Depositional Cyclicity and Evolution of Convergent-Margin Basins

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Convergent-margin basins (CMBs) are typified by rapid uplift and associated subsidence, steep and short river catchments, and elevated sedimentation rates. As a consequence, sediment accumulation rates are significantly greater in CMBs than in intracratonic foreland basins and passive margins, and this is manifested in distinctive stratal architectures and preservation of cyclical sedimentation patterns. The proposed research aims to characterize shallow-marine strata in CMBs to understand how these systems evolve through time, including resolving both climate and earthquake cyclicity. Research will focus on two CMBs and involves developing an allostratigraphic framework for the basins and identifying cyclical sedimentation patterns across the basins. Most of the proposed research focuses on the lower Nanaimo Group in the Georgia Basin, Vancouver Island, Canada. The Georgia Basin is a forearc basin (CMB) and the lower Nanaimo Group locally exceeds 1 km in thickness. Continuous outcrops exposed along rivers will be logged at high resolution and facies analysis will be employed to identify stratigraphically important surfaces. Surfaces will then be used to subdivide strata along and across depositional strike, and detrital zircon data will be acquired to test and refine allostratigraphic correlations. Resolving depositional cyclicity in the lower Nanaimo Group will utilize facies analysis, and recognition of both seismites (earthquake cyclicity) and lateral and vertical changes in sedimentation (climate cyclicity). Cycles considered indicative of tectonism and climate will be corroborated with geochemical proxies, including d13C and C:N ratios. The Western Foreland Basin, Taiwan is a rapidly uplifting CMB and thick sequences of young strata (< 6 Ma) are exposed in closely spaced outcrops in western Taiwan. The ages of outcrops are well established biostratigraphically, and hence it is possible to assess alongstrike and down-dip facies relations in time-equivalent deposits and to study the products of earthquakes and climate cycles. Research will focus on the late Pliocene Kuechulin Formation and early Pleistocene Cholan Formation. Outcrops will be logged in detail and geochemical data (d13C, d18O and C:N ratios) will be used to resolve and refine climate and earthquake cycles. Drone-based 3D photogrammetry will be used to reconstruct outcrops and quantify both bed thicknesses and stratal architectures. The impacts of this work are multiple. In the Georgia Basin, we will produce a basin-wide allostratigraphic framework for the lower Nanaimo Group, assess cyclic deposition and resolve changes in depocenters and subsidence/tectonism. When combined with research in Taiwan, the results of this work will have a global impact in that we will develop tools and models for recognizing and resolving climate and earthquake cycles in shallow-marine strata, and criteria for distinguishing them from cycles induced by changes in relative sea level.