The sedimentary environment in the Ljubljansko barje basin during the pile-dwelling period Tomaž VERBIC Izvleček Geološki procesi na Ljubljanskem barju po zadnjem glacialnem višku so le splošno poznani. Izjemoma sicer poznamo detajlne razmere, vendar so te prostorsko in časovno fragmentarne. Artefakti iz arheoloških najdišč so bili v preteklosti deležni natančnega proučevanja, sami sedimenti s kulturno vsebino, njihova talnina in krovnina pa bistveno manj. Pot do boljšega razumevanja okoljskih razmer v času kolišč verjetno vodi prav preko natančnega poznavanja sedimentov in pokopanih tal ter razumevanja evidentiranih stratigrafskih hiatusov. Ključne besede: Ljubljansko barje, geološki procesi, kvartarno in holocensko okolje, jezerska kreda, gyttja, organski sedimenti, kolišča Abstract Geological processes on the Ljubljansko barje basin after the Last Glacial Maximum are known merely on a general level. At few points more detailed circumstances are known, but this information is fragmented spatially and temporally. While artefacts from the archaeological sites were studied in detail, the sediments were mostly only imperfectly described. Better understanding of the evolution of the environment requires accurate study of these sediments and buried soils, and detection of evident stratigraphical hiatuses. Keywords: Ljubljansko barje, geological processes, Quaternary and Holocene environments, Seekreide, gyttja, organic sediments, pile-dwellings INTRODUCTION This contribution summarizes and comments on the geological perspective of select research results, which by using a variety of methods illuminate the geological processes in the region of the Ljubljansko barje. It also extends some new perspectives concerning the geological phenomena during the period of the Last Glacial Maximum, the Late Glacial and, especially most important from the archaeological perspective, during the Holocene. By no means do I presume that this review provides any definitive answer to an otherwise broad theme. On the contrary, it demonstrates the current exceptionally fragmentary and superficial grasp of the environment's circumstances. As the reader will also be able to judge, this contribution on several occasions is based mainly on comparisons made within the framework of critically scientific deductions. Many readers may query the lack of quantitative data. I believe, howewer, that prior to attempting a quantification of geological processes, their mutual interaction is worthy of detailed review. Otherwise we may face being drawn into a cycle of scientific falsities. I shall also draw notice to such instances in the continuation. Let us first consider the terminology that will be used in this review. Fran Erjavec and Fran Levstik introduced the toponym Ljubljansko barje into the literature as a geographic concept as late as 1880 (Melik 1927, 1946). Professional geological terminology today uses the term Ljubljansko barje in two different contexts. On the one hand it refers to the Quaternary sedimentary basin (sensu lato). It also refers to the Holocene marshland landscape (sensu stricto) - in the sense that Levstik and Erjavec insti- tuted - which developed where the lake had been. Archaeologists also need to understand the term in both contexts. Of course the marshland landscape, the former environment that engendered Erjavec's and Levstik's original labeling, is long gone. However, the sedimentary basin remains. The abridged term is simply Barje (capitalized), effectuated already by Levstik and Erjavec (Melik 1927, 33-34). FORMATION OF THE LJUBLJANSKO BARJE SENSU LATO How was the Ljubljansko barje s.l. formed? There is no doubt that its formation is tectonic, a strong influence on the relative subsidence of this region, or rather on the relative elevation of the Barje area. It is also a fact that the Pre-Quaternary foundation of the Barje is topographically very uneven, which is substantiated by the presence of the many isolated hills. As concerns the formation of the Ljubljansko barje s.l., this is as far as the opinions of geologists reach in unity. Earlier researchers believe that the foundation is composed of tectonic clusters delimited by the vertical faults in the dinaric (NW-SE) and transdinaric (NE-SW) directions (Pleničar 1967; Buser 1968; Grad, Ferjančič 1974; Premru 1982). Mencej (1990) also advocated a similar fault pattern. The initial interpretations are thus based on the cluster structure of the foundation, which then presumably subsided differentially. Vrabec (2001) offered a very different explanation for the formation of the Ljubljansko barje s.l. He anticipated that the Barje formed as a pull-apart sedimentary basin between the dinaric directed faults. Verbič (2006a) placed the origins of the Barje within the context of Quaternary active reverse faults between Ljubljana and Kranj. He adopted the opinion of earlier researchers that the Vič fault runs along the northern edge of the Barje, however that it has a reverse and atypical character (Verbič 2006a). The Vič fault is the most southern in a string of reverse faults between Kranj and Ljubljana. A fault directed E-W runs along the southern edge of the Barje (Verbič, Horvat 2009b), just as Mencej (1990) anticipated, however according to their explanation it is also reverse. The filled-in eroded valleys can explain the dynamic topography of the Pre-Quaternary foundation together with the isolated hills, thus making the tectonic cluster formation unnecessary for its explanation. Regarding recent and Quaternary activity of individual faults in the Barje, we have no appropriate data other than select data for the Vič fault (Verbič 2006a). New data relating to when the Barje s.l. formed have long been lacking. That the formation of the Barje s.l. was a process, as opposed to having oc-cured in a single moment, is particularly noteworthy. Perhaps a comparison between the Vič terrace (fig. 1) (Rakovec 1932, 1954; Šercelj 1967), the borehole near Dolgi most (Šercelj, Grimšičar 1960) and the BV-2 borehole (Šercelj 1966) would be the most revealing for a chronological classification of the beginnings of this process. Both boreholes exhibited Mindel sediments, which used to be attributed to the Lower Pleistocene, above the Pre-Quaternary foundations (cf. Šercelj 1967); today however, some authors more generally connect them with the Marine isotope stage 12 and/or 14 (the period before ca. 400-550 ka BP), which means we can presumably attribute them already to the Middle Pleistocene (Gibbard, Cohen 2008). Also attributed to the Mindel glaciation are sediments from the area of the former Vič brickfield. Earlier sediments (than Mindel) above the Mesozoic and Paleozoic foundations are as yet unknown from the Barje. Any new determinations should take into account that the Barje began to form as a sedimentary basin during the Middle Pleistocene. Little data regarding these earliest sediments are available at present, however several new results and interpretations may be anticipated in the future. LAKE! UNTIL WHEN? It seems to be the case that some evidence in science and geology is less evidenced, while some other evidence is more so. In particular, I am referring to the hypotheses and interpretations of individual analyses. Citing Karel Popper (1998) -which seems appropriate at this stage - the truth is that an individual hypothesis is all the more reliable proportionate to the number of attempts to falsify it and proportionate to how aggressive, in depth and exactness, these attempts were. Why such an introduction? Simply: because it presents such an integrative response to the discussion of the former existence of the lake in the region of the Ljubljansko barje. It is hardly important who first interpreted the lake chalk (the highly accepted geological term in Slovene: "jezerska kreda"; German "Seekreide"; it is used for silty marl from a lake environment, here we will use term lake silt) in the Barje as one characteristic of a lake environment. Fig. 1: Ljubljansko barje, locations cited in the text. The line between the Castle Hill and Rožnik delineates the southern edge of the Sava alluvial fan during the Last Glacial Maximum, when it cut off the alluvial outflow (Paleo-Ljubljanica) from the Barje. (Data: ©Surveying and Mapping Authority of the Republic of Slovenia). Sl. 1: Ljubljansko barje z lokacijami, omenjenimi v tekstu. Linija med Grajskim hribom in Rožnikom prikazuje južni rob prodnatega savskega aluvialnega vršaja v času zadnjega glacialnega viška, ko je zaprl aluvialni iztok (Paleoljubljanico) z Barja. (Podatki: © GURS). Perhaps it was Karl Deschmann or even someone before him, some engineers perhaps who in the mid-19th century set out to design a railway track across the Barje. Certainly these first researchers relied upon the interpretations of the sediment texture, the structure of the lake chalk, as well as on the general geological and geomorphological contexts of the Ljubljansko barje. The principles of actualism led them to such a conclusion; and their hypothesis was confirmed subsequently, especially in that the fossil content in the sediments corroborated the lake environment's existence (cf. Pavlovec 1967, 1973; Kroflič 2007). There is firm grounding for the hypothesis of a former lake environment in the Barje, and its credibility has yet to be contested by a falsification attempt or any other form of interpreting field observations and laboratory analyses. Indeed, the entire issue revolves solely around Sifrer's (1984) interpretation and I do not know of any other discussions that basically challenge the very existence of an Upper Pleistocene and Holocene lake sedimentary environment in the Barje. The theories and conjectures in Šifrer's (1984) work are without geological substantiation and corroboration. For instance, he writes (p. 36): From the perspective of the development of the Barje during the Last glacial period it seems especially significant that the fluvioperiglacial sedimentation here was ample and throughout competed with the sedimentation of the Sava glacier. This also supports why the former made its way only locally toward the Barje, and even then probably only as far as the then taut world of the Barje would allow. The premise follows that during the postglacial periods on the Barje there were no conditions for the stagnation of profuse amounts of water, let alone for the formation of a lake as was hypothesized by earlier researchers of this region (Kramer 1905; Seidel 1912; Rakovec 1939, 1955; Melik 1946). Luckily, the above assertions can be checked and as such have proven erroneous. How far the Sava sediments advance upon the Barje and its interior has little bearing on the formation of the lake; rather, that it closes the mouth of the river, the former Paleo-Ljubljanica, on the surface exiting the Barje (fig. 1). The youngest Sava river (glaciofluvial) infill in Ljubljana, the Last glacial period infill, is in the form of an alluvial fan that crossed through the center of Ljubljana, reaching to Mirje and then along the foot of the Castle hill and probably somehow all the way to the Šentjakob bridge. It literally "ran into" the Castle hill from the north, no doubt, thus closing off the Paleo-Ljubljanica towards the east. These locations are traceable; they have been verified and evidenced during construction and archaeological activities. The above cited excerpt is symptomatic also of Šifrer's assertion only as far as the then taut world of the Barje would allow". How does he know about the tautness of the Barje landscape, which today is buried beneath the lake silt? His next argument negating the former lake environment cites that ^ "no delta sedimentation - which would be anticipated if the streams and rivers flowed out into the former lake - is evidenced anywhere " (p. 41). And yet he fails to cite where he even traced any evidence of lake sedimentation, either in the boreholes or cross-sections, so as to be able to justify that such sedimentation is not evidenced. Currently there are conflicting observations: the execution and recording of research boreholes at the Špica site (fig. 1) (Novšak et al. 2009), as well as subsequently during geologic research studies complementing the archaeological excavations, allowed us to trace in detail the detritic input of non-carbonate terigenous sand sediments into the lake environment, which is otherwise where the lake silt sank. At a distance of more than 100 metres we were able to determine the proximal and distal parts of the small delta of the currently unknown stream, perhaps the one from the erosive indent above Rakovnik. The lake silt was discovered also in the area of the Ljubljana Tribune, directly at the foot of the Castle hill. Other than this, lake silt was also discovered in 2009 during construction and archaeological research works along Tržaška cesta (the road towards Trieste) near the former Tobačna factory. Sand plates were also found among the silty lake silt. This latter determination is indicative of there having been a unified lake sedimentary environment throughout the entire Barje. The majority of the lake sediment in the Vič area (Gradaščica, Mali greben) was later eroded. Sedimentation in these proximal areas of the lake at the end of the Pleistocene was probably a rapid process, as a result of the detritic input of sediment material from the side of the Sava fan. Rapid sedimentation in this proximal lake environment presumably indicates also the small volume of pollen concentration in the lake sediment at the Špica site (pers. comm. by Andrič 2010 and by Culiberg 2010). Indeed several of Šifrer's (1984) citations warrant critique. For instance, (p. 49): "^The findings that the lake clay (snail-clay soil) is limited mainly to the proximity of the limestone and dolomite hinterland are also in accordance with this." Several times the author supports some theory with debatable or even nonexistent arguments. Lake sediment was discovered at the Špica site, the Tribuna site and at the former Tobačna factory site, all of which are very far removed from the "limestone and dolomite hinterland". The premise placing the existence of the lake environment on the Barje into question, or even denying it (Šifrer, 1984), is unfounded. This premise originally served select authors as an additional argument substantiating the interpretation that pile-dwelling settlements were not situated on or near the lake, but rather on the alluvial plain (cf. Budja, 1994). It emerged mainly due to the lack of critically reviewed scientific judgement. It is clear to geologists that Šifrer's (1984) premise for the above-stated interpretation is unnecessary. The essential question in this regard concerns when the lake existed, and how its dimensions altered through time, and into what kind of environment the lake land change. This is a question for which we have only fragmentary answers. Otherwise, the more or less established and general theory asserts, on the one hand, that alluvial (fans, deltas, etc.) sediment created a lateral accretion of the lake sedimentary basin, while at the same time creating vertical accretion of lake sediment over the entire area of the lake. A massive area and amount of material in this field lies available for more detailed investigation, and quite likely several surprises await us all in the ensuing research development. In the past, the predominant opinion claimed the lake silt to be exclusively Holocene sediment. Presumably, certain general and principled opinions, such as that climate conditions promoted sedimentation of the lake silt only from the Holocene onwards (cf. Šercelj 1962, 1965, 1966), contributed to this stance more than did the results from analyses. Similar convictions are also more recent (Pohar, Culiberg 2002; Brenčič 2007). However, recent research is also depicting a different picture of the stratigraphic extent of the lake sediment. Currently four sites evidence only Pleistocene lake sediments, while the Holocene lake sediment was either eroded or never even deposited. These location sites include Notranje Gorice (Šercelj 1976), Zalog near Verd (Culiberg 2006; Verbič 2006b), Hočevarica (Culiberg 2006) and Špica (in the continuation). A relatively long Holocene stratigraphic hiatus was also determined above the lake silt at Resnikov prekop (Šercelj 1963; Andrič 2006). Šercelj (1981-1982) fleetingly mentions the results of trial trenching and pollen analyses along the laying out of the Ljubljana southern bypass road. He cites only Pleistocene sediments between Dolgi Most and the Ljubljanica river, and he explicitly does not cite the presence of any lake sediment. He infers, on the basis of the absence of Holocene sediments, that there were no pile-dwellings in this area. A long stratigraphic hiatus between the Pleistocene and Holocene sediments (younger than the pile-dwellings) is mentioned in the area of the Rudnik industrial zone. He describes a similar situation near the highway clover along the Dolenjska road. Nonetheless, it remains negligible that the Na mahu site (Andrič et al. 2008) is still the sole site where the transition between the lake and marsh sedimentary environment is linked and even chronologically well documented. Several other locations lack a radiometric chronological control. What about the spatial extent of the lake environment? Simple inference tells us that the entire Barje region was under water during the time of the greatest lake formation at a height of approximately 297 m; this height presumably reached as far as to the Sava river infill between Rožnik and the Castle hill. The role played by the saddle between the Castle hill and Golovec is somewhat more ambiguous. The above sea-level height of this saddle prior to the construction of the Gruberjev canal is not known exactly; however, it would seem that it was higher than the transition from the NW edge of the Castle hill, as there are no sedimentation records from Poljane that can be linked to the spilling over of water from the Barje side. If the above stated theory holds in general, then some truly fascinating hydrological conditions reigned in the area between Rožnik and the Castle hill, at least during the formation of the Sava alluvial fan. The water, which ran into the lake from the karst sources and surface streams along the edge of the Barje, had to also flow off from it as well; this took place precisely across the Sava alluvial fan. As to how the water traffic was organized we can only guess. Quite likely there was an antagonism between two hydrological systems, in the sense that the Sava alluvial fan, during its activation, presumably made no allowance for the alluvial efflux of the modern day Ljubljanica to cut through from the lake any more rapidly. Perhaps the hydrological regime was of an exceptionally seasonal nature. Furthermore, two thick strata of fine-grained sediments are traceable between the sand gravel near the construction of the garage house beneath Kongresni trg. These two strata are indicative of sedimentation due to suspension, that is, from the stagnant water in the alluvial fan. The contracting of the lake was connected with the erosive capacity of the lake outflow to incise, as well as the lowering of the local base levels. Nonetheless, caution is called for in evaluating this contraction, as it is undoubtedly also connected with the dynamics of the subsidence of the lakebed. Several issues remain unresolved in this concern. What influence did the sudden static load from this area, coming from an approximately 10m-high water tower, have upon the subsidence? Obviously, it accelerated the subsidence of the lakebed; the problem lies in how to quantify this acceleration. The subsidence of the Barje basin is a complex issue with numerous variables and their reciprocal interactions. As the dynamics of the subsidence of the Barje basin had their influence upon the environmental conditions, I will grant a little extra consideration to this matter in the continuation. THE LJUBLJANICA! SINCE WHEN? The Ljubljanica, which serves as the main drainage vein from the Ljubljansko barje, further substantiates the conclusion that the Ljubljansko barje is an exceptional sedimentary environment in terms of its extreme characteristics. The geomorphological literature rarely refers to such extreme rivers as the Ljubljanica. The Ljubljanica also lacks adequate description and a sufficient number of relevant measurements from a geomorphological perspective. Nonetheless, some characteristics are known: it formed in the region of the former lake, it is fed mainly by the karst aquifers, and it has almost no underground sediment load. The erosive power of the Ljubljanica is exceptionally small, especially as Fig. 2: Geodetic topographic measurements along the Ljubljanica river between Vrhnika and Špica (data from: Stojič 1994). The smoothed curve of the riverbed (a); the level of the Ljubljanica river at average flow (VP Moste) 55 m3/s (b); smoothed curves of the height of the levee on the left (c) and right (d) banks of the Ljubljanica river. Sl. 2: Geodetske topografske meritve vzdolž Ljubljanice med Vrhniko in Špico (podatki po: Stojič 1994). Zglajena krivulja dna struge (a); gladina Ljubljanice pri povprečnem pretoku (VP Moste) 55 m3/s (b); zglajeni krivulji višine obrežnega nasipa na levem (c) in na desnem (d) bregu Ljubljanice. concerns side erosion. For almost its entire length through the Barje, it cuts through the cohesive lake silt. The surface level of the Ljubljanica (fig. 2) along its course between Vrhnika and Ljubljana (a distance of 22 km) indeed falls by 2 m during strong currents (above 100 m3/s) and only 40 cm at a flow of 20 m3/s (Stojič 1994). During lower water levels, the gate levels throughout Ljubljana regulate the surface level of this entire segment of the Ljubljanica. The alluvial outlet from the Ljubljansko barje is an essential element, which throughout history determined the hydrological conditions there. Of course several other environmental variables also affected these conditions, however the water regime was primarily determined by the capacity of water to outflow from the sedimentary basin, that is, from the height of local base levels. The Ljubljanica covered this surface during the infill of the Sava river alluvial fan, and then after the Sava moved northwards it began to cut its bed through the Sava alluvial fan. The oldest segment of the modern Ljubljanica is thus the segment beneath the Castle hill, running from the Šentjakob bridge, down and eastwards to its efflux into the Sava. Throughout the Barje region the Ljubljanica is younger. Currently there exists very little geological data that allows at least indirect inferences regarding the origins of the Ljubljanica at individual segments. Consequently, I can only restate archaeological argumentations that until the Middle Bronze Age, the Ljubljanica undoubtedly formed its own basin in at least select areas of the Barje (Gaspari 2009b, 40). A general geological framework, without chronological dimensions, can be established for the origins of the Ljubljanica. As already mentioned above, almost the entire length of the Ljubljanica in the Barje cuts through the cohesive lake silt. Due to the predominantly karst water systems and the cohesive riverbanks, its bedload is very limited in quantity. The bedload is what enables the formation of alternating ridges, which can then initiate meandering in itself (cf. Leopold et al. 1964; Schumm 1981, 1985). The third distinctive feature of the Ljubljanica is its extremely low gradient. Such conditions (cohesive riverbanks, almost no bedload, extremely low gradient) significantly limit the meandering of the river. The orientation and lineal segment of the Ljubljanica before it reaches Podpeč, almost at the edge of the Barje, is noteworthy. Despite apparent inconsequence, its direction is perhaps determined by entirely natural conditions. A borehole was drilled already in 1953 in the courtyard of the former Hoja works along the left bank of the Ljubljanica and just north of Podpeč; according to my data this borehole revealed the thickest horizon of lake silt (17.5 m) yet known (Grimšičar, Ocepek 1967). It follows that in this area, due to the faster subsidence, the lake was preserved for a longer time and the Ljubljanica coming from the western part of the marsh drained into the then lake, simply because it flowed down the largest gradient. Turk and Horvat (2009) also mention a similar outflow of the Ljubljanica into the lake somewhat upstream. This wide strip with a thick layer of lake silt continues on towards Črna vas. Perhaps it bespeaks the lakes enduring for a longer period between Podpeč and Črna vas than elsewhere in the Barje. Such circumstances would support repeat investigations of the location of the Roman pontonium near Lipe (Gaspari 1998). That it was found directly on the lake silt is perhapsindicative of formerly very shallow and wide canals for filling the lower parts of the Barje with water from the Ljubljanica, while at the same time for outflowing floodwaters back to the Ljubljanica depending on the hydrological conditions. THE LJUBLJANSKO BARJE DURING THE PILE-DWELLING SETTLEMENTS The period of pile-dwellings on the Barje is merely one in the continuum of the formation of the area; to fully understand, it demands familiarity with the environment during the periods before and after the pile-dwellings. Nonetheless, the focal point of scientific archeological interest in the area has always been the actual period of the pile-dwellings. It is quite likely that the marsh environment at the time was not monotone, and the differences between the various parts of it were probably greater than today. The question arises as to whether the same sedimentary context can be expected at all pile-dwelling sites. Contrasting sedimentary environments can have similar individual charateristics. Quite simply, the polemics have currently come to a plateau at the pro et contra level, in general simply trying to account for the pile-dwelling settlements either along the lake's edge or in the alluvial plain; and the Maharski prekop pile-dwelling is just an example of such a situation (cf. Budja, Mlekuž 2008a; Velušček 2009a). Andrič (2009) already noted the inappropriate-ness of these polemics. There are several other intermediary environs, which are otherwise not cited in the basic sedimentology textbooks. These intermediary environs are usually more difficult to recognize, requiring more data, observations and analyses to do so. Pile-dwellings by the lake? The interpretation that places the pile-dwellings along the lakeside supposedly originates from the mid 19th century, during a period when history was idealized, also in the form of romantic images (Grajf 1997). Indeed, idealized portrayals of pile-dwellings amidst the lake do exist from this time. However, there were more modern and entirely realistic analogies known from then as well. The interpretation is also based on the inference to, or actually even the response to the question: 'what kind of environment (with regard to the Barje at the time) would have most suited the inhabitants at the time?' Rightfully though, we may here wonder whether the "expediency" of choosing a location from our perspective is truly the only guideline on the basis of which we may conjecture as to the former pile-dwelling environment. As Grajf cited (1997, p. 12): By emphasizing certain aspects that influenced upon the development of the pile-dwelling settlements we easily fall into a deterministic and simplistic form of explanation. Archaeological excavations were carried out at the site of Špica at the end of 2009 and the beginning of 2010. On the basis of the uncovered groundplan and the cross-section with the connection between the lake silt and the cultural layer in the northern part of the site (fig. 3), I did extend my own hypothesis about how former inhabitants might have settled directly along the edge of the lake. The following field observations served to justify my hypothesis: - absence of soil horizons or at least the onset of pedogenesis directly upon the lake silt; - absence of erosive forms upon the surface of the lake sediment (slanted erosional cuts, basins, gutters, ^), which would otherwise be expected had the terrain, prior to the generation of the cultural layer, been incorporated into the (alluvial) erosion; - absence of alluvial sediments directly above the lake silt, which would at the same time also substantiate possible erosion and/or a sedimentation hiatus; - lamination of the lake silt, traced throughout the entire cross-section, demonstrating a slight inclination towards the Barje; however the same inclination also demarcated the border between the lake silt and the cultural layer. The cross-section characteristics described above could be interpreted as the transition from the lake sedimentary environment into the an-thropogenically conditioned marsh environment at the shore - lake border. Why anthropogenically conditioned? Because between the vertical piles and directly above the lake sediment were lenses (cm and dm dimensions) of alluvial flooding siliciclastic sediments as well as organic detritus, mollusk shells and fragments of pottery. This flooding material, caught between the vertical piles, could also be the consequence of the lake water's undulation, or even the consequence of occasional and modest alluvial flooding from the hinterland. Interpretations of observations to date have always proceeded with full acceptance. Wrongly so! The entire situation has changed exceptionally already between individual excavations. Prior to the end of the excavations, cross-sections showing a poorly defined erosive surface from between the lake sediment and cultural layer were opened in the southern part of the excavation field; concurrently, I received some information by word of mouth (Meta Culiberg and Maja Andrič) that the Fig. 3: Špica, 2010 archeaological excavations. Part of the southeastern cross-section of trench 1001. The stratigraphic hiatus between the lake sediments (lake silt) (JK) and the cultural layer (KP), estimated on the basis of luminescence dating (OSL), extends over approximately 14,000 years. The height of the sampling profile (SPI-P2) measures 1 m. (Photograph by Tomaž Verbič, archaeological excavations directed by the Ljubljana Museum and Art Gallery, 2010.) Sl. 3: Špica, arheološka izkopavanja 2010. Del jugovzhodnega preseka sonde 1001. Stratigrafski hiatus med jezersko kredo (JK) in kulturno plastjo (KP), ocenjen na podlagi luminiscenčne datacije (OSL), obsega približno 14.000 let. Višina profila za vzorčenje (SPI-P2) je 1 m. (Fotografija Tomaž Verbič, vodenje arheoloških izkopavanj Muzej in galerije mesta Ljubljane, 2010.) pollen content suggests assigningthe lake sediment dates to the Pleistocene and not the Holocene. Luminescent analyses of the lake silt sample subsequently provided more exact results: the lake silt is approximately 18,000 years old, so it was generated during the period of the Last Glacial Maximum (Johanna Lomax, electronic mail 27.1.2011). Combining these new observations, or analyses, with all the above mentioned descriptions would seem conducive to helping explain the stratigraphic hiatus in the context of sedimentary, erosive and pedological processes. Was this during the time that people settled in the Špica area, or in the direct vicinity of the lake? Probably not. It will be quite a stretch to explain the evidenced, approximately 14,000-year stratigraphic hiatus between the lake sediment and the cultural layer without a trace of pedogenesis, and with a poorly defined erosive surface. If we disregard the lake's sedimentary environment, with what shall we replace it? These are questions without answers as of yet. Nonetheless, we agree that vertical piles in the lake sedimentation are not in themselves proof of a settlement along the edge of the lake (Budja, Mlekuž 2008a). Pile-dwellings in the alluvial plains? The thesis that the pile-dwellings were situated in the alluvial plains along the watercourses probably originated from the interpretations of aerial photos of Maharski prekop and its surroundings (Bregant 1975, 49); these were subsequently supplemented (excellent quality!) with LIDAR photos together with interpretations of radiometric dates for the fill in the channel of the former watercourses (Mlekuž et al. 2006; Budja, Mlekuž 2010). At the same time, the authors of this hypothesis for the most part also relied upon the interpretation of geologic and sedimentologic data. Obviously, by interpreting the geologic processes they wished to take a step forward in understanding the former environment. The thesis may be appealing, however the data and results from archaeological excavations up to date predominantly fail to support it, in fact sometimes they even contradict it. It would seem that this thesis is currently drawing near a dead end, leaving open in its wake some general and locally conditional scientific questions. I shall limit myself to two. Generally speaking, the most disturbing aspect in this interpretation is the absence of alluvial siliciclastic sediments, which would presumably be connected with the former floodplain and - corresponding to this hypothesis - also with the cultural layers. ^e cultural layer at Maharski prekop is linked to the organic sediments, gyttja1, while elsewhere it is deposited directly on the surface of the lake sediment (Bregant 1975). ^is type of initial conditions implicitly demands that the floodplain be covered exclusively with gyttja during the settlement period. ^is hypothesis in turn preconditions the environment interpretation: preserving the organic sediments, even gyttja, is connected with a more or less constant body of water, or however we choose to call it. It follows that sedimentologically, we cannot classify it as a floodplain. Let it be known that the advocates of this hypothesis (Mlekuž et al. 2006, 257) expressly cite the putative alluvial (river) bedload, which was supposedly even the cause for change in the river's regime. Nonetheless, other than organic sediments, no such bedload was discovered during any of the archaeological excavations and trial trenching. ^e second issue that the hypothesis of pile-dwelling settlements in the alluvial plain left unresolved regards the stratigraphic sequence of events along the Ižica, where the authors gathered samples and dated the fill from the alluvial channel (Budja, Mlekuž 2008b, 2010). ^ey found only a dark, fibril-lar, organic sediment beneath the ground layer in all five boreholes and through their entire depth, and only under this lay the lake silt. None of the five boreholes revealed any type of siliciclastic sediment. A similar situation is known also from the excavated field near Maharski prekop, only that a thin cultural layer is interpreted between the lake sediment and the gyttja in these cross-sections (Bregant 1975). ^e author interpreted these types of conditions to be an alluvial channel filled with organic sediment and concurrent with the settlement (Bregant 1975). ^e stratigraphic sequence is more varied outside these channels. A gyttja deposit (prior to the construction of the pile-dwellings) lies above the lake silt and is covered by a cultural layer (for which gyttja provides the base ingredient), while above it lies predominantly a light grayish-yellow oily clay. In a sedimentary context this clay can probably only be interpreted as alluvial sediment, which corresponds with Bregant's opinion (1975). Furthermore, this would of course be a younger cultural layer, although the real focus would be on the stratigraphic relationship to the channels rather than to the erosive forms and to the fill in the channels. It is probably needless to add that the alluvial sediments were deposited in a continuous plane, as far as the circumstances allowed for the continuous overflow of waters with suspension sediments. What could have obstructed the generation of alluvial sediment above the existing channels, as the latter lay upon topographically lower levels than the so-called alluvial plain? ^e authors (Budja, Mlekuž 2008b, 2010) do not explore this matter. ^e explanation that the channel was chronologically concurrent with the settlement is not self-evident; furthermore, it does not correspond with stratigraphic principles and the sedimentologi-cal circumstances. A more likely and perhaps the only plausible explanation2 for the stratigraphic conditions described would be that the channels are younger than the cultural layers, and are of the light grayish-yellow oily clay as well. ^e alluvial channels at this location probably cut through the already flooded light grayish-yellow oily clay and 1 I use the term 'gyttja' here corresponding to Bregant's usage (1974, 1975), even though in the continuation I express doubt concerning this usage. 2 The concurrency of the water channels and the cultural layers could also be explicated under specific conditions. For instance, all the channels would have to be stable through all the chronological periods, and not just during the formation of the cultural layer and possibly before it. Rather, also later, during the formation of the gyttja above the cultural layer, as well as during the formation of the light grayish-yellow oily clay, that is, the alluvial sediment. In the instance that a channel was not active during the formation of this clay, then the latter would have to cover it; and this fails to hold true. Another consideration would be that the water with the clay suspension material overflowed the alluvial plain directly from these channels. This would prove a relatively inadvertent thesis, as then we would expect an alluvial sediment in the context of the earlier layers as well (in the cultural layer and the gyttja from before the settlement), which would have formed during the period of activity of the water channels. However, the circumstances at hand demonstrate no reason for the absence of alluvial sediments in the context of earlier layers. The conditions at Maharski prekop are to the contrary: the alluvial sediment is linked practically to a single layer in the top part of the cultural layer. No matter how we go about clarifying the recorded stratigraphic conditions according to a model of concurrent channels and cultural layer (Bregant 1975, 13; Mlekuž et al. 2006; Budja, Mlekuž 2010), the line of argument flounders. As such, this explication seems unfounded. It seems that the primary argument for this model of interpretation of a concentration of vertical piles in the shape of a breakwater, is not the only possible explanation (Velušček 2009a, 305). Fig. 4: Conceptual stratigraphic sedimentological model for the formation of the sedimentary environment near Maharski prekop, as can be formulated on the basis of archaeological documentation (Bregant 1974, 1975). Sedimentation of the lake sediments (a); formation of gyttja prior to the pile-dwellings (b); formation of the cultural layer (c); flooding of the light grayish-yellow oily clay (d); alluvial erosion, active stream basin (e); filling-in of erosion channel with sediments (f), select areas with first a thin layer of resedimentation of the cultural layer and then followed by gyttja, entirely on the top, select areas also with a thin layer of yellow clay, layers that Bregant (1975) refers to with the terms humus and subhumus (g). 1 - lake sediments; 2 - gyttja prior to the pile-dwellings; 3 - cultural layer; 4 - grayish-yellow oily clay; 5 - younger gyttja; 6 - yellow clay; 7 - humus and subhumus. Sl. 4: Konceptualni stratigrafsko-sedimentološki model razvoja sedimentacijskega okolja ob Maharskem prekopu, kakor ga lahko konstruiramo na podlagi arheološke dokumentacije (Bregant 1974, 1975). Sedimentacija jezerske krede (a); nastanek gyttje pred kolišči (b); nastanek kulturne plasti (c); naplavljanje svetle sivorumene mastne gline (d); aluvialna erozija, aktivno potočno korito (e); zapolnjevanje erozijskega korita s sedimenti (f), ponekod najprej tanka plast resedimenta kulturnega horizonta, sledi mlajša gyttja, povsem na vrhu pa ponekod še tanka plast rumene gline in plasti, ki jih Bregantova (1975) označuje z izrazoma humus in subhumus (g). 1 - jezerska kreda; 2 - gyttja pred kolišči; 3 - kulturna plast; 4 - svetla sivorumena mastna glina; 5 - mlajša gyttja; 6 - rumena glina; 7 - humus in subhumus. then dug deeper through the cultural layer and the gyttja prior to the building of the pile-dwelling, even also into the lake silt (fig. 4). ^e drawing including the stratigraphic relationships implies this to be a more likely interpretation (Bregant 1975, insert 3; Bregant 1974, insert 1)3. A more firm answer to this problem would give OSL dating of this flood sediment. ^e authors of the hypothesis that the pile-dwelling settlement was situated on the alluvial plain will presumably lean on the radiometric datings of the gyttja and the fibrous organic sediment in these channels (Budja, Mlekuž 2008b, 2010). Nonetheless, 3 At some parts of the profiles from Bregant (1975, insert 3 and 4; 1974, insert 1) she draws grayish-yellow oily clay as it covers gyttja at the edge of alluvial channel, it seems that channel fill is older than the grayish-yellow oily clay at that point. My opinion is that this stratigraphic situation could be due to rain washing, perhaps also due to minor inaccuracy during drawing stratigraphic relationships. In any case, the majority of the profiles (together 80 m) shows that the gyttja is not covered with grayish-yellow oily clay. //////////////////////////////////////////77? C^////////////////////////////// 1 2 irr 3 4 dU 5 there is only one dating from each borehole core. Resedimentation of earlier organic material is an alternative reasoning of the circumstances. Similar resedimentation could even be construed from Bregant's cross-sections (1975, insert 3 and 4) in the thin cultural layers from the channels directly above the lake silt (see also fig. 4f). Apropos Maharski prekop, the fan-like trajectories of piles, as well as the positioning and orientation of the corresponding houses along the postulated current (Bregant 1975, insert 2, 3; Mlekuž et al. b c d e g 6 7 2006, figs. 5, 7, 8), could be descrying a former alluvial dynamic. This led me to cover these trajectories with a LIDAR recording (Mlekuž et al. 2006, fig. 4; Budja, Mlekuž 2010, fig. 4). ^e result was remarkable to behold: the fan-like trajectories of piles coincide well with the postulated water current dating to phase 1, that is, contingent to its flowing north to south and then out into an alluvial fan in the lower lying channel of phase 3. I do not claim that my interpretation is exact; contrarily, I believe that this observation merely demonstrates that reliance solely upon remote sensoring can lead to false conjectures, which further provide the basis for drawing no more than false interpretations and conclusions. THE SUBSIDENCE OF THE BARJE BASIN AND THE INFLUENCE OF THE SEDIMENTARY ENVIRONMENT ^e Ljubljansko barje Park today encompasses an inherited, anthropogenically degraded landscape that is connected only by history with the sedimentary environment of the Barje. Rarely is the influence of mankind on the environment as severe as upon the Barje. In a geological context, the influence of anthropogenic activities on the Barje is the greatest as regards the dynamic of the subsidence of the basin. ^e evaluation of the subsidence during individual periods, that is, recognizing the dynamic of subsidence, could contribute to a better understanding of past environmental changes on the Barje. Furthermore, subsidence might have a determinative impact upon the urbanistic development and settlement pattern on the Barje in the future. Ground subsidence is today presumably the most complex natural geologic process on the Barje, while at the same time it is also partly anthropogenically driven. Even without anthropogenic influence, ground subsidence on the Barje is composed of at least two independent processes: natural compactions of nonlithified sediments and tectonic subsidence. ^e drying up of the Barje further influences new processes: the subsidence and compaction of the soil due to the subsiding level of groundwater, ground subsidence due to the cutting, burning and decomposition of peat, as well as the decaying of organic sediments and the soil. Of course, there is also the question of the kind of influence that the recent unloading of the bog soil has due to the above mentioned consequences of drying up. Other than this, the Barje in the past few decades has witnessed engineering endeavors that have an exceptional, albeit local influence on the subsidence of the basin (for example, Vodarna Brest). Several attempts have been carried out to quantify the subsidence, differing mainly in their methodology. The most successful of the attempts are the geodetic surveys of recent subsidence, especially those in the smaller anthropogenically degraded areas, where the subsidence is monitored for technical reasons (cf. Ježovnik, Jakljič 2003; Ježovnik 2009). ^e methodology for these measurements is straightforward, and errors are ranked; however, the difficulty is that the measured values of the surveys represent the cumulative sum of different causes for the subsidence (local anthropogenically conditioned subsidence, subsidence due to natural compactions of sediments, subsidence due to the decaying of organic soil, tectonic subsidence^). By no means can the results of these measurements be transferred: neither into (geologic) history or the future (urban planning), nor to any other location on the Barje. ^e subsidences due to construction by anthropogenic influences are usually disproportionally larger than natural subsidence. On the other hand, there are some attempts to quantify the subsidence on the Barje according to individual causes (Breznik 2000; Bračič Železnik et al. 2003). Contrary to the geodetic measurements, the methodology with these evaluations is relatively unclear, and the errors are unranked. These evaluations are for the most part unverified values, in a technical sense. Brenčič (2007) aimed to remedy this situation with a relatively original methodology. He established on the basis of linear regressions determined between the depth and dates of the sediments in boreholes BV-1 and BV-2, that the Barje sank in these two locations relatively uniformly during the Holocene, with a speed of 1.235±0.011 mm/ year and 1.357±0.005 mm/year. He deduced the numeric age of the sediments solely on the basis of correlations with pollen diagrams; this puts the results under question, as it is a very inexact and unreliable method. More striking is the conceptual error in this equation. The base premise in his model (Brenčič 2007) was always the sedimentation at the ground level. This of course fails to hold true in the case of the Ljubljansko barje, as ignoring the depth of the sedimentation basin implicitly negates the former lake environment where the majority of sedimentation formed. Figure 5 presents two conceptual models at the same end stance, the formation of a 10 m thick sedimentation column that formed during 10,000 years. ^e first example o m 10.000 čas (leta) tirne (years) 9.000 5.000 danes starost sedimenta age of the sediment (ka) 10 9 5 0 (D "ül C (D 01 J3 S