查看更多>>摘要：The Xindian Ancient City (XAC) site is the most complete and frequently excavated urban site in the lower reaches of the Minjiang River. Archaeological and chronological research of this area helps clarify the history of human activity at the site and restore the geographical background of the ethnic minority regimes who lived in the coastal areas of south China during the Eastern Zhou dynasty and the related influence on regional civilisation. Dating results suggest that the site was built during the Spring and Autumn and Warring States periods (3.2-2.4 thousand years ago), which can reasonably explain the presence of relics from the Warring States period on and within the wall. Our dating results are also consistent with the late Neolithic stone tools and pottery fragments found in the area, suggesting that the site was an ideal settlement before castles were constructed. Based on the spatial distribution of the Neolithic sites and Holocene transgression records in the Fuzhou Basin, it was found that coastline advance and retreat were the main factors affecting the paleo-human activity in the Fuzhou Basin during the late Neolithic period. Previous studies showed that the seawater gradually withdrew from the basin around 2 ka BP. Before this, humans mainly lived in the crescent-shaped area on the west side of the Fuzhou Basin, close to the ancient coastline. Based on existing archaeological results and chronological data, it can be shown that the lower reaches of the Minjiang River, where Fujian Province's capital is located, has long been the centre of ancient human activity in the coastal areas of south China, with a civilisation history of 6-4 ka and a city construction history of at least 2.9 ka.
查看更多>>摘要：The end-Triassic mass extinction (ETE), one of the five largest mass extinctions, occurred at 201.6 Ma. It was characterized by dramatic declines in marine and terrestrial ecosystems and was approximately synchronous with the eruption of the Central Atlantic Magmatic Province (CAMP). Loss of marine biodiversity is linked to extreme global warming while the cause of floral destruction in terrestrial ecosystems remains open to debate. In this paper, biomarker records of higher plants are reported from terrestrial facies in the Haojiagou section of the high palaeolatitude Junggar Basin, northwest China. Strata around the ETE interval are marked by sharp increases in the abundances of cadalene, retene, pimanthrene and furans, which are synchronous with "fern spikes". These results are interpreted as indicating the demise of land vegetation and the enhanced burial of higher plants, consistent with palynological evidence for the loss of floral diversity. The fluctuations in the abundance of n-alkanes series and conversion of n-alkanes peak patterns coincide with wildfires indicated by polycyclic aromatic hydrocarbons. Based on integrated stratigraphic correlation, the increased burial of higher plants, wildfires and CAMP volcanism are synchronous both in the Haojiagou section and other classic Triassic Jurassic boundary sections globally. We propose that widespread deforestation may be due to CAMP-derived acid rain and the rapid and large-scale demise of vegetation may have provided moisture-free fuels for wildfires.
Silva, Fernando A. Borges daFranca, Marlon C.Cohen, Marcelo C. L.Macario, Kita...
12页
查看更多>>摘要：This work aims to understand mangrove resilience to changes in a wave-influenced delta in southeastern Brazil during the late Holocene using an integrated analysis of palynology, sedimentology, and geochemistry (813C, 815N, C:N and C:S ratio), and radiocarbon dating on two sediment cores. The data indicated three mangrove succession phases: 1) an estuarine point bar/tidal flat occupied by a mixture of mangrove species (-2660 - 2050 cal yr BP); 2) a tidal flat dominated by Laguncularia mangroves (-2050 - - 900 cal yr BP); and 3) tidal flats with Laguncularia mangroves upstream and establishment of Rhizophora/Avicennia mangrove at the river mouth (-900 cal yr BP until present). The geochemical results suggest a dominance of C3 terrestrial plants with a mixture of C4 plants and organic matter of marine/estuarine origin throughout the late Holocene. Laguncularia and Rhizophora trees were established since - 2660 cal yr BP as pioneers, followed thereafter by Avicennia. Currently, tidal flats upstream are occupied by mangroves mainly represented by Laguncularia. Rhizophora/ Avicennia mangroves occur at the mouth of the river. The relative sea-level fall during the late Holocene, as well as the channel dynamics, caused the development of tidal flats and mangrove succession inland. The succession of Rhizophora, Laguncularia, and Avicennia, followed by the permanence of only Laguncularia, is likely related to the resilience of each mangrove genus to habitat disturbance (e.g., salinity and sediment grain size fractions) caused by sea-level changes and channel dynamics. Our results show that mangroves may be resilient to the effects of Atlantic sea-level fluctuations, but the floristic structure in the past is different from that of today.
Soutter, Euan L.Kane, Ian A.Martinez-Donate, AnderBoyce, Adrian J....
7页
查看更多>>摘要：The Eocene-Oligocene transition (EOT) was a period of considerable environmental change, signifying the transition from Paleocene greenhouse to Oligocene icehouse conditions. Preservation of the sedimentary signal of such an environmental change is most likely in net-depositional environments, such as submarine fans, which are the terminal parts of sedimentary systems. Here, using sedimentary and stable isotope data from the Alpine foreland basin, we assess whether this major climatic transition influenced the stratigraphic evolution of submarine fans. Results indicate that fine-grained deposition in deep-water environments corresponds to positive delta C-13 excursions and eustatic highstands, while coarse-grained deposition corresponds to negative delta C-13 excursions and eustatic lowstands during the earliest Oligocene. While alternative explanations cannot be ruled out on the basis of this dataset alone, our results suggest that eustatic fluctuations across the EOT and into the early Oligocene influenced sediment supply to deep-water environments.
查看更多>>摘要：The Danube Basin represents a northwestern depocenter of the Middle Miocene Central Paratethys Sea, which was succeed by the Late Miocene Lake Pannon. Although this is an extensively examined area, the application of multidisciplinary studies has proven capable of drawing attention to novel information concerning the depositional environment. Thus, this study aims to reveal climatic and paleoenvironmental changes by using both archive and fresh data drawn from biomarkers, palynology, sedimentology, and geochemistry. The article also addresses the quality, quantity, and thermal maturity of organic matter in relation to hydrocarbon potential. In general, the beginning of Serravallian stage relates to a regression forced by the development of the Antarctic icesheet followed by a pronounced transgression. The results presented here show that the Central Paratethys Sea reacted to the late Badenian (Serravallian) flooding, by an event which triggered a dysoxic, but not euxinic, bottom waters. The climate remained warm and humid, with paratropical to subtropical forests on the continent. Several new depocenters developed during the Sarmatian and divided the depositional environments into a shelfbrake slope in the central part of the Danube Basin, and into deltaic and swamp environments on the basin margins. The climate changed to temperate, leading to the disappearance of subtropical taxa. A shallow lake and swamp environment developed at the beginning of the Pannonian (Tortonian), forcing a salinity decrease connected to the increase in humidity. The degree of hydrocarbon richness of the mudstones is generally fair to good, and the kerogen is of mixed marine-terrestrial origin (II and III). Nonetheless, sediments at the basin margin are clearly immature due to insufficient burial.
查看更多>>摘要：The aeolian loess-paleosol sections on the northeast Tibetan Plateau (NETP) are a valuable source of paleoclimatic information because of their geographical location. In this study, two late Pleistocene-Holocene aeolian loess-paleosol sections were identified based on detailed field investigations in the Maqu reach in the Yellow River source area on the NETP. A robust chronostratigraphic framework for these two sections was established using AMS C-14 dating, optically stimulated luminescence (OSL) dating, Bacon age-depth modelling and strati graphic correlation. Measurements of magnetic susceptibility, hygroscopic water, loss-on-ignition, grain-size, micromorphology, and chemical element analysis suggest that most stratigraphic units in these aeolian loesspaleosol sections are in weak weathering and pedogenesis, whereas the mid-Holocene paleosol approaches to the moderate weathering and pedogenesis, and the sediments are in initial weathering stage of Na+ and Ca2+ leaching is dominated by plagioclase weathering. The main pedogenesis in the mid-Holocene paleosol is calcification process. In terms of intensity of weathering and pedogenesis, the stratigraphic units can be ordered as follows: paleosol > modern soil > transitional loess > aeolian loess. Multi-index comparison shows that the local climatic evolution during the late Pleistocene-Holocene was closely related to the evolution of the East Asian summer monsoon (EASM) and the Westerlies. Overall, the results provide a foundation for further exploration of the pedogenic and paleoclimatic evolution on the NETP.
查看更多>>摘要：The early Ladinian lacustrine ecosystem of the Chang 7 Member in the Ordos Basin was proposed as the earliest known Mesozoic-type, trophically multileveled lacustrine ecosystem after the end-Permian mass extinction (EPME). However, limited evidence of higher-order trophic levels represented by predatory fish has made this conclusion elusive. In this study, we investigated the external morphology, food inclusions, and geochemical composition of 54 vertebrate coprolites from organic-rich lacustrine sediments of Chang 7 Member, Yanchang Formation, in the Bawangzhuang section, Tongchuan City, Shaanxi Province, China. These coprolites were identified as seven morphotypes in three groups: three heteropolar spiral forms, two amphipolar spiral forms, and two non-spiral forms. Preserved inclusions (fish scales, bone fragments, teeth) indicated that the producers of these coprolites were piscivorous animals. Compared with coprolites previously researched, all coprolites described herein were inferred to be produced by fish: three heteropolar types of spiral coprolites derived from three types of hybodonts, two amphipolar spiral coprolites from coelacanth or Saurichthys with simple spiral valves, and non-spiral coprolites from at least two predatory actinopterygians. Thus, the biodiversity of the lacustrine paleoecosystem, particularly that of predators with upper trophic levels, was substantially enriched. The existence of large carnivorous predators of different taxa as apex predators in a trophically multileveled (at least six levels) lacustrine ecosystem indicates that the early Ladinian lacustrine ecosystem of the Ordos Basin marks the rebuilding of the top-predator trophic structure in the lacustrine ecosystem after the EPME.
查看更多>>摘要：The end-Permian mass extinction was the most catastrophic event for life in the Phanerozoic eon because it impacted numerous organisms, from micro-sized photosynthetic organisms to large (meter-long) animals and fundamentally altered marine and terrestrial ecosystems. C33 n-alkyl cyclohexane (C33-ACH), an angstrom-size molecular fossil of phytoplankton, has been widely found in Permian-Triassic (P-Tr) marine sediments, associated with the collapse of the marine ecosystems at the end-Permian mass extinction. Here, we describe multiple C33-ACH spikes in the Lower Triassic succession at the Chaohu section of the South China Block, which imply that phytoplankton blooms occurred repeatedly during the early-middle Early Triassic. Comparison with previous studies shows that C33-ACH was not only globally enriched at the P-Tr boundary, but also abundant at the Induan-Olenekian boundary and middle Smithian in both the South China and Boreal seas. In addition, the Chaohu section record reveals a C33-ACH peak at the Smithian-Spathian boundary. Moreover, the C33-ACH spikes were synchronous with the peaks of mercury and the pristane/phytane (Pr/Ph) ratio. Since the peaks in mercury and the Pr/Ph ratio indicate increased volcanic activity and large influxes of terrestrial source material into the ocean, the correspondence between the high abundance of C33-ACH with mercury and Pr/Ph ratio peaks implies that volcanism and riverine nutrient input fertilized the surface phytoplankton, which triggered the expansion of anoxia that in turn delayed the benthic metazoan recovery.
查看更多>>摘要：Changes in wildfires and paleoclimate during the Late Cretaceous have been widely discussed in the literature, yet terrestrial evidence for these changes is temporally limited. This study presents biomarker evidence for wildfires and paleoclimate using polycyclic aromatic hydrocarbons (PAHs) from drill core J79 of the Nenjiang Formation (K(2)n(1+2), boundary at about 83.3 Ma) deposited during the Late Santonian in the Songliao Basin, NE China. A variety of di-ring to hepta-ring aromatic hydrocarbons, including pyrogenic-derived, petrogenic-derived and mixed PAHs, was identified in the lacustrine deposits using gas-chromatography mass-spectrometry. According to fluorene and its derivates, the PAHs in the K(2)n(1) were dominantly preserved under an anoxic water column, with a shift to preservation under a weakly oxidizing water column (around 83.3 Ma) in the lower part of K(2)n(2). The occurrence of higher-plant-derived PAHs (e.g., retene, simonellite, cadalene, perylene and 6-isopropy-1-isohexyl-2-methylnaphthalene) is as probable plant fingerprint, representing a relatively humid condition and a semi-humid to arid paleoclimate condition during the lower part of K(2)n(1) and lower part of K(2)n(2) and during the upper part of K(2)n(1), respectively. Sharp increases in the abundance of pyrogenic PAHs compounds (e. g., benzo[h]fluoranthenes, benzo[e]pyrene, and coronene) are interpreted as indicators of intense wildfires in the K(2)n. The scale of fire events in the lower part of K(2)n(1) and lower part of K(2)n(2) was larger than that in the upper part of K(2)n(1). This change in wildfire extent may have been caused by the wetter climate stimulating the growth of sufficient biomass to fuel large wildfires. Therefore, the availability of fuel likely played an important role in controlling fire frequency during the Late Cretaceous.
Oien, RachelP.Barr, Iestyn D.Spagnolo, MatteoBingham, Robert G....
12页
查看更多>>摘要：Cirques are glacially eroded, bowl-shaped depressions, characterised by steep headwalls and flat or overdeepened floors. Given their association with past glaciers, cirques are sometimes used as proxies for palaeoclimate. However, cirques are shaped over multiple glacial cycles, and their usefulness as palaeoclimate indicators therefore remains open to question. In this paper, we map 3984 glacier-free cirques across the Scandinavian Peninsula and analyse variations in cirque floor altitude (CFA). We explore the relationships between CFAs and cirque aspect, latitude, longitude, and distance to the coast. We test the validity of using CFAs as indicators of palaeoclimate through comparison with the equilibrium-line altitudes (ELAs) of 513 modern cirque glaciers. Results indicate that both CFAs and modern cirque-glacier ELAs decrease with latitude and vary with aspect, being generally lowest on east-facing slopes. However, the clearest and strongest trend in both CFAs and modern cirque glacier ELAs is an increase in elevation with distance from the modern coast (i.e., distance 'inland'). This likely indicates that similar climatic gradients, particularly an inland reduction in precipitation, acted to regulate former sites of glacier initiation (reflected by CFAs) and modern glacier ELAs. This would imply that CFAs are a useful proxy for palaeoclimate. However, we note that both CFAs and modern ELAs reflect the general topography of this region (with increasing elevations moving inland), and the glacial history of the area (indirectly linked to palaeoclimate) may have played a role in regulating where cirques have formed. For these reasons, we suggest that palaeoclimatic interpretations derived from CFAs should be treated with caution.
NSTL
Elsevier