New Insights
for Correlation in Shoreface-to-Shelf Systems Based
on Observations in the Campanian Blackhawk Formation
to Castlegate Sandstone Stratigraphic
Interval, Book Cliffs, Utah
Pattison, Simon A.J.1,
Huw Williams2, Paul Davies2 (1)
Brandon University, Brandon,
MB (2) Reservoir Geology Consultants
Limited, Rhandirmwyn, United Kingdom
Isolated sandstone bodies of enigmatic
origin and uncertain stratigraphic position are
scattered throughout the Cretaceous Western Interior of North America. An
unusually coarse example occurs in the Middle Mountain to Floy Wash region of the Book
Cliffs, east-central Utah. The coarse-grained
deposits are concentrated in erosively-based patches
which are 0.5 to 4 m thick, up to 40 m2 in areal
extent, and consist of fine- to very coarse-grained sandstones, mudstone clasts, granules, pebbles, bone fragments, shell debris,
fish teeth, Teredolites-bored wood fragments, and oolitic ironstones. Fossils include Scaphites
hippocrepis III, Baculites
and Inoceramus. These coarse-grained patches abruptly
pass into iron-rich siltstones, forming a laterally persistent marker horizon
that can be recognized for tens of kilometers in eastern Utah. Previous studies have
correlated this horizon to a variety of stratigraphic
intervals ranging from the late Santonian Emery
Sandstone to the early Campanian Kenilworth Member.
The recognition of index fossil Scaphites hippocrepis III coupled with the high resolution sequence stratigraphic framework has revealed a definite Campanian age. This layer is comprised of transgressively-modified, detached falling-stage and lowstand deposits that mantle the top Aberdeen Member
sequence boundary, thus defining the Aberdeen-Kenilworth boundary.
The main implication for correlation in shoreface-to-shelf systems is that parasequence-
and member-scale rock packages bracketed by this coarse-grained layer and the
top of the Castlegate Sandstone exhibit a gradual basinward thinning (i.e. 30 % reduction in thickness over
40+ km) not the abrupt clinoform-style pinch-outs
popularized in previous studies. Other shoreface-to-shelf
systems are likely to exhibit similar thickness trends, thus providing an
alternative correlation style to existing models.