Sedimentary Cover of the Canadian Shield through Mesozoic Time Reflected by Nd Isotopic and Geochemical Results for the Sverdrup Basin, Arctic Canada

Abstract

The Sverdrup Basin of the Canadian Arctic Islands contains a sedimentary record, with only short breaks, from Early Carboniferous to Late Cretaceous time and can be used to document the nature of sediments delivered from northern Canada and Greenland. Sm‐Nd isotopic analysis of 72 sedimentary rock samples from the Sverdrup Basin, coupled with trace element characterization, shows that for most of Carboniferous to Late Cretaceous time, the sediment supply in the northern part of North America was dominated by a single broad provenance; 56 of the 72 samples lie squarely within the Nd isotopic evolution of a clastic sedimentary cover delivered to the region following 450–350 Ma Caledonian and Franklinian mountain building in Greenland and the Canadian Arctic Islands. Cratonic Shield sources in Greenland and Canada are hardly evident in the record, and significant contributions to the sediment budget from any source other than the post‐mid‐Paleozoic orogenic cover occurred only during four relatively short periods. First, during Carboniferous time, pre–Late Ordovician rocks of the Franklinian orogen contributed to alluvial clastic rocks in small rift basins in northern Ellesmere Island. Second, during Early Cretaceous time, Shield basement contributed to more widespread deltaic deposits in central and southern Ellesmere Island. Third, minor volcanic contributions to much of the basin occurred during Late Triassic–earliest Jurassic time and also, fourth, during Late Cretaceous time. Sedimentary materials from Caledonian and Franklinian mountains dominated the provenance of the continental and continent‐margin sedimentary system for at least 370 m.yr., a period of time extending far beyond the existence of the mountains themselves. This dominance was achieved by recycling of widespread Middle and Upper Devonian strata into Mesozoic units in the Canadian Arctic and Cordillera. We assess the extent to which the results call for cover of the Greenland‐Canadian Shield from 450 to 80 Ma and conclude that while much of the Shield was probably covered by Ordovician to Middle Devonian carbonate units, the northerly derived Upper Devonian clastic sedimentary rocks probably covered about one‐half of the Shield in its western and northern portions. This cover was progressively removed through Mesozoic time.