Modern foraminifera from coastal settings in northern Argentina: implications for the paleoenvironmental interpretation of Mid Holocene littoral deposits

LAPRIDA, C., CHANDLER, D.D.E., LOPEZ, R.A. Y MARCOMINI, S.

REVISTA MEXICANA DE CIENCIAS GEOLóGICAS

CENTRO GEOCIENCIAS UNAM

Lugar: Mexico; Año: 2011 vol. 28 p. 45 - 64

1026-8774

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman";} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page WordSection1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.WordSection1 {page:WordSection1;} --> In Buenos Aires province?s coasts, sedimentary processes were particularly active during the Quaternary owing to eustatic fluctuations in sea level. As a result, during the Late Quaternary transgressions, marine and marginal marine sediments were deposited in the coastal plain. In order to interpret these holocene litoral secuences, we analyze the distribution, diversity, species composition and taphonomic features of total benthic foraminifera assemblages from modern littoral settings, from the top of the dune to the lower shoreface, in two close but geomorphologically different transects located in the Atlantic coast of Northern Province Buenos Aires (Argentina, South America). Total benthic foraminiferal assemblages from subtidal and supratidal environments are distinguishable in terms of composition, diversity and taphonomic features. In upper shoreface, foreshore, backshore and foredune environments, assemblages are clearly dominated by three species: Buccella peruviana, Ammonia beccarii and Elphidium discoidale (the BAE group). This feature is the result of taphonomic processes that favor the selective preservation of such species. The study of taphonomic modifications of shells in modern assemblages allows a better discrimination between subenvironments than the analysis of taxonomic composition. Although Holocene assemblages have no strict counterparts between total modern assemblages, taxonomic composition and taphonomic modification of shells allow us to infer that the Holocene sequence was deposited between the upper shoreface and the backshore.