Effects of sedimentology and stratigraphy on the distribution of clay minerals within macro-estuarine to deep-water systems

Abstract

Clay minerals present in paralic to deep-water settings may form clay coatings on detrital quartz grains, resulting in the preservation of anomalously high porosity in sand bodies, by inhibiting quartz nucleation during burial. The effects of sedimentology and stratigraphy on the distribution of clay minerals that form clay-coated sand grains remains poorly understood, as most studies lack a stratigraphic framework. Predicting the presence and distribution of clay-coated grains within sedimentary basins is important for assessing the reservoir quality of deeply buried sandstones. Two modern analogues were studied in high-resolution representing estuarine and deep marine depositional systems. The Ravenglass Estuary (NW England, UK) represents a micro tidal incised valley and The Ravenglass estuary is characterised by sedimentary logging, radiocarbon dating, laser particle mastersizer analysis (LPSA), QEMSCAN, sediment characteristics, clay coat mineralogy and coverage through nineteen Holocene sediment cores. This study involved the correlation of incised valley facies since the onset of the Holocene in a stratigraphic framework which can be used to predict sand quality and distribution in similar settings. A detailed study of the distribution of clay minerals within a macro-tidal bar was undertaken, with a high-resolution study on two of the nineteen sediment cores. Clay coat abundance increased with increasing sea-level. The second analogue focusses on the surface sediments of the Bute Inlet submarine canyon system, located in a fjord along the coastline of British Columbia, Canada. The system is fed by two proximal macro-tidal estuarine and deltaic sediments. The results demonstrate that despite minimal clay minerals present in the bulk sediment, clay coats form in the proximal settings and are carried down the canyon with minimal abrasion. The results of this thesis have produced a novel sedimentary and stratigraphic framework of an incised valley fill at Ravenglass, demonstrating that sedimentation commenced towards the end of transgression. Hydrodynamics exerted the most significant control on clay coat distribution and coverage within the Holocene tidal bar, with mid bar facies having the most optimum coverage. Clay coatings may form in such marginal settings and be transported to deep-water with minimal abrasion in more diluted flows. Turbidity flow properties may control whether clay coats are transported with or without abrasion.