Physical Sciences and Mathematics Commons^™

Paleomagnetic Determination Of Vertical Axis Block Rotation Near The Doty Fault In Southwestern Washington, Charles Linneman

WWU Graduate School Collection

In this paper I present the results of paleomagnetically derived vertical axis rotations (VARs) of sites in two different flows of the Columbia River Basalt (CRB) – the 16 Ma Sentinel Bluffs member of the Grande Ronde flow and the 12 Ma Pomona Member of the Packsack Lookout – near the Doty fault in southwestern Washington. In two field seasons, I collected 99 cores from 14 sites, 11 in the Grande Ronde flow and three in the Pomona member flow. Of the 227 specimens that I demagnetized, 212 had well-defined magnetic directions. Positive fold and reversal tests results confirm the …

Magnetic Methods To Characterize The Emplacement Of The Nodule Point Intrusion (Marrowstone Island, Wa), Charlie Nuncio

Geology Graduate and Undergraduate Student Scholarship

The mafic intrusion of Nodule Point, Marrowstone Island, WA has sparse scientific literature to substantiate the local geologic history around its emplacement conditions. To fill this gap, rock magnetism and paleomagnetic methods have been applied to the intrusion and the sandstone of Scow Bay host rock. Samples taken from both lithologies were subject to thermal and alternating field demagnetization to assess paleomagnetic components. The Anisotropy of Magnetic Susceptibility (AMS) of samples was measured, and the maximum axis of susceptibility, K1, was used as an analog to hypothesize emplacement conditions. The host rock: the sandstone of Scow Bay, returned magnetization characteristics …

Paleomagnetism And Rotation History Of The Blue Mountains, Oregon, Usa, Bernard A. Housen

Geology Faculty Publications

An important element in reconstructions of the Cordilleran margin of North America includes longstanding debate regarding the timing and amount of rotation of the Blue Mountains in eastern Oregon, and the origin of geometric features such as the Columbia Embayment, which was a subject of some of Bill Dickinson’s early research. Suppositions of significant clockwise rotation of the Blue Mountains derived from Dickinson’s work were confirmed in the 1980s by paleomagnetic results from Late Jurassic–Early Cretaceous plutonic rocks, and secondary directions from Permian–Triassic units of the Wallowa–Seven Devils arc that indicate ~60° clockwise rotation of the Blue Mountains.

This study …

Paleomagnetism And Detrital Zircon Geochronology Of The Skeena Group, British Columbia, Christopher L. Ward-Guthrie

WWU Graduate School Collection

The mid-Cretaceous Skeena Group of British Columbia is a sedimentary continental margin deposit that overlies the lower Jurassic Hazelton Group of the Stikine Terrane. Nine paleomagnetic sites were collected in 2006 and 2007, demagnetized thermally in 50-15°C steps, and high temperature components fit using principal component analysis. A new Ar⁴⁰/Ar³⁹ age of 93.9 ± 0.6 Ma for a flow of the Rocky Ridge Formation was also collected.

Three volcanic sites of the Rocky Ridge Volcanics possess coherent magnetizations, but did not prove useful. Five of six sedimentary sites from the Rocher de Boule and Bulkley Canyon Formations …

A Paleomagnetic Paleolatitude Determination From The Upper Cretaceous Units Of The Gold Beach Terrane, Southwest Coastal Oregon, Noel Liner

WWU Graduate School Collection

The paleolatitude for the Gold Beach terrane has been under debate from several sources (Bourgeois, 1980b; Bourgeois, 1985; Jayko and Blake, 1985; Seiders and Blome, 1987; Aalto, 1989) since the 1980 publication of Joanne Bourgeois’ PhD thesis connecting the Upper Cretaceous formations of the Gold Beach terrane to the Nacimiento Block, currently in the vicinity of Southern California; During the Cretaceous, the Nacimiento Block was farther south than its present position by about 200 km (Blake and Jayko, 1985). The opposing hypothesis of Seiders and Blome (1987) connects the Gold Beach terrane to the neighboring Klamath block, implying at most …

The Paleomagnetism Of The Stewart’S Point And Anchor Bay Members Of The Point Arena Terrane, Northern California, Kirk Heim

WWU Graduate School Collection

Paleomagnetic investigation of Upper Cretaceous sedimentary strata of the Point Arena terrane has shown the rocks to be remagnetized. The study was initially intended to reconstruct the Cretaceous paleogeography of the Point Arena terrane and resolve conflicting translation estimates, but became one of remagnetization. Samples studied are from the Upper Cretaceous Stewart’s Point member and the Late Cretaceous Anchor Bay Member of the Gualala formation. Specimens surviving the remagnetization have a mean second-removed direction that indicates approximately 20 degrees vertical rotation from the expected direction of the Cretaceous magnetic field at the locality of the Point Arena terrane. The loss …

Paleogeography Of The Spieden Group, San Juan Islands, Washington, Patricia Allison Dean

WWU Graduate School Collection

The Spieden Group in the San Juan Islands of Washington State consists of the Lower Cretaceous Sentinel Island Formation and the Upper Jurassic Spieden Bluff Formation. In order to constrain the location of its origin, paleomagnetism of the sedimentary rocks of the Spieden Group was studied to obtain paleolatitudes. Two components of magnetization were measured in most of the Sentinel Island Formation specimens. The second-removed component had a mean in-situ direction of D = 34.1°, I == 44. 2°, α₉₅ = 12.0° and a mean tilt-corrected direction of D = 49.3°, I = 71.5°, α₉₅ = 6.9°. Uncertainty …

Paleomagnetism Of The Jura-Cretaceous Kyuquot Group, Vancouver Island, British Columbia, Chad K. Hults

WWU Graduate School Collection

The Kyuquot Group is a series of marine clastic deposits of Late Jurassic to Early Cretaceous age located on the NW portion of Vancouver Island. These sediments have been folded, but not metamorphosed, and so provide an attractive target for paleomagnetic study. Results from these rocks fill a significant (50 m.y.) time gap in our knowledge of the paleomagnetic paleolatitude record of Wrangellia. Paleomagnetic results from the underlying Bonanza Volcanics (Symons, 1984) show no significant relative latitudinal displacement of Wrangellia with respect to North America. This, along with geological correlations between other similar-aged clastic sediment units, has led several workers …

Paleomagnetism Of The Late Cretaceous Ventura Member Of The Midnight Peak Formation, Methow-Pasayten Belt, North-Central Washington, David R. (David Richard) Bazard

WWU Graduate School Collection

Paleomagnetic analysis was conducted on 31 sites of the Ventura redbed Member of the Midnight Peak Formation located in the Methow-Pasayten belt, north-central Washington. Single high-stability components of magnetization, chiefly retained by high-unblocking temperature hematite exist in specimens from all but two of the sites. Directions calculated from these components were found to form circular within-site distributions and to be consistent across several meters of section. The single high-stability components, positive inclinations, and pre-folding, thus pre-Paleocene magnetizations suggest that the Ventura Member records a single Late Cretaceous dipole-field.

Proportionally untilting site-mean directions did not produce a reasonable field direction nor …

The Petrography And Tectonic Significance Of The Blue Mountain Unit, Olympic Peninsula, Washington, Jon M. Einarsen

WWU Graduate School Collection

The sedimentary rocks of the early to middle Eocene Blue Mountain unit compose the stratigraphic base of the otherwise predominantly basaltic Crescent Formation in the Olympic Peninsula, Washington. In the study area, primarily in northeastern portions of the Olympic Peninsula, the Blue Mountain unit consists of two distinct petrofacies, one a plagioclase-rich feldspathic arenite, the other a chert-rich lithic arenite. A third petrofacies is a feldspathic-lithic arenite and is a petrologic combination of the two distinct petrofacies. The source areas for the plagioclase-rich and chert-rich petrofacies are interpreted to be the Coast Plutonic Complex and San Juan Islands, respectively. The …

A Paleomagnetic Age Investigation Of Pre-Salmon Springs Drift Pleistocene Deposits In The Southern Puget Lowland, Washington, John L. (John Leo) Roland

WWU Graduate School Collection

The Pleistocene history of the southern Puget Lowland is marked by repeated invasions by the Puget Lobe of the Cordilleran ice sheet. The present stratigraphic sequence is represented by four glaciations (Orting, Stuck, Salmon Springs, and Fraser) of northern provenance, separated by unconformities and two nonglacial formations (Alderton and Puyallup) of central Cascade and Mount Rainier provenances. Paleomagnetic work conducted on pre-Salmon Springs sediments at their type localities and correlative exposures in the Puyallup Valley provide evidence for the ages of the Orting Drift, Alderton Formation, Stuck Drift, and Puyallup Formation.

The silts sampled demonstrate an array of soft (unconsolidated) …

The Paleomagnetism Of A Thick Middle Tertiary Volcanic Sequence In Northern California, Douglas Edward Craig

WWU Graduate School Collection

The mean direction of remanent magnetism for 44 sampling sites from Oligo-Miocene lava flows in northern California points about 12° east of the expected Oligo-Miocene geomagnetic field direction for the area. Our paleomagnetic data and other data indicate that the Cascade Range has rotated clockwise since the middle Tertiary. Similar, but larger, clockwise rotations have been documented in previous studies throughout the Coast Ranges. Two mechanisms are suggested to account for the differential rotation that has occurred within the Coast and Cascade Ranges. First, the Coast Ranges are rotated and then accreted to a curved continental margin during the Eocene, …

Tectonic Rotations In The Cascade Mountains Of Southern Washington, Roger G. (Roger Glenn) Bates

WWU Graduate School Collection

Paleomagnetic directions from 34 widely distributed sampling sites in the Oligocene Ohanapecosh Formation in the Cascade Mountains of southern Washington are well grouped with a mean and confidence interval of: Dec. = 27°, Inc. = 64°, α₉₅ = 4°. When compared to the expected direction, computed from the Oligocene reference pole for stable North America, a clockwise rotation of 31° ± 12° is apparently present. This result is not significantly different from other studies within the Cascades and Coast Range of southern Washington and suggests that the two Ranges have rotated as a single unit during late Eocene to …

Paleomagnetism And Tectonic Significance Of The Goble Volcanics Of Southern Washington, Cynthia D. Burr

WWU Graduate School Collection

The upper Eocene to lower Oligocene Goble Volcanic series of southwest Washington is a thick sequence of areal to submarine basaltic to andesitic flows, pyroclastics, and minor sediments. Major element geochemical analyses suggest that these rocks may represent early magmatism of the Cascade arc. Paleomagnetic results from 37 sites indicate that the direction of remanent magnetization in the Goble Volcanics has a declination of 18.5°, an inclination of 57.5°, and a circle of 95% confidence (∝ ₉₅)of 4.33°. The expected upper Eocene direction in the sampling area is D = 353.5°; Ī = 61.5°. Thus the Goble Volcanics block …

Paleomagnetism Of The Snoqualmie Batholith Central Cascades, Washington, Suzanne J. Beske

WWU Graduate School Collection

Paleomagnetic results have been obtained from eight sites in the Miocene (15-18 m.y.) Snoqualmie batholith, Central Cascades, Washington. After ac magnetic cleaning, four magnetically stable sites remained, yielding a pole at 221.0°E, 84.5°N, (δ_p = 7.9, δ_m = 9.3, k = 286.4). A stability test was formulated based on the ratio of the intensity of natural remanent magnetism, NRM, (after ac demagnetization) to the weak field susceptibility. This ratio, Q_d proved effective in determining magnetically stable samples from samples showing a wide spectrum of stability from within the Snoqualmie batholith, and therefore, was strictly applied to all …