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1.
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.  相似文献   

2.
Danuta Peryt 《地学学报》2013,25(4):298-306
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.  相似文献   

3.
The Pannonian Basin, originating during the Early Miocene, is a large extensional basin incorporated between Alpine, Carpathian and Dinaride fold-thrust belts. Back-arc extensional tectonics triggered deposition of up to 500-m-thick continental fluvio-lacustrine deposits distributed in numerous sub-basins of the Southern Pannonian Basin. Extensive andesitic and dacitic volcanism accompanied the syn-rift deposition and caused a number of pyroclastic intercalations. Here, we analyze two volcanic ash layers located at the base and top of the continental series. The lowermost ash from Mt. Kalnik yielded an 40Ar/39Ar age of 18.07?±?0.07?Ma. This indicates that the marine-continental transition in the Slovenia-Zagorje Basin, coinciding with the onset of rifting tectonics in the Southern Pannonian Basin, occurs roughly at the Eggenburgian/Ottnangian boundary of the regional Paratethys time scale. This age proves the synchronicity of initial rifting in the Southern Pannonian Basin with the beginning of sedimentation in the Dinaride Lake System. Beside geodynamic evolution, the two regions also share a biotic evolutionary history: both belong to the same ecoregion, which we designate here as the Illyrian Bioprovince. The youngest volcanic ash level is sampled at the Glina and Karlovac sub-depressions, and both sites yield the same 40Ar/39Ar age of 15.91?±?0.06 and 16.03?±?0.06?Ma, respectively. This indicates that lacustrine sedimentation in the Southern Pannonian Basin continued at least until the earliest Badenian. The present results provide not only important bench marks on duration of initial synrift in the Pannonian Basin System, but also deliver substantial backbone data for paleogeographic reconstructions in Central and Southeastern Europe around the Early–Middle Miocene transition.  相似文献   

4.
The reconstruction of regional long-term patterns recorded in marine sedimentary successions of the Eastern Paratethys is important in understanding the role of Cenozoic climate change and orogenic activity on the depositional environment and sedimentation dynamics in Western Asia. In this study, the environmental conditions in the early to middle Miocene (Islam Dağ section) in eastern Azerbaijan are elucidated using petrographic–mineralogical relations, detrital indicators, weathering indices and δ13C and δ18O signatures of organic-rich (total organic carbon: ca 3 to 6 wt. %) argillites. Sedimentary facies and chemical proxies (Na/K, K/Al, Si/Al, Ti/Al ratios, chemical index of alteration values) indicate arid conditions, reduced weathering rates in the hinterland and sediment deposition in an euhaline and poorly oxygenated deep-water basin during the early Miocene, followed by a shift to humid conditions, higher weathering rates and an oxygenated water column in the mid-early Miocene. Long-term aridification and deposition of gypsiferous and calcareous argillites under generally more oxygenated, euhaline to polyhaline conditions in a lacustrine or restricted shelf setting until the middle Miocene is evidenced by gradual changes in element ratios and the chemical index of alteration. Discriminant function analysis suggests the Russian Platform, drained by the Palaeo-Volga and Palaeo-Don river systems, to be the source area for the siliciclastic input throughout the Miocene, although a minor contribution of volcanogenic detritus and mafic components from the Greater Caucasus is possible. The C–S–Fe associations and increasing Fe/Al ratios towards the middle Miocene support the concept of continuous influx of detrital Fe and total organic carbon. The formation of ferruginous smectite from alteration of volcanic ash layers could have affected the preservation of total organic carbon and therefore the sedimentary C and Fe budget in the Eastern Paratethys basins. Palaeo-climatic reconstructions based on δ13C (−34·5 to +1·7‰ Vienna Pee Dee Belemnite) and δ18O (−34·7 to −4·8‰ Vienna Pee Dee Belemnite) records of authigenic carbonates should be made with great caution, as the pristine marine signatures may be affected by the oxidation of organic matter and meteoric diagenesis.  相似文献   

5.
The Miocene palaeogeographic evolution of the Paratethys Sea is still poorly constrained. Here, we use modern Mediterranean biochronology to provide an up‐to‐date overview of changing seas in Central Europe. Instead of a Paratethys that waxed and waned with fluctuating global sea levels, we show that the development of different seas was mainly controlled by tectonic phases. The Early Miocene “Ottnangian Sea” (~18 Ma) was connected to the Mediterranean via the Rhône valley, while the “Karpatian Sea” (~16.5 Ma) was initiated by a tectonically induced marine transgression through the Trans‐Tethyan gateway. In most Central European basins, the establishment of the “Badenian Sea” (<15.2 Ma), triggered by subduction‐related processes in the Pannonian and Carpathian domain, is significantly younger (by ~1 Myr) than usually estimated. The updated palaeogeographic reconstructions provide a better understanding of the concepts of basin dynamics, land–sea distribution and palaeoenvironmental change in the Miocene of Central Europe.  相似文献   

6.
Paratethys, the lost sea of central Eurasia, was an anoxic giant during Oligocene – early Miocene (Maikop Series) times. With a size matching the modern-day Mediterranean Sea and a history of anoxic conditions that lasted for over 20 Myrs, the eastern part of this realm (Black Sea-Caspian Sea domain) holds key records for understanding the build-up, maintenance and collapse of anoxia in marginal seas. Here, we show that the collapse of anoxic Maikop conditions was caused by middle Miocene paleogeographic changes in the Paratethys gateway configuration, when a mid-Langhian (Badenian-Tarkhanian) transgression flooded and oxygenated the Eastern Paratethys. We present an integrated magneto-biostratigraphic framework for the early Middle Miocene (Tarkhanian-Chokrakian-Karaganian regional stages) of the Eastern Paratethys and date the lithological transition from anoxic black shales of the Maikop Series to fossiliferous marine marls and limestones of the regional Tarkhanian stage. For this purpose, we selected two long and time-equivalent sedimentary successions, exposed along the Belaya and the Pshekha rivers, in the Maikop type area in Ciscaucasia (southern Russia). We show that a significant but short marine incursion took place during the Tarkhanian, ending the long-lasting Maikop anoxia of the basin. Our magnetostratigraphic results reveal coherent polarity patterns, which allow a straightforward correlation with the time interval 15–12 Ma of the Geomagnetic Polarity Time Scale. The Tarkhanian flooding occurred during a relatively short normal polarity interval that correlates with C5Bn, resulting in an age of 14.85 Ma. The regional Tarkhanian/Chokrakian stage boundary is located within C5ADn at an age of 14.75 Ma and the Chokrakian/Karaganian boundary is tentatively correlated with C5ACn and an age of 13.9–13.8 Ma. Our new Tarkhanian flooding age reveals a paleogeographic scenario that is different from many previous reconstructions. Instead of envisaging marine connections to the Indian Ocean, we show that major changes in connectivity between the Eastern and Central Paratethys seas have caused the influx of marine waters during the Tarkhanian. An increase in marine connectivity with the Mediterranean during a short episode of rapid sea-level rise triggered mixing and ended the widespread anoxia in the Eastern Paratethys. The mixing episode was short-lived (~100 kyr) as the sea-level rise slowed down and connectivity degraded because of tectonic uplift in the gateway area.  相似文献   

7.
《Geodinamica Acta》2001,14(1-3):45-55
Field studies on the Neogene successions in south of İzmir reveal that subsequent Neogene continental basins were developed in the region. Initially a vast lake basin was formed during the Early–Middle Miocene period. The lacustrine sediments underwent an approximately N–S shortening deformation to the end of Middle Miocene. A small portion of the basin fill was later trapped within the N–S-trending, fault-bounded graben basin, the Çubukludağ graben, opened during the Late Miocene. Oblique-slip normal faults with minor sinistral displacement are formed possibly under N–S extensional regime, and controlled the sediment deposition. Following this the region suffered a phase of denudation which produced a regionwide erosional surface suggesting that the extension interrupted to the end of Late Miocene–Early Pliocene period. After this event the E–W-trending major grabens and horsts of western Anatolia began to form. The graben bounding faults cut across the Upper Miocene–Pliocene lacustrine sediments and fragmented the erosional surface. The Çubukludağ graben began to work as a cross graben between the E–W grabens, since that period.  相似文献   

8.
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.  相似文献   

9.
Alluvial fans and shallow carbonate lakes interfered in the Teruel half‐graben during the Late Miocene–Pliocene. Tectonic influence is recorded in alluvial and lacustrine–palustrine successions, with long‐term climate changes being recorded in detail in the isotopic signatures of carbonates. Episodes of tectonic activity induced alluvial fan progradation and lake retraction in the whole basin. Three lacustrine stages have been identified, which support the idea that climate also exerted an important control on sedimentation. The transition between stages 1 and 2 occurred during a tectonically calm episode due to an increase in aridity in the Early Turolian; small fans with source areas next to the lake margin prograded, inducing lake‐shore retraction. The transition from stage 2 to 3 was caused by the superimposition of increasing tectonic activity and aridity effects. Our study demonstrates that discrimination of allogenic factors controlling sedimentation in continental closed basins is possible using sequence stratigraphy in combination with other techniques such as geochemistry of carbonates.  相似文献   

10.
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).  相似文献   

11.
During the Cenozoic numerous shallow epicontinental evaporite basins formed due to tectonic movements in the Northern Province of the Central Iran Tectonic Zone (the Great Kavir Basin). During the Miocene, due to sea‐level fluctuations, thick sequences of evaporites and carbonates accumulated in these basins that subsequently were overlain by continental red beds. Development of halite evaporites with substantial thickness in this area implies inflow of seawater along the narrow continental rift axis. The early ocean basin development was initiated in Early Eocene time and continued up to the Middle Miocene in the isolated failed rift arms. Competition between marine and non‐marine environments, at the edge of the encroaching sea, produced several sequences of both abrupt and gradual transition from continental wadi sediments to marginal marine evaporites in the studied area. These evaporites show well‐preserved textures indicative of relatively shallow‐brine pools. The high Br content of these evaporites indicates marine‐derived parent brines that were under the sporadic influence of freshening by meteoric water or replenishing seawater. However, the association of hopper and cornet textures denotes stratified brine that filled a relatively large pool and prevented rapid variations in the Br profile. Unstable basin conditions that triggered modification of parent brine chemistry prevailed in this basin and caused variable distribution patterns for different elements in the chloride units. The presence of sylvite and the absence of Mg‐sulphate/chlorides in the paragenetic sequence indicate SO4−depleted parent brine in the studied sequence. Petrographic examinations along with geochemical analyses on these potash‐bearing halites reveal parental brines which were a mixture of seawater and CaCl2‐rich brines. The source of CaCl2‐rich brines is ascribed to the presence of local rift systems in the Great Kavir Basin up to the end of the Early Miocene. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

12.
Abstract

Field studies on the Neogene successions in south of ?zmir reveal that subsequent Neogene continental basins were developed in the region. Initially a vast lake basin was formed during the early-Middle Miocene period. The lacustrine sediments underwent an approximately N-S shortening deformation to the end of Middle Miocene. A small portion of the basin fill was later trapped within the N-S-trending, fault-bounded graben basin, the Çubukluda? graben, opened during the Late Miocene. Oblique-slip normal faults with minor sinistral displacement are formed possibly under N–S extensional regime, and controlled the sediment deposition. Following this the region suffered a phase of denudation which produced a regionwide erosional surface suggesting that the extension interrupted to the end of Late Miocene–Early Pliocene period. After this event the E–W-trending major grabens and horsts of western Anatolia began to form. The graben bounding faults cut across the Upper Miocene–Pliocene lacustrine sediments and fragmented the erosional surface. The Çubukluda? graben began to work as a cross garden between the E–W grabens, since that period. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

13.
The northeastern Tibetan Plateau is located at the convergence of the Asian winter and summer monsoons and westerlies; thus, this area has witnessed historic climate changes.The Xunhua basin is an intermontane basin on the northeastern margin of the Tibetan Plateau.The basin contains more than 2000 m of Cenozoic fluvial–lacustrine sediments, recording a long history of climate and environmental changes.We collected the mid-Miocene sediments from the Xunhua basin and used palynological methods to discuss the relationship between aridification in the interior of Asia, global cooling, and uplift of the Tibetan Plateau.Based on the palynological analysis of the Xigou section, Xunhua basin, the palynological diagram is subdivided into three pollen zones and past vegetation and climate are reconstructed.Zone I, Ephedripites–Nitraridites–Chenopodipollis–Quercoidites(14.0–12.5 Ma), represents mixed shrub–steppe vegetation with a dry and cold climate.In zone II, Pinaceae–Betulaepollenites–Ephedripites–Chenopodipollis–Graminidites(12.5–8.0 Ma), the vegetation and climate conditions improved, even though the vegetation was still dominated by shrub–steppe taxa.Zone III, Ephedripites–Nitrariadites–Chenopodipollis(8.0–5.0 Ma), represents desert steppe vegetation with drier and colder climate.The palynological records suggest that shrub–steppe dominated the whole Xigou section and the content gradually increased, implying a protracted aridification process, although there was an obvious climate improvement during 12.5–8.0 Ma.The aridification in the Xunhua basin and surrounding mountains during 14.0–12.5 Ma was probably related to global cooling induced by the rapid expansion of the East Antarctic ice-sheets and the relatively higher evaporation rate.During the 12.5–8.0 Ma period, although topographic changes(uplift of Jishi Shan) decreased precipitation and strengthened aridification in the Xunhua basin on leeward slopes, the improved vegetation and climate conditions were probably controlled by the decrease in evaporation rates as a result of continuous cooling.From 8.0 to 5.0 Ma, the rapid development of the desert steppe can be attributed to global cooling and uplift of the Tibetan Plateau.  相似文献   

14.
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.  相似文献   

15.
Abstract The Miocene sedimentary record of the Madrid Basin displays several examples of palaeokarstic surfaces sculpted within evaporite formations. One of these palaeokarstic surfaces represents the boundary between two main lithostratigraphic units, the Miocene Lower and Intermediate units of the Madrid Basin. The palaeokarst formed in lacustrine gypsum deposits of Aragonian age and corresponds to a surface palaeokarst (epikarst), further buried by terrigenous deposits of the overlying unit. Karst features are recognized up to 5·5 m beneath the gypsum surface. Exokarst and endokarst zones are distinguished by the spatial distribution of solution features, i.e. karren, dolines, pits, conduits and caves, and collapse breccias, sedimentary fills and alteration of the original gypsum across the karst profiles. The development of the gypsum palaeokarst began after drying out of a saline lake basin, as supported by recognition of root tubes, later converted to cylindrical and funnel‐shaped pits, at the top of the karstic profiles. The existence of a shallow water table along with low hydraulic gradients was the main factor controlling the karst evolution, and explains the limited depth reached by both exokarst and endokarst features. Synsedimentary fill of the karst system by roughly laminated to massive clay mudstone with subordinate carbonate and clastic gypsum reflects a punctuated sedimentation regime probably related to episodic heavy rainfalls typical of arid to semi‐arid climates. Duration of karstification is of the order of several thousands of years, which is consistent with previous statements that gypsum karstification can develop rapidly over geologically short time periods.  相似文献   

16.
Organic geochemical characterization of cutting samples from the Abu Hammad-1 and Matariya-1 wells elucidates the depositional environment and source rock potential of the Jurassic and Lower Cretaceous successions and the Middle Miocene to Pleistocene section in the southern and eastern Nile Delta Basin. The burial and thermal histories of the Mesozoic and Miocene sections were modeled using 1D basin modeling based on input data from the two wells. This study reveals fair to good gas-prone source rocks within the Upper Jurassic and Lower Cretaceous sections with total organic carbon (TOC) averaging 2.7% and hydrogen index (HI) up to 130 mg HC/g TOC. The pristane/n-C17 versus phytane/n-C18 correlation suggests mixed marine and terrestrial organic matter with predominant marine input. Burial and thermal history modeling reveals low thermal maturity due to low heat flow and thin overburden. These source rocks can generate gas in the western and northern parts of the basin where they are situated at deeper settings. In contrast, the thick Middle Miocene shows fair source rock quality (TOC averaging at 1.4%; HI maximizing at 183 mg HC/g TOC). The quality decreases towards the younger section where terrestrial organic matter is abundant. This section is similar to previously studied intervals in the eastern Nile Delta Basin but differs from equivalents in the central parts where the quality is better. Based on 1D modeling, the thick Middle Miocene source rocks just reached the oil generation stage, but microbial gas, however, is possible.  相似文献   

17.
系统分析青藏高原新生代中新世50余个沉积盆地的类型、构造背景、岩石地层序列,对青藏高原中新世构造岩相古地理演化特征进行分析和探讨。中新世,青藏高原海相沉积已经全面退出,全部转为陆相沉积,约23Ma时高原及周边不整合面广布,标志高原整体隆升。塔里木、柴达木及西宁-兰州、羌塘、可可西里等地区主体表现为大面积的构造压陷湖盆沉积。约17.2Ma左右,阿尔金山显著隆升,使柴达木盆地西叉沟一带再无生物礁灰岩出现,且在盆地西部出现了短暂的沉积间断。这一时期,柴达木盆地西部开始进入湖退期,而东南部则快速湖进;同时,大约17.7Ma索尔库里山间盆地初始凹陷形成。另外,高原腹地五道梁-沱沱河盆地受南部唐古拉山的挤压抬升,在16Ma左右结束了五道梁组的沉积,在可可西里—唢呐湖一带则再次凹陷接受唢呐湖组沉积,形成高原腹地的大型压陷湖盆。13～10Ma期间,藏南南北向断陷盆地的形成,是高原隆升到足够高度开始垮塌的标志;约8Ma以来,高原东北部几乎所有湖盆均进入湖退期,普遍出现冲积扇、辫状河和水下扇砂砾岩堆积。  相似文献   

18.
全球性的构造运动末期一般伴着海退和干旱的气候环境,而蒸发岩沉积与大地构造条件紧密相关。中亚卡拉库姆盆地、阿富汗_塔吉克盆地、塔里木盆地自晚侏罗世至中新世以来至少发生了3次大规模海侵_海退旋回,每次海侵_海退均受特提斯构造事件控制。卡拉库姆盆地、阿富汗_塔吉克盆地为晚侏罗世—早白垩世蒸发岩沉积、塔里木盆地的莎车次级盆地为晚白垩世—古新世蒸发岩沉积,库车次级盆地为古新世—中新世蒸发岩沉积,形成特提斯构造域自西向东蒸发岩沉积时代逐渐变新的盐湖链。中亚及塔里木盐湖链在海侵_海退旋回的控制下,至少发生5次大规模的蒸发岩沉积,发育2种不同的蒸发岩沉积序列,分别对应3次海退期蒸发岩沉积序列及2次断续海侵期蒸发岩沉积序列,具体为晚侏罗世晚期(海退期)卡拉库姆盆地、阿富汗_塔吉克盆地蒸发岩沉积;早白垩世—晚白垩世早期(断续海侵期)阿富汗_塔吉克盆地蒸发岩沉积;晚白垩世晚期(海退期)莎车次级盆地蒸发岩沉积;古新世—中新世(断续海侵期)莎车次级盆地、库车次级盆地蒸发岩沉积;中新世晚期—上新世早期(海退期)库车次级盆地蒸发岩沉积。塔里木与中亚古盐湖发育受控于特提斯构造事件及海侵_海退旋回,而海侵_海退旋回又控制2种不同的蒸发岩沉积序列。蒸发岩沉积序列、古盐湖演化阶段、蒸发岩物质来源、沉积环境决定了盐类矿物沉积类型(单一化学岩型、陆缘碎屑岩_化学岩型),卡拉库姆盆地、阿富汗_塔吉克盆地盐类矿物与塔里木盆地相比,种类简单,反映了盆地化学岩与陆源碎屑_化学岩沉积的区别及后期构造运动对盐类矿物种类的主控作用。  相似文献   

19.
The evaporitic Hessian Zechstein Basin is a sub‐basin of the Southern Zechstein Basin, situated at its southern margin. Twelve facies groups were identified in the Zechstein Limestone and Lower Werra Anhydrite in order to better understand the sequence‐stratigraphic evolution of this sub‐basin, which contains economically important potassium salts. Four different paleogeographic depositional areas were recognized based on the regional distribution of facies. Siliciclastic‐carbonate, carbonate, carbonate‐evaporite and evaporite shallowing‐upward successions are developed. These allow the establishment of parasequences and sequences, as well as correlation throughout the Hessian Basin and into the Southern Zechstein Basin. Two depositional sequences are distinguished, Zechstein sequence 1 and Zechstein sequence 2. The former comprises the succession from the Variscan basement up to the lowermost part of the Werra Anhydrite, including the Kupferschiefer as part of the transgressive systems tract. The highstand systems tract is defined by the Zechstein Limestone, in which two parasequences are developed. In large parts of the Hessian Basin, Zechstein sequence 1 is capped by a karstic, subaerial exposure surface, interpreted as recording a type‐1 sequence boundary that formed during a distinct brine level fall. Low‐lying central areas (Central Hessian Sub‐basin, Werra Sub‐basin), however, were not exposed and show a correlative conformity. Topography was minimal at the end of sequence 1. Widely developed perilittoral, sabkha and salina shallowing‐upward successions indicate a renewed rise of brine level (interpreted as a transgressive systems tract), because of inflow of preconcentrated brines from the Southern Zechstein Basin to the north. This marks the initiation of Zechstein sequence 2, which comprises most of the Lower Werra Anhydrite. In the Central Hessian Sub‐basin, situated proximal to the brine inflow and on the ridges within the Hessian Basin, physico‐chemical conditions were well suited for sulphate precipitation to form a thick cyclic succession. It consists of four parasequences that completely filled the increased accommodation space. In contrast, only minor sulphate accumulation occurred in the Werra Sub‐basin, situated further southwards and distal to the inflow. As a result of substantially different sulphate precipitation rates during increased accommodation, water depth in the region became more variable. The Werra Sub‐basin, characterized by very low sedimentation rates, became increasingly deeper through time, trapping dense halite brines and precipitating rock salt deposits (Werra Halite). This ‘self‐organization’ model for an evaporitic basin, in which depositional relief evolves with sedimentation and relief is filled by evaporite thereafter, contradicts earlier interpretations, that call upon the existence of a tectonic depression in the Werra area, which controlled sedimentation from the beginning of the Zechstein.  相似文献   

20.
《Sedimentology》2018,65(2):517-539
Enhanced aridification of Central Asia driven by the combined effects of orogenic surface uplift, Paratethys retreat, changes in atmospheric moisture transport and global cooling is one of the most prominent Cenozoic climate change events of the Northern Hemisphere. Deciphering regional long‐term patterns of Central Asian hydrology is, therefore, a key element in understanding the role of Northern Hemisphere mid‐latitude drying in the global hydrological system. This study characterizes long‐term palaeoenvironmental conditions between the late Oligocene and early Miocene in south‐eastern Kazakhstan based on stable isotopes, elemental geochemistry and laser ablation uranium–lead geochronology from alluvial, fluvial and pedogenic deposits. Sedimentary facies and geochemical weathering indices suggest an increased surface and groundwater discharge fed by orographically enhanced precipitation in the Tien Shan hinterland. In contrast, pedogenic stable isotope data and elevated rates of magnesium fixation in clay minerals mirror enhanced rates of evaporation in the vadose zone due to protracted aridification. This study posits that pronounced surface uplift of the Tien Shan Mountains during the Oligocene–Miocene transition promoted regionally increased orographic precipitation and the development of fluvial discharge systems.  相似文献   

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