Sediments are deposited via distal fluvial, lacustrine, deltaic, and marine depositional systems. Detrital sedimentary graded beds are formed from erosional, depositional, and weathering forces. Limestones may also form in lacustrine and evaporite depositional environments. The typical rock formed in a certain depositional environment is called its sedimentary facies. Nodular anhydrite occurs as replacement of gypsum in a variety of sedimentary depositional environments. This affects both erosional processes and depositional processes in pans. The setting in which a sedimentary rock forms is called the depositional environment. In terms of origin and depositional mechanisms they are very similar to sandstones. They form approximately 40 percent of aeolian depositional surfaces. Engineering geologists also classify soils based on their genesis and depositional history. These members represent a distinct change in the depositional environment and are of Pleistocene age. The depositional temperature of these pyroclastic surges ranged up to . The original depositional layering is tilted, such tilting not being the result of post-depositional deformation. Ichnofacies are groups of trace fossils that together help give information on the depositional environment. Primary contacts include depositional, unconformable, and intrusive contacts.