bed

A bed in geology refers to a layer of rock strata, typically tabular or lenticular in shape, that differs in rock type or characteristics from the material above and below it. These layers, also called strata, can vary greatly in thickness and extent.12

A biostratigraphic unit is a group of geologic strata defined by its characteristic fossil content, rather than by its lithologic (rock) features.3

Bedrock is the solid rock that lies beneath unconsolidated surface materials like soil.4

Stratification is the layering observed in most sedimentary rocks and some igneous rocks formed at Earth's surface. These layers are crucial for interpreting geologic events and locating resources like petroleum. A marker bed is a distinct rock layer that can be identified and traced over large distances due to its unique physical characteristics, such as a coal seam or a volcanic ash layer.256