lacustrine sediments
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AbstractThe Oceanic Anoxic Event (OAE) 1b is well documented in western Tethys, however, records in Eurasia are still lacking. Here, we carried out high-resolution organic carbon isotope (δ13Corg), total organic carbon (TOC) contents and mercury (Hg) concentrations analysis of the lacustrine sediments from the Xiagou and Zhonggou formations in the Hanxiagou section, Jiuquan Basin, northwestern China. The lacustrine δ13Corg curve presents three stages of negative excursions above the basalt layer dated at 112.4 ± 0.3 Ma in the lowermost Zhonggou Formation. The three negative δ13Corg excursions, well corresponded with the three subevents (Kilian, Paquier, and Leenhardt) of the OAE1b in Poggio le Guaine (central Italy), Vocontian Basin (SE France) and St Rosa Canyon (NE Mexico) sections, supporting the record of the terrestrial OAE 1b in the Jiuquan Basin. Five mercury enrichment (ME) intervals in Hg/TOC ratios were recognized, indicating that the pulsed volcanism from the southern Kerguelen Plateau likely triggered the OAE 1b. However, the decoupling between NIE shifts and mercury enrichments signifying other carbon reservoir (with no link to mercury) probably contributed to the global carbon cycle perturbation during the OAE 1b period. Our results provide direct evidence to link the OAE 1b and terrestrial ecosystem in the Eurasia.

The reconstruction of environmental and climatic changes in the Pleistocene is an essential contribution to our understanding of human evolutionary and behavioral adaptations. Well preserved fluvio-lacustrine sediments at Nihewan basin have yielded a rich record of Early Pleistocene Paleolithic sites and mammalian fossils which provide a unique opportunity for exploring hominin behavior and paleoecology in North China. Taxonomic studies of mammalian fossils have provided important clues to the general environmental setting and landscapes of Early Pleistocene humans in the fluvio-lacustrine basin of Nihewan, but little is known about their isotopic signatures. In this paper, mammal teeth species at the Madigou archaeological site (ca. 1.2 Ma) were selected for bulk and sequential enamel stable isotope (C, O) analysis. Results show a variety of ecological environments, including grassland and sparse forest landscapes, and distinct patterns across taxa. C3-C4 mixed vegetation predominated, but C4 vegetation was also relevant at times. Madigou early humans likely experienced cold/warm or dry/wet fluctuations in this northern China basin. We hypothesize that the environmental fluctuations and diversified landscapes may have driven flexibility in various aspects of early human technological behaviors, and allowed hominins to face the environmental challenges of northern latitudes after the initial expansion from Africa into East Asia at the onset of the Middle Pleistocene Climate Transition.

Late Cenozoic drying of the Asian inland has not only exerted a profound impact on the regional environment but also affected global climate as an important source of global atmospheric dust. Continuous and accurately dated sediment records from the Asian interior are pivotal to a better understanding of the evolutionary history of Asian inland drying and the associated driving mechanisms. In this study, we present a continuous record of climate change in the Asian interior spanning the past 7.3 Myr, reconstructed by the redox evolution of a paleolake in the western Qaidam Basin, NE Tibetan Plateau. The paleolake redox conditions are linked to the oxygen concentration of lake bottom water and lake level, and were revealed by the manganese (Mn) concentration in the carbonate fraction (leached by the diluted acetic acid) of the carbonate-rich lacustrine sediments retrieved from two drill-cores (SG-1 and SG-1b). The reconstructed regional climate in the western Qaidam Basin shows long-term fluctuations, consistent with the secular evolution of the coeval global climate, especially the sea surface temperature variation in the high latitude North Atlantic. Three transitions of the paleolake hydrochemical system occurred at 6.2, 5.3, and 2.6 Ma, with a short drying stage at 6.2–5.3 Ma and prolonged Quaternary drying since 2.6 Ma. We argue that drying of the Asia interior has been dominantly forced by global cooling, in particular, the high-latitude cooling of the Northern Hemisphere.

At the foothillof Monte Amiata volcano (southern Tuscany, Italy), small extinct lake basins of late Pleistocene age are documented. These lake basins were characterized by the deposition of two very different types of sediment: a) derived from the authigenic precipitation of iron oxides (goethite) and exploited as earth pigments; b) biogenic siliceous sediment composed of fossil diatoms and named diatomaceous earth or diatomite. The lacustrine sediments of Mount Amiata volcano were widely exploited for various applications since ancient times. Literary documents begin in the 16th century, with the descriptions of Cesalpino, Gesner, Agricola, and Imperato. Specific references to the diatomites of Monte Amiata are quoted in the 17th century by Boccone and Bonanno. The quarrying activity was described by Micheli in 1733. During the 18th and 19th centuries, the diatomaceous earths of Monte Amiata are part of the important geological collections of Micheli, Targioni Tozzetti, Baldassarri, Campani, and Tommi. A particular significance has the collection of botanic and ichthyologic fossils collected by Ezio Tongiorgi, and now preserved in the Museum of Natural History of the University of Pisa sited at the Charterhouse of Pisa in the Calci village. These paleontological samples preserve the biological and physical testimonies of the environmental and climatic changes of the late Pleistocene and are now particularly valuable because they are the only remaining evidence of the diatomaceous lacustrine deposits of the paleo-lakes of Monte Amiata. For these reasons, they represent geological materials with a fundamental cultural value.

Chondrichthyans and osteichthyans are widely reported from marine sediments of the Central Paratethys, not only by sporadic occurrences, but also by complex, diverse fish assemblages. Here we present a rich fish fauna from the upper Miocene (Pannonian, Tortonian) lacustrine sediments exposed in the Pécs-Danitzpuszta sand pit, in the SW Pannonian Basin. Altogether 22 227 specimens were investigated, and they could be classified into 17 chondrichthyan and 16 osteichthyan taxa. Among the chondrichthyans Odontaspididae (55.51%) and Myliobatidae (14.4%) are the most abundant, while the bony fishes are dominated by the Sparidae (77.07%). The limonitic, yellow, coarse-grained, gravelly sands yielded an extremely large amount of isolated fish fossils. A considerable part of the vertebrate material of the sands is likely reworked from older, middle Miocene (Badenian and Sarmatian, i.e. Langhian and Serravallian) sediments. The late Miocene calcareous marls underlying the sands also yielded a variety of fish remains. From these remains, associated and articulated latid bones are coeval with the sediment and suggest freshwater and brackish conditions in the area, in accord with other biotic data. Other, isolated fossils, namely teeth, otoliths, cycloid scales and jaw elements of Gadidae, Gobiidae, Sparidae and Latidae could be reworked and thus have a very limited paleoecological significance. Based on habitat preferences of extant relatives, all chondrichthyans and most osteichthyan taxa found in the sands must be of Badenian origin. The abundant remains allow for some conclusions on the environmental conditions during the Badenian. They refer to a shallow, coastal environment with tropical-subtropical climate with connection to more open water habitats. Remains of some osteichthyan taxa were found in coprolites, showing that these taxa were part of the food chain as prey items. Sirenian ribs and odontocete limb bones bearing tooth marks refer to trophic relations between marine mammals and large sized macropredatory sharks. The Pécs-Danitzpuszta record of shark-attributed bite marks on bones of marine mammals is the second of the Badenian of the Central Paratethys. Acipenserids and latids of the sands, linked to brackish and/or freshwater environments, could originate from any Miocene stratigraphic units.

An excavated profile of aeolian-palaeosol-lacustrine sediments (the Wapianliang profile), located at the southeastern part of the Mu Us Desert, Northern China, was studied to reconstruct regional Holocene environmental changes. A chronology was established based on three AMS 14C and two OSL dates, and variations in the lithology and grain size, magnetic susceptibility, soil micromorphology, and chemical elements were used to explore the regional depositional environments during the Holocene. The results showed that since around 14 ka BP, this region had experienced seven alternations of wetting and drying. A shallow lake, which was identified by celadon lacustrine sediments with sporadic freshwater gastropod fossils, occurred in this area from around 13.0 ka BP to 9.9 ka BP. There existed two obvious intervals of soil formation, inferred from the environmental proxies of the palaeosol/sandy palaeosol layers, with relatively fine average grain-size, high magnetic susceptibility value, remarkable pedogenesis features, and strong chemical weathering, in particular, a well-developed palaeosol layer dating from the middle Holocene (8.6 ka BP to 4.2 ka BP). A weakly-developed palaeosol layer (from around 1.2 ka BP) at the upper part of the profile is possibly an indication of the Medieval Warm Period. This implies a forest steppe environment at both of these sedimentary stages. After 0.9 ka BP, a desert environment returned, analogous to before around 13.0 ± 1.4 ka BP, between 9.9 ± 1.1 ka BP to 8.6 ka BP, and between 4.2 ka BP to 1.6 ka BP, indicating the aggravation of aeolian activity and the expansion of mobile sand dunes. The variations in sedimentary environments were mainly triggered by changes in the East Asian Summer Monsoon (EASM).

Methylated 2-methyl-2-(4,8,12-trimethyltridecyl)chromans are salinity-sensitive biomarkers that have been detected in immature – early mature petroleum and sediments. In this study, the occurrence and distribution patterns of 2-methyl-2-(4,8,12-trimethyltridecyl)chromans were investigated in a set of lacustrine sediments from Nördlinger Ries of southern Germany and marine sediments from the South China Sea. Among all of the 2-methyl-2-(4,8,12-trimethyltridecyl)chroman isomers detected, 8-Me-2-methyl-2-(4,8,12-trimethyltridecyl)chroman presented with high abundance in sediments deposited in hypersaline environments, while absent in samples from normal marine environments. In contrast, 5,7,8-triMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman was more enriched in sediments from marine environments. This study also showed that the ratio of 5,7,8-triMe-/5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman can be applied as a potential salinity indicator on account of a positive correlation with other 2-methyl-2-(4,8,12-trimethyltridecyl)chroman salinity indicators. This ratio can be an alternative indicator of paleosalinity when 8-Me-2-methyl-2-(4,8,12-trimethyltridecyl)chroman is absent or present in quite low abundance. The content of 2-methyl-2-(4,8,12-trimethyltridecyl)chroman isomers may be affected by freshwater supply and lithology. Molecular simulations showed that 5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman has a higher thermal dynamic stability than 7,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman. Thus, the ratio of 5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman/7,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman may be a potential maturity parameter for sediments at a low thermal mature stage.