CLINOFORM CONTROL ON SUBMARINE FAN DEVELOPMENT WITHIN DEPOSITIONAL SEQUENCES

Depositional sequences with distinct depositional relief (clinoform development) can occur on the craton and continental shelf, as well as along the continental margin. They can even occur in lacustrine basins. This depositional topography can occur along sequence boundaries, within sequences, or as abandoned (Relict) relief. Detailed analysis of the depositional topography associated with sequences deposited in a variety of tectonic settings reveals that neither the presence of depositional relief or proximity to the continental margin explains basin-floor fan development within sequences. However, in the datasets studied, the magnitude of the depositional relief (clinoform development) along sequence boundaries can be used to explain and predict basin-floor (lowstand) fan development within sequences.

Integration of published seismic, well-log, and outcrop data from the Cretaceous and Tertiary of the U.S. Gulf and Atlantic coasts, offshore Australia, Norway, Russia, as well as the Triassic through Tertiary of the Alaskan North Slope, suggests that 3 distinct types of depositional sequences (Low-, Moderate-, & High-relief) can be defined. Low-relief sequences have poor clinoform development. These sequences typically have clinoforms of less than 1/2 of a degree and depositional relief of less than 50 meters (150') along sequence boundaries. Low-relief sequences, which are common in cratonic basins, lack basin-floor lowstand fans. Moderate-relief sequences display distinct clinoforms of .5 to 3 degrees, and display depositional relief of less than 150 meters (500') along sequence boundaries. These moderate-relief sequences are common in foreland basins and on continental shelves. Moderate-relief sequences also lack lowstand fans. High-relief sequences display clinoforms of 2-5 degrees and depositional relief greater than 150 meters (500') along sequence boundaries. These high-relief sequences typically occur along the continental margins, but can occur in foreland and rift basins. High-relief sequences contain lowstand fans. These observed relationships suggest that there is a Critical “Clinoform” Break that controls slope stability or failure during relative sea-level falls.