Using SHEBI (SHE Analysis For Biozone Identification): To Proceed From The Top Down Or The Bottom Up? A Discussion Using Two Miocene Foraminiferal Successions From Trinidad, West Indies

Abstract

SHE analysis for biozone identification (SHEBI) is a new technique that identifies abundance biozones (ABs) by accumulating species abundance data along a time series, recalculating species richness (S), the information function (H), and the equitability index (E) with the addition of each sample. Boundaries are drawn between ABs where SHE analysis detects a change in either (1) the population structure or (2) the assemblage's species composition, species having joined or left the community in quantities that affect the evenness of the distribution of species abundances. This study uses foraminiferal data from two Miocene sections on Trinidad (Cipero Formation, Catapsydrax stainforthi Zone; San José Calcareous Silt, Globorotalia acostaensis Zone) to test if top-downward or bottom-upward analyses indicate the same AB boundaries. The results differ. In the Cipero there are no matches between AB boundaries determined by bottomup and top-down SHEBIs. In the San José CalcareousSilt, only some boundaries match. It is recommended that SHEBI proceed in the order in which the samples in the ABs were deposited, treating the ABs as successive ecostratigraphic units. Intriguingly, no matter whether ABs were determined by bottom-up and top-down SHEBIs, SHE community structure investigations indicated logarithmic series population structures. A graphical technique for determining the species responsible for the change in ABs reveals that a peak in the per sample percentage abundance of Nuttallides umbonifera in the Cipero Formation is offset by one sample from the AB boundaries it engendered, marking a temporary decrease in nutrient flux.

Distinguishing relative specialist and generalist species in the fossil record

“…The fauna recorded here differs from that recorded from the comparatively homogeneous C. stainforthi Zone of the Cipero Formation by Wilson (2008b), who found assemblages to be dominated by O. umbonatus (9% of total recovery), Siphonodosaria nuttalli gracillima (Cushman and Jarvis, 1934) (6.5%), Cibicidoides mundulus (Brady et al, 1888) (6%), and Gyroidinoides cf. soldanii (d'Orbigny, 1826) (5%).…”

“…Bolli et al (1995) reproduced some of Cushman and Stainforth's (1945) illustrations, brought the taxonomy of species up to date and documented their biostratigraphic ranges. Wilson (2008b) listed species found within the Lower Miocene Catapsydrax stainforthi Zone (=Zone N6 of Blow, 1969), while Hayward et al (2012) illustrated some uniserial benthic foraminifera collected throughout the formation. (2) that by Wilson (2008b).…”

“…Wilson (2008b) listed species found within the Lower Miocene Catapsydrax stainforthi Zone (=Zone N6 of Blow, 1969), while Hayward et al (2012) illustrated some uniserial benthic foraminifera collected throughout the formation. (2) that by Wilson (2008b). Holbourn et al (2013) illustrated a few species from it.…”

The Thermogeographic Model in Paleogeography: Application of an Abiotic Model to a Plate Tectonic World

“…At each step in this accumulation the values for additional new taxa, S, along with an information measure we denote as H, and an evenness measure E, which uses taxon proportions, are each calculated. The boundary of each biofacies is determined from the changing values of estimated evenness of the biomass proportions as we accumulate over samples (Buzas and Hayek, 1998;Osterman et al 2002;Hayek et al, 2007;Wilson, 2008). The entropy of the system is examined as the expected value of this information measure (Hayek and Buzas, 2010) and a comprehensive snapshot of the depth-related fauna is obtained.…”

Determining Boundaries between Abundance Biozones Using Minimal Equipment

“…Crossing an AB boundary results in sampling of a new community, with sharp jumps in S, H, and E indicating significant changes in the composition and structure of the population sampled. One challenge facing this cumulative approach is that eventually the accumulating list becomes so large that even the addition of a sample with a substantially different composition needs not have a large effect on H and E [23]. This paper introduces a method termed SHE bip for use where the standard deviation of the sample size is high (>75%) relative to the mean.…”