Early Silurian Shelf-Prism Clinoforms: Progradation and Implications for Pre-vegetation Sedimentary Source to Sink Systems, a Case Study from Central Arabia

Abstract

An Early Silurian sag basin has been investigated by integration of sedimentological, biostratigraphic, wireline log and seismic data over Central Arabia. This intra-cratonic basin fill includes deep marine, submarine slope, shelf and fluvial deposits, representing a complete basin fill cycle during a long-term post-glacial sea level highstand, with constituent high-order transgressive-regressive cycles. Recent 3D seismic data images large 700 metre high clinoforms downlapping on the base Silurian with an extensive network of slope channels. This study integrates seismic analysis of these features with borehole data, stratigraphic and regional analysis to constrain this ancient depositional system, which is the only documented case (as of 2018) of shelf-prism clinoforms from the pre-vegetation world. Absence of land plants is considered to have enhanced the fine-grained portion of the sediment budget bypassed to the shelf and affected deep water deposition. This study shows these basin margin clinoforms have a very high progradation rate, comparable to that of Quaternary glaciated margin clinoforms of the North Sea. The combined progradation rate and decompacted clinoform thickness indicate an extremely high long-term sediment flux. Sediment provenance and drainage area analysis suggests this high sediment volume into the Rhuddanian basin was provided by a 4-million-square-kilometre catchment extending into the Gondwanan interior. A statistical source-to-sink analysis has helped reconstruction of many of the large-scale morphological and sedimentological parameters of the Rhuddanian succession in central Arabia. The continental-scale drainage is associated with high palaeo-water and -sediment discharge rates, incompatible with the persistent hyperpycnite facies observed throughout the succession, the latter suggesting drainage by smaller rivers. This implies pre-vegetation catchments were drained by many smaller rivers rather than a single large system. Climate simulation of the Early Silurian for an un-vegetated Gondwana shows a cold/temperate climate over the studied depositional system with highly seasonal precipitation, which would promote river flooding and recurring hyperpycnal flows. Analysing Rhuddanian deep-water slope channels shows rapidly-prograding slope clinoforms are associated with low-sinuosity channel elements due to inability of channel-confined turbidity flows to reach equilibrium with the channel floor in such conditions. This study also demonstrates that rapid mud-rich slope progradation associates with highly-organised channel stacked patterns due to the enhanced mud volume entering the slope which increases flow over-spilling and levee development. High slope accretion could lead to basin floor fans made of poorly interconnected lobes because of the constant basinward shift of the sediment entry point into the basin floor.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mads Huuse (Supervisor) & Stephen Flint (Supervisor)