Sedimentology and allostratigraphy of the Upper Cretaceous (Campanian) Lea Park - Belly River transition in central Alberta, Canada.

摘要

The proposition of this dissertation is that the coastal sediments of the Upper Cretaceous (Campanian) Lea Park-Belly River transition were deposited in fine-grained, sandy "braid deltas", in which a maze of shallow channels would distribute sediment all along the shoreline. Rather than having one major fluvial distributary depositing the delta, the deltaic shoreline is interpreted to have been created by numerous smaller fluvial systems simultaneously depositing sediment at the shoreline. The massive-to-laminated beds are interpreted to have been deposited by turbidity currents which carried very large amounts of sand in suspension. These turbidity currents were most likely generated by slumping of pre-deposited delta mouth sediments, but may also have formed as hyperpycnal fluvial density currents.;The deltaic coastal systems are laterally equivalent to thick units of fluvial and associated non-marine sediments to the west. These fluvial systems were undoubtedly supplying the deltaic shorelines further to the east. Sediments indicative of both fine-grained, meandering fluvial systems and coarser-grained, higher energy fluvial systems are present within the study area.;The shoreline cycles are laterally equivalent to incised fluvial sediments, which in some locations sit directly on fine-grained marine shelf sediments. This combination of sharply-based shoreline cycles and incised fluvial sediments is interpreted to be indicative of forced regressions, where a relative drop in sea level causes the shoreline to move rapidly basinward.;This interpretation of rapid drops in relative sea level indicates that the regressive-transgressive cyclicity of the Lea Park-Belly River transition was allocyclically controlled. The overall time frame for deposition of all eight cycles within the study area is thought to be on the order of 1.0-1.25 million years, indicating that the Lea Park-Belly River cycles were deposited in response to fourth-order fluctuations in relative sea level. The underlying control of these fluctuations is speculative, but they may be due to fluctuations in subsidence rates due to active loading in the Cordillera acting in concert with a third-order drop in relative sea level. (Abstract shortened by UMI.).