Seismic Expression of High Frequency Depositional Sequences Around the Globe – Implications for Lowstand Stratigraphic Traps, North Slope Alaska

Abstract

The interplay of high sedimentation rates combined with uniform low subsidence rates frequently results in “giant” foreset successions. Unlike the typical 3rd-order depositional sequences of the Vail model, these foresets are often characterized by high-frequency sequence architecture stepping out onto continental slopes. Seismic delineation of high-frequency sequences calibrated with well control was documented as early as the 1980s in the Cretaceous Pletmos Basin, South Africa. Established interpretation methodologies were carried forward and applied in examples presented here from the Taranaki Basin, offshore New Zealand and the Nile Delta, Egypt. Delineating potential deep-water reservoir geometries include contourites, slope channel fills, levees and splays. Examples of “stratigraphic” fields of this nature from Egypt, Russia, Myanmar, and South Africa also include slope fan and basin floor fan geometries. The availability of high-fidelity reprocessed 3D seismic data has facilitated delineating analogous lowstand elements on Cretaceous North Slope, Alaska, data sets. Shelf-edge trajectories are indicative of the relative fall and rise of 3rd-order cycles, overprinted by 4th-order cyclicity and includes stacking shingled turbidites at toe-of-slope settings. In addition, gravitational tectonic overprint and the presence of an active petroleum system highlight the prospectivity of this extensive area. Recently reported discoveries in the Brookian Nanushuk Play and Lower Cretaceous turbiditic clastics in the Central Artic and National Petroleum Reserve Alaska further confirm the presence of an active petroleum system and play concept validity in these under explored areas. These stratigraphic traps may or may not be complimented by gravitational faults, slumps and mass transport complexes, which often result in combination traps, where present. Confidence in the prospectivity of unexplored areas of the North Slope is strengthened by global experience in similar geological settings and will be the focus of this paper.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018