Compositional evolution of coarse clastic sediments in the southwestern United States from 1.8 to 0.2 Ga and implications for relationships between the development of crustal blocks and their sedimentary cover

On average, compositions of Colorado Province sandstones become more mature in younger sequences. The proportion of framework quartz increases through time at the expense of less robust constituents. The chemical data show that SiO2 increases through time and that all other major oxides decrease progressively. Normative sandstone compositions indicate progressive decrease in the proportion of lithic fragments and feldspar. Conglomerate clast populations in younger sequences tend to become richer in sedimentary clasts. These data are interpreted to reflect an increase through time in the input of sedimentary-rock-derived detritus relative to that derived from crystalline basement rocks. The net result is progressive growth of a more mature clastic sediment mass through time. -from Authors