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Biofacies are identified by an [[Fossil assemblage|assemblage of fossils]] and are interpreted to reflect a specific environment. The mapped distribution of the biofacies assemblage reflects the distribution of the interpreted environment. Biofacies are especially useful in mudstone-dominated facies such as the GOM basin Cenozoic strata.

Biofacies are identified by an [[Fossil assemblage|assemblage of fossils]] and are interpreted to reflect a specific environment. The mapped distribution of the biofacies assemblage reflects the distribution of the interpreted environment. Biofacies are especially useful in [[mudstone]]-dominated facies such as the GOM basin [[Cenozoic]] strata.

==Traditional biofacies model==

==Traditional biofacies model==

[[file:sedimentary-basin-analysis_fig4-29.png|300px|thumb|{{figure number|2}}Biofacies map of the study area in the Gulf of Mexico. After Armentrout;<ref name=ch04r7 /><ref name=ch04r9 /> courtesy Springer-Verlag.]]

[[file:sedimentary-basin-analysis_fig4-29.png|300px|thumb|{{figure number|2}}Biofacies map of the study area in the Gulf of Mexico. After Armentrout;<ref name=ch04r7 /><ref name=ch04r9 /> courtesy Springer-Verlag.]]

At times of low sea level, when the river systems discharge their sediment load directly on the upper slope, the inclined depositional surface may help sustain downslope transport of the terrigenous material and associated fluids. The modification of the local slope environment near the sediment input point could result in seaward excursions in ecological patterns similar to those caused on the shelf by the modern Mississippi River.<ref name=ch04r73 /><ref name=ch04r77 /> These seaward ecological excursions could extend to bathyal depths where downslope transport is sustained by the inclined surface and gravity-flow processes (see [[:file:sedimentary-basin-analysis_fig4-29.png|Figure 2]]).

At times of low sea level, when the river systems discharge their sediment load directly on the upper slope, the inclined depositional surface may help sustain downslope transport of the terrigenous material and associated fluids. The modification of the local slope environment near the sediment input point could result in seaward excursions in ecological patterns similar to those caused on the shelf by the modern Mississippi River.<ref name=ch04r73 /><ref name=ch04r77 /> These seaward ecological excursions could extend to bathyal depths where downslope transport is sustained by the inclined surface and [[gravity]]-flow processes (see [[:file:sedimentary-basin-analysis_fig4-29.png|Figure 2]]).

==Biofacies mixing==

==Biofacies mixing==

The downslope transport of shallow-water faunas by sediment gravity-flow processes may result in the mixing of [[Fossil assemblage|biofacies assemblages]] from different environments.<ref name=ch04r119>Woodbury, H., O., Murray, I., B., Pickford, P., J., Akers, W., H., 1973, [http://archives.datapages.com/data/bulletns/1971-73/data/pg/0057/0012/2400/2428.htm Pliocene and Pleistocene depocenters, outer continental shelf, Louisiana and Texas]: AAPG Bulletin, vol. 57, p. 2428–2439.</ref> The further mixing of stratigraphically separate assemblages by rotary drilling complicates the identification of mixed assemblages. Such problems can be overcome in three ways:

The downslope transport of shallow-water faunas by sediment gravity-flow processes may result in the mixing of [[Fossil assemblage|biofacies assemblages]] from different environments.<ref name=ch04r119>Woodbury, H. O., I. B. Murray, P. J. Pickford, and W. H. Akers, 1973, [http://archives.datapages.com/data/bulletns/1971-73/data/pg/0057/0012/2400/2428.htm Pliocene and Pleistocene depocenters, outer continental shelf, Louisiana and Texas]: AAPG Bulletin, vol. 57, p. 2428–2439.</ref> The further mixing of stratigraphically separate assemblages by rotary drilling complicates the identification of mixed assemblages. Such problems can be overcome in three ways:

* Careful sample analysis, specifically looking for mixed assemblages

* Careful sample analysis, specifically looking for mixed assemblages

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Sedimentary basin analysis]]

[[Category:Sedimentary basin analysis]]