Knowra Unconformity Unconformity An unconformity is a surface separating rock layers of different ages, marking time missing from the geologic record because of erosion or nondeposition.
Stratigraphy : The study of layered rocks, their sequence, and their relationships in space and time. Unconformities are mapped by examining the order and geometry of rock layers.
Sedimentation : The settling and accumulation of particles or precipitated minerals that form sedimentary deposits. Deposition before and after a hiatus creates the rock packages separated by the surface.
Hutton's Unconformity : An angular unconformity at Siccar Point in Scotland, where Devonian sandstone overlies tilted Silurian greywacke. Its exposed geometry makes a long sequence of deposition, deformation, erosion, and renewed deposition visible.
Angular unconformity : An unconformity where younger strata overlie older strata tilted or folded at a different angle. It records deformation and erosion between the formation of the two rock packages.
Stratigraphic hiatus : An interval of geological time absent from a stratigraphic sequence because of nondeposition or erosion. The hiatus is the missing interval represented by an unconformity.
Superposition : The principle that, in an undisturbed sequence, younger sedimentary layers lie above older ones. It helps establish the age order that an unconformity interrupts.
Erosion : The removal and transport of rock or sediment by water, wind, ice, or gravity. Erosion can cut away previously deposited layers and create an unconformity surface.
Great Unconformity : A widespread boundary separating Precambrian crystalline basement or strata from younger sedimentary rocks. This major example represents extensive missing time across parts of the geological record.
Disconformity : An unconformity between parallel sedimentary layers, often recognized by an erosional surface or missing interval. It can conceal a substantial time gap despite the layers remaining parallel.
Sequence stratigraphy : The study of sedimentary strata as packages bounded by surfaces linked to changes in accommodation and sediment supply. Unconformities can bound depositional sequences and help reconstruct changing basin conditions.
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