PETROGENESIS OF SEDIMENTS IN THE ABSENCE OF CHEMICAL-WEATHERING - EFFECTS OF ABRASION AND SORTING ON BULK COMPOSITION AND MINERALOGY

Citation
Hw. Nesbitt et Gm. Young, PETROGENESIS OF SEDIMENTS IN THE ABSENCE OF CHEMICAL-WEATHERING - EFFECTS OF ABRASION AND SORTING ON BULK COMPOSITION AND MINERALOGY, Sedimentology, 43(2), 1996, pp. 341-358
Citations number
59
Categorie Soggetti
Geology
Journal title
ISSN journal
00370746
Volume
43
Issue
2
Year of publication
1996
Pages
341 - 358
Database
ISI
SICI code
0037-0746(1996)43:2<341:POSITA>2.0.ZU;2-N
Abstract
Comminution in the glaciers that debouch into Guys Eight Basin, follow ed by selective sorting in the fluvial system, has had little effect o n the bulk composition, or on the mineralogy, of the basin sands and m uds. Most striking are the feldspar contents, and the feldspar-quartz ratios in sands and muds, both of which remain similar to those of ave rage bedrock. The feldspar contents of sands and muds range from 48 to 52% feldspar whereas average bedrock contains 51.7% feldspar. Feldspa r-quartz ratios average 1.58:1 in bedrock and 1.54:1, 1.66:1 and 1.69: 1 in the medium to coarse sands, fine sands and muds, respectively, in dicating minimal feldspar enrichment in the fine-grained sediments. In the absence of appreciable chemical weathering, extreme abrasion foll owed by hydraulic sorting has not produced mature sediments such as qu artz arenites and clay-mineral-rich muds. There is, however, some chem ical differentiation. Preferential accumulation of mafic minerals in f ine sands and muds is reflected in bulk compositions by higher abundan ces of MgO, FeO and TiO2, and in the mineralogy by enrichment of bioti te in the fine grades. Bulk compositional studies focused solely on mu ds and mudstones will result in an overestimate of the mafic contribut ion from source rocks. This work shows that bulk compositional studies of sediments and sedimentary rocks should include all available granu lometric grades.