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.     

Cyclostratigraphic dating in the Lower Badenian (Middle Miocene) of the Vienna Basin (Austria): the Baden-Sooss core

The scientific borehole Baden-Sooss penetrates a succession of Badenian (Langhian, Middle Miocene) sediments at the type locality of the Badenian, the old brickyard Baden-Sooss in the Vienna Basin. The sedimentary succession of the 102-m-cored interval consists of more than 95% bioturbated, medium-to-dark gray marly shales with carbonate contents between 11 and 25% and organic carbon contents between 0.35 and 0.65%. Biostratigraphic investigations on foraminifera (mainly lower part of Upper Lagenid Zone) and calcareous nannoplankton (standard zone NN5) indicate an early Badenian (Langhian) age. Cycles in carbonate content, organic carbon content, and magnetic susceptibility have been identified by power spectra analysis. Correlations between the three variables are extremely significant. Using cross-correlation, periods around 40 m correlate significantly with the 100 kyr⁻¹ eccentricity cycle, the ∼20 m periods with the obliquity cycle, and the 15 to 11-m periods with both precession cycles. Wavelet transformation and decomposition of composite periodic functions were used to obtain the position of the cycle peaks in the profile. Cross-correlation with orbital cycles (La2004) dates the Baden-Sooss core between −14.379 ± 1 and −14.142 my ± 9 kyr.     

Middle to late Miocene sequence stratigraphy of the Transylvanian Basin (Romania)

The history of Middle to Late Miocene evolution of the Transylvanian Basin was determined by the bordering Carpathian orogen evolution, the tectonic events being well recorded by the sedimentary history. The basin evolved in a back-arc setting, under a regional, compressional stress field. The major tectonic events produced during the Late Sarmatian and Post-Pannonian were related to the reactivation of the pre-Badenian fault systems. The Transylvanian Basin got uplifted after the Late Pannonian (? during the Pliocene), and at least 500 m of sedimentary cover was eroded.

Based on seismic and well-log interpretation, core and outcrop sedimentology, and microfauna, eight sequences were defined. The early Middle Miocene sequences are roughly synchronous to five 3rd order global sea-level cycles. Most of the recognized sequence boundaries are enhanced by regional tectonic events. The sedimentary evolution was also strongly influenced by salt-tectonics, active starting with the Late Sarmatian.

Two sequences were identified in the Lower Badenian deposits. The third sequence (late Early Badenian to early Mid Badenian) preserves information about deeper shelf settings. The lowstand of the following sequence was responsible for the deposition of the salt formation (late Mid Badenian), an important lithostratigraphic marker in the sedimentary record of the basin. In general, the Upper Badenian deposits (parts of the 4th and 5th sequences) belong to deep marine submarine fan systems. The Sarmatian (partially 5th, 6th and partially 7th sequences) was characterized by diverse salinity conditions, stretching from brackish to hypersaline, and by high tectonic instability, which induced several significant relative sea-level falls. During that time, deltaic (north) and fandeltaic (east) systems fed submarine fans, stacked between salt-related submarine heights (“channeled” deep-marine depocenters). Most of the Pannonian deposits (partially 7th and 8th sequences) belong to submarine fan systems, but shallower facies were also found in the western and eastern part of the basin.     

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.     

Backstripping dip-slip fault histories: apparent slip rates for the Miocene of the Vienna Basin

Backstripped basement subsidence histories from both the hanging wall and the footwall blocks adjacent to synsedimentary normal faults can be used to reconstruct the sense of fault motion through time and to quantify the vertical component of fault slip. Consequently, apparent dip-slip rates of faults can be calculated for each stratigraphic interval and times of increased fault activity can be distinguished. An application of this method to well data along a transect through the central part of the Miocene Vienna Basin indicates that two distinct phases of faulting occurred during the Karpatian, with rates as high as 3000 m Myr⁻¹. Changes in the sense of movements during the early Karpatian and the earliest Badenian indicate a major rearrangement in the fault patterns. During the early Sarmatian another short pulse of dip-slip is recorded along the investigated faults.     

Basin formation during the post-collisional evolution of the Eastern Alps: the example of the Lavanttal Basin

The Miocene Lavanttal Basin formed in the Eastern Alps during extrusion of crustal blocks towards the east. In contrast to basins, which formed contemporaneously along the strike-slip faults of the Noric Depression and on top of the moving blocks (Styrian Basin), little is known about the Lavanttal Basin. In this paper geophysical, sedimentological, and structural data are used to study structure and evolution of the Lavanttal Basin. The eastern margin of the 2-km-deep basin is formed by the WNW trending Koralm Fault. The geometry of the gently dipping western basin flank shows that the present-day basin is only a remnant of a former significantly larger basin. Late Early (Karpatian) and early Middle Miocene (Badenian) pull-apart phases initiated basin formation and deposition of thick fluvial (Granitztal Beds), lacustrine, and marine (Mühldorf Fm.) sediments. The Mühldorf Fm. represents the Lower Badenian cycle TB2.4. Another flooding event caused brackish environments in late Middle Miocene (Early Sarmatian) time, whereas freshwater environments existed in Late Sarmatian time. The coal-bearing Sarmatian succession is subdivided into four fourth-order sequences. The number of sequences suggests that the effect of tectonic subsidence was overruled by sea-level fluctuations during Sarmatian time. Increased relief energy caused by Early Pannonian pull-apart activity initiated deposition of thick fluvial sediments. The present-day shape of the basin is a result of young (Plio-/Pleistocene) basin inversion. In contrast to the multi-stage Lavanttal Basin, basins along the Noric Depression show a single-stage history. Similarities between the Lavanttal and Styrian basins exist in Early Badenian and Early Sarmatian times.     

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.     

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.     

Badenian (Middle Miocene) basin development in SW Hungary: subsidence history based on quantitative paleobathymetry of foraminifera

A quantitative paleobathymetric study of Badenian foraminifera was carried out from Tekeres-1 and Tengelic-2 boreholes, north of the Mecsek Mts., SW Hungary. Paleobathymetric data, based on plankton/benthos ratio provided input for the analysis of the subsidence history. The biostratigraphic framework is mainly provided by calcareous nannoplankton (zones NN5-NN7). Changes in sedimentation rates are also considered, partly calculated from number of benthos per unit sediment, and partly estimated from the changes of lithofacies. Relative sea-level changes are calculated from changes of paleowater depth and coeval sedimentary thickness. The result is examined as the sum of accommodation space created by subsidence and eustasy. In that period of time eustatic changes were about an order of magnitude smaller than changes created by movements of the basin floor. According to our model in early Badenian (up to the half of NN5 nannozone) a very rapid transtension-related subsidence of about 500 m occurred. This was interrupted by a short period of uplift of minor magnitude at about the first third of NN5 zone; thereafter, subsidence continued and the basin floor reached its deepest position. Still within the NN5 nannozone (Early Badenian) a significant uplift occurred, terminating the life of the deep basin. The Late Badenian (NN6) is characterized by a relatively small rate of subsidence and presumably quiet tectonism. During this period bathymetric changes are thought to be controlled primarily by eustatic changes. The first uplift - only interrupting subsidence - is regarded as the result of the change of the local stress field because of convergence along the curvature of strike slip faults. The second uplift, which stopped the subsidence of the basin floor is thought to be of a regional character and is attributed to the compression generated between Tisza and Alcapa tectonic units.     

Tectonics and sedimentation in the Fohnsdorf-Seckau Basin (Miocene, Austria): from a pull-apart basin to a half-graben

The Miocene intramontane Fohnsdorf-Seckau Basin is situated at the junction of the sinistral Mur-Mürz-fault system and the dextral Pöls-Lavanttal fault system. The basin comprises a 2,400-m-thick coal-bearing fluviodeltaic-lacustrine succession (Lower to Middle Miocene, Upper Karpatian?/Lower Badenian) which is overlain by a 1,000-m-thick alluvio-deltaic conglomeratic succession (Apfelberg Formation, ?Middle/Upper Badenian) in the south. A three-stage model for the basin evolution has been reconstructed from structural analysis and basin fill geometries. During a first pull-apart phase, subsidence occurred along ENE-trending, sinistral strike-slip faults of the Mur-Mürz fault system and NE-SW to N-S-trending normal faults, forming a composite pull-apart basin between overstepping en-echelon strike-slip faults. The Seckau and Fohnsdorf sub-basins are considered as two adjacent pull-aparts which merged into one basin. During the second phase, N-S to NNW-SSE extension and normal faulting along the southern basin margin fault formed a half-graben, filled by wedge-shaped alluvial strata (Apfelberg Formation). During the third phase, after the end of basin sedimentation, the dextral Pöls-Lavanttal fault system reshaped the western basin margin into a positive flower structure.     

Mineralogical characteristics of upper Jurassic Mikulov Marls,the Czech Republic,in relation to their thermal maturity

The Upper Jurassic Marls of Mikulov present a formation that is considered to be the most promising strata to produce hydrocarbons in the Vienna basin. The marls are composed of dark pelagic marlstones that frequently contain layers of limestone with thickness reaching several hundreds of meters. Twenty-seven core samples from selected wells located in the south-eastern portion of the Czech Republic representing depths ranging from 2300 to 4500 m were analyzed by x-ray diffraction to assess bulk mineralogy and the progress of smectite illitization.Bulk mineralogy of the Mikulov Marls comprises carbonates (mean value = 54.4 mass%), clay minerals (26.6 mass%), quartz (15.0 mass%), and feldspar (1.6 mean%). In the decreasing order, the clay mineral fraction is composed of illite/mica, kaolinite, illite-smectite, and chlorite. The amount of smectite in illite-smectite decreases with depth from 70% to 28%. There is a change from random to ordered interstratification at the depth of 3300 m. The transition from short-range ordering (R1) to long-range ordering (R3) occurs at depths greater than 4,500 m.There was a good correspondence between thermal maturity parameters: the percentage of smectite in illite-smectite structures and vitrinite reflectance as a parameter of organic matter. The increase of the metamorphic grade was compared in respect to the geothermal gradient with adjacent basins.     

Carboniferous–Permian volcanic evolution in Central Europe—U/Pb ages of volcanic rocks in Saxony (Germany) and northern Bohemia (Czech Republic)

Nine SHRIMP U/Pb ages on zircon and two Pb/Pb single zircon ages have been determined from Late Paleozoic volcanic rocks from Saxony and northern Bohemia. Samples came from the Teplice-Altenberg Volcanic Complex, the Meissen Volcanic Complex, the Chemnitz Basin, the Döhlen Basin, the Brandov-Olbernhau Basin, and the North Saxon Volcanic Complex. The Teplice-Altenberg Volcanic Complex is subdivided into an early Namurian phase (Mikulov Ignimbrite, 326.8 ± 4.3 Ma), thus older than assumed by previous studies, and a late caldera-forming phase (Teplice Ignimbrite, 308.8 ± 4.9 Ma). The age of the latter, however, is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint. The Leutewitz Ignimbrite, product of an early explosive volcanic episode of the Meissen Volcanic Complex yielded an age of 302.9 ± 2.5 Ma (Stephanian A). Volcanic rocks intercalated in the Brandov-Olbernhau Basin (BOB, 302 ± 2.8 Ma), Chemnitz Basin (CB, 296.6 ± 3.0 Ma), Döhlen Basin (DB, 296 ± 3.0 Ma), and the North Saxon Volcanic Complex (NSVC, c. 300–290 Ma) yielded well-constrained Stephanian to Sakmarian ages. The largest Late Paleozoic ignimbrite-forming eruption in Central Europe, the Rochlitz Ignimbrite, has a well-defined middle Asselian age of 294.4 ± 1.8 Ma. Ages of palingenic zircon revealed that the Namurian-Westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous Paleozoic geodynamic phases. The Precambrian inherited ages support the chronostratigraphic structure assumed for the Saxo-Thuringian Zone of the Variscan Orogen. The present results help to improve the chronostratigraphic allocation of the Late Paleozoic volcanic zones in Central Europe. At the same time, the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the Variscan Orogeny.     

Biostratigraphy and sedimentology of the Fluviatile Untere Serie (Early and Middle Miocene) in the central part of the North Alpine Foreland Basin: implications for palaeoenvironment and climate

The Early to Middle Miocene Fluviatile Untere Serie lithostratigraphic unit of the Upper Freshwater Molasse (UFM) in the North Alpine Foreland Basin (NAFB) crops out in a 40 m long section at Untereichen-Altenstadt (central part of the NAFB). This section yields a unique superposition of two vertebrate assemblages belonging to different biostratigraphic units: early part OSM C + D (Karpatian) and OSM E (Early Badenian). Detailed taxonomic analyses reveal different diversity patterns in the two assemblages. Nine small mammal and six ectothermic vertebrate taxa occur in the older level UA 540 m, while 20 small mammal and 23 ectothermic vertebrate taxa are recorded for the younger level UA 565 m. From the latter locality comes a small-sized representative of the biostratigraphically significant Megacricetodon lappi lineage. This evolutionary level has not been documented previously for the eastern part of the NAFB. Bioclimatic analysis combined with lithofacies and architectural element analysis indicates that significant changes in the fluvial sedimentation style, surface-water runoff and tectonics occurred between the Early Karpatian and Early Badenian. A meandering fluvial system (marly unit) is erosively overlain by sandy braided river deposits (sandy unit). Overbank deposits of the marly unit revealed that the older vertebrate fossil assemblage (UA 540 m) is deposited in an animal burrow that was presumably produced by owls. Both reptilian and mammalian taxa are indicative of a relatively open environment and dry, probably semi-arid climate. Conversely, vertebrates from the sandy unit (UA 565 m), which are accumulated in channel fill deposits, suggest closed as well as open habitats with a subtropical humid climate and mean annual rainfall of about 1,000 mm. According to the sequence stratigraphic analysis the marly unit is interpreted as a highstand-system-tract of the TB 2.2 global 3rd order sequence. The new results add support to the hypothesis that the erosional unconformity between both sedimentary units spanning the Karpatian-Badenian transition corresponds to the pre-Riesian hiatus, which has been interpreted as part of the Styrian Tectonic Phase, and was previously identified only in the eastern and northeastern part of the NAFB. The biostratigraphic data further indicate that this hiatus lasted longer in the eastern than in the central part of the basin.     

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.     

Geological results of deep exploration in the Vienna basin

The exploration for hydrocarbons in the deepest tectonic »floor« underneath the Vienna basin with depths of 6.5–8.5 km, was undertaken between 1977 and 1985 and based on several important conditions:

-The assumption that an autochthonous sedimentary cover lies upon the Crystalline Basement (Bohemian massif) below the Neogene basin infill and the Alpine-Carpathian nappes.

-Expressed high zones exist within the Vienna basin with exploration targets at depths reachable by drilling.

-The significant accumulation of oil- and gasfields m shallower position over the area of interest.

As a result of the 4 deep wells drilled for the abovementioned targets more information has been acquired concerning the stratigraphy, facies distribution and depth positions of the autochthonous Jurassic, Upper Cretaceous and Tertiary Molasse along the Eastern flank of the Crystalline basement spur of the Bohemian Massif. The allochthonous, Waschberg- und Flyschzone, both Alpine-Carpathian units underneath the Vienna basin, have been penetrated by these wells for the first time and the overthrust of the Calcareous Alps over the Flysch nappes has been proven (well Aderklaa UT1). Additional information about Neogene sedimentation and faulting was obtained. Drilling results made it possible to get a more comprehensive picture of the 3 tectonic »floors« of the Vienna basin, m detail represented by the Zistersdorf and Aderklaa profiles. Thick basin marls of the Upper Jurassic represent a large source potential for hydrocarbons. The favourable reservoir layers, detected in the Mesozoic sections of the foreland area have not been encountered here till now. A high supply of free hydrocarbons within the deepest floor must be assumed on the basis of many oil and gas shows, a major gas kick in Zistersdorf ÜTla and a limited oil production from a fractured zone along a thrustline in the Maustrenk ÜTla well, both occurring in an overpressured environment.     

Time calibration of sedimentary sections based on insolation cycles using combined cross-correlation: dating the gone Badenian stratotype (Middle Miocene, Paratethys, Vienna Basin, Austria) as an example

Cross-correlation between insolation intensities and a combination of sedimentary characters is introduced to obtain precise time calibration of sedimentary cycles. The first step is to transfer the section scale into ages using power spectra comparing the main periods with orbital cycles, while in the second step the standardized values of sedimentary signals are cross-correlated with the standardized insolation curve. As an example for the applicability of the method, we investigated calcium carbonate, organic carbon in a 9-m sampled section from the historical Badenian stratotype at Baden/Sooss (Lower Austria). Comparing courses of geochemical parameters between the historical stratotype and a nearby drilled 102-m scientific core resulted in continuation of the core section into the stratotype. Cross-correlation between magnetic susceptibility (MS) combined with the negatively correlated calcium carbonate content of the drilled section on the one side and summer solar insolation at 65° northern latitude on the other resulted in an extremely significant correlation between −14.221 and −13.982 Ma. This is younger than the before estimated time frame (−14.379 to −14.142 Ma) based on cross-correlation between MS and the orbital 100-kyr eccentricity and 41-kyr obliquity cycles. The direct continuation of the drilled section by the stratotype covering a time span of 17.7 kyr consequently dates the Badenian stratotype between −13.982 and −13.964 Ma. Therefore, the upper limit of the stratotype, assigned to the Early Badenian, puts it close to the Langhian/Seravallian boundary at −13.82 Ma, demonstrating the need for revising the Badenian stratigraphic subdivision based on orbital cycles, especially the middle Badenian Wielician substage.     

月球雨海盆地多环结构的厘定及其深部构造研究

雨海盆地是月球正面最大、月球上研究程度最高的多环结构撞击盆地,已有很多学者对其多环结构的边界进行恢复研究,但在多环结构最初始形状、多环位置/数量、盆地大小等方面,至今未能达成共识。本文利用GRAIL自由空气重力异常数据、LOLA激光测高数据进行了多源数据的融合,结果表明,雨海盆地是具有偏心圆的三环结构特点,其直径从外到内分别为1 500 km、1 100 km、665 km。基于欧拉反演结果研究表明,在雨海撞击盆地中部存在两种不同深度、构造运动性质及方向的断裂构造,即：(1)深度大于40 km,向下逐渐向内倾斜、延伸的深部断裂构造;(2)深度在40 km以内,由月表向下逐渐向外倾斜、延伸的浅部断裂构造。结合物质成分及地球物理特征的研究,雨海地区的地质构造演化过程可分为两个阶段：(1)在月球早期阶段(45~38.5亿年),主要以内动力地质作用即岩浆洋冷凝过程为主,形成了雨海盆地深度在40 km以下逐渐向内倾斜、延伸的构造断裂,其为本区在月球早期深部岩浆洋产生、分异及运移提供了通道,该构造断裂代表了雨海盆地撞击前的月球早期深部岩浆洋的构造地质演化阶段;(2)在月球晚期阶段(≤38.5亿年),主要以内、外动力地质作用并重,形成了雨海盆地深度在40 km以内逐渐向外倾斜、延伸的构造断裂,其应为本区不同期次的玄武质岩浆喷出或溢流到月表提供了运移通道,该构造断裂代表了雨海盆地撞击后的月球晚期不同期次玄武质岩浆喷发、充填溢流的月海岩浆活动作用的构造地质演化阶段。     

Integrated stratigraphy and 40Ar/39Ar chronology of the early to middle Miocene Upper Freshwater Molasse in western Bavaria (Germany)

A detailed integrated stratigraphic study (biostratigraphy and magnetostratigraphy) was carried out on five sections from the western part of the Bavarian Upper Freshwater Molasse of the North Alpine Foreland Basin (NAFB), greatly improving the chronostratigraphy of these sediments. The sections belong to the lithostratigraphic units Limnische Untere Serie (UL) and Fluviatile Untere Serie (UF) and contain 19 (mostly new) small-mammal bearing levels, significantly refining the local biostratigraphy. Radiometric ages obtained from glass shards from tuff horizons are used together with the biostratigraphic information for constructing and confirming the magnetostratigraphic correlation of the studied sections to the Astronomical Tuned Time Scale (ANTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the UL lithostratigraphic unit corresponds to the latest Ottnangian and the Early Karpatian, whereas the UF corresponds to the Karpatian and the Early Badenian. This indicates that the Brackish- to Freshwater Molasse transition already occurred during the late Ottnangian. The pre-Riesian hiatus occurred in the latest Karpatian and lower Early Badenian in Eastern Bavaria and Bohemia and in the Late Karpatian and earliest Badenian in Western Bavaria. The geochemical and Ar–Ar data of volcanic ashes suggest that highly evolved silicic magmas from a single volcano or volcanic center, characterized by a uniform Nd isotopic composition, erupted repetitively over the course of at least 1.6 Myr. Three phases of eruptive activity were identified at 16.1 ± 0.2 Ma (Zahling-2), 15.6 ± 0.4 Ma (Krumbad), and 14.5 ± 0.2 Ma (Heilsberg, Hegau). The correlation of the local biostratigraphic zonation to the ANTS04 enables further the characterization of both the Ottnangian–Karpatian and Karpatian–Badenian boundaries in the NAFB by small-mammal biostratigraphy. According to these results the Ottnangian–Karpatian boundary is contemporaneous with the first appearance datum of Megacricetodon bavaricus (in the size of the type population) and the first common occurrence of Keramidomys thaleri, whereas Ligerimys florancei, Melissiodon dominans and Prodeinotherium aff. bavaricum have been already disappeared during the late Ottnangian. The Karpatian–Badenian boundary is characterized by a significant size increase of the large Megacricetodon lineage and possibly a (re-)immigration of Prodeinotherium bavaricum.     

Seismic stratigraphy based chronostratigraphy (SSBC) of the Serbian Banat region of the Pannonian Basin

Seismic stratigraphy based chronostratigraphic (SSBC) analysis of the Serbian Banat region allows the delineation of the spatial and stratigraphic relationships of the generally regressive and shallowing upward Neogene depositional fill of a tectonically unstable central portion of the Pannonian Basin. When geometrically restored in time and space, the sediment dispersal directions, sediment source directions, types of sedimentation breaks and the tectonic events influencing basin evolution can be delineated. For such an analysis the time-transgressive lithostratigraphic units used in the neighbouring Hungarian part of the Pannonian Basin are conveniently introduced based upon their characteristic seismic facies and constrained borehole log records as mappable seismic stratigraphic sequence units, termed “seismic operational sequences”. The respective Neogene stage and operational sequence equivalents (Hungarian lithostratigraphic units or formations) are the Middle Miocene (Badenian, Sarmatian), Upper Miocene-Lower Pliocene (Pannonian-Endrod and Szolnok Formations; Pontian- Algyo and Ujfalu Formations and Lower Pliocene- Zagyva Formation) and Upper Pliocene-Quaternary (Nagyalfold Formation). SSBC analysis greatly assists in the geological constraint or “geovalidation” of interpreted seismic stratigraphic relationships and provides potentially critical insight into stratigraphic and structural problems of non-unique interpretations. In the specific case, using such an approach on previously unpublished regional seismic lines, SSBC analysis reveals that the Banat region has undergone structural inversion. This may be related to changes in local stress directions along strike slip faults, which initiated in earliest Late Miocene (Endrod Formation), culminating in the reverse tilting and incipient shortening of the western graben. Therefore during the time interval that the Badenian through Endrod sediments were deposited in the graben, autocyclic progradation initiated from the Kikinda Szeged High in the East followed by Szolnok, Algyo, Ujfalu and younger units prograding from the West as the central high uplifted relative to the graben. Such tectonic inversion has substantial hydrocarbon potential implications for exploration in the region.     

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.