Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob (central Slovenia) Značaj okremenjene fosilne združbe zgornjekarnijskih amfiklinskih plasti pri Crngrobu (osrednja Slovenija) Luka GALE1,2, Uroš NOVAK3, Tea KOLAR-JURKOVŠEK2, Matija KRIŽNAR4 & France STARE5 1University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Geology, Privoz 11, SI- 1000 Ljubljana, Slovenia, e-mail: luka.gale@ntf.uni-lj.si 2Geological Survey of Slovenia, Dimičeva 14, SI-1000 Ljubljana, Slovenia 3Lovšetova ulica 4, SI-1260 Ljubljana-Polje, Slovenia 4Slovenian Museum of Natural History, Prešernova 20, SI-1000 Ljubljana, Slovenia 5Žabnica 75, SI-4209 Žabnica, Slovenia Prejeto / Received 29. 9. 2016; Sprejeto / Accepted 28. 2. 2017; Objavljeno na spletu / Published online 9.6.2017 Key words: Slovenian Basin, Southern Alps, Upper Triassic, Tuvalian, diagenesis, chert, silicification, conodonts Ključne besede: Slovenski bazen, Južne Alpe, zgornji trias, tuval, diageneza, roženec, okremenitev, konodonti Abstract The village of Crngrob (central Slovenia) is known to geologists for the silicified fossils found in the thick soil covering the “Amphiclina beds”, a Carnian lithostratigraphic unit of the Mesozoic Slovenian Basin. Due to silicification, the assemblage may provide an important insight into Carnian marine life; however, the nature of the fossil assemblage, as well as the timing and mode of silicification are unknown. A detailed sedimentological section, which covers the uppermost part of the “Amphiclina beds” and their transition to the “Bača Dolomite”, was recorded at one of the fossil-bearing localities. The section consists of limestone (including bioturbated filament and radiolaria-filament wackestones, laminated filament packstone, bioclast wackestone, peloid packstone, floatstone with intraclasts and bioclasts, and intraclast floatstone and rudstone), marlstone and dolomite. Chert is locally present in nodules or as dispersed silicified patches, giving a speckled appearance to the host rock. According to our interpretation, the deposition of the limestone occurred via hemipelagic settling, turbidite currents and debris flows in a slope-to-basin or outer ramp setting. The composition of the grains (which include green algae fragments, thick-shelled bivalves, corals and solenoporacean algae) clearly points to the allochthonous nature of the material, which was largely derived from shallow-water environments. Fossils, as well as the intraclasts and sometimes the matrix, are locally replaced by chalcedony and granular megaquartz. This type of silicification does not appear to be selective to particular microfacies. As the silicification occurred after the down-slope transport of shells and the deposition of the sediment, the Crngrob fossil assemblage represents a thanatocoenosis or even a taphocoenosis, and it is not representative of autochthonous Carnian associations. Izvleček Okolica Crngroba (osrednja Slovenija) je geologom poznana po okremenjenih fosilih, najdenih v preperini, ki prekriva karnijske amfiklinske plasti. Zaradi okremenjenosti bi fosilna združba lahko nosila pomembno paleoekološko vrednost, vendar njen izvor in značaj nista znana, tako kot nista poznani vrsta in čas okremenitve. V okviru raziskave smo na eni od lokalitet, kjer so bili najdeni fosili, posneli sedimentološki profil preko zgornjega dela amfiklinskih plasti in prehoda v baški dolomit. Zaporedje sestavlja menjavanja plasti apnenca (bioturbiranega filamentnega in radiolarijsko-filamentnega wackestona, laminiranega filamentnega packstona, bioklastičnega wackestona, peloidnega packstona, floatstona z intraklasti in bioklasti ter intraklastičnega floatstone do rudstona), laporovca in dolomita. Lokalno se pojavlja roženec v obliki večjih gomoljev ali drobnih, razpršenih zaplat. Glede na našo interpretacijo je sedimentacija potekala na zunanjem delu pobočja ali ob vznožju pobočja, kjer se hemipelagični in deloma pelagični apnenci prepletajo s sedimenti turbiditnih in drobirskih tokov. Gravitacijski tokovi so večino biogenih zrn, kot so zelene alge, debelolupinske školjke, korale in solenoporaceje, prinesli iz plitvomorskih okolij. Fosili, mestoma pa tudi mikritni intraklasti in osnova, so nadomeščeni s kalcedonom in zrnatim megakremenom. Ta vrsta okremenitve ni vezana na posamezen mikrofacies, temveč se pojavlja v vseh apnenčastih in dolomitnih plasteh. Ker je do okremenitve prišlo po prenosu materiala po pobočju navzdol, nabrana fosilna združba ne more predstavljati naravne karnijske življenjske združbe, temveč gre za primer tanatocenoze ali celo za tafocenozo. GEOLOGIJA 60/1, 61-75, Ljubljana 2017 https://doi.org/10.5474/geologija.2017.005 © Author(s) 2017. CC Atribution 4.0 License 62 Luka GALE, Uroš NOVAK, Tea KOLAR-JURKOVŠEK, Matija KRIŽNAR & France STARE Introduction With the right timing, silicification may pro- vide high-quality preservation of fossils, because it preserves fine-scale morphological details and small, fragile or otherwise rarely fossilized organ- isms. Silicified fossil assemblages may thus yield a valuable insight into past life (cherns & wriGht, 2009; MerGl, 2010; Butts & BriGGs, 2011). A large collection of silicified and/or pyritized (limoni- tized) centimetre-sized cephalopods (ammonites), brachiopods, bivalves and gastropods, as well as a few large pieces of colonial corals has been assem- bled through almost 25 years of field work by F. Stare in the vicinity of Crngrob (central Slovenia). This site has raised considerable interest among professional geologists, but the lack of quality ex- posures has prevented a more detailed analysis. According to previous work (raMovš, 1981, 1986, 1987, 1998a, b) the fossils derive from black mic- ritic limestone of Tuvalian (Upper Carnian) age, which belongs to the “Amphiclina beds” (GraD & FerJančič, 1968; rOŽič et al., 2015), an informal lithostratigraphic unit of the Slovenian Basin, but no further account of the fossil-bearing beds has been given until now. A well exposed succession of shale, limestone, marlstone and dolomite at one of the fossil-bear- ing sites near the village of Crngrob has been dis- covered during the geological mapping of the area. The section provided an opportunity to document the composition of the uppermost “Amphiclina beds” and to evaluate the nature of the Crngrob fossil assemblage and its potential use in palae- oecological studies of Carnian marine life. We at- tempted to identify the depositional environment, the diagenetic sequence, the type and relative timing of silicification and/or pyritization, and to characterize the quality of the preservation. This paper also provides the basis for future taxonomic determinations of the Crngrob fossil assemblage. Geological Setting The studied area is located in the vicinity of the village of Crngrob in central Slovenia (Fig 1). The geological structure of this area is covered by the Basic Geological Map of Yugoslavia, Sheet Kranj (GraD & FerJančič, 1968, 1976). A recon- naissance of the area has been carried out by rOŽič et al. (2015). Most recently, the leading au- thor of this paper made a detailed map in order to compare the distribution of lithological units with the positions of fossil sites (Fig. 2). Two ma- jor tectonic units have been identified. The east- Fig. 1. Location of the studied area. Rectangle shows the area of the geological map in Fig. 2. Fig. 2. Simplified geological sketch map of area E of the vil- lage of Crngrob (the mapping was performed by one of the authors, L.G.). ern part of the map belongs to the Tolmin Nappe of the eastern Southern Alps (Placer, 1999, 2008). The oldest lithostratigraphic unit here consists of alternating shale, siltstone, bedded limestone 63Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob and black dolomite, which belong to the “Am- phiclina beds” (sensu turnšeK et al., 1982; Bus- er, 1986). The “Amphiclina beds” grade into the Norian-Rhaetian “Bača Dolomite” (i.e., bedded dolomite with chert). Both are considered to have been deposited in the deeper marine Slovenian Basin (cousin, 1981; Buser, 1986, 1989, 1996), a marine intraplatform trough situated at the western passive continental margin of the Ne- otethys Ocean (see the palaeogeographic recon- struction in haas et al., 1995). To the east, the “Amphiclina beds” are unconformably overlain by uppermost Eocene-lower Oligocene conglom- erates. To the west, the “Amphiclina beds” and the “Bača Dolomite” are in fault contacts with red quartz sandstone (the Permian Gröden For- mation), marly limestone, carbonate siltstone and marlstone with mica (the Lower Triassic Werfen Formation), and Triassic thick-bedded to massive dolomite with some stromatolites, all of which belong to the External Dinarides tectonic unit (Placer, 1999, 2008). A reconnaissance of the area (Fig. 2) shows that the silicified fossils de- rive only from the “Amphiclina beds”. Methods The fossil-bearing succession was recorded along a forest road (Figs. 1-2) at one of the fos- sil-bearing sites. From this section, 26 samples were collected. An additional 10 samples, which were silicified to various degrees, were collect- ed from debris approximately 130 m to the SW after the lateral continuity of the beds had been verified. For optical microscope analysis, 40 thin sections of sizes 47×28 mm and 75×49 mm were prepared. Selected thin sections were stained with Alizarin Red S. Microfacies (MF) types were named according to the terminology of DunhaM (1962) and eMBry and Klovan (1971). The quartz terminology used here follows that of Maliva and siever (1988). Grain proportions were determined by counting 300 random points per section us- ing JMicroVision v.1.2.7 software (© 2002-2008 Nicholas Roduit). Cathodoluminescence (CL) was performed using a cold cathode CITLCL8200/ MK4 (Technosyn, Cambridge) at a voltage of 16 kV and a current of 300-450 mA. Neither filters nor standards were used for image calibration. In addition to sedimentological samples, nine com- posite conodont samples with an average weight of approximately 2 kg were collected and treat- ed with acetic acid. Following this treatment, the conodont elements were hand-picked for determi- nation. The conodont elements were photographed with a JEOL JSM 6490 LV Scanning Electron Mi- croscope. The Conodont Alteration Index (CAI) was determined according to ePstein et al. (1977). Description of section The studied section (46°12´22.59´́ N, 14°18´12.68´́ E) is located in the upper part of the “Amphiclina beds”, and extands to the contact with the “Bača Dolomite” (Figs. 3, 4). The recorded beds are un- derlain by shale and siltstone, whereas the domi- nant lithology in the section is bedded limestone (locally dolomitized), which is interbedded with marlstone. Several MF types were identified within the limestone beds (see Table 1 for a de- tailed description). Wackestone (MF 1 and 3) is bioturbated and mostly thin- to medium-bedded. Some thicker beds display amalgamation, with wavy inter- calations of marl. Thin-shelled bivalves (fila- ments) and radiolaria are common fossils (Fig. 5.1-5.2). In a few beds, filaments form a pack- stone texture, with shells oriented concordant to the bedding plane (MF 4; Fig. 5.3). Small am- monites were found in larger amounts in a few beds. Wackestone containing mollusc fragments and lacking radiolarian fossils and filaments was identified among the samples from the debris (MF 2; Fig. 5.4). Thin- to medium-thick bedded peloid packstone (MF 5) is present, though less common. Some beds are normally graded and/or display parallel laminae. Bioclasts are subordinate to peloids; in addition to filaments, ammonites and Tubiphytes-like microproblematica, fragments of mollusc shells, geniculi of dasyclad green al- gae and benthic foraminifera were also found. Thin- to medium-bedded floatstone with intra- clasts and bioclasts (MF 6; Fig. 5.5-5.8) is charac- terized by a chaotic texture, with clasts floating in a wackestone or packstone matrix containing thin-shelled bivalves and radiolaria, as well as very rare abraded ooids. Besides intraclasts that are identical in composition to those seen in MF types 1-5, rare fragments of corals, sponges, dasy- clad and solenoporacean algae appear among the larger particles. Thin-shelled bivalves are orient- ed with their convex sides upwards. Floatstone sometimes sharply overlies filament wackestone and grades into peloid packstone. Limestone beds were subject to slumping, resulting in disrupted beds up to 120 cm thick, with angular to round- ed wackestone intraclasts kneaded into the marly matrix (MF 7 in Table 1; Fig. 5.9). 64 Luka GALE, Uroš NOVAK, Tea KOLAR-JURKOVŠEK, Matija KRIŽNAR & France STARE Diagenesis Although different lithologies constitute the sequence, it appears that diagenetic processes did not act selectively on the individual MF types: neomorphism, silicification, and precipitation of ferrous dolomite were detected in wackestone, as well as in floatstone. However, due to the larger number of aragonitic shells and intraclasts, these diagenetic processes seem to be most common in floatstone. Micrite, commonly recrystallized into micro- spar (which shows speckled luminescence under CL), is the main supporting medium in all MF types. Early mosaic calcite in places fills vugs and intragranular spaces (Fig. 6.1) in bioclastic wackestone. Bladed spar has also been observed within a brachiopod interior in peloid packstone. Compaction of the sediment is evident from flat- tened peloids, sometimes wrapped around echi- noderm plates, puzzle-like breakage of bivalve or other shells, and alignment of the filaments with- in bioturbations, as well as outside them. Pyrite crystals are present in the matrix and in mic- ritic intraclasts. In thin section 654b (laminated filament packstone), radiolaria appear to be py- ritized within a thin strip of sediment (Fig. 6.2). They preserve many details of their tests, in con- trast to more common calcified specimens. In one case, pyrite also crystallized on the bivalve shell, pre-dating the precipitation of ferrous dolomite. In other cases, however, well-formed and rela- tively large pyrite crystals cross-cut blocky spar or calcite veins. Relatively early changes further incorporate replacement of aragonite with drusy mosaic calcite through the complete dissolution of aragonitic bioclasts (thick-shelled bivalves, gas- tropods, ammonites, sponges, corals) and the for- mation of moulds (Figs. 6.3-6.4). Microfacies type Short description Figures 1 - Bioturbated filament wacke- stone Filaments represent 80 % of grains. Subordinate are putative calcified radiolarian, calcite sponge spicules and echino- derm plates. Fig. 5.1 2 - Bioturbated radiolaria-fila- ment wackestone Radiolaria prevail over sparse filaments and very rare echinoderms plates, nodosariid foraminifers and juvenile am- monites. Fig. 5.2 3 - Laminated filament pack- stone Filaments (50 % of thin section area) are concordant with the bedding and oriented with their convex sides up or down. The space between filaments is filled with dense wackestone consisting of 40 % pellets and rare (2 %) radio- laria. Calcite cement often fills shielded sites below and between the valves. Figs. 5.3 4 - Bioclast wackestone Bioclasts (20 %) are randomly distributed within microsparitic matrix. Mollusc shell fragments represent 10 %, small ammonites 6 %, and echinoderms 3 % of the clasts. Gastropods and ostracods are very rare. With the exception of the ostracods, the bioclasts are replaced by drusy mosaic spar. Some larger bivalve shells show signs of bioerosion and/or endolitization. The patches of drusy mosaic spar (8 % of the area) indicate that part of the micritic matrix was probably winnowed away. Fig. 5.4 5 - Peloid pack- stone Grains are arranged in crude laminae and are sorted by size. Some laminae indicate normal grading. Elongated grains are sometimes aligned with the bedding, but this appears to be mostly due to compaction. Peloids predominate among grains. They range from 0.05 mm to over 1 mm in size. They are ellipsoidal to elongated and angular to well rounded. The smaller ones display only micritic interiors, whereas internal layering may be observed in the larger grains. Due to the presence of Tubiphytes-like microproblematica (1.5 % of the area), some of the peloids probably originated as microbialite intraclasts. Mollusc fragments represent 5-10 % of the area, and echinoderm plates up to 5 %. Geniculi of dasyclad green algae, gastropods, brachiopods, “spherulites”, juvenile ammonites, ostracods, microproblematica Thaumatoporella parvovesiculifera (Raineri) and benthic foraminifera (Decapoalina schaeferae (Zaninetti, Altiner, Dager & Ducret), Palaeolituonella meridionalis (Luperto), Duotaxis sp., Reophax sp., Duostom- inidae, and nodosariid Lagenida) are very rare. Thin-shelled bivalves (“filaments”) may be locally present. They are oriented with their convex sides upwards, and blocky spar sometimes fills the spaces beneath the valves. 6 - Bioclast-in- traclast and intraclast-bioclast floatstone Clasts larger than 2 mm represent 30 % of the area (note that some compaction likely occurred), while wackestone or packstone matrix fills the remaining volume. The distribution of large clasts seems chaotic, although some alignment parallel to the bedding may be present that is due to compaction. Most are intraclasts with subangular edges and cor- respond to MF 1-5. Rrecrystallized sponges (up to 3 cm large fragments) are rarer, as are partly broken bivalve and brachiopod shells, corals, ammonites, solenoporacean algae and presumed genicules of dasyclad algae. Some large echinoderm plates and fragmented gastropods may also be counted among the largest grains. Within the wackestone matrix, some filaments, echinoderm plates, calcified or pyritised radiolaria, gastropods, and foraminifera (Aulotortus sinuosus Weynschenk, Diplotremina subangulata Kristan-Tollmann, ?Duostomina biconvexa Kristan-Tollmann, “Trochammina” almtalensis Koehn-Zaninetti, Variostoma pralongense Kristan-Tollmann, Reophax sp., Duostom- inidae, and nodosariid Lagenida) are present. A similar association of grains is present within the packstone matrix, together with peloids, microbialite aggregate grains, calcimicrobes, Tubiphytes-like microproblematica, fragments of Thaumatoporella parvovesiculifera (Raineri), ostracods, and occasional abraded ooids. Figs. 5.5-5.8 7 - Intraclast floatstone and rudstone Angular to subrounded clasts are up to 16 mm in size and represent up to 60 % of the thin-section area. Mudstone, “calcisiltite” (with small sparitic fragments and nodosariid lagenid foraminifera), wackestone with thin-shelled bi- valves, and wackestone with microbialite fragments and echinoderm plates are seen. The interstitial space is filled with dolomitized matrix. Rarely, echinoderm plates can be found. Fig. 5.9 Table 1. Microfacies types of the uppermost “Amphiclina beds” at Crngrob. 65Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob Fig. 3. Presentation of the recorded section. Numbers in brackets refer to MF type (see Table 1). Other samples (for additional study of the silicification) were collected ex situ. Abbreviations: C- Carnepigondolella, E- Epigondolella, M- Metapolygnathus, P- Paragondolella. 66 Luka GALE, Uroš NOVAK, Tea KOLAR-JURKOVŠEK, Matija KRIŽNAR & France STARE Fig. 4. Field photographs of the recorded section of the uppermost “Amphiclina beds”. 4.1- Part of the recorded section. Beds are in overturned position. 4.2- Intraclastic floatstone to rudstone. Note the black chert, which substitutes for most of one clast (a thin strip of limestone remains on the outer side of the clast). 4.3- Selective silicification, giving a “mottled” appearance to the rock. 4.4- An at least partly silicified ammonite, approximately 2.5 cm in size. 4.5- Small silicified ammonites. The larger ammonite is approximately 5 cm in diameter. 67Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob Fig. 5. Microfacies types of the uppermost “Amphiclina beds” at Crngrob. 5.1- Bioturbated filament wackestone. Thin section 666. 5.2- Bioturbated radiolaria-filament wackestone. Thin section 659. 5.3- Laminated filament packstone. Thin section 654b. 5.4- Bioclast wackestone. A: ammonite. Thin section 652. 5.5- Bioclast- intraclast and intraclast-bioclast floatstone. C: corals; E: echinoderm; A: ammonite (as part of an intraclast); I: intraclasts. Thin section 672a. 5.6- Fragment of solenoporacean red algae. Intraclast-bioclast floatstone. Thin section 672e. 5.7- Tubiphytes sp. Intraclast-bioclast floatstone. Thin section 672c. 5.8- Duostominid foraminifera (white arrowhead) and pyritized radio- laria (black arrowhead). Bioclast-intraclast or intraclast-bioclast floatstone. Thin section 672h. 5.9- Intraclast floatstone and rudstone. Thin section 660. 68 Luka GALE, Uroš NOVAK, Tea KOLAR-JURKOVŠEK, Matija KRIŽNAR & France STARE Fig. 6. Diagenetic features of the uppermost “Amphiclina beds” at Crngrob. 6.1- Mosaic spar, partly infilling the interior of a gastropod. Micrite (automicrite?) clings to the inner wall of the shell. Thin section 652. 6.2- Pyritized radiolarian and small sponge spicules. Thin section 654b. 6.3- Neomorphism of a bivalve shell. Thin section 653. 6.4- Neomorphism of corals. Thin section 672a. 6.5- Replacement of a probable micritic intraclast by chalcedony. Thin section 672h. 6.6- Silicification of an echinoderm plate. Thin section 653. 6.7- Partial silicification of a gastropod. Note that the chert infills the interior of the gastropod and partly replaces its shell. Thin section 653. 6.8- Same view under crossed Nicols. 6.9- Silicification front (arrowhead). Note the adjacent gastropod, which is not yet silicified. Thin section 653. 6.10-6.11- Void-filling chert. Note the rhombic carbonate crystals lining the wall of the void. Chips of crystals are included within the chert. Thin sections 667b and 653. 6.12- Chert, replacing some particles, including presumably rhombic crystals. Thin section 668b. 6.13- Same view under crossed Nicols. 6.14-6.15- Silicification front. Note the large rhombic crystal replaced by chalcedony that is seen under crossed Nicols (Fig. 6.15). Thin section 672h. 69Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob Spherulitic chalcedony and granular megaquartz locally replace the micritic matrix, gastropods, thick-shelled bivalves, echinoderms (excluding the surrounding syntaxial calcite cement), brachiopods, calcimicrobes, some in- traclasts and even lagenide foraminifera (Figs. 6.5-6.9). Microstructure-controlled replacement of brachiopod shells by chalcedony has also been observed, while microbial crusts are often the sites of precipitation of quartz euhedra. Chalced- ony may enclose rhombic carbonate crystals and/ or infill the remaining internal parts of the voids, which are lined with large rhombic crystals of a carbonate mineral (Figs. 6.10-6.11). These rhom- bic crystals may be partly shattered, with chips incorporated into the chert. Rarely, chalcedony appears to replace the rhombic crystals (Figs. 6.12-6.15). In sample 654b, silicification has af- fected some or part of the laminae with higher porosity: it appears to stop at the contact with more matrix-rich lamina (Fig. 7.1). Ferrous do- lomite in large crystals substitutes for the ma- trix between filaments in other parts of the thin section (Fig. 7.2). Ferrous dolomite locally fills gastropod (Fig. 7.3), ammonite (Figs. 7.4-7.5), and thick-shelled bivalve shells (Fig. 7.6), especial- ly in bioclast-intraclast and intraclast-bioclast floatstone. The infill may be partial (in which case the other part of the mould is being filled by drusy mosaic calcite) or complete. Ferrous dolo- mite is also found within veins (Fig. 7.7). Under CL, bright orange, dull red and non-luminescent bands are seen in clearly zoned crystals. The non-luminescent clear mosaic or blocky calcite post-dates ferrous dolomite; the calcite fills the remaining space (Fig. 7.8). In one sample, the clear blocky spar forms patches within the mic- ritic matrix (Fig. 7.9). In rare cases, the clear spar fills veins. The relationship with chert is unre- solved. Another generation of megaquartz, which is reflected by crystals more than 1 mm in size, occurs rarely in veins or fills the spaces between the clear spar crystals (Fig. 7.10). Some samples are completely dolomitized, and dolomitization may have taken place contempo- rary with selective replacement of fossils by fer- rous dolomite (the timing of dolomitization is currently not resolved). Different types of perva- sive dolomitization can be distinguished, hinting at different generations of dolomite. Sedimenta- ry structures are sometimes still preserved, due to the different colours, shapes and sizes of the dolomite crystals. Smaller euhedral to subhe- dral crystals with brownish outer rims (which are enriched in Fe) seem to preferentially sub- stitute for the micritic matrix (Fig. 7.11). Under CL, they exhibit dark red luminescence with thin bright yellow bands. The second type of dolomite is represented by lighter and larger subhedral crystals (Fig. 7.12), which emit very weak, dark red luminescence. Some veins are also filled with dolomite. Calcite veins cut through all other di- agenetic phases. The exception may be the second generation of megacrystalline quartz, for which the relationship with the calcite veins could not be determined. Age of the studied succession Conodont biostratigraphy The Colour Alteration Index (CAI) of the re- covered conodont elements (some of which are shown in Fig. 8) is 5 and/or slightly above 5, demonstrating strong alteration and even a low grade of metamorphism (see Kovacs & arKai, 1987; suDar & Kovacs, 2006; Kovacs et al., 2006). The conodont fauna from the uppermost “Am- phiclina beds” is dominated by the elements Par- agondolella ex gr. polygnathiformis (Budurov & Stefanov) and Carnepigondolella with the rep- resentatives: Carnepigondolella aff. carpathica (Mock), C. nodosa (Hayashi), C. pseudodiebeli (Kozur), C. tuvalica Mazza et al., Carnepigon- dolella zoae (Orchard), Carnepigondolella sp., in association with Metapolygnathus mersinensis (Moix et al.) and M. cf. praecommunisti Mazza et al. As a direct forerunner of Metapolygnathus, the genus Paragondolella can be distinguished by the terminal or subterminal position of the basal pit (Kozur, 2003). Some specimens of Par- agondolella reveal transitional features towards the genus Metapolygnathus, with a prolonged keel behind the basal pit. This feature is consist- ent with observations of Mazza et al. (2012). The genus Paragondolella is confined to the Carni- an, whereas Metapolygnathus ranges from the Late Carnian to the basal Norian. The species M. praecommunisti has not yet been documented from Slovenia, but its successor, M. communisti Hayashi has been reported from the Late Carni- an-Early Norian fauna of the Martuljek Group in the Julian Alps (celarc & Kolar-jurKovšeK, 2008). Carnepigondolella is characterized by a weak ornamentation on the platform margins and by a subterminal basal pit (Kozur, 2003). This genus is a marker of the Upper Carnian that also occurs rarely in the Lower Norian and is regarded as the forerunner of Epigondolella. 70 Luka GALE, Uroš NOVAK, Tea KOLAR-JURKOVŠEK, Matija KRIŽNAR & France STARE Fig. 7. Diagenetic features of the uppermost “Amphiclina beds” at Crngrob. 7.1- Partial silicification of the radiolarian-fila- ment packstone. Note the sharp lower boundary of the chert (Q), which follows a lithological boundary with a greater amount of micritic matrix. Thin section 654b. 7.2- Ferrous dolomite between bivalves. Thin section 654b. 7.3- Replacement of a gastro- pod shell by ferrous dolomite. Thin section 672c. 7.4- Ferrous dolomite filling the dissolved shell of an ammonite. Thin section 667c. 7.5- Same view under CL. 7.6- Ferrous dolomite filling dissolved bivalve shells. Shells are fragmented. Thin section 672c. 7.7- Vein-filling ferrous dolomite. Thin section 667b. 7.8- Blocky calcite (K) filling the interior of the void lined by ferrous dolomite (D). Thin section 672i. 7.9- Blocky calcite (K) precipitated after partial dissolution of the matrix (arrowhead). Thin section 672h. 7.10- Megaquartz (Q) interior to the blocky calcite (K). Thin section 672h. 7.11- Subhedral to euhedral dolomite crystals. Note the brownish colour of the outer rim. Large, undolomitized grains are echinoderm plates. Thin section 660. 7.12- Subhedral dolomite. Note the ghostly image of the clast (C), suggesting a former floatstone texture. Thin section 672g. Fig. 8. Conodont elements from the uppermost “Amphiclina beds” (8.1-8.6) and the lowermost “Bača Dolomite” (8.7-8.8). 8.1- Carnepigondolella tuvalica Mazza et al., sample GeoZS 5661. 8.2- Carnepigondolella zoae (Orchard), sample GeoZS 5661. 8.3- 8.4- Paragondolella ex gr. polygnathiformis (Budurov & Stefanov), samples GeoZS 5540 and 5539. 8.5-8.6- Carnepigondolella aff. carpathica (Mock), sample GeoZS 5660. 8.7- Epigondolella rigoi Noyan & Kozur, sample GeoZS 5643. 8.8.- Epigondolella cf. vialovi (Buryi), sample GeoZS 5643. 71Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob 72 Luka GALE, Uroš NOVAK, Tea KOLAR-JURKOVŠEK, Matija KRIŽNAR & France STARE Among the Carnepigondolella species that were identified, the presence of C. tuvalica and C. zoae that occur in the Late Tuvalian is important. The measured uppermost part of the “Amphiclina beds” is thus Tuvalian in age. A single sample from the “Bača Dolomite” yields a small but significant fauna. It is marked by the exclusive presence of Epigondolella that reveals a more reduced platform, allowing devel- opment of a free blade. This genus is characteris- tic of the Norian, but it had already appeared in the Late Tuvalian. Several morphogenetic line- ages are recognized from the period of their rap- id evolution (orcharD, 2007). The co-occurrence of the species E. aff. spatulata (Hayashi), E. rigoi Noyan & Kozur, and E. cf. vialovi (Buryi) defines the Lacian age of the sample. Norian epigondolel- lids are known to occur extensively in Slovenia (Kolar-jurKovšeK, 1991; Buser et al., 2008), and a similar fauna was recently documented from the Lower Norian strata of the Martuljek Group in the Julian Alps (celarc & Kolar-jurKovšeK, 2008). Foraminifera Concerning foraminifera, the following taxa (listed alphabetically) were identified in thin sections of bioclast-intraclast/intraclast-bioclast floatstone and in peloid packstone: Aulotortus sinuosus Weynschenk, ?Decapoalina schaeferae (Zaninetti, Altiner, Dager & Ducret), Diplotremi- na subangulata Kristan-Tollmann, ?Duostomina biconvexa Kristan-Tollmann, Duotaxis sp., Pal- aeolituonella meridionalis (Luperto), Reophax sp., “Trochammina” almtalensis Koehn-Zaninet- ti, Variostoma pralongense Kristan-Tollmann. Undetermined Duostominidae and nodosariid Lagenida were also recognized. Neither species provides a detailed stratigraphic range. It should be noted, however, that the range of Decapoali- na schaeferae, which was previously known from Norian and Rhaetian strata (Gale et al., 2013), should be extended to the Late Tuvalian. Discussion Depositional model Concerning sedimentation, three types of sediments can be distinguished in the observed section. The bioturbated filament wackestone, radiolaria-filament wackestone and laminated filament packstone are interpreted as hemipe- lagic/pelagic sediments. The concordant position of thin-shelled bivalves in the latter may be due to redeposition out of suspension, compaction, or the presence of weak bottom currents (KiDwell & Bosence, 1991). Traces of bioturbation suggest oxygenated bottom conditions. The presence of radiolaria, ammonites, and thin-shelled bivalves suggests an open-marine environment (FlüGel, 2004). The bioclast wackestone and peloid pack- stone are interpreted as distal turbidites, or as the result of some other gravitational current transport mode. This is supported by the pres- ence of normal grading and laminae in peloid packstone and the presence of grains derived from within the photic zone (green algae, bioero- sion on bivalve shells, foraminifera Decapoalina schaeferae, Palaeolituonella meridionalis). The chaotic distribution of clasts floating in slightly convoluted (fluid) matrix suggests that the bioclast-intraclast and intraclast-bioclast floatstone formed via debris flows. Grains are again partly derived from shallow water (corals, solenoporaceans, green algae, and the foraminif- era Aulotortus sinuosus), but some micritic in- traclasts represent mud chips torn from the sea bottom, and fossils found within the matrix (ra- diolaria, filaments) represent open-marine biota. The intraclast floatstone to rudstone might alter- natively represent a debris flow deposit with a predominance of basin-derived clasts, or a slump conglomerate/breccia. This facies association suggests the slope to toe-of-slope setting, or the outer ramp environ- ment (FlüGel, 2004). Timing of silicification of fossils Although we could clearly distinguish between the megaquartz that post-dates the blocky spar from the chalcedony, which replaces fossils, we are not able to confidently assign the silicification of fossils to the early or late stages of diagenesis. The ammonites, gastropods and bivalves, which were originally made up of aragonite (FlüGel, 2004), were probably already replaced by low-Mg calcite spar when silicification occurred. They are replaced alongside low-Mg calcite calcimi- crobes, brachiopods and lagenide foraminifera, as well as high-Mg calcite echinoderms (FlüGel, 2004). Chalcedony usually replaces only parts of fossils and is not always confined to the fossils itself. As seen in Figure 6.9, silicification did not extend to the gastropod immediately adjacent to 73Characterization of silicified fossil assemblage from upper Carnian “Amphiclina beds” at Crngrob the progressing silicification front. The silicifi- cation thus clearly post-dates deposition of the sediment. Furthermore, the presence of rhombic crystals lining some vugs filled with chalcedo- ny, seemingly shattered and broken-off rhombic crystals, and rhombic crystals replaced by sili- ca suggest that the chalcedony precipitated after the vug-lining spar. The silicification in the “Amphiclina beds” might be somewhat similar to the late diagenet- ic silicification that selectively affected clasts in conglomerates of the Upper Jurassic Toril For- mation in the Bethic Mountains of Spain (Bustil- lo & ruiz-ortiz, 1987). Bustillo and ruiz-or- tiz (1987) additionally recorded nodule- and bed-producing early diagenetic silicification that was restricted to the Ta (partly), Tb and Tc parts of the intercalated turbidite beds. The rare nod- ular chert in the recorded part of the “Amphi- clina beds” may indeed be early diagenetic, as shown by the presence of chert clasts in rudstone shown in Figure 4.2 (which is similar to the nod- ular chert in the Norian-Rhaetian “Bača dolo- mite”; D. Skaberne, pers. com. 2009). In the case of the silicified fossils, however, there seems to be no preference for lithology, as the same type of clasts may be silicified in both bioclast-intraclast floatstone and hemipelagic sediments. The im- pression that silicification is confined to certain lithologies is solely a consequence of the greater amount of calcareous bioclasts in bioclast-intr- aclast and intraclast-bioclast floatstone. There- fore, rather than arguing for lithological control over the silicification of fossils, we suggest that all the investigated types of limestone acted sim- ilarly during the burial diagenesis, which can be attributed to the largely homogenous permeabil- ity of the matrix-rich sediment. Conclusions The uppermost 38 m of the “Amphiclina beds” were sampled at Crngrob in order to define the origin of the silicified fauna, the nature of the as- semblage and the timing of silicification. The sec- tion exposes limestone, dolomite and marlstone of Tuvalian age. Within the limestone, seven mi- crofacies types were determined. Bioturbated filament wackestone, bioturbated radiolaria-fil- ament wackestone and laminated filament pack- stone represent hemipelagic sediments. Peloid packstone and bioclast wackestone were deposit- ed from distal turbidite flows. Bioclast-intraclast and intraclast-bioclast floatstone represent the debris-flow microfacies, while intraclast float- stone and rudstone are interpreted as debris-flow deposits or as slump breccias. The sediments were deposited in the slope to toe-of-slope set- ting or in the outer ramp setting (FlüGel, 2004). A complex diagenetic history has been partly re- solved. Early diagenesis involved compaction of the sediment and replacement of aragonite with drusy mosaic calcite. Local selective silicification affected the fossils, as well as some of the intra- clasts and even parts of the matrix. Silicification (replacement by chalcedony and megaquartz) was detected in all of the limestone types, but it is most evident in bioclast-intraclast and intra- clast-bioclast floatstone, where the majority of the larger fossils are found. Because the silicifi- cation occurred after deposition of the sediment, and because the fossils are partly derived from shallow-water environments, the Crngrob silici- fied fossil assemblage represents a biased thana- tocenosis or even a taphocenosis, and it is not an autochthonous Carnian fossil association. Fer- rous dolomite, sometimes associated with veins, locally replaces non-silicified or partly silicified fossils and matrix. Clear mosaic or blocky cal- cite postdates ferrous dolomite. Some samples are completely dolomitized. Two types of dolo- mitization are suggested by the different sizes, shapes, and colours of the dolomite crystals, and the original texture of the sediment is sometimes preserved. The timing of dolomitization has not been resolved. Acknowledgements The field work and preparation of samples were fi- nancially supported by the Slovenian Research Agency (Programme Number P1-0011). We thank the techni- cal staff of the Geological Survey of Slovenia (Marija Petrović and Mladen Štumergar) and the Faculty of Natural Sciences and Engineering (Ema Hrovatin and Miran Udovč) for the preparation of thin sections and conodont samples. We also thank Bojan Otoničar from the Karst Reseach Institute in Postojna, who gave us access to the cathodoluminescence equipment and a brief tutorial. Conodont elements were photographed with the kind help of Miloš Miler at the Geological Survey of Slovenia. Andrej Novak helped with some of the field work. 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