Provenance of Mesozoic and Cenozoic sediments from the Labrador and western Greenland continental margins

Abstract

Forty-two Cretaceous and Paleocene sand samples from offshore Labrador and onshore western Greenland were examined petrographically. The sands were found to be mineralogically and texturally immature, reflecting rapid erosion and transportation from local, high-relief source areas. The principal source-rock types were acidic plutonics and amphibolite-facies metasediments and metavolcanics. Basic igneous rocks provided minor quantities of detritus, whereas contributions from sedimentary and low-grade-metamorphic sources were negligible. Cretaceous and Paleocene sediment transport was essentially perpendicular to the axis of the 'Labrador–Baffin rift system.In view of the apparent local abundance of amphibolite-facies supracrustal rocks during the Cretaceous and Paleocene, extensive post-Paleocene denudation in Labrador, Baffin Island, and western Greenland is invoked to account for the present scarcity of such rock types.

Erosion of the Laurentide Region of North America by Glacial and Glaciofluvial Processes

“…The theory of deep erosion due to continental glaciation (White 1972) has not been well received in the literature (Gravenor, 1975;Sugden, 1976Sugden, , 1978Higgs, 1978;Rutter, 1980). These authors raise many important issues which suggest that the original concept of shallow erosion (Flint, 1971) is the more correct theory.…”

Belle Fourche River-Cheyenne River Drainage Divide Area in the Wyoming Powder River Basin Analyzed by Topographic Map Interpretation Methods, USA

“…A previously proposed new geomorphology paradigm, involving a continental ice sheet eroded deep "hole" (White, 1972(White, , 1988, did not satisfactorily explain the Bell River system and sediments directly and indirectly associated with it. While White's deep erosion by continental ice sheets paradigm explained some evidence, like most newly introduced paradigms, it encountered resistance with some of the strongest resistance coming from Gravenor (1975), Sugden (1976), Higgs (1978), and Rutter (1980). White's critics argued among other things that glacially deposited debris in Bell River system valleys is evidence those valleys survived ice sheet erosion and mid and late Tertiary sediments in and near Belle River system river valleys were deposited prior to Pleistocene glaciations.…”

Comment on “New Evidence from Beneath the Western North Atlantic for the Depth of Glacial Erosion in Greenland and North America” by E. P. Laine

“…Thus, I strongly support the basic thrust of Laine's study, but I am totally unconvinced that these data can be used to say anything about "deep erosion," especially when we consider that the flow model employed is at variance with the known geological data (Shilts, 1980). It will be important to refine this initial study by: (1) working on the rates of erosion throughout the Quaternary, for example, was most of the erosion accomplished very early, possibly even during the first one or two glacial cycles (e.g., Andrews, 1979); and (2) expanding the work of Higgs (1978) to examine the provenance of the sedi-LETTERS TO THE EDITOR ments. Laine's work is clearly important, Laine, E. P. (1980 …”

“…2. The work of Higgs (1978) on the provenance of Mesozoic and Cenozoic rocks from the Labrador and western Greenland continental margins indicates that the "unroofing" of the Precambrian shield occurred "since the Paleocene, exposing progressively deeper levels of the crust" (Higgs, 1978(Higgs, , p. 1859. Post-Paleocene erosion of high-grade supracrustal rocks is implied.…”