Stratigraphic and structural interpretation of Willapa basin
Willapa basin is a middle Eocene to Holocene depocenter in southwestern Washington and on the adjacent continental shelf. Surface geology, biostratigraphy, and seismic and well data have been used to develop a stratigraphic and structural interpretation of the basin. Middle Eocene deep-water sediments were deposited on convergent margin and accreted to North America prior to the early Miocene. Turbidite sandstones interpreted to be the lower to middle Miocene Astoria(.) Formation overlie this Eocene sequence in onshore wells. Distal turbidites of lower to middle Miocene age (Hoh assemblage) were thrust beneath the Eocene and Astoria(.) Formation rocks during the middle to upper Miocene. Upper Miocene bathyal shales and siltstones unconformably overlie the older rocks. This sequence was then unconformiably(.) covered by upper Miocene sandstones and siltstones deposited in a nearshore shelf environment. This extreme change in water depth is interpreted to be of tectonic origin. The occurrence of redeposited lower to middle Miocene deep-water fauna in the late Miocene shelf sequence is ascribed to erosion at the sea floor of mud diapirs rooted in Hoh assemblage rocks. Activation of these diapirs was probably associated with this tectonic uplift. Pliocene and Pleistocene conglomerates, sandstones, and siltstones were deposited in both marine and deltaic environments and are locally exhibited as an onlap sequence in marine seismic data. Diapiric growth has continued into the Holocene, resulting in both angular truncation of the Pliocene-Pleistocene sequence and diapiric breaching at the sea floor.
- Research Organization:
- Washington Sea Grant Program, Seattle (USA)
- OSTI ID:
- 6027278
- Report Number(s):
- CONF-8905132-
- Journal Information:
- AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States), Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Vol. 73:4; ISSN AABUD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
CENOZOIC ERA
CONGLOMERATES
CONTINENTAL MARGIN
CONTINENTAL SHELF
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
NORTH AMERICA
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SILTSTONES
STRATIGRAPHY
TERTIARY PERIOD
USA
WASHINGTON