The geochemical signatures of the Silurian–Devonian succession in eastern Saudi Arabia

Mohamed Soua

doi:10.3906/yer-1902-13

Abstract

This study was performed on 663 sandstone core and cutting samples taken from the Silurian?Devonian succession in five wells, located in eastern Saudi Arabia. This study aimed to correlate the Tawil Formation in the study wells, defining the lower Qalibah/ Tawil and upper Tawil/Jauf boundaries. The Tawil Formation is mostly characterized by clastic-dominated fluvial to marginal marine depositional environments. A chemostratigraphic correlation workflow was established using key element ratios and comprising four zones (C1 to C4) and five subzones (C2-1 to C2-3 and C3-1-C3-2). The chemostratigraphic zonation allowed robust characterization of stratigraphy in the uppermost Qalibah, Tawil, and lower Jauf Formations. Zone C1 is associated in most cases with the Sharawra Formation. Zones C2 and C3 are generally linked with the Tawil Formation, and Zone C4 broadly defines the lower part of Jauf Formation. In detail, the chemostratigraphic zonal boundaries do not precisely match the biostratigraphical and lithostratigraphic boundaries, indicating that the C1-C2 and C3-C4 boundaries are probably time-transgressive. The ratio Zr/Nb was used to model sequence stratigraphy. This ratio can vary in proportion to grain size, in which the element Zr is known to be concentrated in the heavy mineral zircon; while Nb-bearing heavy minerals along with clay minerals, likely illite, produce Nb. The increasing Zr/Nb ratio values are considered to define the coarsening upward or regressive sequences while decreasing Zr/Nb trends can mark fining upward or transgressive sequences.

Highlights

Background on the Silurian–Devonian During the late Silurian–Early Devonian, the Tawil Formation developed on a stable Paleozoic epicontinental area; its distribution was controlled by the paleotopography ramp setting
The purpose of this paper is to evaluate the Silurian– Devonian section including Sharawra, Tawil, and Jauf Formations from a chemostratigraphic point of view using core and cutting samples to develop a regional correlation for the wells encountered in eastern Saudi Arabia, since biostratigraphy does not provide a high level of resolution in most of the study wells
Study material The present study focuses mainly on the Silurian–Devonian section focusing on Tawil Formation

Summary

Introduction

Background on the Silurian–Devonian During the late Silurian–Early Devonian, the Tawil Formation developed on a stable Paleozoic epicontinental area; its distribution was controlled by the paleotopography ramp setting. It is characterized as a clastic-dominated depositional environment, which varies from fluvial to marginal marine conditions, in an overall progradational sequence. This reflects the beginning of a new transgressive cycle during the Devonian (Steineke et al, 1958; Powers et al, 1966; Janjou et al, 1997; Rahmani et al, 2002; Laboun, 2010). The purpose of this paper is to evaluate the Silurian– Devonian section including Sharawra, Tawil, and Jauf Formations from a chemostratigraphic point of view using core and cutting samples to develop a regional correlation for the wells encountered in eastern Saudi Arabia, since biostratigraphy does not provide a high level of resolution in most of the study wells

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