Fossilization potential in modern shallow-water benthic foraminiferal assemblages

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Abstract
Selected Holocene shallow-water benthic foraminiferal assemblages illustrate significant taphonomic differences in transition from living to total accumulated to fossil assemblages. One subtropical fauna is composed of approximately 225 living, mostly calcareous, species. Empty tests of more than 40 other species also were found. Five (abundant) species dominate numerically, 10 more are common, and another 25 are numerically significant; species equitability or evenness is relatively high. The total assemblage (living plus dead) appears to have high fossilization potential. Two calcareous and one agglutinated species strongly dominate a living fauna from Alaskan waters. The aggglutinated tests disaggregate easily, whereas the two calcareous dominants remain in the death and fossil assemblages along with as many as 25 other species. Loss of the agglutinated species means a significant percent of specimens are lost and the dominance pattern alters greatly. Yet, the taxonomic composition and diversity (number of species) is little changed. Quite different relationships were observed among three faunas living in a slough off Monterey Bay, California. (1) Moist bottom mud of a very-high-tide pond supports two abundant and one less-abundant living agglutinated species. The dry sediment yields no tests. (2) Seven living and two fossil species constitute the assemblage from a nearby high-tide pond. One calcareous perforate, one imperforate and one agglutinated taxon are common. (3) As many as 21 mainly living (two are dead), mostly calcareous species compose an assemblage from a nearby tidal channel. Two calcareous and two agglutinated taxa dominate numerically. The calcareous tests dissolve and agglutinated tests collapse and soon disaggregate upon the individual''s death at these three sites. Thus these living faunas show little to no fossilization potential. Here, then, are cases in which the fossilization potential (1) is high for the total assemblages, (2) is high for many taxa but very low for an important faunal element, and (3) is nil. Such differences illustrate the difficulties encountered in attempting to relate many fossil assemblages to their living communities and to compare then with one another.

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