Compositional suites of terrigenous deep-sea sands of the present continental margins



The compositional variability shown by sands of present continental margins was determined through conventional microscopic techniques. This allowed the establishment of a descriptive classification of deep-sea terrigenous sands based on a restricted number of commonly used parameters. The fundamental sand types include: (1) QF suite—sands in which quartzose and/or feldspathic grains predominate. Carbonate-L-bearing sands (on average richer in lithics) occur within this suite. (2) QL suite—in which quartzose and/or lithic grains predominate. Little compositional diversification is apparent within this suite. (3) FL suite—in which lithic and/or feldspathic grains predominate. Two compositional members can be identified based on the K-feldspar/plagioclase ratio. (4) LV suite—consists of sands in which volcanic grains largely dominate the lithic types. Vitric and serpentine sands occur within this suite.

The suites are related to distinct source-area types defined as follows: (1) cratonic block; (2) sedimentary orogenic belt; (3) volcanic orogenic belt; (4) volcanic arc.

Some sands cannot be easily assigned to a single compositional suite because petrologic parameters overlap with an adjacent suite. Such critical compositions are commonly arkosic. Using roundness of the framework components, it is possible to define a category identified as matured sands, which are greatly enriched in resistates.