Abstract

There is not yet a precise classification of or terminology for ecostratigraphic boundaries. SHE analysis for biozone identification (SHEBI) objectively places boundaries between abundance biozones (ABs). Alpha diversity ( = SE  =  eH, where H is the information function) measures the community diversity within an AB in units of effective species, whereas the dimensionless β diversity ( =  SE2/SE1, where SE1 and SE2 are the α diversities of successive ABs) quantifies the difference in α diversity between successive ABs. Three categories of AB boundary are recognized depending on the value of β. In Type –1β, the α diversity of the younger AB is significantly less than that of the older. In Type 0β, SE2 ≈ SE1, while in Type +1β, the α diversity of the younger AB is significantly greater than in the older. Benthonic foraminifera were sampled from the ∼124-m-thick Pleistocene strata of DSDP Hole 148 (eastern Caribbean Sea). SHEBI indicated 18 ABs; of the 17 AB boundaries, seven were Type –1β, two were Type 0β, and eight, Type +1β. The direction of inflection of the graph of lnE versus lnN did not indicate AB boundary type. Although the Pleistocene was characterized by repeated alternations between glacial and interglacial conditions, there was no regular alternation of Type –1β and +1β AB boundaries. Complementarity (i.e., species level distinctiveness of successive ABs) was measured using a percentage similarity index, CP. Differing complimentarities show that boundaries between ABs varied with respect to permeability to species, while beta diversities and CP were uncorrelated.

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