No description available.

The stratigraphy and structure of Upper Palaeozoic and Mesozoic sedimentary and volcanic rocks, and of amphibolitic rocks of unknown age, were studied in an area of about 140 square miles in the Cascade Mountains of southwestern British Columbia. The amphibolitic rocks are probably of diverse origins; their stratigraphic relationship to the other rocks is not known, although they may, in part, be equivalent to pre-Devonian rocks in northwestern Washington. Upper Palaeozoic rocks comprise the Chilliwack Group. The base is not exposed. Oldest rocks are volcanic arenites and argillites which are overlain by an argillaceous limestone, about 100 feet thick, in which Early Pennsylvanian (Morrowan) fusulinids occur. Apparently conformably overlying the limestone is a succession of argillites, coarse volcanic arenites, minor conglomerate and local tuff, which contains both marine and terrestrial fossils and ranges in thickness from 450 to 800 feet. A cherty limestone, generally about 300 feet thick, in which there is an Early Permian (Leonardian) fusulinid fauna, is conformable upon the clastic sequence. Altered lavas and tuffs are in part laterally equivalent to this Permian limestone, and, in part, overlie it; these volcanic rocks range in thickness from 700 to 2,000 feet. Disconformably above the Permian volcanic rocks are argillites and volcanic arenites of the Cultus Formation. This formation is apparently about 4,000 feet thick, contains Late Triassic, Early and Late Jurassic fossils and no stratigraphic breaks have been recognized within it. All of these rocks underwent two phases of deformation between Late Jurassic and Miocene time. The first phase, correlated with mid-Cretaceous deformation in northwestern Washington, was the most severe., and thrusts and major, northeast-trending recumbent folds were formed. These structures subsequently were folded and faulted along a northwest trend, possibly in response to differential uplift of the Cascade Mountains. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Near Terrace, British Columbia, the eastern margin of the Central Gneiss Complex (CGC) is a 3-4 km thick, gently northeast dipping, ductile-brittle shear zone with northeast movement of the upper plate. Along Shames River, deformed amphibolite-facies rocks to the west are juxtaposed against lower greenschist to amphibolite facies units to the east along the steep, east side down, brittle Shames River fault (SRF). Gentle to moderate northwest and northeast dips west of SRF contrast with steep southeast dips to the east. Lineations plunge gently northeast and southwest. West of SRF, the Shames River mylonite zone (SRMZ) separates granitoid rocks below from less deformed granitoid rocks, orthogneiss and metasedimentary rocks above. West of Exstew River, the moderately northeast dipping, ductile Exstew River fault, juxtaposes the SRMZ against metamorphic rocks and granitoids of the CGC. The SRMZ is cut by anastomosing brittle-ductile shear zones. Most kinematic indicators show northeast directed shear. Heterogeneous strain in SRMZ accommodates a minimum upper plate movement of 25 km to the east-northeast. Hornblende geobarometry indicates a structural omission of 13.4 km across SRMZ. East of SRF, amphibolite and greenschist facies supracrustal and plutonic rocks of Lower Permian and older Stikine Assemblage are thrust above greenschist facies volcanic strata correlated with Telkwa Formation of the Lower to Middle Jurassic Hazelton Group. Foliation in late synkinematic, 69 Ma granodiorite which intrudes this thrust package dips steeply southeast. Stikine Assemblage is comprised of lower greenstone, granitoid rocks, volcanic breccia and flows overlain by fusulinid-rich marble. A deformed intrusive rock in Stikine Assemblage has a minimum Pb-Pb date of 317 ± 3 Ma. Hazelton Group contains lower andesitic and upper dacitic to rhyolitic packages comprised of agglomerate, volcanic breccia, tuff, and plagioclase porphyry flows. The earliest recognised metamorphism and deformation in the SRMZ, at upper amphibolite grade, affects 188 ± 8 Ma orthogneiss, and occurred before intrusion of a garnet-biotite granite dated by Woodsworth et al. (1983) at 83.5 Ma. Early fabrics are overprinted by Campanian to Paleocene ductile deformation and a second metamorphism. The second deformation waned during intrusion of three granitic intrusions with concordant U-Pb zircon crystallization dates of 68.7 - 69 Ma. A late to post-kinematic granite dyke in the SRMZ has a U-Pb zircon crystallization date of 60 ± 6 Ma. The second phase of metamorphism began before, and outlasted ductile deformation. The SRF and other high angle normal faults cut 69 Ma granodiorite, but do not significantly offset Eocene (46.2-52.3 Ma) K-Ar biotite cooling isothermal surfaces. The 60 Ma granite is deformed by low angle semi-brittle faulting with upper plate movement to the northeast. A 48 ± 3 Ma synkinematic granite dyke in the footwall of SRMZ was intruded during this deformation, which ended before 46.2 - 46.5 ± 1.6 Ma, the K-Ar biotite cooling dates from SRMZ. The entire region is deformed by post-ductile open, upright, east-northeast plunging folds. K-Ar biotite dates for granitoid rocks range from 51.1 Ma in the upper plate to 46.2 Ma in SRMZ, indicating downward progression of cooling. North-northwest trending brittle faults and lamprophyre dykes cut the SRMZ, and are therefore younger than mid-Eocene. Thermobarometry of pelitic and granitoid rocks indicates increasing metamorphic grade with increasing structural depth. Al-j; in hornblende geobarometry indicates slightly lower pressure of crystallization for the interior than the margin of a granodiorite body east of SRF.In the upper plate of SRMZ, west of SRF, sillimanite-staurolite-garnet schist records ductile deformation and metamorphism at 3.8 ± 1.6 kbar and 570 ± 50°C. The schist is intruded by orthogneiss cut by 68.7 Ma granodiorite. The granodiorite crystallized at 3.4 ± 1 kbar, and was deformed at 2.2 ± 1 kbar at 68.7 Ma. In SRMZ, hornblende in pre-kinematic, 188 ± 8 Ma granodiorite crystallized at 5.5 ± 1 kbar. Deformation and synkinematic metamorphism occurred at 4.9 ± 1 kbar, between 83.5 and before 60 ± 6 Ma. East of SRF, greenschist conditions prevailed, except near the southern margin of the 69 Ma granodiorite body, where amphibolite facies was stable during ductile deformation. A metapelitic sample gives near-peak metamorphic conditions of 4.9 ± 1.6 kbar and 700 ± 50°C, and contact metamorphic conditions of 2.9 ± 1.6 kbar and 610 ± 50°C during intrusion of late synkinematic, 69 Ma granodiorite. P-T-time paths for the upper plate of SRMZ west of Shames River indicate initial rapid, near-isothermal decompression beginning before 69 Ma, continuing to 69 Ma, followed by rapid cooling to 0.9-1.1 kbar, at 51.1 Ma. Paleogene to middle Eocene deformation was probably extensional in nature. It occurred in a vigorous magmatic arc, in response to, and possibly coeval with, crustal thickening. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

A well preserved, fossiliferous Middle Triassic to Early Cretaceous section lies on the west side of Harrison Lake in the southern Coast Mountains. The study of this area involves a re-evaluation of the stratigraphic nomenclature first described by Crickmay (1925, 1930a) together with a lithologic description of the units and age determinations based on collected, identified and described fossils by the writer. Discussions on the biostratigraphy, paleogeography, regional correlations and structure of the thesis area and an overview of the regional tectonics of southwestern British Columbia and northwestern Washington, help to better understand the relation of this Mesozoic section to other rock assemblages in this geologically complex region. The oldest unit, the Middle Triassic Camp Cove Formation, comprises conglomeratic sandstone, siltstone and minor volcanic rock. Unconformable7 overlying this unit is the Toarcian to Early(?) Bajocian Harrison Lake Formation, divided into four distinct members by the writer, Celia Cove Member (basal conglomerate), West Road Member (siltstone, shale), Weaver Lake Member (flows, pyroclastic rocks, minor sediments) and Echo Island Member (interbedded tuff, siltstone, sandstone). Thickness of this formation is estimated at 3000 m. A hiatus probably is present between this unit and overlying shale, siltstone and sandstone of the Early Callovian Mysterious Creek Formation which is 700 m thick. Conformably above this are 230 m of sandstone and volcaniclastic rock of the Early Oxfordian Billhook Creek Formation. Late Jurassic fluvial conglomerate, sandstone and siltstone of the Kent Formation, perhaps 1000 m thick south of Harrison River, unconformably(?) overlies the last two units mentioned. Berriasian to Valanginian conglomerate and sandstone, 218 m thick, of the Peninsula Formation overlies the Billhook Creek Formation with slight angular unconformity. The Peninsula Formation is conformably overlain by tuffaceous sandstone, volcanic conglomerate, crystal tuff and flows of the Valanginian to Middle Albian Brokenback Hill Formation which is several km thick. Nine Jurassic ammonite genera are identified and described in this report. Triassic radiolaria and conpdonts and Cretaceous ammonites and bivalves are also present in the section. The most significant structure in the thesis area is the post-Albian to pre-Late Eocene Harrison Fault which strikes north-northwest through Harrison Lake, separating the Mesozoic section along the west side from the northern extension of the Cascade Metamorphic Core on the east side of the lake. A strong sub-horizontal stretching lineation within the fault zone may indicate right-lateral strike-slip movement. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The level of organic maturation, thermal history, and source rock potential of Mesozoic and Tertiary strata in the Queen Charlotte Islands have been investigated with vitrinite reflectance measurements (%Ro rand)> numerical modelling (modified Arrhenius and Lopatin models), and Rock-Eval pyrolysis (source rock potential). The level of organic maturation increases from north to south and is primarily controlled by high heat flow associated with plutonism on Moresby Island. Upper Triassic-Lower Jurassic strata are overmature on Moresby Island with vitrinite reflectance values ranging from 2.40 to 5.80 %Ro rand Jurassic, Cretaceous, and Tertiary strata are immature to overmature on Graham Island with values ranging from 0.15 %Ro rand (Skonun Formation) to 2.43 % Ro rand (Haida Formation). Constant and variable geothermal gradient thermal regimes were numerically modelled with modified Arrhenius and Lopatin methods. Numerical modelling (assuming constant geothermal gradients) predicts high paleogeothermal gradients (45 to 90 °C/km) for up to 180 million years from the Late Triassic to the Tertiary. Variable paleogeothermal gradient modelling (utilizing a 30 °C/km background geothermal gradient) predicts peak geothermal gradients ranging up to 150 °C/km during Yakoun (183-178 Ma) and Masset (35-10 Ma) volcanism. The timing of hydrocarbon generation was estimated with numerical modelling. The levels of organic maturation for Mesozoic and Tertiary strata reflect the timing of plutonism and associated high heat flow. Triassic strata from west Graham Island and Cretaceous strata from north and south Graham Island entered the oil window during the Early Miocene and are still in the oil window. Jurassic strata in central Graham Island and north Moresby Island entered the oil window during the Bajocian and remain within the oil window. The Skonun Formation is generally immature except for strata at west Graham Island (Port Louis well) and at northeast Graham Island (basal strata in the Tow Hill well) which entered the oil window during the Late Miocene. Mean total organic carbon (TOC) contents are generally low (0.06 %) to moderately high (3.6 %) for Mesozoic and Tertiary strata. Some organic-rich horizons with TOC values up to 11.2 % occur in Upper Triassic (black limestone member of the Kunga Group) and Lower Jurassic (Sandilands and Ghost Creek Formations) source strata. Mesozoic and Tertiary strata generally contain gas prone Type III organic matter except for the Lower Jurassic Ghost Creek Formation and the Upper Triassic-Lower Jurassic Kunga Group which contain oil and gas prone Type II organic matter and significant amounts of oil prone Type I organic matter. Lateral variations in TOC and the quality of organic matter (QOM) for Triassic and Jurassic strata are primarily related to the level of organic maturation. The strata have poor to good hydrocarbon source potential on Graham Island. High heat flow associated with plutonism on Moresby Island has overmatured the strata resulting in poor source potential on Moresby Island. Hydrocarbon source potential for Cretaceous and Tertiary strata is primarily controlled by the level of organic maturation and depositional patterns. The Cretaceous Haida and Honna Formation generally contain terrestrially derived Type III organic matter with poor to fair gas source potential. The Skidegate Formation contains a mixture of Types II and III organic matter with decreased (terrestrial) Type III organic matter input and increased Type II (marine) organic matter input relative to the Haida Formation. Cretaceous strata from Moresby Island are generally overmature and have poor source potential whereas equivalent strata from Graham Island are immature to overmature and have fair to moderate gas source potential. Generally immature coal and lignite from the Tertiary Skonun Formation have poor to fair gas source potential. Resinite horizons containing hydrogen-rich organic matter have good oil and gas source potential where mature. Siltstone and shale facies of the Skonun Formation contain moderate amounts of Type II organic matter and have good hydrocarbon source potential. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Studies of Vibroseis reflection profiles over the exposed Triassic-Jurassic Culpeper, Richmond, and Scottsville Basins, and another profile over a probable early Mesozoic basin (Toano) beneath the Atlantic Coastal Plain sediments, in Virginia indicate that resolution of the geometry of the basins is inhibited by small impedance contrasts between the rock units within the basin and those bordering the basin. None of the seismic sections exhibit reflections which can be directly attributed to a Triassic-pre-Triassic interface. Resolution of the geometry of the basin sediments depends upon the presence of anomalously high or low velocity/density rock units within the basin, and similarly the presence of large amplitude reflections from within these and possibly other basins may imply the presence of these units, which include basalt and lignite. A method of analyzing the refracted waves in the seismic reflection data with large receiver offsets for determination of apparent velocities and the geometry of the refraction interface is presented. The Culpeper seismic lines indicate a basin with a maximum thickness of 2500 m along the western side and approximately 1750 m along the eastern side of the basin. The maximum thickness of the Richmond Basin below the seismic line is approximately 2700 m. The Scottsville Basin contains sedimentary strata with a thickness of 1750 m and the seismic data from the Toano Basin indicate a thickness of 3000 m. The compressional wave velocity of the strata within these basins has a range of 4000-5300 m/sec. / M.S.

No description available.

The oldest sedimentary and metasedimentary rocks exposed in the Himalayan foothills of Pakistan record a gradual transition seaward from the evaporites of the Salt Range Formation to pelitic sediments deposited in deeper water to the north. The Upper Proterozoic Tanawal Formation was derived from erosion of a northern highland produced during the early stages of Late Proterozoic to early Ordovician tectonism. Early Paleozoic tectonism is indicated by an angular unconformity at the base of the Paleozoic section, the intrusion of the Mansehra Granite, and the local removal of Cambrian strata. Paleozoic shallow-marine strata are preserved in half-grabens created during extensional tectonism that began during the Carboniferous and climaxed with rifting during the Permian. Paleozoic rocks were largely or completely eroded from northwest-trending highlands on the landward side of the rift shoulder. Thermal subsidence of the rifted margin resulted in transgression of the highlands and deposition of a Mesozoic section dominated by carbonates. Compressional tectonism related to the impending collision with Asia commenced in the Late Cretaceous. Rocks north of the Panjal-Khairabad fault were deformed and metamorphosed during Eocene subduction of northern India beneath the Kohistan arc terrane. Following their uplift and exhumation, rocks metamorphosed beneath Kohistan were thrust southward over unmetamorphosed rocks along the Panjal and Khairabad faults which are inferred to be connected beneath alluvium of the Haripur basin. Contrasts in stratigraphy and metamorphism on either side of the Panjal-Khairabad fault indicate that shortening on this structure exceeds that of any other fault in the foothills region. The migration of deformation towards the foreland produced south- or southeast-vergent folds and thrust faults in strata south of the Panjal-Khairabad fault and reactivated Late Cretaceous structures such as the Hissartang fault. The Hissartang fault is the westward continuation of the Nathia Gali fault, a major structure that thrusts Proterozoic rocks in the axis of a Late Paleozoic rift highland southward over Mesozoic strata. Fundamental differences in stratigraphy, metamorphism, and relative displacement preclude straightforward correlation of faults and tectonic subdivisions of the central Himalaya of India and Nepal with the northwestern Himalaya of Pakistan. / Graduation date: 1994