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Boletín de la Sociedad Geológica Mexicana

versão On-line ISSN 1405-3322

Resumo

SANTA ROSA-DEL RIO, Miguel Ángel et al. Distribution and abundance of thanatocenosis in benthonic foraminifera of the Colorado River delta. Bol. Soc. Geol. Mex [online]. 2011, vol.63, n.3, pp. 445-458. ISSN 1405-3322.

Benthonic foraminifera are important indicators of environmental conditions in coastal and marine areas since they are very sensitive to changes in their surroundings, resulting in presence and abundance of species of the thanatocoenosis communities. The objective of this work is to compare the spatial and temporal changes in the composition and structure of the benthonic-foraminifera thanatocoenosis communities of the upper Gulf of California. Samples were collected seasonally (summer, fall and winter of 2009, and spring of 2010) in the area between Campo Don Abel and the southern end of Isla Montague. Four transects of the subtidal area were run perpendicular to the Baja California coastline, and a total of 56 sediment samples were taken. To differentiate the biocoenosis from thanatocoenosis, the samples were stained with rose bengal. Silt and clay were eliminated by wet sieving and the 63 to 180 µm fractions retained for picking. From each sample, 300 individuals were separated, identified and their relative abundance computed to determine the dominant species. Cluster analysis in Q & R modes was performed on the data and the Shannon-Weaver diversity index calculated; dominance was obtained using Simpson’s index, and a distribution map was constructed. The most abundant genera were: Ammonia, Cribroelphidium and Rosalina; these represent preferably marine conditions, which show change in the upper Gulf of California. Also present were four genera of agglutinated foraminifera: Ammoscalaria, Reophax, Anomaloides and Nouria, but their distributions were centered at the southernmost stations of the study area, at the limits of the ancient estuary north of San Felipe.

Palavras-chave : Colorado River Delta; spatial and temporal change in foraminiferal communities; environmental change.

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