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 sediments indicate a deposition in a somewhat deeper restricted shelf environment. The Dogger oolitic rocks are overlain by the so- called Korinj breccias, composed of various, more or less angular limestone and dolomite frag-

190 Stevo Dozet: Ho~evje oolitic group, Central Slovenia ments and calcitic to dolomitic cement. The overlying sedimentary succession consits of lime- stones, dolomites and carbonate breccias. Sedimentary structures of the succession indicate a high energy shallow-water environment.

Laze Formation

Distribution The considered formation is named for exposures of the dark oolitic limestone at the hamlet Laze at Krka lying at the road Krka-V. Korinj. About a 500-metre wide belt of this limestone can be followed from [mihel to Ilova Gora. The considered rock group occupies the lithological inter- val between the underlying Upper Liassic platy spotted limestones and the first layers of the grey- ish oolitic limestone with the Lower Malm fossils. The dark oolitic succession lies conformably upon the already mentioned platy spotted limestone, which can occasionally be partly eroded be- fore the deposition of the oolites.

Lithology The Laze formation is almost exclusively developed as ooid grainstones, which laterally can also be somewhat dolomitized. In the described lithologic sequence, light to dark grey ooid-fossil and ooid-oncoid grainstones prevail. The uppermost beds of the sequence are rich in foraminifers of Dogger age. The thickness of the considered carbonate oolitic sedimentary succession ranges from 80 to 100 metres.

Fossils and age Generally speaking, the beds of the Laze formation are rather poor in fossils. More common than other are foraminifers, but the remains of algae and rare mollusc fragments can be seen as well. In up to date collected fossil material the following species and genera have been determined: Dictyoconus cayeuxi Lukas, Mesoendothyra croatica Gu{i}, Mesoendothyra sp., Thaumatoporella parvovesiculifera (Raineri), Verneulinidae, Trohaminiidae, Textulariidae and blue-green algae detritus. The described sequence is without any doubt of Lower Dogger age; the topmost beds of the described lithologic sequence are rich in the foraminifera Dictyoconus cayeuxi and Mesoendothyra croatica, which are well-known index fossils of the Lower Dogger in the Dinarides (Radoi~i}, 1966, 1969; Gu{i}, 1969). Outside Slovenia these foraminifera are known from the Lower to Middle Dogger (Kemper, 1976). On the basis of determined fossils R. Radoi~i} is of the opinion that at least the Callovian (or the upper part of Callovian) is not developed in the investi- gated area (Strohmenger & Dozet, 1991).

Environment In the described sedimentary succession as many oosparitic as oomicritic limestones occur. Consequently, these ooids were probably formed in a more or less restricted environment with minor water energy. The isopach granular cement A indicates an episodic meteoric influence.

Diagenesis Diagenetic changes in the Dogger oolitic succession are well-marked and common. In most cases a late dolomitization of different degree can be seen in the limestones of the Laze formation.

191 Acta carsologica, 29/1 (2000)

The extent of dolomitized rocks are commonly small. In the dark oolitic succession stylolites, cutting individual grains, can also be present, proving their late diagenetic origin.

[entrumar Formation

Distribution The carbonate oolitic rocks directly overlying the beds of the Laze formation are denominated as the [entrumar formation. These rocks are much more extensive than the beds of the Laze forma- tion. They are exposed at the surface to the south of the dark oolitic belt belonging to the underly- ing Laze formation, and they support the elevations such as Srebotov Hrib (663 m), [entrumar (677 m) and Ma~kov Vrh (708 m). The [entrumar formation also includes two minor units: the so- called “Nace oncoid member” lying in the middle of the lower part of the [entrumar formation, and “Brujek dolomite member” lying in the uppermost part of the same formation. The [entrumar formation occupies the geologic interval between the two discordances occurring most probably in the Middle Dogger and in the Middle Kimmeridgian.

Lithology Upon the partly eroded beds of the Laze formation rests the unconformable carbonate succes- sion of the [entrumar formation. It is represented by massive, rarely weakly stratified oolitic lime- stones, intercalated here and there with micritic and biomicritic limestones or coarse-grained dolo- mite. The oolitic sediments are commonly cross-bedded. The considered oolitic formation contains a large amount of radial, micritic and tangential ooids as well as fossil remains and detritus. At first sight monotonous ooid carbonate succession is composed of several structural types of limestones such as biolithite, biointrasparite, but oosparites, biooosparites and bioointrasparites prevail. Ac- cording to depositional texture (Dunham, 1962), the limestones are moderate gray open-marine grainstones with various lithoclasts and bioclasts, namely: well-sorted, well-formed, multiple-coated, round and sphaeroidal ooids, oncoids, intraclasts, pellets, corals, hydrozoans, sponges molluscs (pelecypods, gastropods, brachiopods) hydrozoans, crinoids, foraminifera and algae; further on, pelloid and skeletal wackstones and mudstones. Corals and hydrozoans were the main reef-build- ing organisms. The considered formation mainly composed of greyish ooid-fossil and ooid-oncoid grainstones, ocassionally, contains intercalations and minor bodies of brownish, coarse-grained dolomites, carbonate breccias and patch reefs. The thickness of this formation ranges from 350- 400 metres.

Nace Oncoid Member Oolitic limestone forms the 450-metre thick Malm-Dogger formation. In the lowermost part of the formation there occurs about 3 metres of thick-bedded, grey micritic limestone with oncolites. The oncolites may be associated with rather numerous corals, sponges, gastropods, pelecypods, echinoderms, foraminifers and algae. The primary component of the algally coated-grains (oncolites) is the blue-green alga “Girvanella” Paleoecologically, the “Girvanella” oncolites were formed in shallow-marine waters on the slowly subsiding Dinaric carbonate platform.

192 Stevo Dozet: Ho~evje oolitic group, Central Slovenia

Fossils and age Commonly, the fossils in the oolitic limestones are rather rare and poorly preserved, but some horizons are relatively abundantly fossiliferous. However, in the lower part of the formation there occurs about 3 metres of thick-bedded, grey micritic limestone with oncolites (Dozet, 1985). The oncolites are associated with rather numerous corals, sponges, gastropods, pelecypods, echinoderms, foraminifers and algae. Foraminifera: Protopeneroplis striata Weynschenk, Nautiloculina oolithica Mohler, Pfenderina salernitana Sartoni & Crescenti, Kurnubia palastiniensis Henson, Lepidocyclina sp., Verneuilinidae, Textulariidae, Trochaminidae, Ophtahlmidiidae. Algae: Bacinella irregularis Radoi~i}, Solenopora sp., Codiaceae, Cyanophyta and nodules “Girvanella”. Corals: Stylosmilia corallina Koby, Cladophyllia cf. excelsea Koby, Allocoenia trochyformis Etallon, Pseudocoenia limbata (Goldfuss), Thamnasteria concina (Goldfuss), as well as pelecypods, gastropods, echinoderms, molluscs and bryozoans. The above mentioned corals indicate the age of Oxfordian-Kimmeridgian. In the beds below the Nace oncolite horizon foraminifera Protopeneroplis striata Weynschenk, Trocholina elongata Weynschenk, Nautiloculina oolitica Mohler, Alzonella cuvillieri Bernier & Neumann as well as corals, sponges and hydrozoans have been found. In the ooid grainstones at Laze the following fossils have been found: (Strohmenger & Dozet, 1991) Cladocoropsis mirabilis Felix, Trocholina elongata Leupold, Protopeneroplis sp., Meandrophyllia amedei Etallon, Calamophylliopsis flabellum Michelin, Thamnasteria concina Goldfuss, Thamnasteria sp., Halisitastraea sp. and Stomatopora sp. The above-enumerated fauna testifies the Lower Malm age of the considered succession.

Environment The oolitic prevalently massive limestones are typical tidal-bar winnowed carbonate sands (Wilson, 1985), belonging to standard facies belt 6. The Lower Malm oncolites of the Suha Krajina area were formed predominantly in periodi- cally and intermediately agitated water in a shallow subtidal environment. Some data suggest that a part of the Nace oncolites were deposited in water of greater turbulence. The greater abundance of algal material in the oncolite deposits also suggests that the water was shallow and well-illumi- nated. The restriction of the biota may be evidence for severe and very special life and depositional conditions. The Nace oncolites were formed within the Suha Krajina Malm lagoon, in well-illumi- nated marine water within a depth range of approximately 25 metres.

GEOCHEMISTRY

The interpretation of microfacies of the Ho~evje oolitic group has been supplemented by geochemical analyses (see: Strohmenger, 1988, Strohmenger & Dozet, 1991). The obtained values of Mg, Sr, Fe, Mn, K, Zn and Al in the examined samples of the gathered calcareous rocks demonstrate a significant facies dependence. Generally speaking, the ooid grainstones are markedly depleted in above-enumerated elements. The values of manganese and

193 Acta carsologica, 29/1 (2000) strontium are in some cases relatively low. The loss of these elements might be explained by diagenetic processes. In any case, the measured elements in the two investigated sections reflect the environmental conditions under which the carbonate rocks were deposited. Similar geochemical results appear also in other Jurassic sections of the Slovenian Dinaric carbonate platform (Orehek & Ogorelec, 1979, 1981; Dozet, 1989). According to the literature they are within the general limits of carbonate rocks. DIAGENESIS

After the consolidation the oolitic limestones were in some places submitted to extremely strong late diagenetic changes such as recrystallization, cementation and dolomitization. Selective late dolomitization was present at different levels of the oolitic complex. Accordingly, smaller and larger patches of coarse-grained late diagenetic dolomite occur in the oolitc complex. However, the larger late diagenetic dolomite body occurs in the uppermost part of the [entrumar formation at Brujek. The most important diagenetic changes in the Nace oncolite horizon are dolomitization, cementation and recrystallization. The great majority of the observed algal thalli are totally recrystallized to blacky sparry calcite.

TECTONIC MOVEMENTS

From the geotectonic point of view the considered area belongs to the Outer Dinarides, Dinaric carbonate platform respectively. The geologic investigations in the Suha Krajina area performed in the last years showed that the Jurasic sedimentation was provoked and controlled by sea-level variations as well as fault and block tectonic activity. Tectonic movements in the area investigated were reflexive consequences of the Alpine tec- tonic cycles. Jurassic movements did not have any particular influence on the tectonic structure of this part of Slovenia, but they had a very strong influence on the sedimentation during that time (Dozet, 1989). We may state that in the study area no orogenic movements in the Jurassic period occurred since no folding can be found there, nor are there any traces of thrusting or nappe tectonic movements, volcanism or metasomatic changes of sedimentary rocks. There are nowhere any greater tectonic discordant contacts. Furthermore, in the area investi- gated no thicker coarse-grained basal transgressive formations can be found, so that we may be correct in affirming that the continuity of sedimentation had only been disturbed by periodical interruptions as a reflection of weaker or stronger epeirogenic movements of the carbonate plat- form. These periodical movements created the paleogeography in the Jurassic period. They also affected the differentiation of the carbonate platform and thus had a considerable influence on sedimentation. We came to the conclusion that epeirogenic movements alone could not cause all changes of the Malm sedimentation in the Suha Krajina area. From our point of view the fault tectonic activity played an essential role in the formation of Korinj breccias and bauxites. During the Kimmeridgian the subsidence of the Dinaric carbonate platform stopped and intensified posi- tive epeirogenic movements began causing locally an emergence of the area. Malmian bauxites on the Dinaric platform proved that such emersions occurred. On the other hand, the absence of baux-

194 Stevo Dozet: Ho~evje oolitic group, Central Slovenia ite deposits at some places suggests that the emersion was only a local phenomenon, and that the degree of subaerial exposures in Outer Dinarides was not everywhere the same. On the Dinaric platform, the Malm emersion phase had a different character. It was generally relatively short, but at some places, allowing for shorter and longer interruptions, it lasted through the greater part of the Upper Malm because of the late Kimmerian movements (Dozet et al., 1993). Regional geology, sedimentological data, vertical and lateral developments and extent, varia- tion of facies, the thickness of individual lithostatigraphic units, usually non-defined lithologic boundaries with other sediments and extremely poorly sorted carbonate rock indicate a close rela- tionship between breccias and syn-sedimentary block faulting of different scale and extent. How- ever, negative forms i.e. relatively narrow and shallow basins made possible the origin of subma- rine talus breccias. While the unconsolidated sediment was still in the environment of deposition it was decomposed by gravity-induced movements, displaced from scarps and accumulated in nega- tive forms at the base of scarps. The studied Jurassic stratigraphic sequence clearly indicate a stratigraphic gap during Dogger. The index fossils which could be identified point to an age older than Callovian, Upper Callovian respectively (Strohmenger & Dozet, 1991). Whereas on the Dinaric carbonate platform in the Jurassic period a shallow-water sedimenta- tion was carried out (with the exception of a short-lived interruption at the transition from the Lower to Upper Malm, during which the short-lasting emersion of thinner lenses of bauxite were formed), in the transition area (Suha Krajina) between the Slovenia trough and the Dinaric carbon- ate platform the epeirogenic activity was intensified, which caused an uplifting of marginal areas of the Dinaric carbonate platform, being completely elevated above the sea-water level at the end of the Middle Liassic. With the origin of dry land the sedimentation in the carbonate edge area was interrupted. Such conditions lasted until the Lower Malm. The stratigraphic gap Middle Liassic- Lower Malm in the edge area is marked by an absence of the Upper Liassic and Dogger sedimen- tation and fossils. The stratigraphic gap is sufficient evidence for relatively long-lived emersion, after the deposition of the Middle Liassic beds, lasting as long as the Lower malm transgression. Since it appeared in several parts of the Slovenian, Croatian and Bosnian Dinarides as well as in Italy the mentioned emersion was not a local phenomenon. Accordingly, in the time interval Mid- dle Liassic-Lower Malm some areas of the Dinaric carbonate platform were partly or completely without any sedimentation, considered by many authors as a bar with larger and smaller elevations, which could be presented like a part of an uniform island arc, a chain of islands respectively, rising from the deep sea floor near dry land, passing from Bosanska Krajina across Kordun, Banija, @umberak, Bela Krajina, Suha Krajina and Trnovski Gozd still forward to the northeast and to Italy. This, morphologically well-expressed belt, a narrow elongated bar respectively, was rela- tively closely connected with a differentiation of until that time uniform sedimentary area of the Dinaric carbonate platform. At that place Malm hydrozoan-coral reefs were also formed. The treated bar separated in this way in the uniform sedimentary area of Outer Dinarides an expressively shal- low-water area of the carbonate shelf from the tectonic trench with a deep sea-water sedimentation. The shallow water deposits, the breccias and the subaerial exposures evidenced by bauxite at some places in the Suha Krajina area, are considered to be connected with eustatic sea-level varia- tions as well as syn-sedimentary fracturing and block-faulting (Dozet & Strohmenger, 1991). The identified karst breccia intercalated within the Lower Malm carbonate succession contains

195 Acta carsologica, 29/1 (2000) clasts of both Lower and Upper Malm indicating a long term emergence of the Dinaric carbonate platform during the Upper Malm (Strohmenger & Dozet, 1991). On the Jurassic/Lower Cretaceous boundary some parts of the Suha Krajina area were sub- jected to tectonic movements as a consequence of the Late Kimmerian orogenetic phase (Dozet, 1989), resulting in an uplifting and rupturing of individual parts of the bottom of the sea. The new formed land gave the material for origin of heterogeneous limestone-dolomite sedimentary breccias (Dozet, 1996). A new paleogeographic disposition between the dry land and the sea developed. Genetically closely related to the mentioned paleogeographic changes are Neocomian carbonate breccias, formed predominantly in shore regions.

MINERAL RESOURCES

Bauxite

The bauxite in the Suha Krajina area occurs as low-grade very small lenses or pockets in the top of the [entrumar formation along the Lower Kimmeridgian-Upper Kimmeridgian contact at or near the present land surface. They belong to the so-called karst bauxites, or the “terra rossa” type of bauxites. The main minerals of the bauxites are kaolinite, beohmite, gibbsite and hematite. The bauxites derive from limestone residuum as well as from alluvium and aeolian material. The bauxites treated in this study were developed during the Late Kimmerian emersion phase. The movements that created dry land were mainly of epeirogenic type. This is suggested by biostratigraphy and concordance or slight discordance of bauxites and their footwall and hanging- wall carbonate rocks. The late Kimmerian epeirogenic movements, together with fault tectonics, produced a paleotopography on which weathering, leaching, dissolution, karstification and denu- dation subsequently took place. Karstification was soon interrupted and entirely halted by bauxitization and deposition of the bauxitic material particularly of the terra rossa type. Preserva- tion of the deposits is probably due to their deposition in sinkholes formed primarily along the faults in the underlying oolitic limestones. The combination of low grade and small size makes these deposits of no economic interest. The deposits are too small to be of more than scientific significance. No other mineral resources are known from these two formations in the study area and wider vicinity. CONCLUSIONS

- The 450 to 500-metre thick carbonate oolitic succession in the Suha Krajina area is proposed to be denominated the Ho~evje oolitic group. The mentioned group consists of the underlying Laze formation and overlying [entrumar formation. - The platy limestone succession, which represents the footwall of the Ho~evje group, is of Upper Liassic age. - The Laze formation consits of dark oolitic limestones. On the other hand, the overlying [entrumar formation is composed of greyish oolitic limestones passing at some places irregularly into a thick-grained dolomite.

196 Stevo Dozet: Ho~evje oolitic group, Central Slovenia

- During sedimentation and/or directly after the deposition the sedimentary rocks were subjected to different diagenetic processes, namely: cementation, recrystallization micritization, stylolitization and dolomitization. - The upper boundary of the Ho~evje group is chiefly discordant. The [entrumar formation passes upwards into the Neocomian Korinj breccias. - With regard to the stratigraphic position, lithology and macro- and micro-fauna and flora, the considered carbonate oolitic succession is of the Dogger and Lower Malm age. - Geochemical data, textures and structures indicate a shallow-marine, rather turbulent environ- ment. - The thickness of the considered carbonate oolitic succession in the Suha Krajina area ranges from 450 to 500 metres. - Geotectonically, the study area belongs to the Outer Diarides, Dinaric carbonate platform re- spectively. ACKNOWLEDGEMENTS

The outhor is much obliged to the Ministry of Science and Techology as well as to the Geologi- cal survey of Slovenia for financial support of his investigations in the field.

REFERENCES

Buser, S. 1965: Stratigrafski razvoj jurskih skladov na juænem Primorskem, Notranjskem in zahodni Dolenjski. Disertacija. - Arhiv Geolo{kega zavoda Ljubljana, 101 str., Ljubljana. Buser, S. 1969: Osnovna geolo{ka karta SFRJ, list Ribnica 1:100 000. Zvezni geolo{ki zavod, Beograd. Buser, S. 1974: Tolma~ k Osnovni geolo{ki karti SFRJ 1:100 000 lista Ribnica L 33-78. Zvezni geolo{ki zavod, 60 str., Beograd. Dozet, S. 1982-1991: Stratimetrijske raziskave Zunanjih Dinaridov. Geolo{ki zavod Slovenije, Ljubljana. Dozet, S. 1982-1991: Jura Zunanjih Dinaridov, Suha krajina. Geolo{ki zavod Slovenije, Ljubljana. Dozet, S. 1989a: Tektonska premikanja na Ko~evskem v mlaj{em paleozoiku in mezozoiku (juæna Slovenija). Rud. met. zbornik, 36, 4, 663-673, Ljubljana. Dozet, S. 1989b: Razvoj mezozojskih plasti na Ko~evskem in v okolici. Univerza v Ljubljani - NTF, 178 str., Ljubljana. Dozet, S., 1994: Stratigraphy of the Suha Krajina area (Slovenia) and stratigraphic gap Middle Liassic - Lower Malm. Rud.-met. zbornik, 41, 231-238, Ljubljana. Dozet, S., 1995: The Malm algal nodules (oncolites) from the Suha Krajina region (Slovenia). Rud.-met. zbornik, 42, 3-4, 165-169, Ljubljana. Dozet, S., 1997: Ambrus beds- Important key for interpretation of Neocomian paleogeography, sea-level changes, depositional setting and tectonics in Suha Krajina area (Slovenia). Geologija, 39, (1996) 119-131, Ljubljana. Dozet, S. & Strohmenger, C., 1996: Late Malm carbonate breccias at Korinj and their significance for eustacy and tectonics (central Slovenia). Geologija, 37, 38 (1994/95), 215-223, Ljubljana.

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Dozet, S. & [ribar, Lj. 1998: Biostratigraphy of shallow-marine Jurassic beds in southeastern Slovenia. Geologija, 40 (1997), 187-221, Ljubljana. Dunham, R.J., 1962: Classification of carbonate rocks according to depositional texture. In Ham, W.E. (ed.): Classification of carbonate rocks. AAPG, Mem., 1, 108-121, Tulsa. Folk, R., 1959: Practical petrographic classication of limestones. Bull.Am.Ass.Petrol.Geol., 43, 1, 2-38, Tulsa. Gu{i}, I., 1969: Some new and inadequatly known Jurassic foraminifers from Central Croation. Geol. vjesnik, 22, 55-177, Zagreb. Kemper, E., 1976: The foraminifera in the Jurassic limestone of West Thailand. Geol.Jb., 21, 129- 153, Hannover. Melik, A., 1959: Posavska Slovenija II/3. Slovenska matica, 389-427, Ljubljana. Orehek, S. & Ogorelec, B., 1981: Correlation of microfacial and geochemical characteristics of Jurassic an Cretaceous rocks of the southern carbonate platform in Slovenia. Glas. republ. zav. za{t. prir. Prir. muzeja (Titograd), 14, 161-181, Titograd. Orehek, S. & Ogorelec, B., 1979: Sedimentological features of the Jurassic and Creataceous car- bonate rocks of Trnovski Gozd.Geol.vjesnik, 32, 185-192, Zagreb. Pleni~ar, M., 1967: Osnovna geolo{ka karta SFRJ, list Postojna 1:100 000. Zvezni geolo{ki zavod, Beograd. Pleni~ar, M., 1970: Tolma~ k Osnovni geolo{ki karti Slovenije 1:100 000, list Postojna L 33-77. Zvezni geolo{ki zavod, 62 str., Ljubljana. Radoi~i}, R., 1966: Microfaciès du Jurassic des Dinarides externes de la Yougoslavie. Geologija, 9, 5-377, Ljubljana. Strohmenger, C., 1988: Mikrofazielle und diagenetische Entwicklung jurassischer Karbonate (Unter Lias bis Ober-Malm) von Slowenien (NW Jugoslawien). Heidelberger Geowiss. Abh., 24, 249 str., Heidelberg. Strohmenger, C., Dozet, S. & Koch, R., 1987a: Oolith-Sequenzen im Jura Südwest-Sloweniens (Mala Gora - Bebirge, Ober-Lias bis Ober-Malm). In: Koch, R., Müller, G. & Schmitz, W. (eds.): Heidelberger Geowiss. Abh., 8, 245-248, Heidelberg. Strohmenger, C., Dozet, S. & Koch, R., 1987b: Diagensemuster-Stratigraphie: Oolith-Horizonte im Jura von SW-Slowenien. Fazies, 17, 253-266, Erlangen. Strohmenger, C. & Dozet, S., 1991: Stratigraphy and geochnemistry of Jurassic carbonate rocks from Suha Krajina and Mala gora mountain (southern Slovenia). Geologija, 33 (1990) 315- 351, Ljubljana. Strohmenger, C., Deville, Q. & Fookes, E., 1991: Kimmeridgian/Tithonian eustacy and its im- prints on carbonate rocks from the Dinaric and the Jura carbonate platforms. Bull.Soc. Géol. France, 162, 4, 661-671, Paris. [ribar, Lj., 1966: Jurassic sediments between the villages Zagradec and Randol in Krka vally. Geologija, 9, 379-383, Ljubljana. Turn{ek, D., 1964: Hidrozojska favna iz zgornjejurskih skladov na Dolenjskem, Notranjskem in Primorskem. Disertacija. Slov. akad. za znan. in umetn. 147 str., Ljubljana. Turn{ek, D., 1969: Prispevek k paleoekologiji jurskih hidrozojev v Sloveniji. Razprave SAZU, 4 razr., 12, 15, 211-235, Ljubljana. Wilson, J. L., 1985: Carbonate facies in geologic hystory. Berlin-Heidelberg-New York Springer, 471, str., Heidelberg.

198 Stevo Dozet: Ho~evje oolitic group, Central Slovenia HO»EVSKA OOLITNA SKUPINA Povzetek

V tem ~lanku je opisan 450 do 500 m debel oolitni kompleks z obmo~ja Suhe krajine, ki leæi konkordantno na zgornjeliasnih plo{~astih in tanko plastnatih apnencih in diskordantno pod zgornjemalmskimi Korinjskimi bre~ami. Manj{a diskordanca lo~i oolitni kompleks v dva dela: v spodnji del ~rnega oolitnega apnenca doggerske starosti in v zgornji del sivkastega oolita, ki pripada spodnjemu malmu. Za zgoraj omenjene oolitne kamenine predlagam ime “Ho~evska skupina”, ki jo sestavljata spodaj leæe~a “Formacija Laze” in nad njo leæe~a “[entrumarska formacija”. Mikropaleontolo{ke preiskave so pokazale, da vrhnje doggerske plasti manjkajo in da najverjetneje sploh niso bile odloæene. Formacija Laze sestoji iz temno sivega, sivkasto ~rnega, temno rjavkasto ~rnega in ~rnega masivnega oolitnega apnenca, ki med drugim vsebuje tudi zna~ilni doggerski foraminiferi Dictyoconus cayeuxi in Mesoendothyra croatica. Nad plastmi z omenjenimi foraminiferami leæi svetlo siv preteæno masiven oolitni apnenec [entrumarske formacije, ki v spodnjem delu vklju~uje Nacetov onkolitni ~len, v vrhnjem pa Brujekov dolomitni ~len. Spodnja meja Ho~evske skupine je normalna do rahlo diskordantna. Tudi zgornja meja omenjene skupine je na raziskovanem ozemlju diskordantna. Plasti [entrumarske formacije prehajajo namre~ navzgor v neokomske Korinjske bre~e. Manj{a diskordanca deli Ho~evsko skupino v dva dela. Paleontolo{ki, sedimentolo{ki in geokemi~ni podatki Ho~evske skupine kaæejo na plitvomorsko precej razgibano okolje nastanka. Debelina obravnavanega karbonatnega oolitnega zaporedja na obmo~ju Suhe krajine je 450 do 500 metrov. V geotektonskem pogledu pripada raziskovano ozemlje Zunanjim Dinaridom oziroma Dinarski karbonatni platformi.

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