The Kamloops Group is a widespread assemblage of Eocene volcanic and sedimentary rocks in south-central British Columbia. Detailed mapping of the type area near Kamloops has resulted in its subdivision into two formations and thirteen formal and informal members. The Tranquille Formation, 0-450 metres thick, consists of lacustrine sediments which grade upward into pillowed flows, hyaloclastite breccia and aquagene tuff. The overlying Dewdrop Flats Formation, with nine members, consists of up to 1000 metres of basalt to andesite phreatic breccia, flow breccia and flat-lying flows. In one large and four minor volcanic cones, basal phreatic volcanic rocks pass upward into subaerial flows and breccia. A fault zone of inferred strike-slip displacement to the southwest, and a complex reverse-faulted zone to the south of the area, localized deposition of the Tranquille Formation. Later fault activity created the complex Tranquille Canyon graben, in part filled with Dewdrop Flats Formation volcanics. Reconnaissance of the Kamloops Group throughout the Thompson-Okanagan region, and detailed mapping at McAbee and Savona, have shown that most Kamloops Group sections consist of a lower sedimentary and volcanosedimentary unit, followed by thicker, dominantly basalt to andesite, flow and breccia units. Thick sedimentary accumulations were localized in zones of extension within a network of strike-slip faults. The Kamloops Group is a high-alkali calc-alkaline volcanic suite dominated by augite - pigeonite - labradorite andesite and basalt, with unusually high K, Sr and Ba. Initial strontium isotopic ratios distinguish a boundary between 'old' crust upper mantle to the east and 'young' or Rb-depleted materials to the west. Petrographic and chemical data are consistent with magma genesis by partial melting of alkali-enriched peridotite between 40 and 75 km depth, with subsequent deep- and shallow-level fractional crystallization producing the observed volcanic chemistry. Compilation of Paleogene geology and geochronometry in the Pacific Northwest shows the Kamloops Group to be part of a robust calc-alkaline volcanic arc extending from Wyoming to Alaska. Superimposed on this arc were dextral, strike-slip faults, sedimentary basins and reset metamorphic terranes. These elements formed a tectonic, network which accommodated 90 to 450 kilometres of right-lateral displacement between coastal British Columbia and North America. A tentative plate-tectonic reconstruction is based on the compilation. A northeast-dipping subduction zone, active along the entire coast of the Paleocene Pacific Northwest, ceased to be active after 53 Ma. The transform motion between Pacific and North American plates was distributed inland, driving the Eocene tectonic activity, while the remnant subducted slab gave rise to the Eocene magmatic arc. Transform motion later became localized along the continental margin, as the east-dipping subduction zone south of 49° latitude intiated the Cascade volcanic arc in the Late Eocene and Oligocene. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Tatla Lake Metamorphic Complex (TLMC) underlies 1000 km² on the western side of the Intermontane Belt (1MB) northeast of the Yalakom fault Three fault-bounded lithotectonic assemblages are recognized in the area studied: an amphibolite grade gneissic and migmatitic core, structurally overlain by a 1 to 2.5 + km-thick zone of amphibolite and greenschist grade mylonite and ductilely sheared metamorphic rocks, the ductilely sheared assemblage (DSA), which is in turn structurally overlain by weakly deformed to unstrained subgreenschist grade rocks of the upper plate which flank the TLMC on three sides. Structures in the gneissic core include a gneissic foliation and schistosity (Sic), which has been deformed by west to northwest-trending tight to isoclinal folds (F2c). Tectonic fabrics observed throughout the DSA which formed during Ds deformation include a gently dipping mylonitic foliation (Ss), containing a mineral elongation (stretching) lineation (Ls) which trends towards 280° ± 20°. Minor folds of variable trend (Fs), almost exclusively confined to DSA metasedimentary rocks, are interpreted as coeval with ductile shear. Vergence of these folds defines movement sense and direction of top towards 290° ± 20°. Kinematic indicators from DSA rocks which have not been deformed by syn-ductile shear folds indicate a top-to-the-west sense of shear while those deformed by Fs folds yield conflicting results, with a top-to-the-west sense predominating. The entire lower plate comprising the TLMC has been deformed by broad, upright, west to west-northwest trending, shallowly plunging map-scale folds (F3) during D3, which deform Sic and Ss surfaces. The steeply dipping, northwest-trending Yalakom fault truncates all units and structures of the TLMC. Gently to moderately dipping normal faults of Ds and post-D3 relative age are the southern and eastern boundaries between DSA upper plate rocks and 1MB lower plate rocks. U-Pb zircon dates from igneous arid meta- igneous rocks from the lower plate range from Late Jurassic (157 Ma) through Eocene (47 Ma). These dates bracket the timing of Cretaceous (107 Ma to 79 Ma, in the core) and Eocene (55 Ma to 47 Ma, in the DSA) deformation and metamorphism in the lower plate. Biotite and hornblende K-Ai dates of 53.4 Ma to 45.6 Ma for lower plate rocks are in sharp contrast to Jurassic dates from nearby upper plate rocks; they record the uplift and cooling of the TLMC. Whole rock initial ⁸⁷Sr/⁸⁶Sr ratios (and for most samples present-day values) of less ≤0.704 have been determined for igneous and meta-igneous rocks of the TLMC; such values are typical of magmatic arc rocks of the 1MB and Coast Plutonic Complex of B.C. Whole rock major and trace element chemistry of lower plate igneous and meta-igneous rocks indicate sub-alkaline, calcalkaline, volcanic arc affinities. Garnet-biotite temperatures (interpreted as Eocene in age), from pelitic schist in the southern part of the DSA increase from about 400 ± 50 to 650 ± 50 C with increasing structural depth. A GT-BI-QZ-Al₂SiO₅ pressure of 8 ± 3 kb has been calculated for one of these samples. A T-P of 650 ± 50 C and 5.3 ± 3 kb, calculated from inclusions and garnet cores in a small pelitic pendant in the northwest part of the DSA, reflects conditions during intrusion of the surrounding 71 ± 3 Ma igneous body. A pressure of 7.2 ± 1.4 kb, based on the total Al in hornblende, has been calculated for this body. Cretaceous ductile deformation in the gneissic core may be related to folding and thrusting which occured in high level rocks to the west and east of the field area. During Early Eocene time (55-47 Ma) the TLMC acquired the characteristics of a Cordilleran metamorphic core complex. Mylonites of the DSA were emplaced by faulting beneath weakly deformed, low metamorphic grade rocks of the upper plate. Synchronously, metamorphic rocks of the gneissic and migmatitic core of the TLMC were moved to higher crustal levels along the footwall of the DSA normal ductile shear zone. The formation of F3 folds and final uplift of the TLMC (47-35 Ma) is postulated to be the consequence of transpression related to later Eocene dextral motion along the Yalakom fault The TLMC has structural style and timing of deformation similar to metamorphic core complexes in southeastern B.C. Local and regional evidence is consistent with the formation of the TLMC in a regional extensional setting within a vigorous magmatic arc. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Published paleomagnetic studies have shown that the Oregon Coast Range has rotated 60° clockwise since middle Eocene time, probably by pivoting either during collision of a seamount terrane or during an episode of asymmetric extension within western North America. Eocene sedimentary deposits within the Oregon Coast Range basin, in particular the Tyee Formation, document changes in basin evolution that provide geologic constraints for proposed rotation models. The Tyee Formation comprises an arkosic petrofacies which is different from underlying lithic sandstones that were derived from the adjacent Klamath Mountains. Isotopic study of sandstones of the arkosic petrofacies, including Sm-Nd, Rb-Sr, K-Ar, and ¹⁸O analyses, indicate that much of the sandstone was not derived from the Klamath Mountains or nearby Sierra Nevada. The source area most likely included S-type granites of the Idaho Batholith. Lithofacies within the Tyee Formation include a sandy deltaic system to the south, a thin muddy shelf/slope sequence farther north, and a thick basinal sequence of sandy high-density turbidites that grade northward into low-density turbidites. Absence of facies segregation within the turbidite sequence precludes application of classical deep-sea fan depositional models and forms the basis for the delta-fed submarine ramp model introduced here. Delta-fed submarine ramps are short-lived sandy systems that result from rapid rates of progradation as well as aggradation. Synchronous changes in depositional style, structural deformation, sandstone composition, and rates of tectonic subsidence of the Oregon Coast Range basin are interpreted to record the transition from collisional trench-fill deposition to a subsiding forearc basin. The Tyee Formation was deposited after collision was complete and yet is rotated as much as the seamounts on which it lies; therefore, rotation must have occurred subsequent to collision. Since these sediments were partially derived from the Idaho Batholith region, the Oregon Coast Range probably lay much farther east during deposition and subsequently rotated westward to its present position. Tectonic rotation of the Oregon Coast Range may have resulted from continental extension that began in the Pacific Northwest about 50 Ma. Paleogeographic reconstructions show that basin development was synchronous with regional extension, arc migration, and tectonic rotation throughout the Pacific Northwest.

The study area lies in southwest Douglas County 5 kilometers south from Camas Valley and is accessible by state highway 42. The purpose of the study was to map the geology at a 1:31,250 scale, determine the stratigraphy, study the petrology of the formations, and determine the provenance within a tectonic setting.

An almost complete sequence of middle and upper marine strata, informally designated in this study as the "Strata of Cascade Head", has yielded 334 species and varieties of fossil Foraminifera. The Foraminifera were collected from 38 localities in four stratigraphic sections measured along the Salmon River, Neskowin Creek, Cascade Head Road, and near the town of Three Rocks in the central Oregon Coast Range.

Within the thesis study area Spencer Formation arkosic/arkosic lithic sandstone lithofacies of Narizian age crop out in a sinuous north-northwesterly band from the Corvallis area into the Henry Hagg Lake vicinity ten kilometers southwest of Forest Grove, Oregon.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 15-16. / by Anna Catarina Shaughnessy. / M.S.

No description available.

Late Middle Eocene time marks one of the most dynamic periods of the Paleogene in the western interior of North America. Analysis of an extensive, new collection of plant, invertebrate, and vertebrae fossils from the Uinta Formation in the Uinta Basin, south of Myton, Utah, USA, provides evidence of environmental change. Paleobotanical specimens are preserved in late stage Uinta Lake sediments and coarse-grained fluvial sediments which are stratigraphically 650 to 660 m above the Green River Formation. Deposition rates estimates of 18 to 55 cm/kyr, for Uinta Lake sediments in the Uinta Basin suggest a period of 1.18 Ma to 3.69 Ma to deposit the thick section of lacustrine and fluvial sediments that separates the well-documented Green River Flora from this new fossil leaf assemblage, the Wells Draw flora. Prolific invertebrate trace fossils and invertebrates have a preference for areas with high to fluctuating water tables and soil moistures. The trace fossils are similar to traces of extant invertebrates found in temperate to tropical climates. A variety of reptiles, namely eight species of turtles/tortoise, one lizard (first report of Saniwa from the Uinta Formation), and at least two crocodilian species, are indicative of warm-temperate to subtropical climatic zones. Flow direction data derived from sedimentary structures in sandstone channel-fills confirms previous studies which indicate the major sediment source area was to the east with a prevailing westward to northwestward flow direction. The presence of higher elevation plant material within the flora, however, implies possible hydraulic transport from the nearby Uinta Mountain highlands, located north of the basin. The first report of Palmoxylon from the Uinta Formation, included in this report, corroborates the faunal indicators of a tropical climate. Physiognomical analysis of the flora yields a mean annual temperature (MAT) of 16.1◦C and a mean annual precipitation (MAP) of 56 cm. Compared with older Green River flora, these new data suggest a slight drying and cooling trend toward the end of the Eocene. Leaf types also indicate possible seasonality with seasonally dry periods and an overall warm-temperate environment with extreme minima temperatures not much below freezing.

No description available.