Clinostratification

The principle of original horizontality is one of the basic principles of stratigraphy. It states that sediments are deposited in essentially horizontal layers, and it was enunciated already by Steno in his Prodromus (1669, p. 30): "...adeoque strata omnia praeter infimum duobus planis horizontis parallelis contineri" (...all strata, therefore, except the lowest, were bounded by two planes parallel to the horizon). There are, however, exceptions to this principle. Strata can be deposited at an angle when sediment is being transported over a sloping substrate. This occurs, for example on the stoss face of sand dunes, on fluvial bars, or, at an even larger scale, on the front of submerged deltas. This type of stratification is known as "clinostratification" and the inclined layers or laminae are called "foresets." This picture shows nice clinoforms (foresets dipping to the left) overlain by horizontal beds, in the Pennsylvanian Minturn Formation (CO, USA). Backpack for scale, about 50 cm in size.

stratigraphy Steno clinostratification foresets sedimentary geology Pennsylvanian