGIJA 64/2, 221-252, Ljubljana 2021 https://doi.org/10.5474/geologija.2021.013 Introduction The plicative and disjunctive structures in the northwestern part of the External Dinarides in the hinterland of the Gulf of Trieste and Istra Peninsula are curved in the northwest direction (Fig. 1). This deformation was the result of the movement of the Adria Microplate Structural Block (Microadria) between the left-lateral strike- slip Sistiana Fault and the right-lateral strike-slip Kvarner Fault toward the Dinarides (Placer et al., 2010). This structural block was called the Istra Block, while the vast deformed hinterland area of Uvod V severozahodnem delu Zunanjih Dinaridov so plikativne in disjunktivne strukture v zaled- ju Tržaškega zaliva in polotoka Istre izbočene proti severovzhodu (sl. 1). Po Placerju in sode- lavcih (2010) je deformacijo povzročilo premika- nje strukturnega bloka Jadranske mikroplošče (Mikroadrije) med Sesljanskim in Kvarnerskim prelomom proti Dinaridom. Prvi naj bi bil le- vozmični, drugi desnozmični. Blok so poimeno- vali istrski blok, obsežno deformirano območje Dinaridov v zaledju pa istrsko potisno območje. 222 Fig. 1. Istra Pushed Area. Sl. 1. Istrsko potisno območje. 1 Fault: proven, inferred / prelom: ugotovljen, domneven 2 Relative direction of the fault block displacement / relativna smer premika prelomnega krila 3 SF – Sistiana Fault / Sesljanski prelom, KF – Kvarner Fault / Kvarnerski prelom 4 Laterally bent structures of Dinarides / bočno upognjene strukture Dinaridov 5 Approximate boundaries of the Istra Pushed Area effects / približna meja vidnih učinkov istrskega potisnega območja Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 223The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) the Dinarides was named the Istra Pushed Area. While the exact direction of the block’s movement has not yet been established, it could be assumed, in view of the recent orientation of Microadria, that the block traveled in a northeasterly to east- erly direction. While this was a multiphase event, details of the exact timing of such have not yet been determined. Northwest of the Sistiana Fault, along with the Istra Block, also the Friuli Block was displaced toward the Dinarides, but not to such an extent as the Istra Block, owing to the geometry of the dis- placements. Consequently, the Istra Block was the northeastern-most displaced part of Microadria. The theory of underthrusting and pushing against the Dinarides (Placer et al., 2010) is based on analysis of existing geological maps and field investigations. The Čičarija and Trieste-Komen Anticlinorioum formed mainly as the result of Dinaric thrusting, while its lateral deformation developed later, definitely during the pushing of the Istra Block against the Dinarides. Under- thrusting was the extreme expression and conse- quence of these movements, while the entire area experienced a multiphase contraction in the form of folding and displacements along secondary re- verse faults. Blašković & Aljinović (1981) and Blašković (1991) already discussed this pushing toward the Dinarides in the Istra and Kvarner areas. Carulli & Cucchi (1991) first described the Sistiana Fault in the Sistiana Bay northwest of Trieste. Later, different aspects of it were investigated by Carul- li (2006, 2011), Busetti et al. (2010), Placer et al. (2010), Cucchi & Piano (2013), Placer (2015) and others. It was discovered that it pinches out after a few kilometers from the shore inland, in the NE direction, while in the offshore direction it contin- ues below the sea-bottom towards the southwest. In the northeast, in the direction of the fault’s ap- parent continuation, there are laterally-bent Di- naric structures. Their axis of bending could be approximately determined, therefore Placer et al. (2010, Fig. 27) introduced the term Sistiana Zone and established its direction. Displacements along the Sistiana Fault were determined as a left-lat- eral strike-slip based on the position of the bent structures. In eastern Istria, opposite the Sistiana Zone, we find bent structures in a mirrored configura- tion that are probably connected with the sup- posed Kvarner Fault in the SSW-NNE direction. The direction and position of the bent structures can be determined in the same way as they can for the Sistiana Zone, although the axis of bending is Natančnejša smer premika bloka še ni določena, vsekakor pa se je, glede na današnjo orientaci- jo Mikroadrije, pomaknil proti severovzhodu do vzhodu. Dogajanje je bilo večfazno, pričetek še ni natančneje ugotovljen. Poleg istrskega bloka naj bi bil proti Dinari- dom pomaknjen tudi furlanski blok severozaho- dno od Sesljanskega preloma, vendar je zaradi geometrije premikov istrski blok najbolj proti se- verovzhodu potisnjeni del tega dela Mikroadrije. Ideja o podrivanju in potiskanju proti Dinari- dom (Placer et al., 2010) je utemeljena na analizi podatkov geoloških kart in terenskega opazova- nja. Čičarijski in Tržaško-Komenski antiklinorij sta v glavnem nastala pri narivanju Dinaridov, njuna bočna deformacija pa je nastala pozneje, vsekakor pri potiskanju istrskega bloka proti Dinaridom. Pri tem se je v najbolj ekstremnih primerih uveljavilo podrivanje, na celotnem ob- močju pa stiskanje prostora v obliki gubanja in premikov ob sekundarnih reverznih prelomih. Dogajanje je bilo večfazno. O strukturah potiskanja proti Dinaridom na območju Istre in Kvarnerja sta pisala že Bla- šković in Aljinović (1981) in Blašković (1991). Sesljanski prelom sta v Sesljanskem zalivu, se- verozahodno od Trsta, odkrila Carulli in Cucchi (1991), pozneje so ga iz različnih vidikov obrav- navali Carulli (2006, 2011), Busetti in sodelavci (2010), Placer in sodelavci (2010), Cucchi in Piano (2013), Placer (2015) idr. Pri teh raziskavah je bilo ugotovljeno, da se od obale proti severovzhodu že po nekaj kilometrih izklini, proti jugozahodu pa naj bi se domnevno nadaljeval v podmorju Trža- škega zaliva. Na severovzhodu, kjer ni več prelo- ma, se v njegovi smeri nahajajo bočno upognjene dinarske strukture, katerih os upogiba je mogo- če približno določiti, zato so Placer in sodelavci (2010, sl. 27) uporabili izraz sesljanska cona in ji določili smer. Glede na lego upognjenih struktur, so vsi raziskovalci opredelili Sesljanski prelom kot levi zmik. Nasproti sesljanske cone ležijo v vzhodni Istri v zrcalni legi upognjene strukture, ki naj bi bile povezane z domnevnim Kvarnerskim prelomom v smeri SSW-NNE. Enako kot sesljanski coni je mogoče tudi tu upognjenim strukturam določi- ti smer in lego, vendar os upogiba tu ne leži ne- posredno v podaljšku domnevnega Kvarnerske- ga preloma. Govorimo o kvarnerski coni, ki pa je bistveno večja in kompleksnejša od sesljanske. Kvarnerski prelom ne izdanja nikjer, kot hipote- tičnega sta ga zaradi neskladja med zgradbo Istre in otoka Cresa uvedla Šikić in Polšak (1973). Po- jem Kvarnerskega preloma je potrebno razumeti 224 Fig. 2. Structural sketch of the Istra Pushed Area. Amended after Placer et al. (2010, Fig. 4). Basic data according to Basic geological map of Yugoslavia (OGK) and Carulli (2006). Sl. 2. Strukturna skica istrskega potisnega območja. Dopolnjeno po Placer et al. (2010, sl. 4). Osnovni podatki Osnovna geolo- ška karta Jugoslavije (OGK) in Carulli (2006). Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 225The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) not positioned in the continuation of the supposed Kvarner Fault. This is the Kvarner Zone, and it is significantly larger and more complex compared to the Sistiana Zone. There are no known outcrops of the Kvarner Fault. Due to the disparity between the structures of Istra and the island of Cres, it was introduced by Šikić & Polšak (1973). The term Kvarner Fault needs to be understood in the wider sense, as it could represent a fault or a wider and more complex tectonic zone of uncertain origin. In the coastal area, structures in the north- western block of the Sistiana Zone strike in the W-E direction (the northwest part of the Tri- este-Komen Anticlinorium), while in the south- eastern block of the Kvarner Zone (southeastern part of the Čičarija Anticlinorium, Cres Island), structures strike in the N-S direction. The Istra Pushed Area therefore took on a semicircular shape, which covers the frontal part of the Dinar- ides between the Southern Alps and the central Kvarner area, while in the interior its effects are visible up to the Ljubljana Basin (Placer, 2008; Placer et al., 2010, Fig. 27; Placer et al., 2921). The flexural structures associated with the Kvarner Fault occupy a far larger area than those in the extension of the Sistiana Fault. They also have a significantly more complex structure, with overprinting deformations from different evolu- tionary stages, which makes their study more dif- ficult. Therefore, the Sistiana Zone is more suita- širše, lahko da gre resnično za prelom, lahko pa za široko in kompleksno tektonsko cono nejasne geneze. Strukture v severozahodnem krilu sesljanske cone imajo v priobalnem pasu smer W-E (seve- rozahodni del Tržaško-Komenskega antiklino- rija), v jugovzhodnem krilu kvarnerske cone pa imajo smer N-S (jugovzhodni del Čičarijskega antiklinorija, otok Cres). Istrsko potisno območje ima zaradi tega polkrožno obliko, ki zajema čelni del Dinaridov med Južnimi Alpami in osrednjim Kvarnerjem, v notranjost pa sega njen vidni uči- nek nekako do Ljubljanske kotline (Placer, 2008; Placer et al., 2010, sl. 27; Placer et al., 2021). Upognjene strukture povezane s Kvarnerskim prelomom zavzemajo mnogo večji prostor kot tis- te v podaljšku Sesljanskega preloma. Imajo tudi kompleksnejšo zgradbo, kar pomeni, da se v njih prekrivajo deformacije različnih stopenj razvoja, zaradi česar je njihovo proučevanje težavnejše. Zato je sesljanska cona primernejša za pilotsko raziskavo geneze prečno upognjenih struktur Zunanjih Dinaridov. Zaradi terminološke korektnosti je izraz sesljanska cona dopolnjen z opisom tipa in smeri deformiranja, zato smo uporabili izraz sesljan- ska bočno upogibna cona, skrajšano sesljanska upogibna cona. Enako velja za kvarnersko cono, oziroma kvarnersko bočno upogibno cono, skraj- šano kvarnersko upogibno cono. Fig. 2. / Sl. 2. 1 Dinarides: External Dinaric Thrust Belt: T – Trnovo Nappe, H – Hrušica Nappe, S – Snežnik Nappe / Dinaridi: Zunanjedinarski narivni pas: T – Trnovski pokrov, H – Hrušiški pokrov, S – Snežniški pokrov 2 Dinarides: External Dinaric Imbricate Belt / Dinaridi: Zunanjedinarski narivni pas 3 Microadria: Parautochton sensu stricto / Mikroadrija: paravtohton sensu stricto 4 Microadria: Stabile core / Mikroadrija: stabilno jedro 5 Southern Alps / Južne Alpe 6 Southern Alps Thrust boundary / meja narivne cone Južnih Alp 7 External Dinaric Thrust Belt boundary / meja Zunanjedinarskega narivnega pasu 8 Boundary of the Dinarides / meja Dinaridov 9 Istra-Friuli Underthrust Zone: 1 – Črni Kal Thrust Fault, 2 – Palmanova Thrust Fault / istrsko-furlanska podrivna cona: 1 – Črnokalski narivni prelom, 2 – Palmanovski narivni prelom 10 BuF – Buje reverse Fault / Bujski reverzni prelom 11 Anticlinorium: a – axis of the Čičarija Anticlinorium, b – axis of the Ravnik Anticlinorium, c – axis of the Trieste-Komen Anticlinorium / antiklinorij: a – os Čičarijskega antiklinorija, b – os Ravenskega antiklinorija, c – os Tržaško-Komenskega antiklinorija 12 Synclinorium: d – axis of the Brkini Synclinorium, e – axis of the Vipava Synclinorium / sinklinorij, d – os Brkinskega sinklinorija, e – os Vipavskega sinklinorija 13 Important sub-vertical faults: SF – Sistiana Fault, KF – Kvarner Fault, RF – Raša Fault, IF – Idrija Fault / pomembnejši subvertikalni prelomi: SF – Sesljanski prelom, KF – Kvarnerski prelom, RF – Raški prelom, IF – Idrijski prelom 14 Microadria structural block: A – Istra Block (A1 – South Istra Structural Wedge, A2 – North Istra Structural Wedge), B – Friuli Block / strukturni blok Mikroadrije: A – istrski blok (A1 - južnoistrski strukturni klin, A2 – severnoistrski strukturni klin), B – furlanski blok 15 Relative displacement direction / relativna smer premika 16 Cargnacco 1 borehole / vrtina Cargnacco 1 17 Koromačno Bay / zaliv Koromačno 226 ble for the pilot investigations of the transversely bent structures of the External Dinarides. In order to apply a correct and common ter- minology, the term Sistiana Zone is supplement- ed with a description of the type and direction of deformation, which is why we have used the term Sistiana Lateral Bending Zone, abbreviated as Sistiana Bending Zone. The same applies for the Kvarner Zone, or the Kvarner Lateral Bending Zone, abbreviated as Kvarner Bending Zone. The tectonic push also resulted in the under- thrusting of the Istra-Friuli Underthrust Zone, which is strongly emphasized on the northeastern boundary of the Istrian Block, but is significantly weaker in the Friuli Block. The structural sketch of the Istra Pushed Area (Fig. 2) is simplified and amended after Placer et al. (2010, Fig. 4). The Southern Alps are separated, but internally remain undivided. The Dinarides are divided in the context of the thrust structure into the External Dinaric Thrust Belt and the Ex- ternal Dinaric Imbricate Belt. Microadria is divid- ed into the imbricated edge of the autochthone or parautochtone sensu stricto and autochthone. The boundary between both units is the Buje Reverse Fault (BuF). The Istra Block is denominated with A, and the Friuli Block with B. The Istra Block is further subdivided into two structural wedges, namely the South Istrian (A1) and the North Istri- an (A2) Structural Wedge. The Istra-Friuli Underthrust Zone is segment- ed: the central fault structures in the zone are the Črni Kal and Palmanova thrust faults. The first can be ascribed to the Učka Thrust, while second the can be traced also northwest from the Sistiana Fault based on deep borehole data and geophysi- cal sounding (Nicolich et al., 2004, Tavola 1, Tav- ola 2; Carulli, 2006). The Istra-Friuli Underthrust Zone stretches to the Kvarner Fault in the south- eastern direction. According to the field investi- gations, the Istra-Friuli Underthrust Zone is the most tectonically deformed at the tip of the South Istra Structural Wedge. Available data from the Cargnacco 1 borehole well south of Udine (Ven- turini, 2002) and from the last visible outcrop of the Dinarides thrust boundary in Koromačno on the eastern coast of Istra point (Fig. 2) to the pro- portionally lesser tectonic deformation. It is clear from the general structural sketch of the Istra Pushed Area that the deformations of underthrusting and pushing due to the activity of the Microadria are most pronounced in the ex- tension of the axis of the South Istrian Structural Wedge, where the Čičarija Anticlinorium and the Brkini Synclinorium are bent due to lateral push Posledica potiskanja v istrsko-furlanski pod- rivni coni je bilo tudi podrivanje, ki je močno po- udarjeno na severovzhodni meji istrskega bloka, bistveno šibkeje pa v furlanskem bloku. Strukturna skica istrskega potisnega obmo- čja na sliki 2 je povzeta po Placerju in sodelavcih (2010, sl. 4) ter poenostavljena in dopolnjena. Juž- ne Alpe so ločene toda nerazčlenjene, Dinaridi so razčlenjeni v smislu narivne zgradbe na Zuna- njedinarski narivni pas in Zunanjedinarski na- luskani pas, Mikroadrija je razdeljena na nalu- skani rob avtohtona ali paravtohton sensu stricto in avtohton. Meja med obema enotama je Bujski reverzni prelom (BuF). Istrski blok je označen z A, furlanski blok z B. Istrski blok je nadalje raz- deljen na dva strukturna klina, južnoistrski (A1) in severnoistrski strukturni klin (A2). Istrsko-furlanska podrivna cona je segmenti- rana; osrednji prelomni strukturi v njej sta Čr- nokalski in Palmanovski narivni prelom. Prvega je mogoče povezati z narivom Učke, drugega pa je mogoče na podlagi podatkov globokih vrtin in geofizikalnega sondiranja (Nicolich et al., 2004, tavola 1, tavola 2; Carulli, 2006) slediti tudi se- verozahodno od Sesljanskega preloma. Proti ju- govzhodu sega istrsko-furlanska podrivna cona formalno do Kvarnerskega preloma. Po podatkih terenskega profiliranja je istrsko-furlanska pod- rivna cona najbolj tektonizirana v konici južno- istrskega strukturnega klina. Dostopni podatki vrtine Cargnacco 1 južno od Vidma/Udin (Ven- turini, 2002) in na skrajnem vidnem izdanku na- rivne meje Dinaridov v Koromačnem na vzhodni obali Istre (sl. 2) kažejo na sorazmerno manjšo stopnjo porušenosti. Iz splošne strukturne skice istrskega potisne- ga območja izhaja, da so deformacije podriva- nja in potiskanja zaradi aktivnosti Mikroadrije najbolj izražene v podaljšku osi južnoistrskega strukturnega klina, kjer sta zaradi bočnega po- tiska usločena Čičarijski antiklinorij in Brkinski sinklinorij (a in d na sl. 2). Potisk je kombiniran s podrivanjem; pod istrsko-furlansko podriv- no cono je proti VSV potisnjen jugovzhodni del Bujskega preloma (BuF) in skupaj z njim ustrezni del paravtohtona sensu stricto, pod Snežniški pokrov pa del severovzhodnega krila Brkinskega sinklinorija in jugovzhodni del Ravniškega an- tiklinorija. Sesljanski prelom je del vertikalne segmen- tacije Mikroadrije, sesljanska bočno upogibna cona pa je prizadela Zunanjedinarski naluskani in Zunanjedinarski narivni pas. Zaradi tako jas- nih razmerij med Mikroadrijo in Dinaridi nudi to območje možnosti za posredno ugotavljanje Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 227The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) (a and d on Fig. 2). The pushing is combined with underthrusting; beneath the Istrian-Friuli Under- thrusting Zone, the southeastern part of the Buje Fault (BuF) and its corresponding part of the au- tochthonous sensu stricto are pushed, while part of the northeastern limb of the Brkini Synclinori- um and the southeastern part of the Ravnik An- ticlinorium is pushed under the Snežnik Nappe. The Sistiana Fault is part of the vertical seg- mentation of the Microadria, and the Sistiana Lateral Bending Zone affected the External Di- naric Imbricate Belt and Thrust Belt. Due to such clear relationships between the Microadria and the Dinarides, this area offers the opportunity to indirectly determine in depth the geometric rela- tionship between these two units and provide the necessary data for structural modeling. Sistiana Fault The Sistiana Fault is visible on the surface only along the coast of the Sistiana Bay. A structural sketch of the vicinity of the bay is represented in Fig. 3A and is based on data from the Carta Ge- ologica del Carso Classico Italiano (Cucchi & Pi- ano, 2013) and our own investigations. All main components of the composition were confirmed: the Sistiana Fault (I), the N-S directed fault (II), and the Trieste reverse fault (III), which is part of the thrust system of the wider area. There are flysch and marlstone outcroppings between faults no. I and II, while the neighboring units are com- posed of Cretaceous, Paleocene, and Eocene lime- stones. Flysch beds appear in the inverse position. The Sistiana Fault outcrops only on the north- ern slopes of the Sistiana Bay in the northeastern block of fault no. IV (30/80) (Fig. 4); however, its fault plane is visible only in the rock-face under the starting point of the Rilke Path (point no. 1). Only the dip direction, and not the dip angle, could be measured (310/?). Further to the east-northeast, the fault plane is identifiable only up to fault no. III. From here and up to fault no. II, the situation is unclear, because the area is covered. On the other side of fault no. II there is a surface 350/80, which is visible in the highway cut and probably belongs to the Sistiana Fault. In the southwestern block of fault no. IV, the Sistiana Fault is displaced in the southeastern direction, but it is covered with tail- ings of the abandoned quarry. Its extension can be reconstructed after the limestone outcrop on the coast. Fault no. IV and some faults further north, of which two are represented on the map, prove that the Sistiana Fault is segmented. Some faults are positioned transversely and obliquely on the Sistiana Fault. They are visible in the rock-face geometrijskega razmerja med tema dvema eno- tama v globini in potrebne podatke za izvajanje modelnih raziskav. Sesljanski prelom Seljanski prelom je na površju viden edino v Sesljanskem zalivu, zato si oglejmo strukturno skico okolice zaliva, ki je prikazana na sl. 3A, njena izdelava temelji na podatkih s Carta geolo- gica del Carso classico italiano (Cucchi & Piano, 2013) in lastnem orientacijskem ogledu. V obmo- čju zaliva so bile potrjene vse bistvene kompo- nente zgradbe: Sesljanski prelom (I), prelom N-S (II) in Tržaški reverzni prelom (III), ki je del na- rivne zgradbe širšega ozemlja. Med prelomoma št. I in II izdanjata fliš in lapor, bližnje kamnine so kredni, paleocenski in eocenski apnenci. Fli- šne plasti so prevrnjene. Sesljanski prelom izdanja le v severnem po- bočju Sesljanskega zaliva v severovzhodnem krilu preloma IV (30/80) (sl. 4); vendar je nje- govo prelomno ploskev mogoče videti le v steni pod začetnim delom Rilkejeve poti (točka št. 1), kjer pa se da določiti le njeno smer ne pa tudi vpadnega kota (310/?). Naprej proti vzhodu-se- verovzhodu je trasa določljiva le do preloma št. III. Od tu do preloma št. II so zaradi prekritosti razmere nejasne. Na drugi strani preloma št. II pripada Sesljanskemu prelomu verjetno ploskev 350/80, ki je vidna v useku avtoceste. V jugoza- hodnem krilu preloma IV je Sesljanski prelom zamaknjen proti jugovzhodu, vendar na površju ni več viden, saj je zasut z jalovinskim materi- alom opuščenega kamnoloma. Njegov potek je mogoče rekonstruirati po izdanku apnenca na obali. Prelom IV in nekaj prelomov severno od tega, od katerih sta na sliki 3 vrisana dva, doka- zujejo, da je Sesljanski prelom segmentiran. Pre- lomov, ki ležijo prečno ali poševno na Sesljan- skega, je v jugozahodnem krilu preloma IV več; vidni so v steni opuščenega kamnoloma, vendar je njihov odnos do Sesljanskega preloma neznan. Po analogiji bi ga lahko tudi ti sekali, kot je hi- potetično prikazano na sliki 3A. Interpretacija smeri Sesljanskega preloma na tem odseku je povzeta po prvotni morfologiji severozahodne- ga dela Sesljanskega zaliva, ki je vidna na karti druge izmere Vojaškega zemljevida Habsburške monarhije 1806-1869 na sliki 2B - levo (Histori- cal Maps of the Habsburg Empire. The Second Military Survey 1806-1869). Tu je izrisana pr- votna obala zaliva, ki so jo sestavljali kredni, paleocenski in eocenski apnenci pred pričetkom izkoriščanja kamnoloma. Zgradbo in potek oba- le potrjuje tudi Geološka karta 1:75.000 (Stache, 228 Fig. 3. Sistiana Bay. A. Structural sketch. Amended after Cucchi & Piano (2013); B. Sistiana Bay: left – Historical Maps of the Habsburg Empire 1806–1869, The Second Military Survey; right – satellite picture, Mapaire. Sl. 3. Sesljanski zaliv. A. Strukturna skica. Dopolnjeno po Cucchi in Piano (2013); B. Sesljanski zaliv: levo – Vojaški zemljevid Habsburške monarhije 1806-1869, druga izmera; desno – satelitski posnetek, Mapaire. Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 229The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) of the abandoned quarry, but their relationship to the Sistiana Fault is unknown. By analogy, they could also cut it, as is hypothetically represented in Fig. 3A. An interpretation of the direction of the Sistiana Fault in this stretch is summarized after the morphology of the northwestern part of Sisti- ana Bay, as represented in the Historical Maps of the Habsburg Empire. The Second Military Sur- vey 1806–1869 (Fig. 2B – left). The original coast is presented, with Cretaceous, Paleocene, and Eocene limestones before quarrying. The com- position and shape of the coast before quarrying is also confirmed in the Geological map 1:75.000 1920), ki je bila izdelana v drugi polovici 19. sto- letja, ko tam še ni bilo kamnoloma. Na karti se vidi tudi geološka meja, ki jo danes interpretira- mo kot prelom št. IV (30/80). Na območju točke št. 1 (sl. 3A) so v jugovzho- dnem krilu Sesljanskega preloma vidne prehodne plasti, ki pa so priključene flišnim kamninam. Razmere so poenostavljene. Prelom št. II v smeri N-S je bil določen po morfološkem kriteriju in po izdanku v useku ceste v zaliv (260/90). Prelom št. III je viden v vhodnem delu Malega pristana (Portopiccolo), kjer ima smer 60/55; tu ga spremljajo razpoke v Fig. 3. / Sl. 3. 1 Cretaceous and Paleogene limestones / kredni in paleogenski apnenci 2 Eocene Transitional marlstone and Flysch / eocenski prehodni lapor in fliš 3 Important fault: visible, covered or interpolated or extrapolated, uncertain / pomembnejši prelom: viden, prekrit ali interpo- liran ali ekstrapoliran, negotovo določen 4 Important reverse fault: visible, covered / pomembnejši reverzni prelom: viden, prekrit 5 Faults: no. I – Sistiana Fault, no. II – N-S fault (260/90), no. III – Trieste reverse fault (60/55), no. IV – sub-vertical fault (30/80) / prelomi: št. I – Sesljanski prelom, št. II – prelom N-S (260/90), št. III – Tržaški reverzni prelom (60/55), št. IV – subvertikalni prelom (30/80) 6 Dip of strata: normal, inverse / plasti: normalne, inverzne 7 Fault planes: vertical, inclined / prelomne ploskve: navpične, poševne 8 Subsided fault block / ugreznjeno krilo preloma 9 Direction of the horizontal component of the displacement along fault / smer horizontalne komponente premika prelomnega krila 10 Combined or oblique displacement of the fault block / kombiniran ali poševen premik prelomnega krila 11 Significant joint zone / pomembnejša razpoklinska cona 12 Fig. B left – location of the contact between Upper Cretaceous and Paleocene limestone after Stache (1920). At this location it is fault no. IV (30/80) in fig. A / sl. B levo, mesto stika zgornjekrednega in paleocenskega apnenca po Stache (1920). Na sl. A je na tem mestu prelom št IV (30/80) 13 Road / cesta 14 Embankment / nasip 15 Edge of the vertical face; position of the coast between 1806–1869 / rob prepadne stene; obala med letoma 1806-1869 Fig. 4. Sistiana Bay. In the middle of the photo is fault no. IV (30/80), cutting the Sistiana Fault. Left: Cretaceous limesto- ne. Right: Eocene Transitional marlstone, above is a rock face as a fault plane of the Sistiana Fault, behind it is Cretaceous limestone. Sl. 4. Sesljanski zaliv. Sredi slike je prelom IV (30/80), ki seka Sesljanski prelom. Levo: Kredni apnenec. Desno: eocenski pre- hodni lapor, nad njim stena kot prelomna ploskev Sesljanskega preloma, zadaj kredni apnenec. 230 (Stache, 1920), elaborated in the second half of the 19th century. The geological boundary, now inter- preted as fault no. IV (30/80), is well represented. In the southeastern block of the Sistiana Fault (area of point no. 1 in Fig. 3A) transitional beds incorporated into the flysch are visible. The situa- tion has been simplified. Fault no. II in the N-S direction was deter- mined according to the morphological criteria and after the outcrop in the roadcut (260/90). Fault no. III is visible in the eastern part of Portopiccolo, with a 60/55 dip, accompanied by joints in the limestone (75/55). Toward the north, up to fault no. II, the fault is determined according to the mor- phologic step between flysch marlstone and lime- stone. On the western part of fault no. II, fault no. III is determined after the direction of the western slopes of the valley of the same direction (point no. 2), which we believe is formed in the jointed lime- stone. Fault no. II is part of the joint-fault zone, as reflected in the series of dolines north of the highway. If we compare the displacements of the Sistiana Fault and fault no. III along fault no. II, it is clear that we are looking at two different phases of displacements. The carbonate strata along Sistiana Bay are po- sitioned in an easterly, Dinaric direction NW-SE; in the northern and northwestern part they divert to the west-east direction, and from their normal position in the north they divert to the overturned position (360/80). In the direction of Duino, they gradually divert again into the normal position. In the hinterland of the Bay, flysch beds appear in an overturned position and dip to the north. Cucchi & Piano (2013) considered the Sistiana Fault and fault no. II strike-slip faults, the former with a left-lateral and the latter with a right-lat- eral displacement. The Sistiana Fault is consid- ered unsegmented, as fault no. II does not cut the first one. Such an interpretation requires at least two strike-slip phases. Our interpretation is slightly different. From the structural sketch (Fig. 3A) it is obvious that a vertical component of the displacement of the block between faults no. I and II larger than the horizontal component. The dis- placement consisted of a number of components. The displacement of the Sistiana Fault along fault no. II is of secondary origin along the joint-fault zone directed north-south, which part is also fault no. II. Joint-fault zones in this direction are usual in several parts of the Trieste-Komen Anticlinori- um. Multiphase displacements are also evidenced by the segmentation of the Sistiana Fault. From the description above it follows that the origin of the flysch block between the Sistiana apnencu (75/75), proti severu do preloma št. II, pa je določljiv po morfološki stopnji med flišnim la- porjem in apnencem. Na zahodni strani preloma št. II je prelom št. III določen po smeri zahodnega pobočja doline enake smeri (sl. 3A, točka št. 2), za katero smatramo, da se je razvila v razpokanem apnencu. Prelom št. II je del razpoklinsko-pre- lomnega snopa, kar se odraža v nizu kolinearnih vrtač severno od avtoceste. Če vzporejamo pre- mika Sesljanskega preloma in preloma št. III ob prelomu št II, je jasno, da gre za dve različni fazi premikov. Plasti karbonatnih kamnin okoli Sesljanskega zaliva slemenijo vzhodno od tod pretežno v meri Dinaridov NW-SE, na severni in severozahodni strani pa se iz dinarske obrnejo v smer zahod – vzhod in se iz normalne lege proti obali prevrne- jo v inverzno lego (360/80). Severno, proti Devinu se plasti polagoma spet obrnejo v normalno lego. Fliš ima v zaledju zaliva inverzno lego ter vpada proti severovzhodu. Cucchi in Piano (2013) sta Sesljanski prelom in prelom št. II obravnavala kot zmična prelo- ma, prvega kot levi in drugega kot desni zmik. Sesljanski prelom naj bi bil nesegmentiran, pre- lom št. II pa naj ga ne bi sekal, za kar pa bi bili potrebni vsaj dve fazi premikov. Sedaj predlo- žena interpretacija je nekoliko drugačna. Iz strukturne skice na sliki 3A izhaja, da je imela navpična komponenta premika bloka med pre- lomoma št. I in št. II večji obseg od vodoravne in da je bilo premikanje večkomponentno. Pre- mik Sesljanskega preloma ob prelomu št. II je sekundarnega izvora, dogodil se je vzdolž raz- poklinsko prelomne cone sever-jug, katere del je prelom št. II. Razpoklinsko-prelomne cone te smeri so na območju Tržaško-Komenskega an- tiklinorija dejavne na več mestih. Večfaznost premikov dokazuje tudi segmentacija Sesljan- skega preloma. Iz napisanega sledi, da je blok flišnih kamnin med Sesljanskim prelomom in prelomom št. II najlažje razložiti z dvigom. To potrjuje tudi po- jemanje intenzivnosti Sesljanskega preloma pro- ti vzhodu. Da bi morali ob Sesljanskem prelomu obstajati levozmični premiki izhaja iz njegove regionalne vloge, vendar ima ta komponenta pre- mika v Sesljanskem zalivu sekundarni pomen. Zaradi lažje komunikacije imenujemo blok dvig- njenega oziroma vertikalno izrinjenega fliša v zalivu sesljanski izrivni blok. V zahodni steni opuščenega kamnoloma v Sesljanskem zalivu, imajo tektonske drse različ- ne smeri, zdi pa se, da prevladujejo subhorizon- talne in subvertikalne. Podobno je v severnem Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 231The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) Fault and fault no. 2 is best described with the uplift. This also confirms the pinching-out of the Sistiana Fault in the easterly direction. The re- gional role of the Sistiana Fault infers left lateral strike-slip displacement, although this compo- nent of displacement in the Sisitiana Bay is of sec- ondary importance. For the sake the simpler com- munication, we named this uplifted or vertically erected block the Sistiana Pushout Block. In the western rock face of the abandoned quarry in the Sistiana Bay, slickensides take dif- ferent directions, but it appears that sub-horizon- tal and sub-vertical ones prevail. A similar situ- ation is visible on the northern slopes of the bay and in other areas, which makes the Sistiana Bay a first-class structural-geological object for de- tailed mapping and structural analysis. For purposes of this paper, we conclude that the Sistiana Block between the Sistiana Fault and fault no. II is vertically erected and that over- turned flysch strata at the bottom of the bay most likely belongs to the footwall block of the reverse fault no. III, which represents the deformed posi- tion of the Trieste Thrust. Sistiana Bending Zone General findings The more pronounced laterally bent Tri- este-Komen Anticlinorium and the less pro- nounced Vipava Sinclinorium are observable in the Sistiana Bending Zone. The bending axis can be precisely determined only in the Sistiana Bay, while on the northeastern side of the Tri- este-Komen Anticlinorium such determinative precision is not possible. We can, with a certain degree of probability, assign its location near Spodnja Branica (Fig. 12). The Vipava Sinclinori- um is bent, but there are no adequate structures available to help determine the bending axis. However, what is interesting is the fact that the Idrija Fault is also laterally bent in the continua- tion of the Sistiana Bay – Spodnja Branica direc- tion. With the position of the boundary between the Trnovo and Hrušica Nappes, we can suggest a modification of the original relationship between thrust-units. Based on the Sistiana Bay – Spodn- ja Branica line, the approximate axis direction of the Sistiana Bending Zone is 60°–65°. The bending axis is not represented as a line, but rather as an area of tolerance seen as a circular section with an angle of about 5° (Fig. 5). The size of the angle of the lateral bending of individual structural units in the Sistiana Bend- ing Zone can be determined only approximately, pobočju zaliva in drugod, zato je Sesljanski zaliv prvovrstni strukturno-geološki objekt za detajl- no kartiranje in strukturno analizo. Za potrebe tega članka zadostuje ugotovitev, da je sesljanski blok med Sesljanskim prelomom in prelomom št. II izrinjen navzgor in da inverzi- ja flišnih plasti v dnu zaliva najverjetneje kaže na to, da pripada talninski grudi reverznega prelo- ma št III, ki predstavlja deformirano lego Trža- škega nariva. Sesljanska upogibna cona Splošne ugotovitve V sesljanski upogibni coni sta vidno boč- no upognjena Tržaško-komenski antiklinorij in Vipavski sinklinorij; prvi bolj, drugi nekoli- ko manj. Os upogiba je mogoče natančno dolo- čiti le v Sesljanskem zalivu, kjer se sprememba smeri plasti dogodi vzdolž prelomne ploskve Sesljanskega preloma, na severovzhodni strani Tržaško-Komenskega antiklinorija pa taka na- tančnost ni mogoča, lahko pa s precejšnjo mero gotovosti ugotovimo, da se nahaja blizu Spodnje Branice (sl. 12). Vipavski sinklinorij je upognjen, toda za določanje osi upogiba ni na voljo ustrez- nih struktur, preseneča pa dejstvo, da je v po- daljšku smeri Sesljanski zaliv – Spodnja Branica bočno usločen tudi Idrijski prelom. Po legi meje med Trnovskim in Hrušiškim pokrovom je mo- goče domnevati, da je spremenjen tudi prvotni odnos med omenjenima krovnima enotama. Gle- de na črto Sesljanski zaliv – Spodnja Branica, znaša približna smer osi sesljanske upogibne cone 60° do 65°. Na sliki 5 ni izrisana os upogi- ba temveč območje njene tolerančne lege, zato je sesljanska upogibna cona prikazana kot krožni izsek s kotom okoli 5°. Velikost kota bočnega upogiba posameznih strukturnih enot v sesljanski upogibni coni je mogoče določiti le približno, kar pa ne moti, saj stopnja natančnosti podatka ne vpliva na končno interpretacijo (sl. 5). V Sesljanskem zalivu ga je mogoče določiti po legi plasti, kjer znaša okoli 20°. Za Tržaško-Komenski antiklinorij je kot upogiba najlaže določiti iz slemenitve Kraške grupe formacij (Jurkovšek et al., 2013) plasti v severovzhodnem krilu antiklinorija (a1, a2) in iz- ven vpliva Raškega preloma. Ta znaša približ- no 18°. Iz slike 5 izhaja, da ima velikost kota v Sesljanskem zalivu le ožji pomen, zato je za iz- hodiščno vrednost najbolje vzeti podatek o upo- gibu celotnega antiklinorija, torej 18°. Velikost upogiba osi Vipavskega sinklinorija je težko do- ločiti, ker je deformirana zaradi izpostavljene 232 but this is not of particular importance, because the degree of accuracy of the data does not affect the final interpretation (Fig. 5). In Sistiana Bay, it can be determined after the position of the stra- ta, which amounts to approximately 20°. In the Trieste-Komen Anticlinorium, a bending axis of approx. 18° can be determined from the strike lege Nanosa v čelnem delu Hrušiškega pokrova, je pa gotovo manjša od upogiba Tržaško-Komen- skega antiklinorija. Naprej proti severovzhodu sprememba smeri v nakazani smeri ni več tako očitna, vendar obstajajo, saj je bilo že rečeno, da je v širokem loku ukrivljena tudi trasa Idrijskega preloma. Če je tako, bi morala biti eden nasproti Fig. 5. Sistiana Bending Zone. Sl. 5. Sesljanska upogibna cona. 1 Sistiana Bending Zone / sesljanska upogibna cona 2 SF – Sistiana Fault / Sesljanski prelom 3 Faults in direction of Dinarides / dinarsko usmerjeni prelomi: DSF – Divača splay of faults / Divaški snop prelomov, RF – Raša Fault / Raški prelom, TF – Tomačevica Fault / Tomačevski prelom, BF – Bela Fault / Belski prelom, IF – Idrija Fault / Idrijski prelom / ZF – Zala Fault / Zalin prelom, PF – Predgriže Fault / Predgriški prelom 4 PTF – Palmanova Thrust Fault / Palmanovski narivni prelom 5 Rotating structures / zasukane strukture: a1, a2 – Direction of the Trieste-Komen Anticlinorium / smer Tržaško-Komenskega antiklinorija, b1 – Nanos Anticline in the Hrušica Nappe thrust-front / smer Nanoške antiklinale v čelu Hrušiškega pokro- va, b2 – Direction of the Trnovo Nappe thrust-front / smer čela Trnovskega pokrova, c – Planina Syncline in the Vipava Synclinorium / smer Planinske sinklinale v Vipavskem sinklinoriju 6 Ss – Sistiana Sigmoid, dip of strata / sesljanska sigmoida, vpad plasti 7 Komen Wedge Structural Step / komenski klinasti strukturni prag 8 Relative direction of displacement / relativna smer premika 9 Continuation of the fault, no detailed geological mapping performed / prelom se nadaljuje, ni podrobno geološko kartirano Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 233The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) direction of the Kras Group Formation (Jurkovšek et. al., 2013) in the northeastern limb of the an- ticlinorium (a1, a2), and outside the influence of the Raša Fault. Based on the Fig. 5, the amount of the angle in Sistiana Bay has only minor in- fluence, consequently we took 18° as a base value. The size of the bending of the axis of the Vipava Sinclinorium is difficult to determine because of the exposed position of Nanos in the thrust-front of the Hrušica Nappe. It is certainly smaller, com- pared to the bending of the Trieste-Komen Anti- clinorium. Further to the northeast, the change in direction in the indicated continuation is not so obvious, but does exist, since it has already been said that the line of the Idrija Fault is also curved in a wide arc. If this assumption is cor- rect, the Trnovo and Hrušica Nappes also need to be rotated against each other. The amount of the angle of eventual rotation between the two thrust units is difficult to determine, but some general information can be determined. The direction of the thrust-unit is generally determinable by the direction of the dominant slickensides in the prin- cipal thrust plane, which are perpendicular to the strike direction of the thrust unit, and by the po- sition of the folds axis formed during the thrust- ing. In both cases, owing to the inhomogeneity of the thrust units and consequent oscillations in displacement directions the data is only statisti- cal. Under the given conditions, the direction of the Nanos Anticline axis (b1) in the Hrušica Nappe can be determined, while no such information is available for the Trnovo Nappe, but it is possible to approximate the direction of the thrust front (b2), which is not possible at Nanos, because the thrust front is not reliably fixed. Therefore, both figures were used for orientation. The axis of the frontal anticline of the Hrušica Nappe dip in the northwestern direction (304/23) (Placer, 1981, Fig. 1). The thrust-front of the Trnovo Nappe strikes approx. in the 295° direction. Although the data does not represent a reliable starting point, it is nevertheless interesting that the 9° direction obtained is consistent with the decreasing angle of arch of the Sistiana Bending Zone to the north- east. The Trnovo Nappe should therefore be ro- tated counterclockwise, just like the rest of the blocks northwest of the Sistiana Bending Zone. The direction of the dominant slickensides in the Planina Quarry (Placer, 1994/95, Fig. 6) was not considered, since it is too far from the thrust front of the Hrušica Nappe and does not represent the statistical average. Clear evidence of a decrease in lateral bend- ing from the southwest to the northeast is seen in drugemu zasukana tudi Trnovski in Hrušiški pokrov. Velikost kota morebitnega zasuka med omenjenima krovnima enotama je težko določlji- va, mogoče pa je dati splošno informacijo. Smer krovne enote je na splošno določljiva po smeri do- minantnih tektonskih drs v glavni narivni plo- skvi, ki ležijo pravokotno na smer narivne enote in po legi osi gub, ki so nastale med narivanjem. V obeh primerih je podatek lahko le statističen, saj so narivne enote nehomogene, zaradi česar do določene mere niha tudi smer premikov. V da- nih razmerah je pri Hrušiškem pokrovu mogoče določiti smer osi Nanoške antiklinale (b1), med- tem ko pri Trnovskem pokrovu takega podatka ni, vendar je mogoče približno izmeriti smer čela krovnega nariva (b2), česar pri Nanosu ni mogo- če, ker čelo nariva ni zanesljivo določeno. Zato sta bila za orientacijo uporabljena omenjena po- datka. Os čelne antiklinale Hrušiškega pokrova vpada proti severozahodu 304/23 (Placer, 1981, sl. 1), čelo Trnovskega pokrova poteka približ- no v smeri 295°. Čeprav podatka ne predstavljata zanesljivega izhodišča, je vseeno zanimivo, da je dobljena razlika v smereh, 9° skladna z manj- šanjem kota usločitve sesljanske upogibne cone proti severovzhodu. Trnovski pokrov naj bi torej bil zasukan v nasprotni smeri urinega kazalca tako kot ostali bloki severozahodno od sesljan- ske upogibne cone. Smer dominantnih drs v ka- mnolomu pri Planini (Placer, 1994/95, sl. 6 ) ni bila upoštevana, ker je kraj preveč oddaljen od čela Hrušiškega pokrova in ne predstavlja stati- stičnega povprečja. Fig. 6. Diagram of external rotation of the structural units of the northeastern wing of the Sistiana Bending Zone. Sl. 6. Diagram eksterne rotacije strukturnih enot severoza- hodnega krila sesljanske upogibne cone. 1 Sistiana Bay (bedding strike) / Sesljanski zaliv (smer plasti) 2 a2 – Northern edge of the Trieste-Komen Anticlinorium / severni rob Tržaško-Komenskega antiklinorija 3 c – Axis of the Planina Syncline is identical with the di- rection of the Vipava Synclinorium / os Planinske sinklinale je identična s smerjo Vipavskega sinklinorija 4 b2 – Trnovo Nappe thrust-front / čelo Trnovskega pokrova 234 the change in the azimuth of those structures in the northwestern wing of the Sistiana Bending Zone, which was originally oriented in the Dinar- ic direction (Fig. 6). The strike of bedding in the Sistiana Bay is approx. 270° (point 1), and in the Liburnian Formation in the northeastern limb of the Trieste-Komen Anticlinorium approx. 285° ( a2, point 2), while the azimuth of the axis of the northwestern and central part of the Vipava Syn- clinorium, as determined by the axis of the syn- cline from the flysch calcarenites, and breccias in the Planina area, is approximately 290° (c, point 3), and the strike of the front of the Trnovo Nappe is 295° (b2, point 4). The linear relationship between the points indicates the corresponding order. The syncline with flysch calcarenites, and brec- cias in the Planina area on the axis of the Vipava Synclinorium (Planina Syncline) is purely hori- zontally rotated, together with the northwestern limb of the synclinorium, although it does extend beyond the axis of the Sistiana Bending Zone. The horizon of calcarenites, and breccias is over 100 m thick and represents a weakly ductile unit in flysch rocks of high ductility. It did not bend in the flexural zone, but twisted rigidly. This was possi- ble because the axis of the Planina syncline dips in the west-northwest direction and the bulk of its mass is positioned in the rotating wing of the bending zone. As this paper is dedicated to the re- gional importance of the Sistiana Bending Zone we have only raised the issue of the “anomalous position” of the clastites in the Planina Syncline. Differences in rock ductility play an important role in the structural and geomorphological anal- ysis of the Istra Pushed Area. Deformation of the faults in the Dinaric direction In addition to the units described during the period of thrusting (the Trieste-Komen Anticlino- rium, the Vipava Synclinorium, and the Trnovo and Hrušica Nappe), the Dinaric-directed faults are also important: the Paleodivača, Raša, Belsko (Placer et al., 2021) and Idrija faults. The Paleo- divača Fault represents the primary structure of the Divača Splay Faults (Fig. 7). Both terms in this article are mentioned in the geological liter- ature for the first time, but we address them only to the extent that it is necessary for a complete presentation of the Sistiana Bending Zone. All faults are bent in the Sistiana Bending Zone, except that their bending angles are dif- ferent. The Paleodivača and Idrija faults are bent as much as their bearing units, in the first case the Trieste-Komen Anticlinorium, and in the second, the Trnovo Nappe opposite the Hrušica Nazoren dokaz manjšanja bočnega upogiba od jugozahoda proti severovzhodu daje sprememba azimuta tistih struktur v severozahodnem kri- lu sesljanske upogibne cone, ki so prvotno imele dinarsko smer (sl. 6). Azimut slemenitve plasti v Sesljanskem zalivu znaša okoli 270° (točka 1), liburnijskih plasti v severovzhodnem krilu tr- žaško-komenske antiforme znaša okoli 285° (a2, točka 2), azimut osi severozahodnega in osre- dnjega dela Vipavskega sinklinorija, ki ga določa os sinklinale iz flišnih apnenih peščenjakov in breč na območju Planine, znaša približno 290° (c, točka 3), azimut smeri čela Trnovskega pokrova znaša 295° (b2, točka 4). Linearen odnos med toč- kami kaže na ustrezno zakonitost. Sinklinala flišnih apnenih peščenjakov in breč na območju Planine v osi Vipavskega sinkli- norija (Planinska sinklinala) je v celoti horizon- talno zasukana skupaj s severozahodnim krilom sinklinorija, čeprav sega preko osi sesljanske upogibne cone. Paket apnenčevih peščenjakov in breč je v najmočnejšem delu debel več 100 m in predstavlja vložek slabo duktilne kamnin- ske mase v flišnih plasteh visoke duktilnosti. V upogibni coni se ni usločil temveč togo zasukal. To je bilo mogoče zato, ker vpada os Planinske sinklinale proti zahodu-severozahodu in leži pretežni del njegove mase v zasukanem krilu upogibne cone. Ta prispevek je posvečen regio- nalnemu pomenu sesljanske upogibne cone, zato smo na vprašanje »anomalne lege« paketa debe- lozrnatih flišnih klastitov v Planinski sinklinali le opozorili. Razlike v duktilnosti kamnin imajo pomembno vlogo v strukturni in geomorfološki analizi istrskega potisnega območja. Deformacije prelomov dinarske smeri Poleg opisanih enot, ki so nastale v obdobju narivanja (Tržaško-Komenski antiklinorij in Vi- pavski sinklinorij ter Trnovski in Hrušiški po- krov), so pomemben označevalec upogiba tudi dinarsko usmerjeni prelomi: Paleodivaški, Ra- ški, Belski (Placer in sodelavci, 2021) in Idrijski prelom. Paleodivaški prelom predstavlja primar- no strukturo divaškega snopa prelomov (sl. 7). Oba pojma sta v tem članku prvič omenjena v geološki literaturi, vendar ju obravnavamo le to- liko, kolikor je potrebno za celovito predstavitev sesljanske upogibne cone. Vsi omenjeni prelomi so v sesljanski upogibni coni upognjeni, le da je njihov kot upogiba raz- ličen. Paleodivaški in Idrijski prelom sta upog- njena toliko kot njuni nosilni enoti, v prvem pri- meru Tržaško-Komenski antiklinorij, v drugem Trnovski pokrov nasproti Hrušiškemu. Raški Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 235The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) Nappe. The Raša Fault is less bent than the Tri- este-Komen Anticlinorium and the Vipava Syn- clinorium. The relationship in the Belsko Fault is different because it is related to the deformation of Nanos, but an interpretation of this case would require special discussion, so it is not discussed further here. The term Divača Fault Splay is based on the data of the Geological map of the Northern part of the Trieste-Komen Plateau 1: 25,000 (Jurkovšek, 2010; Jurkovšek et al., 2013), where a group of dis- locations accompany the Divača Fault. Their gen- esis has been linked to several kinematic phases, which are not the subject of this article. Only the initial formation of the splay, whose central ele- ment was the Paleodivača Fault, is relevant. Fig- ure 7A depicts the current shape of the splay, con- sisting of the Divača Fault, the Brestovica Fault, the Jamiano Fault, the faults between the Divača and Jamiano faults that lean on the Brestovica Fault, and the accompanying faults that extend to the Divača Fault in its northeastern block. prelom je upognjen manj od Tržaško-Komenske- ga antiklinorija in Vipavskega sinklinorija. Pri Belskem prelomu je odnos drugačen, ker je po- vezan z deformacijo Nanosa, vendar bi razlaga tega primera zahtevala posebno razpravo, zato ga puščamo ob strani. Termin divaški snop prelomov je postavljen na podlagi podatkov Geološke karte severnega dela Tržaško-Komenske planote 1: 25.000 (Jurkov- šek, 2010; Jurkovšek in sodelavci, 2013), po kateri spremlja Divaški prelom skupina dislokacij. Nji- hova geneza je bila povezana z več kinematskimi fazami, kar pa ni predmet tega članka, pomemb- na je le izhodiščna oblika snopa, katere središčni element je bil Paleodivaški prelom. Na sliki 7A je narisana današnja oblika snopa, ki ga sestavlja- jo Divaški prelom, Brestoviški prelom, Jameljski prelom, prelomi med Divaškim in Jameljskim prelomom, ki se naslanjajo na Brestoviški prelom, in prelomi, ki spremljajo Divaškega v njegovem severovzhodnem krilu. Trase vseh teh so jasno vidne na digitalnem modelu reliefa iz lidarskih Fig. 7. Paleodivača Fault. Geological bases after Jurkovšek (2010). A. Recent structure. Divača splay of faults; B. Undeformed primary position of the Paleodivača Fault. Sl. 7. Paleodivaški prelom. Geološka osnova po Jurkovšek (2010). A. Sedanja zgradba.Divaški snop prelomov; B. Nedeformirana prvotna lega Paleodivaškega preloma. 1 Divača splay of faults / divaški snop prelomov: JF – Jamiano Fault / Jameljski prelom, BrF – Brestovica Fault / Brestoviški prelom, DF – Divača Fault / Divaški prelom 2 Paleodivača Fault, recent structure / Paleodivaški prelom, sedanja lega 3 Brje Formation (Early Cretaceous), the oldest unit of the Trieste-Komen Anticlinorium / Brska formacija spodnjekredne starosti. Najstarejše plasti Tržaško-Komenskega antiklinorija 4 Povir Formation and younger units (Late Cretaceous, Paleocene and Eocene) / Povirska formacija in mlajše plasti zgornje- kredne, paleocenske in eocenske starosti 5 Sistiana Bending Zone / sesljanska upogibna cona 236 Traces of all these faults are clearly visible on the digital terrain model based on lidar data. The Paleodivača Fault is now deformed in the splay and connects the Divača Fault branch southeast of Gorjansko, the Brestovica Fault, and the Jami- ano Fault branch northwest of Jamlje. During the formation, the fault plane was straight (Fig. 7B) and its north block was subsided, so that the units of the Brje Formation in the southern block met the units of the Sežana Formation in the north- ern block. The originally straight surface of the Paleodivača Fault is today bent in the Sistiana Bending Zone, together with the Trieste-Komen Anticlinorium. The bending of the Paleodivača Fault is equal to the bending of the Trieste-Komen Anticlinori- um. The Raša Fault cuts the northeastern part of the Trieste-Komen Anticlinorium and the west- ern part of the Vipava Synclinorium (Figs. 2 and 5). If we ignore its genesis and look only at its relation to the Sistiana Bending Zone, three pe- culiarities are important: 1. In the Sistiana Bending Zone, the fault line is curved, but not as pronounced as the Tri- este-Komen Anticlinorium. 2. Shear lenses, which are bounded by the Tomačevica, Kobjeglava, and Lukovica faults, along with some minor ones (Figs. 5 and 8A), are present in the bending zone. We can conclude that the three faults were formed due to the tendency to straighten the curved shear plane of the Raša Fault. 3. The Tomačevica, Kobjeglava, and Lukovica faults are also bent in the Sistiana Bending Zone, but the bending is not so pronounced, so it can only be considered an assumption. The Tomačevica, Kobjeglava, and Lukovi- ca faults represent secondary faults that are ar- ranged in a series of strike-slip duplexes. Their peculiarity is that they were not formed accord- ing to the standard models of the development of the fault zone, but after lateral bending of the strike-slip fault plane. During the subsequent strike-slip, the resistance due to the bulge of the bent surface is counterbalanced by the formation of one or more faults forming one or more fault lenses with the principal fault plane. The result- ing faults reflect the tendency to flatten the shear plane or zone, so it is more appropriate to name them in more detail. The terms fault splay, shear lenses, bend, strike-slip duplex, linkage duplex, flower structure, sidewall ripout, and ripout structure are used in the literature for the sake of similar fault geometry terminology (Swanson, 2005; Cunningham & Mann, 2007), but none of the podatkov. Paleodivaški prelom je v snopu danes deformiran in povezuje krak Divaškega preloma jugovzhodno od Gorjanskega, Brestoviški prelom in krak Jameljskega preloma severozahodno od Jamelj. Ob nastanku je bila obravnavana prelom- na ploskev ravna (sl. 7B), njeno severno krilo je bilo ugreznjeno, tako da so prišle v stik kamni- ne Brske formacije v južnem krilu s kamninami Sežanske formacije v severnem krilu. Prvotno ravna ploskev Paleodivaškega preloma je danes upognjena v sesljanski upogibni coni skupaj s Tr- žaško-Komenskim antiklinorijem. Upogib Paleodivaškega preloma je enak upo- gibu Tržaško-Komenskega antiklinorija. Raški prelom seka severovzhodni del Trža- ško-Komenskega antiklinorija in zahodni del Vi- pavskega sinklinorija (sl. 2 in 5). Če zanemarimo njegovo genezo in si ogledamo le njegov odnos do sesljanske upogibne cone, izstopajo tri posebno- sti: 1. V sesljanski upogibni coni je trasa prelo- ma ukrivljena, vendar ne tako močno kot Tržaško-Komenski antiklinorij. 2. V območju upogiba nastopajo prelomne leče, ki jih omejujejo Tomačevski, Kobjeglavski in Lukovški prelom ter nekaj manjših (sl. 5 in 8A). Iz tega izhaja sklep, da so omenjeni tri- je prelomi nastali zaradi težnje po izravnavi ukrivljene strižne ploskve Raškega preloma. 3. V Sesljanski upogibni coni so enako upogn- jeni tudi Tomačevski, Kobjeglavski in Luk- ovški prelom, vendar upognjenost ni izrazi- ta, zato jo je moč obravnavati le kot domnevo. Tomačevski, Kobjeglavski in Lukovški prelom predstavljajo sekundarne prelome, ki so razpore- jeni v niz strižnih dupleksov. Izstopajo po tem, da niso nastali po standardnih modelih razvoja prelomne cone, temveč po bočnem upogibu zmič- ne prelomne ploskve. Pri ponovnem zmikanju se upor zaradi grbine upognjene prelomne ploskve uravna z nastankom enega ali več novih prelo- mov, ki tvorijo z glavno prelomno ploskvijo eno ali več prelomnih leč. Nastali prelomi so odraz težnje po izravnavi strižne ploskve ali cone, zato jih je smiselno določneje poimenovati. V literatu- ri se za po videzu podobno geometrijo prelomov uporabljajo izrazi snop prelomov (fault splay), strižne leče (shear lenses), prevoj (bend), zmični dupleks (strike-slip duplex), povezovalni dupleks (linkage duplex), pahljačasta struktura (flower structure), stranski izriv (sidewall ripout) in izriv- na struktura (ripout structure) (Swanson, 2005; Cunningham in Mann, 2007), vendar nobeden od teh izrazov in pojavov, ki jih opisujejo, ne defi- nira opisanega primera sekundarnih prelomov Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 237The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) ob Raškem prelomu. Zato zanje predlagamo nov termin izravnalni prelomi (adjusting faults), za samo zgradbo pa izravnalna zgradba (adjusting structure). O odnosu izravnalnih prelomov do glavnega preloma v globini v vertikalni ravnini osi upogibne cone, ne moremo razpravljati brez laboratorijskih preizkusov. Tomačevski prelom se glede na upogibno cono asimetrično naslanja na traso Raškega preloma; na severozahodu je kot priključka večji (odcepil- na stran), na jugovzhodu je kot manjši (priključ- na stran). Domnevamo, da je razlika posledica geometrije napetostnega stanja v območju upo- giba, ki je izpeljana iz lege izravnalnega preloma (sl. 8B). Ta značilnost izstopa pri Tomačevskem prelomu, ker leži na zunanji meji izravnalnega snopa, medtem ko pri ostalih dveh ni tako očitna. Verjetno zaradi drugotnih vplivov, na kar bi bilo mogoče sklepati po zapletenih razmerah znotraj lukovške zmične leče in nekoliko manj znotraj kobjeglavske. Iz tega sledi, da je verjetno najprej nastal Lukovški, nato Kobjeglavski in nazadnje Tomačevski prelom. V nasprotju z lečama med Tomačevskim in Kobjeglavskim ter Kobjeg- lavskim in Lukovškim prelomom je odcepilna stran leče med Lukovškim in Raškim prelomom ugreznjena, priključna pa dvignjena, oboje kaže na učinek desnozmične divergence in konvergen- ce. Pojav je izraziteje razvit le v tem primeru, kar ponovno kaže na to, da je Lukovški izravnalni prelom najstarejši (sl. 8A). O regionalni kinema- tiki Raškega preloma bo tekla razprava v dru- gem članku. Primer na sliki 8B prikazuje inicialno fazo nastanka izravnalnega preloma, pri nadaljnjem desnem zmikanju se razvijeta desnozmična di- vergenca in konvergenca, v končni fazi pa se obprelomna leča vključi v širšo prelomno cono vodilnega preloma. Razvoj tega procesa ne sodi v okvir pričujočega članka. V literaturi ni podatkov o usmerjenih labo- ratorijskih preizkusih o nastanku izravnalnih prelomov, zato podajamo predlog izdelave pre- izkusnega vzorca in način izvedbe eksperimenta (sl. 8C). Na prostoru med Dornberkom in Ilirsko Bi- strico (okoli 50 km) obstajajo dokazi za desnoz- mično in vertikalno komponento premika ob Raškem prelomu. Razmerje med posameznimi komponentami in bočnim upogibanjem ni pred- met tega članka. Pri interpretaciji izravnalne zgradbe Ra- škega preloma, se postavlja zanimivo vpraša- nje nastanka spremljajočih prelomov Idrijske- ga preloma kot so prikazani na Geološki karti terms and the phenomena they describe define the presented example of secondary faults along the Raša Fault. Therefore, we propose a new term, ad- justing faults, and for the structure itself, adjust- ing structure. The relation of the adjusting faults to the principal fault deep in the vertical plane of the axis of the bending zone cannot be discussed without proper laboratory modeling. The Tomačevica Fault leans asymmetrical- ly toward the Raša Fault trace with respect to the bending zone; in the northwest the leaning angle is larger (splitting side), in the southeast it is smaller (connecting side). We assume that the difference is a result of the geometry of the stress in the bending zone, which is derived from the position of the adjusting fault (Fig. 8B). This characteristic appears in the Tomačevica Fault because it is positioned on the external boundary of the adjusting fault, while the same is not as obvious for the other two faults. This is proba- bly because of the secondary effects, which could be inferred from the complex situation inside the Lukovica strike slip lens and slightly less inside the Kobjeglava strike slip lens. It follows that the Lukovica Fault probably formed first, then the Kobjeglava Fault, and finally the Tomačevi- ca Fault. In contrast to the two lenses between the Tomačevica and Lukovica faults, the split- ting part of the lens between the Lukovica and Raša faults is subsided, while the connecting side is uplifted, indicating the effects of dexral strike slip divergence and convergence. This feature is pronouncedly developed only in this case, which again indicates that the Lukovica adjusting fault is the oldest of the three (Fig. 8A). The regional kinematics of the Raša Fault is discussed in an- other article. The example in Figure 8B shows the initial phase of the formation of the adjusting fault, with further dextral strike slip activity, dextral strike slip divergence and convergence develop, and in the final phase, the tectonic lens is includ- ed in the wider fault zone of the main fault. The development of this process beyond the scope of this article. In the literature, there is no data to support laboratory modeling for the study of adjusting faults, so we propose a design for a method to conduct an experiment (Fig. 8C). In the area between Dornberk and Ilirska Bis- trica (about 50 km) there is evidence of dextral strike slip and vertical component of movement along the Raška fault; however, the relation- ship between individual components and lateral bending is not the subject of this article. 238 Fig. 8. Origin of the adjusting faults. A. Adjusting structure of the Raša Fault. Geological bases after Jurkovšek (2010) and Placer (2015); B. Dynamic model, initial phase; C. Laboratory modeling proposal. Sl. 8. Nastanek izravnalnih prelomov. A. Izravnalna zgradba Raškega preloma. Geologija po Jurkovšek (2010), Placer (2015); B. Dinamski model, inicialna faza; C. Predlog laboratorijskega preizkusa. 1 Raša Fault / Raški prelom 2 Adjusting structure of the Raša Fault, adjusting faults / izravnalna zgradba Raškega preloma, izravnalni prelomi: TF – Tomačevica Fault / Tomačevski prelom, KF – Kobjeglava Fault / Kobjeglavski prelom, LF – Lukovica Fault / Lukovški prelom 3 SF – Sistiana Fault / Sesljanski prelom 4 Sistiana Bending Zone / sesljanska upogibna cona 5 Uplift, subsidence, negligible vertical displacement / dvig, ugrez, neznaten vertikalni premik Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 239The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) In interpreting the adjusting structure of the Raša Fault, an interesting question arises related to the occurrence of the accompanying faults of the Idrija Fault, as represented on the Geological map of the Idrija-Cerkno Hills between Stopnik and Rovte 1: 25.000 (Mlakar & Čar, 2009). Zala and Podgriže Fault are shown in Figure 5. The analogy with the Raša Fault is obvious, as the difference in size and the fact that the adjusting structure of the Idrija Fault indicate a greater degree of development, which would mean that the Idrija Fault is older than the Raša Fault. The latter is also confirmed by the fact that the Idrija Fault is bent as much as its bearing unit (the Trnovo Nappe opposite the Hrušica Nappe), while the Raša Fault is bent less than its bear- ing unit (northwestern part of the Trieste-Komen Anticlinorium opposite the southeastern part). Deformations of the Trieste-Komen Anticlinorium In addition to the bending of the major elements of the structure (Trieste-Komen Anticlinorium, Vipava Synclinorium, Trnovo Nappe opposite the Hrušišica Nappe) and the adjusting structures of the bent strike slip faults (Raša Fault, Idrija Fault), there are other deformations which are di- rectly related to the bending. The most important are the Komen Wedge Structural Step (Komen Wedge Step), the Sistiana Sigmoidal Structure (Sistiana Sigmoid), the Ermada Push-out Block, and the Sistiana Push-out Block (Fig. 9). Komen Wedge Structural Step. In the digital terrain model of Spodnji Kras (Fig. 10), a small difference in the average elevation of the Karst Plateau north and south of Komen (profile A) is visible in the Komen area. There is no such differ- ence east of there, but towards the west it gradual- ly increases and reaches about 100 m in the profile of Ivanji Grad (profile B). There is obviously a step there, which is wedge-shaped and runs in a west- east direction between Ivanji Grad and Komen. On the southwest side of the Divača Fault, west of Ivanji Grad, the step maintains its direction and reaches the Monte Cosici Hill (113 m) above Mon- falcone. In a later tectonic development, it suffered several transformations west of the Divača Fault and collapsed into several sections but retained its original direction. In this article, we are in- terested in the Komen Wedge Structural Step as the primary phenomenon, and which originated together with the Sistiana Bending Zone, so we do not consider later deformations. For the pur- poses of this paper it is enough to conclude, that upon its formation it had a distinct wedge shape Idrijsko-cerkljanskega hribovja med Stopnikom in Rovtami 1:25.000 (Mlakar & Čar, 2009). Na sli- ki 5 sta zabeležena Zalin in Predgriški prelom. Analogija z Raškim prelomom je očitna, razlika je v velikosti in v tem, da kaže izravnalna zgrad- ba Idrijskega preloma višjo stopnjo razvoja, kar bi pomenilo, da je Idrijski prelom starejši od Ra- škega. Slednje potrjuje tudi dejstvo, da je Idrijski prelom upognjen toliko kot njegova nosilna enota (Trnovski pokrov nasproti Hrušiškemu), Raški prelom pa manj od njegove nosilne enote (severo- zahodni del Tržaško-Komenskega antiklinorija nasproti jugovzhodnemu delu). Deformacije Tržaško - Komenskega antiklinorija Poleg upogiba večjih elementov strukture (Tržaško-Komenskega antiklinorija, Vipavskega sinljinorija, Trnovskega pokrova nasproti Hru- šiškemu pokrovu) in izravnalnih struktur upog- njenih zmičnih prelomov (Raški prelom, Idrijski prelom), obstajajo tudi druge deformacije, ki so neposredno povezane z upogibom. Najpomemb- nejše so komenski klinasti strukturni prag (ko- menski klinasti prag), sesljanska sigmoidna zgradba (sesljanska sigmoida), izrivna gruda Grmade in sesljanska izrivna gruda (sl. 9). Komenski klinasti strukturni prag. Na digi- talnem modelu reliefa Spodnjega Krasa (sl. 10) je na območju Komna vidna neznatna razlika v povprečni nadmorski višini kraške uravnave se- verno in južno od Komna (profil A). Te razlike vzhodno od tod ni, proti zahodu pa se postopoma veča in doseže v profilu Ivanji Grad že okoli 100 m (profil B). Obstaja torej prag, ki je klinaste obli- ke in ima med Ivanjim Gradom in Komnom smer zahod – vzhod. Na jugozahodni strani Divaškega preloma, zahodno od Ivanjega Grada, prag zadr- ži smer in sega do hriba Košnik / Monte Cosici (113 m) nad Tržičem / Monfalcone. V poznejšem tektonskem razvoju je prag zahodno od Divaške- ga preloma doživel več transformacij in razpadel na več odsekov, vendar je zadržal prvotno smer. V tem članku nas zanima kot primarni pojav, ki je nastal skupaj s sesljansko upogibno cono, zato kasnejših deformacij ne obravnavamo. Za ta pri- spevek zadostuje ugotovitev, da je ob svojem na- stanku imel vzhodno od Divaškega preloma iz- razito klinasto obliko, zahodno od le-tega pa je danes ta spremenjena. Profila Vojščica (profil C) in Sela na Krasu (profil D) kažeta stanje po več transformacijah. Na karti sta narisana Divaški in Selski prelom (Placer, 2015). Konica klina leži v območju sesljanske upo- gibne cone. Že na prvi pogled je videti, da sesljanska upogibna cona ni nastala z bočnim 240 Fig. 9. Structures of the Sistiana Bending Zone in the Trieste-Komen Anticlinorium: Komen Wedge Structural Step, Sistiana Sigmoidal Structure, Monte Ermada Push-out Structure, Sistiana Push-out Block. Geological bases after Jurkovšek (2010) and Cucchi & Piano (2013), structural bases after Placer (2015). Sl. 9. Strukture sesljanske upogibne cone v Tržaško-Komenskem antiklinoriju: komenski klinasti strukturni prag, sesljanska sigmoidna zgradba, dvignjena gruda Grmade, sesljanska dvignjena gruda. Geološka osnova po Jurkovšek (2010) ter Cucchi in Piano (2013), strukturna osnova po Placer (2015). 1 Cretaceous, Paleocene and Eocene carbonates / kredni, paleocenski in eocenski karbonati 2 Eocene Transitional marlstone and Flysch / eocenski prehodni lapor in fliš 3 Bedding: horizontal, inclined, inverse / plasti: vodoravne, poševne, inverzne 4 Sistiana Bending Zone / sesljanska upogibna cona 5 Active block of bending zone (AKT) / aktivno krilo upogibne cone 6 Passive block of bending zone (PAS) / pasivno krilo upogibne cone (PAS) 7 Komen Wedge Structural Step / komenski klinasti strukturni prag 8 Sistiana Sigmoidal Structure / sesljanska sigmoidna zgradba: a – Gorjansko Syncline / Gorjanska sinklinala, b – Brestovica Anticline / Brestoviška antiklinala, c – Brje Anticline / Brska antiklinala 9 Steep fault: sign for subsided block, relative direction of displacement / strmi prelom: oznaka ugreznjenega krila, relativna smer premika 10 Reverse fault, thrust fault / reverzni prelom, narivni prelom: SRF – Sela Reverse Fault / Selski reverzni prelom, PTF – Palmanova Thrust Fault / Palmanovski narivni prelom 11 SF – Sistiana Fault / Sesljanski prelom, II – fault no. II / prelom št. II 12 GB – Monte Ermada Push-out Block / izrivna gruda Grmade, SB – Sistiana Push-out Block / sesljanska izrivna gruda 13 Direction of external rotation of the active block of bending zone / smer eksterne rotacije aktivnega krila upogibne cone 14. Internal rotation, direction of displacement along the more important planes of the internal discontinuities / interna rota- cija, smer premika vzdolž pomembnejših ploskev internih diskontinuitet Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 241The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) east of the Divača Fault, while west of the fault it is now modified. The profiles Vojščica (profile C) and Sela na Krasu (profile D) show the situation after several transformations. The map shows the Divača and Sela faults (Placer, 2015). The tip of the wedge is positioned in the area of the Sistiana Bending Zone. It is apparent al- ready upon first glance, that the Sistiana Bending Zone was not formed by a lateral bending char- acterized by a symmetrical structure, but by a pushing of the southeastern wing of the Sistiana Bending Zone in the northeast to east-northeast direction and a rotation of its northwest wing in a counter-clockwise direction (Fig. 9). Although upogibom za katerega je značilna simetrična zgradba, temveč pri potisku jugovzhodnega kri- la sesljanske upogibne cone proti severovzhodu do vzhodu-severovzhodu in rotaciji njenega se- verozahodnega krila v nasprotni smeri urinega kazalca (sl. 9). Čeprav obravnavamo Tržaško -Komenski antiklinorij, je pri opisovanju doga- janja bolje uporabljali izraz antiforma, ker gre v bistvu za veliko antiklinalo dinarske smeri z blago nagnjenimi krili in subhorizontalnim ter blago nagubanim širokim jedrom. V rotirajočem krilu so se napetosti kompenzirale z interni- mi zdrsi po obstoječih diskontinuitetah, zato je imelo v kinematskem smislu jugovzhodno krilo Fig. 10. Komen Wedge Structural Step. Topographic profiles. Sl. 10. Komenski klinasti struktur- ni prag. Topografski profili. A – Profile Komen / profil Komen B – Profile Ivanji Grad / profil Ivanji Grad C – Profile Vojščica / profil Vojščica D – Profile Sela na Krasu / profil Sela na Krasu SRF – Sela Reverse Fault / Selski reverzni prelom DF – Divača Fault / Divaški prelom 242 the Trieste-Komen Anticlinorium is examined, use of the term antiform is better, because it is ba- sically a large anticline in the Dinaric direction with slightly inclined limbs and a sub-horizon- tal, slightly folded and broad hinge zone. In the rotating limb, the stresses were compensated by internal slips along the existing discontinuities, so in a kinematic sense the southeast wing of the bending zone played a passive role (PAS in Figs. 9 and 11) and the northwestern one an active role (AKT in Figs. 9 and 11). The rotational relaxation displacements in the active wing were compen- sated for by the bedding-planes, joints, and faults. According to the geological map (Jurkovšek, 2010; Cucchi & Piano, 2013), the faults take a largely Di- naric (NW-SE) direction and are sub-vertical, or they dip steeply to the northeast, while the joints are sub-vertical and run in various directions, most often in the Dinaric and N-S direction. In the limbs of the active antiform, internal slips oc- curred mainly along the bedding-planes and to a minor extent along other discontinuities, so that a large, apparently oblique anticline formed in the northeastern wing; and in the southwestern wing, initially, apparently oblique synclines and later several normal folds formed. We use the qualifier “apparent,” because they are actually monoclinic folds. In the central part of the active limb of the antiform, where the bedding was sub-horizontal, the internal rotation could not occur along the bedding-planes but along the joints and faults in- stead, most easily along the sub-vertical and as perpendicular as possible to the direction of the bending zone. upogibne cone pasivno vlogo (PAS na sl. 9 in 11), severozahodno pa aktivno (AKT na sl. 9 in 11). Razbremenilne premike rotacije v aktivnem kri- lu so prevzele lezike, razpoke in prelomi. Slednji so po podatkih geološke karte (Jurkovšek, 2010; Cucchi in Piano, 2013) imeli večinoma dinarsko smer NW-SE in bili subvertikalni ali vpadali strmo proti severovzhodu, razpoke so bile sub- vertikalne in imele različne smeri, pogoste so zlasti v dinarski smeri in v smeri N-S. V krilih aktivne antiforme so se interni zdrsi dogaja- li predvsem po lezikah in manj po drugih dis- kontinuitetah, tako je v severovzhodnem krilu nastala obsežna navidezna poševna antiklinala, v jugozahodnem krilu pa najprej navidezna po- ševna sinklinala, pozneje pa več normalnih gub. Navidezna zato, ker gre za monoklinalni gubi. V osrednjem delu aktivnega krila antiforme, kjer so bile plasti subhorizontalne, pa se inter- na rotacija ni mogla dogajati po lezikah temveč po razpokah in prelomih, najlažje po tistih, ki so bile subvertikalne in čim bolj pravokotne na smer upogibne cone. Poenostavljeni kinematski model komenske- ga klinastega strukturnega praga je prikazan na sliki 11. Bistven pogoj za njegov nastanek so bile subhorizintalne plasti v jedru Tržaško-Komen- skega antiklinorija in razbremenitev ob Selskem reverznem prelomu, ki je nastal v fazi narivanja in ne sega do sesljanske upogibne cone, temveč se izklini že okoli 8 km prej (sl. 9 in 10). Prelom je bil torej inicialna struktura po kateri je priš- lo do reaktiviranja reverznega premika. Poleg reverzne je morala, v skladu s pravilom interne Fig. 11. Kinematic model of the Komen Wedge Structural Step. Legend in Fig. 9. Sl. 11. Kinematski model komenskega klinastega strukturnega praga. Legenda na sl. 9. Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 243The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) The simplified kinematic model of the Komen Wedge Structural Step is represented in Figure 11. The necessary prerequisite for its formation is the sub-horizontal bedding at the core of the Trieste-Komen Anticlinorium and the relaxation along the Sela Reverse Fault, which formed during the thrusting phase and does not reach as far as the Sistiana Bending Zone, but pinches-out some 8 km before (Figs. 9 and 10). The fault was there- fore the initial structure along which the reverse displacement was reactivated. In addition to the reverse component, according to the internal ro- tation rule there must also be a weak right-lateral displacement component present. Instead of a re- verse displacement, a flexure was formed to the east of the area, where the Sela Fault pinches-out, which shallowed in the eastward direction and disappeared at Komen on the axis of the Sistiana Bending Zone (Figs. 10 and 11). The formation of a wedge structural step is therefore the result of the rigidity of the central part of the antiform and the limited folding possibilities. It is clear from the geometry of the wedge structural step that its pro- nounced shape is developed only in its eastern part near the bending zone, while towards the west it is diminished or subjected to secondary processes. Before the formation of the Komen Wedge Structural Step there were other existing faults other than the Sela Fault that were not reactivat- ed. This is probably because the Sela Fault formed as a reverse fault and reactivated as such, while others, especially those in the Divača Fault Splay, formed as normal faults. As a result, greater fric- tion was created due to the changed kinematics in their fault planes. Sistiana Sigmoidal Structure. The north and south slopes of the Trieste-Komen antiform are deformed in different ways in the active wing of the bending zone. In the first case the bending was unimpeded, while in the second the area was con- fined. The Gorjansko Syncline formed here first as an apparent fold, and then from its limbs as the Brestovica Anticline in the northwestern and as the Brje Anticline in the southeastern wing of the bending zone, both of which were normal flexural folds. This is inferred from the fact that all three folds form a characteristic sigmoidal structure (Figs. 9 and 11). The Brje Anticline in the passive wing of the bending zone is less distinct than the Brestovica Anticline in the active wing. The fold- ed area was mapped by Jurkovšek (2010), the folds were spatially determined by Placer (2015), and the names of folds were defined in this article. The Gorjansko Syncline is integrated into the structure of the wedge structural step, so it must rotacije, obstajati tudi šibka desna horizontalna komponenta. Vzhodno od območja, kjer se Selski prelom izklini, je namesto reverznega premika nastala fleksura, ki se je proti vzhodu plitvila in pri Komnu izklinila v osi sesljanske upogibne cone (sl. 10). Nastanek klinastega praga je torej posledica togosti osrednjega dela antiforme in omejene možnosti gubanja. Iz geometrije klina- stega praga izhaja, da ima izrazito klinasto obli- ko le njegov vzhodni del v bližini upogibne cone, proti zahodu pa se ta izgubi, oziroma je bila pod- vržena sekundarnim procesom. Pred nastankom komenskega klinastega pra- ga, so poleg Selskega preloma obstajali tudi dru- gi prelomi, ki pa niso bili reaktivirani. Vzrok tiči verjetno v tem, da je Selski prelom nastal kot reverzni in se kot tak reaktiviral, medtem ko so drugi, zlasti tisti v divaškem snopu prelomov, nastali kot normalni prelomi. Zaradi tega je bilo trenje ob spremenjeni kinematiki v njihovih pre- lomnih ploskvah večje. Sesljanska sigmoidna zgradba. Severno in južno krilo Tržaško-Komenske antiforme je v aktivnem krilu upogibne cone različno deformi- rano. V prvem primeru je bil upogib neoviran, v drugem je bil prostor utesnjen. V utesnjenem delu je nastala najprej Gorjanska sinklinala, ki je bila zasnovana kot navidezna guba, nato pa iz njenih kril izhajajoči Brestoviška antiklinala v severo- zahodnem in Brska antiklinala v jugovzhodnem krilu upogibne cone, ki sta bili normalni fleksiv- ni gubi. Na to sklepamo po tem, da tvorijo vse tri gube značilno sigmoidno zgradbo (sl. 9 in 11). Brska antiklinala v pasivnem krilu upogibne cone je manj izrazita od Brestoviške v aktivnem krilu. Območje gub je kartiral Jurkovšek (2010), prostorsko jih je izločil Placer (2015), poimenova- ne pa so bile v tem članku. Gorjanska sinklinala je vključena v zgradbo klinastega praga, zato je morala biti zasnovana, ali celo nastati, pred začetkom njegove rasti. Če odnos Gorjanske sinklinale razširimo na celotno sigmoidno zgradbo, je klinasti prag moral nastati v zrelem obdobju razvoja sigmoidne zgradbe. Izrivna gruda Grmade. Pomemben element Brestoviške antiklinale so prelomi v smeri SW- NE severozahodno od Sesljanskega zaliva, ki le- žijo v njenem apikalnem delu. Tip gube, prelomi in morfologija tega območja kažejo na dve fazi razvoja, v prvi je nastala guba, ki ima komponen- te fleksivnega gubanja v drugi fazi pa je prišlo zaradi nezmožnosti nadaljnega gubanja do iz- rivov posameznih blokov med prelomi vzpore- dnimi osni ravnini gube, za katere domnevamo, da so se regenerirali po conah razpoklinskega 244 have its roots, or was even formed, before it began to evolve. If we extend the Gorjansko Syncline re- lation to the entire sigmoidal structure, the wedge structural step must have originated during the mature period of the sigmoidal structure’s devel- opment. Ermada Push-out Block. The SW-NE direct- ed faults northwest of the Sistiana Bay, which are positioned in its apical part, are important elements of the Brestovica Anticline. The type of fold, faults, and morphology of the area indicate two stages of evolution: the first is the formation of the fold, with components of flexural folding; and in the second stage, due to the impossibility of further folding, the individual blocks between the faults, parallel to the fold axis plane and pre- sumably regenerated along the zones of fissure cleavage, were pushed out. In this way, a ridge of Ermada was formed between Ermada (323 m) and Ter (284 m), as well as some reverse faults (Fig. 9). Without detailed analysis, however, it is not possi- ble to determine whether the two phases of evolu- tion took place consecutively or periodically. The vertical displacement is inferred from the relief itself, while the strike-slip displacement inter- preted by Cucchi & Piano (2013) is based on an apparent horizontal movement. Sistiana Push-out Block. Its formation is de- scribed in the description of the structure of Sisti- ana Bay in the chapter on the Sistiana Fault (Figs. 3 and 9). Deformation sequence. Based on the relation- ship between the four structures of the Sistiana Bending Zone in the Trieste-Komen Anticlinori- um, we can conclude the following: 1. The sigmoidal structure began to form be- fore the Komen Wedge Structural Step. 2. The Komen Wedge Structural Step formed due to the limited possibility of contraction of the area in the sigmoidal structure and due to the rigidity of the central part of the anticlinorium. 3. The Komen Wedge Structural Step was formed after the formation of the level sur- face of the Trieste-Komen Anticlinorium. 4. The Grmada Push-out Block and one or two smaller blocks in the vicinity are the result of extreme contraction in the area of a sig- moidal structure. 5. The Sistiana Push-out Block is positioned along the Sistiana Fault. Its formation is re- lated to the corresponding joint-fault frame- work and rotation of the active wing of the Sistiana Bending Zone. klivaža. Tako je nastal greben Grmade med Grmado / Ermada (323 m) in Terom (284 m) ter nekaj reverznih prelomov (sl. 9). Ali sta obe fazi potekali zaporedoma ali s prekinitvijo, brez podrobne analize ni mogoče ugotoviti. Da gre za vertikalno izrivanje kaže sam relief, interpre- tacija Cucchi-ja in Piano-ve (2013) z zmikanjem sloni na navideznem horizontalnem premiku. Sesljanska izrivna gruda. Opis njenega na- stanka je podan pri opisu zgradbe Sesljanskega zaliva v poglavju o Sesljanskem prelomu (sl. 3 in 9). Zaporedje deformacij. Na podlagi razmerja med omenjenimi štirimi strukturami sesljanske upogibne cone v Tržaško-Komenskem antiklino- riju lahko sklenemo naslednje: 1. Sigmoidna zgradba je pričela nastajati pred komenskim klinastim pragom. 2. Komenski klinasti prag je pričel nastajati zaradi omejene možnosti krčenja prostora na območju sigmoidne zgradbe in zaradi togosti osrednjega dela antiklinorija. 3. Komenski klinasti prag je nastal po izoblikovanju uravnave na območju Tržaško-komenskega antiklinorija. 4. Izrivna gruda Grmade in ena ali dve manjši v bližini, so skrajni izraz krčenja prostora v območju sigmoidne zgradbe. 5. Sesljanska izrivna gruda leži ob Sesljan- skem prelomu, njen nastanek je povezan z ustreznim razpoklinsko-prelomnim predri- som in rotacijo aktivnega krila sesljanske upogibne cone. Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 245The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) Deformation sequence From the characteristics of the Sistiana Bend- ing Zone and its relationships with the fault deformations that cross it, we can establish a deformation sequence for the zone. The criteria for classifying faults preceding the formation of the Sistiana Bending Zone requires that they be as bent as the host tectonic unit. Such, for ex- ample, is the Paleodivača Fault, which is bent much like the Trieste-Komen Anticlinorium, and the Idrija Fault, whose bending is approximately the same as the degree of rotation of the Trnovo Nappe opposite the Hrušica Nappe. The Raša Fault formed during the second half of the growth of the Sistiana Bending Zone, because its bending is smaller than for the Tri- este-Komen Anticlinorium. After the bending and subsequent shearing, which may have been a single or multi-stage process, secondary faults of the adjusting structure formed. These, together with the main fault, may have been bent again, but no such research has been undertaken. The associated faults of the Idrija Fault are in- cluded conditionally in the analysis; however, we can reasonably assume that they formed the same way they did at the Raša Fault. This remains an assumption due to the absence of mapping evi- dence of the trace of the Zala Fault and the Lome Zone towards the southeast (Fig. 5). The morphology of the Komen Wedge Struc- tural Step indicates that a leveled morphology prevailed before its formation. Since this is a leveled Trieste-Komen Anticlinorium, further research is required in order to open a discussion of the leveled areas inside the External Dinaric Imbricated Belt (parautochton) and their rela- tion to the leveled areas of the External Dinaric Thrust Belt (allochthonous) and Microadria. The Sistiana Bending Zone is an important in- dicator of the deformation sequence in a certain time period in a certain space after the formation of the Dinaric thrust structure. Said deformations will need to be related to deformations outside the area. The kinematic phases described in this arti- cle were formed in the following order: 1. The formation of the Sistiana Bending Zone evolved gradually in the direction of the pushing of the Istria Block towards the Di- narides. The precise direction of pushing has not yet been determined. At first, the north- western part of the Trieste-Komen Anticlino- rium began to rotate, then the process grad- ually extended to the Vipava Synclinorium and the Trnovo Nappe. Together with these units, disjunctive deformations inside them, Zaporedje deformacij Iz značilnosti sesljanske upogibne cone in nje- nih odnosov s prelomnimi deformacijami, ki jo prečkajo, je mogoče postaviti zaporedje deforma- cij tega območja. Merilo za uvrstitev prelomov v čas pred nastankom sesljanske upogibne cone je, da morajo biti enako usločeni kot tektonska eno- ta v kateri ležijo. Tak je Paleodivaški prelom, ki je enako usločen kot Tržaško-Komenski antikli- norij, in Idrijski prelom, katerega usločenost je približno tolikšna, kot znaša zasuk Trnovskega pokrova nasproti Hrušiškemu pokrovu. Raški prelom je nastal v drugi polovici rasti sesljanske upogibne cone, ker je njegova usloče- nost manjša od usločenosti Tržaško-Komenskega antiklinorija. Po usločitvi in ponovnem strigu, kar je bilo lahko enkratno ali večkratno dejanje, so nastali njegovi sekundarni prelomi izravnal- ne zgradbe. Ti bi bili skupaj z glavnim prelomom lahko domnevno ponovno usločeni, vendar razi- skave v to smer niso bile opravljene. Pridruženi prelomi Idrijskega preloma so vključeni v analizo pogojno, čeprav upravičeno domnevamo, da so nastali na enak način kot pri Raškem prelomu. Vzrok je v odsotnosti dokazov kartiranja o poteku Zalinega preloma in lomske cone proti jugovzhodu (sl. 5). Morfologija komenskega klinastega struk- turnega praga kaže na to, da je pred njegovim nastankom obstajala uravnava. Ker gre za urav- nani Tržaško-komenski antiklinorij, bo pri na- daljnjih raziskavah potrebno odpreti razpravo o uravnavah znotraj Zunanjedinarskega naluska- nega pasu (paravtohtona) in njihovem odnosu do uravnav Zunanjedinarskega narivnega pasu (alohtona) in Mikroadrije. Sesljanska upogibna cona je pomemben kaza- lec zaporedja deformacij določenega časovnega obdobja in določenega prostora, po nastanku di- narske narivne zgradbe. Nanje bo potrebno veza- ti deformacije izven tega območja. V tem članku omenjene kinematske faze so nastale po nasled- njem zaporedju: 1. Nastanek sesljanske upogibne cone je po- tekal postopoma v smeri potiskanja istrs- kega bloka proti Dinaridom. Natančnejša smer potiskanja še ni določena. Najprej se je pričel upogibati severozahodni del Tržaško-komenskega antiklinorija, na kar se je proces postopoma širil na Vipavski sinklinorij in Trnovski pokrov. Skupaj s temi enotami so se sukale tudi disjunktivne deformacije znotraj le-teh od Istrsko-fur- lanske podrivne cone do Paleodivaškega in Idrijskega preloma. Začetek nastajanja 246 from the Istra-Friuli Underthrust Zone to the Paleodivača and Idrija faults, also under- went rotation. Determination of the start of the formation of the Sistiana Bending Zone could be possible with an analysis of the cave sediments in the active wing of the Sistiana Bending Zone in the Trieste-Komen Anti- clinorium. 2. In conjunction with the rotation of a part of the Trieste-Komen Anticlinorium the Gor- jansko Syncline, the oldest structure of the Sistiana Sigmoidal Structure, began to form. 3. The Komen Wedge Structural Step began to form after the formation of the Gorjansko Syncline and before the formation of the Sis- tiana Sigmoidal Structure. The leveling of the Trieste-Komen Anticlinorium predates the Komen Wedge Structural Step. 4. The Raša Fault formed after a relatively extended period of growth of the Sistiana Bending Zone. 5. The Raša Fault bent in the further evolution of the bending zone. The reverse component of displacement along the fault with the up- lifting NE block is likely to develop or begin to develop at this stage. 6. An adjusting structure of the Raša Fault is formed in the right-lateral shearing condi- tions, which gradually includes the Lukovica, Kobjeglava, and Tomačevica faults. It is un- clear whether all three adjusting faults rep- resent three stages of bending and displace- ment or whether this is simply a continuous process. 7. Assuming that the adjusting structure of the Raša Fault is bent, the bending zone start- ed to grow again. Finally, the Sistiana Sig- moidal Structure and the Ermada Push-out Block have been fully developed. The Sisti- ana Push-out Block is also formed. The origi- nally uniform Komen Wedge Structural Step assumes its present fragmented appearance, but its formation is also related to other pro- cesses. 8. Recent dynamics is a matter of detailed ge- odetic surveying and proper interpretation; the position of the geodetic points would have to be based on a sound theoretical frame- work. The timing of the inception or formation of the individual phases and dynamics of the events con- stitutes the fundamental issue of the described deformation sequence. We know only a little about this now, but we can roughly estimate the timing for the inception of the Raša right-lateral strike sesljanske upogibne cone bi bilo mogoče določiti z analizo jamskih sedimentov ak- tivnega krila sesljanske upogibne cone v Tržaško-komenskem antiklinoriju. 2. Skupaj s sukanjem dela Tržaško-Komens- kega antiklinorija je pričela nastajati Gor- janska sinklinala, ki je najstarejši člen sesl- janske sigmoidne zgradbe. 3. Komenski klinasti strukturni prag je pričel rasti po nastanku Gorjanske sin- klinale in pred dokončnim izoblikovanjem sesljanske sigmoidne zgradbe. Uravnava Tržaško-Komenskega antiklinorija je stare- jša od komenskega klinastega praga. 4. Raški prelom je nastal po sorazmerno dal- jšem obdobju rasti sesljanske upogibne cone. 5. Pri nadaljnji rasti upogibne cone se je Raški prelom usločil. V tej fazi verjetno nastane, ali prične nastajati, reverzna komponenta premika severovzhodnega krila preloma. 6. V desnostrižnih pogojih nastane izravnal- na zgradba Raškega preloma, ki postopo- ma vključuje Lukovški, Kobjeglavski in Tomačevski prelom. Ni jasno ali trije iz- ravnalni prelomi pomenijo tri faze upogib- anja in zmikanja, ali gre za kontinuiran proces. 7. Če privzamemo domnevo, da je izravnal- na zgradba Raškega preloma usločena, se po njenem nastanku prične ponovna rast upogibne cone. Do sedanjega stanja se dokončno razvije sesljanska sigmoid- na zgradba in izrivni blok Grmade. Nas- tane tudi sesljanska izrivna gruda. Prvotno enoten komenski klinasti strukturni prag dobi sedanjo fragmentirano podobo, vendar je njgov nastanek povezan tudi z drugimi procesi. 8. Sedanje dogajanje je stvar podrobnih geo- detskih meritev in ustrezne interpretacije. V ta namen je potrebno postaviti merske točke na podlagi trdnega teoretskega modela. Temeljni vprašanji opisanega zaporedja sta čas nastanka ali nastajanja posameznih faz in dinamika dogajanja. O tem vemo v tem trenut- ku malo, vsaj približno pa lahko ocenimo čas nastanka Raškega desnozmičnega preloma. Ob Raškem prelomu je v Ilirski Bistrici nastal pull apart-ski bazen (Placer in Jamšek, 2011), v kate- rem se je sedimentiral premog in nad njim oko- li 100 m gline. Ta je po Osnovni geološki kar- ti srednjepliocenske starosti (Šikić in Pleničar, 1975). Podatki so posredni, pridobljeni so bili po primerjavi prikamnin premoga iz rudarskih del v premogovniku in vrtinah, kjer niso našli fo- Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 247The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) slip fault. Along the Raša Fault, a pull-apart basin formed at Ilirska Bistrica (Placer & Jamšek, 2011), in which coal deposited with some 100 m of clay over the top. According to the Basic Geological Map (Šikić & Pleničar, 1975) it is of Middle Pliocene age. However, the related age-data obtained is only in- direct, and was determined by comparing the host rock of the coal from mining works and boreholes free of fossils with similar strata in Istria (Petra- schek, 1926/26). A Mastodon arvenensis was found here, whose age was used to date the basin. The age of the horizon at the lower part of the basin would be about 3.6 myr based on the Internation- al Chronostratigraphic Chart (2020/03). The fault formed earlier, probably in the Lower Pliocene or some 5 million years ago. This data is consistent with the results of the modeling of the shear heat- ing connected with heat flow data, which indicates that displacements along the regional right-lateral strike-slip faults in southwestern Slovenia started at the beginning of the Pliocene (Caporali et al., 2013). The Raša Fault originated in the second half of the evolution of the Sistiana Bending Zone, so the onset of such is probably far older. Moulin et al. (2016) propose activation of the right-lateral strike-slip displacement along the Raša Fault in the Early to Middle Pleistocene, and along the Idrija Fault in the Late Pliocene, based on geomorphological data for western Slovenia. In both cases, the data is valid for a particular segment, which may or may not apply to the en- tire fault. In addition, calculations assume that a constant average displacement velocity along the faults, which also may or may not be the case. In general, the onset of the regional phase of right-lat- eral strike-slip activity along the Dinaric faults is set in the beginning of the Pliocene (Vrabec & Fodor, 2006; Čar, 2010; Žibert & Vrabec, 2016). We have shown that the Paleodivača and Idrija faults originated before the evolution of the Sisti- ana Bending Zone. The Belsko Fault has not been sufficiently investigated, so it is reasonable to leave it aside; it is mentioned only because it is signifi- cantly deformed in the area between the Hrušica and Trnovo Nappes in the Sistiana Bending Zone. Among the faults, only the Raša Fault originated during the growth of the bending zone; as a result, it represents a suitable subject for investigations of the dynamics of bending, right-lateral strike- slip displacements, and formation of the adjusting faults. The initiation and mechanism of the evo- lution of the Raša Fault is not the subject of this paper. Assuming a constant counter-clockwise rotation of the Adria Microplate (Weber et al., 2010) and the constant growth of the Istra Pushed silov, s plastmi v Istri (Petraschek, 1926/29). Tu je bil najden Mastodon arvenensis, po katerem so sklepali na starost. Po današnji mednarodni časovni lestvici (2020/03) bi bile plasti spodnjega dela bazena potemtakem stare okoli 3,6 milijona let. Prelom je moral nastati pred tem, verjetno v spodnjem pliocenu ali na njegovem začetku pred približno 5 milijoni leti. Ta podatek se uje- ma z rezultati modeliranja strižnega segrevanja prostora v povezavi s podatki toplotnega toka, ki nakazujejo, da so se premiki ob regionalnih desnozmičnih prelomih v jugozahodni Sloveniji pričeli v začetku pliocena (Caporali in sodelav- ci, 2013). Raški prelom je nastal v drugi polovici razvoja sesljanske upogibne cone, zato je začetek njenega nastajanja precej starejši. Aktivacijo desnozmičnega premika ob Ra- škem in Idrijskem prelomu na podlagi geomor- foloških podatkov v zahodni Sloveniji, umešča- jo Moulin in sodelavci (2016) za Raški prelom v spodnji do srednji pleistocen, za Idrijski prelom v zgornji pliocen. Seveda gre v obeh primerih za podatke določenega segmenta, ki morda ne velja- jo za celotni prelom. Poleg tega temeljijo izraču- ni na predpostavki, da je bila povprečna hitrost premika ob prelomih ves čas enaka, kar morda ne drži. Na splošno je začetek regionalne faze desnozmične aktivnosti ob dinarskih prelomih postavljen v začetek pliocena (Vrabec & Fodor, 2006; Čar, 2010; Žibert & Vrabec, 2016). Videli smo, da sta Paleodivaški in Idrijski prelom nastala pred pričetkom rasti sesljan- ske upogibne cone. Belski prelom še ni dovolj raziskan, zato ga je smiselno pustiti ob strani, omenjen je le zato, ker je na prostoru med Hru- šiškim in Trnovskim pokrovom, torej v območju sesljanske upogibne cone, močno deformiran. Od ostalih je med rastjo upogibne cone zanesljivo nastal le Raški prelom, ki je zato primeren za študij dinamike upogibanja, desnega zmikanja in nastajanja izravnalnih prelomov. Vzrok in mehanizem nastanka Raškega preloma ni pred- met obravnave tega članka. Pri predpostavlje- ni konstantni rotaciji Jadranske mikroplošče v nasprotni smeri urinega kazalca (Weber et al., 2010) in konstantni rasti Istrskega potisnega ob- močja, bi po nastanku Raškega preloma proces lahko tekel po treh kinematskih scenarijih: 1. Hkratno ukrivljanje prelomne ploskve v sesljan- ski upogibni coni in desno zmikanje, ki je lahko vodoravno ali poševno; ko zmikanje po glavni prelomni ploskvi ni več mogoče, nastane izrav- nalni prelom. 2. Izmenično ukrivljanje in zmi- kanje; v fazi ukrivljanja so mogoči tudi reverzni premiki. 3. Tektonska zrcala in neravne zglajene 248 Fig. 12. DTM of the Sistiana Bending Zone. A. Structural basis after Simplified Structural-geological Map of Kras (Placer 2015). CW – Timavo Compressional Wedge; AS – Adjusting structure of the Raša Fault; B. DTM. Sl. 12. Relief sesljanske upogibne cone. A. Strukturna podlaga po Poenostavljeni strukturno-geološki karti Krasa (Placer 2015). CW – Timavski kompresijski klin; AS – Izravnalna zgradba Raškega preloma; B. Relief. 1 Quaternary sediments / kvartarni sedimenti 2 Transitional Eocene marlstone and Flysch / prehodni eocenski lapor in fliš Ladislav PLACER, Petra JAMŠEK RUPNIK & †Bogomir CELARC 249The Sistiana Fault and the Sistiana Bending Zone (SW Slovenia) Area following the initiation of the Raša Fault, the process could have evolved according to one of three kinematic scenarios: 1. Simultaneous bend- ing of the fault plane in the Sistiana Bending Zone and horizontal or oblique right-lateral strike-slip displacement; when movement along the princi- pal fault plane is no longer possible, the adjusting fault is formed. 2. Alternate bending and strike- slip displacement; during the bending phase, re- verse displacements are also possible. 3. Tectonic mirrors and unevenly smoothed planes in the Raša Fault Zone indicate a mixed scenario, in addition to the planes with sub-horizontal and sub-vertical slickensides. This question cannot be definitively answered without a detailed investigation. Conclusions Analysis of the Sistiana Bending Zone provid- ed new insight into a certain section of the Istra Pushed Area deformation sequence and suggests the possibility of future qualitative and quantita- tive studies of the structure and dynamics of the northeastern part of Microadria. The Sistiana Push-out Block, the sigmoidal structure with the Ermada Push-out Block, the Komen Wedge Structural Step, and the adjusting structure of the Raša Fault (Fig. 12) are the most prominent structural effects of the evolution of the Sistiana Bending Zone in the Trieste-Komen Anticlinorium. The Wedge-shaped Structural Step and ad- justing faults are new terms in the geological lit- erature. The sigmoidal structure finally evolved in the area between the Komen Wedge Structural Step and the Sistiana Bending Zone. We propose name Timavo Compressional Wedge for this particular ploskve v coni Raškega preloma, poleg ploskev z subhorizontalnimi in subvertikalnimi drsami, kažejo na mešani scenarij. Na to vprašanje ne bo mogoče odgovoriti brez detajlnih raziskav. Sklepi Analiza sesljanske upogibne cone je dala vpogled v določeni izsek zaporedja deformacij Istrskega potisnega območja in nakazala mož- nost nadaljnega kvalitativnega in kvantitativne- ga študija zgradbe in dinamike severovzhodnega dela Mikroadrije. Najvidnejše strukturne posledice nastanka sesljanske upogibne cone v Tržaško-komenskem antiklinoriju so sesljanska izrivna gruda, sigmo- idna zgradba z izrivno grudo Grmade, komenski klinasti strukturni prag in izravnalna zgradba Raškega preloma (sl. 12). Klinasti strukturni prag opisanega tipa in iz- ravnalni prelomi predstavljajo novosti v geološki literaturi. Sigmoidna zgradba se je dokončno izoblikova- la na prostoru med komenskim klinastim struk- turnim pragom in sesljansko upogibno cono, ki ga zaradi oblike in lažjega sporazumevanja ime- nujemo timavski kompresijski klin. Ta predsta- vlja specifični strukturni objekt, ki združuje več vidikov kompresije; narivanje, gubanje, izriva- nje in interne razbremenilne zdrse (sl. 12). Sesljanska upogibna cona je nastajala dolgo obdobje, začetek njenega nastajanja je starej- ši od 5 milijonov let. Današnje stanje je mogoče oceniti po razmerah v Sesljanskem zalivu, kjer je Sesljanski prelom presekan s prelomom št. IV (30/80) (sl. 4) in nekaj šibkejšimi prelomi severno od tod. Zaradi tega verjetno ni več aktiven, ali pa je njegova aktivnost sekundarnega pomena. Po Fig. 12. / Sl. 12. 3 Carbonates of Cretaceous, Paleocene, and Eocene age. Darker green Brje Formation of Early Cretaceous age, the oldest outcropping unit in the Trieste-Komen Anticlinorium / karbonati kredne, paleocenske in eocenske starosti, temnejše zeleno Brska formacija spodnjekredne starosti, najstarejše razgaljene plasti Tržaško-Komenskega antiklinorija 4 Dip of bedding / vpad plasti 5 Principal faults / glavni prelomi: RF – Raša Fault / Raški prelom, PF – Paleodivača Fault / Paleodivaški prelom, SF – Sistiana Fault / Sesljanski prelom 6 Secondary faults / drugotni prelomi: LF – Lukovica Fault / Lukovški prelom, KF – Kobjeglava Fault / Kobjeglavski prelom, TF – Tomačevica Fault / Tomačevski prelom, DF – Divača Fault (northwestern part) / Divaški prelom (severozahodni del) 7 Tear fault / raztržni prelom 8 Reverse fault in the Timavo compressional wedge / reverzni prelom v timavskem kompresijskem klinu 9 Reverse and thrust fault of the Istra-Friuli Underthrust Zone / reverzni in narivni prelom istrsko-furlanske podrivne cone: SRF – Sela Reverse Fault / Selski reverzni prelom, TTF – Trieste Thrust Fault / Tržaški narivni prelom 10 Monte Ermada Push-out Block / izrinjena gruda Grmade 11 Sistiana Push-out Block / sesljanska izrivna gruda 12 Sistiana Sigmoidal Structure / sesljanska sigmoidna zgradba: a – Gorjansko Syncline / Gorjanska sinklinala, b – Brestovica Anticline / Brestoviška antiklinala, c – Brje Anticline / Brska antiklinala 13 Komen Wedge Structural Step / komenski klinasti strukturni prag 14 Sistiana Bending Zone / sesljanska upogibna cona 15 Axis of the Trieste-Komen Anticlinorium and Vipava Synclinorium (Planina Syncline) / os Tržaško-Komenskega antikli- norija in Vipavskega sinklinorija (Planinska sinklinala) 250 area. This is a specific structural object that com- bines several aspects of compression: thrusting, folding, push-out, and internal relaxation dis- placements (Fig. 12). The Sistiana Bending Zone evolved over a long period of time, which began more than 5 million years ago. The current situation in the Zone can be inferred from the situation in the Sistiana Bay, where the Sistiana Fault is cut by fault no. IV (30/80) (Fig. 4) and some less important faults further north. As a result, it is probably no longer active, or its activity is of secondary importance. By analogy, the Sistiana Fault is probably cut by faults, positioned south of fault no. IV (Fig. 3). The rate of bending decreases gradually to- wards the northeast in the active wing of the Sis- tiana Bending Zone. The adjusting structure of the Idrija Fault is also included in the conclusions, although it is only hypothetically related to the Sistiana Bending Zone (Fig. 5). The lateral defor- mation of the Belsko Fault is different because of factors, which are not addressed in this article. The direction of the Sistiana Fault offshore in the Trieste Bay is most likely indicated by the di- rection of the bending zone. After describing the Sistiana Bending Zone, it is possible to execute an in-depth study of the relationship between the External Dinarides and the active Microadria. analogiji verjetno sekajo Sesljanski prelom tudi prelomi južno od preloma št. IV (sl. 3). Velikost upogiba aktivnega krila sesljanske upogibne cone se proti severovzhodu polagoma manjša. V zaključke je vključena tudi izravnalna zgradba Idrijskega preloma, čeprav je s sesljan- sko upogibno cono povezana hipotetično (sl. 5). Bočna deformacija Belskega preloma je drugač- na zaradi dejavnikov, ki jih v tem članku nismo obdelali. Smer upogibne cone zelo verjetno nakazuje tudi smer Sesljanskega preloma v podmorju Tr- žaškega zaliva. 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