Paleo-weathering and paleoclimate of the Miocene syn-rift sandstones in the Midyan Basin, NW Saudi Arabia: Petrographic and geochemical constrains

Abstract

This study aims to investigate the provenance, tectonic setting, paleo-weathering, and paleoclimate of sandstones of the syn-rift Oligocene?-Middle-Miocene Sharik and Nutaysh formations in the Midyan Basin, located in the northwestern portion of Saudi Arabia. This has been achieved by a multidisciplinary approach combining fieldwork, petrographic analysis, and bulk-rock geochemistry (major, trace and rare earth elements) of sandstones of the Sharik and Nutaysh formations. Integrated petrographic and geochemical data indicate that the studied sandstones are predominantly of sublithic and subarkose arenites. These sandstones were mainly derived from felsic plutonic igneous (mainly granite) and volcanic (mainly andesite and rhyolite tuff) rocks, with a lesser contribution from recycled sedimentary (mainly sandstone, mudrock and chert) and metamorphic (mainly gneiss) sources. These source rocks are typical of a craton interior with notable input from transitional continental and quartzose recycled orogenic tectonic provenance. They were belonged to the nearby Neoproterozoic basement rocks located in the northwest of the study area, as indicated by paleocurrent direction. These source rocks were tecttonically linked to an active continental margin to a continental island arc. These tectonic settings were subsequently influenced by rifting, as evidenced by discrimination function diagrams based on the high-and low-silica sandstone samples. In terms of paleoweathering and paleoclimate,the studied sandstones experienced a week to moderate chemical weathering under semi-arid to semi-humid climatic condition (low to moderate rainfall ranges from 250 to 1000 mm per year). With respect to tectono-sedimentary evolution, the alluvial sandstones of the Sharik Formation were deposited during the initial stages of continental extension and gradual subsidence linked to the early syn-rift phase in the Oligocene?-Early Miocene. The deposition of the deep-sea sandstones of the Nutaysh Formation were deposited during a period of accelerated subsidence in the Early-Middle Miocene, corresponding to the rift climax. Findings of the present study is consistent with the Oligo-Miocene broader tectono-sedimentary evolution of the region.