Foraminiferal paleodiversity and paleoenvironments at the NE coastal plain of Buenos Aires province (Argentina) during the Mid-Holocene sea level highstand

Abstract

In this investigation, we carried out a Mid-Holocene paleoenvironmental reconstruction based on fossilized benthic foraminifera, retrieved from sedimentary deposits located in Bahía Samborombón coastal plain. A total of 38 species, grouped into 19 genera, were identified. The assemblage, constituted mainly by Buccella peruviana (d’Orbigny), Cribroelphidium poeyanum (d’Orbigny), Ammonia parkinsoniana (d’Orbigny) and Ammonia tepida (Cushman), indicate predominantly abnormal marine conditions, characterized by low oxygen levels between ca. 6880–6640 and 5600–5430 yrs cal. BP. During this interval, a quantitative analysis carried out on the assemblages as well as indexes suggest found three different paleoenvironments. The first one, occurring ca. 6880–6640 yrs cal. BP, was a brackish environment with low oxygenation levels and low bottom energy. Then, ca. 6500–6250 yrs cal. BP, an environment with more marine influence, increased oxygen levels and higher energy prevailed. This higher oxygenation could be related to the flow of seawater into the area during the Mid-Holocene sea-level highstand. The third paleoenvironment developed ca. 5590–5430 yrs cal. BP, was under a gradual transition back to a brackish environment with low oxygen levels as well as low energy.