Palaeogeography, Palaeoclimatology, Palaeoecology最新文献

An 18,000 km² area of the Guyana Shield of South America, known as the Gran Sabana, is characterized by savannah vegetation that contrasts strongly with surrounding rain forests. Its origin has been linked to multiple episodes of forest fires. In this paper, we report a deposit encountered in two piston cores sampled during the CASEIS marine cruise, at 6000 m-depth at the southern entrance of the Puerto Rico Trench. The existence of this deposit call into question our understanding of the evolution of the Gran Sabana. We sampled its upper ∼60 cm, which comprises leaves and wood fragments, seeds, and charcoal, intermixed with siliciclastic sediment of igneous-metamorphic continental provenance. Radiocarbon dates of the vegetal fragments and charcoal range between 30 and 23 kyr BP. We propose that these deep ocean charcoal-rich sediments, located 2500 km offshore from the Orinoco Delta, may be remnants of gigantic forest fires of the Guyana Shield. We infer that this material was eroded during an extreme regional rainfall event, transported down rivers during one or more episodes to the Orinoco delta, and then travelled offshore via a deep turbiditic submarine system flowing on the Atlantic seafloor. It finally reached the Puerto Rico Trench, forming what we term, the Baracuda Trench Debrite. While published paleoclimatic analyses of lacustrine sediments have suggested that the Gran Sabana originated during episodes of wildfire ∼12.5 kyr BP ago, radiocarbon dating of Baracuda Trench Debrite suggests the occurrence of earlier fires in this region, leading us to re-evaluate the age of the Gran Sabana. These fires occurred during the low glacial maximum (LGM) and were likely promoted by climate change.

In 2017, sediment cores were retrieved from sites M0080, M0079, and M0078 in the Corinth basin during IODP Expedition 381. This study focuses on the Holocene and middle Pleistocene ostracod assemblages retrieved from sites M0080, in the Gulf of Alkyonides, and M0078 in the Corinth Gulf. It explores the paleoenvironmental constraints that affected the Tuberoloxoconcha species' distribution in these two sites and investigates the stratigraphic appearance of the new species Tuberoloxoconcha aielloi in the Corinth basin during deglacial and glacial periods over the last 400,000 years. In the Gulf of Corinth, fossil assemblages dominated by T. aielloi n. sp. have identified brackish shallow water environments corresponding to deglacial and glacial phases, when the basin was likely semi-isolated from Mediterranean waters, with high fluvial input lowering the salinity of the waterbody. The study highlights the discontinuous occurrence of T. aielloi and its morphotypes, identifying cold phases during MIS 10 and MIS 7d, and warmer phases during MISs 2–3-4-5a. The variability in ornamentation potentially reflects different water chemistry in the two sites. The post-400 ky appearance of T. aielloi, coinciding with the development of the marine connection through the Rion Strait, implies a Mediterranean/Atlantic origin for the genus. This study provides insights into the environmental conditions and evolutionary history of T. aielloi species in the Corinth basin, contributing to a broader understanding of benthic species' responses to past and future sea level changes.

The Sea of Okhotsk is a transitional zone between East Asia and northwestern Pacific Ocean. As a result, its massive thick sediments contain numerous important records of geological past, such as the mechanisms of materials and energy exchanges. However, the scarcity of studies tracing the provenance of clay-sized sediments in the sea has limited the progress of reconstructing the paleoclimate of East Asia. In this study, clay mineral analysis was conducted on 31 surface stations and the LV87–54-1 core. These results were combined with grain-size to provide reliable evidence for distinct mechanisms controlling the influx of clay-sized sediments into the northern shelf of the Sea of Okhotsk since 23 ka. Results of provenance analyses suggested that clay-sized sediments in the northern shelf mainly originated from its northwestern shelf, the Okhotsk–Chukotka volcanic belt, and the Kamchatka Peninsula. Clay-sized sediments of the northern shelf was primarily transported from the northwestern shelf and the Okhotsk–Chukotka volcanic belt after 23 ka, while those analogues from the Kamchatka Peninsula increased after 11.7 ka. Based on variations in clay mineral ratios, sediments from the northwestern shelf were mainly transported by the North Okhotsk Countercurrent, wherein rapid millennial-scale variations were influenced by the high-latitude Arctic Oscillation (from the Last Glacial Maximum to the Last Deglaciation) and the low-latitude East Asian summer monsoon (including the Holocene), respectively. By contrast, the influx of clay-sized sediments from the western Kamchatka Peninsula might be mainly controlled by the intensity of the West Kamchatka Current. From the Last Glacial Maximum to the Last Deglaciation, north and northwest geostrophic winds dominated in winter, and the West Kamchatka Current shifted eastward. Since the Holocene, weakened north and northwest geostrophic winds, but strengthened east winds caused a series of rapid millennial-scale variations in the West Kamchatka Current.

In this paper, Cretaceous trace fossil assemblages are reported from aeolian facies within four units from Patagonia, Argentina, to evaluate the usefulness of the aeolian ichnofacies concept. From oldest to youngest, studied units comprise the Agrio (Valanginian-Hauterivian), Cerro Barcino (Aptian-Cenomanian), Candeleros (Cenomanian), and Allen (Campanian-Maastrichtian) formations. Twenty one ichnotaxa were recorded, including ten of invertebrate origin (Archaeonassa fossulata, Arenicolites tenuis, Beaconites isp., Digitichnus laminatus, Edaphichnium lumbricatum, cf. Octopodichnus isp., Palaeophycus tubularis, Skolithos linearis, Taenidium barretti, and an unidentified arthropod trackway), seven tetrapod footprints and burrows (Avipeda isp., Brasilichnium isp., cf. Chelonipus isp., Reniformichnus katikatii, two types of indeterminate footprints, and burrow fills) and four rhizolith types. Entradichnus meniscus (formerly used as eponym of an aeolian ichnofacies) is considered a junior synonym of Taenidium barretti. Common ichnotaxa in aeolian and fluvial sequences like Taenidium barretti, Skolithos linearis and Palaeophycus tubularis are facies-crossing ichnotaxa and should not be used to distinguish ichnofacies. Trace fossil assemblages and ichnofabrics from aeolian dune, dry interdune and wet interdune facies are interpreted in terms of the potential producers and their palaeoecological and palaeoenvironmental constraints. This procedure is more informative than the ichnofacies approach in aeolian deposits. Based on a literature review of 32 examples of trace fossil assemblages from Cretaceous aeolian sequences worldwide, we conclude that the most distinctive ichnotaxa occur in aeolian dunes, including Brasilichnium, Farlowichnus, lacertoid footprints, Octopodichnus and Paleohelcura. It is recommended to abandon the usage of the Chelichnus, Entradichnus and Entradichnus-Octopodichnus ichnofacies, which are poorly defined in terms of recurrence and environmental significance or based on uncharacteristic or unavailable ichnotaxa. We propose a new definition of the Octopodichnus ichnofacies, diagnosed by the presence of subequant tetrapod footprints in quadrupedal trackways and/or selected arachnid /insect trackways. This ichnofacies is a taphofacies recorded from the Permian to the Cretaceous, and probably extends to the Cenozoic.

Marginal sea sediments offer one of the most stable and critical carbon repositories of sequestered organic carbon (OC). Quantification of the magnitude and the potential of OC sequestration in marginal sea sediments could provide data supporting the formulation of coastal carbon management strategies in the future. Nonetheless, controversies and difficulties still exist given the lack of integrity on statistical data, the incomplete understanding of the complex OC sources and the dynamic processes in the marginal seas. This work presents a systematic and holistic analysis of the OC stock and carbon stock accumulation rate (CSAR) in surface sediments (0–5 cm) of the Eastern China Marginal Seas (ECMS). The estimated total OC stock in the top 5 cm sediments in the ECMS (9.57 × 10⁵ km²) was 201.48 ± 15.98 Tg and the sequestration rate was 24.24 ± 9.93 Tg per year. Because only the preservation of fresh terrestrial OC and the marine OC is regarded as a valid CO₂ sink on modern timescale, we further elucidated the magnitude and the potential of the valid OC stocks and CSAR with different sources and ages based on the δ¹³C and Δ¹⁴C. This study quantifies high resolution OC stock and CSAR and presents the magnitude and potential of the valid sedimentary carbon sink in the ECMS.

Glacial Termination V (T-V) comprised a relatively rapid shift from glacial to interglacial conditions (MIS 12 glacial to the MIS 11c); it was one of the greatest climatic changes of the Pleistocene, and forms part of the major climatic reorganization known as the Mid-Brunhes Event (MBE). The Fucino Basin, located in the Central Apennine chain of central Italy, contains a continuous and well-preserved lacustrine sedimentary record of T-V and MIS 11, dated using tephrochronology. In this paper, we report a high-resolution palynological analysis, supported by geochemical proxies, from the lowermost section of the F4-F5 composite record, to improve understanding of T-V in this region. This record reveals a substantial transition between MIS 12 and MIS 11c at 424.5 ± 4.0 ka, from a very cold and dry environment indicated by the herbaceous and xerophytic association of Poaceae, Artemisia, Amaranthaceae, Ephedra, and Hippophäe, and sedimentation dominated by inorganic siliciclastic sediments, to a warm and humid period characterised by a significant increase in Abies and a deciduous tree association mainly formed by Betula, Carpinus, Corylus, Quercus, Ulmus, and dominated by more organic calcareous sediments. This transition was correlated with a significant lake-level rise, with an enhanced nutrient input into the lake between 425.0 ± 4.5 ka and 424.0 ± 3.9 ka, as inferred from the variance between algae, aquatic plants, and terrestrial herbaceous taxa. Following the MIS 11c temperature maximum at 424.2 ± 3.9 ka, a reduction in summer insolation occurred, provoking a significant increase in humidity that produced the widespread development of Abies. The results from this study suggest that, at Fucino, fluctuations in humidity are predominantly responsible for the vegetation changes observed during T-V.

The Permian sponge reefs belong to several distinct types, and their taxonomic composition and distribution vary. Their development and succession depend both on intrinsic and extrinsic control mechanisms. The well-documented outcrops in South China, encompassing Permian sponge reefs have been sampled and investigated in aspects of palaeontology, stratigraphy, sedimentology, and paleogeography. Two major reef-forming intervals, namely the Roadian to Capitanian and the late Wuchiapingian to Changhsingian, were recorded mainly in the Maokou and Changxing formations. The sponge reefs in these formations could be morphologically subdivided into three types: fringing reef, patch reef, and barrier reef. From the Roadian to Capitanian, fringing reefs developed near a littoral clastic shelf, and barrier reefs mainly presented on the margin of the isolated carbonate platforms within the Dian-Qian-Gui Basin. These reefs were dominated by frame-building hypercalcified sponges, including Amblysiphonella, Tebagathalamia, Rhabdactinia, Intrasporeocoelia, and Cystothalamia of sphinctozoa and Peronidella, Stellispongia, Guangxinella and Grossotubenella of inozoa. From late Wuchiapingian to Changhsingian, patch reefs distributed on the middle-upper Yangtze Platform and on the isolated platforms within the North Yangtze Basin and Dian-Qian-Gui Basin. The barrier reefs located on the margin of the Yangtze Platform facing the North Yangtze and Jiangnan basins and on the margin of the isolated platforms within the Dian-Qian-Gui Basin. Frame-building hypercalcified sponges were dominated by Amblysiphonella, Sollasia, Lichuanospongia, Intrasporeocoelia of sphinctozoa, and Peronidella of inozoa. The highly diversified and abundant hypercalcified sphinctozoans and inozoans, as well as massive microencrusters and binders made great contributions to the formation of sponge reefs. The subtidal high-energy shoal and the stable carbonate platform environment at the low-latitudes provided the favorable habitat for the growth of sponge reefs. Once these conditions could not be met simultaneously, sponge reefs would rapidly decrease and disappear, as it happened during the latest Capitanian and the latest Changhsingian.

Paleoceanographic reconstructions in the Caribbean Sea during past climate transitions, namely the Late Oligocene to Early Miocene (up to the Miocene Climatic Optimum and Monterey Excursion) are crucial to understanding the effects of the Eastern Pacific interchange with the Atlantic Ocean. Studies of the planktonic domain in the Yucatan Basin during the Early Miocene are limited, with most Caribbean research focused on reconstructing the series of events that precede the final closure of the Isthmus of Panama in the Early Pliocene. Furthermore, paleoceanography of the Yucatan Basin is largely unrefined during this time, even though it is an important transition for ocean gateways, and development of Atlantic deepwater and Atlantic Meridional Overturning Current (AMOC), driving global ocean circulation. Here we conduct a relative percent abundance analysis of calcareous nannofossils and stable isotopes from bulk sediment of drill cores spanning the Upper Oligocene to Lower Miocene in the central Yucatan Basin, collected by the Ocean Drilling Program Leg 165 at Site 998 Hole A. Nannofossil assemblage data record a shift from a eutrophic to oligotrophic system ∼19.2–17.65 Ma. Eutrophic taxa (Reticulofenestra spp. and Cyclicargolithus floridanus) decline at ∼20.23 Ma, while oligotrophic taxa (discoasters and sphenoliths) increase as stable carbon isotope values decline. The palaeoecological turnover coincides with a possible restriction in the Central American Seaway (CAS) ∼20.7–21 Ma. Population dynamics of the Hole 998 A nannofossil assemblage track with global declines in C. floridanus relative abundance between ∼20.2 to ∼20.5 Ma, followed by a subsequent decrease in Reticulofenestra spp. These data suggest water mass stratification in the Yucatan Basin during the Early Miocene ∼19.2–17.65 Ma, likely due to restriction of the CAS.

The Paleozoic Era was an interval of profound changes in metazoan reef ecosystems, which became magnificent in scale and diversity, owing to the evolution of various skeletal reef builders especially corals and sponges. This special issue comprises 16 papers that improve our understanding on the complex evolution and paleoecology of corals and metazoan reef ecosystems, and their response to environmental changes through the Cambrian to Permian. The case studies present detailed evidence that helps to reconstruct the complicated interactions among reef organisms, the succession of metazoan reefs, and their relations to paleoenvironments. Some key findings address (i) Cambrian reefs and microbe–metazoan reef transition to the Ordovician, (ii) reef component and paleoecological features of Siluro-Devonian coral-stromatoporoid reefs, and (iii) growth characteristics, paleogeography, and reef formation of Late Paleozoic corals and sponges. As such, this special issue will stimulate further work on reef studies and be of interest to a broad community of paleoecologists, to scholars in various fields of the geosciences as well as to reef biologists.

After the highly perturbed, post-crisis environments of the Early Triassic, the Middle Triassic was characterized by stabilization of environmental and climatic conditions, as evidenced by geochemical profiles, including the carbon cycle. Here, we identify an unexpected new episode of global carbon cycle perturbation during the early Middle Triassic (∼244–243 Ma), indicated by the Pelsonian negative carbonate carbon isotope excursions (PENCIE) and mercury anomalies, which occurred widely across Tethys. These perturbations may have been driven by volcanic activity, as indicated by anomalous peaks in the Hg, Hg/TOC and Hg/TS signals. In addition, Sr isotope, gamma ray and other data suggest that the Hg anomalies were driven by increased terrestrial inputs. Environmental change during the Pelsonian was coupled with the emergence of diverse marine faunas that represented a fully recovered ecosystem. Nutrients brought in by volcanism or inputs from terrestrial sources during environmental perturbation may have contributed to biotic recovery.