--> ABSTRACT: The Role of Volcanism, Inversion, and Neotectonics in the Puget-Willamette Lowland Petroleum System, Washington and Oregon, by Jackson, James S.; #90026 (2004)
[First Hit]

Datapages, Inc.Print this page

Jackson, James S.1 
(1) Portland State University, Portland, OR

ABSTRACT: The Role of Volcanism, Inversion, and Neotectonics in the Puget-Willamette Lowland Petroleum System, Washington and Oregon

Eocene sediments deposited west of an ancestral Cascade Range include a coal-bearing sequence covering much of the Puget-Willamette Lowland. The terrestrial deposits pass into marine deposits to the west. Syn-depositional normal Previous HitfaultingNext Hit and strike-slip Previous HitfaultingNext Hit are evident in several sub-basins, which are interpreted to represent a transtensional setting. Eocene volcanism locally effected sedimentation. Eocene fluvial sandstones overlain by intra-formation claystones are potential reservoir-seal couplets. Eocene coals and carbonaceous claystones represent a potential gas-prone source interval. 
Locally preserved sediments indicate that subsidence continued into Miocene and Pliocene time, and was followed in the Puget Lowland by extensive Pleistocene glaciation. At present, active Previous HitfaultingNext Hit affects the Lowland in several discrete zones. 
Models of vitrinite reflectance data from wells located in the Lowland indicate that from the Eocene to the Present, the regional geothermal gradient ranged from 28 to 32°C/km. The eastern margin of the Lowland was bordered by the Cascade volcanic arc, and was subjected to advective heat flow. Modeling of vitrinite reflectance data indicates local geothermal gradients reaching 40 to 50°C/km on the eastern side of the Lowland. 
In the southern Lowland, normal faults were modified by episodes of late Eocene and Miocene transpression, which resulted in mild inversion of older normal faults. In the northern Lowland, Holocene Previous HitfaultingNext Hit is recognized in outcrop and is interpreted on seismic data acquired in Puget Sound. 
Structures formed by early Miocene or earlier events may have trapped migrating hydrocarbons. Structures formed or modified by Holocene Previous HitfaultingTop very probably post-date hydrocarbon generation and migration.

 

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.