sedimentology Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of m ...

, imbrication is a primary depositional

fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not ...

consisting of a preferred orientation of

clast Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

s such that they overlap one another in a consistent fashion, rather like a run of toppled dominoes. Imbrication is observed in conglomerates and some

volcaniclastic Volcaniclastics are geologic materials composed of broken fragments ( clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...

deposits.

Types

: In conglomerates the shape of many clasts can be approximated to an ellipsoid, with a long axis (A), an intermediate axis (B) and a short axis (C). * ''A-axis imbrication'' where the long axes of the clasts are oriented parallel to the flow direction. This fabric is characteristic of clasts carried in suspension and this is only preserved in the case of a fast-waning flow in which the clasts are deposited without any significant rolling. This fabric is typical of conglomerates at the base of

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites wer ...

beds but is also occasionally observed in

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

deposits reworked by flash floods * ''AB-plane imbrication'' where the long axes of the clasts are oriented perpendicular to the flow direction and the imbrication is of the flattened AB plane, with the intermediate axes in the flow direction. This fabric is characteristic of clasts carried as

bedload The term bed load or bedload describes particles in a flowing fluid (usually water) that are transported along the stream bed. Bed load is complementary to suspended load and wash load. Bed load moves by rolling, sliding, and/or saltating (hopp ...

. This imbrication forms as the clasts are rolled along the base of a channel. The flat clasts roll onto those downstream and come to rest with their downstream end propped up by the downstream pebbles and can be used to diagnose original flow directions.

Relation to paleocurrent

The type of imbrication is generally related to paleoflow direction. Wadell found the long axis aligned with

paleocurrent A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient deposit ...

, and dipping basinward in

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...

sediments, whereas deltaic gravels may be oppositely inclined.

References

{{reflist Sedimentology