February 15. Facies

facies (Latin): appearance, aspect, look, condition

• conveys abstraction, not a concrete thing

1838 A. Gressly: inductively arrived at the concept

For a particular facies:

• the lithological aspect is everywhere associated with same paleontology assemblage
• fossils that are common in other facies are excluded

GRESSLY'S 'LAWS' OF FACIES

• the lithologic and paleontologic characteristics of a facies are quite different from those in adjacent parts of the same horizon
• same lithology is consistently associated with same paleontological assemblage regardless of stratigraphic unit or horizontal position
• some facies have sharp boundaries and some have transitional zones
• diversity of facies increases from the bottom to top of stratigraphic section (evidently refers to pattern in Jura Mtns; not generally applicable)
• diversity of facies maybe greater or less in along environmental gradients (e.g. greater diversity near shore)

ADVANTAGES OF FACIES CONCEPT

• some paleontological details make sense context of lithological and geological aspects of rocks, but would be 'devoid of meaning' otherwise
• move from mere description to interpretation
• paleotopography and paleo-processes determined
• orogeny interpreted

USE AND MISUSE OF FACIES CONCEPT

• in plant and animal ecology facies refers to developmental unit of associates characterized by specific grouping of dominants

E.g. "sandy facies"

• in stratigraphy: sandstone or noticeably sandy lithology
• in marine ecology: various associations of plants and animals that live on a sandy seafloor

• 19th century ecologists assigned the term 'facies' to varying biotic associations that were associated with the same lithological setting, which confused the original definition
• Walther (1910) referred to the sediment themselves as "facies" and different sedimentological facies were characterized by different animal communities; this restored the concept to its original meaning
• 20th century ecologists sometimes use the term 'facies' in place of 'community' when the community is described in relation to its habitat
• many stratigraphic facies are not fossiliferous
• some animal communities exist on non-sedimentary rock substrates
• some animal communities exist independent of substrates; e.g. pelagic nektonic/planktonic communities

Imbrie (1955) used the term 'biofacies' to mean the total recognizable organic content (he meant fossils) of a designated portion of a stratigraphic unit; this is a descriptive definition

Phleger (1954) expected stratigraphic biofacies to differ from original ecologic biofacies and didn't believe that the latter could be reconstructed with certainty because

• many organisms don't fossilize
• organisms from different ecologic biofacies can mix to form one stratigraphic biofacies; e.g. planktonic forams collect along with benthic forams in the same sediments

Teichert (1958) suggests a number of definitions:

• paleontologic facies instead of biofacies, in order to take into account the taphonomic processes that cause the taphocoenosis to different from the biocoenosis
• fossil communities for fossils with apparent ecological relationships
• fossil assemblages for fossils that consist of several fossil communities or are wholly unrelated
• not all fossils in an assemblage are facies fossils