GEOL. CROAT . 50/2 243·250 2 F igs. ZAGREB 1997 Triassic Deposits of Hrvatsko Zagorje Antull SIMUNIC and Alka SIMUNIC Key word s: Triass ic , Sandstones, Dolomites, Lime ­ stones, C lastics, Tuffs, Andesi tes, Basalts, J-Irva tsko Zagorje, Croatia. Abstract In the area of Hrvalsko Zagorjc, T riassic deposits crop-oul in the form of tccton ic emplacemen ts, formi ng the cores of all the Inajor mountains. 'nlCY also underlie Neogene deposi ts, as proven in nume­ rous boreholes. During the Triass ic reriod , contin uous sedi mentation occurred mainly in $h:lliow marine env ironment s, though transient subsidence occurred in the Anisian and Lad inian epochs. In the Lower Triass ic, the ncmshorc clastic and carbonate sediments were deposited, which were succeeded in the Middle and Upper Triassic by shall ow·wat cr limestoncs. The lallcr for their most par! have undergone later do lo · miti salioo. Ow ing (0 rapid sub si dence during Middl e Ani siun and Ladinian limes . sedime ntation of the fin e-grained c lastics, pelagic limestones lind chc rl.~ occurred together wi th loca l vo lcanic intru­ sions. 1. INTRODUCTION Geologica l research on the Tri ass ic sediments 111 Hrva ts ko Zago rje was initi a ted by Austro· Hunga rian geologists in Ihe middle of Ihe last century. Many trea­ ti ses we re publi shed on these inves tigations, the work by HA UER ( 1868), who distinguished Lower Triass ic sed im ents in the Ivanscica and Strahin scica Mts., and ass igned all limestone and dolomite rocks in Hrvatsko ZagOlj e to " I-Iall stattc r und Esino Schichten", bei ng the mOSI imponant. The resu lt s of previous inves tiga ti ons were col lated by GORJANOVIC>KRAMBERGER (1902, 1904a, b), inc luding his own works, and pub­ lished in the fOl1n of geological maps, and explanations or the shee ts Vi nica, Rogatec- Kozje and Zlatar-Krap­ ina. After GOlj anovic's works had been published, the regiona l geological investigations in the area of Hrvat­ sko Zagorje were terminated. Some fifty years later, a new cycle of invest iga tion of the Triassic deposits in Hrvatsko Zagorje was com­ menccd by the academic ian M. Herak. Coworking wilh tn stitute of Geology, Sachsova 2. P.O. Box 268, HR· 10000 Zagreb, Croatia. M. Malez he proved for the firs t time, using the disco­ ve ry of the alga Telll/oporella !Jercu/ea (STO PPANl). that Ladinian deposits deve loped in the carbonate facies also exist in this area (HERAK & MALEZ, 1956). Sev­ e ral years la ter he describcd the Lad inian sponges fou nd on the north side of Ivanscica MI. , aner which he publ i­ shed a review of Tri assic sed imen ts o f Yugos lav ia , emphasizing the impac t of tec tonic s tages on the sedi­ mentary conditions (HERAK, 1960, 196 1). T hi rty years later, di viding the tectonic zones of the Dinar ides and de finin g the ir northe rn limits, he inc luded Hrvatsko Zago rje in "S upradinari eum '" (H ERAK, 1986. 1991; HERAK et al. . 1990). Other geological inves ti gati ons o j" Ihc Triass ic sedi ­ ments of Hrvatsko Zago~je were re lated mainly either to work on the sheets of the Bas ic Gcological Maps: Zag­ reb (S IKI C c t a I. , 1979), Varazd in (S IMUN IC et a I. , 1981), Rogatce (AN1C IC & JUR1SA. 1985) ancl l vanic G rad (BASCH. 1983), or to some minor works with re f­ erence to specific geological problems. Thesc works are referred to in the explana tio ns of the Basic Geolog ical Map, and they will be rev iewed later in the tCXI in order to avoid repet ition. It should be emphasized tha t thi s paper rcp resents the first attempt to display the Triassic System of Hrva t­ sko Zagorje integrally. Comprehensive atten tion is paid to lesser known topics such as the relationships between specific lithostratigraphic units, as well as to geological boundaries, sedimentary conditi ons, reexa mination of stratigraphic determination of c lasti cs with vo lcanites, and corre lat ion of contcmporaneous depos it s in the wider regi on. 2. LITHOSTRATIGRAPHI C CHARACTERISTICS Triassic sediments foml the central parts of the maj­ ority of the Zagorje mountains, where they appear in the form of tectonic emplacement s, mainly in the corcs of the Neogene anticlines (Fig. 1). The exception is Med - This paper was presented at the scientific meeting dedicated to the 80th anniversary of the life of Professor Milan Herak, held on March 5th, 1997 in Zagreb 244 N ...... d 0 , EB O.Konjicina : .. ' o .' .' . .... .. ' ........ ZOQreb Ueologia Croatica 5uri Fig. 1 Distribution of Triassic dc­ posits in the area of Hrvatsko Zagorje. Legend: I) Study ar­ ea; 2) Mostly Triassic dolomi­ tes and limestones; 3) Mostly Triassic tuffs; 4) Neogene and Quaternary sedimems; 5) Deep boreholes with pierced Trias­ sic deposits; 6) Mountains of Hrvatsko Zagorje: I - Ravna gora, 2 - Hum , 3 - Brda, 4 - Sv. Duh, 5 - Zeljeznica, 6 - Varazdinske loplice, 7 . Kost­ run, 8 - Kuna gora, 9 - Slmhin­ sCica, 10 - Ivanscica, 11 - Cc­ sarsko brdo, 12 - Strugaca, 13 ,:1 EEls Vucak, 14 - Ljubelj, 15 - Hum-Sagudovec, 16 - Zakic­ nica. vednica Mt., where Triassic rocks occur in a much mo­ re complicated form, most ly as the remnants of over­ thrusts (SIKIC et aI., 1979). Furthermore, it is proven by numerous boreholes that in the greater part of Hrvat­ sko Zagorje Triassic sediments underlie Neogene car­ bonates and clastics. The mountains of Hrvatsko Zagorjc display a very intricate tectonic configuration, which is the reason why hardly a single tectonically quiescent area can be found to establish the integral geologic column. The given geologic column (Fig. 2) is composed of partially drawn c ross sections and data assessed by geological mapping. On the basis of lithological and palaentological charac teristics, the Triassic of Hrvatsko Zagorje is divi­ ded into three major parts. Clastic and carbonate depo­ sits relate to the Lower Triassic, the carbonate and vol­ cano-clastic sediments belong to the Middle Triassic, whereas only the carbonate rocks pertain to the Upper Triassic. Occasionally, one can arrive at more detailed division of the Triassic system into eight lithostrati- graphic units, but, due to the major dislocation of sedi ­ ments and scarcity of fossil findings, it is hardly feasi ­ ble over the entire area of Hrvatsko Zagorje. 2.1. THE LOWER TRIASSIC (SCYTHIAN) The Lower Triassic sediments occur on almost all mountains of Hrvatsko Zagorje, except fo r the Kalnik and Strugaca Mts. Their greatest exposure is on the Ravna Gora Mt., while elsewhere they appear in the form of narrow zones, erosional remnants, or enclosed tectonic blocks. During hydrothermal research, their extension was also established beneath the surface, as they are partially drilled in Krapinske Toplice at a depth of 6S0-720 m, and in Stubicke Toplice at depths of 260- 390 m. Due to later tectonic movements, the exposure of Lower Triassic clastics is irregular and unpred ictable. Sometimes they are accumulated in a single place resulting in deposits several hundred metres thick, while sometimes they can be found only in traces. Tnte- Simunic & Simunic· Tri·\ssic Deposits of J Irvatsko Zagorje 24, u VI I / / VI ... Triaslna hantkenl ell/plica 1= . /1/ / / Permodtscus pragsoldes ~ I I I Megalodus sp. a: I I I "' Il. I / Il. ::> -/--if f-t fU u f-t I-J I- H H z - Ladlnella porata -j -/1-... - - " TeulloporeUa herculea f !1t+tt1-t Z Dlplopora annulala debUts - ~ I v •••.•• Uvanella lrreg ularL'i 0 '" v (f) ... +1 -f'it + i- T- o ...J II- ~ Hr+~ ~ / Dlplotremmtna aslrojlmbrlala (f) ~ I--f; f --4 t;i 4- f -I- Macroporella alpina ~ Anlsoporella anlslca Rtf H.ff It Z ~ Meandrosplra dlnarlca ... « .... ....... . 0 A A - , V V - - - -. . . . . . . . . . . '" , A / - VI v v v v v· •• G lomosplra densa - ~ iT -f-.:t +; ~ if + MacroporeUa aiplna f If-t-t Frondlcularla woodwardi z " -I- + -f- Physoporella pauctjorata a: ... / I I - .... 0; Ammodiscus cj (ncerius Fig. 2 Schematic geological ~ Z ~ Meandrosplra pussilla column of the Triassic ... -=--:;: N . . . . . . deposits in Hrvatsko " Natlcella castala >= " ZagOlje. Legend: I) mi - U • . . . . . .. . . Myaclles (Anodonlophora) jw;saensis caceous sandstones and c 0 0 0 0 0 0 VI ~ - - - Pseudomanotls (elaraia) daral siltites; 2) shales; 3) 00-.. litie limestones; 4 lime- ~~~F;:r=;=lr:z::;:z:::l~~ ~~ 1~2~3tiI±:rn 4L::::d 5tz:::::zj6~7~8~9~ stones; 5) bedded dolo­ mites; 6) massive dolo­ mites; 7) andesite-ba­ salts; 8) luffs; 9) cherts. nsive [olding is part icularly evident on the thrust fronts as, for example, near l ab lanovec on the Medvednica Mt., in the vicini ty of the road tunnel on the Strahin­ scica Mt., and in the crests of folds in the Ravna Gora MI. or at Hromec village in the li ne o[ Hum na Sutli - Lepoglava - Belctinec. Up to the present lime various opinions ex ist con­ cerning the nature of the geological boundary between lhe Upper Permian and Lower Triassic. On the sheets of the Basic Geological Map of Varaidin and Rogalec, this boundary is deduced as an uninterrupted sequence, while on the sheets of Zagreb and Ivanic Grad it appears as an eros ional unconformity. Recent investiga­ tions have shown that the undisturbed relat ionship between the Upper Permian and Lower Triassic only ra re ly occurs in Hrvatsko Zagorje, while for the most part Ihe boundary appears as an erosional unconfor­ mity. The scarce outcrops in the wes tern paIl of Ivanscica Mr., and in the area of Strahinscica Me reveal that Lower Triassic clastics overlie the brown-red conglo- merates and coarse-grained sandstones, or the so-called "Groden deposits" (Perm ian). The layers are mutually concordant making their appearance on the terrain as the norm al transition of Permian into Lowcr Triassic clastics. Such a boundary, regardless of the absence of angular discordance can not be considered as an unin­ terrupted sequence because in the Lower Triassic sand­ stones the content of terrigenous material changed as the particle size reduced, and the quantity of muscovite increased. This was caused by signifi can t palaeogeo­ graphic modifications which brought about a change in provenance of the clastic material, a reduction in relief, and longer transporlation distances. In the eastern part o f Ivanscica Mt. and on Cesarsko Brdo Mt., a 1-2 m thi ck layer of grey porous dolomite sporadically appears at the boundary of Palaeozoic bla­ ck shales and sandstones with overlying brow n-red Werfenian (Lower Triassic) sediments. The occurrence of dolomite, sometimes with salt or gypsum, shows that the input of clastic material was sporadically interrupt­ ed, with emergence of a lagoon where the evaporitic 246 sediments had been formed. There is a well-known saIl deposit on the northern slopes of Mcdvednica Mt., in Siani Potok (Salt Creek). The salt appears at the border between metamorphic rocks and Lower Triassic sand­ stones. Ncar Rude, in neighbouring Samoborska gora MI., well-known deposits of gypsum can be found, whereas in the valley of the Bregana brook dolomite occurs instead of gypsum, containing the Upper Permi­ an calcareous algae (HERAK & SKALEC. 1967). In the area of Hrvatsko Zagorje, the Lower Triassic sediments maintain the overall uniform development and can be divided into two parts: the Lower (clastic) and Upper (carbonate) Werfenian. In the Lower Triassic, which can be considered as an equivalent of the Lower Wcrfenian sediments, the recurrent alternations of micaceous sandstones, mica si ltites, shales, marls and, more rarely, oolitic lime­ stones has been observed . Thei r colour is mostly red­ brown, brought about by the content of haematite and limonite. Lon g ago, the iron ore was mined in these rocks, leaving on the s lopes of Medvednica Mt. nume­ rous pits, remnants of smelting furnaces, and even the traces of slag at some places . Sediments without the iron content are yellow, grey or greenish-grey in colour. Red-brown, micaceous sandstones occur as the most extensive lithological member of the Lower Triassic sedi rn ent s. They are determined as sublithie arenites and quartz arcnites. The main components of sublithic areni tes are quartz, feldspars (albite and andesine) and muscovite, while quartz prevails in the quartz arenites. The sandstone cement is variable in composition: some­ times it is quartz and limonite, or haematite and limo­ nite with additional sericite, and sometimes it is calcite with a mixture of limonite. Among the heavy minerals, rounded apatite and zi rcon prevail, while garnet and epidote occur more rarely. The sandstones sometimes appear schis tose as a result of the parallel orientation of foliate minerals, and they sometimes display vestiges of metamorphosis. Ripple-marks and smooth laminations are common. Fine-grained sandstones and silt ites are very mica­ ceous, sometim es co ntaining ferruginous substances. The bl ack and grey varieties of these are enriched in carbon. The sandstones and marls are interbedded with thin layers or lenses of oolitic limestones. The main compo­ nents arc ooids varying in size between 0.04-0.5 mm, with mixtures of non-carbonate and arenitic particles. The ooid core can be a microfossil, a fragment of mac­ rofossil or intraclast. The limestone cement is com­ posed of the fine-grained calcite wh ich envelops the ooids and fills the interstices. The main components of shale are clay, muscovite and sc ri cite, while quartz, chlorite and calcite occur rather rarely. In thc marls, the quantity of microcry­ stalline calc ite, togethcr with previously quoted compo­ nents, amounts to 65% of the rock. Strat igraphic determination of the Lower Triassic clastics is established from the abundant fossil content Geologia Croatica 50(2 found in almost all the ZagOlje mountains. The follow ­ ing species of lamellibranchiata and gastropoda have been determined: Myacites (Anodontophora) jassaensis WISSMAN, Pseudomol1tis (Claraia) ciarai EMM­ RICl-I, and Naticel/a costata (MONSTER) (LIPOLD, 1862; SIKIC et aI., 1979; SIMUNIC et aI. , 1980; ANICIC & JURISA, 1985; BASCH, 1983). The Upper Werfenian consists of dark-grey, tabu ­ late and thin to middle-bedded limestones that outcrop on the Ravna Gora Ml. and in the Ivanseica - Strahin­ seica - Kostrun Mt. range. On other mountains their thickness is small (10-20 m) , wh ich is why they arc generally not displayed on geological maps. On the Ravna Gora Mt., a gradual transition has been observed from the Lower to the Upper Werfenian. In the upper levels of the Lower Werfcnian clast ics intercalations of the dark-grey limestones appear, which afterwards completely prevail. Thi s boundary is rather interesting in a geological sense since it points to the initial deposition of carbonates which, although inter­ mittent through the Anisian and Ladinian, proceeded into the Jurassic. The limestones along thc lower boundary can also contain mixtures of quartz and limonitic-clayey mate­ rial, while fine-grained, microsparite calcite gradually prevails in the upper levels. The following types of limestones are determined: microsparites, fossiliferous microsparites and crinoidal microsparites. Freq uently there appear "schistose" or "breccia-like" textures, whi­ ch arc associated with the disposition of joints, thin vei­ ns and microstyloJites, being caused by post-Triassic tectonic activity. In the arca of Ravna Gora, the fossiliferous micro­ sparites are abundant with foraminifera, crinoid debris and mollusc shells, while intraclasts, peliets and ooids arc sparse. Crinoidal limestones, specifj cally crinoidal microsparites, also frequently occur. These rocks arc formed exclusively from the crinoid sterns and forami­ nifera, while ooids, mollusc shell s and non-carbonate arenitic components arc sparse. Calcareous dolomites and black shales may occur in alternation with the limestones. Dolomites are thin-bed­ ded, finc-grained, and sometimes contain mixtures of clay and limonite. In the upper parts of the Upper Wcr­ fenian deposits, the number and thickness of dolomite layers ever incrcase up to th e absolute prevailance of dolomites at the Anisian boundary. From the Upper Werfenian limestones of the Ivans­ cica and Ravna Gora Mts. the fo llowin g species of microfossils were determined by M. Milanovic (in SIMUNIC ct aI., 1980): Meandrospira pus ilia (HO), Ammodiscus incertlls (d' ORBIGNY) and Glomospira sp. 2.2. THE MIDDLE TRIASSIC During the Middle Triassic shallow-water lim e­ stones were predominantly deposited, their origin relat­ ed to a "carbonate platform". Today these rocks arc for the most part dolomitised and tectonically displaced, Silllllilic & Si11llJllic: Trial>si(.; Del}()\ils or Ilr\':lIsko Z:lgorjc though on the basis of rare fossil finds and their mutual superposition they can be divided into the Anisian and Ladinian series. In the middle of the Anisian and Ladinian epochs the fine~graincd clas tics, cherts and tuffs were deposit ­ ed, with sporad ic occu rrences of volcanic intrus ions. The origin of the c las tics and volcanites is related to the abrupt and relat ively shorl~lived periods of subsidence with s ubsequ ent recc urrcnee or sedimentation in the s hall ow~water marine basins. The Anis ian dolomites and limestones form mosl of the l vansc ica - Strahinseica - Ravnu Gora ~ Kostrun Mts. range, but they ca n also be found on the other mount ai ns (except MI. Kalnik). Almos t alt thcnnal wa­ ter boreholes have reached the triassic dolomites and dolomite breccias (Fig. I ). Up to the present, a continu~ ous sequence of sedimentation from the Upper Scythi an to the Anisian has only been discovered on Ravna Gora MI. , while on the othe r mountains the said boundary is tec toni call y dislocated or concealed. A similar geolog i ~ cal cross section ncar Rimske Toplice in Eastern Slove~ nia (RAMOYS & ANICIC, 1995) proves this to be, at any rate, nOI an iso lated phenomenon. Dark-grey dolomites are the Illost frequent and most identifiable mcmber of the lower part of thc Anisian stage in Ilrvatsko Zago rje. Fragments of crinoids can o rt en be found in these rocks , suggesting that these dolomites originated by the process of dolomitisation of the c rinoidal limcstones. This rules out any sign ificant palaeogeographic va riations having occurred at the Uppe r Wcrfcnian ~ Lower Anisian boundary. Not on ly did sedi mentation of carbonates never cease bUI , CO J1 ~ versc ly, layers of conside rable thickness have been pro­ duced. On the bas is of chemi cal analyses it has been de te rmined that the dark dolomite colo uring der ives from an increased co nccntration of organic matter. Sometimes, these rocks include the intercalations of che rt of 1111ll -CIll dimensions which arc supposed to be di agenetic in origin (S IM UNIC & SIM UNIC, 1980). It can be observed at outcrop that dolomites abrupt ­ ly change from black to grcy, which is most probably a conseq uence of reg ressive movement s in the sedimen~ tary bas in which caused al gal limestones to be dcpos it ~ cd instead of c rinoida l ones. SedimenLa ry~peLrographie anal yses have de te rmined that these do lomites be long to the middle-grained calcarcous , stromatolite and algal Iypes. They have arisen by dolomiti zation of algal lime­ stones, a llowing 1'01' all possible trans itions in appear­ ance. Major bodies of limestones, not affected by dolomi ­ tization , c rop oul on the Ravna Gora and eastern part of Ivanse ica Mts., but the se can also be seen in minor exposu res in other Zago rjc mountains . They arc very important ror the clari fi cation of st ratigraphic relation­ sh ips, having been the only source of determinable fos~ sils. The fo llowin g spec ies of algae and foraminife ra have been determined by M. Milanovic (i n SIMUNIC c t aI., 1980) : Meal/drospira dil/arica KOCl-lANSKY­ DEVIDE & PANTI C, G/olllospira del/sa (PANTIC), 247 Macroporefla a/pina PIA, Pacel/refla hexasler (P IA ), Physoporel/a pGllei/orata (GUMB EL). On thc northern s lopes of the Ivanscica and Strahin ~ seica Mts. great bodies of grey and dark~grey dolomi te breccia are exposed. These originated from crushing of dolomites and their subseq uent recementing. They arc intersected by numerous joints fill ed with recrystalli zed dolomite and calcite. Large slickensides, trac ing major fault s, fault zones, o r thrust pl anes, can be found in these rocks. Due to their great porosity, thesc breccias have proven to be ve ry good fresh~wa t e r and the rmal water aquifers (Semnicke Topliee, Yratno) In Ihe Middle Anisian an abrupt change in sed imen­ tation occurred with deposition of deep-water c last ics and vol canites instead of shallow-wate r carbonates. These rocks are present in almost all the mountains or Hrvatsko Zagorje, having been drilled ncar Konjseina at depths of 3,850-4,250 m (DRAGI CEYIC ct aI., 1995), and ncar Krapinske toplice at 550 m. The st rati ­ graphic position of these rocks was variollsly int erpret ~ ed in the works of previous authors and subsequent explanations of the Basic Geologica l Maps, while the ir supposed age extended roughly from the Palaeozoic to the Lower Miocene. Among the scdim entary rocks, the most common arc the black and rcd shales, black and grey siltites, and rcd-brown radiolarian cherts. In addition , the grey, fin e­ grai ned limestones with radiolaria and filam e nt s, as well as luffilic limcs tones wi th radiola ri a, turfs and andes ite-basalts sporadically occur (S IMUNIC & S IM­ UNIC, 1980/81). Great expanses 01" tuffs and bas ic eHusives arc present on the northern slopes of Jvanse iea MI. , but they can al so be found on St rahinscica, Kuna Gora, and Kostrun Mts. They arc intercalated wit h dolomites, and vary in thickncss from 20-200 m. GORJANOYIC-KRAMBERG ER (1904a. b) eon­ sidcred the clastics with volcanites in the area of l vans~ eiea, StrahinsCiea and Kostrun Mts. as being or Palaeo­ zoic agc, while similar rocks on Kuna Gora Ml. were class ified as an Anisian "eoquina" on thc bas is of the ammonit e fossil s. SALOPEK ( 1918) studied the co l­ lected cephalopod fauna of Kuna Gora Mt. and came to the conc lusion that it indicated an Upper Anisian age. TUCAN (1922) supposed the andes ites and basalts on Ivanseica to be olde r than "Carbonife rous sla tcs" and "Werfen ian schists" on the basis of the latter bein g without ev idence of contact metamorphi sm. Sed imentation of the Middle Triassic c lastics wi th volcanites occurred suddenly, which is not easy to ex p­ lain in the face of familiar sedimentary processes. Pre­ viously they werc supposed to be deposited in a eugeo­ syncline , but recently the majority of geologist s are of the opinion that Ihay have arisen during the birth of a "rift va ll ey". Thus, indeed , the sw ift subsidence and sediment ation of the deep~ sea deposit s can be exp la ~ ined, but it is not easy to elucidate the rapid regress ion and recurrent sedimentation or shal low-water carbon­ ates. Were the "rift val ley" closed by compression, the rocks wit hin would have been compressed 100 , and .,. could certainly not be preserved. The low~ang l e thrust can a lso be infe rred w hi ch , owing to its immen sity, resembles an overlying rock mass, though it is not easy to assume it wi ll always affect the same stratigraphic level. In other words, an arrangement of strata such as this, along with pe riodic thickening or thinning of the clastics and volcanitcs, can be traced from Ivanscica to Kostrun Mts. (about 50 km). Perhaps the most accept­ able is Boillot 's concept (BOILLOT, 1983 ) whereby s im ilar phe nollle na are expla ined by subduc tion on a carbonate platform. After the subduction processes had been terminated, the entire area was uplifted with sub­ sequent recurrence of the sedimentation of the shallow­ water carbonates. Light-grey, fi nc-grained , intensely sili ci fi ed tuffs, ex tending fro l11 Rogatec throu gh Lepoglava to Vara­ zdinskc Toplice. arc also included in the Midd le Trias­ sic (Fig. 1). They are determined as vitric, crystallo-vit­ ri c, c rystallic and lithi c tuffs and tuffites. T hese arc sometimes "pierced" by the altered spili ti zed diabase and sporadica lly interbedded with quartz schists. They o ften overlie Lower Miocene clastics which is why they were ass igned to the Lower Miocene by GORJA­ NO VIC- KRAMBERG ER ( 1904a), while KISPATIC ( 1909) never conside red these rocks as tuffs, but as fine-gra ined quartz rocks instead. Even on the separate shee ts o f the Bas ic Geo logical Map of Varazdin and Rogatcc these arc varioLisly interpreted. More recent research has shown the presence of two types of tuffs in thi s series. Earl ie r tuffs usually include in their basal part the Lower Triass ic deposits overlain sporadically by Ani sian dolomites and limestones. In addition, they are proven to be occasionally thrusted over Lower Mi oce ne clastics, which made earl ier auth ors ass ign them to the Lower Mioce ne. Later tuffs arc of the andesite-dacite typc, bcing weakly li th ifi cd and placed a t the Egerian-Eggenburg ian bou ndary (S IMUNIC & PAMIC, 1993). Therefore, there are two groups of vol­ canic rocks in thc " Gorjanovic andcsitc Iinc" which points to the instabili ty o f the area and a reccurrence of the volcanic activ ity. In the upper part of the Anisian sed imen tation of algal limesto nes con tinued wh ich werc late r mostly dolom itised. However, in the eastern part of Ivanscica MI. , on ly a few metres above the clastics, blue-gree n algae have been fOLind . The following speci es have been dctermined from the Belski Do l area by Mi lanovic (in SIMUNIC et a I. , 1980): Diplotremino ostrofimbriato KRISTAN-TOLL­ MANN, Macroporella a/pina PIA, Anisoporel/a anisi­ co (ZANIN-BURI) , Mendrospira dinorico KOCHAN­ SKY-DEVIDE & PANTIC. According to the geological map and partially estab­ lished geologic columns one can suppose the total thi ckness of the Ani sian deposits to be 400-500 m. Herein a zone of tu ffs running from Hum l1 a Sutli - Lepoglava - Beletinec - to Varazdinske Toplice must be sorted out, the thickness of which occasionally exceeds 400 m. Sedimentation of shall ow-water limestones contin­ ued through the Ladinian and these were late r largely dolomitiscd and recrystalli zed. Thi s extensive mass of grey, fine- to medium-grained dolomites infrequently contains re lic blocks of li mestones . The limestones are fine-grained . often recrystallized, and sporadically sili ­ cified. T heir occurrence is important for stra ti graphic de termination because they are the only source of the de terminable fo ssil remnant s . For the time being the Ladinian sediments have been proven only in the area of Ivanscica Mt. The first Ladinian fossils found there had been decribed by HERAK & MALEZ (J 95 6) and HERAK (1960), but they were subsequently discovered elsewhere. The following species have been detennined by Milanovic (in SIMUNIC e t a I. , 1980) : Uvane llo irregularis OTT, Dictyocoelia mOllon (MONSTER), Lodillello porow OTT, Teutloporello haw lea (STOP­ PANI), Diploporo anllulata debilis PIA and other. On the southwestern slopes of Ivanscica MI. , a nar­ row and intermittent zone of shales, siltites and weath­ ered pyroclastics has been observed wi thin the shallow­ water carbonates. The pyroc las tics are determined as vitric and crystallo-lithic tuffs, tes tifying by their pres­ ence volcan ic activity wi th in the same basin. At the moment, the true thickness of Ladinian depo­ sits remains unknown due to continuous sedimentation into the Upper Triassic, while both their great ext ent and intensive tec tonics did not a llow direct fi e ld mea­ surements. According to the geo log ical map and cross sect ions, the th ickness of Ladinian deposits is assumed not to exceed 300 m. 2.3. THE UPPER TRIASSIC The Upper Triassic deposits are most ex tens ive ly exposed in the ce ntral and eastern parts of Ivan sc ica MI. , but more rare ly o n the northern slopes of Kalnik Mt. and in the western part of Medvednica Mt. The Upper Triassic dolomites and limestones encoun tered elsewhere in the Zagorje mountains on ly occur in the form of isolated blocks. Most of the Upper Triass ic rocks on the southwestern s lopes of Medvedni ca and southern slopes of Ivan sc ica Mt s. rcpresent the rem­ nants of thrust faults (SIKIC et aI. , 1979; SIMUNIC et aI. , 198 1). Due to occurrence of largely dislocated rocks, cont i­ nuity of sed imentation from the Midd le to the Uppe r Triassic has never been proven in the field , whereas it can be assumed on the basis of the unaltered litholog i­ cal composition of the sediments. In the Upper Triassic, the stromatolitic, intraclastic, fine- to medi um-grai ned dolomites dom inate over the algal, peloidal and. more rarely. oncoidal limestones. Dolomite and calc-dolom ite breccias can be frequently found , being occasionally interbedded with dolomites. Moreover, in the area of the Kal nik and Medvednica MIS. cherts and radiolarian shales have been found , the Karnian and Karnian-Norian age of which have been determined on the basis o f radiolaria (HALAMIC & GORICAN, 1995). Simunic & Simunic: rriassic Deposits of Hrvatsko Zagorjc Tn the area of Ihe lvanscica and Kalnik MIS., find­ ings of megalodonts have been known since the times of Austro-Hungarian geologists (FOETTERLE, 1861/ 62), and were lat er found on a few different sites. Occurrences of Upper Triassic fossils are abundant only on the southern slopes of Strahinscica Mt. The follow­ ing spec ies have been determined by Milanovic (in SIMUNIC et aI. , 1980): Triasina hanlkeni elliplica MAJZON, Permodiscl/s pragosides (OBERI-IAUSER), Glol1lospira sp., TrocholillG sp. and other. The most detailed geological cross section through Upper Triassic deposits in Northwestern Croatia was discovered in a quarry ncar Podsused, in the northwest­ ern part of Medvednica Ml., but later, unfortunately, completely destroyed due to mining. For 200 metres across the site, a rh ythmic sequence from cryptocrys­ talline through microcrystalline dolomite and dolomi­ crite, to LLH stromatolite and fenestral stromatolite, as well as dolomicrite was determined. Investigation of thi s geological cross seclion allowed the sparse fossil assemblage to be documented, but only the forami­ nifera TriasillG haf1fkeni was determined (FUCEK ct aI., 1995). In the area of Hrvatsko Zagorje, detai led division of the Upper Triassic stage could never have been per­ fo rmed because of dolomitisation, recrystallization, scant fossil findings, and extensive tectonic disruptions. Furthermore, true thickness has not been determined, although, according to fie ld observations and represen­ tat ion on the geo logical map, it can be inferred to be approximately 250-400 m. 3, CONCLUSION The Triassic deposits form the central parts of most of the Zagorje Mountains, with the exception of Mec!­ vednica MI., where these rocks are thrusted over younger deposits. Besides, the Triassic rocks also un­ derlie Neogene clastics, which is proven by numerous boreholes. During Triassic sedimentation was continuous, mos­ tly within shallow marine basins , whereas the intermit­ tent subsidence occured during the Anisian and Ladi­ nian. In the lower part of the Scythian, fine-grained clastics were deposited, whereas in the Upper Scythian sed imentation of carbonate rocks began which, regard­ less of temporary cessations, continued into the Liassic. Deposition of the carbonate rocks was temporarily interrupted in the middle An isian and in the Ladinian, when deep-sea clastics, cherts and pyroclastics were deposited along with sporadic intrusions of volcanites. 1n Hrvatsko Zagorje the existence of all the Triassic series has been proven due to the fossil occurrences, but because of intensive tectonism, no single area could be found to es tabli sh the complete geological column. Nevertheless, on the basis of the aforementioned char­ acterist ics, the Triassic sediments of Hrvatsko Zagorje can be divided into eight lithostratigraphic units that 249 will be di splayed on the new Geological Map of the Republic of Croatia, scale 1 :50.000, which is currently being compiled. On thc Ivanscica MI. the Lower, Middle and Upper Triassic has been proven, though the conformity is only incompletely established. It is supposed that all the series of the Triassic exist on the Medvednica MI., but only their lower and upper parts are proven palaeontologically. The Lower and Upper Triassic deposits are proven on Ravna Gora, Strah inscica, Kuna Gora, Kostrun and Cesarsko Brdo Mts., as well as in the Hum na Sutl i - Lepoglava - Beletinec - Varazdinskc Toplice range of hills. In the area of MI. Kalnik, the Middle and Uppcr Tri­ assic was determined, whereas on Strugaca Mt. no fos­ sil remains were found aided the st ratigraphic determi­ nation of the grey dolomites which was the reason of their assignation to the Middle Triassic. 4. REFERENCES ANICIC, B. & JURISA, M. (1985): Osnovna geoloska karta SFRJ, I: 100.000. Tumac za list Rogatcc L33- 68 (Geology of Rogatec sheet). - Geoloski zavod Ljubljana & Geoloski zavod Zagrcb ( 1983), Savezni geol. zavod Beograd, 76 p. BASCH, O. (1983): Osnovna geoloska karta SFRJ, 1:100.000. 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(1980): Petrografski sastav i geneza trijaskih naslaga Ivanscice, Kalnika i Ravne gore (Hrvatsko zagorje) (Petrographic com­ position and genesis of Triassic deposits or Ivans­ cica, Kalnik and the Ravna gora Mountain).- Geol. vjesnik, 32 (1979), 243~253. SIMUNIC, AI. & SIMUNIC, An. (1980/81): Dliboko~ vodni sedimenti srednjeg trijasa Kostruna (zapadni dio Hrvatskog zagorja) (Deep waleI' sediments or the middle Triassic of Kostrun Montain (Western parts of Hrvatsko zagOlje».- Vcsnik zav. geoL geo­ Iiz. istrai., (A), 38 ~ 39, 205~221, Beograd. SIMUNIC, An. & PAMIC J. (1993): Geology and pet~ rology of Egerian-Eggenburgian andcsites from (he easternmost parts of the Periadriatic zone in Hrvatsko Zagorjc (Croatia).- Acta Geol. Hungarica, 36/3, 315~330, Budapest. SIMUNIC, An., PIKIJA, M., HECIMOYIC, I. & SIM~ UNIC, AI. (1981): Osnovna geoloska karta SFRJ, 1:100.000. Tumac za list Yaraidin, L33~69 (Geolo~ gy of Varazdin sheet).-Institut za geol. istraz. Zag­ reb (1981), Savezni geol. zavod, Beograd, 75 p. SIMUNIC, An., SIMUNIC, AI. & MILANOVIC, M. (1980): Geoloska grada Tvanscice i Ravne gore (Geology of ML Ivanscica and Mt. Ravna gora (Northwestern Croatia)). ~ Geol. vjesnik, 31 (1979), 157~174. TUCAN, F. (1922) : Starije eruptivno kamenje u sjeve~ rozapadnom dijelu Hrvatske.- Glasnik Hrv. PrJI'. drus., 34, 169~184, Zagreb. ManusGript received April 14, 1997. Revised manuscript accepted November 10, 1997.