High-Resolution
Sequence Stratigraphic Study of the Blackstone
Formation,
Tyagi, Aditya1,
A.G Plint1 (1)
Sedimentological and stratigraphic
concepts as applied to marine-shale dominated successions are still evolving.
This study addresses some of the questions pertaining to the high-resolution
sequence stratigraphic studies of such successions on
a regional scale (200,000 Km2). Blackstone Formation (Cenomanian-Turonian) constitutes an important source rock
in the Western Interior Basin, is a clastic wedge
(40-500 m thick) deposited over a period of more than 3.5 my during the
Greenhorn transgressive-regressive cycle.
High-resolution sequence stratigraphic analysis has
been carried out with a view to test the applicability of the existing models
of sequence stratigraphy to marine-shale successions.
Correlation of the regional flooding surfaces, discontinuity surfaces, bentonites, and foraminiferal biozones permits to divide the study interval into 14 time-stratigraphic mappable units.
Based on lapout patterns, and biostratigraphic
data 5 surfaces have been interpreted as Maximum Flooding Surfaces. Basinal area towards the east is riddled with hiatal surfaces, indicating that significant part of the stratigraphic record is missing. Thus, interpretation of
sedimentation rates, and climatic cycles in the study interval needs to be
approached with caution. Stratigraphic succession is
punctuated by two regional unconformities, one of which is Middle Cenomanian in age, erosional in
nature, and dies out towards the west. This unconformity may have implications
for hydrocarbon exploration in the eastern part of the basin. Isopach maps of individual units suggests that the
subsidence pattern in the basin was changing dramatically over a time span of
500 thousand years, indicating lateral shifts in thrust loading along the
deformation front.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California