Seismic facies, sedimentology, and significance of a lacustrine delta in Neogene Lake Idaho' deposits: Western Snake River Plain, Idaho and Oregon

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5025251

Wood, S H ^[1]

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1. Boise State Univ., ID (United States)

The top of a buried fine-grained delta system of paleo- Lake Idaho' is detected by high-resolution seismic profiles, 300 m beneath the western Snake River Plain near Caldwell, Idaho. Characteristic 3--5[degree] dip of seismic reflectors in the prodelta-mud facies plus electrical-resistivity logs and cuttings from a 670-m well show a 150-m coarsening-upward prodelta sequence overlain by well-sorted fine sand and thin mud layers. Slope and vertical relief (compaction corrected) of prodelta clinoforms indicate the delta was prograding north into a lake basin 250-m deep. Elevation of the top of the delta front is a measure of a paleolake stand. The detected buried delta front is presently at 405 m elevation, about 500 m below what is regarded as the last high lake stand (elev. 850--975 m). The present low elevation of the delta front is partly explained by about 300 m of downward tectonic movement on faults and about 200 m of subsidence by basin-sediment compaction with respect to the basin margins. Distribution of lake deposits around the northwest end of the lake indicates the lake level reached 850--975 m elevation about 2 million years ago. Location of the former outlet of Lake Idaho' and the ancestral Snake River is still a puzzle. Present geomorphology suggests that about 2 million years ago a southward-migrating, ancestral Hells Canyon tributary of the Columbia-Salmon Rivers system captured the lake drainage by overflow of a sill at Dead Indian Ridge near Weiser, Idaho. Hells Canyon and the enlarged Snake River subsequently cut down about 215 m to the present river elevation of 635 m at Dead Indian Ridge.

• OSTI ID: 5025251
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CENOZOIC ERA
COASTAL REGIONS
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
GEOPHYSICAL SURVEYS
IDAHO
LAKES
NORTH AMERICA
OREGON
RIVER DELTAS
SEDIMENTS
SEISMIC SURVEYS
SNAKE RIVER PLAIN
STRATIGRAPHY
SURFACE WATERS
SURVEYS
TERTIARY PERIOD
USA