Abstract: Use of Vitrinite Reflectance as a Maturation Indicator in the Brookian Petroleum System of the Alaskan North Slope

Charles R. Landis, Michael R. Werner, Todd Salat

The Upper Cretaceous through Tertiary Brookian sequence records thick time-transgressive clastics unroofed from the ancestral Brooks Range. Apatite

fission track analysis indicates several phases of uplift due to northward and northwestward thrusting since the Jurassic. As a result, the maturation history of the Brookian sequence is a complex interplay of tectonic and depositional processes that yield significant fractions of reworked kerogen. Isolated kerogen mounts of Albian through Tertiary clastics from the Brooks Range foothills show broadened reflectance histograms due to redistributed vitrinite eroded from organic-rich shales and coals. Without scrutiny, these data would indicate significantly higher levels of maturation than would be expected. Representative maturities are best estimated from whole rock mounts (whole cores, sidewall cores, outcrops, and cuttings) where fabric relationships are preserved. Elongate indigeno s vitrinite is distinguished from allochthonous coals and rounded, reworked vitrinite. These maturation data indicate that the Brookian sequence in the Colville trough underwent eastward time transgressive maturation, generally paralleling depositional dip of axial Upper Cretaceous progradational fill or Aptian/Albian clastics derived from the ancestral Brooks Range to the west and south. To the east, maturation in Paleocene and early Eocene depocenters is evidently truncated by Eocene uplift. Along the Barrow arch to the north, the Brookian section is immature.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994