Sedimentological Characterization and High Resolution Chronostratigraphic Framework of Channel-Levee Systems Across a 135 km-Long Strike-Oriented Outcrop Transect, Cretaceous Nanaimo Group, Canada
Integration of high-resolution geochronological data with regional stratigraphy can be used to establish a basin-scale paleogeographic framework for deep water systems. In southwestern British Columbia, Canada, the Maastrichtian Geoffrey Formation (Nanaimo Group) crops out over a 135 km-long strike-oriented outcrop belt. The formation consists of three distinct, 300-500 m thick and 3-5 km wide channel-levee system deposits spaced between 50-75 km apart, suggesting a basin characterized by multiple point sources. The objective of this research is to: (1) establish the presence and character of channel-levee systems in the previously understudied outcrop belt; and (2) determine the duration and timing of the conduits through the use of maximum depositional ages (MDAs) derived from detrital zircon geochronological analysis. Although the tectonic setting and rates of sedimentation are distinct, the composite stratigraphic product shares analogous architecture and facies attributes with systems off continental margins globally (e.g., Angola, Ghana, Nile Delta, Tanzania). Based on data including 1733 m of measured section and 3495 paleocurrent measurements, channel levee systems in the Geoffrey Formation consist of sandstone- and conglomerate- dominated channel fills bound by thin-bedded turbidites and mudstone-prone mass transport deposits. The three systems comprise 200-400 m thick composite sedimentary units (i.e., channel-levee complexes) that are characterized by laterally offset channel bodies at the base of the succession followed by vertically aligned channel bodies upwards. They record the broadly interpreted trend of early degradation and lateral channel migration followed by later establishment of levees and enhanced channel aggradation. The channel-levee systems generally consist of at least two distinct, nested channel-levee complexes. MDAs from ten DZ samples (n=300/sample) reveals that the three channel-levee systems were approximately contemporaneous, persisting for 9 myr, between 72-63 Ma. The long-lived input of conglomeratic detritus to multiple points along the strike-oriented basin margin transect suggests that orogen-scale processes such as arc denudation and drainage basin expansion controlled widespread sediment-delivery to deep-water.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017