Organic Geochemistry and Paleoenvironments of Deposition of the Middle Jurassic Sediments from the Tabas Basin, Central Iran

In an attempt to reconstruct the paleoenvironments of deposition for the Middle Jurassic Baghamshahformation, samples collected from six outcrop sections along the Shotori swell were subjected todetailed geochemical analyses. Bulk geochemical and biological marker data indicate a logical trendof the variation of organic input, salinity, and oxicity within Baghamshah paleoenvironments acrossthe studied area. An increase in terrestrial character from southern end towards the central parts of theShotori swell parallels with a uniform increase in the oxicity and a decrease in the salinity. Thenorthernmost sections are characterized by less terrestrial impact, reduced oxicity, and elevatedsalinity compared to the central and southern sections. These variations are interpreted in theframework of past geometric configuration and a hypothetical paleogeomorphologic model istentatively proposed for the Middle Jurassic of the area. According to these results, the depositionalsetting of the studied formation decreased in depth from Section-1 towards Section-4, suggesting thatthe proximity of the latter section to the Yazd Block may have had a strong control over the observedgeochemical variations. The terrestrial organic input and the oxicity of the environment areconspicuously low for northern sections and their salinity shows a sharp increase compared to othersections. We hypothesize that a fault plan exists across the northern and southern Shotori Mountainsthat had played an active role in creating the current geochemical variations.

کلیدواژه ها:

Paleoreconstruction ، Biological Markers ، Middle Jurassic ، Tabas Basin ، Central Iran