Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Accommodation as a Control on Coastal-Plain Architectures: Observations and Analyses of the Cretaceous Versus Paleocene Prince Creek Formation, North Slope, Alaska
(1) University of Texas-Austin, Austin, TX.
Predominant facies, facies thickness, and stacking pattern in coastal-plain settings are strongly influenced by subsidence rate and local accommodation. A field study of the Prince Creek Formation (PCF) on the North Slope of Alaska offers an opportunity to examine the importance of accommodation on the character of coastal-plain deposits of varying ages. The PCF records Cretaceous-Paleocene alluviation on clastic wedges that filled the east-west trending Colville Basin, a foreland basin bounded on the south by the Brooks Range and on the north by the Barrow Arch and Canada Basin. The PCF forms shallow viscous-to-heavy oil reservoirs and rare outcrops offer a glimpse into facies, alluvial architecture, sandbody interconnectivity, and stacking pattern that is difficult to resolve from seismic and core.
The Cretaceous PCF exposed along the Colville River is composed of semi-interconnected fine-grained meandering and fixed (anastomosed?) channels, splays, thin lacustrine facies (typically < 2 m thick), thin coals (< 0.5 m thick), carbonaceous shale, and weakly-developed paleosols (Entisols and Inceptisols). Alternatively the Paleocene PCF exposed along the Toolik and Sagavanirktok Rivers exhibits isolated medium-to coarse-grained meandering channels encased in organic-rich floodplain facies including thicker lacustrine deposits (some > 20 m thick) and thicker coals (up to 6 m thick).
Channel-forms incised into pre-existing channels, thin lacustrine deposits, thin coals, and weakly-developed paleosols suggest a lower subsidence rate and lower accommodation during deposition of the Cretaceous succession. Isolated sandbodies encased in organic floodplain facies, thick lacustrine successions, and thick coals suggest a higher subsidence rate and higher accommodation for Paleocene deposits. Reduced accommodation during Cretaceous PCF deposition may have resulted in part from a more distal position relative to the orogenic belt and proximity of the alluvial systems to a paleo-high (Barrow Arch) formed by the interaction of an uplifted rift shoulder and the Ancestral Brooks Range forebulge. Higher accommodation during Paleocene PCF deposition likely resulted from proximity to the basin access and a higher subsidence rate driven by lithospheric response to orogenic loading. A better understanding of the relationship between differing stacking patterns, basinal position, active tectonism, and tectonic quiescence should improve net/gross estimates for PCF reservoirs.