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Lesson Flashcards: Geological Structures and Unconformities Geology

Fault

A fracture in a rock along which there has been an observable amount of displacement

Mud cracks

Primary sedimentary structures formed as muddy sediment dries and contracts, forming in hot, clay-rich depositional environments

Primary geological structures

Nontectonic structures that form prior to or during the deposition of a rock

Ripple marks

Primary sedimentary structures that are ridges of sediment that form in response to currents or wind flowing over a layer of sediment

Nonconformity

An unconformable surface that exists between sedimentary rocks and igneous or metamorphic rocks

Fold

A wavelike structure formed by the bending of any type of rock due to compressional stress

Disconformity

An unconformable surface that exists between two parallel sets of sedimentary rocks with a gap in time

Secondary geological structures

Structures that have formed after the deposition of a rock in response to applied tectonic forces

Joint

A fracture in a rock along which no observable movement has occurred

Unconformity

An erosional or nondepositional surface that represents a gap in the geological record

Angular unconformity

An unconformable surface that exists between two nonparallel sets of sedimentary layers

Cross-bedding

A primary sedimentary structure that appears as layering within a bed and at an angle to the main bedding plane and forms in many depositional environments either by flowing water or wind

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