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

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 paleo-weathering 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* = similar to 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.

Automated summary

Campanian lacustrine organic-rich mudstones in Egypt were deposited under a warm greenhouse climate. Geochemical analyses suggest they originated from intermediate igneous parent rocks, underwent moderate to intense chemical weathering, and were sourced from a moderate energy depositional environment.