Geochemistry and palynology of the upper Albian at the Abu Gharadig Basin, southern Tethys: Constraints on the oceanic anoxic event 1d

Abstract

The mid‐Cretaceous period was a time of abnormal polar temperature warming and consequent global oceanic anoxia that enhanced the widespread accumulation of organic matter‐rich marine sediments. The current contribution focuses on the late Albian oceanic anoxic subevent 1d (OAE 1d) that represents a period of increased perturbation of the global carbon cycle. Palynological and geochemical investigations, including TOC/Rock‐Eval pyrolysis and stable carbon isotope of organic matter (δ13CTOC), were conducted for the upper part of the Kharita Formation from the Abu Gharadig Basin, north Western Desert, Egypt, to (a) confirm the age of this unit, (b) assess the depositional environments and prevalent redox conditions, and (c) confirm the occurrence of the OAE 1d within the sedimentary record in this part of the southern Tethys. Based on the TOC content and Rock‐Eval pyrolysis parameters, the organic matter in the upper Kharita Formation is expected to have a limited hydrocarbon generation potential consisting of gas only. The sedimentation patterns and role of continental weathering and runoff influx were assessed through trace element ratios and relationships. Redox conditions were interpreted based on Stotal–TOC relationship, Stotal–TOC–Fetotal ternary plot, Rock‐Eval S2, trace element proxies and relationships (including Cr vs. V + Ni, V/Cr vs. Stotal, and Stotal/Fe vs. Mn/Stotal). The ratio of TOC/Ptotal was implemented to assess both marine primary productivity and oceanic anoxia during this period. Biostratigraphic constraints showed that the upper part of the Kharita Formation spanned a late Albian age (Cretacaeiporites densimurus Interval Zone). Results showed that the OAE 1d was characterized by organic matter deposition during dysoxic‐suboxic to anoxic redox conditions in a fluvio‐deltaic to shallow marine depositional environment in this part of the Tethys. A low to moderate primary productivity was also prevalent during a fairly high rate of sediment accumulation. Regional correlation of positive δ13CTOC excursion during the OAE 1d throughout the Tethys and Atlantic oceans matched well, in several parts, with the current study interval that confirm the global distribution of the OAE 1d. In this region of the southern Tethys, an overall collapse of water column stratification during the OAE 1d principally related to decreased terrestrial input at low relative sea level, as evidenced from freshwater algae Pediastrum and pteridophyte spore Crybelosporites pannuceus; however, orbital forcing likely induced monsoonal activity at low‐latitudes in the SE, N, and W Tethys.

Controlling Factors and Formation Models of Organic Matter Accumulation for the Upper Permian Dalong Formation Black Shale in the Lower Yangtze Region, South China: Constraints from Geochemical Evidence

“…Elemental geochemistry is the most extensively employed method for quantitatively reconstructing the paleoenvironment. ,− Generally speaking, organic carbon, phosphorus (P), and biogenic barium (Ba bio ) are the popular proxies for qualitatively evaluating the paleomarine productivity. − Several redox-sensitive elements (e.g., V, U, and Ni) and their ratios (e.g., U/Th, V/Cr, Ni/Co, and V/(V + Ni)) have been widely applied to interpret the paleoredox conditions over the past couple of decades. ,,,− REE distribution patterns and ratios of (La/Yb) N , Th/U, and Na/K are the important geochemical indices to qualitatively characterize the sedimentary rate. − …”

Short-Term Sea-Level Changes and Sequence Stratigraphy of the Mid-Cretaceous Kharita Formation Reservoirs in Egypt: Insights from Geochemical and Palynological Data

“… 33 Based on palynofacies and palynomorph analyses, the Kharita Formation was deposited under successive oscillations between fluvio-deltaic to marginal and shallow marine environments. 11 The sedimentary record of the Kharita Formation is principally dominated by siliciclastic sediments that showed cyclic alternations between coarse-grained sandstones and siltstones and shales ( Figure 3 ). As a result, the T–R sequence stratigraphic model was used following the third-order approach to subdivide the Kharita Formation into distinctive stratigraphic units.…”

“…The Kharita Formation was investigated with a detailed focus on the late Albian oceanic anoxic event 1d by addressing biostratigraphy, assessing the depositional paleoenvironment, and evaluating the redox conditions and role of sediment fluxes based on palynofacies analysis and palynomorph composition as well as inorganic and isotope geochemistry. 11 Therefore, the present study aims to (1) employ the palynofacies and palynomorph composition along with the geophysical gamma ray log data and the lithological characteristics of the Kharita Formation to reconstruct the relative sea-level fluctuations and subdivide them into distinctive systems tracts and stratigraphic sequences and (2) compare the sequence stratigraphic reconstructions based on the major and trace elemental geochemical composition to the results obtained from the palynofacies and palynomorph composition.…”

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

“…Paleoproductivity refers to the total amount of organic matter fixed per unit area per unit time (Algeo et al, 2011;Pan et al, 2020). Generally speaking, high organic productivity is one of the key factors for the formation of hydrocarbon source rocks (Talbot, 1988;Nelson et al, 1995;Mansour et al, 2020a;Mansour et al, 2020b;Yang et al, 2016;Zhao et al, 2021), and a large number of studies have shown that siliceous plankton in marine source rocks is the main provider of marine primary productivity (De Wever and Baudin, 1996;Chou et al, 2012;Xiang et al, 2013;Shaldybin et al, 2017;Jiang et al, 2019;Zhang et al, 2019), whose content is closely related to the biological reproduction in surface water, and its temporal and spatial distribution can be used to reflect the changing process of paleoproductivity. In recent years, many studies have shown that radiolarians enriched in marine hydrocarbon source rocks can gather together and absorb a lot of symbiotic algae in their bodies by using a large number of pseudopodia, forming a good symbiotic relationship with them (Lyle et al, 1988;Erbacher and Thurow, 1997;Xiang et al, 2013;Khan et al, 2019).…”