Depositional conditions for Lower–Middle Jurassic sedimentary rocks from Northern Bulgaria inferred from whole-rock elemental composition

Abstract

The Lower–Middle Jurassic sedimentary rocks from Northern Bulgaria represent important stratigraphic markers and a potential source for oil and gas accumulation. Here, we present preliminary major and trace element results for 22 sedimentary rock samples from the Bachiishte, Ozirovo, and Etropole Formations collected from the Balkanides and the Moesian Platform in Central-northern and Northwestern Bulgaria. The three studied formations have largely similar geochemical characteristics. The application of established geochemical proxies and comparison with recent and ancient sediments suggests that the samples were deposited in a shallow, high-energy environment with no water restriction. Eroding mafic to intermediate lithologies provided the sediment into the submerging Moesian Platform. Most redox-sensitive geochemical parameters suggest an overall oxygenated environment during sediment deposition, although specific samples show evidence for periodically dysoxic or anoxic water column conditions.