Fluvial
Sand-Body Dimensions and Architecture, Neslen and
Cole, Rex D.1 (1) Mesa State
College, Grand Junction, CO
The objectives of this study were to
create a statistical database for lenticular and channel-form sand bodies in
the Neslen and lower Farrer Formations. Three measured sections (total of 1,622
ft) were established and 55 sand bodies mapped (GPS) within an area of 1.4 mi2.
Paleocurrent measurements (N = 374) were also collected. The Neslen Formation
(260 ft thick), which consists of carbonaceous mudrock, fine- to medium-grained
sandstone, and coal, was deposited in a coastal-plain setting, whereas the
lower Farrer Formation (290 ft thick), which contains more sandstone and very
little carbonaceous mudrock and no coal, was deposited in an alluvial-plain
setting. The average sandstone-mudrock ratio is 22:78 for the Neslen and 38:62
for the lower Farrer. Sand-body connectivity is very low (<5%) in both
units. For the Neslen sand bodies (N = 18), the thickness range is from 1.4 to
12.9 ft and the apparent-width range is from 52 to 1,222 ft; for the lower
Farrer (N = 37), these ranges are 1.5 to 27.0 ft and 92 to 2,556 ft,
respectively. The apparent-width parameter is the linear distance between
pinchouts of a given sand body. In the Neslen Formation, 11% of the sand bodies
consist of single channel fills, 39% are compound channel fills, and 50% are
splays; whereas in the lower Farrer Formation, these proportions are 65%, 22%,
and 13%, respectively. Paleocurrent data have a vector mean of 40.8º and
suggest that the Neslen channel-form sand bodies have greater sinuosities that
those in the lower Farrer.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California