Rapid changes in paleoclimate in the Early Cretaceous had profound impacts on the global ecosystem, which is recorded not only in marine sediments but also in coeval sediments deposited in ...continental lake systems. This study performed the lake sedimentary characteristics and paleontological data of the upper member of Bayingebi Formation (K1b2) of Lower Cretaceous in the Yin'e Basin (North China) and revealed the paleoclimate disturbances and the evolution of paleovegetation and paleoenvironment recorded in the continental lake. The sediments of K1b2 can be divided into 10 kinds of lithofacies according to grain size, sedimentary structure and overall lithofacies. The three lithofacies associations are nearshore subaqueous fan, semi-deep lake/deep lake and shallow lake respectively. Seventy-eight palynomorph genera and two hundred and thirty-one palynomorph species were identified in the K1b2 samples, which allowed distinguishing 3 palynozones. The sporopollen spectrum and the ecological characteristics of sporopollen parent plants indicate that there was abundant temperate coniferous forest vegetation during the deposition of Bayingebi Formation. The mixed phenomenon of a few cold-loving molecular spores and pollen such as spruce, cedar and fir with tropical and subtropical spores and pollen suggest vertical zoning of plants. It is inferred that the ground shape and height difference around Yin'e Basin in Early Cretaceous is large, and there may be paleogeomorphic features of high mountains, and the paleoclimate has vertical zoning. The K1b2 depositional period was mainly in the warm temperate-temperate paleoclimate background, and oil shale was mainly developed in the semi-humid warm temperate climate. The suitable paleotemperature and the sedimentary environment of semi-deep lake/deep lake provide rich organic matter sources and good preservation conditions for the formation of oil shale. The dropstone structures commonly found in the lower strata of the oil shale member of the Bayingebi Formation in the study area were deposited in a semi-humid temperate climate and were inferred to be ice-rafting deposits, which may be related to a brief climatic cooling event or seasonal freezing during the Early Cretaceous in northern China. The typical East Asian paleontological fossils (Jehol Biota) and lacustrine hydrocarbon source rocks developed in the Early Cretaceous in the study area were affected by the paleoclimate warming in the early Aptian, which was closely related to the increase of global CO2 concentration in this period.
•The sedimentary characteristics in the Bayingebi Formation were revealed.•The Early Cretaceous vegetation in Yin'e Basin is dominated by coniferous tree.•The dropstones in the Bayingebi Formation is inferred to be ice-rafted debris.•The rise of palaeotemperature promoted the formation of oil shale.•The OAE 1a may have promoted the evolution of Jehol Biota in East Asia.
We provide the magnetostratigraphy of the Ladinian/Carnian Punta Grohmann stratigraphic section (Dolomites, Italy), calibrated with UPb ages from the literature (237.58 ± 0.04 Ma; 237.68 ± 0.05 Ma). ...The FO of ammonoid Zestoceras lorigae, the base of the vigens-densus palynomorphs Zone, and sequence stratigraphy suggest a Carnian age for the upper part of the section, which has been confirmed by the magnetostratigraphic correlation between Punta Grohmann and Prati di Stuores (Carnian GSSP). Additional magnetostratigraphic correlation between Punta Grohmann and key time-calibrated Ladinian–Carnian sections from the literature (e.g., Mayerling, Seceda, Rio Nigra) lead to a more precise age of the Carnian base (∼236.5 Ma) and to a better definition of the Middle–Late Triassic Geomagnetic Polarity Time Scale.
•New magnetostratigraphic data of a UPb constrained Ladinian section improves Triassic chronology.•The Punta Grohmann time-calibrated magnetostratigraphy allowed the update of the Ladinian Geomagnetic Polarity Timescale.•Updated Geomagnetic Polarity Timescale led to a revised age of the Ladinian/Carnian boundary (∼236.5 Ma).
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•First Permian palaeopalynological assemblage is reported from Karoo-aged Lebombo Basin, South Africa.•Palynostratigraphical comparison confirms a Guadalupian age for lowermost ...Emakwezini Formation macrofossil flora.•Increase in diversity of the middle Permian floras of Africa, including plant groups known only from the Triassic of Gondwana.
The Permian Emakwezini Formation (Adelaide Subgroup, Beaufort Group, Karoo Supergroup) of the Lebombo Basin in northeastern South Africa, has previously yielded two macrofloras comprising mostly Glossopteridales and sphenophyte taxa. Here we describe a palynological association from the Somkhele Mine locality in KwaZulu-Natal, the first recorded for the Emakwezini Formation, and for the basin as a whole. The association consists of a palynoflora with a good to fair quality of preservation, from which 142 species are identified. Elements of stratigraphic value are highlighted (e.g., Falcisporites stabilis, Guttulapollenites hannonicus, inter alia), which, when contrasted with the palynostratigraphic schemes known for the Main Karoo Basin and neighbouring basins, suggest a Guadalupian age for the deposits. Furthermore, the microflora points to a higher plant diversity than documented in the macrofloral record. The occurrence of Filicophyta, Lycophyta, Cordaitales, Coniferales, Peltaspermales and Voltziales, suggests the presence of complex forests, with a diversity of tree taxa. These inferences about the parent flora have expanded our understanding of the forests in the Lebombo Basin during Permian times and have helped to clarify the temporal and regional floristic relationships of floras in the Main Karoo Basin.
Oceanic Anoxic Event 2 (Cenomanian–Turonian: ca 94 Ma) represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic ...matter entered the marine burial record, probably triggered by increased availability of nutrients for planktonic biota. Three sections (Eastbourne, Sussex, UK; Raia del Pedale, Campania, Italy; and Tarfaya, Morocco) recording this event illustrate the influence on marine geochemistry of mafic volcanic rock‐seawater interaction, anoxia to euxinia, and re‐oxygenation and cooling during the so‐called ‘Plenus Cold Event’. The Eastbourne section represents the organic‐lean epicontinental pelagic deposits of the English Chalk; the Raia del Pedale section represents a shallow‐water platform carbonate on the Tethyan continental margin, also largely devoid of organic matter; and the Tarfaya core represents an Atlantic margin site where cyclically bedded organic‐rich sediments were well developed. Correlation between all three sections is readily achieved by biostratigraphy and carbon‐isotope stratigraphy (δ13Ccarb and δ13Corg) over the Oceanic Anoxic Event 2 interval, represented by a characteristic broad positive carbon‐isotope excursion. The stratigraphic range of the Plenus Cold Event, defined by the presence, in two discrete levels, of boreal fauna and an excursion to heavier oxygen‐isotope values in the English Chalk, can be identified in Raia del Pedale and Tarfaya by using the carbon‐isotope curve as a correlative tool. Similarly, a section in southern France allows its co‐existing osmium‐isotope excursion to relatively unradiogenic values to be placed in the context of the Oceanic Anoxic Event in all three analysed sections. A fall to lower osmium‐isotope values clearly pre‐dated the onset of Oceanic Anoxic Event 2, as defined by the initial rise in carbon‐isotope values, allowing the putative magmatic/mafic event as a trigger for the Oceanic Anoxic Event. An initial drop in sulphur‐isotope ratios (δ34SCAS) at Eastbourne correlates with the osmium‐isotope curve, suggesting that isotopically light sulphur could have been derived from a mafic igneous source. Re‐oxygenation of sediments of all three investigated sections during the Plenus Cold Event is variably illustrated by change in cerium:calcium, iodine:calcium, molybedenum:calcium and uranium:calcium ratios, according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature. Changes in molybdenum‐isotope ratios from Tarfaya and portions of the sulphur‐isotope curve from Eastbourne and Raia del Pedale also indicate the probable presence of more oxygen‐rich bottom waters during the Plenus Cold Event. Oxidation by such waters of previously deposited organic‐rich shales, as well as loss of anoxic/euxinic sinks, is credited with temporarily enriching global seawater in a range of other redox‐sensitive trace metals (for example, V, Cr, Co, Ni, Cu, Zn and Cd) during ongoing basalt‐seawater interaction indicated by persistent relatively non‐radiogenic osmium‐isotope seawater values. However, early diagenetic enrichment of manganese in the English Chalk over much of the Oceanic Anoxic Event interval is broadly correlative in time with relatively low osmium‐isotope values in sections elsewhere: a relationship that may be due to the lack of affinity of manganese with carbon‐rich shales, hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks, unlike other redox‐sensitive species. The calcium‐isotope and lithium‐isotope ratios from Eastbourne and Raia del Pedale indicate an increase in global weathering during the initial phase of Oceanic Anoxic Event 2, and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more Large Igneous Provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean. Globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that, in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of Oceanic Anoxic Event 2, caused the Plenus Cold Event.
The lower Cretaceous sandstones of Zubair and Nahr Umr formations are the main producing reservoirs in Subba oilfield in southern Iraq. Key differences in their petrophysical and depositional ...attributes exist affecting their reservoir characteristics. The evaluation of well logs and core porosity-permeability data show better reservoir properties in Nahr Formation. The Litho-saturation logs indicate greater thickness of oil-saturated reservoir units for Nahr Unr Formation associated with lower values of shale volume, and higher values of effective porosity. In addition, higher values of permeability for Nahr Umr Formation is suggested by applying porosity-irreducible water saturation cross plot. The reducing reservoir quality of Zubair Formation sandstones is related to finer grains of sandstone reservoirs, higher clay volume, and more effect of compaction resulting from greater depth. A reservoir layering scheme is proposed by sequence stratigraphic analysis leading to the identification of systems tracts and their key surfaces within Zubair and Nahr Umr formations, and forms the basis for predicting of reservoir architecture and quality. Laterally continuous, and thick amalgamated sandstone reservoirs are formed during highstand systems tract in Nahr Umr Formation as a result of low accommodation/sediment supply conditions. Within the transgressive systems tract of Zubair Formation, the sandstone reservoir bodies become isolated as accommodation exceeds sediment supply.
Changes in sea level are global and cyclical; however, the understanding of the processes that control them is still very limited owing to the low rate of progress in technology to reconstruct the ...trajectory of global sea level change. Based on the reconstruction of the Cenozoic sea level change curve in the northern South China Sea, discrimination criteria for global sea level (GSL) and relative sea level (RSL) changes are proposed for the first time, and five technical difficulties in single-period trajectory reconstruction are addressed. The findings show that the recorded sea level changes are dominated by the GSL change component in only a small number of basins worldwide. The Cenozoic sea level showed an increasing trend of sea level, and the fluctuation amplitude of the second-order cycle was considerably smaller than that of the third-order cycle. These findings challenge the consensus that the Cenozoic sea level continues to fall and that the magnitude of the second-order cycle is greater than that of the third-order cycle. In terms of technological advancement, the accuracy of the third-order single-period trajectory was improved to approach the cosine locus by correcting the deviation between the sea level indicated by the residual accommodation space and the GSL, and eliminating the trajectory distortion caused by the differences in the deposition rate. The new technique has the potential to reconstruct original single-period trajectories, which can provide technical support for comparing the single-period sea level trajectory with the corresponding celestial orbit and studying the mechanisms driving primary cycles.
•The global sea-level (GSL) curve since 33 Ma has been reconstructed.•A criterion for distinguishing GSL and RSL trajectories is proposed.•Five technical difficulties in single-period curve construction are addressed.•New findings challenges the consensus on GSL change.
Neoproterozoic tectonic geography was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana. The Neoproterozoic was a tumultuous time of ...Earth history, with large climatic variations, the emergence of complex life and a series of continent-building orogenies of a scale not repeated until the Cenozoic. Here we synthesise available geological and palaeomagnetic data and build the first full-plate, topological model of the Neoproterozoic that maps the evolution of the tectonic plate configurations during this time. Topological models trace evolving plate boundaries and facilitate the evaluation of “plate tectonic rules” such as subduction zone migration through time when building plate models. There is a rich history of subduction zone proxies preserved in the Neoproterozoic geological record, providing good evidence for the existence of continent-margin and intra-oceanic subduction zones through time. These are preserved either as volcanic arc protoliths accreted in continent-continent, or continent-arc collisions, or as the detritus of these volcanic arcs preserved in successor basins. Despite this, we find that the model presented here still predicts less subduction (ca. 90%) than on the modern earth, suggesting that we have produced a conservative model and are likely underestimating the amount of subduction, either due to a simplification of tectonically complex areas, or because of the absence of preservation in the geological record (e.g. ocean-ocean convergence). Furthermore, the reconstruction of plate boundary geometries provides constraints for global-scale earth system parameters, such as the role of volcanism or ridge production on the planet's icehouse climatic excursion during the Cryogenian. Besides modelling plate boundaries, our model presents some notable departures from previous Rodinia models. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, such that these two cratons act as ‘lonely wanderers’ for much of the Neoproterozoic. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The GPlates files of the model are released to the public and it is our expectation that this model can act as a foundation for future model refinements, the testing of alternative models, as well as providing constraints for both geodynamic and palaeoclimate models.
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•Summary of Neoproterozoic geology and palaeomagnetic data•New model of Rodinia with India and South China omitted•Model full plate boundaries and plates through the Neoproterozoic•Reconstruct tectonic palaeogeography for the Neoproterozoic
This paper analyzes the groundwater of the Chambo aquifer in the Llío and San Pablo sector, with emphasis on the temporary alternation of nitrate concentration, identifying the anthropogenic ...activities that may influence this area. This from the cartographic definition of the areas of begging influence the crossing of geological, hydraulic and anthropic activities. The temporality of the geochemical data is 5 years (2016-2020), these results show that water quality meets the requirements of the Ecuadorian national standard, and that the main composition of water is bicarbonated type of calcium-magnesium. Even if the groundwater in this sector meets the standard, variation in nitrate concentration is evident. This type of concentration is presented by the effect of agricultural activities on the surface of the soil, where nitrates occur naturally due to the nitrogen cycle, and that are dragged into the water table by infiltration when the rainy season occurs. In addition, it was found that the type of rock found underground cannot naturally generate nitrates.
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