MICKEY, MICHAEL B., and HIDEYO HAGA
Micropaleo, Consultants, Inc., Encinitas, CA

Abstract: Construction of a Relative Sea Level (Base Level) Curve from High Resolution Biostratigraphic Analyses for the Jurassic to Early Cretaceous (Neocomian) from the North Slope of Alaska

A Relative Sea Level (Base Level) Curve for Jurassic to Early Cretaceous (Neocomian) time was constructed for the North Slope of Alaska using High Resolution Biostratigraphic Analyses

A composited, "complete" biostratigraphic section was compiled from wells drilled on the North Slope utilizing foraminiferal and palynomorph (spore-pollen and dinoflagellate) biostratigraphy. Foraminiferal faunal diversity and abundance plots were generated for the composite section to assist with identifying depositional cycles. High resolution (30 ft composite) paleoenvironmental multivariate cluster analysis techniques were used to establish detailed paleoenvironments. Midpoint water depth values were assigned to the base and maximum flooding horizon of each transgressive-regressive (T-R) cycle.

This approach resulted in the construction of a Relative Sea Level (Base Level) Curve based on 4th order depositional cycles for the Jurassic to Early Cretaceous (Neocomian) age strata. It also provided a first order approximation of water depth changes associated with each transgression and regression. The study identified 35 T-R cycles exhibiting a range in water depths from 50 ft to 2700 ft, with most water depth changes in the range of 100 to 500 ft. A mirror image logarithmic scale plot better illustrates the shelfal depositional cycles. The linear scale plot gives an unexaggerated comparison of water depths associated with each depositional cycle. In general, depositional cycles in the Jurassic represent deeper marine conditions and have larger water depth changes associated with them compared to the depositional cycles of the overlying Early Cretaceous (Neocomian).

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas