查看更多>>摘要：As documented in several studies, lake sediments in south-western China are important archives to decipher Indian Summer Monsoon (ISM) variability through reconstructions of precipitation and temperature changes, based on multi-proxy analysis of lake sediments. However, lacustrine records on glacial-interglacial timescales in south-western China remain limited because of a lack of reliable long chronologies. In this paper, we provide a 53 ka chronology for the Beihai wetland (core TCBH14) deposits in combination with luminescence and radiocarbon dating of sediments for the upper 13.4 m of a 36.6 m long drill core. The reliability of our chronological framework was verified within two independent chronology sequences and validated by correlations with regional chronostratigraphy. Results suggest that luminescence dating is a feasible method that can provide reliable age controls for lake sediments in south-western China. The depositional history of the Beihai wetland was characterised by alternating lake and wetland facies. Lakes existed at 52-47 ka, 41-32 ka, 26-19 ka and 11-7 ka, whereas a wetland system prevailed at 47-41 ka, 32-26 ka, 19-11 ka, and after similar to 7 ka. The patterns and formation periods of alternate lake-wetland successions are consistent with speleothem delta O-18 and lake delta D-wax records in South Asia, indicating that the sedimentary evolution of the Beihai wetland and other lake-wetland systems in this region are closely linked to ISM-dominated hydroclimate changes. Correlation of sedimentation rates (SRs) of the studied core (TCBH14) with the cores from 11 additional lakes in south-western China suggest that higher SRs occurred during the periods 47-34 ka, 26-19 ka,15-3 ka, and the early Holocene (11-7 ka). In contrast, lower SRs existed during the periods 50-47 ka, 34-26 ka, the last deglaciation (19-15 ka and 12-11 ka), and the middle Holocene (7-5 ka). Thus, we infer that such quasi-synchronous variations of the SRs from these different lakes in south-western China were strongly controlled by the suborbital- or millennial-scale regional hydroclimate, keeping pace with the Northern Hemisphere insolation-induced ISM variability since the last glaciation.
查看更多>>摘要：The Qinghai-Tibet Plateau (QTP) contains rock successions that record the detailed history of the evolution of the Tethyan oceans. The purpose of this Special Issue is to improve understanding of the complex evolution of the blocks/terranes and oceans in the QTP. It comprises 21 papers covering diverse disciplines including stratigraphy, palaeontology, geochemistry, paleomagnetics and sedimentology. Some of the major findings of the collection are as follows: (1) There exist many branches of the Prototethys Ocean in the QTP with complex history of evolution and subduction; (2) The Paleotethys Ocean along the Longmu Co-Shuanghu suture zone began to widen in Early Carboniferous times; (3) The Mesotethys Ocean opened during Early Permian times as indicated by both paleobiogeographic and provenance studies; (4) There are more than two forearc basins developed during the subduction of the Neotethys Ocean. The various contributions in this Special Issue provide detailed evidence to reconstruct the complicated evolution of the Tethyan oceans involved in the formation of the QTP. The articles will be of interests to scholars across many disciplines in the geosciences.
查看更多>>摘要：During the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma) the synergy between tectonic and climatic processes promoted the deposition of evaporites throughout the Mediterranean Basin. The disappearance of calcareous nannofossils and foraminifers at the MSC onset has been traditionally interpreted as the result of the establishment of hypersaline conditions in the water column, which were lethal for most marine eukaryotes. Here, we investigate the calcareous micro and nannofossil assemblages from the Sorbas Basin (SE Spain) spanning the onset and the first phase of the MSC (~ 5.9-5.7 Ma) in order to test whether their disappearance was related to adverse environmental conditions and/or to preferential dissolution of biogenic calcite. Micropaleontological analyses and petrographic observations suggest that the disappearance of calcareous fossils was the result of a taphonomic bias related to paleoceanographic changes that favoured the oxidation of both pyrite and organic matter at the sea floor. A poorly preserved benthic and planktic assemblage and aragonitic laminated sediment characterize the deposits of the first phase of the MSC from 5.93 Ma onward; aragonite deposition was likely biomediated in response to enhanced photosynthesis, as suggested by its delta C-13 signature. The fossil assemblage preserved in these deposits indicates a shallowing upward trend of the basin with respect to the pre-evaporitic phase, and the establishment of a lagoon-like environment characterized by episodic improvement of the connections with the open sea. We conclude that the temporary disappearance of calcareous fossils approximately at the MSC onset was related to ongoing basin restriction, which increased the sensitivity of the basin to fresh-water input and temperature changes, promoting marked fluctuations of the redox conditions in bottom sediments. This finding challenges the view of a marine biotic crisis related to hypersaline conditions at the MSC onset and opens new perspectives on the paleoenvironmental conditions that characterized this time interval.
查看更多>>摘要：The focus of this paper is to reconstruct late Quaternary wildfire and vegetation history in Chinese Loess Plateau (CLP) region, and to determine the interrelationships between wildfire, climate, and vegetation. To achieve this aim, we analyzed the black carbon concentration and pollen assemblages within an interval correlated with Marine Isotope Stage (MIS) 5 (equivalent to paleosol S1) to MIS 4-2 (equivalent to Loess L1) in the Xifeng section of the CLP. Findings show that during the MIS 5-2 intervals, changes in precipitation and temperature were essentially synchronous on the CLP, and changes in biomass reflected by total organic carbon content and pollen assemblages were determined mainly by the climatic conditions. Wildfire was controlled mainly by fuel humidity and vegetation type, which influenced by precipitation; however, there was no significant relationship between wildfire occurrence and temperature or the amount of combustible plant material. During the MIS 5 interval, the climate was warmer and wetter than today, while during the MIS 3 interval (Loess L1SL1) it was similar to today; however, during the MIS 2 (L1LL1) and MIS 4 (L1LL2) the climate was cooler and drier. Fires were less frequent during the MIS 5 interval compared to the MIS 3, and fires during the MIS 2 and MIS 4 were more frequent than the MIS 3. Results suggested that if the climate on the CLP became warmer and wetter in the future, natural fires would not necessarily occur more frequently and intensively. However, if climate evolved towards cooler and drier conditions, natural fires may be more likely to occur.
查看更多>>摘要：The Adriatic Platform, Croatia is a large isolated carbonate platform that developed under a warm greenhouse climate interspersed with cooler episodes in western Tethys. However, the delta(13C) record and high-resolution sequence stratigraphy of the Middle and Upper Jurassic portion generally is poorly known. The-1900 m thick (30 Myr duration) mainly Middle to Upper Jurassic succession of the platform was studied bed-by-bed to track the fluctuations of delta(13C) , facies stacking into bundles, superbundles, and sequences and potential sea-level changes within ongoing studies of evidence of astronomical forcing of the units. The study interval consists of cyclic subtidal intervals (upper Toarcian-lower Aalenian, lower Callovian, Oxfordian, lower Kimmeridgian, and lower Tithonian) interspersed with highly cyclic peritidal units (upper Bajocian-lower Bathonian, upper Kimmeridgian, and upper Tithonian-basal Berriasian). Ages were constrained by biostratigraphy and delta(13C) chemostratigraphy. The absolute delta(13C) values obtained from the shallow-marine bulk carbonate matrix are similar to those from coeval pelagic carbonates and exhibit similar trends, are characterized by overall little data spread (< 2 parts per thousand), and generally show little resetting associated with disconformities and/or burial. This rock-buffered record likely preserved at least relative marine delta(13C) values with several major excursions, including the BjBaE (Bajocian-Bathonian), CaOxBE (Callovian-Oxfordian boundary), EOxE, and MOxE (Early and Middle Oxfordian). The studied interval provides a detailed record of Milankovitch induced platform-flooding and exposure at scales from ~ 1Myr to ~ 20 kyr. The study suggests that detailed research of similar thick Jurassic isolated platform successions could provide valuable records of delta(13C) , climate, and sea-level changes over relatively long geological intervals.
查看更多>>摘要：The uppermost Pliensbachian (Margaritatus Zone) - upper Toarcian (Pseudoradiosa Zone) sediments (silty and variably calcareous claystones, marlstones, silty sandstones, and sandy limestones) recovered from the Kerr McGee 97/12-1 well were deposited in the Portland-Wight Basin. The foraminiferal assemblages of these sedimentary succession are dominated by calcareous forms of the suborder Lagenina and locally Robertinina. Three main ecostratigraphic intervals have been identified, based on changes in the foraminiferal and ostracod assemblages that occurred before, during and after the sedimentation of the earliest Toarcian black, organic-rich, non-calcareous claystones. The ecostratigraphic interval I (upper Pliensbachian) is characterized by a diverse assemblage with specialist, opportunist and intermediate forms, but dominated by Lenticulina muensteri. The ostracods in this interval are dominated by Metacopina. This assemblage is interpreted to represent a phase that pre-dates the biotic crisis. The ecostratigraphic interval II, related to the deposition of the lower Toarcian black claystones, shows an abrupt increase in the opportunist form Reinholdella (91%) with very low diversity and a high abundance of specimens, mainly Reinholdella macfadyeni and R. dreheri. In this interval the ostracods Metacopina dissapear. The top of the black claystones is almost barren of foraminifera and ostracods (only two specimens recorded of Trochammina eoparva). This second interval represents the biotic crisis phase related to the Jenkyns Event. The ecostratigraphic interval III (upper part of the lower Toarcian through to the upper Toarcian) is characterized by an increase in the diversity and abundance of foraminifera, as well as the dominance of Lenticulina. The ostracod assemblage shows a turnover with respect to the upper Pliensbachian assemblage with dominance of Cytherocopina, Platycopina and Bairdiocopina. This assemblage is interpreted to reflect the increased availability of oxygen from deep-infaunal to epifaunal microhabitats and the return to normal conditions at the sea floor. The incidence of the global warming related to the Jenkyns Event in the biotic crisis is also considered. Ecostratigraphic fluctuations in microfossil assemblages from the Kerr McGee 97/12-1 well across the T-OAE event are comparable with those described from the Mochras Borehole (west Wales), the Lusitanian Basin (Portugal), and the Atlassic Basin (North Africa).
查看更多>>摘要：Based on reconstructions from geological records, the precipitation during the Last Glacial Maximum (LGM) was markedly different from that of the preindustrial (PI) period. Especially in the terrestrial monsoon regions and arid regions of the Northern Hemisphere (hereafter referred to as NHTMR and NHTAR, respectively), the precipitation is more sensitive to changes in boundary conditions. However, the relative contributions of individual LGM forcings to precipitation in NHTMR and in NHTAR are still unclear. In this study, a series of climate model experiments were carried out to evaluate their contributions. The results showed that, compared with the PI period, the precipitation and area of NHTMR were both reduced in the LGM. In NHTAR, the precipitation was significantly reduced, but there was an increase in total area. Sensitivity experiments demonstrated that a decrease in sea surface temperature and an expansion of the ice sheet were the two principal contributors to lessening NHTMR precipitation, while the decrease in precipitation in NHTAR can be mainly attributed to icesheet-induced albedo and topography changes. Comparatively, the ice-sheet albedo effect had a greater impact on precipitation change than the topographic effect. The atmospheric circulation anomalies associated with the individual forcings were the underlying dynamic mechanism that drive the precipitation changes.
查看更多>>摘要：Detrital zircons are commonly used to identify sediment provenance, but usually only their ages are employed for interpretation. We here test the combination of four data types: crystallization ages, Th/U values, cathodoluminescence-induced internal textures, and grain shapes. Six samples of zircons from Triassic and Cretaceous deposits from the northeastern foreland of the Bohemian Massif (Poland) were used to identify as accurately as possible source rocks and their paleolocations, changes in erosional levels of source areas, and transport directions. The samples contain ten age populations, among which Carboniferous and Neoproterozoic zircons dominate, but the use of four parameters allowed subtle differences between the samples to be recognized; this makes interpretation more accurate and more reliable. A comparative analysis based on over 20,000 data points collected from similar to 200 contributions allowed us to identify the equivalents of crystalline source rocks, which were high-grade and medium-grade metamorphic rocks of the Bohemian Massif (mostly granulites) in the case of complex-textured zircons, and Bohemian magmatic rocks along with pyroclastics in the case of oscillatory-zoned grains. The source rocks were located in the northeastern and eastern parts of the massif, where the proportions of the specific rocks exposed to erosion have changed significantly from the Mesozoic to the present. We found distinct changes in the erosional levels of source areas caused by removal of sedimentary cover and the erosion of crystalline rocks, combined with tectonic movements, particularly in the Olenekian and Coniacian. The transport of debris from the southwest and west during the Induan-Anisian, as well as from the south and north during the Norian, were largely controlled by paleogeography. The Cretaceous transgression resulted in the supply of grains mainly from the nearest units during the Cenomanian and Coniacian. We strongly recommend using a combination of at least these four parameters in provenance studies.
查看更多>>摘要：The Shanxi Rift System is an intracontinental rift system located between the North China Plain and Ordos Plateau, which was infilled with thousands of meters of Cenozoic fluvio-lacustrine deposits. A comprehensive chronological framework will help better understand the formation and evolutionary process of the rift system. Here, we present a new magnetochronology for the Datong Basin sedimentary sequence in the northern Shanxi Rift System based on high-resolution magnetostratigraphic investigations of the DY-1 core. Correlation of the recognized magnetic polarity sequence of the DY-1 core with the Astronomically Tuned Neogene Time Scale shows that the fluvio-lacustrine sequence in the Datong Basin spans from Chron C3Bn to Chron C1n. The age of the Datong Basin sedimentary sequence can thus be paleomagnetically constrained to an interval from the late Late Miocene to Middle Pleistocene. The basal age of the sediments is ca. 7.0 Ma, which indicates that the initial extension of the northern segment of the Shanxi Rift System was no later than 7.0 Ma. The Datong Basin in the northern Shanxi Rift System has experienced a three-stage evolution: During the initial stage (7.0-4.2 Ma), fluvial environments are dominant. Then during 4.2-1.8 Ma, lacustrine environments are developed due to dipslip fault activities, as part of the Nihewan paleolake. After 1.8 Ma, the lake gradually shrank. The northeastward progressive growth and expansion of the Tibetan Plateau may have driven the evolution of the Shanxi Rift System.
查看更多>>摘要：The Guadalupian was a key epoch for the evolution of tetrapod faunas. It includes the earliest unambiguous occurrences of therapsids and stereospondyls (groups that later became dominant in terrestrial and freshwater environments, respectively) and the late Capitanian mass extinction event. The low-latitude faunas from this time interval, where sufficiently dated, comprise rare tetrapod body fossils whereas the most complete records are provided by ichnoassociations, especially coming from the Provence basins of France. In this paper, we revise the tetrapod ichnoassociation from the Pe ' litique Formation of the Le Luc Basin of Provence, identifying the following tetrapod ichnotaxa: Batrachichnus salamandroides (temnospondyls/lepospondyls), Capitosauroides talus comb. nov. (therocephalian therapsids), Dicynodontipus isp. (cynodont therapsids), Varanopus isp. (bolosaurian parareptiles), Hyloidichnus bifurcatus (captorhinomorph eureptiles) and Rhynchosauroides isp. (neodiapsid eureptiles). According to our revised ichnotaxonomy and stratigraphic correlations, we date the Pe ' litique Formation as late Capitanian and assign its tetrapod ichnoassociation to the newly defined Association V (Dicynodontipus sub-biochron of the Erpetopus biochron). The Pe ' litique Formation ichnoassociation shows a typical composition for a post-dinocephalian extinction ichnofauna, as shown by preliminary multivariate statistics on Guadalupian-Lopingian tetrapod ichnoassociations. It is similar to the contemporaneous skeletal faunas described from the mid- to high-latitude sites of Russia and South Africa and is arguably the earliest evidence of postdinocephalian extinction recovery at low-latitudes. Our results confirm the global and abrupt impact of the late Capitanian terrestrial mass extinction and the subsequent recovery in the low-latitude realm. This extinction was probably time-equivalent with a global benthic marine mass extinction, and both events may have been linked to climatic perturbation caused by the Emeishian volcanic activity in China, which reached its peak around 260 Ma.
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Elsevier