Sedimentology, ichnology, and stratigraphy of modern conglomeratic depositional environments.

摘要

Modern, conglomeratic depositional environments in the Bay of Fundy, Canada are studied to further understanding of the sedimentological, ichnological, and stratigraphic relations possible in ancient conglomeratic successions. Four main conclusions are derived. Firstly, the stratigraphic and sedimentological architecture of Waterside Marsh is assessed as a tool for predicting coastal geomorphology. Gravel is commonly transported into the marsh by ice and/or storm waves. The amount of gravel decreases away from the beach, such that the gravel content in a marsh deposit can be used to predict beach proximity. Secondly, facies modelling of the transgressive, gravel-dominated Waterside Beach suggests that depending on the rate of transgression, sedimentation, and tidal range, it is possible to preserve transgressive beach deposits up to 8 m thick. Increasing beach thickness correlates to slow transgression (partial aggradation) and/or increasing tidal range. Gravel systems are rarely tide dominated, yet tides influence both beach topography and the morphology of associated depositional environments. For Waterside Beach, the megatidal regime has resulted in large cross-sectional areas for the tidal creeks that drain the salt marsh. Overlying the tidal-creek scours, thick beach successions, oriented perpendicular to the depositional strike, are deposited.; Where possible, ichnological and sedimentological relationships are semi-quantified. Ichnologically, it is determined that to achieve 5% bioturbation in backshore sediments requires two consecutive seasons of colonization. Consequently, highly bioturbated backshore sediments are likely to occur in low wave-energy environments. Semi-quantification of sedimentological properties was done for average grain size (in phi values) versus the areas extent of the intertidal zone of Waterside Beach, Alma delta, and Big Salmon River delta. A log-linear relationship is derived suggesting that the areal extent of conglomeratic deposits is directly proportional to the average grain size.; Relative hydraulic influences on the geomorphology and sedimentology of the three systems is established and the systems classified. The Big Salmon River delta is considered river-dominated with low to moderate wave modification and the Alma delta river-dominated with high wave modification. Waterside is classified as a highly tide-modified, wave-dominated beach.