The Ordovician-Lower Silurian siliciclastics deposited on the Jordanian Platform represent a transitional sedimentary system between their granitoid Gondwana source area and the Paleo-Tethys. While fluvial fining upward cycles (FUCs) of quartz arenite dominate braid plain deltas/upper shore face environments of the Lower Ordovician, arkosic tempestite and oxygen-deficient bituminous pelite/tuffite cycles cover upper/lower shore face environments of the Sandbian and Katian. The mineral deficit (feldspar, unstable heavy minerals) relates to acid sturz-rain events during volcanic degassing (SO2, HCl, HF, NOx) sourced in an Infracambrian/Cambrian Large Igneous Province (LIP) around S Sinai/Wadi Araba Rift-Zone. The change of sedimentary architectural elements/lithofacies types during the Upper Darriwilian took place after an L-chondrite of the Main Asteroid Belt (MAB) crossed the Earth’s orbit (~470 Ma), which resulted in some small meteorite craters (i.e., Lockne). Through the Sandbian and Katian, this insignificant impact series was accompanied by massive tephra production during worldwide explosive subduction-related volcanic arc magmatism. During the Upper Ordovician High Stand-System Tract (HST), the glass-bearing tephras were transformed under marine conditions into montmorillonite (K-bentonite), contributing to green tuffitic pelite interbedded with storm-generated arkosic clastics. Transtensional tectonics (pull-apart type) caused the main Ordovician-Silurian unconformity (“paleovalleys”) in SE Jordan and Saudi Arabia. Their sedimentary fills expose arkosic FUCs originated by shallow-water turbidites during the Hirnantian. The intensive explosive volcanism generated almost continuously negative climate forcing (“cosmic winter”) by tephra, aerosols, smog, and clouding that led to regional glaciation in the S Hemisphere. The abrupt 87Sr/86Sr-ratio decrease accompanies, at the Sandbian base, the onset of magmatism, while δ13C excursions follow a Transgressive System Tract (TST) and three T-maxima indicating increasing phytoplankton growth. The undulation—0% mirrors a cyclicity of volcanic events, climate forcing, Eh, and pH conditions. The δ18O rise shows a continuous CO2 assimilation until its stop (~1200 ppm CO2) and the following formation of black-shale facies.
Schneider, W. & Salameh, E., 2026. Ordovician sedimentary processes and related driving forces: Jordan, Arabian Plate. Open Journal of Geology 16: 214-242. Article.
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