Provenance Characterization of Campanian Lacustrine Organic-Rich Mudstones on the Southern Tethyan Margin, Egypt

Abstract

Campanian lacustrine organic-rich mudstones were deposited under a warm greenhouse climate in Egypt. In this study, integrated elemental geochemical analyses have been applied to discriminate the paleoweathering conditions, provenance, and tectonic setting of these mudstones. The studied samples are relatively enriched in Al, Ca, V, Sc, and Cr compared to Post-Archean Australian shales (PAAS). Their chondrite normalized REE patterns show enrichment in the light REE compared to heavy REE, with a negative Eu anomaly (Eu/Eu* = ∼0.77). The low values of Th/Sc (0.42), Zr/Sc (5.05), and Zr/Hf (36.3) for the studied samples indicate no input from recycled older sedimentary strata. The ratios of the compositional variability index (ICV = 0.76), K/Al (0.072), Al/Si (0.34), and K/Si (0.025) suppose that the mudstones are compositionally mature source rocks and originated in quiescent and low energy depositional environments. The average values of the chemical index of alteration (CIA = 82), chemical proxy of alteration (CPA = 94), and plagioclase index of alteration (PIA = 87) and ln­(Al2O3/Na2O = 3.6) for the studied mudstones imply moderate to intensive chemical weathering. Moreover, the provenance sensitive elemental proxies (e.g., La/Sc, Th/Sc, Th/Cr, Cr/Th) and multiple discrimination diagrams reveal that the mudstones could be derived from intermediate igneous parent rocks. The lacustrine organic-rich sediments were sourced from a Phanerozoic to Proterozoic arc setting based on various tectonic discrimination diagrams.

Controlling the Iron Migration Mechanism for the Cretaceous Sediment Color Variations in Sichuan Basin, China

“…The bulk compositions of the representative samples were used to calculate the geochemical indices for reconstructing paleoclimate conditions and evaluating chemical weathering processes in samples. 3 The CIA index shows that the average value of Guankou Formation in the Late Cretaceous is 67, ranging from 60 to 72; the average value of the Early Cretaceous is 66, ranging from 59 to 72. The Early Cretaceous nonred bed samples are slightly lower than red bed samples (the average value of the grayish-green sample is 61, the red sample is 68, and the garnish yellow sample is 70).…”

“…37 The chemical weathering for the sediments can be estimated from the chemical index of alteration (CIA). This proxy is calculated from the following equation: CIA = molar (Al 2 O 3 )/ molar (CaO* + Al 2 O 3 + Na 2 O + K 2 O) × 100%; 3,44 CaO* stands for CaO in silicate minerals and is corrected by the method provided by McLennan. 46 The chemical index of weathering (CIW = molar (Al 2 O 3 )/molar (CaO* + Al 2 O 3 + Na 2 O) × 100%), 48 weather eluviation index (Ba = (CaO + K 2 O + Na 2 O + MgO)/Al 2 O 3 ; the oxide index is also the number of molecular moles 91 ), indicators for climate change such as CaO/(MgO × A1 2 O 3 ), 92 and the index of clayeyness A1 2 O 3 /SiO 2 53 were also used.…”

“…They are usually used to reconstruct the paleoclimate and reveal the intensity of chemical weathering, which plays a vital role in indicating the controlling factors of rock weathering and the environment. 1 − 3 The iron element widely present in sedimentary rocks is susceptible to changes in redox conditions and is very useful for determining the redox conditions of sediments and rocks. 4 , 5 At the same time, iron-bearing minerals can make the rock show a specific color.…”

“…Mineral composition and elemental composition of sediments are closely related to the parent rock and paleoclimate. They are usually used to reconstruct the paleoclimate and reveal the intensity of chemical weathering, which plays a vital role in indicating the controlling factors of rock weathering and the environment. − The iron element widely present in sedimentary rocks is susceptible to changes in redox conditions and is very useful for determining the redox conditions of sediments and rocks. , At the same time, iron-bearing minerals can make the rock show a specific color. Sediment color is considered one of the best indicators of climate. − It is used to identify rock types and divide and compare the strata, and it is an important index of climate and environmental change. , According to the genetic sediments, the color of the sediments can be categorized into inherited color, authigenic color, and secondary color.…”

Geochemical Characterization of the Eocene Coal-Bearing Source Rocks, Xihu Sag, East China Sea Shelf Basin, China: Implications for Origin and Depositional Environment of Organic Matter and Hydrocarbon Potential

“…The formation and distribution of source rocks is mainly controlled by sedimentary basin, palaeoclimate, palaeohydrodynamic conditions, productivity, and preservation of organic matter [6]. Therefore, geochemical characterization of the source rocks is a key to understanding their type and origin of organic matter, thermal maturity, capacity for hydrocarbon generation, palaeoceanographic, and paleoclimatic conditions [7,8].…”