Provenance Characterization of Campanian Lacustrine Organic-Rich Mudstones on the Southern Tethyan Margin, Egypt
Douaa Fathy, Michael Wagreich, Theodoros Ntaflos, Mabrouk Sami
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.