The mud-size fraction of terrigenous sediments is dominated by clay minerals. This category accounts for minor constituents of clastic rocks that are chemically stable, but not abundant in the parent rocks. Obviously this is not a category of minerals. That is, it is possible to reconstruct the minearalogy of the parent rock and also its proximity to the depositional basin. Not all clastic particles are from other rocks.
Biogenic material is obviously a more abundant and steadier source.
Small organisms such as foraminifers, small gastropods, pelecypods and brachiopods persists as whole shells in the sediment. Larger organisms, such as trilobite and crinoids, disarticulate into small pieces at death. Other organisms are disarticulated by scavengers, decomposers and burrowing organisms. We consider clastic rocks that are predominantely made up of carbonate in the next lecture. The cement in a sedimentary rocks may constitute as much as one-third of its volume.