Geology topics

Martin A. Buzas

Publications and source records attributed to Martin A. Buzas.

5 recordsLinked to original sources

USGS2024

Benthic foraminiferal community changes across the Miocene climatic optimum Identified by SHEBI analysis (SHE analysis for biozone identification), Calvert Cliffs, Maryland, USA

The Calvert Cliffs, MD, an iconic section of Middle Miocene strata, have been well studied both paleontologically and stratigraphically for over a century. However, few studies of the Calvert Cliffs have looked at the benthic foraminifera. This study uses SHEBI analysis (SHE analysis for biozone identification) of benthic foraminiferal assemblages to analyze community change in the Calvert and Choptank formations of the Calvert Cliffs deposited during the Miocene Climatic Optimum (MCO; 17–14.8 Ma) and the Middle Miocene Climate Transition (MMCT; 14.8–13.8 Ma). SHE analysis differs from traditional analytical methods by defining communities based on changes in diversity rather than the relative abundance of individual species. This study uses SHE analysis on a composite section of benthic foraminiferal assemblages from three vertical transects that span the MCO and MMCT. Two communities were identified from the studied strata. Community 1 was deposited during the MCO and includes incised valley fill (IVF), transgressive system tract (TST), and highstand system tract (HST) deposits. Community 2, deposited during the MMCT, is composed of samples from TST, HST, IVF, and another HST. The assemblages of community 1 are representative of an inner to middle shelf environment whereas those of community 2 are representative of an inner shelf environment. The two foraminiferal communities differentiated by SHE analysis indicate a high relative sea level in the Salisbury Embayment during the warm MCO followed by a decrease in sea level during the subsequent cooler MMCT.

Maryland↗

USGS2016

Ecological and evolutionary consequences of benthic community stasis in the very deep sea (>1500 m)

An enigma of deep-sea biodiversity research is that the abyss with its low productivity and densities appears to have a biodiversity similar to that of shallower depths. This conceptualization of similarity is based mainly on per-sample estimates (point diversity, within-habitat, or α-diversity). Here, we use a measure of between-sample within-community diversity (β 1H ) to examine benthic foraminiferal diversity between 333 stations within 49 communties from New Zealand, the South Atlantic, the Gulf of Mexico, the Norwegian Sea, and the Arctic. The communities are grouped into two depth categories: 200–1500 m and >1500 m. β 1H diversity exhibits no evidence of regional differences. Instead, higher values at shallower depths are observed worldwide. At depths of >1500 m the average β 1H is zero, indicating stasis or no biodiversity gradient. The difference in β 1H -diversity explains why, despite species richness often being greater per sample at deeper depths, the total number of species is greater at shallower depths. The greater number of communities and higher rate of evolution resulting in shorter species durations at shallower depths is also consistent with higher β 1H values.

Arctic Ocean;Gulf Of Mexico;Norwegian Sea;South At↗

USGS2015

On the distribution of species occurrence

The distribution of species abundance (number of individuals per species) is well documented. The distribution of species occurrence (number of localities per species), however, has received little attention. This study investigates the distribution of species occurrence for five large data sets. For modern benthic foraminifera, species occurrence is examined from the Atlantic continental margin of North America, where 875 species were recorded 10,017 times at 542 localities, the Gulf of Mexico, where 848 species were recorded 18,007 times at 426 localities, and the Caribbean, where 1149 species were recorded 6684 times at 268 localities. For Late Cretaceous molluscs, species occurrence is examined from the Gulf Coast where 716 species were recorded 6236 times at 166 localities and a subset of this data consisting of 643 species recorded 3851 times at 86 localities. Logseries and lognormal distributions were fitted to these data sets. In most instances the logseries best predicts the distribution of species occurrence. The lognormal, however, also fits the data fairly well, and, in one instance, better. The use of these distributions allows the prediction of the number of species occurring once, twice, …, n times. Species abundance data are also available for the molluscan data sets. They indicate that the most abundant species (greatest number of individuals) usually occur most frequently. In all data sets approximately half the species occur four or less times. The probability of noting the presence of rarely occurring species is small, and, consequently, such species must be used with extreme caution in studies requiring knowledge of the distribution of species in space and time.

Paleobiology↗

USGS2007

Community structure of foraminiferal communities within temporal biozones from the western Arctic Ocean

Community structure is often an overlooked dimension of biodiversity. Knowledge of community structure, the statistical distribution of the relative species abundance vector, makes possible comparisons and contrasts across time, space, and/or environmental conditions. Our results indicate that species of Arctic foraminifera in age-correlated cores from abyssal depths are each best described by log-series distributions. Using this structural information, we were able to determine that structural stability exists for at least 50 ka. The foraminiferal communities in this study show remarkable concordance, distributional similarity and support the neutral theory of biodiversity.

Journal of Foraminiferal Research↗

USGS1973

Species diversity: Patterns in modern and Miocene foraminifera of the eastern margin of North America

Patterns of foraminiferal species diversity were examined along the eastern margin of North America by utilizing the number of species, S, the information function, H(S), and species equitability, E. The 350 modern samples we studied extended from the Arctic to the Gulf of Mexico at depths ranging from a few meters to more than 5,000 m. In addition, 29 samples from Miocene strata of the Atlantic Coastal Plain and continental shelf were studied. Modern species diversity as measured by S and H(S) generally increases as depth increases and latitude decreases. Some notable exceptions occur, however, which are difficult to explain. For example, species diversity in the Arctic depth interval of 0 to 100 m is as high or higher than that found immediately south of Nova Scotia, in the Gulf of Maine, on Browns and Georges Banks, and even off the Gulf of Mexico deltas. At the moderate depth interval of 100 to 1,000 m, however, the entire margin north of Browns and Georges Banks has lower diversities than that to the south. The highest diversity by far in this depth interval occurs in the northeastern Gulf of Mexico. At the depth interval greater than 1,000 m, the more southern areas studied generally have a higher species diversity than the more northern Cape Cod to Maryland area. An exception to this is the northwestern Gulf of Mexico; this area is also an exception in that species diversity is significantly lower in the deeper waters than in the shallower waters in the same area. The measure of species equitability, E, showed no clear pattern with depth or latitude. This may be so because no simple pattern of species proportions exists or because the sampling was inadequate to measure it. Samples from the Miocene strata show a striking resemblance in species diversity to modern samples at similar depths and latitudes. Our observations indicate that species diversity and equitability have not increased during the last 15 × 10 6 yrs. The fossil and modern data indicate that each environment has its own carrying capacity and that this capacity is reached rather quickly. Although time and environmental stability are undoubtedly important in determining species diversity, as presently defined they are inadequate to explain all observed patterns. Long-term observations in various environments will be required to determine the relative importance of variables that affect species diversity.

Geological Society of America Bulletin↗