Lithostratigraphy Quiz

Fundamental Unit of Lithostratigraphy: Summary

• A geological formation is a body of rock with a consistent lithology that distinguishes it from adjacent rock bodies and occupies a particular position in the stratigraphic column.
• Formations are the fundamental unit of lithostratigraphy, the study of strata or rock layers.
• A formation must be large enough that it can be mapped at the surface or traced in the subsurface.
• Formations are tabular and may consist of a single lithology or a heterogeneous mixture of lithologies.
• Geologic maps showing where various formations are exposed at the surface are fundamental to fields such as structural geology.
• The boundaries of a formation are chosen to give it the greatest practical lithological consistency.
• The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures, and fossils regarded as rock-forming particles.
• The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region.
• Geologic formations are typically named after a permanent natural or artificial feature of the geographic area in which they were first described.
• As with other stratigraphic units, the formal designation of a formation includes a stratotype, which is usually a type section.
• The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata.
• "Formation" is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes.