Conglomerate is a sedimentary rock formed from rounded pebbles or clasts held together by a finer matrix. Its classification depends on pebble composition, sorting, and matrix abundance.
Well-sorted conglomerates signify gradual deposition by water currents, while poorly sorted types indicate rapid deposition from mudflows, glaciers, or gravity-driven processes, offering insights into Earth’s dynamic geological history.
Classification of conglomerate :
The classification of conglomerate is based on the range of lithologies represented in pebbles, the degree of size sorting, the composition of the matrix, and whether or not clasts are in contact with each other. Each of these criteria is a genetic implication. There are two board types of conglomerate:
- Those whose pebbles are generally of one lithology, well sorted and poor matrix.
- Those with a heterogeneous pebble lithology, poorly sorted and abundant matrix.
The degree of sorting indicates the method of deposition. Well sorted conglomerates are produced by normal water current, whereas the poorly sorted varieties result from rapid deposition, as in the case of mudflow or subaqueous slides.
A well-sorted conglomerate implies erosion and deposition over a long time period, resulting in the loss of unstable minerals and a rock dominated by quartz or chert pebble. The geologic environment of deposition is usually a widespread basal formation of overlapping marine units. The poorly sorted conglomerates have a matrix of clay or sand.
The abundance of unstable minerals with poor sorting indicates rapid mechanical erosion and deposition, as in alluvial fans or density currents resulting from gravity flows. In contrast to well sorted conglomerates, formations are usually thick and of limited spatial distribution.
Deposition by ice either in glacial till or by ice rafting also produces poorly sorted conglomerates or diamictites (larger non-sorted conglomerates).
