Submarine Fan Stratigraphy: A Jekyll and Hyde Story

Elliott, Trevor E.¹, Andrew J. Pulham², Gillian M. Apps³ (1) Liverpool University, Liverpool, United Kingdom (2) Earth Science Associates, Boulder, CO (3) BHP Billiton Petroleum, Houston, TX

A hypothesis is presented that predicts that most delta-fed turbidite systems comprise distinctive stratigraphic signatures that record bimodal distributions of gravity flow events.

Evidence from outcrop investigations, modern and subsurface studies suggest that tur­bidite systems (submarine fans) are constructed by a combination of (1) numerous, rela­tively low volume and relatively low-density sediment gravity flows, and (2) rare, quasi-ran-dom, extremely high volume and relatively high density/concentrated sediment gravity flows punctuated by (3) periods of little or no sediment supply.

The large, rare events erode and sculpture the proximal and mid-parts of submarine fans and are responsible for the transfer of large volumes of coarse, reservoir quality grade sed­iments into most distal fan settings. Low volume events are the principal building blocks of sandy, proximal to mid-fan settings.

Key stratigraphic elements that define the fan architecture are regional by-pass surfaces that owe their origin to almost instantaneous re-setting of the fan surface palaeogeography. Recognition of regional by-pass surfaces results in descriptions of turbidite complexes as linked, often overlapping, but separate depositional systems that have their origins to con­trasting frequencies and volumes of gravity flows.