Eocene Green River Multiple Insects IF-PCM-16-005

Multiple Insects
Green River Formation
Parachute Creek Member
Middle Eocene
Uintah County, Utah

This is a very interesting assemblage of insects arrange in a linear strand.  They include:  Chilosia sp.(fly), Pronemobius sp.(cricket), Tipula sp. (crane fly), Dicranomyia sp. (crane fly), Sakenia sp.(gnat), and Limetopum sp.(ant).  There are also several unidentified insects.  Multiple insects on a single specimen are not unusual but this variety of insects is rare on a single plate.  This type of orientation and variety of insects has been interpreted by some to represent an accumulation of insects that may have been trapped in a spider web.  All identifications are based on Scudder (Tertiary Insects of North America) 1890. 

The upper part of the Green River Formation in the eastern Uinta Basin is present in two stratigraphic intervals separated by approximately 250 m of sandstone, siltstone, marlstone and lacustrine limestone (micrite, boundstone, grainstone).  The lower sequence, in the Garden Gulch Member, represents an early lacustrine phase of Lake Uinta and consists of approximately 29 m of interbedded clay-rich oil shale, gastropod grainstone and packstone, ostracode grainstone, algal boundstone and calcareous silty claystone. Fish fossils, plant debris, and pelecypods are locally present. Detrital clay minerals (smectite, chlorite and illite) are common and calcite abundance is greater than dolomite. The second oil-shale interval is located in the upper 10 m of the Parachute Creek Member. The Mahogany ledge crops out in the lower 15 m of this sequence. Oil shale in the Parachute Creek Member is a kerogenous dolomicrite (dolomite greater than calcite). Analcime, quartz, K-feldspar, and albite are also common. Illite is the dominant clay mineral. Fossils include insects, insect larvae, and plant debris. Marlstone and volcanic tuff are interstratified with oil shale.