Lower Jurassic carbonate succession between Predole and ... - RMZ

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia168division of the Jurassic stratigraphicsequence in Dinarides. Do z e t (1999a, b) explored and described LowerJurassic shallow-water carbonate successionwith coal on the Dinaric CarbonatePlatform in Southern Slovenia.The coal occurs in the form of lensesand thin seams among the limestoneand dolomite beds of middle part of theLower Jurassic age. Mi l e r and Pav š i č(2008) described the development ofthe Triassic and Jurassic beds in theKrim Mountain area. The Jurassicstratigraphic sequence involves Lowerand Middle Jurassic shallow marinecarbonate rocks.Mat e r i a l s a n d m e t h o d sapplied. For formation analaysis thecross-section Spodnja Slivnica-Predolehas been chosen (St r o h m e n g e r &Do z e t, 1991). Around 150 samples ofcarbonate rocks have been collectedalong the road on the southeastern borderof Radensko polje and another 65rock samples in the cross-section Ilovagora-Čušperk for micropaleontologicalanalyses carried out by Rajka Radoičićand S. Dozet.Carbonate rocks are classified accordingto Fo l k’s (1959) practical petrographicclassification of limestones andDu n h a m’s (1962) classification of carbonaterocks according to depositionaltexture.This work is based on data, obtainedduring the systematic regional geologicmapping in the field on the MapSheet Grosuplje for elaboration of GeologicMap of Slovenia on the scale of1 : 50 000, performed by GeologicalSurvey of Slovenia. During geologicmapping of Central Slovenia we werefocused on stratimetric researches inthe field and systematic labor examinations.For planning of geologic mappingon the Map Sheet Grosuplje theBasic Geologic Map of SFRJ – MapSheet Ribnica on the scale of 1:100000 and its Explanatory text has beenRe s u lt s o f t h e r e s e a r c h w o r kLower JurassicIn the area between Spodnja Slivnicaand Račna (Figure 2) five litostratigraphicunits of the Lower Jurassic ageis separated. Superpositionally frombottom to top they follow one otherlike that: 1 – bedded micritic and oolitic-oncoliticlimestones, 2 – beddedOrbitopsella Limestones, 3 – beddedLithiotis Limestones, 4 – bedded tomassive oolitic and reef limestones, 5– platy Spotty Limestones.RMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia174Figure 5. ExplanationRMZ-M&G 2009, 56

175 Do z e t, S.Figure 6. Grey bedded Lower Lower Jurassicmicritic limestoneFigure 7. Bedded and banded Lower LowerJurassic micritic limestoneOolitic limestone interbeds are composedof ooids with radial microstructureand micritic ooids. They are boundwith fibrous and mosaic calcite cement.The oolitic limestones with radial ooidsoriginated in shoals with moderatelyagitated water (Ti š l j a r & Ve l i ć, 1991).Micritic ooids are the result of diageneticchanges, chiefly due to micritizationby Cyanophiceae and cryptocrystallinerecrystallization.Limestones of wackestone and mudstonetype were deposited in a shallowsubtidal environment in a restrictedpart of lagoon, while coarse-grainedsparitic limestones originated in anintertidal belt, what is proved by erosionalsurfaces, stromatolitic belts,fenestral structures and textures, intraclasts,shrinkage pores and intertidalbreccias.The lower unit of Lower Jurassic carbonatesequence is relatively poor infossils, what point at unfavourable lifeconditions for the then fauna and flora.Important characteristics of the oldestunit is especially an absence of echinodermsand rarity of foraminifers andmolluscs (Figure 8). Limestones of thelowermost unit of Lower Jurassic successioncontain the following fossils:Figure 8. Black bedded limestone withmegalodontid lumachelles, Lower LowerJurassic, Radensko poljePalaedasycladus mediterraneus (Pia)(Pl. 1, Fig. 1), P. elongatulus (Pratur-RMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia180The described oolitic limestones wereformed in an evironment with high-waterenergy, in shoals and bars respectively.In the limestones of the Oolitic Limestoneunit sections of alga Palaeodasycladusmediterraneus (Pia), rare foraminifersPseudocyclammina liassicaHottinger and Haurania deserta Henson,pointing at upper part of middleLower Jurassic (Domerian) as well asrare fragments of crinoids, molluscs,corals, stromatoporoids and pelecypodPecten sp. were found.The Oolitic Limestone unit is foundin several places of central and southernSlovenia. In the oolitic-bioclasticlimestones, that lie above the LithiotisLimestone and are accordingly anequivalent of the Oolitic Limestoneunit of the Lower Jurassic stratigraphicsequence, a corral patch reef with richassociations of corals and stromatoporoidswere detected on Krim (Tu r n š e k& Ko š i r, 2000) and Trnovski gozd(Tu r n š e k et al., 2003). Tu r n š e k andKo š i r (2000) described systematicallyseven coral species, from which threespecies are new: Thecactinastraea krimensisTurnšek, Siderosmilia perithecataTurnšek and Cuifastraea lopatensisTurnšek. Tu r n š e k et al. (2003)found in Trnovski gozd in the LowerJurassic patch reef, lying upon the LithiotisLimestone, a finding of LowerJurassic corals. Systematically weredetermined and described 12 coral speciesbelonging to eight genera. Fourspecies were new: Protoheterastraeatrnovensis Turnšek, Apocladophylliagozdensis Turnšek, Phacelophyllia bacariTurnšek and Heterostraea angelaeTurnšek. Corals built at least 70 meterslong and 4 meters large patch reef, thatgrew on the northern border of the DinaricCarbonate Platform. The coralsrange the Lower Jurassic reef limestoneof the Trnovski gozd in Upper Pliensbachian,Domerian respectively.The Domerian Oolitic Limestone originatedin shallow and open parts of theDinaric Carbonate Platform.The thickness of Uppermost Pliensbachianoolitic limestones ammountsfrom 15 to 25 meters.5 th Unit – Spotty Limestones, ToarcianThe youngest unit of considered carbonatesequence (Figure 16) is composedof medium dark grey, dark greyand grayish black, platy (predominate)and bedded prevalently micritic (mudstone)and pelmicritic bioturbatedlimestones, which are due to activity ofnumerous organisms, that ate mud, becamespotty. For the Spotty Limestones(Figures 3, 5) is also pretty characteristicthat they are poor in fossils. Theycontain only rare remains of algae, benthicforaminifers and echinoderms. Accordingto texture they are mostly mi-RMZ-M&G 2009, 56

181 Do z e t, S.critic, oomicritic and biomicritic limestones.In the limestones of the fifthunit locally a gently lamination can beobserved. The stratigraphic sequenceof Spotty Limestones include sporadicthinner interbeds of oolitic and bioclasticlimestones (crinoid limestones: Pl.2, Fig. 5).Plate 2. Fig. 1. Bioclastic-peloid packstone to grainstone with foraminifersOrbitopsella praecursor (Gümbel) Trochaminidae and Textulariidae,Middle Lower Jurassic, Predole at Račna; Fig. 2. Foraminifer Involutinafarinacciae Bronnimann & Zaninetti in an intrasparitic packstone, MiddleLower Jurassic, Predole at Račna; Fig. 3. Ooid grainstone with foraminiferInvolutina farinacciae Bronnimann & Zaninetti, Middle Lower Jurassic,Predole at Račna; Fig. 4. Alga Linoporella (Tersella ?) lucasi Cross& Lemoine coated with algal (cyanobacterial) envelope, Middle LowerJurassic, Predole; Fig. 5. Crinoid limestone: bioclastic-intraclastic packstone,Upper Lower Jurassic, Predole at Račna; Fig. 6. Recrystallized ooidmudstone with foraminifer Ophthalmidium sp., Upper Lower Jurassic/Dogger, Predole at Račna.RMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia182According to dark colour, abundant bituminousorganic matter, structures andtexture and regarding the fauna (ostracods,molluscs with thin shells) andflora can be concluded that the SpottyLimestones were deposited in restrictedparts of shelf, where there were nofavorable conditions for greater diversityof organisms.The thickness of upper part of the LowerJurassic limestones varies from 55 mto 75 m.Midle JurassicFigure 16. The contact between the underlyingmedium grey massive Middle LowerJurassic oolitic limestone and the verlyingdark platy Upper Lower Jurassic SpottyLimestoneUpper part of the Lower Jurassic limestonescontain rare foraminifers Hauraniadeserta Henson, Ophthalmidiumsp. (Pl. 2, Fig. 6), Pseudocyclamminasp., crinoids, small gastropods as wellas algae Aeolisaccus dunningtoni Elliotand Thaumatoporella parvovesiculifera(Raineri).The age of considered carbonate rocksis defined also by their stratigraphic position,since they lie between the LowerJurassic biostromal (coral) beds anddark oolitic limestones with diagnosticMiddle Jurassic fossils, so that they aresurely of Toarcian age.Hanging wall of the considered carbonatesuccession is represented by astratigraphic sequence (Figure 4, 5) ofdark brownish grey to grayish blackoolitic limestones (ooid grainstones)that are an equivalent of the Middle JurassicLaze Formation (Do z e t, 2000 a).They are overlain by around 50 metersthick horizon of “pisolitic” limestones(pisolite grainstones).Around 85 meters thick Middle Jurassiclithologic column is composed ofthin- and thick-bedded, well-sorted,prevalently medium-grained ooliticlimestones (Figure 17). In the consideredcarbonate sediments predominatefrom 0,5 mm to 0,75 mm largeooids, but there are also more or lessrounded intraclasts, bioclasts, pelletsand pelletoids. In the field can be followedoosparitic (ooid grainstones),oointrasparitic, intrasparitic (intraclastgrainstones), biosparitic (bioclastgrainstones) as well as smaller patchesof oomicritic and pure micritic limestones.In the composition of ooliticlimestones strongly prevail medium-RMZ-M&G 2009, 56

183 Do z e t, S.Figure 17. Medium grey massive Doggeroolitic limestoneFigure 18. Grey to medium grey platy orbedded Lowermost Malm “pisolitic” limestonegrained well-sorted radial ooids boundwith mosaic calcite cement, here andthere with isopach granular cement Aas well.Among organogenic remains prevailforaminifers (Textulariidae, Trochaminidaeand Verneuilinidae), that representmostly cores of ooids. Paleontologicallyand biostratigraphically significant(RADOIČIĆ, 1987) for these carbonaterocks are Aalenian alga Holosporellasiamensis Pia (Pl. 3; Fig. 1, 2, 3, 4)as well as foraminifers Spiraloconulusgiganteus Cherchi & Schroeder (Pl. 3;Fig. 5, Fig. 6) and Gutnicella (Dictyoconus)cayeuxi Lucas. Oolitic limestonescontain also greater or minorfragments of molluscs, echinoderms,pretty rare sections of stromatoporoids,alga Thaumatoporella parvovesiculifera(Raineri) and corals, that representfree clasts in sparitic cement.Interbeds of micritic and sparitic limestonesin the considered oolitic complexspeak for subtidal to intertidal sedimentaryenvironment in close vicinityof tidal channels. The isopach granularcement A indicates an episodic meteoricinfluence.Upward follows 50 m thick lithologicinterval (Figure 4, 5) represented byplaty and bedded medium dark grey“pisolitic” limestones (Figure 18) composedof 1 cm to 2,5 cm large concentricpisolites, bound with coarse-crystallized(sandy) greatly dolomitizedsparitic cement. Late diagenesis usuallydid not embrace pisolites. It took onlysparitic cement, and in spots it changesthe rock in a pure dolosparite. Similar“pisolitic” horizon is also found alongthe road between Vrhnika and Logatec,on Hrušica, at Vodice and to the eastof Col (BUSER, 1978), This horizonwithin the Middle and Upper Jurassicoolitic limestones has been up to thenranged to Middle Jurassic, but BUSERRMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia184Plate 3. Fig. 1. Ooid wackstone-packstone with alga Holosporella siamensisPia, Lower Dogger (Aalenian), Predole at Račna; Fig. 2. Ooid packstonewith a section of alga Holosporella siamensis Pia, Lower Dogger(Aalenian), Predole at Račna; Fig. 3. More ore less recrystallized ooidwackestonewith section of alga Holosporella siamensis Pia, Lower Dogger(Aalenian), Predole at Račna; Fig. 4. Ooid grainstone with alga Holosporellasiamensis Pia, Lower Dogger (Aalenian), Predole at Račna; Fig.5. Foraminifer Spiraloconulus giganteus Cherchi & Schroeder in a coarsegrainedooid grainstone, Dogger, Predole at Račna; Fig. 6. ForaminiferSpiraloconulus giganteus Cherchi & Schroeder in a coarse-grained ooidgrainstone, Dogger, Predole at Račna.(1978) found bellow that horizon coralsand hydrozoans, that proved the“pisolitic” horizon belongs already tothe lowermost (basal) part of Upper Jurassic.The “pisolitic” limestone at Predolecontains the following fauna and flora:Trocholina alpina (Leupold), Clado-RMZ-M&G 2009, 56

185 Do z e t, S.coropsis mirabilis Felix, Aeolisaccusdunningtoni Elliott and Cayeuxia sp.In the succession of oolitic limestones,that lie above the Lower Jurassic beds,we found and determined the followingfossils: Trocholina elongata (Leupold),Salpingoporella annulata Carozzi andKurnubia palastiniensis Henson.On the basis of determined fauna andflora as well as considering correlationof the “pisolitic“ limestones at Predoleand “pisolitic” horizons on Hrušica, atVodice, between Vrhnika and Logatecas well as east of Col (Bu s e r, 1978)the 50 meters thick succession of “pisolitic”limestones at Predole is attributedto Upper Jurassic, to the lowermostpart of Upper Jurassic more precisely,that is overlain by the Upper Jurassicoolitic complex corresponding to theŠentrumar Formation (Do z e t, 2000 b)or to the upper part of the Verd OoliticComplex (Do z e t, 2000 a).Pa l e o g e o g r a p h i c e vo l u t i o n a n d c o r-r e l at i o n o f u p p e r t r i a s s i c t o Mi d d l eJu r a s s i c s e d i m e n tat i o nThis chapter deals with sedimentationand paleogeography in the Predole areaon the northern margin of the DinaricCarbonate Platform.In the Norian and Rhaetian periodsoriginated in the Predole area and thewhole southern Slovenia on the stableDinaric Carbonate Platform thewell-known 900 to 1300 meters thickformation of Main Dolomite. It wasformed in pretty shallow restricted environment,where supratidal, intertidaland subtidal conditions alternated. Themost typical for the Main Dolomite isso-called Lofer facies (Sa n d e r 1936,Fi s c h e r, 1964) respectively cyclic alternationof red or green residual sediments(supratidal unit A), fenestraland stromatolitic dolomites, breccias(intertidal unit B) and micritic dolomiteswith megalodons – subtidal unitC (Og o r e l e c, 1988; Do z e t, 1990 b,1991; Og o r e l e c & Ro t h e, 1992). TheRhaetian-Lower Jurassic developmentin the Krim Mountain area is interpreted(Mi l e r & Pav š i č, 2008; Mi l e ret al., 2007) as a consequence of shorttermedmarine regression that was alsoevidenced in the Northern CalcareousAlps (Mc Ro b e rt s et al, 1997; Kry s t y net al., 2005).The sea-level changes in the NorthernCalcareous Alps are explained as a consequenceof a short-termed tectonic uplift,possibly a regional thermal upliftconnected to the activity in the CentralNorth Atlantic Magmatic Province, andslow rebound within a locally or regionallylimited area (Kry s t y n et al., 2005).In the Lower Jurassic the sea was deepenedand a sedimentation of variouslygrey, bedded micritic limestones interbeddedwith rare oolitic ones in preva-RMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia186lently quiet-water of restricted and episodicallyopen lagoon followed. Thedeepening of the environment is interpretedas a consequence of global sealevelrise (Ha l l a m, 1997; Mc Ro b e rt set al, 1997; Mi l e r & Pav š i č, 2008).In the Predole area the variously greybedded micritic (mudstone), sparitic,oncolitic, laminated and stromatoliticdolomites of the Main Dolomite Formationpass upwards directly into thebedded prevalently micritic (mudstone)Lower Jurassic limestones sothat the geological relations at the Triassic/Jurassicboundary were normal.Namely, in the Predole area the Rhaetian-LowermostJurassic breccia unitoccurring in central Dolenjska (Bu s e r,1974; Do z e t 2003 and Mi l e r et al.) isnot developed, what testifies that in theUppermost Rhaetian and LowermostJurassic there were no larger tectonicmovements in this area.Sedimentologic particularities, faunaand flora show that the Lower JurassicKrka Limestones in central Dolenjska(Do z e t & St r o h m e n g e r, 1993) originatedin similar sedimentary conditionsas Dachstein Limestone and Main Dolomitein Northern and Southern CalcareousAlps. All three formations arenamely characterized by typical Loferrhythmic sedimentation.The Lower Jurassic epoch is markedby lithiotid limestones. Lithiotid bivalvesformed in southern Slovenia inprevalently quiet water environmentof the restricted shelf sea-bottom matsor biostromes. Their shells can be onlyrarely found in their growth position(Bu s e r & De b e l j a k, 1994/1995). Theup to 75 m thick horizon with lithiotidbivalves is attributed to Pliensbachian.At high tides and storms the fresh wateroverflowed the adjacent barring“oolitic sand”. Consequently, insidethe former lagoon with lithiotid biostromes,dark oolitic limestones can befound as well.Uppermost part of the middle LowerJurassic is represented by a horizon ofoolitic limestones originated in highenergy open shallow-water environment(Do z e t & Šr i b a r, 1997; Do z e t &St r o h m e n g e r, 2000).The upper part of the Lower Jurassicintensively bioturbated Spotty Limestoneswith high organic contents wereformed in a low-energy restricted lagoonenvironment. The Spotty Limestonescontain rare interbeds of ooliticlimestone that indicates an alternationwith episodic high energy openshallow-water environment (Or e h e k& Og o r e l e c, 1981; Do z e t & Šr i b a r,1997) The high organic contents in theSpotty Limestones is explained as aconsequence of Toarcian Ocean anoxicevent (Ha l l a m, 1986; Je n k y n s, 1998;RMZ-M&G 2009, 56

187 Do z e t, S.Mi l e r & Pav š i č, 2008).During the Lower Jurassic epoch inthe region of Tethys vivaceous tectonicmovements occurred. In northernSlovenia area a short land phase tookplace, and afterwards it rapidly subsidedand disintegrated (Bu s e r, 1989).These events reached also the DinaricCarbonate Platform. In the Stična,Šentvid, Radohova vas, Trebnje, VelikiGaber and Valična vas areas the UpperJurassic beds transgressively overlie themiddle Lower Jurassic ones. In centralDolenjska numerous coal occurrencesare known (Bu s e r, 1974; Do z e t, 1999a, b). All this may be understood as anevidence of an uplift of the area afterthe deposition of the Lower Jurassicsediments with bivalves. The same tectonicactivity was reported also fromthe neighbouring Italy. On the TrentoCarbonate Platform the shallow marinebeds with bivalves are overlain bydeep marine limestone of the ammoniticorosso type (Bo s e l l i n i & Br o g l i oLo r i g a, 1971).During the Middle Jurassic the paleoeogeographyof southern Slovenia wasmarked by high-energy environmentsespecially on the northern margin ofthe Dinaric Carbonate Platform.Jurassic rocks and fossils from thecross-section Krka-Mali Korinj in Suhakrajina (St r o h m e n g e r & Do z e t, 1991)clearly indicate a smaller stratigraphicgap during the Middle Jurassic epoch.The identified index fossils indicate anage older than Callovian or older thanUpper Callovian respectively. Perhapsthe break in sedimentation coincideswith the assumed fall of sea-level duringthe Callovian or at the end of theBathonian (Ha l l a m, 1987, 1997; Bose l l i n i et al., 1981).Co n c l u s i o n s• The considered territory is situatedin the southeastern border ofRadensko polje (southeasterly ofLjubljana) comprising smaller hillsGradišče (486 m) and Griči (492m and 488 m). From the palaegeographicpoint of view the areain question belongs to the DinaricCarbonate Platform (Bu s e r, 1989),geotectonically however, to themacrotectonic unit of External Dinarides(Pl a c e r, 1998).• According to the mineral compositionmonotonous, and with referenceto texture pretty diversecarbonate succession, consistingprevalently of various limestoneswith some dolomite interbeds andlying conformably upon the MainDolomite and conformably (gradualtransition) under the dark ooliticlimestones of Laze Formation(Do z e t, 2000 b), is considered asan equivalent of the PodbukovjeFormation (Do z e t & St r o h m e n g e r,2000) .RMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia188• The discussed stratigraphic sequencebetween Predole andMlačevo is composed of five lithostratigraphicunits:• 1 – Micritic and oolitic-oncoliticlimestones, 2 – Orbitopsella Limestones,3 – Lithiotis Limestones, 4– Oolitic and reef limestones and 5– Spotty Limestones.• The first Jurassic lithostratigraphicunit is composed of bedded micritic(mudstone) limestones interbeddedwith oolitic (ooid grainstones)and oncolitic ones. The consideredlimestones are of Lower Jurassic(Hetangian a. Sinemurian) age (Palaeodasycladusmediterraneus Pia,Sestrosphaera liasina Pia). Thelimestones of mudstone type weredeposited in a shallow subtidal environmentin a restricted part of lagoon.The thickness of the first unitis about 125 m.• In the second Lower Jurassic lithostratigraphicunit predominatethick-bedded variously grey prevalentlysparitic limestones containingbenthic foraminifers Orbitopsella.They are known under thename Orbitopsella Limestones andare ranged according to microfaunaand microflora in the Lower Pliensbachian.The Orbitopsella Limestoneswere formed in a restrictedshallow-marine environment withperiodically agitated water, lagoonand shallow-subtidal environments.The thickness of the second unitranges from 55 m to 75 m.• Limestones with rock-buldingshells of Lithiotidae represent thethird unit of the lower Lower Jurassicsequence. The main characteristicof this facies are bivalves ofthe family Lithiotidae that form lumachelles.According to the fossilsCochlearites loppianus (Tausch),Lithioperna scutata (Dubar) andPalaeodasycladus mediterraneus(Pia) they belong to the UpperPliensbachian, Domerian respectively.During Middle and LowerJurassic the depositional environmentswere marked by continuousdeposition of sheltered subtidaland intertidal zones with suitableconditions for an extensive growthof calcareous alga, foraminifers,lamellibranchs, gastropods and brachiopods.The thickness of the thirdunit ranges from 45 m to 55 m.• The fourth lithostratigraphic unit,lying concordantly between theLithiotis Limestones and SpottyLimestones and consisting of greymassive, bedded and platy ooliticlimestones is denoted as OoliticLimestones. The Oolitic Limestonespass horizontally into reeflimestones containing corals thatrange both facies into the UpperPliensbachian, Domerian respectively.The Oolitic Limestones originatedin an environment with highenergy, in tidal channels respectively.The thickness of UppermostRMZ-M&G 2009, 56

189 Do z e t, S.Pliensbachian Oolitic Limestonesunit varies from 15 m to 25 m.• The fifth Lower Jurassic unit iscomposed of prevalently dark, micritic(mudstones), bioturbated,so-called Spotty Limestones, withrare interbeds of oolitic and crinoidlimestones that are all added to Toarcian.Spotty Limestones were depositedin restricted parts of shelf.The thickness of this unit variesfrom 55 m to 75 m.• The Predole area and wider environslie in southern Slovenia territorybelonging paleogeographycallyto the northern margin of DinaricCarbonate Platform (Bu s e r,1974), geotectonically however, toExternal Dinarides (Bu s e r, 1989;Pl a c e r, 1998). It is built of UpperTriassic and Jurassic carbonaterocks. Upper Triassic sedimentationis represented by the MainDolomite Formation composed ofcyclic Lofer facies (Sa n d e r, 1936;Fi s c h e r, 1964) and originated in ashallow lagoonal subtidal, intertidaland supratidal environments. Inthe Predole area sediments of theMain Dolomite Formation pass upwardscontinually without any interruptionin sedimentation directlyinto bedded, micritic Lower Jurassiclimestones. The geological relationsat the Triassic/Jurassic boundarywere normal. Consequently,there were no larger tectonic movementsin that time.• The Lower Jurassic sedimentationis exclusively lagoonal and carbonateby character. In the lower partvariously grey bedded prevalentlymicritic (mudstones) limestoneswith interbeds of oolites and dolomitesoccur. The middle part ofthe Lower Jurassic stratigraphicsequence consists of Orbitopsellaand Lithiotis Limestones as wellas Oolitic and Reef Limestones atthe top. The above-enumerated carbonatesediments were formed inalternating restricted and open lagoonalenvironments. They coreespondto the outer part of the innerplatform environments, proximalto the northern margin of DinaricCarbonate Platform (Bu s e r, 1989;Bu s e r & De b e l j a k, 1996; Tu r n š e k& Ko š i r, 2000; Mi l e r & Pav š i č,2008). Uppermost Lower Jurassicbioturbated Spotty Limestoneshave high organic contents. Theywere formed in high energy openshallow-water envioronment (Do z-e t & Šr i b a r, 1997; Do z e t & St r o-h m e n g e r, 2000). Oolitic limestonesinterbeds in the Spotty Limestonesindicates an alternation with episodichigh energy open shallow-waterenvironment (Or e h e k & Og o r e l e c,1981; Do z e t & Šr i b a r, 1997). Thehigh organic contents in the SpottyLimestones is explained as a consequenceof Toarcian Ocean anoxicevent (Ha l l a m, 1986; Je n k y n s,1998; Mi l l e r & Pav š i č, 2008).RMZ-M&G 2009, 56

Lower Jurassic carbonate succession between Predole and Mlačevo, Central Slovenia190• The described stratigraphic sequenceis of Lower Jurassic age.Bedded, prevalently banded micriticlimestones with oolitic-oncoliticinterbeds (1) belong to Hettangianand Sinemurian, the OrbitopsellaLimestones (2) to the Lower Pliensbachian(Carixian), Lithiotis Limestones(3) to the Upper Pliensbachian(Domerian), oolitic and coralreef limestones (4) to the UppermostPliensbachian, and the SpottyLimestones to Toarcian.• Biostratigraphically, in the LowerJurassic carbonate sequence arerecognized: the cenocona Palaeodasycladusmediterraneus (Pia),subzones Palaeodasycladus barrabei(Lebouche & Lemoine), Orbitopsellapraecursor (Gümbel) andLithiotidae, subzone with corals, aswell as the interval zone of SpottyLimestones (Figure 7).• The Middle Jurassic stratigraphicsequence in the Predole area iscomposed of various dark ooliticlimestones of grainstone type thatcontain the Middle Jurassic diagnosticforaminifers: Spiraloconulusgiganteus Cherchi & Schroeder andGutnicella (Dictyoconus) cayeuxiLucas as well as alga Holosporellasiamensis Pia.• The beds with above-mentionedfossils in the Predole area correspondto the beds of Laze Formationrepresenting the lower partof Hočevje Group (Do z e t, 2000b) and are quite comparable withMuča ooid-bioclastic unit in Croatia(Ve l i ć & Ti š l j e r, 1988). Mučaooid-bioclastic Limestones are infact positioned within the Lim unit.The shallow-water limestones ofthe Muča unit are typical tidal-barwinnowed carbonate sands i.e sedimentsof the sixth Wi l s o n’S (1975)standard facies belt. They originatedby the transport of ooid sand andfossil detritus by tidal streams andwaves and the deposition on tidalsand bars.• With regard to determined fossilfauna and flora and on the basis ofcorrelation of “pisolitic” horizonat Predole with “pisolitic” horizonselsewhere in Slovenia (Bu s e r,1978), the 50 meters thick sequenceof “pisolitic” limestones at Predoleis ranged into the lowermost partof Upper Jurassic.AcknowledgementsThis research was performed in theframework of the Programme GroupRegional Geology of Geological SurveySlovenia. It was financially enabledby Slovenian Research Agencyand Geological Survey of Slovenia.For ambitious and efficient determinationof the relatively scarce Jurassicmicro fauna and flora the author owesa great debt of thanks to Ph. D. RajkaRadoičić.RMZ-M&G 2009, 56

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