SHE ANALYSIS FOR BIOFACIES IDENTIFICATION

Most quantitative methodologies for designating biofacies do so by ord ering, in some way, all the possible similarities between stations alo ng some gradient. The procedure is considered successful when the orde ring produces mappable units (biofacies or biotopes), In contrast, SHE analysis for biofacies identification (SHEBI) serially accumulates co ntiguous stations and designates biofacies as groups of contiguous sta tions that exhibit the properties of known statistical distributions f or biological communities, SHEBI identifies biological communities and always insures mappability. The number of species, S, the information function, H, and the measure of evenness, E, are related by the decom position equation H = InS + InE. Each of these quantities is calculate d as N, the number of individuals, is accumulated by adding successive samples (stations). In all cases, for a multispecies population (comm unity) these variables form linear trends on a log scale. As N accumul ates with each sample, S usually increases and the decomposition equat ion establishes constraints on H and InE. If H remains constant, then InE must decrease precisely as InS increases. If InE remains constant, then H must increase precisely as InS increases. If H increases and I nE decreases as InS increases with accumulation, then the ratio InE/ln S may remain constant. Sometimes, InS and H increase while InE and InE /lnS decrease. Departures from linear trends indicate a mixture of com munities and, hence, a new biofacies. The total population from 35 sta tions ranging in depth from 20m to 2696m in traverse 6 of Parker (1954 ) in the northeastern Gulf of Mexico was analyzed using the SHEBI tech nique. Seven biofacies were recognized. These biofacies compare favora bly with the six recognized by Parker. However, the SHEBI procedure re cognized three biofacies at depths shallower than 100m while Parker re cognized one. At depths greater than 200m SHEBI recognized two biofaci es while Parker recognized three. SHEBI establishes boundaries by exam ining departures from the linear trends expected for the statistical d istribution describing a multispecies population or community. Thus, S HEBI provides us not only with a means of designating biofacies, but a lso with a quantitative definition of a community.