Palaeogeography, Palaeoclimatology, Palaeoecology

Light at the end of the tunnels? The origins of microbial bioerosion in mineralised collagen Publication date: 1 September 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 529 Author(s): Gordon Turner-Walker Abstract Microbial bioerosion, in all its manifestations, is one of the major factors determining the long-term survival of archaeologically and environmentally important artefacts and ecofacts made from mineralised collagen – bones, antler, teeth and ivory. The bone diagenesis literature contains extensive descriptions of different morphologies and classifications of microbial bioerosion – microscopical focal destruction, Wedl tunnels, linear longitudinal, budded and lamellate tunnelling, etc. but the causative agents remain to be discovered. Palaeontologists are in a similar situation when describing ichnofossils where bioerosion is classified by its characteristic morphology and only tentatively assigned to specific causes. In archaeological bones, Wedl tunnels have traditionally been ascribed to fungi but a re-examination of Wedl's original paper and subsequent literature has shown that all the early specimens examined came from aquatic environments and that euendolithic microflora (cyanobacteria or chlorophytes) might have been responsible. These microorganisms are known to tunnel into marine shells. Linear longitudinal, budded and lamellate tunnelling have all been ascribed to bacteria. However, analyses using a combination of backscatter SEM (BSEM) and mercury intrusion porosimetry (HgIP) of bones excavated from terrestrial soils suggest that the various tunnelling morphologies described by earlier researchers are actually all manifestations of a single architecture, the differences arising from the inherent variability of bone microstructure and the hydrology of the burial environment. An examination of the BSEM and HgIP data also indicates that the bacteria responsible may spread through dead bone tissues by expanding the canalicular network (or dentinal tubules in teeth) rather than creating new tunnels. Long-term field burial experiments using de-fleshed cow bone specimens have now demonstrated that bacterial tunnelling develops over decades rather than months as was previously thought, even in warm tropical soils. This has obvious implications for the origin of the bacteria responsible (soil bacteria versus endogenous gut bacteria) since the bone specimens were quickly isolated from gut contents. Although no attempt is made here to identify a specific organism or organisms responsible for tunnelling in terrestrial archaeological bones a tentative model is proposed for how cycles of wetting and drying, or changes in local dissolved oxygen levels, could lead a common gram positive soil bacterium to produce the pattern of bacterial bioerosion seen in exhumed bones. This soil organism may act in a similar way to Staphylococcus aureus which proliferates in living bone (causing osteomyelitis) by infiltrating and enlarging the canalicular network.

Origin of chert in Lower Silurian Longmaxi Formation: Implications for tectonic evolution of Yangtze Block, South China Publication date: 1 September 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 529 Author(s): Zihui Lei, Shahin E. Dashtgard, Jian Wang, Mou Li, Qinglai Feng, Qian Yu, Ankun Zhao, Lintao Du Abstract Upper Ordovician (Katian) to Lower Silurian (Rhuddanian) strata in the Middle–Upper Yangtze Block, South China contain extensive chert beds, although the origin of microcrystalline silica in these cherts is largely unknown. In this study, the mineralogy and structure of chert as well as major, trace, and rare earth elements are used to determine the origin of microcrystalline silica in 29 chert samples from Longmaxi Formation (Rhuddanian) in Baizitian outcrop, west of Kangdian Uplift (KU). Results show that 21 of the 29 chert samples have a biogenic origin, 2 indicate a hydrothermal origin, and 6 show a mixed origin. Cherts from Baizitian outcrop are compared to contemporaneous cherts deposited east of KU. Cherts both east and west of KU are mainly biogenic in origin, which is attributed to high productivity in the paleo-seaway. Hydrothermal microcrystalline silica is relatively uncommon in the Longmaxi Formation across the Middle-Upper Yangtze Block, and only occurs in Baizitian outcrop. Terrigenous influx contributed to chert accumulation both east and west of KU; however, cherts east of KU received much more clastic material than those in Baizitian outcrop. A comparison of chert composition and geochemistry to geological reconstructions of the Middle-Upper Yangtze Block reveal that accumulation of hydrothermal chert is closely linked to tectonic evolution. During the Early Silurian, the Middle-Upper Yangtze Block was in a compressional tectonic regime with limited heat supply, and hence, low hydrothermal circulation; this is manifested in the paucity of hydrothermal microcrystalline silica in cherts east of KU. In contrast, hydrothermal microcrystalline silica in cherts west of KU is interpreted to have formed in an extensional tectonic regime with sufficient heat supply. This research demonstrates that chert source is, in part, tectonic controlled, and chert geochemistry can be used in reconstructing paleoenvironments.

The expression of the Oceanic Anoxic Event 2 (OAE2) in the northeast of Brazil (Sergipe-Alagoas Basin) Publication date: 1 September 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 529 Author(s): Bruno Valle, Patrick Führ Dal' Bó, Marcelo Mendes, Julia Favoreto, Ariely Luparelli Rigueti, Leonardo Borghi, Joalice de Oliveira Mendonça, Roberto Silva Abstract Global oceanic anoxic events occurred throughout the Cretaceous and changed the sedimentation patterns in many sedimentary basins around the world. There is still a lack of data and the need to identify new sections affected by these events in the Southern Hemisphere in order to provide insights on the extent of low-oxygen oceanic conditions. This study presents sedimentological, petrographic, and geochemical data from a continuous 439-m-thick well core drilled in the Sergipe-Alagoas Basin. The analytical data suggest that anoxic conditions prevailed at the end of Cenomanian and the beginning of Turonian, being globally correlatable to the Oceanic Anoxic Event 2 (OAE2). The results on the delimitation and extent of the OAE2 in the Sergipe-Alagoas Basin aid to better define the paleoceanographic changes that occurred in the South Atlantic Ocean during OAE2 and provide a new set of data that enables further studies and correlation to other sections distributed worldwide.

Characterization of bone surface modifications on an Early to Middle Pleistocene bird assemblage from Mata Menge (Flores, Indonesia) using multifocus and confocal microscopy Publication date: 1 September 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 529 Author(s): Hanneke J.M. Meijer, Francesco d'Errico, Alain Queffelec, Iwan Kurniawan, Erick Setiabudi, Indra Sutisna, Adam Brumm, Gerrit D. van den Bergh Abstract Island Southeast Asia (ISEA) is a key region for the study of human evolution. New fossil and archaeological evidence, from several islands, suggests an Early to Middle Pleistocene colonisation date by hominins. A taphonomic framework, however, such as that exists for Africa, is currently lacking, and taphonomical studies of ISEA vertebrate assemblages are very limited. In this paper, we apply multifocus and confocal microscopy to surface modifications on an Early to Middle Pleistocene avian assemblage from Mata Menge, in the So'a Basin of central Flores, Indonesia, with the aim of characterizing material and testing the relevance of 3D reconstructions to study the taphonomy of ISEA bone assemblages. Our observations document a number of bone surface modifications, including individual parallel grooves, overlapping spindle-like striations, elongated impacts, short composite grooves, and rows of pits. These features suggest that several taphonomic agents were at play during and after the accumulation of the Mata Menge small vertebrate assemblage. We find no unambiguous evidence for the exploitation of birds by the So'a Basin hominins, or for hominins being a significant accumulating agent of avian remains at Mata Menge. However, our work should be seen as preliminary, as direct comparative data on relevant biological agents are lacking. The markedly distinct faunal composition and climatic regimes of many Southeast Asian islands, and the potential use of different tools by hominins, warrants the development of a comprehensive taphonomical framework that is specifically relevant for ISEA.

Redox conditions and manganese metallogenesis in the Cryogenian Nanhua Basin: Insight from the basal Datangpo Formation of South China Publication date: 1 September 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 529 Author(s): Zhixin Ma, Xiting Liu, Wenchao Yu, Yuansheng Du, Qiuding Du Abstract In South China, the Datangpo Formation was deposited during the Cryogenian interglacial stage between the Sturtian and Marinoan glaciations. The variations in paleoocean chemistry recorded in the Datangpo Formation are important to understand the formation of Mn ore as well as the early evolution of animals, which are not well constrained. Based on lithological observation and multi-geochemical proxies (iron speciation, Mo, U, V, Mn, Al and pyrite sulfur isotope) from drill core ZK43-6 from southeastern Chongqing, South China, the results indicate an anoxic (mostly euxinic) water condition for the lower black shales of the Datangpo Formation, which can be further divided into four intervals (I, II, III, IV). Among of them, very high Mn content and manganese metallogenesis is related to the suboxic Interval II between two euxinic depositions (Interval I and Interval III). Thus, our new findings suggest that the general euxinic condition at the basal Datangpo Formation is interrupted by a suboxic deposition (Interval II) where the manganese deposits formed. An updated model is proposed to shed light on the evolution in redox conditions of the Datangpo Formation as a function of sea-level and terrigenous input, and the genesis of "Datangpo-type" manganese in light of the temporal seawater redox conditions and microbial activity.

Advances in characterizing the cyclostratigraphy of binary chert-mudstone lithologic successions, Permian (Roadian-lower Capitanian), Chaohu, Lower Yangtze, South China Publication date: 15 August 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 528 Author(s): Xu Yao, Linda A. Hinnov Abstract Successions of Mesozoic and Paleozoic radiolarian-bedded cherts display a "binary" cyclic hierarchy of cm-scale chert and mudstone couplets. Some of these couplet successions contain an apparent imprint of Milankovitch cycles, in which the couplets may reflect changes in silica deposition related to Milankovitch forcing, for example, high insolation for chert deposition, and low insolation for mudstone. The challenge has been how to represent such binary lithologic series in a format that is suitable for signal processing to search for Milankovitch cycles. Here we present an analysis of chert-mudstone binary series by considering, in lieu of a "boxcar" linear interpolation, a "midpoint-triangle" linear interpolation. The procedure is demonstrated first on synthetic data, then on the binary chert-mudstone stratigraphic series of the Permian (Guadalupian: Roadian-lower Capitanian) Gufeng Formation, Chaohu, Lower Yangtze, South China. We assign −1 to the midpoint of each mudstone bed and 1 to the midpoint of each chert bed, then linearly interpolate from midpoint to midpoint along the succession. Time-frequency analysis of the midpoint-triangle series highlights a previously unnoticed stratigraphic alternation of obliquity and precession band power. Finally, we present a revised astrochronology for the Gufeng succession that is anchored at 270 Ma at the base of the Jinogondolella nankingensis conodont zone (base of Roadian stage) and ending at 264.6 Ma in the undifferentiated Follicucullus scholasticus-Ruzhencivisponus uralicas radiolarian zone (mid-Capitanian Stage), for a duration of 5.4 Myr.

The mid-Homerian (Silurian) biotic crisis in offshore settings of the Prague Synform, Czech Republic: Integration of the graptolite fossil record with conodonts, shelly fauna and carbon isotope data Publication date: 15 August 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 528 Author(s): Štěpán Manda, Petr Štorch, Jiří Frýda, Ladislav Slavík, Zuzana Tasáryová Abstract The middle Homerian biotic crisis resulted in the almost complete eradication of graptolites. The shale-dominated Kosov Quarry section, central Bohemia, preserves the most complete graptolite record across the crisis in peri-Gondwanan Europe. The pre-extinction graptolite assemblage of the upper lundgreni Biozone, composed of ten species vanished in three extinction phases recognized in an interval 1.6 m thick. The crisis commenced with the increasing dominance of generalist taxa and subsequent extinction of several abundant species including Cyrtograptus lundgreni. The second phase coincided with the extinctions of genera Cyrtograptus and Testograptus, whereas long-ranging, generalist monograptids prevailed before they became extinct as the crisis culminated in its third phase in the flemingii Biozone. The lower part of the overlying parvus Biozone contains only Pristiograptus parvus, which became abundant in the upper part of the biozone, together with incoming Gothograptus nassa. The recovery interval is marked by a moderate diversification of monograptids and retiolitids. The extinction did not affect the diversity of pelagic cephalopods although their abundance was reduced. A bivalve-dominated benthic fauna disappeared throughout the extinction interval and re-appeared not earlier than in the latest Homerian. It was temporarily replaced by a time-specific fauna of anachronistic trilobites and brachiopods. The extinction interval coincided with sea-level fall, indicated by limestone slump-beds in a generally shaly succession. The post-extinction interval corresponds with a lowstand systems tract with deposition of condensed shelly limestone and burrowed shale. A positive carbon isotope excursion started in the flemingii Biozone and δ13C values increased up to the lower parvus Biozone above which the plateau of the first peak started. The beginning of the graptolite extinction predated the early phase of the late Homerian carbon isotope excursion. The terminal phase of the extinction, nevertheless coincided with the onset of the carbon isotope excursion and change in benthic fauna.

Astronomical constraints on deposition of the Middle Triassic Chang 7 lacustrine shales in the Ordos Basin, Central China Publication date: 15 August 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 528 Author(s): Rui Zhang, Zhijun Jin, Quanyou Liu, Peng Li, Zhenkai Huang, Juye Shi, Yunjin Ge, Kefeng Du Abstract The Middle Triassic was a key period that witnessed the evolution of Earth system processes and the commencement of a terrestrial lake in the Ordos Basin, Central China. A high-precision stratigraphic framework is the key to understanding the nature and pattern of critical geological events. Detailed time series analyses of magnetic susceptibility (MS) data were performed on the deep lacustrine shale-dominated Chang 7 Member of the Yanchang Formation from the Y1011 well core. The results reveal well documented cyclic variations with wavelengths of 5.37 m, 1.39–1.78 m, 0.48 m, and 0.24–0.30 m, which are driven by long-eccentricity, short-eccentricity, obliquity, and precession in the Middle Triassic. The stable 405-kyr tuned floating astrochronological time scale (FATS) reveals that the depositional duration of the Chang 7 Member is approximately 5 Myr, and the sedimentation rates range from 0.90 cm/kyr to 1.69 cm/kyr. In particular, the lower part of the Chang 7 Member is characterized by an organic-rich, black shale, called "Zhangjiatan Shale", whose depositional duration can be estimated at about 1.7 Myr. Along with the published biostratigraphic divisions and UPb age constraints, our FATS further confirms that the Chang 7 Member mainly developed in the Ladinian Stage, and that the upper part of the Chang 7 spanned the Middle/Late Triassic boundary. The duration of the Chang 7 deposition suggests a temporal and genetic linkage between the responses of the Chang 7 shales in the Ordos Basin and the Indosinian Orogeny in the Qinling orogenic belt. The Ladinian Stage of the Middle Triassic probably witnessed a dramatic shift in the evolution of the regional geodynamic system.

Are light-dark coupled laminae in lacustrine shale seasonally controlled? A case study using astronomical tuning from 42.2 to 45.4 Ma in the Dongying Depression, Bohai Bay Basin, eastern China Publication date: 15 August 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 528 Author(s): Ke Zhao, Xuebin Du, Yongchao Lu, Shipeng Xiong, Yong Wang Abstract As a typical sedimentary structure in fine-grained rocks, laminae are widely distributed in shales and mudstones in sedimentary basins. The Shahejie Formation (42.2–45.4 Ma) formed during the Eocene of the Paleogene in the Dongying Depression of China is recognized as a typical area to study lacustrine shale. According to the composition of different lamina, four types of couplets are identified, including carbonate-clay couplets, carbonate-organic couplets, clay-organic couplets and carbonate-clay-organic triplets. All couplets are composed of light and dark layers. A combination of core images, microscopic observations, mineral compositions, geochemical data, carbon and oxygen isotopes, and strontium isotopes verifies that the laminae are primarily developed in a saline and anoxic, or even euxinic environment, with a high organic matter (OM) flux. Through astronomical cycle analysis of the natural gamma ray (GR) curve from sample site well NY1, the data suggest that the lacustrine shale laminae are formed annually with an average duration of 1.34 yr. The formation of laminae is affected by the season, which is closely related to the seasonal growth and death of algae. During the period of algae growth, a large number of light-colored carbonate laminae are deposited, whereas when the algae dies, organic matter accumulates at the bottom of lakes and forms dark organic-rich laminae. The interbedded and lenticular laminae, which are subdivided by layering characteristics, are primarily affected by diagenesis in postdepositional processes. Study of the laminae is helpful in understanding the formation process of lacustrine shale, and it provides invaluable sources of information for paleoclimate reconstruction.

n-Alkane distribution in ombrotrophic peatlands from the northeastern Alberta, Canada, and its paleoclimatic implications Publication date: 15 August 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 528 Author(s): Dashuang He, Haiping Huang, Gabriela Gonzalez Arismendi Abstract In this paper, the stratigraphic occurrence of n-alkanes (Cn) is investigated in three peat cores (Mildred, JPH4 and McMurray) from the ombrotrophic peatlands in northeastern Alberta, Canada, to determine their origin, biomass input, and paleoclimatic significance. The molecular composition of n-alkanes is dominated by the >C21 medium- to long-chain homologues, with a strong odd over even predominance. A number of n-alkane-based indices (e.g. predominant n-alkane, C23/C29, C23/(C27 + C31), Paq, ACL, and CPI), show changing conditions in the organic matter (OM) input from Sphagnum species or terrestrial vascular plants, which increasingly contributed upwards in the peat profiles, and through time. Paq and C23/(C27 + C31) proxies are similar in the three cores, and allow us to infer vegetation variations that coincide with the climate alternations of the Medieval Warm Period (MWP), Little Ice Age (LIA), and modern Recent Warming (RW). The utilization of ACL-ket and (C23 + C25)/(C27 + C29 + C31)-ket proxies, performed in comparison with n-alkane proxies, further support the biomarker-based reconstructions of paleoclimate variations over recent centuries. This study suggests that n-alkane homologues are sensitive to vegetation and climate changes and thus are reliable biomarkers for tracking past shifts in vegetation and climate variations in peat archives.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
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6948891480

alsfakia@gmail.com