Facies

Facies:

1. The sum total of features such as sedimentary rock type, mineral content, sedimentary structures, bedding characteristics, fossil content, etc, which characterise a sediment as having been deposited in a given environment. Facies which are particularly characterised by rock type are referred to as lithofacies, whereas those especially characterised by their fauna are called biofacies. It should be noted that a particular lithofacies may be see diachronous, and this may be only detectable if the fossil evidence is adequate. Study of the distribution of facies leads to the reconstruction of past geographies.
2. In geology, the “appearance” and hence the composition and characteristics of a rock formation. Cores are taken from a well, for example, so that the reservoir facies can be studied. A Facies Trap for a hydrocarbons is one in which the seal or closure is provided by a change in rock characteristics, a form of stratigraphic trap.