Road Cut Unconformity at Berowra, New South Wales

April 30, 2011

Unconformity24 aug 09 013resepod

Photographer: Phil Lachman
Summary Author: Phil Lachman

This photograph of a classic unconformity was taken at a road cut at Berowra, New South Wales, Australia. An unconformity is a geological structure that's significant because it represents a time during which no sediments were preserved in a region. Because the local record for that time interval is missing, geologists must use other clues to discover the part of the geologic history that's absent. The interval of geologic time not represented is called a hiatus. An unconformity is often a buried erosion surface separating two rock masses or strata of different ages. This indicates that the deposition of sediments was not continuous and that the rock below the unconformity, which is the older layer, was exposed to erosion for an interval of time before deposition of the younger, overlying strata.

The unconformity featured above is an angular unconformity. In this type of unconformity, horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal strata. Photo taken on August 16, 2009.

Photo details: Camera Maker: FUJIFILM; Camera Model: FinePix S7000; Focal Length: 11.0mm; Aperture: f/8.0; Exposure Time: 0.0029 s (1/340); ISO equiv: 200; Exposure Bias: none; Metering Mode: Matrix; Exposure: aperture priority (semi-auto); White Balance: Manual; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.