Conglomerate (geology)

Conglomerate
Sedimentary rock
Boulder of quartz-pebble conglomerate with large clasts, from Sharon Conglomerate
Carmelo Formation (conglomerate) at Point Lobos
Nagdong Formation at Sangju

Conglomerate (/kənˈɡlɒmərɪt/) is a sedimentary rock made up of rounded gravel-sized pieces of rock surrounded by finer-grained sediments (such as sand, silt, or clay). The larger fragments within conglomerate are called clasts, while the finer sediment surrounding the clasts is called the matrix. The clasts and matrix are typically cemented by calcium carbonate, iron oxide, silica, or hardened clay.

Conglomerates form when rounded gravels deposited by water or glaciers become solidified and cemented by pressure over time. They can be found in sedimentary rock sequences of all ages but probably make up less than 1 percent by weight of all sedimentary rocks. They are closely related to sandstones in origin, and exhibit many of the same types of sedimentary structures, such as tabular and trough cross-bedding and graded bedding.[1][2][3]

Fanglomerates are poorly sorted, matrix-rich conglomerates that originated as debris flows on alluvial fans and likely contain the largest accumulations of gravel in the geologic record.[4]

Breccias are similar to conglomerates, but have clasts that have angular (rather than rounded) shapes.

  1. ^ Boggs, S. (2006) Principles of Sedimentology and Stratigraphy., 2nd ed. Prentice Hall, New York. 662 pp. ISBN 0-13-154728-3
  2. ^ Friedman, G.M. (2003) Classification of sediments and sedimentary rocks. In Gerard V. Middleton, ed., pp. 127-135, Encyclopedia of Sediments & Sedimentary Rocks, Encyclopedia of Earth Science Series. Kluwer Academic Publishers, Boston, Massachusetts. 821 pp. ISBN 978-1-4020-0872-6
  3. ^ Neuendorf, K.K.E., J.P. Mehl Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
  4. ^ Leeder, Mike (2011). Sedimentology and sedimentary basins : from turbulence to tectonics (2nd ed.). Chichester, West Sussex, UK: Wiley-Blackwell. p. 290. ISBN 9781405177832.