Journal of Palaeogeography最新文献

The Cretaceous was a significant greenhouse period in Earth's history with higher atmospheric CO₂ levels and temperatures than today. Although evidence of combustion has been widely described from the Cretaceous deposits, our understanding of the spatiotemporal diversification pattern and process of the Cretaceous wildfires is still limited. In this study, we comprehensively synthesize a total of 271 published Cretaceous wildfire occurrences based on the by-products of burning, including fossil charcoal, pyrogenic inertinite (fossil charcoal in coal), and pyrogenic polycyclic aromatic hydrocarbons (PAHs). Spatially, the dataset shows a distinctive distribution of reported wildfire evidence characterized by high concentration in the middle latitudinal areas of the Northern Hemisphere (30°N–60°N) over the Cretaceous. Temporally, an overall increasing trend of the reported wildfire data from the Early Cretaceous to the Late Cretaceous is coincident with higher atmospheric O₂ levels. However, the spatial and temporal patterns may result from many types of factors, such as taphonomy, preservation, and researcher biases, instead of a real picture of the Cretaceous wildfire evolution. To better understand the spatiotemporal diversification of the Cretaceous wildfire, more investigations on the record of wildfire occurrences during this period would be necessary in the future.

The Indian Peninsula is one of the most well-studied regions for Holocene sea-level fluctuations in the world, however, standardized relative sea-level datasets are missing. This study provides an archive of sea-level indicators (n = 162, 20 locations) along the western and the eastern sides of the peninsula, that have been used to develop Relative Sea Level (RSL) plots. Each dated sea-level indicator is recalibrated for its elevation based on tidal and tectonic correction, as well as age with reservoir correction, and have been separated into six zones based on coastal geomorphology and number of datasets. The database spans throughout the Holocene and covers sea-level depth/elevations from −45 m to +5 m from mean sea-level (MSL). Approximately 90 % of the dataset range from 8 ka to the present day. The first transgression is highly variable and identified between 8.5 - 8 ka BP in Gujarat (Zone 1), ∼ 5.5 ka BP in Maharashtra (Zone 2), between 8 and 7 ka BP in Tamil Nadu (Zone 4) and between 8 and 7.5 ka BP in the Bengal coasts (Zone 6). No transgression above present sea-level is observed along Andhra Pradesh (Zone 5) (no data for Kerala - Zone 3). Further, Zones 1, 2, 4 and 6 show a strong uplift component (tectonic), whereas Zone 5 exhibits subsidence during the Holocene (Zone 3-insufficient data). Based on these findings, and given the region's coastal topography and tidal components, Zones 6 and 1 will likely undergo the largest coastal inundation, followed by Zones 5, 4, 2, and 3. These insights are critical in planning future coastal inundation measures across the Indian Peninsula.

Carbonate deposits in the Ordovivian Majiagou Formation are significant source rocks for natural gas generation in the Ordos Basin, northwestern China. Previous studies mainly focused on the organic matter enrichment mechanism of shales rather than carbonate rocks. The biological sources and paleoenvironment of carbonate source rocks, and the main controlling factors of organic matter enrichment in the carbonate source rocks were studied in this paper in combination with evidence from biomarkers, microfossils and inorganic geochemistry analysis. The results show that four types of microfacies were identified in the Majiagou Formation, respectively as: mud flat microfacies, mud–dolomite flat microfacies, dolomite flat microfacies, and open marine microfacies. The biological sources of organic matter are chiefly planktonic algae, followed by bacteria. The mud flat and mud–dolomite flat contain a high abundance of terrigenous detrital inputs, as indicated by the high content of Al₂O₃, TiO₂, Th, and Zr. The low Sr/Cu and high Rb/Sr values reveal warm and humid paleoclimate conditions in the mud flat and mud–dolomite flat, whereas the dolomite flat and open marine were likely formed in hot and arid paleoclimate conditions. The mud flat and mud–dolomite flat deposits were characterized by high paleoproductivity of the Majiagou Formation. Low Sr/Ba values were found in the mud flat samples, indicating fresh to brackish water condition, whereas samples of other facies have a relatively high degree of salinity. Based on U_auth, Mo_auth, Cr_auth, Co_auth, δCe, and δEu values, the mud flat microfacies was formed in a suboxic and anoxic environment, whereas the mud–dolomite flat, dolomite flat and open marine microfacies were within dysoxic to oxic conditions. A model of organic matter enrichment in the Majiagou Formation is thus established. The level of terrigenous detrital inputs is the principal factor of organic matter enrichment in the Majiagou Formation, secondly are redox condition and then paleoproductivity. The mud flat and mud–dolomite flat microfacies show abundant terrestrial detrital inputs and nutrient elements, indicative of warm and humid climate that facilitated biotic productivity, including an abundance of planktonic algae (microfossils). The suboxic and anoxic environments promoted the preservation of organic matter, as evidenced by the relatively high TOC content. The mud flat as well as the mud–dolomite flat of the Majiagou Formation is prospecting for forming source rocks.

Precise taxonomy and the chronostratigraphic calibration of the Middle Eocene Alveolina from Central Iran is here undertaken from the Chah-Talkh section of the southern Sabzevar region (Central Iran). We have identified Alveolina kieli, Alveolina stercusmuris and Alveolina nuttalli along with the new species Alveolina ozcani n. sp. that we include into the Alveolina elliptica group. We have also found Nummulites uroniensis, Nummulites obesus and Nummulites cf. verneuili and associated calcareous nannofossils that look reliable to make thoughtful correlations with the Shallow Benthic Zones (SBZ). The foraminiferal biostratigraphy suggests an assignment to the upper part of the lower Lutetian–lower part of the middle Lutetian, SBZ13 (Middle Eocene), further strengthened through the identification of the calcareous nannofossil NP14b–NP15b or CNE8–CNE10 biozones, providing a solid correlation with the global stratigraphic standards.

The shallow marine carbonates of the upper Oligocene Qom Formation yielded several occurrences of the foraminiferan genus Neoplanorbulinella Matsumaru. Neoplanorbulinella saipanensis Matsumaru has so far been recorded from the late Eocene–early Miocene of Japan and late Oligocene of NE Italy whereas N. malatyaensis Gedik is only reported from the Oligocene from its type locality in the Malatya Basin, eastern Turkey. The new records reported here from the Qom Formation indicate that both species occur in the Dobaradar section, ca. 10 km south of the city of Qom in North–Central Iran. The palaeogeographic distribution of these two species therefore has to be extended as far as the palaeolongitude of current Central Iran. The accompanying larger benthic foraminifers, including Miogypsinoides complanatus (Schlumberger), M. formosensis Yabe and Hanzawa, Spiroclypeus margaritatus (Schlumberger), Operculina complanata (Defrance), and Risananeiza pustulosa Boukhary et al., indicate the upper Chattian SBZ 23 Zone. The co-existence of the N. saipanensis and N. malatyaensis points to suitable palaeobiogeographic conditions of Central Iran to host Western and Eastern Tethyan taxa.

After the extinction of Archaeocyatha (sponges), microbial bioherms were well developed in the lower Cambrian of the Yangtze cratonic basin, especially in the Qingxudong Formation (Cambrian (Stage 4)) of the Huayuan area, northwestern Hunan Province, southern China. Herein, four sections from this area were chosen for investigating and analyzing their microfacies and depositional environment. Twelve microfacies types were recognized through petrographic analysis of textural attributes and calcimicrobes (including Epiphyton, Renalcis, Girvanella and Kenella), respectively as: laminated calcareous mudstone (MF1), algal wackestone (MF2), intraclastic grainstone (MF3), algal intrasparrudite (MF4), oolitic algal intrasparrudite (MF5), sparry oolitic grainstone (MF6), Epiphyton framestone (MF7), Renalcis bafflestone (MF8), Kenella bafflestone (MF9), Girvanella boundstone (MF10), thrombolitic boundstone (MF11), and dolomite (MF12). These microfacies represent four major depositional environments: carbonate ramp, carbonate platform, slope and tidal flat. Calcimicrobes played an important role in the transition from carbonate ramp to platform, while the evolution from ramp to tidal flat must be ascribed to sea-level fall during the Cambrian Age 4.

For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mass flow processes, are here reviewed. Detailed studies of data offered in support of pre-Pleistocene glaciations have led to revisions that involve environments of mass movements. Similarities and differences between Quaternary glaciogenic and mass movement features are examined, to provide a more systematic methodology for analysing the origins of more ancient deposits. Analyses and evaluation of data are from a) Quaternary glaciogenic sediments, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass movements (and occasionally tectonics). Multiple proxies are assembled to develop correct interpretations of ancient strata. The aim is not per se to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual framework.

Regularly occurring pre-Pleistocene features interpreted to be glaciogenic, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features include, for example, environmental affinity of fossils, grading, bedding, fabrics, size and appearance of erratics, polished and striated clasts and surfaces (“pavements”), dropstones, and surface microtextures. Recent decades of progress in research relating to glacial and sediment gravity flow processes have resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than glaciation.

The most coherent data of this review, i.e., appearances of features produced by glaciation, sediment gravity flows and a few other geological processes, are summarized in a Diamict Origin Table.

The stratigraphic surface represented by a major contact between the Archean Bundelkhand Granite and the extensive Proterozoic Vindhyan sediments is a regional basement cover unconformity. This crystalline–sedimentary interface reflects an intense weathering of continental crust during marine transgression. Three time-transgressive sand deposition events viz. Kaimur, Rewa and Bhander are mainly witnessed during the entire Vindhyan sedimentation. Stratigraphically, the Upper Rewa Sandstone comprises one of these events in the Vindhyan Basin. Considerable progress has been made in interpreting these sandstones as a function of entirely marine process to a combination of tidal–fluvio–eolian activities. All the results have so far been attained on the basis of sedimentary facies, provenance, palaeocurrent analysis, and some of petrography. A distinct differentiation between marine and fluvial components of the Upper Rewa Sandstone still remains uncertain. Here, we use diagenesis as a parameter for the first time along with facies and palaeocurrent analysis to acquire a clear comprehension of marine- and fluvial-dominated processes. The present study spans 27 square kilometer area covering 15 stratigraphic sections with a collection of 571 directional data from the facies specific sedimentary structures, and 28 samples obtained for the thin section analysis.

The lower unit of the Upper Rewa Sandstone shows facies association typical of tidal environment, along with polymodal palaeocurrent. These rocks are well sorted and dominantly lithified by authigenic cement. Profuse development of a complex of syntaxial, passive pore fills, and grain replacive cements reflect normally pressured nature of the lower unit sandstones. The upper unit of the Upper Rewa Sandstone however, reveals a facies pattern resembling fluvial processes and unimodal palaeocurrent plot. They exhibit poor sorting, siliceous, and ferruginous matrix, and development of intense stylolites. Since, pressure solution is a dominant mode of lithification; the upper unit rocks therefore, are overpressured. Sand deposition event pertaining to the Upper Rewa Sandstone is found to comprise both marine and fluvial processes. Such a diagenesis based approach can be applied for marking a possible facies based unconformity between genetically different depositional units.

Early Cretaceous succession of the Oued Fodda Formation in the Ouarsenis Mountains (northwestern Algeria) is mainly composed of marl–limestone alternations, which are subdivided into four informal units (Units 1 to 4), based on distinct lithological, stratonomical, and ichnological features. The ichnological analysis reveals a low diversity of the trace-fossil assemblage, which is exclusively reported from Units 2 and 3. The ichnoassemblage contains six ichnotaxa (Chondrites intricatus, Ophiomorpha isp., Planolites isp., Thalassinoides isp., Zoophycos brianteus, and Zoophycos cauda-galli), among which Zoophycos and Chondrites are the most common elements of the assemblage and occur in distinct mud-rich substrates showing different bioturbation intensities. The development of Zoophycos in the middle part of Unit 2 shows a high degree of bioturbation (bioturbation index (BI) = 4). Zoophycos specimens are of large size, between 45 cm and 75 cm in width, which were interpreted to have formed in a lower offshore environment where the oxygenation amount was optimal, the sedimentation rate was low, and the benthic food was abundant on the seafloor. Toward the upper part of Unit 2, Zoophycos-bearing levels exhibit a less intense degree of bioturbation (BI between 1 and 2) in contrast to Planolites- and Chondrites-bearing levels which have a bioturbation index (BI) between 3 and 4. At these levels, Zoophycos displays relatively small, coiled to U-shaped spreiten, probably in response to stressful and dysoxic conditions prevailing in the water bottom. With improved oxygenation in a quiet lower offshore to shelf margin environment in Unit 3, the benthic organisms recovered, as represented by medium to large size Zoophycos in association with Ophiomorpha and scarce Chondrites burrows, even if the overall bioturbation intensity is very low. The combination of trace-fossil assemblage and lithofacies of the Oued Fodda Formation indicates relatively stable outer shelf environments below the storm wave base, which corresponds classically to the lower offshore to shelf edge environments, and the prevailing palaeoecological conditions are optimal and stressful for the benthic organisms.

The paleoclimate change impacts the sedimentary environment and process, which in turn control the accumulation of organic carbon. Numerous studies have shown that the paleoclimate is controlled by astronomical cycles. Hence, understanding how these cycles impact the accumulation of organic carbon is a critical question that requires in-depth discussion. Previous studies have shown that Milankovitch cycle can be revealed from the sediments of the 7^th Oil Member (Chang 7 Member for short) of the Triassic Yanchang Formation in the southern Ordos Basin, suggesting that the deposition was controlled by astronomically-forced climate changes. Building on previous research, this study collected natural gamma (GR) data of Chang 7 Member from the N36 Well to further analyze astronomical cycles, combined with X-ray fluorescence (XRF) analysis and total organic carbon (TOC) tests, to reconstruct the paleoenvironment and analyze the organic matter enrichment characteristics. The results of this contribution show that, paleoclimate, paleo-redox conditions, paleo-water level, paleo-productivity and sediment accumulation rate (SAR) collectively controlled the enrichment of organic matter. Notably, this study identified the presence of eccentricity, obliquity, precession, and the 1.2 Myr long obliquity cycle in the Chang 7 Member. These cycles controlled the paleoenvironmental changes at different timescales and influenced the enrichment of organic matter, which has implications for subsequent energy exploration.