slovenski

Geologija Krasa

Kras, a picturesque landscape on the northern end of the Adriatic Sea, has a special place among the karst regions of the world, as its name became the basis of the internationally used term karst. Another name for Kras often used among geologists is the Trieste-Komen plateau. It lies at the northern edge of the deformed Adria microplate, which is characterized by folding and thrusting to the central part of the plate, i.e., south and southwest. Kras represents, together with much of the southwestern part of Slovenia, part of the External Dinarides, which, in paleogeographic terms, built of sediments of the former Adriatic-Dinaric Carbonate Platform. The Late Carboniferous to early Triassic prehistory of the Adriatic-Dinaric Carbonate Platform is linked to the Gondwana continental shelf, and from the Middle Triassic onwards, it existed as a more or less isolated intraoceanic carbonate platform, which was surrounded by the deep basin of the Tethys Ocean. The Adriatic-Dinaric Carbonate Platform was geotectonically relatively stable, and until its demise in the late Cretaceous and Paleogene, it successfully maintained a balance between global sea-level changes and influence of synsedimentary tectonics within the dynamic area between the Laurasia and Gondwana continents. Comparison of the Kras carbonate rocks, which were formed in the inner part of the carbonate platform, with other areas of the External Dinarides, reveals that the platform in the early Cretaceous and in the lower part of the late Cretaceous was paleogeographically homogeneous. This is indicated by the similarity of many of the lithostratigraphic units in the entire Cretaceous territory of the External Dinarides. Particularly evident is the close correlation of most stratigraphic levels, members and formations with the global eustatic events. Only in the upper part of the late Cretaceous was there a more pronounced difference in the sedimentary environment. In this work, ten main formations are presented that constitute Kras and its peripheral area. On the plates, a basic field and macroscopic presentation of rocks is given for each unit, and a large portion is devoted to the fossil content. The most comprehensive is the selection of photomicrographs of rock thin-sections that were prepared in the laboratory of the Geological Survey Slovenia parallel to the geological mapping of the Kras area, as it was often only with the help of microfossil associations possible to define the lithostratigraphic units accurately (Fig. 37, 38). The oldest carbonate rocks belong to the Brje Formation, which was built mainly in a shallow calm shelf with the lagoonal character. In the lower, dolomitic part of the Brje Formation, there are no preserved fossils, so perhaps the lowermost dolomite beds belong to the Berriasian stage. In the limestone above the dolomite, favreinas abundantly appear in places and belong to the Neocomian coprolite horizon. Further upward, there is limestone with bacinellas, which represents a reflection of the oceanic anoxic event OAE-1a. Among the microfossils of the upper part of the Brje Formation, there is the important lower Aptian species Palorbitolina lenticularis (Blumenbach), whereas just below the Aptian-Albian emersion boundary, the alga Salpingoporella dinarica Radoičić occurs in massive amounts. The generally known eustatic sea level drop below the edge of the carbonate platform during Aptian and Albian and its re-raising started sedimentation of the Povir Formation and the beginning of a new megasequence of the carbonate platform. The emersion boundary between the Brje and Povir Formations is characterized by a breccia layer, which is also evident in other parts of the Adriatic-Dinaric Carbonate Platform. The Albian part of the Povir Formation generally displays a slightly higher energy level of the sedimentary environment. In the lowest part, the most important foraminifera is Orbitolina (Mesorbitolina) texana Roemer, which is widely found in the clasts of emersion breccia and in the layers above it. The Albian-Cenomanian part of the Povir Formation is characterized mainly by dolomitic, postsedimentary tectogeno-diagenetic breccia and bedded bituminous dolomite. In the upper Cenomanian part of the Povir Formation, next to chondrodonts, the foraminifera Broeckina (Pastrikella) balcanica Cherchi, Radoičić & Schroeder is of great stratigraphic importance, being later known from a number of middle and late Cenomanian sites in the Mediterranean. Platy and laminated limestones of the Kras area occur within various formations ranging from the Albian to the Campanian. Most of these strata are exposed in the surrounding areas of Komen. A large portion of the Komen limestone, which occurs within the Povir Formation, was deposited in an intraplatform basin in the vicinity of the exposed areas (tidal flats, supratidal environment). The bottom water in the basin was occasionally dysoxic to anoxic ; the changing of different facies was the result of slight changes in sea level rise and local subsidence of the area. The eustatic sea level rise between the Cenomanian and Turonian was among the major events that marked the further development of the Adriatic-Dinaric Carbonate Platform and life on it. This global event almost entirely submerged the carbonate platform. The result was the Repen Formation, which is characterized by the appearance of many pelagic fossils. The Repen Formation is a combination of three main types of limestones that pass laterally and vertically to each other. The basic core of the formation consists of stratified limestone that locally contains abundant calcispheres and Komen Limestone with pelagic fossils. The latter is associated with the oceanic anoxic event OAE-2. The upper part of the formation includes the Repen/Kopriva member with displaced and locally fractured rudist shells. This part of the formation belongs to the economically very promising types of natural stone in Kras. The eustatic sea level drop in the Turonian terminated sedimentation of the Repen Formation. Shallow water limestones of the Sežana Formation were deposited. In the lowest part of the formation, the Oncoidal Limestone is developed, which locally includes bioclastic rudist lenticular bodies. Above it, a mostly medium- to thick-bedded biomicrite follows, with a low to very low energy index. The fossils are represented by a number of benthic foraminifera, which have wide stratigraphic ranges and can also be found in the Lipica Formation. Within the Sežana Formation, there is Komen Limestone with chert, which is, in terms of basic lithological characteristics, similar to the Komen Limestone of the Povir Formation. The small and insignificant benthic fauna, pyrite pigment and organic matter indicate a lagoonal model of sedimentation with occasional anoxic and dysoxic conditions on the seabed. In the central Santonian portion of the Sežana Formation, the Pliskovica Limestone with pelagic fossils was sedimented. In addition to numerous calcispheres in this limestone, some opportunistic planktonic foraminifera are present and also occur in the matrix of bioclastic limestone of this member. In general, it can be concluded that this limestone was formed in one of the tectonically induced depressions on the platform that had a good connection with the open sea. In the Lipica Formation, several types of limestone with prevailing bioclastic varieties are present. There are quite numerous bedded and massive biomicrites and biosparites with a partially or completely washed micritic matrix and relatively large rudist fragments, complete rudist shells, rarely rudist bouquets, clusters and parts of rudist thickets. Due to thick layering and homogeneous texture, this limestone represents the most economically interesting part of the Kras carbonate rocks. Foraminifera in the Lipica Formation are similar to those in the Sežana Formation. In the highest part of the Lipica Formation, the species Calveziconus lecalvezae Claus & Cornella and Pseudocyclamina massiliensis Maync indicate that the sedimentation of the Lipica Formation in certain parts of the platform continued into the Campanian. In general, the limestone of the Lipica Formation was deposited in different environments of the carbonate platform, mostly in the open part of the shelf, locally in its restricted part, as well as in an environment with littoral conditions. Within the Lipica Formation, in the central part of the Trieste-Komen plateau, thin, platy and laminated Tomaj Limestone is present. Bioclastic intercalations with gradually decreasing grain size, slumping structure, absence of primary benthos and the presence of pelagic micro-and macrofossils testify to a deeper environment, good connection with the open sea, and nektonic and planktonic organisms in the water column just above the anoxic or dysoxic bottom of the lagoon. Fossil macroflora with dominant conifers came from the nearby land that already in the late Santonian began to form the "Tomaj lagoon" in the south. At the same time, the Tomaj Limestone provides a comparison with the Santonian-Campanian transgression and perhaps the oceanic anoxic event OAE-3, which will be the subject of future research. Gradual paleogeographic differentiation, which in the Santonian and later in the Campanian already heavily influenced the sedimentary environments of the Adriatic-Dinaric Carbonate Platform, continued into the Maastrichtian and Paleogene. After the break in limestone sedimentation of the Lipica Formation, the beds of the Kras Group were sedimented and represent the beginning of the new megasequence. Shallow marine and paralic carbonates of the Kras Group (Liburnia and Trstelj Formations, Alveolinid-nummulitid Limestone) are, at their lower boundary, clearly limited by the regional discordance and at the upper boundary by the basinal clastites. The Liburnia Formation was deposited on the distinct paleokarstic relief during the Maastrichtian and Paleocene. The sediments are characterized by interchanging shallow marine, brackish and freshwater environments. The "Vreme" facies is characterized by rudist genera Gyropleura, Apricardia, Bournonia, Biradiolites, and the foraminifera Rhapydionina liburnica Stache. In freshwater and brackish phases of sedimentation, coal beds were formed, and associated with the common occurrence of numerous characeans and gastropods of the genus Stomatopsis. The Cretaceous-Tertiary boundary is characterized by breccia with micritic matrix and Microcodium structures. The "Kozina" facies, which usually occurs in the upper Paleocene parts of the formation, is characterized by darker, slightly marly limestone with frequent thin-shelled bivalves, tiny gastropods, ostracods, characeans and miliolids. In between there are stromatolitic laminae and Microcodium. The Lower Trstelj Beds, which are dominated by bioclastic limestone with numerous miliolids, are resting above the Liburnia Formation. The most common benthic foraminifera belong to the genera Periloculina, Miscellanea, Coskinon and Fallotella, and among dasycladaceans, the genera Clypeina and Cymopolia are present. The Lower Trstelj Beds were deposited in a shallow marine environment of the innermost ramp with occasional emersions and shoals. Based on the benthic community, these beds are placed in the Thanetian. In the lowest part of the Upper Trstelj Beds, there commonly lies the Coral-algal Limestone, which appears in the form of lenticular bodies of different thickness throughout the Kras region. Most of the Upper Trstelj Beds are characterized by bioclastic limestone with larger foraminifera, which inhabited different niches within the slightly deeper part of the carbonate ramp. Among the fossils, foraminifera of the genera Assilina, Lacazina and Pseudolacazina are important. These layers are placed at the top of the Thanetian. Above the Trstelj Formation lies the Alveolinid-nummulitid Limestone with larger benthic foraminifera: alveolinids, nummulitids, orbitolitids and discocyclinids. The lower boundary of this Kras formation is, in many places, indicated by alveolinid mass occurrence. The upper boundary is gradual or sharp. Locally, a hardground can also be observed. The thickness of the Alveolinid-nummulitid Limestone is not constant. Where these layers are missing, the Transitional Beds or Flysch Formation lie directly on the Trstelj Beds. As a rule, in this formation, from the bottom to top, there is alveolinid limestone, followed by nummulitid limestone and limestone dominated with discocyclinids and flat nummulitids. The Alveolinid-nummulitid Limestone was formed largely in the middle part of carbonate ramp and, based on benthic foraminifera, placed in the Ilerdian. The carbonate platform was finally buried in the Eocene with the advancing hemipelagic marls, marly limestones and resedimented carbonates (Transitional Beds) and with deepwater clastics (Flysch). The Transitional Beds are characterized by a high proportion of glauconite and planktonic foraminifera. In the higher parts of the Transitional Beds, Basal Marl is locally developed, that, with reducing carbonate content, finally pass into flysch. In a wider context, the Potok Breccia also belongs to the Transitional Beds. On the basis of foraminifera and nanoplankton, the Transitional Beds are placed in the middle Ypresian and lower Cuisian. Above the Transitional Beds, or in some cases erosionally above the carbonate rocks of the Kras Group, lies a several hundred meters-thick succession of flysch sandstone, siltstone, claystone and marlstone, which forms the Flysch Formation. In the lowest part of this formation, conglomerate and breccia are often developed. In the flysch of the wider area of the Vipava-Gorizia synclinorium, all characteristic sequences of turbidity currents can be observed. Near the Ustje in the Vipava Valley, which is closest to the flysch edge of the Kras area, flysch sedimentation of the lower to middle Cuisian age was documented with plankton, nanoplankton and nummulitids.

litostratigrafske jedinice; kreda; paleogen; Kras; Slovenija

nije evidentirano

engleski

Geology of Kras

Kras, a picturesque landscape on the northern end of the Adriatic Sea, has a special place among the karst regions of the world, as its name became the basis of the internationally used term karst. Another name for Kras often used among geologists is the Trieste-Komen plateau. It lies at the northern edge of the deformed Adria microplate, which is characterized by folding and thrusting to the central part of the plate, i.e., south and southwest. Kras represents, together with much of the southwestern part of Slovenia, part of the External Dinarides, which, in paleogeographic terms, built of sediments of the former Adriatic-Dinaric Carbonate Platform. The Late Carboniferous to early Triassic prehistory of the Adriatic-Dinaric Carbonate Platform is linked to the Gondwana continental shelf, and from the Middle Triassic onwards, it existed as a more or less isolated intraoceanic carbonate platform, which was surrounded by the deep basin of the Tethys Ocean. The Adriatic-Dinaric Carbonate Platform was geotectonically relatively stable, and until its demise in the late Cretaceous and Paleogene, it successfully maintained a balance between global sea-level changes and influence of synsedimentary tectonics within the dynamic area between the Laurasia and Gondwana continents. Comparison of the Kras carbonate rocks, which were formed in the inner part of the carbonate platform, with other areas of the External Dinarides, reveals that the platform in the early Cretaceous and in the lower part of the late Cretaceous was paleogeographically homogeneous. This is indicated by the similarity of many of the lithostratigraphic units in the entire Cretaceous territory of the External Dinarides. Particularly evident is the close correlation of most stratigraphic levels, members and formations with the global eustatic events. Only in the upper part of the late Cretaceous was there a more pronounced difference in the sedimentary environment. In this work, ten main formations are presented that constitute Kras and its peripheral area. On the plates, a basic field and macroscopic presentation of rocks is given for each unit, and a large portion is devoted to the fossil content. The most comprehensive is the selection of photomicrographs of rock thin-sections that were prepared in the laboratory of the Geological Survey Slovenia parallel to the geological mapping of the Kras area, as it was often only with the help of microfossil associations possible to define the lithostratigraphic units accurately (Fig. 37, 38). The oldest carbonate rocks belong to the Brje Formation, which was built mainly in a shallow calm shelf with the lagoonal character. In the lower, dolomitic part of the Brje Formation, there are no preserved fossils, so perhaps the lowermost dolomite beds belong to the Berriasian stage. In the limestone above the dolomite, favreinas abundantly appear in places and belong to the Neocomian coprolite horizon. Further upward, there is limestone with bacinellas, which represents a reflection of the oceanic anoxic event OAE-1a. Among the microfossils of the upper part of the Brje Formation, there is the important lower Aptian species Palorbitolina lenticularis (Blumenbach), whereas just below the Aptian-Albian emersion boundary, the alga Salpingoporella dinarica Radoičić occurs in massive amounts. The generally known eustatic sea level drop below the edge of the carbonate platform during Aptian and Albian and its re-raising started sedimentation of the Povir Formation and the beginning of a new megasequence of the carbonate platform. The emersion boundary between the Brje and Povir Formations is characterized by a breccia layer, which is also evident in other parts of the Adriatic-Dinaric Carbonate Platform. The Albian part of the Povir Formation generally displays a slightly higher energy level of the sedimentary environment. In the lowest part, the most important foraminifera is Orbitolina (Mesorbitolina) texana Roemer, which is widely found in the clasts of emersion breccia and in the layers above it. The Albian-Cenomanian part of the Povir Formation is characterized mainly by dolomitic, postsedimentary tectogeno-diagenetic breccia and bedded bituminous dolomite. In the upper Cenomanian part of the Povir Formation, next to chondrodonts, the foraminifera Broeckina (Pastrikella) balcanica Cherchi, Radoičić & Schroeder is of great stratigraphic importance, being later known from a number of middle and late Cenomanian sites in the Mediterranean. Platy and laminated limestones of the Kras area occur within various formations ranging from the Albian to the Campanian. Most of these strata are exposed in the surrounding areas of Komen. A large portion of the Komen limestone, which occurs within the Povir Formation, was deposited in an intraplatform basin in the vicinity of the exposed areas (tidal flats, supratidal environment). The bottom water in the basin was occasionally dysoxic to anoxic ; the changing of different facies was the result of slight changes in sea level rise and local subsidence of the area. The eustatic sea level rise between the Cenomanian and Turonian was among the major events that marked the further development of the Adriatic-Dinaric Carbonate Platform and life on it. This global event almost entirely submerged the carbonate platform. The result was the Repen Formation, which is characterized by the appearance of many pelagic fossils. The Repen Formation is a combination of three main types of limestones that pass laterally and vertically to each other. The basic core of the formation consists of stratified limestone that locally contains abundant calcispheres and Komen Limestone with pelagic fossils. The latter is associated with the oceanic anoxic event OAE-2. The upper part of the formation includes the Repen/Kopriva member with displaced and locally fractured rudist shells. This part of the formation belongs to the economically very promising types of natural stone in Kras. The eustatic sea level drop in the Turonian terminated sedimentation of the Repen Formation. Shallow water limestones of the Sežana Formation were deposited. In the lowest part of the formation, the Oncoidal Limestone is developed, which locally includes bioclastic rudist lenticular bodies. Above it, a mostly medium- to thick-bedded biomicrite follows, with a low to very low energy index. The fossils are represented by a number of benthic foraminifera, which have wide stratigraphic ranges and can also be found in the Lipica Formation. Within the Sežana Formation, there is Komen Limestone with chert, which is, in terms of basic lithological characteristics, similar to the Komen Limestone of the Povir Formation. The small and insignificant benthic fauna, pyrite pigment and organic matter indicate a lagoonal model of sedimentation with occasional anoxic and dysoxic conditions on the seabed. In the central Santonian portion of the Sežana Formation, the Pliskovica Limestone with pelagic fossils was sedimented. In addition to numerous calcispheres in this limestone, some opportunistic planktonic foraminifera are present and also occur in the matrix of bioclastic limestone of this member. In general, it can be concluded that this limestone was formed in one of the tectonically induced depressions on the platform that had a good connection with the open sea. In the Lipica Formation, several types of limestone with prevailing bioclastic varieties are present. There are quite numerous bedded and massive biomicrites and biosparites with a partially or completely washed micritic matrix and relatively large rudist fragments, complete rudist shells, rarely rudist bouquets, clusters and parts of rudist thickets. Due to thick layering and homogeneous texture, this limestone represents the most economically interesting part of the Kras carbonate rocks. Foraminifera in the Lipica Formation are similar to those in the Sežana Formation. In the highest part of the Lipica Formation, the species Calveziconus lecalvezae Claus & Cornella and Pseudocyclamina massiliensis Maync indicate that the sedimentation of the Lipica Formation in certain parts of the platform continued into the Campanian. In general, the limestone of the Lipica Formation was deposited in different environments of the carbonate platform, mostly in the open part of the shelf, locally in its restricted part, as well as in an environment with littoral conditions. Within the Lipica Formation, in the central part of the Trieste-Komen plateau, thin, platy and laminated Tomaj Limestone is present. Bioclastic intercalations with gradually decreasing grain size, slumping structure, absence of primary benthos and the presence of pelagic micro-and macrofossils testify to a deeper environment, good connection with the open sea, and nektonic and planktonic organisms in the water column just above the anoxic or dysoxic bottom of the lagoon. Fossil macroflora with dominant conifers came from the nearby land that already in the late Santonian began to form the "Tomaj lagoon" in the south. At the same time, the Tomaj Limestone provides a comparison with the Santonian-Campanian transgression and perhaps the oceanic anoxic event OAE-3, which will be the subject of future research. Gradual paleogeographic differentiation, which in the Santonian and later in the Campanian already heavily influenced the sedimentary environments of the Adriatic-Dinaric Carbonate Platform, continued into the Maastrichtian and Paleogene. After the break in limestone sedimentation of the Lipica Formation, the beds of the Kras Group were sedimented and represent the beginning of the new megasequence. Shallow marine and paralic carbonates of the Kras Group (Liburnia and Trstelj Formations, Alveolinid-nummulitid Limestone) are, at their lower boundary, clearly limited by the regional discordance and at the upper boundary by the basinal clastites. The Liburnia Formation was deposited on the distinct paleokarstic relief during the Maastrichtian and Paleocene. The sediments are characterized by interchanging shallow marine, brackish and freshwater environments. The "Vreme" facies is characterized by rudist genera Gyropleura, Apricardia, Bournonia, Biradiolites, and the foraminifera Rhapydionina liburnica Stache. In freshwater and brackish phases of sedimentation, coal beds were formed, and associated with the common occurrence of numerous characeans and gastropods of the genus Stomatopsis. The Cretaceous-Tertiary boundary is characterized by breccia with micritic matrix and Microcodium structures. The "Kozina" facies, which usually occurs in the upper Paleocene parts of the formation, is characterized by darker, slightly marly limestone with frequent thin-shelled bivalves, tiny gastropods, ostracods, characeans and miliolids. In between there are stromatolitic laminae and Microcodium. The Lower Trstelj Beds, which are dominated by bioclastic limestone with numerous miliolids, are resting above the Liburnia Formation. The most common benthic foraminifera belong to the genera Periloculina, Miscellanea, Coskinon and Fallotella, and among dasycladaceans, the genera Clypeina and Cymopolia are present. The Lower Trstelj Beds were deposited in a shallow marine environment of the innermost ramp with occasional emersions and shoals. Based on the benthic community, these beds are placed in the Thanetian. In the lowest part of the Upper Trstelj Beds, there commonly lies the Coral-algal Limestone, which appears in the form of lenticular bodies of different thickness throughout the Kras region. Most of the Upper Trstelj Beds are characterized by bioclastic limestone with larger foraminifera, which inhabited different niches within the slightly deeper part of the carbonate ramp. Among the fossils, foraminifera of the genera Assilina, Lacazina and Pseudolacazina are important. These layers are placed at the top of the Thanetian. Above the Trstelj Formation lies the Alveolinid-nummulitid Limestone with larger benthic foraminifera: alveolinids, nummulitids, orbitolitids and discocyclinids. The lower boundary of this Kras formation is, in many places, indicated by alveolinid mass occurrence. The upper boundary is gradual or sharp. Locally, a hardground can also be observed. The thickness of the Alveolinid-nummulitid Limestone is not constant. Where these layers are missing, the Transitional Beds or Flysch Formation lie directly on the Trstelj Beds. As a rule, in this formation, from the bottom to top, there is alveolinid limestone, followed by nummulitid limestone and limestone dominated with discocyclinids and flat nummulitids. The Alveolinid-nummulitid Limestone was formed largely in the middle part of carbonate ramp and, based on benthic foraminifera, placed in the Ilerdian. The carbonate platform was finally buried in the Eocene with the advancing hemipelagic marls, marly limestones and resedimented carbonates (Transitional Beds) and with deepwater clastics (Flysch). The Transitional Beds are characterized by a high proportion of glauconite and planktonic foraminifera. In the higher parts of the Transitional Beds, Basal Marl is locally developed, that, with reducing carbonate content, finally pass into flysch. In a wider context, the Potok Breccia also belongs to the Transitional Beds. On the basis of foraminifera and nanoplankton, the Transitional Beds are placed in the middle Ypresian and lower Cuisian. Above the Transitional Beds, or in some cases erosionally above the carbonate rocks of the Kras Group, lies a several hundred meters-thick succession of flysch sandstone, siltstone, claystone and marlstone, which forms the Flysch Formation. In the lowest part of this formation, conglomerate and breccia are often developed. In the flysch of the wider area of the Vipava-Gorizia synclinorium, all characteristic sequences of turbidity currents can be observed. Near the Ustje in the Vipava Valley, which is closest to the flysch edge of the Kras area, flysch sedimentation of the lower to middle Cuisian age was documented with plankton, nanoplankton and nummulitids.

lithostratigraphic units; Cretaceous; Paleogene; Kras; Slovenia

nije evidentirano