Late Eocene-Early Miocene paleoenvironmental shifts in the NW south American margin: Tectonic and climatic drivers inferred from benthic foraminifera

Abstract

The strategic importance of northwestern South America, particularly along the southwestern Caribbean margin, lies in its critical role in global oceanic circulation and the impacts that marine ecosystems have experienced throughout the Cenozoic. Paleoenvironmental reconstruction in this region is essential for understanding how deep tropical ecosystems respond to changes in global climate and/or regional tectonic instability. This study presents a benthic foraminiferal record from a stratigraphic core (ANH-San Jacinto-1) in the central San Jacinto Fold Belt (SJFB) in northwestern South America. The record reveals significant shifts in nutrient input to the seafloor, bottom currents, and carbonate compensation depth (CCD) during the late Eocene to Early Miocene. The Eocene interval comprises two distinct environments: one near the base of the core, characterized by shallower, more energetic conditions with relatively well‑oxygenated waters and consistent nutrient supply, followed by a deeper environment with a high abundance of agglutinated foraminifera. The dominance of epifaunal taxa suggests nutrient influxes potentially driven by volcanic activity or fluvial systems in the southwestern Caribbean that may have depleted bottom-water oxygen.

Additionally, the high abundances of agglutinated species Psammosiphonella cylindrica and P. discreta indicate stronger and corrosive bottom waters during the late Eocene. At the beginning of the Oligocene, a notable shift in productivity and a deepening of the CCD led to a predominance of calcareous taxa, coinciding with global changes associated with the Eocene-Oligocene Transition. During the Oligocene, benthic foraminiferal communities appear to have been influenced by seasonal nutrient delivery, likely from different fluvial systems along the Caribbean margin of NW South America, possibly driven by a northward shift of the Intertropical Convergence Zone, directly impacting the SJFB. The upper Oligocene and Lower Miocene intervals record a significant increase in paleoproductivity, potentially linked to cooling events at high latitudes in the Atlantic Oceans or sustained organic influx from river systems in NW South America. This study enhances our understanding of the paleoenvironmental evolution in NW South America. It highlights the utility of benthic foraminiferal as sensitive proxies for tectonic, climatic, and oceanographic changes that shaped the paleoenvironments in this tropical region between the late Paleogene and early Neogene.