Abstract

TREJOS-TAMAYO, Raúl et al. Paleoenvironments in the central San Jacinto Fold Belt (Colombian Caribbean) during the late Eocene and early Miocene: inferences from benthic foraminifera. Bol. geol. [online]. 2024, vol.46, n.3, pp.169-191.  Epub Nov 28, 2024. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v46n3-2024007.

The distribution of benthic foraminifera from the upper Eocene to lower Miocene interval was studied in a marine sedimentary succession recorded by the ANH-SAN JACINTO-1 well, located in the central San Jacinto Fold Belt (Colombian Caribbean). The study included the estimation of diversity, the ratio between calcareous and agglutinated benthic foraminifera, the planktonic to benthic (P/B) ratio, the distribution of dissolved oxygen indicators, and morphogroup analysis, aiming to understand the paleoenvironmental evolution of the succession. During the upper Eocene, the lithological transition from calcareous sandstones and limestones to black mudstones indicates a discordant contact between the San Jacinto and El Carmen formations. In the San Jacinto Formation, calcareous benthic foraminifera predominate, and the low P/B ratio indicates shelf environments with a constant nutrient flux and suboxic bottoms influenced by turbiditic currents. In contrast, at the onset of the El Carmen Formation, the P/B ratio increases, indicating deeper conditions typical of the slope. The predominance of agglutinated foraminifera suggests corrosive bottom waters, likely below the lysocline and the calcite compensation depth (CCD). This scenario aligns with the global cooling during the late Eocene when the CCD was shallower. In the early Oligocene, a resurgence of calcareous foraminifera occurred, coinciding with the global deepening of the lysocline and/or the CCD, which allowed their preservation. During this interval, the assemblages indicates mesotrophic bottom waters with low oxygen levels. During the late Oligocene and early Miocene, benthic foraminifera indicate increased nutrient availability, reflecting a transition to more eutrophic conditions in bottom environments.

Keywords : Morphogroups; Lysocline; Calcite compensation depth; San Jacinto Formation; El Carmen Formation.

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