Lake Deposits

(also lacustrine deposits), sedimentary formations on the floor of modern lakes and of lakes that existed in previous geologic eras. Classified as continental deposits, they also possess features inherent to marine deposits, for example, good sorting of material and horizontal bedding. The distinguishing features of lake deposits are lenticularity, few remains of specific fauna, few remains of terrestrial plants and animals, and a close connection with alluvial and other types of continental sediments. Glaciolacustrine deposits are classified in a separate category.

Mechanical sediments accumulate in freshwater lakes, with fine-grained sediments having pronounced horizontal bedding often predominating; sapropel and diatomite are also common. As lakes become overgrown, they frequently turn into peat bogs. The character of lake deposits changes depending on the climate. In areas with a cold climate fragmental sandy-argillaceous material is deposited, sometimes with banded lamination. In lakes of the temperate zone, iron (bean ores), silica (diatomites), calcium carbonate, and organic matter (peat, sapropel) accumulate along with the fragmental material. In arid zones, where subsaline and saline lakes are found, carbonates, halite, and gypsum are deposited; in lakes without an outlet dolomite sediments and sometimes sodium carbonate are deposited.

In ancient sedimentary strata lake deposits consist of Devonian and Permian clays and marls, dolomites, and salt-bearing deposits.