Journal of Palaeogeography最新文献

The marl and limestone alternations of the Lower Jurassic Ain Ouarka and Ain Rhezala formations (Pliensbachian–Toarcian) in the western Saharan Atlas, Northwest Algeria, yield a diverse micro- and macrofauna, including moderately numerous crinoids, which are represented by remains of isocrinids, i.e., Balanocrinus ticinensis Hess and columnals of the genus Percevalicrinus. So far, the latter genus has been observed from the Upper Jurassic–Lower Cretaceous strata of Eurasia, North America, and the African continent. Thus, the present find is the oldest record of this crinoid genus, and the second one from the southern Tethyan margin. In this paper, it is shown that Percevalicrinus, which is traditionally regarded as a representative of the subfamily Balanocrininae, displays several features of the subfamily Isocrininae. The crinoid assemblage and associated facies and invertebrate fauna are typical of a low-energy deep outer shelf/ramp (below the storm wave-base) setting.

The Poso Depression provides a record of Plio-Pleistocene environments and palaeogeography of Central Sulawesi. Outcrop-based sedimentological and provenance studies suggest that during the Pliocene the Poso Depression was a sea channel connecting Gorontalo and Bone bays formed in an asymmetric half-graben. The Pliocene history began with deposition of the Puna Formation with fan deltas at the eastern basin margin and channel complexes in the deep-water basin further east. Analyses of light and heavy minerals indicate the main sediment source was ultrabasic rocks in East Sulawesi with minor and intermittent magmatic and metamorphic input from West Sulawesi. Later, in the Middle to Late Pliocene, carbonates of the Poso Formation accumulated on the eastern basin margin. They are unconformably overlain by shallow marine glaucophane-rich siliciclastics of the Pleistocene Lage Formation that are associated with the rapid exhumation and uplift of the Pompangeo metamorphic complex. This uplift led to the development of a land bridge connecting western and eastern Sulawesi. The terrane evolution favoured increasing the area of exposed land due to rapid tectonic uplift, which when combined with the tropical climate, contributed to faunal speciation and dispersal in Sulawesi.

Wildfire bears a close relationship with vegetation as its fuel source. The southeastern margin of the Tibetan Plateau witnesses frequent wildfires among various types of vegetation, whereas such wide interactions between wildfire and vegetation remain poorly studied from geological times. In this study, we reported a local fire using sedimentary macroscopic charcoals from the latest Miocene to early Pliocene of the Baoshan Basin in this region, and then inferred the local vegetation at the time of the fire event based chiefly on the coexistent fruit and seed fossil assemblage. Our taxonomic results show that the charcoal assemblage is probably dominated by broadleaved plants and the fruit and seed fossil assemblage is apparently dominated by Salix (Salicaceae) followed by Sambucus (Adoxaceae), suggesting a deciduous broadleaved forest in which the fire likely occurred. Under a seasonally dry climate associated with the Asian monsoon, this type of vegetation might be prone to natural fire, because in the wet rainy season the plants grew well to accumulate biofuel and in the dry season abundant ground litter resulting from leaf decay would be desiccated to become highly flammable. Due to the fire-tolerant habit of Salix as the dominant plant, the forest might be in return adapted to the fire event or even more fires that potentially followed. All these may suggest a close relationship between the fire event and the reconstructed vegetation. Our finding documents a new type of wildfire–vegetation interaction, namely the interaction between wildfire and deciduous broadleaved forest, from the geological past at the southeastern margin of the Tibetan Plateau. It therefore sheds new light on the wildfire history coupling vegetation change in the region.

The unequivocal identification of soft-sediment deformation structures (SSDS) is a significant attribute to constrain the effect of transient geological events in the spatio-temporal evolution of ancient sedimentary basins. This paper reports and discusses, for the first time, the occurrence of several cm- to dm-scale SSDS within sandstone successions of the Mesoproterozoic Kaimur Group (Vindhyan Supergroup), exposed at the Hanumandhara Hill of Chitrakoot-Satna border region, Madhya Pradesh State, India. The SSDS are confined to a deformed interval comprising seven individual sedimentary units of variable composition and texture, which are sandwiched between nearly horizontally undeformed sandstone beds. The SSDS consist of load structures (load casts, flame structures, pseudonodules and ball-and-pillow structures), contorted lamination, convolute lamination, boudins and pinch-and-swell structures, deformed cross-stratification, slump structures, clastic injections, fluid escape structures, and syn-sedimentary fractures/faults. The present study suggests that the formation of these SSDS is essentially related to a combination of processes (gravitational instability, liquefaction, fluidization, and fluid escape) predominantly induced by seismic shocks. In addition, the restricted occurrence of fractures/faults in these deformed layers emphasizes the passage of seismically-induced Rayleigh waves. Considering the observed types of SSDS, their lateral homogeneity and geographic distribution along with the geodynamic framework of the Vindhyan Basin, the whole area can be tentatively attributed to having experienced moderate- to high-magnitude (M ≥ 5) seismicity. The present study combined with earlier reports of seismically-induced SSDS, from other regionally disposed formations belonging to the Lower (e.g., Kajrahat Limestone, Chopan Porcellanite, Koldaha Shale, Rohtas Limestone, and Glauconitic Sandstone of the Semri Group) and Upper (e.g., Bhander Limestone of the Bhander Group) Vindhyan Supergroup, respectively, provides evidence for the constant regional-scale seismo–tectonic activity within the Paleo-Mesoproterozoic Vindhyan Basin. Importantly, this observation further suggests that the intracratonic basins can be active tectonically contrary to the earlier propositions.

Biomineralization was a key development in a wide variety of organisms, yet its history prior to the Ediacaran remains poorly understood. In this paper, we describe ∼1420–1330 million year old microscopic tubes preserved as siderite (FeCO₃). In size and shape these tubes closely resemble cyanobacterial sheaths forming mineralized mats. We consider two competing explanations for their formation. First, the tubes and associated sediment were originally composed of Ca-carbonate that was subsequently replaced by siderite. In this case, siderite mineralization was early, but post-mortem, as in early silicification, and preferentially preserved the more resilient sheath. However, no relict calcite is observed. Second, the Fe-carbonate mineralogy of the tubes and sediment is synsedimentary. In this case, photosynthetic oxygen may have precipitated Fe-oxyhydroxide that was promptly converted to siderite by dissimilatory iron reduction (DIR). Primary siderite mineralization of cyanobacteria has not been described before. Both explanations link photosynthetic processes to preferential sheath mineralization during the life of the cyanobacteria, as observed in present-day calcified cyanobacteria. This process might include CO₂-concentrating mechanisms (CCMs) linked to relatively low levels of atmospheric CO₂, consistent with empirical estimates of mid-Proterozoic CO₂ levels based on paleosols and weathering rinds. In either case, these cyanobacterium-like fossils preserved in siderite provide an early example of biomineralization and suggest the interactive influences of both metabolic processes and ambient seawater chemistry.

This paper describes newly discovered dinosaur and crocodylomorph egg fragments from the Upper Cretaceous Sanshui and Dalangshan formations of the Sanshui Basin of Guangdong Province, southern China. Despite the absence of macroscopic information, the eggshell specimens can be identified to the oofamilies Prismatoolithidae, Elongatoolithidae and Krokolithidae, and it is hypothesized that these three families of eggs correspond to troodontids, oviraptorids and crocodiloids, respectively. Comparison with egg fossils from Nanxiong Basin, Heyuan Basin and Ganzhou Basin highlights the similarity between these egg assemblages and those from Nanxiong Basin. The egg fossils found in the Sanshui and the Dalangshan formations enrich the known faunal types in the research area and facilitate further studies on the diversity of Late Cretaceous vertebrate assemblages in the Sanshui Basin.

Tracks previously examined between 2002 and 2015 from an incompletely-studied, and now partially lost tracksite site in the Santai Formation of Shandong Province were restudied based on new excavations of additional surfaces. In contrast to the previous reports of tridactyl tracks, including Grallator, the present study discovered an additional assemblage of unequivocal pterosaur tracks (Pteraichnus) and a possible didactyl deinonychosaurian track. The age of the Santai Formation is controversial but it is probably Late Jurassic, which corresponds to the epoch when pterosaur tracks appear worldwide. Age interpretations, based on palynology and isotopic data, tentatively suggests an earlier Middle-Late Jurassic age and might suggest that the pterosaurian tracks are as old or somewhat older than any previously reported.

The sedimentary successions around the Carboniferous–Permian boundary (CPB) in the Ordos Basin were investigated using extensive outcrop, borehole, well logging, thin section, and geochemistry data to study sedimentary and sequence stratigraphic responses to glaciation and volcanism in paleotropical transitional strata. Within the studied interval, five distinct lithofacies have been identified, including bauxite, coal, and carbonaceous shale (No. 8 + 9 coal seams), sandstone (Qiaotou), limestone (Baode), and mudstone, which can be classified into three lithofacies associations. The most complete lithofacies association is composed of bauxite, coal, carbonaceous shale, sandstone, limestone/mudstone or their combinations from the bottom to the top, while coal and carbonaceous shale, as well as sandstone, are absent locally, resulting in the formation of the other two types of lithofacies associations. The occurrence of bauxite indicates shelf exposure and weathering, the occurrence of coal and carbonaceous shale indicates swampiness of the shelf, and the occurrence of sandstone reveals river rejuvenation; all of these are thought to be sedimentary responses to the transcontinental glacier expansion in Gondwana around the CPB. The presence of limestone and mudstone indicates carbonate platform and lagoon deposition, respectively, in the context of the earliest Asselian transgression caused by volcanism-induced glacier melting. The lithofacies associations record the regressive–transgressive cycles that occurred because of glaciation and volcanism near the CPB. The top surface of bauxite can be used as a sequence boundary, while the lowstand systems tract consists of the No. 8 + 9 coal seams and the Qiaotou sandstone, and the transgressive systems tract consists of the overlying Baode limestone and laterally equivalent mudstone. The lowstand systems tract, which contains source rock and hydrocarbon reservoirs, and the overlying transgressive systems tract, which serves as cap rock, form an excellent source-reservoir-seal combination.