Paleosalinity and hydrothermal characteristics of the Upper Cretaceous Duwi black shales, Aswan Governorate, Egypt

The Upper Cretaceous Duwi black shales of Nile Valley district, Aswan Governorate, Egypt, were geochemically examined to determine their paleosalinity and hydrothermal characteristics present at the time of their deposition. Elemental ratios such as strontium/barium (Sr/Ba) and TOC/S were applied for paleosalinity reconstruction. The Duwi black shales show Sr/Ba >0.5 and TOC/S ˂5. The values of the elemental ratio show that the Duwi black shales were deposited in a marine environment. For hydrothermal activities ratio, Sc/Cr was used and Binary diagrams TOC vs P were constructed to discriminate between normal water, mixed and hydrothermal influence. The Duwi black shales have values of the Sc/Cr ratio that vary from 0.01 to 0.43, with an average of 0.1. Nearly all of the samples are shown to fall within the range of hydrothermal deposition in the binary plot of Sc/Cr. Also, the binary diagram of TOC vs. P shows that the majority of the samples fall within the zone of hydrothermal activity.