Facies and chemostratigraphic definition of the P/T boundary of Mts. Velebit : master’s thesis

Ovim radom prikazane su facijesne i kemostratigrafske karakteristike naslaga gornjega perma i donjega trijasa na području Brušana (planina Velebit). Istraživani slijed predstavlja kontinuiranu karbonatnu sedimentaciju na prijelazu iz paleozoika u mezozoik, a moguće ga je pratiti profilom Brušane Sy smještenom u zasjeku šumske ceste južno od Brušana. Na temelju mikropetrografskih karakteristika spomenutog profila utvrđeni su okoliši taloženja ovih, u potpunosti dolomitiziranih stijena. Određena je sedimentacija na karbonatnoj platformi, u relativno plitkome okolišu, a karakterizira je obilje mikritnih taloga, prisustvo mikrobijalnih (cijanobakterijskih) proslojaka, povremeno sačuvano obilje mikrofosila te taloženje u subtajdalnoj, tajdalnoj i supratajdalnoj zoni. Gornjopermska starost naslaga potvrđena je foraminiferama, a osim njih slijed je bogat fosilnim ostacima vapnenačkih zelenih algi i njihovih spora, gastropoda te ostrakoda. Utvrđeno je izronjavanje primarnih taloga u zonu intertajdala/supratajdala usred povremenih oscilacija morske razine, što je ujedno rezultiralo i pretaloživanjem djelomično litificiranog sedimenta iz ovih zona u zonu subtajdala. Posljedica izronjavanja karbonatnih taloga je i intenzivna dijageneza u vadoznoj zoni. Rezultati izotopne analize ugljika i kisika uspoređeni su s vrijednostima karakterističnim za ovo razdoblje. Izostanak negativnog otklona u sastavu ugljikovih izotopa na P/T granici objašnjen je kao utjecaj vadozne dijageneze na primarni izotopni signal pri čemu ni promjene uzrokovane procesom dolomitizacije nisu isključene.Facies and chemostratigraphic characteristic of the transitional Permian and Triassic interval were differentiated by investigating dolomites near the village Brušane (Velebit Mts.) along the road-cut south from Brušane village. Investigated section “Brušane Sy” represents a continuous deposition of carbonates at the P/T boundary interval. All deposits in the vertical column are determined as dolostones. Related to their main micropetrographic features a deposition in a shallow part of carbonate platform was discerned – in subtidal, intertidal and supratidal zones. The sedimentation is characterized by the prevalence of micritic component, the presence of microbial (cyanobacterial) interlayers and fairly preserved fossils: foraminifers, green algae and their spores, gastropods and ostracods. The Upper Permian age of the lower part of the section “Brušane Sy” is confirmed by Permian foraminifers genera. Occasional emerging of the subtidal/intertidal deposits to supratidal condition occurred that has resulted partially with the desiccation and local resedimentation of desiccated lime-mud fragments to subtidal zone. A significant process related to the deposition in the supratidal zone was vadose diagenesis observed in many Permian dolostones. The periodic emergence of the platform was interpreted due to sea-level oscillation. The values of the δ13C, δ18O isotope content resulted in the isotope curve that was compared to the P/TB isotope curve from several world known P/TB localities. A composite isotope curve from Brušane (“Brušane Sy” and “Brušane 2” sections) is missing the extreme negative values pointing to an exact position of P/TB. This can be interpreted as a consequence of the vadose diagenesis observed along almost entire “Brušane Sy” section

Facies and chemostratigraphic definition of the P/T boundary of Mts. Velebit : master’s thesis

Ovim radom prikazane su facijesne i kemostratigrafske karakteristike naslaga gornjega perma i donjega trijasa na području Brušana (planina Velebit). Istraživani slijed predstavlja kontinuiranu karbonatnu sedimentaciju na prijelazu iz paleozoika u mezozoik, a moguće ga je pratiti profilom Brušane Sy smještenom u zasjeku šumske ceste južno od Brušana. Na temelju mikropetrografskih karakteristika spomenutog profila utvrđeni su okoliši taloženja ovih, u potpunosti dolomitiziranih stijena. Određena je sedimentacija na karbonatnoj platformi, u relativno plitkome okolišu, a karakterizira je obilje mikritnih taloga, prisustvo mikrobijalnih (cijanobakterijskih) proslojaka, povremeno sačuvano obilje mikrofosila te taloženje u subtajdalnoj, tajdalnoj i supratajdalnoj zoni. Gornjopermska starost naslaga potvrđena je foraminiferama, a osim njih slijed je bogat fosilnim ostacima vapnenačkih zelenih algi i njihovih spora, gastropoda te ostrakoda. Utvrđeno je izronjavanje primarnih taloga u zonu intertajdala/supratajdala usred povremenih oscilacija morske razine, što je ujedno rezultiralo i pretaloživanjem djelomično litificiranog sedimenta iz ovih zona u zonu subtajdala. Posljedica izronjavanja karbonatnih taloga je i intenzivna dijageneza u vadoznoj zoni. Rezultati izotopne analize ugljika i kisika uspoređeni su s vrijednostima karakterističnim za ovo razdoblje. Izostanak negativnog otklona u sastavu ugljikovih izotopa na P/T granici objašnjen je kao utjecaj vadozne dijageneze na primarni izotopni signal pri čemu ni promjene uzrokovane procesom dolomitizacije nisu isključene.Facies and chemostratigraphic characteristic of the transitional Permian and Triassic interval were differentiated by investigating dolomites near the village Brušane (Velebit Mts.) along the road-cut south from Brušane village. Investigated section “Brušane Sy” represents a continuous deposition of carbonates at the P/T boundary interval. All deposits in the vertical column are determined as dolostones. Related to their main micropetrographic features a deposition in a shallow part of carbonate platform was discerned – in subtidal, intertidal and supratidal zones. The sedimentation is characterized by the prevalence of micritic component, the presence of microbial (cyanobacterial) interlayers and fairly preserved fossils: foraminifers, green algae and their spores, gastropods and ostracods. The Upper Permian age of the lower part of the section “Brušane Sy” is confirmed by Permian foraminifers genera. Occasional emerging of the subtidal/intertidal deposits to supratidal condition occurred that has resulted partially with the desiccation and local resedimentation of desiccated lime-mud fragments to subtidal zone. A significant process related to the deposition in the supratidal zone was vadose diagenesis observed in many Permian dolostones. The periodic emergence of the platform was interpreted due to sea-level oscillation. The values of the δ13C, δ18O isotope content resulted in the isotope curve that was compared to the P/TB isotope curve from several world known P/TB localities. A composite isotope curve from Brušane (“Brušane Sy” and “Brušane 2” sections) is missing the extreme negative values pointing to an exact position of P/TB. This can be interpreted as a consequence of the vadose diagenesis observed along almost entire “Brušane Sy” section

Granica perm–trijas na Velebitu: nova facijesna, biostratigrafska i kemostratigrafska obilježja

The Permian–Triassic boundary (PTB), one of the most investigated stratigraphic boundaries, is marked by dramatic changes in oceanic and atmospheric chemistry that consequently caused the most severe mass extinction of all time. These changes can be seen in the type and style of deposition in the PTB interval that is characterized by transition from skeletal-dominated to microbial-dominated carbonate production. Most of the studies concerning this important time interval have been made in shallow to deep marine depositional environments in addition to some terrestrial sections. However, there is very little information about how shallow lagoonal, sabkha and intertidal sediments reacted to these drastic changes. Indeed, shallow marine deposition was often prone to dolomitization and thus difficult to date. In the Brušane-Sy section located south of the village Brušane (Velebit Mountains) in the External Dinarides (Croatia), we have observed continuous dolostone sedimentation throughout the Permian- Triassic boundary interval and obtained new facies, bio- and chemostratigraphic data (conodonts, foraminifers, δ13C curve). A high-resolution micropetrographic study shows different dolostone texture and preservation of primary constituents in the Permian vs. the Early Triassic dolostone. The Permian dolostone deposits are differentiated as: 1) dolomicrite/mudstone with microbial (cyanobacterial) interlayers, the occurrences of stromatactoid fabric, desiccation cracks/tepee structures signifying deposition in intertidal/supratidal conditions; and 2) dolobiomicrite/wackestone and dolobiomicrite/packstone microfacies types with fairly preserved abundant calcareous algae and their spores (acritarchs), foraminifers (Hemigordiopsids with some Nodosariids and Fusulinids), gastropods, bivalves and ostracods that were deposited in the subtidal low energy zone of a shallow lagoon. Primary structures of the Permian dolostone show well-preserved fabric due to favourable dolomitizing conditions, i.e., primary dolomitization. However, significant appearances of dissolution voids indicate diagenesis in the meteoric/ marine vadose zone. The presence of the vadose sediment features is not likely for the sabkha-dolomitizing conditions under arid climate conditions usually related to this type of dolomitization. The inf luence of microbial activity should rather be taken into consideration for interpreting the intense dolomitizing process. On the contrary, the Triassic dolostone, whose age is confirmed by finding of the conodont species Hindeodus parvus for the first time in the PTB interval of the Velebit Mts., exhibits a completely different dolostone texture in comparison to the Permian microcrystalline dolomite type. Early Triassic dolostone strata conformably overlie Late Permian dolostone deposits and exhibit medium- to coarse crystalline unimodal planar-s type texture, possibly indicating exceptional aftermath dolomitizing conditions (shallow burial-like) and the influence of microbial and decaying organisms to the formation of the coarse crystalline dolomite texture. The δ13C values do not represent the global oceanic signal but either depict the values of a restricted basin or were influenced by the early dolomitization. Moreover, the meteoric diagenesis subsequently overprinted this signal

Granica perm–trijas na Velebitu: nova facijesna, biostratigrafska i kemostratigrafska obilježja

The Permian–Triassic boundary (PTB), one of the most investigated stratigraphic boundaries, is marked by dramatic changes in oceanic and atmospheric chemistry that consequently caused the most severe mass extinction of all time. These changes can be seen in the type and style of deposition in the PTB interval that is characterized by transition from skeletal-dominated to microbial-dominated carbonate production. Most of the studies concerning this important time interval have been made in shallow to deep marine depositional environments in addition to some terrestrial sections. However, there is very little information about how shallow lagoonal, sabkha and intertidal sediments reacted to these drastic changes. Indeed, shallow marine deposition was often prone to dolomitization and thus difficult to date. In the Brušane-Sy section located south of the village Brušane (Velebit Mountains) in the External Dinarides (Croatia), we have observed continuous dolostone sedimentation throughout the Permian- Triassic boundary interval and obtained new facies, bio- and chemostratigraphic data (conodonts, foraminifers, δ13C curve). A high-resolution micropetrographic study shows different dolostone texture and preservation of primary constituents in the Permian vs. the Early Triassic dolostone. The Permian dolostone deposits are differentiated as: 1) dolomicrite/mudstone with microbial (cyanobacterial) interlayers, the occurrences of stromatactoid fabric, desiccation cracks/tepee structures signifying deposition in intertidal/supratidal conditions; and 2) dolobiomicrite/wackestone and dolobiomicrite/packstone microfacies types with fairly preserved abundant calcareous algae and their spores (acritarchs), foraminifers (Hemigordiopsids with some Nodosariids and Fusulinids), gastropods, bivalves and ostracods that were deposited in the subtidal low energy zone of a shallow lagoon. Primary structures of the Permian dolostone show well-preserved fabric due to favourable dolomitizing conditions, i.e., primary dolomitization. However, significant appearances of dissolution voids indicate diagenesis in the meteoric/ marine vadose zone. The presence of the vadose sediment features is not likely for the sabkha-dolomitizing conditions under arid climate conditions usually related to this type of dolomitization. The inf luence of microbial activity should rather be taken into consideration for interpreting the intense dolomitizing process. On the contrary, the Triassic dolostone, whose age is confirmed by finding of the conodont species Hindeodus parvus for the first time in the PTB interval of the Velebit Mts., exhibits a completely different dolostone texture in comparison to the Permian microcrystalline dolomite type. Early Triassic dolostone strata conformably overlie Late Permian dolostone deposits and exhibit medium- to coarse crystalline unimodal planar-s type texture, possibly indicating exceptional aftermath dolomitizing conditions (shallow burial-like) and the influence of microbial and decaying organisms to the formation of the coarse crystalline dolomite texture. The δ13C values do not represent the global oceanic signal but either depict the values of a restricted basin or were influenced by the early dolomitization. Moreover, the meteoric diagenesis subsequently overprinted this signal

Retrieving planktonic foraminifera from lithified rocks, examples from the Eocene limestones and marls (External Dinarides, Croatia)

Paleoecologic (paleoclimatologic) and biostratigraphic studies of pelagic and deep-water deposits rely on the identification of planktonic foraminifera. Here we report and compare the results of planktonic foraminiferal assemblages from the Middle Eocene indurated limestones and marls collected in the External Dinarides extracted with acetic acid of different concentrations (50%, 60%, 70% and 80%) and different reaction (exposure) times. The deposits originated within the Dinaric foreland basin, have been assigned to the so-called Transitional beds and Flysch, and are characterized by different ratio of carbonate content and degree of lithification. The aim of this paper is to compare the efficiency of the laboratory procedures for obtaining isolated specimens and to evaluate the impact of preparation procedure on the quality of tests (complete test vs. secondary dissolution effects). For each acetic concentration we assessed: (1) the effectiveness of the treatment in terms of the time required for successful extraction of planktonic foraminifera, and (2) the degree of dissolution by analyses of dissolution proxies, including the weight percentage of sieved residues after disaggregation and preservation features of the tests. Our results indicate that accurate taxonomic analysis of carbonate rocks requires the use of 60% acetic acid for a shorter reaction time, and hydrogen peroxide methods for marls