Seismic Facies and Reservoir Distribution in a Prograding Shelf-Slope-Basin Plain System: Chandler and Torok Formations, North Slope, Alaska: ABSTRACT

Abstract

The Chandler-Torok sequence is one of several Cretaceous-Tertiary clastic wedges shed north and east from the ancestral Brooks Range hinterland into a rapidly subsiding foredeep trough. Each wedge consists of a End_Page 935------------------------------ lower sequence of hemipelagic shales and submarine-fan deposits succeeded by slope-deposited silty shales and culminating in shelf and fluvio-deltaic sandstones, shale, and coal. Basinal facies are expressed seismically as convergent bottomset reflectors of moderate to high amplitude and continuity, grading updip into mounded and channelized events of poor continuity and variable amplitude that onlap the base of the slope. This hummocky facies represents a combination of overlapping submarine fan lobes and gravity-failure deposits. The overlying slope sequences are expressed as complex sigmoid-oblique clinoform bundles of low amplitude bracketed by discrete continuous events of high amplitude. Clinoform bundles downlap over mounded facies onto bottomset events except where removed by eeply incised submarine canyons. Mounded submarine fans generally onlap the base of toplapped foresets, documenting their development during periods of low stand and shelf bypass. They were blanketed by high-amplitude foresets during transgressive periods of relative sea level rise. Shelf and nonmarine facies are seismically expressed as prograding and aggrading topset reflectors that respond to fluctuating sea level and sediment supply. Amplitude and continuity are high in the eastern wave-dominated shelf setting, low in the western river-dominated setting, and uniformly variable in the alluvial-plain setting owing to discontinuous channels and coal measures. Maximum reservoir development parallels the wave-dominated shelf setting. End_of_Article - Last_Page 936------------