Mio-Pliocene magnetostratigraphy in the southern Carpathian foredeep and Mediterranean–Paratethys correlations

A full understanding of the Mio-Pliocene palaeogeographical and palaeoenvironmental changes in the circum-Mediterranean region during the Messinian Salinity Crisis (MSC) is at present hampered by the lack of reliable chronostratigraphic correlations between the Mediterranean and Paratethys regions. Here, we present magnetostratigraphic ages for the Upper Miocene to Pliocene deposits of the southern Carpathian foredeep in Romania. These ages are in good agreement with those recently obtained from the eastern Carpathian foredeep and define a new chronology for the eastern Paratethys. The Meotian/Pontian boundary is not biostratigraphically constrained in our sections, but according to the geological map of the region arrives at ∼5.8 Ma. The Pontian/Dacian boundary is dated at c. 4.8 Ma and the Dacian/Romanian boundary at c. 4.1 Ma. The main part of the MSC (5.96–5.33 Ma) is thus represented by the Pontian Stage, but the observed palaeoenvironmental and biostratigraphic changes in our sections of the eastern Paratethys do not indicate any relation with the dramatic desiccation and reflooding events of the Mediterranean.     

Sea-level fluctuations on the northern shelf of the Eastern Paratethys in the Oligocene-Neogene

Sea-level fluctuations in the terminal Eocene, Oligocene, and Neogene of the Eastern Paratethys are quantitatively assessed on the basis of facies and old coastlines traced on the northern platform shelf, levels of river valley incisions, and the study of seismic profiles. The first data massif allows the characterization and correlation of transgression stages in the history of the Eastern Paratethys. The greatest transgressions fall within the first half of the Late Eocene, mid-Early Oligocene, initial Late Oligocene, initial Early Miocene, the initial Tchokrakian, Karaganian and Sarmatian in the Middle Miocene, the middle and late Sarmatian and early Pontian in the Late Miocene, and the Akchagylian in the Caspian basin of the Pliocene. In contrast, the greatest incisions of northern rivers running from the platform allow us to establish the time and extent of the main declines in the base levels of the erosion. Maximal incisions date back to the terminal Eocene-initial Oligocene, terminal Solenovian time in the terminal Rupelian, the terminal Maikop in the Early Miocene, the terminal Sarmatian and middle Pontian in the Late Miocene, and the Early Pliocene in the Caspian basin. Large regressions also formed unconformity surfaces, traced on seismic profiles as erosion boundaries of several orders. The surfaces are confined to the Eocene/Oligocene boundary, middle and late Maikop, Sarmatian/Meotian boundary, middle Pontian, and terminal Miocene-initial Pliocene, as well as being traced even in the most deep-water basins. The synthesis of these data suggests a preliminary version for the curve of transgression-regression cyclicity. Its correlation with the eustatic curve shows their similarity only in the lower part-prior to the initial Middle Miocene, when Paratethys became a semi-closed basin.     

Cyclostratigraphy of Pontian deposits of the Eastern Paratethys (Zheleznyi Rog section,Taman Region)

The first data on the cyclostratigraphy of Pontian deposits of the Eastern Paratethys were obtained by studying the magnetic susceptibility of Upper Miocene rocks of the Zheleznyi Rog section in the Taman Region. Based on statistical methods, using the Lomb-Scargle and REDFIT periodograms, cycles related to long-period insolation oscillations (precession of the Earth’s orbit and variations in Earth’s axial tilt) were revealed. It is proposed that a hiatus occurred (about 150000–200000 years) at the Novorossian/Portaferian boundary (Lower Pontian/Upper Pontian) due to the onset of the maximum Messinian Salinity Crisis.     

鄂尔多斯盆地三叠系延长组长8—长7油层组高分辨率层序地层格架及其地质意义

鄂尔多斯盆地三叠系长8—长7油层组位于延长组中下部,代表湖盆最大扩张期,主要属于湖成三角洲相。运用高分辨率层序地层学原理,详细分析了鄂尔多斯盆地三叠系延长组长8—长7油层组地层沉积的基准面旋回特征,识别出1个长期旋回、3个中期旋回(MSC3、MSC4、MSC5)和15~25个短期旋回,分析得出长8油层组为三角洲环境,到长7油层组则演变为半深—深湖环境。3个中期旋回当中,MSC3、MSC4是以上升半旋回为主的不对称旋回,并在MSC4上升半旋回顶部形成盆地最大湖泛面,MSC5以下降半旋回为主的不对称旋回,发育浊积扇。对不同井基准面旋回的分析得出:储集层段多发育于短期基准面上升半旋回的水下分流河道、河口坝和浊流沉积砂体中,且砂体与前三角洲泥构成的烃源岩相匹配,形成岩性油气藏。运用高分辨率层序地层学原理建立地层格架对指导鄂尔多斯盆地延长组油气勘探具有重要指导意义。     

Maeotian mammalian localities of Eastern Paratethys: Magnetochronology and position in European continental scales

The Maeotian of Eastern Paratethys corresponds to the interval of the magnetochronological scale from the base of the subchron C4Ar2n to upper parts of the Chron C4n (9.6–7.5 Ma). Fission-track dates of Maeotian deposits are in general agreement with paleomagnetic chronology. In the continental stratigraphic scale of Western Europe this interval corresponds to zones MN10 (save the lowermost parts), MN11, and MN12 (upper part). Taking into account age estimates of MN zones boundaries established in Western Europe, the East European mammalian localities of Ukraine and Moldova can be stratified as follows: MN10, Raspopeni, Grebeniki, Novaya Emetovka 1, ?lower bed of Ciobruci; MN11, Novaya Emetovka 2; MN12, Cimislia, Ciobruci upper bed, Cherevichnoe, Tudorovo, Dzedzvtakhevi, and sites in the lower Pontian deposits. The faunal criteria used to distinguish MN zones in Western Europe cannot be completely applied to sites of the Eastern Paratethys because of paleozoogeographic distinctions between West and East European provinces. Specific criteria of zone boundaries definitions should be developed for the East European province.     

The Antarctic viewpoint of the Central Paratethys: cause, timing, and duration of a deep valley incision in the Middle Miocene Alpine–Carpathian Foredeep of Lower Austria

Global, glacio-eustatic sea-level changes massively influenced the depositional history of the Central Paratethyan region. Here, we correlate Middle Miocene global δ¹⁸O-shifts with ice volume changes on Antarctica and sea-level changes with corresponding phases of erosion (valley incision) and deposition in the Lower Austrian part of the Alpine–Carpathian Foredeep. This allows the exact dating of the valley formation. Two periods of positive δ¹⁸O-shifts resulted in sea-level drops of about 60 and 40 m, respectively. The first drop in the late Langhian (middle Badenian) at c. 13.9 Ma (Mi3b) was fast and caused severe erosion on the emerged foredeep. In a second, less pronounced step around 13.0 Ma (Mi4) in the middle Serravallian (late Badenian), the base level was further deepened after a period of alternating erosion and deposition. The combined sea-level change (80–120 m) fits well with the maximum thickness of Sarmatian sediments drilled within incised valley (110 m). The global sea-level falls affected not only the geological history of the foredeep. The intensive erosion (valley incision) is combined with delta progradation in the adjacent Vienna Basin. Due to this massive sea-level drop, the interruption of marine connections resulted in vast salt deposits and faunal crises within the Central Paratethys during this time.     

Sedimentology and sequence stratigraphy of a retrogradational fan-delta system within Lower Triassic in the Mabei area,Junggar Basin (northwestern China)

The sedimentology and sequence stratigraphy of a retrogradational fan-delta system within Lower Triassic in the Mabei area of Junggar Basin in northwestern China were investigated using seismic, well log, and core data, complemented by the modern deposition and a flume tank experiment. The Lower Triassic in the Mabei area is dominated by fan deltas, which are composed of fan-delta plain (including subaerial debris flow, braided channel, conglomerate overbank, and floodplain), fan-delta front (including conglomerate shoal and sandy shoal), and prodelta. The braided channels form during the low flood period. The conglomerate overbanks form during the flood period and occupy most part of the fan-delta plain. The conglomerate shoals and sandy shoals form by a sheet flow prograding into lakes and occur as a sheet. The braided channels, conglomerate shoals, and sandy shoals are easy to form high-porosity reservoirs. One long-term base level cycles (LSC1), three middle-term base level cycles (MSC1, MSC2, and MSC3), and fifteen short-term base level cycles are identified. MSC1 is dominated by the fan-delta plain; MSC2 is dominated by the fan-delta front; and MSC3 is dominated by the fan-delta front and prodelta. The stratigraphy shows a proximal-middle-distal trend demonstrating an overall retrogradation stacking pattern. The sequence architecture is controlled by an interplay between lake level changes and sediment supply. The quick rise in the lake level and the creation of accommodation outpacing the rate of sediment supply result in a retrogradational fan-delta syste.     

A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin

Oligocene–Miocene chronostratigraphic correlations within the Paratethys domain are still highly controversial. This study focuses on the late Early Miocene of the Swiss and S-German Molasse Basin (Late Burdigalian, Ottnangian–Karpatian). Previous studies have published different chronologies for this time interval that is represented by the biostratigraphically well constrained Upper Marine Molasse (OMM, lower and middle Ottnangian), Upper Brackish Molasse (OBM, Grimmelfingen and Kirchberg Formations, middle and upper Ottnangian to lower Karpatian, MN 4a–MN 4b) and Upper Freshwater Molasse (OSM, Karpatian–Badenian, MN 5). Here, we suggest a new chronostratigraphic framework, based on integrated magneto-litho-biostratigraphic studies on four sections and three boreholes. Our data indicate that the OBM comprises chrons 5D.1r and 5Dn (Grimmelfingen Fm), chron 5Cr (lower Kirchberg Fm) and the oldest part of chron 5Cn.3n (upper Kirchberg Fm). The OSM begins during chron 5Cn.3n, continues through 5Cn, and includes a long reversed segment that can be correlated to chron 5Br. The OMM-OSM transition was completed at 16.0 Ma in the Swiss Molasse Basin, while the OBM-OSM changeover ended at 16.6 Ma in the S-German Molasse Basin. As the lower Kirchberg Fm represents a facies of the Ottnangian, our data suggest that the Ottnangian–Karpatian boundary in the Molasse Basin is approximately at 16.8 Ma, close to the 5Cr–5Cn.3n magnetic reversal, and thus 0.4 Myr younger than the inferred age of 17.2 Ma used in recent Paratethys time scales. Notably, this would not be problematic for the Paratethys stratigraphy, because chron 5Cr is mainly represented by a sedimentation gap in the Central Paratethys. We also realise, however, that additional data is still required to definitely solve the age debate concerning this intriguing time interval in the North Alpine Foreland Basin. We dedicate this work to our dear friend and colleague Jean-Pierre Berger (8 July 1956–18 January 2012).     

Paleoceanography and climate of the Badenian (Middle Miocene, 16.4–13.0 Ma) in the Central Paratethys based on foraminifera and stable isotope (δ18O and δ13C) evidence

Benthic foraminifera and stable isotopes analyses revealed changes emerging in the paleoceanographic scenery in the Paratethys. The percentage of inbenthic, oxyphylic taxa and diversity in the benthic foraminiferal assemblage showed increasing food supply (organic matter), decreasing oxygen level and growing stress on the sea floor. Oxygen isotopes measured in planktonic and benthic foraminifera pointed to strengthening stratification during the Badenian period. The carbon isotopes indicated intensified accumulation of light marine organic matter. This increasing stratification trend is especially pronounced by Late Badenian (13.5–13 Ma) when surface water oxygen isotope values are rather negative. A simple two-layer circulation model was worked out for the Badenian Paratethys explaining these characteristic environmental changes. An antiestuarine (lagoonal) circulation is assumed for the Central Paratethys during the Early (16.4–15 Ma) and mid Badenian (15–13.5 Ma). The mid Badenian period of time comprises the short episode of evaporite formation in the Carpathian Foredeep and the Transylvanian Basin. Evidence presented here supported a reversal of circulation to estuarine type after the deposition of salts by Late Badenian (13.5–13 Ma). The Early Badenian antiestuarine circulation is suggested to associate with the high temperatures of the Mid-Miocene Climatic Optimum, and the Late Badenian estuarine circulation with the cooler period following it.     

Relationship between erosion surfaces and Late Miocene Salinity Crisis deposits in the Valencia Basin (northwestern Mediterranean): evidence for an early sea‐level fall

Although the main events of the Messinian Salinity Crisis (MSC) are today mostly known, the exact succession of the different episodes remains unclear. This, in particular, is because (i) no drilling has reached the base of the Salt, and thus the onset of the MSC in the basins is unknown, and (ii) lateral correlations between the margins and the deep basins are missing. The Valencia Basin, which is intermediate in depth between the marginal basins and the deep basins, is an ideal location for studying the transitional domain. It displays the relationships between the polygenic erosion on the margins, the deposition of the thin Upper Evaporites bracketed by basal and top erosion surfaces in the central part of the basin, and the thick MSC sequence in the deep oceanic Provençal Basin. Early detrital deposits located below the MSC sequence of the deep basin suggest an early lowering of the sea level prior to the MSC desiccation.     

Middle-Upper Miocene stratigraphy of the Taman Peninsula, Eastern Paratethys

The stratigraphy of the Taman Peninsula is defined using the sections at Zelensky Hill ?? Panagia, Popov Kamen, Taman and Zheleznyi Rog. The stratigraphy is constructed from distribution of mollusks, foraminifers, nannofossils, diatoms, and organic-walled phytoplankton, as well as incorporating paleomagnetic data. The occurrence of oceanic diatom species in the Middle-Upper Sarmatian, Maeotian and Lower Pontian makes a direct correlation possible between the sections studied, the Mediterranean basin and oceanic zonation. The new data on planktonic and benthic biotic groups suggests a pulsating connection of the Eastern Paratethys with the open marine basins, especially during transitional intervals within constant environments. Comprehensive studies of the Chokrakian-Kimmerian microbiota provide evidence for several levels of marine microbiotic associations that are related to short-term marine invasions. The biotic and paleomagnetic data of the Taman Peninsula sections give a more comprehensive, but sometimes a controversial picture on the Eastern Paratethys history and the nature of its relationship with the adjacent marine basins.     

陆相断陷湖盆基准面旋回对沉积砂体的控制 ——以海拉尔盆地贝尔凹陷贝西地区为例

依据岩芯、录井及测井等方面的资料,对海拉尔盆地贝尔凹陷贝西地区南屯组内各级次基准面旋回的演化规律及高分辨率层序发育模式进行研究。研究结果表明:研究区南屯组发育有5类层序界面,共可划分为3个长期基准面旋回和12个中期基准面旋回,地层厚度受古地貌和基准面升降的双重控制,其中古地貌对于南屯组的厚度变化影响较大,形成了由"南厚-北薄"逐渐过渡为"北厚-南薄"的地层发育模式;以南一段下部LSC1为例分析了基准面升降对相序、相域及源储分布的控制作用,认为在LSC1沉积时期,基准面的变化共经历了早期的缓慢上升阶段和快速上升阶段、中期的缓慢上升至缓慢下降阶段以及末期的快速下降阶段,主要发育有扇三角洲、湖底扇和湖泊沉积体系。其中储集体主要发育在MSC1、MSC2和MSC5沉积时期内,类型为向上变深型非对称中期基准面旋回在上升早期所形成的厚层分流河道砂体,砂体物性较好、几何形态以多层式为主。MSC3沉积时期为最大湖泛期,深湖相泥岩广泛分布、为优质烃源岩层,源储上下紧邻、成藏条件优越,是有利的勘探层系。     

华北盆地西部太原组遗迹化石组合对古水深变化的响应*

通过对豫西—晋中南地区上石炭统—下二叠统太原组碳酸盐岩中遗迹化石的组成、产状及分布特征的研究,结合部分生物潜穴中Sr含量、Sr/Ba值、1000×(Sr/Ca)值和δ¹³C值,得到不同地区太原组沉积期古水深的变化曲线,建立了3种不同水深的遗迹组合: (1)Nereites-Chondrites遗迹组合,产生于氧化还原界面附近水体相对较深的浅海下部环境;(2)Zoophycos-Teichichnus遗迹组合,形成于浪基面至氧化还原界面之间的浅海中部沉积环境;(3)Zoophycos-Thalassinoides遗迹组合,出现在平均海平面至浪基面之间的浅海上部或较为闭塞的海湾潟湖沉积环境。依据这3种遗迹组合在各剖面上的变化特征和古水深,认为在豫西—晋中南地区太原组沉积期发生过2次较大规模的海侵。这一成果为精细研究华北西部地区太原期沉积环境演变规律及对比地层提供了生物遗迹学方面的依据。     

Biostratigraphical and palaeoenvironmental implications of isotopic studies (18O, 13C) of middle Miocene (Badenian) foraminifers in the Central Paratethys

The cause of the middle Miocene Badenian salinity crisis in the Central Paratethys is addressed by examining the palaeotemperature evolution of Badenian waters before and after the deposition of evaporites. Selected foraminifer taxa ( Globigerinoides spp., Globigerina bulloides , and Uvigerina ) characterizing, respectively, the near-surface, intermediate, and bottom layers of the water column, were studied in two boreholes of SW Poland. The δ¹⁸O and δ¹³C values for these taxa show distinct differences which can be explained by the temperature difference between surface and bottom waters during deposition. These values also show temporal changes corresponding to the water temperature evolution in the Badenian basin. Different and quickly changing environmental conditions have been inferred from changes in foraminifer assemblages. They explain why biostratigraphic subdivisions based on well-recognized assemblages are the most accurate approach for determining the biostratigraphy of middle Miocene deposits in the Central Paratethys. The results of isotopic studies indicate that evaporites occur in a part of the Badenian section that was characterized by the lowest temperatures in the studied sections.     

Extreme aridity prior to lake expansion deciphered from facies evolution in the Miocene Ili Basin,south‐east Kazakhstan

Central Asia witnessed progressive aridification during the Miocene, commonly related to mountain uplift, the Paratethys retreat and global climate cooling. However, the formation of Miocene lakes in Central Asia seems to oppose drier conditions, suggesting that the precise timing, extent and forcing of the aridification is still not well constrained. This study presents a facies model for the alluvial–lacustrine part of the Middle to Late Miocene of the Ili Basin, obtained from two successions. The model enables the semi‐quantitative assessment of regional water level and salinity, and characterizes the control of water level on evaporite formation and diagenesis. Both the proximal Kendyrlisai and the distal Aktau successions show an overall increase in water availability from dry mudflat deposits to lacustrine sedimentation with a transitional playa phase. Increasing evaporation rates outpaced the water supply and caused groundwater salinization. Subsequent lake expansion coincided with a basin‐wide desalinization and required a shift to a positive water budget. A climatic control of the hydrological evolution is inferred due to abrupt salinization and a minor tectonic influence. The long‐term water accumulation is probably related to the hydrological closure of the basin in the early Middle Miocene (15·3 Ma). Starting at 14·3 Ma, the step‐wise salinization occurred simultaneously with the global cooling of the Miocene Climate Transition. The Miocene Climate Transition led to extreme aridity in the Ili Basin, highlighted by the early diagenetic formation of displacive anhydrite in the basin centre. The expansion of the freshwater lake (12·7 to 11·5 Ma) was possibly promoted by lower evaporation rates due to decreasing air temperatures in the Ili Basin after the Miocene Climate Transition. The extreme aridity in the Ili Basin is interpreted as a continental counterpart to the Badenian Salinity Crisis in the Central Paratethys. This emphasizes the role of atmospheric forcing on evaporite sedimentation across Eurasia during the Middle Miocene.     

Central Paratethys paleoenvironment during the Badenian (Middle Miocene): evidence from foraminifera and stable isotope (δ<Superscript>13</Superscript>C and δ<Superscript>18</Superscript>O) study in the Vienna Basin (Slovakia)

Stable isotope data of the foraminiferal carbonate shells and bulk sediment samples from the Central Paratethys were investigated to contribute to better knowledge of the paleoenvironmental changes in Badenian (Middle Miocene). Five benthic (Uvigerina semiornata, U. aculeata, Ammonia beccarii, Elphidium sp. and Heterolepa dutemplei) and three planktonic taxa (Globigerina bulloides, G. diplostoma and Globigerinoides trilobus), characterising the bottom, intermediate and superficial layers of the water column, were selected from the Vienna Basin (W Slovakia). The foraminiferal fauna and its isotope signal point out to temperature-stratified, nutrient-rich and consequently less-oxygenated marine water during the Middle/Late Badenian. Negative carbon isotope ratios indicate increased input of ¹²C-enriched organic matter to the bottom of the Vienna Basin. Positive benthic δ¹⁸O implies that the global cooling tendency recorded in the Middle Miocene has also affected the intramountain Vienna Basin. In this time, the Central Paratethys has been in the process of isolation. Our stable isotope trend suggests that the communication with Mediterranean Sea has been still more or less active on the south of Vienna Basin (Slovak part) in the Late Badenian, whereas the seawater exchange towards north was apparently reduced already during the Middle Badenian.     

Foraminiferal record of marine transgression during deposition of the Middle Miocene Badenian evaporites in Central Paratethys (Borków section,Polish Carpathian Foredeep)

Benthic and planktonic foraminifera from a marly clay intercalation sandwiched between mid‐Badenian (Middle Miocene) gypsum deposited in an environment of an evaporitic shoal (<1 m deep) at Borków (southern Poland) indicate a major marine flooding event in the previously isolated Carpathian Foredeep Basin (Central Paratethys). After this very short‐term environmental change, benthic foraminifers started to colonize a new niche which was previously defaunated, and the pattern of benthic foraminiferal colonization is similar to that related to the reflooding which terminated the Badenian evaporite deposition. The benthic foraminifer assemblages are composed of pioneer, opportunistic, r‐selected species dominated by elphidiids. The connection of the Carpathian Foredeep Basin with the marine reservoir was short‐lived. The marly clay intercalations in evaporite sequences originating in bared basins can thus register major environmental changes.     

墙角型陡坡带岩性圈闭油气成藏条件研究——以渤海湾盆地石南陡坡带中段BZ3区古近系东营组为例

BZ3区西部陡坡带位于渤海湾盆地渤中凹陷石南陡坡带中段,构造上处于石臼坨凸起与凸起倾没端相交的夹角地带,石南一号断裂和石南二号断裂在此处相交,形成由多个复杂断阶所组成的复式墙角型陡坡坡折带.通过高精度层序地层学研究认为,BZ3区东营组东二下亚段发育3个4～5级基准面旋回,每个基准面旋回的上升半旋回的下部和下降半旋回均控...     

The myth of the brackish Sarmatian Sea

The biota of the 1.5 Ma period of the Middle Miocene Sarmatian of the Central Paratethys lack stenohaline components. This was the reason to interpret the Sarmatian stage as transitional between the marine Badenian and the lacustrine Pannonian stages. However, our new data indicate that brackish water conditions could not have prevailed. Sarmatian foraminifera, molluscs, serpulids, bryozoans, dasycladacean and corallinacean algae as well as diatoms clearly indicate normal marine conditions for the entire Sarmatian. During the Lower Sarmatian, however, a sea-level lowstand forced the development of many marginal marine environments. During the Late Sarmatian a highly productive carbonate factory of oolite shoals, mass-occurrences of thick-shelled molluscs and larger foraminifera, as well as marine cements clearly point to normal marine to hypersaline conditions. This trend is not restricted to the western margin of the Pannonian Basin System but can be observed in the entire Central and even Eastern Paratethys.     

From Tethys to Eastern Paratethys: Oligocene depositional environments, paleoecology and paleobiogeography of the Thrace Basin (NW Turkey)

The Oligocene depositional history of the Thrace Basin documents a unique paleogeographic position at a junction between the Western Tethys and the Eastern Paratethys. As part of the Tethys, shallow marine carbonate platforms prevailed during the Eocene. Subsequently, a three-staged process of isolation started with the Oligocene. During the Early Rupelian, the Thrace Basin was still part of the Western Tethys, indicated by typical Western Tethyan marine assemblages. The isolation from the Tethys during the Early Oligocene is reflected by oolite formation and endemic Eastern Paratethyan faunas of the Solenovian stage. The third phase reflects an increasing continentalisation of the Thrace Basin with widespread coastal swamps during the Late Solenovian. The mollusc assemblages are predominated by mangrove dwelling taxa and the mangrove plant Avicennia is recorded in the pollen spectra. The final continentalisation is indicated by the replacement of the coastal swamps by pure freshwater swamps and fluvial plains during the Late Oligocene (mammal zone MP 26). This paleogeographic affiliation of the Thrace Basin with the Eastern Paratethys after ~32 Ma contrasts all currently used reconstructions which treat the basin as embayment of the Eastern Mediterranean basin.