Towards a Hierarchical Classification of Clinoforms

Clinoforms (large scale sloping depositional surfaces) and clinothems (the rock units bounded by clinoforms) occur with a great variety of geometries and scales. They form when sediments accrete into standing bodies of water and they give direct information about paleobathymetry and paleogeomorphology. They also have important reservoir potential and they are keys in understanding the transfer of coarse material from shallow to deep water. In this paper we attempt to present a new hierarchical classification of siliciclastic clinoforms that highlights different modes of origin and accompanying variations in scale.

"Shoreline clinoforms", including clinoforms produced by the progradation of deltas, barrier islands and strandplains, are typically a few to a few tens of metres high and have their rollover at the shoreline or in the immediate vicinity of the shoreline. Clinoform gradients are highly variable, partly controlled by grain-size and partly by the processes of sediment dispersal (e.g. fluvial, wave, tide). 'Subaqueous delta clinoforms' are formed in front of large deltas and have their clinoform-rollover at water depths from a few meters to 40m with fronting relief ranging from 20m to 100m. They are typically muddy with low gradients and indicate bypass of fine material across a subaqueous topset. 'Shelf prism clinoforms' are produced by stacking of progradational wedges. After flooding shoreline clinoforms are separated from the fronting prism of stacked progradational wedges. However, when the shoreline transits across the shelf and re-establishes at the shelf prism clinoform rollover, shoreline and shelf prism clinoforms coincide. Shelf prism clinoforms are typically 100’s of meters high and form over time scales of ten thousand to million years. Clinoform gradients are typically conditioned both by grain size, slope stability and accommodation/supply constraints. 'Continental margin clinoforms' reflect outbuilding of the entire margin, such as when sediments are accreting the slope of the continental-oceanic crust transition, and have relief in terms of 1000’s of meters. These clinothems accumulate over time spans of millions of years and are typified by large scale deformational features.

Classifying clinoforms according to the proposed scheme can help in assessing both clinoform reservoir potential and the potential of the clinoform slope to bypass coarse material to the basin floor.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California