Benthic foraminifera as paleoecological indicators of the Uscari Formation (Early to Middle Miocene), Limón Basin (south), Costa Rica

Abstract

The Uscari Formation (Torito and Calvario rivers, 3X, Peralta and Alto Guayacán), shows a shallowing from lower bathyal zones to neritic zones during the Early Miocene. In the Middle Miocene there was a change back to bathyal zones, but not as deep as those found in the 3X area during the previous interval.
During the Early Miocene bathyal zones were characterized by eutrophic to mesotrophic environments deposited under oceanic upwelling and turbidity flows conditions, except for the 3X area that had a more stable fauna. The shallowing towards neritic zones is characterized by oligotrophic environments with hard substrates and high-energy sands, with the presence of reefs, algae and warm waters. During the Middle Miocene, bathyal zones were oligotrophic and diversity was low possibly due to increased predation or a change in the circulation of intermediate waters by the influence of Northern Component Water (NCW), a precursor of the current North Atlantic Deep Water (NADW), which is characterized by oxygenated waters, is carbonate-rich and is low in nutrients.
The bathyal zone of the study area correlates with the bottom of the Terciopelo creek section and Early Miocene Period of the Reventazón river. Both the bathyal and abyssal deposits of the Reventazón river section, and the mid bathyal zone of the Terciopelo creek section were subject to turbidites flows which brought shallow taxa into deep water. During the late Early Miocene and early Middle Miocene, the middle and upper Terciopelo creek section was deposited in the upper slope to shelf environments transition. The early Middle Miocene type section of the Uscari creek was deposited on the continental shelf and is tentatively correlated to the top of the Terciopelo creek section.