Tunnel valleys: current knowledge and future perspectives
Published:January 01, 2012
P. van der Vegt, A. Janszen, A. Moscariello, 2012. "Tunnel valleys: current knowledge and future perspectives", Glaciogenic Reservoirs and Hydrocarbon Systems, M. Huuse, J. Redfern, D. P. Le Heron, R. J. Dixon, A. Moscariello, J. Craig
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Tunnel valleys are elongated incisions that are commonly interpreted as being the result of erosional processes by subglacial meltwater occurring under continental ice sheets. The abundance, size and the primarily coarse-grained infill of these features have made tunnel valleys important hydrocarbon and groundwater reservoirs. Although numerous tunnel valleys have been described over the last century, their formation and infill remain poorly understood. This review summarizes and discusses the current knowledge of tunnel valleys, providing an overview of the observations around the world. Morphological aspects that separate tunnel valleys from other landforms are discussed, as well as the wide variety of sedimentary environments found to contribute to the infilling of these features. The depth of the incision and the character of ice retreat significantly determine the final infill architecture. The formational hypotheses proposed in the literature are assessed to test their wider applicability to all other tunnel valleys in order to find a generic model that helps in the prediction of the morphology and infilling of both Pleistocene and pre-Pleistocene age. A quasi-steady-state model, with small meltwater outbursts that erode tunnel valleys near the ice margin, seems compatible with most of the known valleys. Other proposed models require specific geographical or climatic conditions.
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Glaciogenic Reservoirs and Hydrocarbon Systems
Glaciogenic reservoirs and hydrocarbon systems occur intermittently throughout the stratigraphic record, with particular prominence in Neoproterozoic, Late Ordovician, Permo-Carboniferous and Late Cenozoic strata. Recent interest in glaciogenic successions has been fuelled by hydrocarbon discoveries in ancient glaciogenic reservoirs in North Africa, the Middle East, Australia and South America. Glaciogenic deposits of Pleistocene age are noteworthy for their content of groundwater onshore and potentially prospective and/or hazardous gas accumulations offshore. The abundant imprints of Pleistocene glaciations in both hemispheres can be used to reconstruct complex histories of repeated ice cover and retreat, and glacier-bed interactions, thus informing our view on the dynamics of older ice caps and predictions of future glaciations. This volume aims to provide a better understanding of glaciogenic processes, their stratigraphic record and reservoir characteristics of glaciogenic deposits. The book comprises 3 overview papers and 16 original case studies of Neoproterozoic to Pleistocene successions on 6 continents and will be of interest to sedimentologists, glaciologists, geophysicists, hydrologists and petroleum geologists alike.