6533b858fe1ef96bd12b600b

RESEARCH PRODUCT

Subglacial depositional models and tunnel valley infill : example in the Quaternary record (Bray, Ireland) and application to the Upper Ordovicien record in the anti-Atlas (Alnif, Morocco)

subject

description

The icehouse period during the lower Palaeozoic led to the development of large continental ice-sheet over the Gondwana. This ice-sheet fluctuated in size and repeatedly recovered the north-Gondwana platform. The resulting glacial record includes major erosional surfaces of regional extent, with subglacial landforms and morphologies, as well as glacial valleys and specific glaciogenic sedimentary record. Among these valleys, tunnel valleys refer to Quaternary analogues, associated with the development of ice-sheets over Europe and North-America. Tunnel valley defines elongated, linear to slightly sinuous depressions, measuring few kilometers in width and several kilometres in length. They start and terminate abruptly, are generally a few hundred of meters deep, and display frequent overdeepening along the floor. Ordovician tunnel valleys are described from North Africa to the Middle East. Ordovician glacial deposits are considered as a major target for hydrocarbon exploration in these regions, with tunnel valleys forming lithological heterogeneities with excellent reservoir properties. In Europe, Quaternary tunnel valleys are targeted for groundwater resources as they form reliable aquifers. A major interest therefore exists for these valleys, as well as a need for better understanding of the nature and the stratigraphy of the infill, their origin and the parameters controlling their distribution. The recherché project presented in this thesis is based on an extensive fieldwork that focused on three main issues, regarding tunnel valleys: (1) the subglacial environment, (2) the sedimentary processes and depositional environments associated with their infill and (3) the parameters controlling their distribution