Sedimentary Succession: Its Components

Coarse terrigenous sediments (dominant clast size >2mm) are found in recent sedimentary deposits as well in stratigraphic records. Unlithified products are commonly known as gravel deposits, whereas lithified equivalents are either known as CONGLOMERATE or SEDIMENTARY BRECCIA, depending upon the degree of roundness of the coarse clast fractions. They are known as conglomerate when the coarse clast fractions are dominantly rounded and as sedimentary breccia when these are dominantly angular. The composition of the coarser clasts may be either siliciclastic or carbonate. The classification of conglomerate, as proposed by Folk (1965 ), appears to be more meaningful sedimentologically amongst many such classifications (see Pettijohn 1975 ). Following Folk’s classification, when clast fraction (>2 mm) constitutes 80% or more, the deposit is classified as conglomerate. When the coarser fraction varies between 30 and 80%, the deposit is grouped as sandy conglomerate/muddy conglomerate, depending upon the proportion of sand and mud components.