Statistical analysis of Neogene sediment thickness deposited during the first transtensional and first transpressional evolutionary stages in the Bjelovar Sub-basin, Northern Croatia

Abstract The Bjelovar Sub-basin is situated in Northern Croatia and constitutes the southwestern branch of the Drava Basin. The Neogene-Quaternary sedimentary section can be subdivided into three megacycles, which are separated by regional unconformities. The data analyzed in this study are related to the first megacycle, which is characterized by a tectonic-erosional unconformity above the Neogene basement (electric log, abbr. e-log marker Pt or Tg); its top is the regional e-log marker Rs7. It is generally assumed that the Rs7 marker separates Sarmatian and Pannonian sediments and indicates the period just after the first transtensional and first transpressional events. The youngest elog marker, Rs5, represents the Lower/Upper Pannonian boundary (in Croatian stratigraphic nomenclature) and more generally the early period of the second transtensional event. The lithology of the Lower and Middle Badenian is characterized by coarse and medium-grained sediments, while the Upper Badenian to Lower Pannonian section is dominantly pelitic as a result of flattening of the eroded paleorelief, as well as of reduced amounts of fans and energy. Thickness maps for the stratigraphic intervals Pt/Tg-Rs7 (4.9 Ma) and Rs7-Rs5 (2.2 Ma) were statistically analyzed using a regular grid with individual cells of 500 × 500 m. It is demonstrated that the first transpressional event in this sub-basin continued during the Lower Pannonian, causing a significant decrease of sediment thickness and a large unconformity in the east. Statistics based on histograms and averages confirmed that the first transtension and first transpression can be clearly distinguished by the presented methodology

Stratigraphic, petroleum geological and paleoecological features of the sarmatian deposits in the western part of the Sava Depression

Tijekom srednjeg miocena područje zapadnog dijela Savske depresije dio je jugozapadnog ruba nekadašnjega Središnjeg Paratetisa, odnosno današnjega hrvatskoga dijela Panonskoga bazenskog sustava. Zbog prekida veze s Mediteranom i Indopacifikom tijekom sarmata započela je izolacija Središnjeg Paratetisa. što se očituje kroz pojavu endemske faune. Ovisno o paleoreljefu, intenzitetu erozije i energiji vode razvijaju se različiti tipovi okoliša. Razmatrajući bušotinske podatke uočeno je kako je sarmat vrlo rijetko prepoznat i izdvojen kao zaseban kat. Gornja granica sarmatskih taložina obično je bolje izražena te ju je moguće prepoznati po EK markeru Rs7, jer jezgre sedimenata ispod EK markera Rs7 sadrže miocensku fosilnu faunu stariju od panona. U cilju stjecanja uvida u rasprostranjenost i razvoj sarmata na površini prikupljeni su podatci iz brojnih radova te je istraživana i srednjomiocenska (sarmatska) fosilna flora i fauna na izdancima Svetonedeljskog brega. Rasprostranjenost sarmatskih taložina u dubini kreirana je i na temelju izvješća dubokih bušotina. Uspoređujući mikropaleontološke i petrografske karakteristike stijenskog materijala iz bušotina i karotažnih krivulja, na karotažnoj krivulji prirodne radioaktivnosti (engl. skr. GR) uočen je interval porasta vrijednosti prirodne radioaktivnosti ispod EK markera Rs7. Taj interval povećane radioaktivnosti na istraživanom području približno odgovara donjoj granici sarmatskih naslaga. U svrhu izradbe karte taložnih okoliša u vrijeme sarmata, svi površinski i dubinski podatci o taložnim okolišima grupirani su u četiri kategorije i to: (1) plitkog, (2) prijelaznog, (3) dubljeg i (4) kopnenog okoliša. Na taj je način svakoj analiziranoj točci u prostoru pridružena indikatorska vrijednost nazvana indikator okoliša. Na podatcima je primijenjeno više metoda kartiranja, te je utvrđeno da je najprimjerenija metoda koja prikazuje razdiobu okoliša tijekom sarmata metoda najmanjih kvadrata.During the Middle Miocene (Sarmatian), sedimentary basins in the western part of the Sava Depression belonged to the south-western part of the Central Paratethys. Area belongs to the south-western part of the Croatian part of Pannonian Basin System. Sea. Isolation of the Central Paratethys from the Mediterranean and Indo-Pacific began during the Sarmatian period and led to the occurrence of the endemic fauna. Evolution of environments was controlled by paleorelief, erosional intensity and water energy. Sarmatian is very rarely recognized and distinguished as a stage in well data. The approximate boundary between the Sarmatian and the Lower Pannonian is recognized by e-log marker Rs7 and sediments below the Rs7 contain Miocene fossil fauna older than the Pannonian. In order to define the distribution and development of Sarmatian outcrops, data from numerous papers were collected and the Middle Miocene (Sarmatian) fossil flora and fauna were analyzed at outcrops in the area of Svetonedeljski breg. Distribution of Sarmatian sediments was also determined based on deep wells reports. Potential boundary was observed on the gamma-ray well log curve (abb. GR). This interval of increased radioactivity roughly corresponds to the bottom of the Sarmatian deposits. In order to map depositional environments during the Sarmatian, all outcrops and well data of depositional environments are grouped into four categories: (1) shallow, (2) transitional, (3) deeper and (4) terrestrial environments. In this way, each analyzed point is assigned an indicator value called an environmental indicator. The few mapping methods were applied and the most appropriate method that represents the spatial data distribution was the least-squares method

Stratigraphic, petroleum geological and paleoecological features of the sarmatian deposits in the western part of the Sava Depression

Tijekom srednjeg miocena područje zapadnog dijela Savske depresije dio je jugozapadnog ruba nekadašnjega Središnjeg Paratetisa, odnosno današnjega hrvatskoga dijela Panonskoga bazenskog sustava. Zbog prekida veze s Mediteranom i Indopacifikom tijekom sarmata započela je izolacija Središnjeg Paratetisa. što se očituje kroz pojavu endemske faune. Ovisno o paleoreljefu, intenzitetu erozije i energiji vode razvijaju se različiti tipovi okoliša. Razmatrajući bušotinske podatke uočeno je kako je sarmat vrlo rijetko prepoznat i izdvojen kao zaseban kat. Gornja granica sarmatskih taložina obično je bolje izražena te ju je moguće prepoznati po EK markeru Rs7, jer jezgre sedimenata ispod EK markera Rs7 sadrže miocensku fosilnu faunu stariju od panona. U cilju stjecanja uvida u rasprostranjenost i razvoj sarmata na površini prikupljeni su podatci iz brojnih radova te je istraživana i srednjomiocenska (sarmatska) fosilna flora i fauna na izdancima Svetonedeljskog brega. Rasprostranjenost sarmatskih taložina u dubini kreirana je i na temelju izvješća dubokih bušotina. Uspoređujući mikropaleontološke i petrografske karakteristike stijenskog materijala iz bušotina i karotažnih krivulja, na karotažnoj krivulji prirodne radioaktivnosti (engl. skr. GR) uočen je interval porasta vrijednosti prirodne radioaktivnosti ispod EK markera Rs7. Taj interval povećane radioaktivnosti na istraživanom području približno odgovara donjoj granici sarmatskih naslaga. U svrhu izradbe karte taložnih okoliša u vrijeme sarmata, svi površinski i dubinski podatci o taložnim okolišima grupirani su u četiri kategorije i to: (1) plitkog, (2) prijelaznog, (3) dubljeg i (4) kopnenog okoliša. Na taj je način svakoj analiziranoj točci u prostoru pridružena indikatorska vrijednost nazvana indikator okoliša. Na podatcima je primijenjeno više metoda kartiranja, te je utvrđeno da je najprimjerenija metoda koja prikazuje razdiobu okoliša tijekom sarmata metoda najmanjih kvadrata.During the Middle Miocene (Sarmatian), sedimentary basins in the western part of the Sava Depression belonged to the south-western part of the Central Paratethys. Area belongs to the south-western part of the Croatian part of Pannonian Basin System. Sea. Isolation of the Central Paratethys from the Mediterranean and Indo-Pacific began during the Sarmatian period and led to the occurrence of the endemic fauna. Evolution of environments was controlled by paleorelief, erosional intensity and water energy. Sarmatian is very rarely recognized and distinguished as a stage in well data. The approximate boundary between the Sarmatian and the Lower Pannonian is recognized by e-log marker Rs7 and sediments below the Rs7 contain Miocene fossil fauna older than the Pannonian. In order to define the distribution and development of Sarmatian outcrops, data from numerous papers were collected and the Middle Miocene (Sarmatian) fossil flora and fauna were analyzed at outcrops in the area of Svetonedeljski breg. Distribution of Sarmatian sediments was also determined based on deep wells reports. Potential boundary was observed on the gamma-ray well log curve (abb. GR). This interval of increased radioactivity roughly corresponds to the bottom of the Sarmatian deposits. In order to map depositional environments during the Sarmatian, all outcrops and well data of depositional environments are grouped into four categories: (1) shallow, (2) transitional, (3) deeper and (4) terrestrial environments. In this way, each analyzed point is assigned an indicator value called an environmental indicator. The few mapping methods were applied and the most appropriate method that represents the spatial data distribution was the least-squares method

GREBENI I DRUGE BIOGENE TVOREVINE U MIOCENSKIM NASLAGAMA SJEVERNOHRVATSKOGA BAZENA – ČUDESNA RAZNOLIKOST KOJU TEK TREBA ISTRAŽITI

During the early stages of the Middle Miocene transgression marine biota invaded the newly formed Paratethys Sea. Reefs and reef-like structures particularly flourished with life, supported by the favourable climate conditions. Miocene biogene buildups show a variety of fossil assemblages and lithologic features. The main reef-builders were bryozoans, coralline algae, corals, oysters, vermetids, sponges and serpulids. Water turbidity and depth were major ecological factors controlling the reef biota. Lithofacies types at the studied localities in Northern Croatia show significant similarity with the Upper Langhian (Middle Badenian) of the Leitha Mountains in Austria, but can also be well compared with Miocene to recent reef structures in the Mediterranean. The Miocene reef-like buildups exhibit different porosity rates and other lithological characteristics.Tijekom početne faze srednjomiocenske transgresije marinski organizmi naselili su novonastalo more Paratethys. Zahvaljujući pogodnim klimatskim i okolišnim uvjetima život je bio posebno raznolik na grebenima i grebenolikim strukturama. Miocenske biogene tvorevine na raznim lokalitetima u području sjeverne Hrvatske pokazuju raznolikost fosilnih zajednica i litoloških osobina. Glavni grebenotvorci bili su mahovnjaci, koralinacejske alge, kamenice, vermetidi, spužve i serpulidi. Glavni ekološki faktori koji su kontrolirali grebensku biotu bili su donos čestica i hraniva s kopna i iz dubina vode. Tipovi litofacijesa pokazuju veliku sličnost s gornjolangijskim (srednji baden) gorjem Leitha u Austriji, a mogu se usporediti i s miocenskim i recentnim grebenskim strukturama u Mediteranu. Razne vrste miocenskih grebenolikih tvorevina pokazuju različitu šupljikavost i druge petrofizičke osobine. Koraligenske biokonstrukcije danas nastaju kao konkrecije u slabo osvijetljenim uvjetima, pogodnim scijafilnim algama, u vodi relativno hladne, ali stalne temperature, jednoličnoga saliniteta i niske energije. Nastaju na stjenovitoj podlozi i na pokretnoj podlozi u donjoj litoralnoj zoni i katkad na obalnome detritusu. Rast im započinje nastankom rodolita unutar pijeska i šljunka (platformske koraligenske zajednice). Aktualistički princip pomaže nam razumjeti ranu pojavu koraligenskih tvorevina na početku srednjomiocenske transgresije. Početna rodolitna faza rezultira slabo vezanim bioklastičnim naslagama. Dijagenetski procesi dodatno povećavaju njihovu šupljikavost, uslijed otapanja aragonitnih bioklasta. To je otapanje agresivno u vrlo plitkim staništima i povećava se s dubinom. Promjenjiva šupljikavost koraligenskih tvorevina istraživana je tijekom terenskoga rada na području Medvednice. Uzorci stijena s velikim rodolitima već na prvi pogled pokazuju najveću šupljikavost, dok su briozojsko-koralinacejski frejmstoni najkompaktniji. Time se otvara prostor za daljnja istraživanja ovih zanimljivih naslaga

Stratigraphic, petroleum geological and paleoecological features of the sarmatian deposits in the western part of the Sava Depression

Tijekom srednjeg miocena područje zapadnog dijela Savske depresije dio je jugozapadnog ruba nekadašnjega Središnjeg Paratetisa, odnosno današnjega hrvatskoga dijela Panonskoga bazenskog sustava. Zbog prekida veze s Mediteranom i Indopacifikom tijekom sarmata započela je izolacija Središnjeg Paratetisa. što se očituje kroz pojavu endemske faune. Ovisno o paleoreljefu, intenzitetu erozije i energiji vode razvijaju se različiti tipovi okoliša. Razmatrajući bušotinske podatke uočeno je kako je sarmat vrlo rijetko prepoznat i izdvojen kao zaseban kat. Gornja granica sarmatskih taložina obično je bolje izražena te ju je moguće prepoznati po EK markeru Rs7, jer jezgre sedimenata ispod EK markera Rs7 sadrže miocensku fosilnu faunu stariju od panona. U cilju stjecanja uvida u rasprostranjenost i razvoj sarmata na površini prikupljeni su podatci iz brojnih radova te je istraživana i srednjomiocenska (sarmatska) fosilna flora i fauna na izdancima Svetonedeljskog brega. Rasprostranjenost sarmatskih taložina u dubini kreirana je i na temelju izvješća dubokih bušotina. Uspoređujući mikropaleontološke i petrografske karakteristike stijenskog materijala iz bušotina i karotažnih krivulja, na karotažnoj krivulji prirodne radioaktivnosti (engl. skr. GR) uočen je interval porasta vrijednosti prirodne radioaktivnosti ispod EK markera Rs7. Taj interval povećane radioaktivnosti na istraživanom području približno odgovara donjoj granici sarmatskih naslaga. U svrhu izradbe karte taložnih okoliša u vrijeme sarmata, svi površinski i dubinski podatci o taložnim okolišima grupirani su u četiri kategorije i to: (1) plitkog, (2) prijelaznog, (3) dubljeg i (4) kopnenog okoliša. Na taj je način svakoj analiziranoj točci u prostoru pridružena indikatorska vrijednost nazvana indikator okoliša. Na podatcima je primijenjeno više metoda kartiranja, te je utvrđeno da je najprimjerenija metoda koja prikazuje razdiobu okoliša tijekom sarmata metoda najmanjih kvadrata.During the Middle Miocene (Sarmatian), sedimentary basins in the western part of the Sava Depression belonged to the south-western part of the Central Paratethys. Area belongs to the south-western part of the Croatian part of Pannonian Basin System. Sea. Isolation of the Central Paratethys from the Mediterranean and Indo-Pacific began during the Sarmatian period and led to the occurrence of the endemic fauna. Evolution of environments was controlled by paleorelief, erosional intensity and water energy. Sarmatian is very rarely recognized and distinguished as a stage in well data. The approximate boundary between the Sarmatian and the Lower Pannonian is recognized by e-log marker Rs7 and sediments below the Rs7 contain Miocene fossil fauna older than the Pannonian. In order to define the distribution and development of Sarmatian outcrops, data from numerous papers were collected and the Middle Miocene (Sarmatian) fossil flora and fauna were analyzed at outcrops in the area of Svetonedeljski breg. Distribution of Sarmatian sediments was also determined based on deep wells reports. Potential boundary was observed on the gamma-ray well log curve (abb. GR). This interval of increased radioactivity roughly corresponds to the bottom of the Sarmatian deposits. In order to map depositional environments during the Sarmatian, all outcrops and well data of depositional environments are grouped into four categories: (1) shallow, (2) transitional, (3) deeper and (4) terrestrial environments. In this way, each analyzed point is assigned an indicator value called an environmental indicator. The few mapping methods were applied and the most appropriate method that represents the spatial data distribution was the least-squares method

Seismic geomorphology of Pannonian clastic reservoirs in Drava and Zala Basins, Pannonian Basin System

Mature basins provide a wealth of data for the reconstruction and mapping of their sedimentary evolution and architecture as well as regional paleo-geographic changes. In turn, these often lead to a better understanding of geological processes and thus provide a basis for novel concepts in exploration of subsurface. The Neogene Pannonian Basin System (PBS) nested between the Dinarides, Alps and the Carpathian arc in Central Europe is such a mature area with more than a century hydrocarbon exploration and production history. The upper Miocene to Pliocene sediments, referred to as Pannonian Stage, were initially deposited in an under-filled lake basin displaying gradual transgression followed by a powerful regression characterized by prograding and aggrading clinoforms on reflection seismic data. Relative chronostratigraphic framework was defined by clinoform sets mapped along with their rollover points across Drava and Zala basins. Based on seismic attributes, log patterns and available core data, clastic depositional features and architectures were delineated across different depositional environments within lake basin clinoforms. Each depositional feature is described upon its position within clinoforms, type of clinoform trajectory and typical log pattern. Finally, depositional features are described in their typical sizes (based on 3D seismic data) and reservoir quality. Integrating various data resulted in more complete temporal and spatial development of depositional environments during clinoform deposition as well as depositional features. Mapping of the depositional features across clinoforms resulted in considerable range of reservoir sandbody types that can be recognized on 3D seismic within Pannonian Basin System

Seismic geomorphology of Pannonian clastic reservoirs in Drava and Zala Basins, Pannonian Basin System

Mature basins provide a wealth of data for the reconstruction and mapping of their sedimentary evolution and architecture as well as regional paleo-geographic changes. In turn, these often lead to a better understanding of geological processes and thus provide a basis for novel concepts in exploration of subsurface. The Neogene Pannonian Basin System (PBS) nested between the Dinarides, Alps and the Carpathian arc in Central Europe is such a mature area with more than a century hydrocarbon exploration and production history. The upper Miocene to Pliocene sediments, referred to as Pannonian Stage, were initially deposited in an under-filled lake basin displaying gradual transgression followed by a powerful regression characterized by prograding and aggrading clinoforms on reflection seismic data. Relative chronostratigraphic framework was defined by clinoform sets mapped along with their rollover points across Drava and Zala basins. Based on seismic attributes, log patterns and available core data, clastic depositional features and architectures were delineated across different depositional environments within lake basin clinoforms. Each depositional feature is described upon its position within clinoforms, type of clinoform trajectory and typical log pattern. Finally, depositional features are described in their typical sizes (based on 3D seismic data) and reservoir quality. Integrating various data resulted in more complete temporal and spatial development of depositional environments during clinoform deposition as well as depositional features. Mapping of the depositional features across clinoforms resulted in considerable range of reservoir sandbody types that can be recognized on 3D seismic within Pannonian Basin System