D.Phil. / The amalgamation of SW Gondwana after the break-up of Rodinia supercontinent during the Neoproterozoic-early Palaeozic was one of the most active tectonic periods of the earth history and its geological evolution remains controversial. Recently, diverse hypotheses such as mantle plume activity, orthogonal continent-continent and strike-slip collisions according to different models try to explain the complex evolution of the Pan-African Brasiliano orogens and the associated sedimentary basins. In order to get insight of the SW Gondwana reconstruction, provenance analyses were performed on two Neoproterozoic-early Palaeozic sedimentary units: (1) the Arroyo del Soldado Group representing a —5000 meter thick platform succession unconformably overlying the mainly Archaean to Neoproterozoic rocks of the Rio de la Plata Craton in Uruguay and, (2) the Nama Group, a —2000 meter thick shallow marine to fluvial deposit interpreted as a foreland basin in response to tectonism in the adjacent northern Damara and western Gariep Orogenic Belts and unconformably overlying the mainly Mesoproterozoic rocks of the Kalahari Craton in Namibia. Several techniques including petrography, heavy mineral analysis, geochemistry, Sm-Nd isotope analysis and zircon dating were applied to both sedimentary basins. The petrographic, heavy mineral analyses and geochemical results from the Nama Group indicate a recycled upper crust composition characterized by metamorphic and granitic sources and minor mafic rocks. Palaeocurrent analyses of the chromian spinet bearing sandstones of the Nama Basin point to a volcanic island arc source located in the Damara Belt. Detrital zircon dating of the Nama Group display major peaks of Neoproterozoic and Mesoproterozoic ages suggesting a provenance from the Damara/Gariep Belts and their basements. Palaeocurrents from the west and the dominance of Neoproterozoic-Cambrian detrital zircon ages (76%) in the "Molasse" stage of the foreland evolution probably indicate exhumation of the felsic volcanic arc root which probably occurred after the time indicated by the younger zircon dated at 531 ±9 Ma. The petrographic and geochemical results from the Arroyo del Soldado Group indicate a recycled upper crust composition characterized by source diversity composed of granite-gneissic and mafic-metamorphic rocks. On average, Nd isotopes account for negative ENd values and TDM ages in a range of variation found elsewhere within SW Gondwana. Detrital zircon dating indicate sources dominated by Palaeoproterozoic (1.7-2.0-2.2 Ga) and subordinate Archaean ages (2.5-2.9-3.5 Ga). The scarcity of Mesoproterozoic and Neoproterozoic zircons and palaeocurrent directions towards the east indicate that the Arroyo del Soldado Group was fed by detritus from the Rio de la Plata Craton favouring a passive margin tectonic setting for their deposition. Deformation of the Arroyo del Soldado Group took place ca. 530 Ma, after strike-slip collision with an African affinity terrane. Finally, based on the palaeogeographic evaluation, the provenance of Nama foreland basin and the passive margin deposit of the Arroyo del Soldado basin suggest that continent-continent collision of the Kalahari/Congo Cratons with the Rio de la Plata Craton and the Cuchilla Dionisio Pelotas Terrane most likely occurred due to strike slip accretion related to a component of N—S shortening in the period between 530 and 495 Ma.

No description available.

The Haveri Au-Cu deposit is located in southern Finland about 175 km north of Helsinki. It occurs on the northern edge of the continental island arc-type, volcano-sedimentary Tampere Schist Belt (TSB) within the Palaeoproterozoic Svecofennian Domain (2.0 – 1.75 Ga) of the Fennoscandian Shield. The 1.99 Ga Haveri Formation forms the base of the supracrustal stratigraphy consisting of metavolcanic pillow lavas and breccias passing upwards into intercalated metatuffs and metatuffites. There is a continuous gradation upwards from the predominantly volcaniclastic Haveri Formation into the overlying epiclastic meta-greywackes of the Osara Formation. The Haveri deposit is hosted in this contact zone. This supracrustal sequence has been intruded concordantly by quartz-feldspar porphyries. Approximately 1.89 Ga ago, high crustal heat flow led to the generation and emplacement of voluminous synkinematic, I-type, magnetite-series granitoids of the Central Finland Granitoid Complex (CFGC), resulting in coeval high-T/low-P metamorphism (hornfelsic textures), and D₁ deformation. During the crystallisation and cooling of the granitoids, a magmatic-dominated hydrothermal system caused extensive hydrothermal alteration and Cu-Au mineralisation through the late-D₁ to early-D₂ deformation. Initially, a pre-ore Na-Ca alteration phase caused albitisation of the host rock. This was closely followed by strong Ca-Fe alteration, responsible for widespread amphibolitisation and quartz veining and associated with abundant pyrrhotite, magnetite, chalcopyrite and gold mineralisation. More localised calcic-skarn alteration is also present as zoned garnetpyroxene- epidote skarn assemblages with associated pyrrhotite and minor sphalerite, centred on quartzcalcite± scapolite veinlets. Post-ore alteration includes an evolution to more K-rich alteration (biotitisation). Late D₂-retrograde chlorite began to replace the earlier high-T assemblage. Late emanations (post-D₂ and pre-D₃) from the cooling granitoids, under lower temperatures and oxidising conditions, are represented by carbonate-barite veins and epidote veinlets. Later, narrow dolerite dykes were emplaced followed by a weak D₃ deformation, resulting in shearing and structural reactivation along the carbonate-barite bands. This phase was accompanied by pyrite deposition. Both sulphides and oxides are common at Haveri, with ore types varying from massive sulphide and/or magnetite, to networks of veinlets and disseminations of oxides and/or sulphides. Cataclastites, consisting of deformed, brecciated bands of sulphide, with rounded and angular clasts of quartz vein material and altered host-rock are an economically important ore type. Ore minerals are principally pyrrhotite, magnetite and chalcopyrite with lesser amounts of pyrite, molybdenite and sphalerite. There is a general progression from early magnetite, through pyrrhotite to pyrite indicating increasing sulphidation with time. Gold is typically found as free gold within quartz veins and within intense zones of amphibolitisation. Considerable gold is also found in the cataclastite ore type either as invisible gold within the sulphides and/or as free gold within the breccia fragments. The unaltered amphibolites of the Haveri Formation can be classified as medium-K basalts of the tholeiitic trend. Trace and REE support an interpretation of formation in a back-arc basin setting. The unaltered porphyritic rocks are calc-alkaline dacites, and are interpreted, along with the granitoids as having an arc-type origin. This is consistent with the evolution from an initial back-arc basin, through a period of passive margin and/or fore-arc deposition represented by the Osara Formation greywackes and the basal stratigraphy of the TSB, prior to the onset of arc-related volcanic activity characteristic of the TSB and the Svecofennian proper. Using a combination of petrogenetic grids, mineral compositions (garnet-biotite and hornblendeplagioclase thermometers) and oxygen isotope thermometry, peak metamorphism can be constrained to a maximum of approximately 600 °C and 1.5 kbars pressure. Furthermore, the petrogenetic grids indicate that the REDOX conditions can be constrained at 600°C to log f(O₂) values of approximately - 21.0 to -26.0 and -14.5 to -17.5 for the metasedimentary rocks and mafic metavolcanic rocks respectively, thus indicating the presence of a significant REDOX boundary. Amphibole compositions from the Ca-Fe alteration phase (amphibolitisation) indicate iron enrichment with increasing alteration corresponding to higher temperatures of formation. Oxygen isotope studies combined with limited fluid inclusion studies indicate that the Ca-Fe alteration and associated quartz veins formed at high temperatures (530 – 610°C) from low CO₂, low- to moderately saline (<10 eq. wt% NaCl), magmatic-dominated fluids. Fluid inclusion decrepitation textures in the quartz veins suggest isobaric decompression. This is compatible with formation in high-T/low-P environments such as contact aureoles and island arcs. The calcic-skarn assemblage, combined with phase equilibria and sphalerite geothermometry, are indicative of formation at high temperatures (500 – 600 °C) from fluids with higher CO₂ contents and more saline compositions than those responsible for the Fe-Ca alteration. Limited fluid inclusion studies have identified hypersaline inclusions in secondary inclusion trails within quartz. The presence of calcite and scapolite also support formation from CO₂-rich saline fluids. It is suggested that the calcic-skarn alteration and the amphibolitisation evolved from the same fluids, and that P-T changes led to fluid unmixing resulting in two fluid types responsible for the observed alteration variations. Chlorite geothermometry on retrograde chlorite indicates temperatures of 309 – 368 °C. As chlorite represents the latest hydrothermal event, this can be taken as a lower temperature limit for hydrothermal alteration and mineralisation at Haveri.The gold mineralisation at Haveri is related primarily to the Ca-Fe alteration. Under such P-T-X conditions gold was transported as chloride complexes. Ore was localised by a combination of structural controls (shears and folds) and REDOX reactions along the boundary between the oxidised metavolcanics and the reduced metasediments. In addition, fluid unmixing caused an increase in pH, and thus further augmented the precipitation of Cu and Au. During the late D₂-event, temperatures fell below 400 °C, and fluids may have remobilised Au and Cu as bisulphide complexes into the shearcontrolled cataclastites and massive sulphides. The Haveri deposit has many similarities with ore deposit models that include orogenic lode-gold deposits, certain Au-skarn deposits and Fe-oxide Cu-Au deposits. However, many characteristics of the Haveri deposit, including tectonic setting, host lithologies, alteration types, proximity to I-type granitoids and P-T-X conditions of formation, compare favourably with other Early Proterozoic deposits within the TSB and Fennoscandia, as well as many of the deposits in the Cloncurry district of Australia. Consequently, the Haveri deposit can be seen to represent a high-T, Ca-rich member of the recently recognised Fe-oxide Cu-Au group of deposits.

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

Upper Triassic and Jurassic rocks in the central Graham Island area comprise shale, siltstone, sandstone, and conglomerate of the Kunga, Maude, and Yakoun Groups. Volcanic rocks are common in the Middle Jurassic Yakoun Group. The oldest unit exposed within the study area is the Lower Jurassic Sandilands Formation of the Kunga Group, a more than 250 metre thick sequence of interbedded organic-rich shale, tuff, siltstone, and sandstone. The Lower Jurassic Maude Group conformably overlies the Kunga Group and is divisible into four formations. The Ghost Creek Formation is an organic-rich black fissile shale, and is overlain by calcareous sandstone of the Fannin Formation. The Whiteaves Formation consists of fissile calcareous grey shale that grades upwards into fossil-rich medium- to coarse-grained, sandstone of the Phantom Creek Formation. The base of the Middle Jurassic Yakoun Group is marked by an angular unconformity. The unit is more than 1500 metres thick and is divided into four lithofacies. The lowermost shale and tuff lithofacies is a sequence of interbedded shale, tuff, siltstone, and sandstone, with shale dominating. The sandstone lithofacies overlies and partly interfingers with the shale and tuff lithofacies and comprises medium- to thickly-bedded lithic arenite interlayered with thinly-bedded shale. The conglomerate lithofacies exists within the sandstone lithofacies and consists mostly of thickly-bedded pebble and cobble conglomerate. The volcanic lithofacies interfingers with, and overlies the sedimentary rocks of the Yakoun Group, and includes lava flows, pyroclastic rock deposits, and lahars. The Kunga and Maude Groups record several relative changes in sea level. They formed in a progressively deepening basin. In Pliensbachian time, the basin shallowed and deposition, represented by the upper Fannin Formation of the Maude Group, was near-shore. Toarcian time is marked by an abrupt transgression. The upper part of the Whiteaves Formation and the Phantom Creek Formation of the Maude Group indicate a subsequent regression. The sedimentary rocks of the Yakoun Group were deposited in local shallow marine basins. Volcanic rocks are most abundant in the eastern parts of the map area, and indicate that an igneous source is located in that direction. All rock units in the map area are deformed by major northwest-trending faults and folds, reflecting at least four northeast-southwest oriented deformational events. The angular unconformity at the base of the Yakoun Group restricts one compressional phase to mid-Jurassic time. Abundant southwest-verging folds suggest development of northeast-dipping thrust faults during this compressional event. Northeast-trending normal faults cut through the thrust faults, postdating them and indicating a period of extension. Rocks of the Sandilands Formation are observed thrust on top of the Yakoun Group, thus indicating a second compressional event. Several small-scale strike-slip faults cut through all described rock units and overlying Tertiary sections, suggesting a late Tertiary deformational event. The Middle Jurassic compressional event may be a result of collision of Wrangellia with North America, or could have been caused by changes in relative plate motion between the North American and Pacific plates during the break-up of Pangaea. Lithologic similarities between the Jurassic and older units of Wrangellia on the Queen Charlotte Islands and coeval rocks of the Alexander terrane in southeastern Alaska suggest that there are no clear differences between the two, and that they were contiguous since Upper Paleozoic time. / 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

Amphibolite grade pelites from the Buchan type metamorphism of the Meguma Group in southwestern Nova Scotia contain the assemblage And+Grt+Bt+Q+Pl+Ms+Ilm+Mgt±St±Crd±Sil±Po±Py. Grt-Bt geothermometry and Pl-Grt-And-Q geobarometry on samples from three widely separated 3-8 km traverses yield temperatures and pressures that cluster in two groups; (1) two traverses near Shelburne with T=500-510°C and P=3.5 kbar; and (2) one traverse on the West Pubnico peninsula, 40 km to the southwest, with T=530-560°C and P=1.5-2. 5 kbar. P_H₂O estimates based on Ms-and-Pl-V assemblages indicate that P_H₂O = .4-.9 P_Total for rocks from the Shelburne area and P_H₂O=P_Total for the rocks south of West Pubnico. Whole rock chemical analyses on samples from the three traverses show no systematic variations over the region. In the Pubnico traverse, the presence or absence of staurolite is dependent both on slight variations in the Fe/Mg ratios of the rocks and on temperature differences. In the staurolite-bearing rocks the assemblages and mineral chemistries indicate that the systems represent divariant continuous reactions and contain cordierite only where P_H₂O < P_Total. Thus the large number of phases is neither the result of disequilibrium nor representative of a low variance assemblage, but can be described as a divariant assemblage involving 8 to 9 major components. / Master of Science

The Late Silurian-Early Devonian Helderberg Group, Central Appalachians, is a sequence of mixed siliciclastic-carbonate sediments that was deposited during relative tectonic quiescence on a ramp that built out from low-relief tectonic highlands bordering the eastern side of the Appalachian Basin. Three transgressive-regressive sequences are recognized. Each sequence was deposited over 2-3 m.y.; subsidence rates during deposition were 1 to 2 cm/1000 years. Skeletal grainstone/rudstone formed fringing skeletal banks that formed during regression and prograded away from the eastern side of the basin. Thick Middle Devonian siliciclastic sediments buried the Helderberg Group and updip subaerial exposures accompanying the onset of the Acadian Orogeny. Cementation of the Helderberg Group began on the seafloor, but most cements formed under shallow (<300 m depth) to deep burial (300 m to 4 km) conditions. Regional cathodoluminescent zonation patterns in early, clear calcite cements indicate meteoric groundwaters, that become progressively more reducing away from recharge areas, were involved in shallow burial cementation. Progressive downdip reduction of meteoric groundwaters resulted in updip nonluminescent calcite cements that pass downdip into timecorrelative "subzoned" dull cement and finally, nonzoned dull cements. Calculated stable isotopic compositions of Helderberg shallow burial pore fluids are similar to values in modern coastal meteoric groundwaters. Extensive meteoric groundwater systems developed over a 3-4 m. y. period when the Helderberg Group was subaerially exposed along the eastern basin margin and when Helderberg aquifers were confined by fine-grained sediments at <300 m burial depth. Meteoric groundwaters had recharge areas in eastern tectonic highlands which supplied sufficient hydraulic heads to expel connate marine pore fluids and discharge at least 150 km offshore onto the floor of the Appalachian Basin. Void-filling dull calcite cement formed from deep burial (300 m to 4 km) pore fluids with calculated chemical compositions similar to modern oil field brines. Migration of hydrocarbons and high-temperature, high-pressure brines occurred during Late Paleozoic deformation after Helderberg sediments were totally cemented. Brines probably came from eastern overthrusted terranes and migrated through fractures without altering conodont CAI values. Late hydrocarbons probably had several source rocks. / Ph. D.

M.S.