Investigation of the lateral continuity of sandstone bedsets containing hummocky cross stratifications

Hummocky Cross Stratifications (HCS) are low-angle sedimentary structures found in association to sediments from the offshore transition. They are traditionally interpreted as representing storm-induced bedforms, whereby a combined flow is created including an oscillation component from storm waves and a unidirectional component from a density current, with debate on the intensity of each component. 

 

Here, the lateral evolution of bedsets containing HCS is investigated from field exposures. Drone images were collected from outcrops in the Moroccan Anti-Atlas from the Jbel Bani, a several hundred meters thick succession of shoreface to offshore sandstones and shales deposited during the Late Ordovician. Outcrops were targeted specifically for configurations where a vertical series of HCS sandstone bedsets occurred within silty-shale to flazer background interbeds.

 

Over a few hundred meters of lateral distance, HCS beds are found to splay out into channel cuts. Outside these channel features, individual bedsets are seemingly discontinuous, either amalgamating into underlying beds or laterally passing into ripple beds. This preliminary study offers new insights into the depositional dynamics of HCS sandstone beds, feeding a long-lasting discussion over the last 50 years.