Detrital modes of recent deep-sea sands and their relation to tectonic setting: a first approximation

Complete petrographic analyses of modern deep-sea sands are surprisingly rare, but are needed if problems such as the influence of tectonics on petrology, or changes in petrology due to diagenesis, are to be understood in ancient sandstones. This paper is a first attempt, using data from our own study of 80 sands plus data from the literature, to establish a baseline for modern deep-sea sands with which ancient sandstones can be compared. We assigned sands to five plate-tectonic categories, each of which has a distinct average petrologic composition: (1) basins associated with trailing-edge continental margins, Q₆₂F₂₆L₁₂; (2) with leading-edge continental margins, either subduction, Q₁₆F₅₃L₃₁, or (3) strike-slip, Q₃₄F₃₉L₂₇; (4) back-arc basins, Q₂₀F₂₉L₅₁; (5) fore-arc basins, Q₈F₁₇L₇₅. The amount and type of lithic fragments and the type of feldspar are particularly important discriminators, the amount of quartz less so. Trailing-edge and fore-arc basins have quite distinctive compositions, but back-arc basins and basins near the two types of leading-edge margins show some overlap, and thus may be hard to differentiate in ancient sandstones.