Composition and Importance of Upper Triassic (Upper Ladinian – Lower

Composition and Importance of Upper Triassic (Upper Ladinian – Lower

107 Original scientific paper Received: October 7, 2014 Accepted: October 15, 2014 Composition and importance of Upper Triassic (Upper Ladinian – Lower Carnian) breccia in stratigraphy of External Dinarides Sestava in pomen zgornje triasnih (zgornje ladinijskih – spodnje karnijskih) breč v stratigrafiji Zunanjih Dinaridov Luka Gale1, 2, *, Dragomir Skaberne2 1Faculty of Natural Sciences and Engineering, Department of Geology, Privoz 11, 1000 Ljubljana, Slovenia 2Geological Survey of Slovenia, Dimičeva ul. 14, 1000 Ljubljana, Slovenia *Corresponding author. E-mail: [email protected], [email protected] Abstract Izvleček A sequence of boulder breccia, separated by several emersion horizons is recognized as part of the Upper - Na območju Medvedice (osrednja Slovenija) smo v Ladinian – Lower Carnian Cassian Dolomite and Lime- zgornje ladinijski – spodnje karnijski formaciji kasi stone Formation in the area of Medvedica (central Slo- - janskega dolomita in apnenca prepoznali zaporedje venia). The composition of clasts, determined from thin blokovnih breč, ločenih z več emerzijskimi površina sections in the context of Late Ladinian – Early Carnian mi. Sestava klastov, določena na podlagi zbruskov ob platform models suggests their origin in the transition upoštevanju modelov zgornje ladinijskih – spodnje between the inner platform/lagoon and the back-reef - karnijskih karbonatnih platform kaže na sedimentacijo area, alternatively in the internally differentiated la- - apnenca na prehodu iz notranje platforme/lagune v za goon with swells. The emergence of the platform is sug- grebensko območje ali na notranje diferencirano lagun gested to correspond to the upper sequence boundary sko okolje z lokalnim reliefom. Emerzija platforme bi se of the Car1 depositional sequence from the Southern - lahko skladala z zgornjo sekvenčno meje depozicijske Alps. The platform growth subsequently continued un- sekvence Car1 Južnih Alp. Rast platforme se je nada til the uppermost Julian, when the second emergence ljevala do konca jula, ko je bila dokončno prekinjena (upper sequence boundary of the Car2 depositional z drugo emerzijo, ki ustreza zgornji meji depozicijske sequence) finally terminated the growth of the Cassian sekvence Car2 v Južnih Alpah. platform. Ključne besede: - ne Alpe, »cordevolski apnenec in dolomit«, Cassianska Dinarska karbonatna platforma, Juž Key words: Dinaric Carbonate Platform, Southern Alps, »Cordevolian limestone and dolomite«, Cassian platforma, sekvenčna stratigrafija platform, sequence stratigraphy 108 Introduction Geological setting A substantial amount of the carbonate sequence Medvedica is a largely forested low hilly area of the External Dinarides and Southern Alps belongs to carbonate platforms established basin (Fig. 1). According to Placer[27, 28], this area after the cessation of Ladinian volcanism[1, 2]. structurallysituated on thebelongs SW brink to External of the GrosupljeDinarides, karst dur- Until the Early Julian, up to 600 m of limestone ing the Triassic and Early Jurassic situated on deposited, later mostly transformed to do- the southern passive continental margin of the lomite[2]. In terms of lithostratigraphy, these Neotethys (Meliata) Ocean[29, 30]. The evolution carbonates are known in the Slovenian litera- of this area was strongly affected by the Middle ture as the »Cordevolian limestone and dolo- Triassic extension, and, after cessation of tec- mite«[3–5] or the Diplopora Limestone[6, 7]. The tonic activity, by a gradual recovery of carbon- term Cassian Dolomite and Limestone Forma- ate production and levelling of topography[31, 32]. tion (CDLF) is used herein (see also[8–12]). The The following description of lithological units debate about the correct interpretation of age is based on author’s personal observations. of the CDLF mostly revolved around the correct determination of dasycladacean algae[10, 13]. Buser[20, 22] and Dozet[23]. The studied area is During geological mapping of a smaller area Reader may further refer to descriptions by sequence of breccia with up to 2 m large boul- andsituated the Ortnekbetween fault two to major the west NW-SE (Fig. directed 2). Nu- derssouth-west was noted of Grosupljeinside the CDLF(central along Slovenia), the newly a merousfaults, namely minor faultsthe Dobrepolje create a complex fault to picture the east of cut forest road. The scope of this paper is to de- fault-bound blocks. This, however, is in contrast scribe and interpret the origin of breccia. with interpretation made by Buser[19], showing a generally undisturbed Lower to Upper Trias- sic succession. Previous research of the studied The oldest succession belongs to the Lower area Triassic Werfen Formation (Fig. 3). The lower part of the formation is missing, while the rest The first geological mapping of this area was of it consists of light brown or reddish cal- carried out by M. V. Lipold and G. Stache[14]. cisiltite and dark grey silty marlstone, and me- Their work, however, remained in the form of dium bedded oolite. Small flakes of mica are a manuscript map[15]. Stache[16] and Vetters[17, 18] later produced less detailed maps. In the scope LJUBLJANA of geological mapping of Yugoslavia, geological mapping was carried out by Buser and co-work- SLOVENIA N ers[19, 20] of Medvedica, was re-ambulated in the 1980s. The area around Županova jama, east[21]; however, the supplemented geological map The results were published by Gospodarič is too general for the purposes of this study. Škofljica Buser[22] later gave a short description of the - Ig Grosuplje Pijava ofgeological Ladinian structure volcanoclastics between in Št.Medvedica. Jurij and TheVe Gorica stratigraphylike Lipljene. ofEspecially the wider notable area south is his andmention east Št.Jurij [3–5, 23–26] Dozet . 5km of Grosuplje has recently been investigated by Vel.Lipljene Figure 1: Position of the studied area. The rectangle represents position of Figure 2. RMZ – M&G | 2014 | Vol. 61 | pp. 107–123 Gale, L., Skaberne, D. 109 N laminated dolomite and micriticlaminated limestone dolomite and Št.Jurij 500m N micritic limestone Udje DobrepoljeŠt.Jurij fault Jurassic 500m497m Udje Dobrepolje fault Jurassic faulted 497m faulted stromatolitic dolomite (Mainstromatolitic Dolomite) dolomite Vrbičje (Main Dolomite) Vrbičje bauxite, red clastics, dolomite (Mohorjebauxite, red fm) clastics, dolomite bxbx bx bx bxbx bx bx bxbx bx bx Carnian Nor.-Rhae. breccia(Mohorje fm) bxbx bx bx bxbx bx bx bxbx bx bx Carnian Nor.-Rhae. brecciamedium to thick bedded limestonemedium to with thick green bedded algae M e d v e d i c a (CDLF)limestone with green algae M e d v e d i c a MMoravčeoravče e (CDLF) e d conglomerate/breccia, tuffite, MMoravčeoravče d v tuffaceousconglomerate/breccia, sandstone, micritictuffite, Ortnek fault e v bx bx bx limestonetuffaceous with sandstone, chert micritic ? Ortnek fault e d limestone with chert i bx bx ? bx d c VVelikeelike LLipljeneipljene i a VVelikeelike LLipljeneipljene medium-thick bedded or c massivemedium-thick dolomite bedded or a Anisian Ladinian massive dolomite Predole beds (Lower Jurassic) Anisian Ladinian Predole beds (Lower Jurassic) Main Dolomite (Upper Tuvalian?-Norian-Rhaetian) Main Dolomite (Upper Tuvalian?-Norian-Rhaetian) calcisiltite, marlstone, oolite Mohorje Formation (Upper Julian-Tuvalian) (Werfencalcisiltite, fm) marlstone, oolite Mohorje Formation (Upper Julian-Tuvalian) (Werfen fm) Cassian Limestone (Upper Ladinian-Lower Julian) Cassian Limestone (Upper Ladinian-Lower Julian) Lower Triassic Cassian Dolomite (Upper Ladinian-Lower Julian) Cassian Dolomite (Upper Ladinian-Lower Julian) Lower Triassic Volcanoclastics, limestone with chert (Ladinian) calcisiltite massive dolomite Volcanoclastics, limestone with chert (Ladinian) calcisiltite massive dolomite Anisian Dolomite marlstone massive limestone Anisian Dolomite marlstone massive limestone Werfen Formation (Lower Triassic) oolitic limestone boulder breccia Werfen Formation (Lower Triassic) oolitic limestone boulder breccia Fault (visible; covered; assumed) bedded dolomite bx bx bauxite Fault (visible; covered; assumed) bedded dolomite bx bx bauxite Normal geologic boundary tuff sandstone Normal geologic boundary tuff sandstone cherty limestone marly dolomite cherty limestone marly dolomite Figure 2: Geologic map of the studied area. The section with micritic limestone breccia is marked by bar. micritic limestone Figure 3: Schematic lithostratigraphic column for the characteristic. Various bivalves, gastropod Nat- Medvedica area (not in the scale). Note that the stratigraphic Munster, ammonite (? sp.) position of the breccia inside the Cassian Dolomite and iria costata Tirolites Limestone Formation (CDLF) is only tentative. and ichnogenus Rhizocorallium were found. Oolitic limestone may contain numerous small gastropods. tuffite, tuffaceous sandstone, conglomerates, In the upper part of the Werfen Formation, breccias, and black micritic limestone with thin to medium bedded dolomite of dusty ap- black chert and claystone partings follow. A si- pearance predominates, gradually passing into licified ammonite has been found in Medvedica medium-thick bedded or seemingly massive coarse dolomite. No attempt has been made to the genus Kellnerites (L. Krystyn, pers. com. to recover microfossils from the latter, and An- by B. Vičič in 2009, and questionably attributed- isian age is assumed solely on the basis of su- tabase[33], this genus ranges from Late Anisian perposition. byto EarlyB. Vičič). Ladinian. According Thus, to the the dolomite

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