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Along-strike variations in sediment provenance within the Nanaimo Basin reveal mechanisms of forearc basin sediment influx events

Daniel S. Coutts, William A. Matthews, Rebecca G. Englert, Morgan D. Brooks, Marie-Pier Boivin and Stephen M. Hubbard
Along-strike variations in sediment provenance within the Nanaimo Basin reveal mechanisms of forearc basin sediment influx events
Lithosphere (February 2020) 12 (1): 180-197

Abstract

The along-strike variability in sediment provenance within the Nanaimo basin is important for understanding the tectonic evolution of North America's Late Cretaceous Pacific margin, providing context for paleogeographic reconstructions. Here, we provide 35 point-counted sandstone samples and 22 new detrital zircon samples from the Nanaimo basin. These new detrital zircon samples compose a portion of a basin-wide data set (N=49, n=10,942) that is leveraged to discern spatio-temporal changes in sediment provenance. Provenance data demonstrates that the majority of Nanaimo basin strata were sourced from regions within and east of the Coast Mountains Batholith, while only the southernmost Nanaimo basin, exposed in the San Juan Islands, was supplied sediment from the North Cascade thrust system. Additionally, near-identical age modes and synchronous changes in detrital zircon facies are used to hypothesize a correlation between the Nanaimo Group and the protolith of the Swakane Gneiss. These observations, along with previously identified events in the Cordillera, are used to define two basin-wide events that affected the Nanaimo basin: the first at 84 Ma and the second at 72 Ma. The first event is correlated to the onset of Kula-Farallon spreading, which affected basin subsidence, introduced Proterozoic detrital zircon to the central and southern Nanaimo basin, and uplifted the North Cascade thrust system. The second basin-wide event, which is speculated to have been driven by increased rates of subduction and obliquity, resulted in localized high-flux events in the arc, increased exhumation of the Cascade Crystalline Core, underplating of the Swakane Gneiss, and coarse-grained sedimentation across the basin. The data presented here provides added context for the evolution of the basin and provides insight into the protracted geodynamics of forearc basins undergoing oblique subduction.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 12
Serial Issue: 1
Title: Along-strike variations in sediment provenance within the Nanaimo Basin reveal mechanisms of forearc basin sediment influx events
Affiliation: University of Calgary, Department of Geoscience, Calgary, AB, Canada
Pages: 180-197
Published: 202002
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 116
Accession Number: 2020-039334
Categories: Structural geologySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N48°10'00" - N49°00'00", W123°45'00" - W122°04'60"
N48°19'60" - N49°45'00", W125°00'00" - W122°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 2020
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