Wave-Dominated Clastic Coasts in Lakes

Abstract

Clastic depositional systems are of major interest since they represent potential reservoir rocks. Among these, wave-dominated marine coasts have been extensively studied, because wave-related processes can generate large-scale sand bodies composed of well-sorted clastics. Wave-dominated coasts also exist in lakes, as evidenced by multifarious coastal morphosedimentary features in modern lakes and sedimentary basins (e.g. beach-foredune ridges, strandplains, barrier islands, spits, washover fans, lobate to cuspate deltas) similar to those found on marine coasts. However, they comparatively have received much less attention. Thus, this paper puts emphasize on lacustrine wave-dominated clastic shoreline landforms and deposits, that are key features to later characterize related sedimentary bodies, and resulting stratigraphic architectures.

A world wide overview of modern, recent, and ancient lakes, based on remote sensing and bibliographic surveys, reveals that a great number of lakes and paleolakes show evidences for wind-induced reworking of clastics on their coasts. Three case studies from our published papers, all located in different climatic and tectonic settings, illustrate well the nature, dynamics, and significance of lacustrine wave-dominated coasts. Megalake Chad (>350,000km²), the last major highstand of Lake Chad (Africa, Sahara), is the archetype of a lake where most, if not all, clastics have been redistributed by wind-induced processes, resulting in the development of prominent clastic paleoshorelines (length: >2,500 km; width: several km; height: tens of m). Lake Turkana (East African Rift System) provides an example of a large rift lake with well-developed coastal (paleo-)landforms, that brings some interesting diversity in classical depositional models for such lakes. The post-glacial Lake Saint-Jean (Canada) exemplifies the global wind-driven hydrodynamics in lakes, revealing notably deep currents able to generate erosional surfaces and sediment drifts at the lake bottom.

Thus, wind-dominated coasts should be integrated in updated depositional models for lakes. Their identification in the geological record is crucial to determine the backshore-foreshore-shoreface zonation of paleolakes, and so to decipher base-level variations and lake extents, or to trace sediment sources and sinks. It has straightforward consequences on both source and reservoir rocks potential in lakes.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018