Palaeoenvironmental study of the Palaeotethys Ocean: the Givetian-Frasnian boundary of a shallow-marine environment using combined facies analysis and geochemistry (Zefreh Section/Central Iran)

Abstract

The Zefreh section in central Iran represents a carbonate ramp succession with a general shallow-marine palaeoenvironment. This section represents most of the Bahram Formation (Givetian to at least Middle falsiovalis Zone) and consists of a very heterogeneous succession of medium- to coarse-grained sandstones, skeletal pack- to grainstones with local biostromes, massive or laminated dolostones, and shales. Microfacies analysis allowed the discrimination of 12 microfacies reflecting supratidal to open marine palaeoenvironments. The shallow-marine environment was investigated using facies analysis and geochemical proxies. Redox conditions in the Zefreh section appear to be primarily oxic and support the facies and sedimentological results. The provenance of the Zefreh sediments using La, Sc, Zr, and Th indicates that they are most likely derived from continental arc volcanics which is consistent with the preliminary tectonic interpretations. Conodonts and brachiopods were used for establishing the biostratigraphical framework. The lack of important zonal index taxa of the widely applied conodont standard zonation requires the application of an alternative shallow-marine conodont zonation. Based on conodont and brachiopod data, the Zefreh section covers sediments ranging from the upper Givetian to lower Frasnian.