APPLYING A MODERN ANALOG TECHNIQUE TO FORAMINIFERA TO TRACK NEOGENE PALEO-WATER DEPTHS OF THE SOUTHERN BASIN IN TRINIDAD

Major tectonic and climatic shifts are primary controls on water depth in sedimentary basins, especially for marginal marine basins that have a protracted geologic history. Paleo-water depth is typically determined for basins in terms of broad numeric ranges or as relative measures by using sedimentological, biostratigraphic, or fossil records; absolute estimates of paleo-water depth often prove more elusive. Here, we developed a new derivation of Modern Analogue Technique (MAT) and applied it to foraminiferal core assemblages from mid-Miocene to Pliocene sandstone well-cutting samples the Southern Basin of Trinidad (Caribbean) to quantify Mio-Pliocene water depths. Modern foraminiferal distribution data for extant benthic foraminifera were assembled from the Ocean Biogeographic Information System (OBIS). The OBIS dataset was used to determine water depths for each of the taxa of interest, and depth distributions for all taxa in each core sample were combined. Maximum likelihood was used to determine the most probable water depth for each of the 170 core samples that contained identifiable foraminiferal material. Using these data, a water depth curve was constructed representing the entire sampled core. Overall, results suggest a major water depth trend that gradually shallows from ~3000 m in the mid-Miocene to a depth of ~650 m in the mid-late Miocene and then deepening to ~2500 m in the latest Miocene. This broadest trend of shallowing-to-deepening corresponds with the timing of regional tectonic shifts from a passive margin to compression (uplift of the basin) and then to tectonic extension and the arrival of the Orinoco River to the region in the latest Miocene. The smaller-scale fluctuations in our paleo-water depth curve are likely related to periodic fluctuations in climate, sea level, sedimentation, and localized tectonic uplift or subsidence. The general agreement between the region’s geological history and existing models provides confidence that our new MAT method is reliable and could be applied to other settings and biological systems to estimate absolute paleo-water depth in marginal marine basins.