LAGOE, MARTIN B., and SARAH D. ZELLERS, University of Texas at Austin, Department of Geological Sciences, Austin, TX

ABSTRACT: Complementary Subsurface Stratigraphic Analysis Using Microfossil Distributions and Seismic Interpretation: An Example from Southern Alaska

Subsurface stratigraphic analysis of the Yakataga continental margin, Gulf of Alaska, illustrates how seismic interpretation and micropaleontologic analysis complement one another. This sub arctic setting poses problems for both the geophysicist and biostratigrapher. Late Cenozoic glaciation and contemporaneous structural deformation produced complex stratigraphic/structural geometries, leading to marginal seismic quality in many areas. The sub arctic setting also results in limited planktic microfossil diversity and extinction/origination datums, preventing the use of standard, low latitude biozonations. An integrated approach overcomes many

of these problems. Microfossil analysis concentrates on 11 exploration wells drilled in the area. Paleobathymetry is determined from benthic foraminiferal biofacies analysis and a biozonation is developed from climatically controlled coiling shifts in Neogloboquadrina pachyderma and some planktic foraminiferal and diatom datums. Paleobathymetric and coiling curves are scaled to the seismic using velocity functions to promote direct comparison.

This leads to the correlation of several prominent, area-wide reflectors with relative sea level falls. Regional mapping of the reflectors yields several unconformity-bounded stratigraphic packages with complex interrelationships, reflecting both glacial erosion and structural truncation. How these packages relate to commonly applied sequence stratigraphic principles is still being investigated. The internal stratigraphic geometries can then be used to recognize gaps in the biozonation, which, like paleomagnetic stratigraphy, has a dominantly bipolar character. Increased confidence in both the biostratigraphic and seismic interpretation results from this procedure. Serious mistakes are avoided in both disciplines by the complementary nature of the analyses.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.