Sedimentological Model for Lacustrine Shoreline Deposition, Lower Green River Formation (Eocene), Northeastern Uinta Basin, Utah
James W. Castle
Sedimentological analysis
and subsurface
paleoenvironmental
mapping in a
250-mi2 area of the northeastern Uinta basin indicate that laterally
continuous sandstone bodies represent deposition in lacustrine barrier-beach
complexes. A lacustrine shoreline depositional model was developed using
interpretations from approximately 1,500 ft of continuous core from 24 wells in
the general area of Wonsits Valley and Red Wash oil fields. The model can be
applied to interpreting depositional environments of ancient lacustrine deposits
and to predicting subsurface distribution of lacustrine shoreline sandstones.
Coarsening-upward sequences observed in cores represent deposition in high-energy, wave-dominated shoreline systems that prograded into low-energy, open lacustrine environments. The vertical sequence consists of: lacustrine shale overlain by transitional siltstone and silty sandstone beds; lower shoreface very fine-grained sandstone; upper shoreface fine-grained sandstone; swash-backwash fine to medium-grained sandstone; and backshore fine to medium-grained sandstone and interbedded algal-laminated shale.
Paleoenvironmental
mapping using interpretations from cores and well logs
indicates that maximum dimensions of the barrier-beach complexes studied are
approximately 10 mi long and 3 mi wide. Thickness ranges from approximately 10
to 35 ft. Mapping shows that barrier complexes were separated from onshore
fluvial systems by a mudflat-lagoon depositional environment.
The barrier-beach deposits in the lower Green River Formation are similar to some modern and ancient, marine, siliciclastic shoreline deposits formed along microtidal coasts.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.