Journal of Palaeogeography最新文献

Two well-preserved petrified palm stems from the latest Maastrichtian (Late Cretaceous) to earliest Danian (Early Paleocene) sediments of the Deccan Intertrappean Beds of Madhya Pradesh, Central India are described. Their significant anatomical characteristics include a Calamus-type general stem pattern, the presence of well-preserved fibrovascular bundles (fvbs) with two wide metaxylem vessel elements (230 μm–250 μm) and one phloem strand, uniform density of fvbs, lack of continuity between protoxylem and metaxylem vessel elements, and an absence of centrifugal differentiation of sclerenchymatous fibrous parts. These features reveal a close resemblance to those of extant genera of scandent Calamoideae. The permineralized stems are described as a new species namely, Palmoxylon calamoides Kumar, Roy et Khan sp. nov. The fossils represent the oldest reliable fossil records of this family, supporting their Gondwanan origin, their importance in tracing their migration pathways from India to Europe and other continents after the docking of the Indian subcontinent with Eurasia during the Paleocene, and an “Out-of-India” dispersal hypothesis. Today the subfamily Calamoideae is disjunctly occurred in Africa, Asia, Australia, Europe, and South America, but the poor deep-time fossil record of this subfamily with a small number of Cenozoic fossils makes hypotheses concerning its origin and dispersal difficult to evaluate. The present study has significant implications for the origin and migration of this subfamily and the paleoclimate.

Geochemical and mineralogical studies were performed in the La Pesca (LP) and Tesoro Altamira (TA) beach sediments, located in the Tamaulipas state, northern Gulf of Mexico. The main aim of this study is to infer the weathering history and provenance and to discriminate the tectonic environment of the beach sediments. The sediments are composed of quartz with small amounts of accessory minerals such as plagioclase, calcite, orthoclase, microcline, and zircon. Both beach sediments are classified as fine-grained and very well sorted, however LP has coarse skewed and leptokurtic sediments, whereas TA has fine-skewed and very leptokurtic sediments. The chemical index of weathering (CIW’) indicates intense weathering in the source area. The quartz grain microtextures in the LP and TA are classified into mechanical, chemical, and mechanical/chemical origin. Mechanical features such as fractures, pits, percussion marks, abrasion fatigue, and V-shaped marks favor high-energy littoral, fluvial, subaqueous-marine, and aeolian environments. The chemical features indicate solution pits and crystalline overgrowth, which suggests a silica saturated marine environment. The mechanical/chemical features display adhering particles and elongated depressions suggest formation in a sub-aqueous nearshore marine environment. Major and trace elements-based provenance discrimination diagrams indicate a felsic source derived from the Mesa Central (MC), Sierra Madre Oriental (SMOr) and Oaxaquia terranes. The major and trace element concentrations imply a passive margin setting for the northern Gulf of Mexico, which is consistent with the general geology.

Despite their potential for providing important information for paleobiogeography, studies using ostracod assemblages compiled from global datasets have been scarce so far. In this study, the paleogeographic implications of the relationship between different ostracod assemblages are analyzed and discussed for the Albian and Cenomanian. We compiled an ostracod dataset at the genus level, with 168 genera for the Albian and 174 for the Cenomanian, to which different multivariate statistical methods of grouping were applied. The affinity between different ostracod assemblages from different regions allowed for the delineation of 30 operational geographic units (OGUs) for the Albian, and 32 OGUs for the Cenomanian, grouped in three paleobiogeographic units (PBUs; Megatethys, Persia, and Austral) and one sub-unit (PBSU; Maghreb associated to the Megatethys). The Maghreb PBSU showed minor changes between the Albian and Cenomanian. The relationship among the OGUs grouped in each PBU is related to different factors, such as eustatic sea level events, similar climatic zones, and marine current circulation patterns. A relationship was observed between the Gabon and Nigeria OGUs with the Persia PBU, which suggests a direct east–west connection between them during the Cenomanian. The affinity observed in the Austral PBU between the South American, South African, and Australian regions during the Albian can be explained by their relative geographic isolation due to the Walvis Ridge barrier. The eventual flooding of this barrier led to the relationship observed between the SE Brazilian and Bolivian regions with the Austral PBU. Finally, the data also suggested that the separation of the Indian subcontinent from the Austral PBU took place during the Cenomanian.

Lower Buntsandstein small–scale cycles recognized in the Central European Basin (CEB) are readily used for astrochronological calibration of the Early Triassic time scales, although they are not well studied sedimentologically. Three borehole sections from the eastern part of the CEB, forming a south-north transect perpendicular to the basin axis, were studied in terms to better understand the depositional history of the Lower Buntsandstein developed as the Baltic Formation in the studied Polish part of the basin. Eleven sedimentary facies were recognized, based on lithological and sedimentological investigations of 655.7 m of drill cores from the Otyń IG 1, Gorzów Wielkopolski IG 1 and Kamień Pomorski IG 1 boreholes. The facies can be grouped according to a lithological criterion into facies of predominantly siliciclastic lithology (including 9 facies types) and facies of predominantly carbonate lithology (including 2 facies types). Facies analysis allowed to distinguish 8 facies associations of: 1) alluvial fan, 2) playa, 3) sandy-muddy coastal plain, 4) embayment and distal delta, 5) lagoon, 6) sand bars or shoals, 7) ooidal shoals or bars, and 8) offshore. Deepening-upward (DC) and shallowing-upward (SC) sedimentary cycles were recognized in parts of the Baltic Formation, with DCs dominating in the southernmost located Otyń IG 1, and SCs dominating in Gorzów Wielkopolski IG 1, located in the axial part of the basin. Symmetrical cycles are very rare. The statistical significance of the sedimentary cycles is relatively low according to Markov-chain analysis conducted with the phpSedistat software of Stanova et al. (2009). Analysis of small–scale cycles performed on well logs of investigated boreholes and additional boreholes in the vicinity of Otyń IG 1, implementing the earlier study of Becker (2005), showed that the correlation of well-log cycles (GR cycles) and sedimentary cycles is not obvious. GR cycles can be roughly correlated with lithological carbonate–siliciclastic cycles (c-s cycles), reflecting alternations of facies groups of predominantly carbonate and siliciclastic lithology. Calibration of GR cycles to earlier magnetostratigraphic results of Nawrocki (1997) and Becker and Nawrocki (2014) showed that neither the boundaries of GR cycles serve as reference horizons, nor the cycles document equal time periods. All existing depositional models of the Lower Buntsandstein were discussed, stressing the possible simultaneous interaction of allochthonous and autochthonous processes. Moreover, the tectonic overprint of the Central European Basin system during the Early Triassic should be taken into account. The presented results suggest that the Lower Buntsandstein cyclicity of the CEB cannot serve as a basis for astrochronological analysis.

Detailed sedimentological analysis of the Pokaran Boulder Bed, representing the most basal unit of the Neoproterozoic-Lower Cambrian Marwar Supergroup, clearly indicates its glacial origin. The glacial sediments are interpreted as an ice-contact submarine fan deposit. Based on the detrital and inherited zircon population of the Marwar Supergroup sediments and interlayered pyroclastic deposits, a Marinoan cryochron of the Cryogenian Period is envisaged for the Pokaran Boulder Bed. The well-preserved Ediacaran elements in the post-glacial sedimentary succession also support a Cryogenian to Early Cambrian age of the Marwar Supergroup. The glacial deposition at the base of the Marwar Supergroup strengthens the regional correlation between the studied sediments with the Lesser Himalayan Blaini-Krol-Tal sediments and the Haqf Supergroup of Oman. The available zircon ages and paleomagnetic data of the Malani Igneous suite, along with the Marinoan glacial deposits, detrital zircon ages, and Ediacaran fossil elements of the Marwar Supergroup add significant information to the Neoproterozoic Earth history.

The late Maastrichtian witnessed substantial surges in Deccan volcanism, prompting the hypothesis that these voluminous pulses may have instigated repeated episodes of ocean acidification during this period. The Cretaceous-Palaeogene (K/Pg) boundary at Bidart (France) is preceded by a ∼0.5 m thick interval with geochemical and taphonomic vestiges of an ocean acidification event linked with Deccan volcanism. New planktic foraminifera census and morphometric data now confirm biotic stress conditions related to acidification in the Deccan benchmark interval. The absolute abundance data of larger (>150 μm) heavily calcified planktic morphogroups show fluctuating populations throughout zone CF1 (spanning the final ∼225 ky), lowest peaks within the Deccan benchmark, and a demographic collapse (>90%) at the K/Pg boundary. The analyzed species are generally reduced in size, with thinner test walls in this ∼0.5 m interval, indicating the likelihood of calcification stress as a contributor to the overall biotic stress. At the K/Pg boundary, maximum biotic stress is recorded in all the tested faunal proxies. A preliminary graphic correlation of zone CF1 at Bidart with the auxiliary GSSP at Elles (Tunisia) constrains the Deccan benchmark interval of high biotic stress to the final ∼58 ky of the late Maastrichtian, culminating in the K/Pg mass extinction. The volcanogenic Hg peaks coincident with faunal and taphonomic evidence of ocean acidification strengthen the Deccan-related ocean acidification hypothesis.

Coniopteris simplex is a common component in many Jurassic floras. However, due to morphological variations in sterile fronds and incomplete preservation of reproductive organs, its classification has been controversial for a long time. Here, we present new material collected from the Middle Jurassic Yan'an Formation in the Ordos Basin, Inner Mongolia. The new material reveals important morphological characters, including hemi-dimorphic fronds, two forms of sterile pinnae, short-stalked sori and sporangia on fertile fronds, annulus of sporangium composed of about 30 cells, in situ rounded triangular spores with protruded suture, and the lips of trilete laesura encircled by one or two rows of small ostioles. Based on these observations, we emended the diagnosis of this common species. The spatio-temporal distribution of Coniopteris simplex shows that the iconic species was restricted to the paleolatitudes ranging from 19.5°N to 48.9°N in the Northern Hemisphere during the Early–Late Jurassic, mainly distributed in the tropical to paratropical zones, and the paleolongitude ranging from 9.6°E to 129.3°E, which may be limited by the opening of the Viking Corridor and the splitting of the Central Atlantic Ocean.

It is reported a multi-proxy palaeoclimatic study conducted on a MIS 5e calcarenite from the Mar Piccolo Basin (MP), Gulf of Taranto (GT) (Central Mediterranean). The calcarenite returned a rich malacofauna consisting of 120 extant species, including four of the tropical Senegalese Fauna, today absent in the Mediterranean. The biogeographic-climatic affinity of the assemblage shows, compared to today, a double percentage of warm affinity species, while the cold affinity species are nearly equally represented, indicating a warmer but not strictly tropical SST. This is confirmed by the most recurring preferred SST ranges of the assemblage, indicating an average of 20 °C. The skeletal compositions of five well-preserved molluscan and coral specimens were analyzed for trace elements and stable isotopes for further mean SST estimations. From the comparison of the results of several equations available in literature, it appears that only some SST estimations are realistic, converging into similar values of, on average, 20.8 ± 0.9 °C. Considering all the used proxies, the MIS 5e SST difference compared to today falls in the range 1.2–2.0 °C for the GT (being a more reasonable scenario) and 2.0–2.8 °C for the MP. This is not a firmly tropical-like SST setting as suggested by the sole Senegalese fauna, indicating at least 2.7 °C–3.5 °C more than today's GT and MP, respectively. The approximations and assumptions made for obtaining SST values with any single proxy indicate the need of a multi-proxy approach to define the best SST estimation.