Pleistocene tephrostratigraphy and paleogeography of southern Puget Sound near Olympia, Washington

Walsh, Timothy J.; Polenz, Michael; Logan, Robert L.; Lanphere, Marvin A.; Sisson, T. W.

doi:10.1130/0-8137-0004-3.225

Cited by 3 publications

(1 citation statement)

References 16 publications

(16 reference statements)

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“…to the west (Walsh et al, 1987(Walsh et al, , 2003Logan and Walsh, 2004). Eocene uplift of the Black Hills is consistent with documented uplift and northwest-trending anticlinal folding of thrust fault-and reverse fault-bound crustal blocks to the south and southeast of the Black Hills beginning in the middle Eocene (Globerman et al, 1982;Wells and Coe, 1985;Stanley et al, 1994Stanley et al, , 1996.…”

Section: Introductionmentioning

confidence: 99%

Shallow geophysical imaging of the Olympia anomaly: An enigmatic structure in the southern Puget Lowland, Washington State

et al. 2016

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Gravity and magnetic anomalies suggest that the Olympia structure beneath the southern Puget Lowland (western Washington State, U.S.) vertically displaces Eocene Crescent Formation strata. Northeast of the Olympia structure, middle Eocene Crescent Formation is beneath 4-6 km of Paleogene-Neogene and Quaternary strata of the Tacoma basin, whereas the Crescent Formation is exposed at the surface immediately to the south. Although numerous marine seismic reflection profiles have been acquired near the surface location of the Olympia structure as defined by potential field anomalies, its tectonic character remains enigmatic, in part because inlets of southern Puget Sound are too shallow for the collection of deep-penetration marine seismic profiles across the geophysical anomalies. To supplement existing shallow-marine data near the structure, we acquired 14.6 km of land-based seismic reflection data along a profile that extends from Crescent Formation exposed in the Black Hills northward across the projected surface location of the Olympia structure. The reflection seismic data image the Crescent bedrock surface to ~1 km depth beneath the southern Tacoma basin and reveal the dip on this surface to be no greater than ~10°. Although regional potential field data show a strong linear trend for the Olympia structure that implies folding over a blind thrust and/or bedrock juxtaposed against a weakly to nonmagnetic sediment section, high-resolution magnetic anomaly analysis along the land-based profile suggests that the structure is more complex. Overall, seismic and potential-field profiles presented in this study identify only minor shallow faulting within the projected surface location of the Olympia structure. We suggest that the mapped trace of the Olympia structure along the northern flank of the Black Hills, at least within the study area, is constrained by juxtaposed normal and reversely magnetized Crescent Formation units and minor tectonic deformation of Crescent Formation bedrock. Black Hills Uplift and the Olympia Structure The Black Hills are one of the largest uplifted exposures of basement rocks in the area surrounding the Puget Lowland. Uplift began in the early or middle Eocene, based on the stratigraphic relationship between onlapping latest Eocene to Oligocene sediments on the west and south sides of the Black Hills and evidence for the influence of an uplifted Black Hills on basin sedimentation GEOSPHERE

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Section: Introductionmentioning

confidence: 99%

Shallow geophysical imaging of the Olympia anomaly: An enigmatic structure in the southern Puget Lowland, Washington State

et al. 2016

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A refined understanding of the paleoenvironmental history recorded at the Okanagan Centre section, an MIS 4 stratotype, south‐central British Columbia, Canada

Lesemann

Brennand

Lian

et al. 2013

J Quaternary Science

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The Okanagan Centre section is the stratotype for marine oxygen isotope stage (MIS) 4 sediments (Okanagan Centre Drift) in the southern interior of British Columbia, Canada. Previous work suggested that these sediments record two glacial and two interglacial cycles. This study reports on detailed sedimentological and geochronological investigations of lithostratigraphic units comprising the Okanagan Centre sequence, revealing successive deposition of subaqueous and subaerial outwash, a subglacial till and glaciolacustrine sediments during MIS 4. A limiting optical age of 113 AE 8 ka defines the base of this sequence. Sedimentological, paleopedological, optical dating and tephrochronological data from sediments near the middle of the sequence reveal soil development (MIS 3) in eolian sediments deposited on a river terrace overlying a deglaciated surface. Within these sediments, identification of Mt. St. Helens set C tephra suggest sedimentation between 50 and 35k 14 C a BP. Optical dating corroborates the tephrochronology and suggests that this surface formed after $52 AE 7 ka. The record of MIS 2 glaciation is restricted to deglaciation, and overlies MIS 3 sediments above an unconformity possibly related to regional subglacial meltwater erosion. Eolian sediments containing Mt Mazama set O tephra ($7.62k cal a BP) cap the sequence.

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Publications of the Volcano Hazards Program 2003

Nathenson¹

2005

Open-File Report

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Pleistocene tephrostratigraphy and paleogeography of southern Puget Sound near Olympia, Washington

Cited by 3 publications

References 16 publications

Shallow geophysical imaging of the Olympia anomaly: An enigmatic structure in the southern Puget Lowland, Washington State

Shallow geophysical imaging of the Olympia anomaly: An enigmatic structure in the southern Puget Lowland, Washington State

A refined understanding of the paleoenvironmental history recorded at the Okanagan Centre section, an MIS 4 stratotype, south‐central British Columbia, Canada

Publications of the Volcano Hazards Program 2003

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