Organic C-Rich
Mudstone Sedimentation in Arctic
Keller, Margaret A.1, Joe H.S.
Macquaker2 (1) USGS Menlo Park, Menlo Park, CA (2) University of
Manchester, Manchester, United Kingdom
New models for mudstone deposition and diagenesis have come from recent studies utilizing
high-resolution petrography and SEM. These and geochemical techniques applied
to the Lower Cretaceous of Arctic Alaska address basic questions about lithofacies, organic facies,
depositional settings and processes, and petroleum source potential.
Results from the pebble shale unit (psu) and Gamma Ray Zone (GRZ) of the Hue Shale at 3
localities (Canning River, Mikkelsen Bay State-1 and
Orion-1 wells) indicate that the succession consists of a basal pebbly to sandy
mudstone and sandstone, overlain primarily by burrowed and pelleted
clay-rich mudstones that are either silt or fine-sand-bearing or clay
dominated. Subordinate, bedding-parallel carbonate-cemented mudstones, tuff and
tuffaceous/bentonitic mudstones, and sandstones are
also present. Importantly, mud-supported sand-sized clasts,
some rounded and pitted, with rare granules and pebbles occur scattered
throughout much of this succession; and psu genetic
beds (2-5 mm) are more crudely bedded and poorly sorted than GRZ. Rock-Eval pyrolysis on Mikkelsen cores indicates that both formations contain
primarily Type II, oil prone kerogen.
During deposition of the psu, in addition to distal fluvial, volcanic, and eolian sources, melting of sediment-laden, seasonal sea-ice
-- recently recognized in the modern Arctic – probably episodically contributed
silt, mud, primary organics, and coarser sediment to this basin. While
regionally, fluvial input to the studied psu successions
is considered less important than sea-ice, locally its influence is likely to
be greater. For the GRZ, distal turbidites and
volcanic ash contribute more sediment than sea-ice, and hiatuses with carbonate
cementation are more common.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California