ACTA CARSOLOGICA 29/1 14 185-199 LJUBLJANA 2000 COBISS: 1.08 HO»EVJE OOLITIC GROUP, CENTRAL SLOVENIA HO»EVSKA OOLITNA SKUPINA, OSREDNJA SLOVENIJA STEVO DOZET1 1 Geolo{ki zavod Slovenije, Dimi~eva 14, 1001 LJUBLJANA, SLOVENIJA, e-mail: [email protected] Prejeto / received: 6. 3. 2000 185 Acta carsologica, 29/1 (2000) Izvle~ek UDK: 551.762.2/.3(497.4) Stevo Dozet: HoËevska oolitna skupina, osrednja Slovenija ^lanek opisuje in poimenuje 450 do 500 m debel, prete‘no oolitni kompleks v Suhi krajini, le‘e~ konkordantno na zgornjeliasnih plo{~astih in tanko plastnatih apnencih in diskordantno pod zgornjemalmskimi Korinjskimi bre~ami. Manj{a diskordanca lo~i oolitni kompleks na dva dela: spodnji ~rni oolitni del doggerske starosti in zgornji sivkasti oolitni del spodnjemalmske starosti. Za omenjene oolitske kamnine predlaga avtor ime “Ho~evska skupina”, ki jo sestavljata spodaj le‘e~a “Formacija Laze” in “[entrumarska formacija” nad njo. Mikropaleontolo{ke raziskave so pokazale, da vrhnje doggerske plasti manjkajo in da najverjetneje sploh niso bile odlo‘ene. Klju~ne besede: stratigrafija, geografija, sedimentologija, okolje nastanka, tektonika, apnenec, dogger in spodnji malm, Zunanji Dinaridi, Suha krajina. Abstract UDC: 551.762.2/.3(497.4) Stevo Dozet: Ho~evje oolitic group, Central Slovenia A 450 to 500 metre thick and prevalently oolitic complex in the Suha Krajina area, lying conformably upon the Upper Liassic platy and thin-bedded limestones and discordantly under the Upper Malm Korinj breccias, has been denominated and described in this paper. A minor discordance separates the oolitic complex into two parts: the lower black oolitic part of Dogger age and the upper greyish oolitic part of Lower Malm age. The proposed name of the above-mentioned oolitic rocks is the “Ho~evje group” consisting of the underlying Laze formation and overlying [entrumar formation. The micropaleontological study showed that at least the topmost part of Dogger was not deposited. Key words: stratigraphy, geography, sedimentology, environment, tectonics, limestone, Dogger and Lower Malm, Outer Dinarides, Suha Krajina. 186 Stevo Dozet: Ho~evje oolitic group, Central Slovenia INTRODUCTION The aim of the present study is to lithologically subdivide the Jurassic stratigraphic sequence in the Suha Krajina area. The study is based on data of numerous previous works and our researches in the years 1981, 1985, 1986, 1987 and 1988. In the years from 1959 to 1965 Buser (1965) geologically mapped the territory of south Slovenia from the Italian-Slovenian border in the west, across Trnovski gozd, Hru{ica, Nanos, Logatec and Bloke plateau, Javorniki, Krim-Mokrec hills and Lower Carniola to Suha Krajina in the east. Melik (1959) gave in the Posavje Slovenia a detailed geographic description of Dolenjska, which includes Suha Krajina as well. [ribar described the Jurassic sediments between Zagradec and Randol in the Suha Krajina area. On the basis of microfossils and the stratigraphic position she divided the Jurassic succession into the Lower and Middle Liassic, Upper Liassic-Dogger, Lower Malm, and Upper Malm. The systematic regional mapping of the Slovene territory between Logatec, @uæemberk and the river Kolpa (Fig. 1) was carried out in the years between 1960 and 1980 within the framework of regional mapping for the Geologic map of Yougoslavia on the scale of 1:100 000. Fig. 1: Location map. Sl. 1: Poloæajna skica. 187 Acta carsologica, 29/1 (2000) In the study area this enormous project was accomplished by Pleni~ar (1967, 1970) and Buser (1969, 1974). In a comparatively small region of southern Slovenia, Turn{ek (1969) distinguished three types of Hydrozoan fauna formed during the Lower Malm that are connected with three separated areas. These are hydrozoan Cladocoropsis in the southern faunistic area, the parastromatoporidian Hydrozoa, corals and Chaetetidae in the central faunistic, area, and the actinostromaridian Hydrozoa in the northern faunistic area. Stratimetric measurements and profil- ing in this area was done from 1982 to 1991 in the framework of the project “The Jurassic of the Outer Dinarides” by Dozet and Stojanovi~, who at the same time mapped this area for the Geologi- cal map of Slovenia on the scale 1:50 000. The graduate student Strohmenger from the University of Heidelberg, working in Slovenia for his doctorate under the direction of S. Dozet, carried out detailed sedimentological investigations in the sections Kompolje-Ogorelec at the Mala Gora Mt., and in the section Krka - Mali Korinj in the Suha Krajina area. These investigations in the field were reviewed and accomplished in the years 1986, 1987 and 1988. The results of field and labo- ratory investigations were published in the papers Strohmenger, Dozet & Koch (1987a,b), Strohmenger (1988), Strohmenger & Dozet (1991) and Strohmenger, Deville & Fookes (1991) studying the oolitic facies, stratigraphy, diagenesis, facies developments, the Malm eustacy and geochemistry of the Jurassic carbonate rocks in Suha Krajina. Dozet and Strohmenger (1994/95) described Late Malm carbonate breccias at Korinj discussing their significance for eustacy and tectonics. Shallow-water deposits, breccias and subaerial exposures, evidenced by bauxite at some places in the Suha Krajina area, are considered to be connected with eustatic sea-level variations as well as syn-sedimentary fracturing and block-faulting. Dozet (1995) described various types of the Malm algal nodules (oncolites) from the Suha Krajina region in central Slovenia. Dozet and [ribar (1998) lithologically described and biostratigraphically subdivided the shal- low marine Jurassic beds in the southeastern Slovenia. The carbonate rocks are classified according to Folk’s (1959) practical petrographic classifica- tion of limestones and Dunham’s (1962) classification of carbonate rocks according to depositional texture. The microflora and microfauna are determined by R. Radoi~i} and the author of this paper. Hydrozoans, sponges and corals were determined by D. Turn{ek. GEOGRAPHIC SETTING The study complex lies about 30 km southeast of Ljubljana comprising about 100 square kilo- metres of the Suha Krajina area. Jurassic carbonate deposits exposed southeast of Ljubljana consist of more or less developed shallow subtidal, intertidal and supratidal facies. Datailed stratimetric and sedimentological investigations have been performed in the sections Krka-Ho~evje-Zdenska vas, Ilova gora-Ra~na vas, Krka-Mali Korinj and Zagradec-Ambrus is the Suha Krajina area. In the considered area a complete sedimentary succession of the Jurassic carbonate rocks is exposed, including the contacts between the Upper Triassic and Lower Cretaceous. The measured thickness of the Jurassic sequence is about 1500 metres. The study area is bounded in the north by the river Krka and in the south by the Mala Gora Mts. (964 m). The most significant peaks of the area are [entrumar (677 m) Ma~kov Vrh (708 m) and Srebotov Hrib (663 m). The highest elevation noted on the topographic map is 731 metres (Ciganov Vrh) high and the lowest one is 272 metres. The difference gives a maximum relief of approximately 460 metres. The road system is relatively 188 Stevo Dozet: Ho~evje oolitic group, Central Slovenia Fig. 2: Stratigraphic position and subdivision of the “Ho~evje oolitic formation”. Sl. 2: Stratigrafski poloæaj in raz~lenitev Ho~evske oolitne formacije. 189 Acta carsologica, 29/1 (2000) well-developed. The climate is of continental type with hot summers, relatively cold winters and moderate precipitation. The seat of Suha Krajina is @uæemberk. Besides, there are some smaller towns in the area and that: Ambrus, Zagradec, Krka, Ho~evje, ^u{perk and Ra~na. METHODS Our work is based on regional geological mapping of the study area for the Geological map of Slovenia on the scale of 1:50 000 as well as several detailed field surveys including stratimetric measuring and profiling as well as a precise sedimentologic and facies study of the Jurassic rocks in the considered area. Besides, the whole area is documented by about 1000 rock samples, numer- ous thin-sections, X-ray diffraction, scanning electron microscopy and geochemical analyses. The stratigraphic relationships have been established by means of micro- and macrofossils, and by lithologic correlations. STRATIGRAPHY GENERAL STATEMENT The Suha Krajina area is built of the Triassic and Jurassic beds, which are at many places covered with a couple of metres of Pliocene and Quaternary deposits. The Triassic system is repre- sented by the Main dolomite, which is concordantly overlain by the Rhaetian-Liassic carbonate succession. The Jurassic beds are relatively completely developed. The mentioned Triassic and Jurassic beds are the result of more or less continuous sedimentation on the Dinaric carbonate paltform. JURASSIC SYSTEM DOGGER AND LOWER MALM Ho~evje Oolitic Group Stratigraphic position The oolitic limestones, the most extended rocks exposed at the surface in the Suha krajina area, range in age from the Lower Dogger to the Lower Malm. Lithologically and according to fauna we can separate the Ho~evje oolitic group into two units: 1) - the Laze formation and 2) - the [entrumar formation. The underlying sedimentary succession, which we ranged to the Upper Liassic, is composed of platy, spotted, usually more or less nodular limestones. The limestone is micrite, pelmicrite, oomicrite, intrasparite and rarely boointrasparite by structure. The sequence is characterized by uniformity and lack of fossils. The characteristics of these