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Palaeogeography, Palaeoclimatology, Palaeoecology
Elsevier
Palaeogeography, Palaeoclimatology, Palaeoecology

Elsevier

0031-0182

Palaeogeography, Palaeoclimatology, Palaeoecology/Journal Palaeogeography, Palaeoclimatology, Palaeoecology
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    Revisiting the supposed oldest bilaterian trace fossils from Uruguay: Late Paleozoic, not Ediacaran

    Verde M.Netto R.G.Lavina E.L.Azurica D....
    5页
    查看更多>>摘要：? 2022 Elsevier B.V.Grazing trails found in the rhythmite beds attributed to the Ediacaran Tacuarí Formation (northern Uruguay) had been identified as the oldest evidence of bilaterians in the world. However, a diverse and abundant invertebrate, mostly arthropod, trace fossil assemblage is found associated with Upper Paleozoic palynomorphs in these same beds at the original localities from where the oldest bilaterian burrows were reported. These ichnoassemblages include Arborichnus repetita, Crescentichnus tesiltus, Cruziana problematica, Diplichnites aff. gouldi, Diplopodichnus biformis, Gluckstadtella cooperi, Helminthoidichnites tenuis, Kingella aff. natalensis, Maculichna varia, Rusophycus isp., Treptichnus pollardi, and Umfolozia sinuosa. The palynological assemblages yielded 89 species composed of 33 spores, 49 pollen grains, four chlorophycean algae, a fungal spore, an acritarch, and an indeterminate species. These occurrences point to a Phanerozoic record. The dominant botanical groups recorded are Lycophyta, Cordaitean, Coniferalean, Glossopteridalean, Corystospermaceae/ Peltaspermaceae, Pteridophyta, algal (Botryococcus, Tetraporina, Brazilea, Quadrisporites), and other groups (Deusilites tenuistriatus, Portalites gondwanensis). The high ichnodiversity, the prevalence of unquestionable arthropod biogenic structures, along with the abundance of ichnotaxa suggests a Carboniferous–Permian age. Therefore, the ichnoassemblages indicate that these strata are not Ediacaran in age and belong to the San Gregorio Formation, which represents the Upper Paleozoic Gondwanan glacial deposits in Uruguay. The ichnofauna is equivalent to others that are well known in deposits of the Late Paleozoic Ice Age from Brazil, Argentina, and South Africa. Furthermore, the new palynologic data from the trace-fossil bearing strata show that they can be correlated to the latest Carboniferous–early Cisuralian Cristatisporites inconstans-Vittatina saccata (IS) Zone of Paraná Basin in Uruguay.
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    • NSTL
    • Elsevier

    Coral community of Holocene coral reef in the southern South China Sea and its significance for reef growth

    Zhao M.Zhong Y.Zhang S.Zhang H....
    5页
    查看更多>>摘要：? 2022Ancient coral reefs are rich archives of historical process and vital baselines for future development. Coring gives a window into the growth of ancient coral reefs and the fossil coral community's response to paleoenvironment. Well NK-1 drilled from Meiji Reef is the longest scientific core with the highest recovery in the South China Sea. This study focused on the upper section of the Well NK-1 accumulated during the Holocene. From 8200 yr BP, Holocene reef initiated on the substrates of Pleistocene limestone and stopped accreting vertically at 4800 yr BP. It consisted of an initiation and fast reef growth (5.6 mm yr?1) from 8200 yr BP to 7300 yr BP, a shift to slow reef growth (2.0 mm yr?1) between 7300 yr BP and 5400 yr BP, a return to a rapid reef growth (8.8 mm yr?1) from 5400 yr BP to 4800 yr BP, and finally a cessation of upward accretion and a reinforced lateral progradation since 4800 yr BP. A total of 11 coral genera and 16 Acropora species were identified from the Holocene segment of the core. The diversity of coral communities had an impact on reef growth. Coral communities with less genera and absolute predominance of branching Acropora were corresponded with a rapid vertical accumulation of reef framework with higher accretion rate. Acropora corals with rapid growth and dispersion by fragmentation were principal reef-builders during the Holocene, with A.valida being the most prevalent coral species. The highest Acropora species richness occurred at the geological era of 5400–5300 yr BP when reef accumulated with the fastest upward accretion rate of 23.1 mm yr?1. This intricate and detailed pattern presented a new and novel model for the development of Holocene reef, indicating that the coral community and key reef builders were crucial to reef growth. These findings are extremely helpful for understanding the current ecological state of modern coral reefs as well as their potential response to global climate change.
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    • NSTL
    • Elsevier

    Tropical environmental change in North Sumatra at the Last Glacial Maximum: Evidence from the stable isotope composition of cave guano

    McCarthy R.Hamdi R.ErniBird M.I....
    5页
    查看更多>>摘要：? 2022Insular Southeast Asia is of critical importance to global biodiversity, climate, and socioeconomics. Past environmental histories are a crucial factor influencing contemporary patterns and, in this region, fluctuating sea-level and climate change during the Last Glacial Period (LGP) resulted in drastic changes in both land extent and vegetation cover. However, understanding the past environments of this tropical region is hampered by its sheer size and relative lack of traditional continental proxy records, such as lake sediments. To provide further insight into the response of vegetation to the changing environmental conditions, we use the stable carbon isotope composition (δ13C) of a bat guano sequence from Liang Mbelen Cave in North Sumatra, to determine whether tropical grass (C4 vegetation) or forest (C3 vegetation) was present in the area from c. 30 to 10 cal kyr BP. Our results confirm the presence of C4 vegetation during the LGP; however, we find that the timing of grass expansion was just prior to the Last Glacial Maximum (LGM; 23–19 kyr BP). Comparing Liang Mbelen with the other evidence from across the region, we find a generally consistent pattern of peak tropical grasses often occurring prior to the LGM in Sundaland, with the timing of forest encroachment variable, although beginning at c. 25 cal kyr BP. We find that the timing of the shift from savanna to forest systems in Sundaland is similar to changes in obliquity, likely resulting in a decrease or elimination of the dry season that favoured forest expansion. Understanding past vegetation history will help the management and protection of the fragile and ecologically valuable ecosystems of SE Asia.
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    • NSTL
    • Elsevier

    Synchronous positive δ13Ccarb and δ13Corg excursions during 497–494 Ma: From a CO2 concentrating mechanism dominated photosynthesis?

    Wang H.Deng Q.Cheng B.Liao Z....
    5页
    查看更多>>摘要：? 2022Steptoean Positive Carbon Isotope Excursion (SPICE) event is featured particularly as the synchronous positive δ13Ccarb and δ13Corg excursions, which are recorded worldwide in the Late Cambrian (ca. 497–494 Ma). However, the cause of this event remains elusive. To better understand the underlying mechanism of the contemporaneous positive isotope excursions, here we present a series of geochemical data from two drilling wells of the Tarim Basin, China and some relevant data reported from worldwide sections. CO2 concentrating mechanisms (CCMs, e.g., utilized by cyanobacteria) developed in response to decrease in pCO2 and increase in pO2 during the SPICE event, in which the HCO3? enriched in 13C but depleted in 2H is utilized for photosynthesis, is proposed to result in the synchronous positive excursions of δ13Ccarb and δ13Corg coupled by a negative shift of δDorg as exemplified by the samples from the Tarim Basin. The SPICE event was followed by an increase in plankton, which could relate to triggering CCMs and maintaining the biodiversity of marine organisms during the event.
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    • NSTL
    • Elsevier

    Microstructures and sclerochronology of exquisitely preserved Lower Jurassic lithiotid bivalves: Paleobiological and paleoclimatic significance

    de Winter N.J.Kaskes P.Posenato R.Frijia G....
    5页
    查看更多>>摘要：? 2022 Elsevier B.V.Lithiotids are enigmatic, large-sized bivalves that formed an important biotic component of tropical shallow marine environments during the Early Jurassic. Lithiotis problematica and Cochlearites loppianus are the most peculiar lithiotids, characterized by stick-like shells of predominantly aragonite which is generally calcitized or replaced by sparry calcite. Uniquely preserved specimens of these two species from the upper Sinemurian-Pliensbachian (Lower Jurassic) Rotzo Formation (Trento Platform, northern Italy), containing large parts of pristine shell (based on SEM, cathodoluminescence, and μXRF analysis), were selected for a sclerochronological and sclerochemical study, allowing to describe in detail the lithiotid microstructures, to decipher seasonal patterns and to investigate their functional and paleoenvironmental significance. We show that the outer shell layer of lithiotids, rarely preserved, consists of a calcitic simple prismatic microstructure with an asymmetrical thickness between the two valves, whereas the inner layer is aragonitic and is mainly composed of a fibrous irregular spherulitic prismatic fabric, which allowed a very fast shell growth. The latter microstructure is currently unknown in other mollusc shells. We recognized diurnal, fortnightly and annual growth increments, documenting a maximum annual growth of about 25 mm/yr in ventral direction. Stable isotopes show a clear annual periodicity suggesting seasonal changes in the paleoenvironment, which also affected the shell microstructures. During the warm season, first-order prisms are very elongated and show a massive structure without growth breaks, whereas during the cold season prisms are short and with growth cessations. Our results highlight the unique adaptation of lithiotid bivalves that allowed them to dominate the tropical shelf seas during the Early Jurassic.
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    • NSTL
    • Elsevier

    Editorial preface to special issue: Palaeosols in the sedimentary record: Implications for understanding the depositional processes, sedimentary architecture and the palaeoenvironment

    Basilici G.Benvenuti M.Cojane I.Varela A....
    5页
    查看更多>>摘要：? 2022 Elsevier B.V.Palaeosols are common in terrestrial successions from the Archean to the Holocene, locally dominating entire stratigraphic sections. The types of palaeosols developed are influenced by four key palaeoenvironmental controls (atmosphere, biosphere, lithosphere and hydrosphere) on time scales ranging from hundreds to potentially millions of years. As a result, palaeosols may preserve a valuable record of palaeoclimate, palaeotopography, palaeobiology, palaeodepositional processes, and their changes over time. The integrated study of palaeosols in their depositional context improves knowledge of the dynamic evolution of terrestrial sedimentary successions, and enables prediction of the future behaviour of landscapes. This special issue is divided into two themes and comprises 17 papers that address the wider significance of palaeosols. The first theme exclusively considers the characteristics of palaeosols and uses them as proxies for palaeoenvironmental conditions, especially palaeoclimate factors. Some keys findings include (i) proposals for new climofunctions, based on modern soils with pedogenic carbonate, (ii) critical observations on the chemical pre-treatment of palaeosol samples after application of climofunctions and (iii) climate variations identified by mineralogical, macroscopic and micromorphological evidence in a succession of palaeosol profiles. The second theme considers palaeosols as a tool to understand the relationships between sedimentation and pedogenesis, and its application to define depositional sedimentary architecture and aid sequence stratigraphic interpretations. Some key findings address (i) how tectonic or climatic factors may act to minimise the influence of sea level variations on the characteristics of the palaeosols, and (ii) the importance of understanding lateral variations in the palaeosol profiles before extrapolating results extracted from a single palaeosol profile to the basin scale. As such this special issue highlights the great value of palaeopedology for academic and applied knowledge.
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    • NSTL
    • Elsevier

    Relatively deep subtidal microbial–lithistid sponge reef communities in Lower Ordovician rocks reveal early escalation of the Great Ordovician Biodiversification Event

    Hong J.Park J.Kim D.Kim S.-M....
    5页
    查看更多>>摘要：? 2022 Elsevier B.V.The timing and magnitude of early stage of the Ordovician radiation with respect to reef consortia are still not well understood. In this study, we analysed the constructional style and environmental conditions of middle Tremadocian patch reefs in the middle Dumugol Formation of Korea, and assessed the temporal-spatial patterns of Furongian–Lower Ordovician reefs, to obtain a better insight into the transition of reef development during the Early Ordovician. The metre-scale microbial–sponge patch reefs, which are some of the oldest Ordovician reefs in this region, formed when carbonate-prevailing depositional systems were being re-established after deposition of shale-dominated outer shelf systems. These reefs and the enclosing lenses of normally graded packstone to grainstone change laterally to limestone–shale couplets, indicating that the reef-builders had settled in low-energy mid-ramp habitats. The main reef-building organisms are laminar, columnar–domal microbialites (peloidal crusts and stromatolites) and annulated obconical to cylindrical specimens of the anthaspidellid sponge Archaeoscyphia, most of which are mutually attached and form vertically and laterally connected reef frameworks. These reef attributes are comparable to those of their middle–upper Tremadocian counterparts in peri-Gondwana and Laurentia, but differ from Cambrian–lower Tremadocian microbial-lithistid sponge reefs that are largely concentrated in shallow subtidal deposits. Bio- and/or chemostratigraphic data from these Lower Ordovician successions reveal that the occupation of deeper subtidal ecospace by microbial–anthaspidellid consortia occurred rapidly at a global scale during the middle Tremadocian. This appearance, and the nearly contemporaneous emergence of novel skeletal reef-builders, may represents a pulse of the early Great Ordovician Biodiversification Event, shortly after the occurrence of the Top Skullrockian Isotopic Carbon Excursion (TSICE).
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    • NSTL
    • Elsevier

    Bioturbation supplying young carbon into West Antarctic continental margin sediment

    Kim S.Lee J.I.Yoo K.-C.Lee M.K....
    5页
    查看更多>>摘要：? 2022 Elsevier B.V.Accelerator Mass Spectrometry (AMS) 14C dating is a widely applied method for establishing high-precision chronologies used to underpin late Quaternary paleoclimatic studies. Feedbacks associated with Antarctic Ice Sheets (AIS) and Southern Ocean variance are thought to have played a critical role in regulating past global climate changes since the Last Glacial Maximum. However, determining the exact role of the AIS and Southern Ocean in these changes has proven difficult because of the sparse occurrence of biogenic carbonate suitable for AMS 14C dating in Antarctica. Consequently, AMS 14C dating is often measured on acid insoluble organic matter (AIOM) from bulk sediment samples, which are often biased towards ages that are older than the depositional age, due to pervasive reworking of old carbon. In this scenario, ages can still potentially provide maximum deposition ages, but such interpretations need to be assessed carefully. Here, we document AIOM and foraminifer AMS 14C dates at the same depth intervals from Antarctic continental margin cores, and we find AIOM AMS 14C dates can range between 2000 and 16,000 years younger than those of foraminifera samples. The younger AIOM 14C dates were found in bioturbated sedimentary facies, which often have extremely low sedimentation rates in Antarctica. In cores with low sedimentation rates, the down sediment contribution of organic carbon from macro-benthos can be quite significant in the sediment column with low organic carbon concentration. After considering possibilities of contamination, foraminifer reworking, and remineralization of secondary carbonate to explain this offset, we conclude that bioturbation plays an important role in the Antarctic carbon cycle as a young carbon supplier to depth into the sediment column. This has clear implications for using condensed sedimentary sections to date post-LGM records in Antarctica. These bioturbation processes also have implications for novel radiocarbon dating methods that have recently been developed to overcome sediment reworking processes and more accurately constrain timing of past AIS retreat, including ramped pyrolysis and compound specific isotopes methods.
      原文链接:
    • NSTL
    • Elsevier

    Relict proglacial lake of Spituk (Leh), northwest (NW) Himalaya: A repository of hydrological changes during Marine Isotopic Stage (MIS)-2

    Jena P.S.Bhushan R.Raj H.Dabhi A.J....
    5页
    查看更多>>摘要：? 2022 Elsevier B.V.In the northwestern Himalaya (Ladakh and Karakoram), the spatial and temporal changes in the late Quaternary glaciation were modulated by a combination of two contrasting moisture sources (viz., the Indian Summer Monsoon and the mid-latitude westerlies). The inferences about their relative contribution to glacier expansion are based on the ages obtained on moraines. Since the moraines suffer from poor preservation and chronological uncertainty, the present study, therefore, resorted to a near-continuous relict proglacial lake succession in order to reconstruct the continuous pattern of glacier fluctuations during Marine Isotopic Stage-2 (MIS-2). Since the AMS radiocarbon ages (both organic and inorganic matter) suffered from various complexities such as dead carbon contribution and hard water effect, the paleohydrological inferences in this study were drawn primarily based on optical ages (along with sedimentological and geochemical analysis). The proglacial lake sedimentation was modulated by the temporal changes in meltwater discharge. This is attributed to the waning and waxing of proximal valley glaciers. Evidence accrued from the lake sediment supported by the published moraine chronology suggests that valley glaciers expanded during the onset of MIS-2 and persisted until around the Last Glacial Maximum (LGM). The beginning of MIS-2 is marked by the onset of cooling (~ 30 ka), which led to a marginal advance in the glaciers. Additionally, early MIS-2 was characterised by millennial-scale climatic fluctuations. For example, a short-lived increase in humidity was observed between 30.2 ka and 29.3 ka, followed by a reversal towards a drier climate between 29.3 ka and 28.1 ka. During the early part of MIS-2, glaciers were driven by the decrease in temperature, whereas the enhanced moisture contribution during mid MIS-2 was responsible for extensive glacier growth. We hypothesise that the enhanced moisture was contributed by the mid-latitude westerlies, with subordinate contribution from the Indian Summer Monsoon (ISM). This we attribute to the southward positioning of the Intertropical Convergence Zone (ITCZ) during MIS-2.
      原文链接:
    • NSTL
    • Elsevier