The Lower Cretaceous Gates and Moosebar Formations in the Northeast Coalfields of British Columbia comprise a 350-450 m thick interval of marine and non-marine, coal bearing clastic sediments. The Moosebar Formation and lowermost unit of the Gates Formation (the Torrens Member) consist of between 2 and 4 coarsening-upward marine cycles. In the northern part of the study area, non-marine sediments in the Gates Formation occur interbedded with 3 major marine tongues (the Sheriff member, Falher C and Babcock member) which pinch out towards the south. In the study area south of Duke Mountain, sediments in the Gates Formation above the Torrens Member are entirely non-marine. The coarsening-upward marine cycles in the Moosebar-lower Gates interval were deposited mainly during regressions when the shorelines prograded northwards. The cycles are comprised of up to 3 main facies interpreted as offshore, transition zone and shoreface-beach (and locally distributary channel) deposits. Thin transgressive deposits are present at the base of the Sheriff member. Lower Gates shorelines are interpreted as high energy and wave dominated. Shoreline trends for the Torrens, Sheriff and Babcock Members are approximately E-W, and approximately NW-SE for the Falher C. Non-marine deposits in the Gates Formation are interpreted as forming in lagoons, fluvial channels and overbank environments within a coastal plain setting. The channels are mainly braided river types with anastomosing or straight (non-braided) and meandering river channels also present. The rivers flowed towards the northwest, north, northeast and east with northeasterly directions most common. Up to three separate very coarse fluvial conglomerates, interpreted as proximal braided river-alluvial fan deposits are present in the south near Mount Belcourt. Overbank sediments were deposited in levee, crevasse splay, lacustrine and well to poorly drained swamp environments The upper Gates marine unit (Babcock member) contains both transgressive and regressive deposits. Three types of transgressive deposits are recognised: 1. Thick (maximum 40 m) estuary mouth |shoal retreat massif) sandstones and conglomerates preserved in linear belts approximately 0.4-2 km wide trending NW-SE and N-S. 2. A thin (maximum 90 cm) but laterally extensive marine lag. 3. Lagoon-intertidal deposits. Upper Gates regressive deposits include shelf to shallow marine sandstones overlain by estuarine subtidal channel and shoal deposits which in turn are overlain locally by tidal flat and coastal plain deposits with thin coal seams. Upper Gates shorelines appear to be strongly tidally influenced. Thick (maximum 10 m), laterally extensive coal seams occur in the lower part of the Gates Formation. Coal seams in the upper Gates are thin (generally <1.0 m). With the exception of few very thin seams, the Gates coals appear to be entirely autochthonous and to have accumulated as peat in swamps in a coastal plain depositional setting. Some of the coals in the lower Gates were deposited in swamps which extended inland for at least 75 km from the shoreline. The maximum coal development in the Gates Formation (28 m total coal and 6 seams >1.5 m thick) occurs in the Foothills south of Kinuseo Creek, near the boundary between transitional marine and non-marine facies belts. Cross-sections based on closely spaced borehole and outcrop sections illustrate the occurrence and distribution of coal seams in the Duke, Honeymoon, Babcock, Frame and McConkey Pits. Thinning and pinchout of coal seams occurs adjacent to fluvial channel and splay deposits and near the landward pinchout of the Sheriff member. Draping of coal seams over fluvial channel deposits causes rapid variations in interseam thickness which may lead to correlation problems in the early stages of exploration and affect the potential mineability of coal seams. The main detrital components in the Gates sandstones are quartz and chert with siliceous rock fragments, carbonate rock fragments, clastic sedimentary and metasedimentary rock fragments, igneous rock fragments and feldspar present in lesser amounts. Mesozoic to Cambrian sedimentary rocks of the Rocky Mountain Front and Main Ranges are interpreted as the principal source of the detrital components. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Albian Lower Skeena Group in the Telkwa coalfield comprises more than 500 metres of conglomerate, sandstone, siltstone, mudstone and coal deposited during two regressive/transgressive cycles. The stratigraphic sequence is divisible into four lithostratigraphic units. The basal unit, Unit I, may be more than 100 metres thick and comprises conglomerate, sandstone, mudstone, coal, and seat earth. Conglomerate and sandstone are composed dominantly of chert and volcanic rock fragments, and mudstones are kaolinitic. Unit I was deposited in a fluvial environment on an eroded volcanic basement. Gravel and sand were deposited in braided channels and bars, and mudstone accumulated in floodplains. Coal formed in poorly drained, peat-forming backswamps. In the northern part of the study area, coal seams thin and split, a result of periodic flooding of peat swamps with sediment-laden water from nearby streams. Deposition of Unit I ended with a marine transgression and deposition of Unit II. Unit II consists of up to 140 metres of silty mudstone, bioturbated or cross-bedded, chert and muscovite-rich sandstone, and rare thin coaly mudstones deposited in a deltaic/shallow marine environment. Sand was deposited in distributary channels and mouth-bars, mud accumulated in bays, and thin discontinuous peat beds accumulated in local salt marshes. There is structural evidence for the presence of an unconformity within Unit II, but palynological and paleontological data suggest that the strata are all similarly aged. Unit III averages 90 metres thick, and comprises bioturbated or rippled, chert and muscovite-rich sandstone, siltstone, carbonaceous mudstone and thick, laterally extensive coal seams deposited in a variety of low-energy, paralic environments. Sand and mud were deposited and biogenically reworked in tidal flats, and siltstone accumulated in a restricted, nearshore marine environment in the eastern edge of the study area. Peat accumulated in freshwater coastal marshes which periodically prograded over tidal flats. All but the lowermost coal seams pinch out eastward into restricted, nearshore marine sediments, and the ash content of the coal increases toward the margin of the seam. Locally, the sulphur content of the coal is high, reflecting occasional inundation of the fresh-water swamps by brackish water. High sulphur coal contains relatively more pyritic sulphur and less organic sulphur, compared to low-sulphur coal. Unit IV is at least 150 metres thick and is composed of chloritic, green sandstone overlain by silty mudstone, deposited in a marine environment. The basal sandstone is a transgressive lag deposit, and silty mudstone, the predominant lithofacies, was deposited in a nearshore, shallow marine environment. The provenance of the sediments in the Telkwa coalfield changes from the base to the top of the stratigraphic section. Conglomerate and sandstone of Unit I contain an abundance of volcanic clasts and grains, locally derived from underlying and surrounding volcanic rocks of the Jurassic Hazelton Group, which were uplifted as part of the Skeena Arch and subsequently eroded and reworked. Sandstones of Units II, III and IV, which contain much less volcanic-derived material and an abundance of mica flakes, were derived from high-grade metamorphic rocks in the Omineca Belt. Chert grains are abundant throughout, reflecting continued clastic influx from the Pinchi Belt-Columbian Orogen. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate