EXPLORING THE NEODYMIUM ISOTOPIC SIGNATURES OF MARINE SEDIMENTS FROM OUTCROPS ACROSS PANAMA: A CASE STUDY TO BETTER UNDERSTAND SHOALING OF THE CENTRAL AMERICAN SEAWAY

Tectonic and volcanic activity in the Isthmus of Panama region led to the gradual shoaling of the Central American Seaway (CAS) from ~13 to 2 Ma and ultimately gave rise to the Isthmus itself. The resulting interconnection of the two Americas is an ecologically important event reported to have prompted the Great American Biotic Interchange between these once isolated landmasses. However, recent examinations of tectonic, molecular, and fossil evidence have refined this timeline, suggesting that the rise of the Isthmus and CAS closure may have occurred earlier than previously thought.

Numerous paleoceanographic studies have demonstrated that the neodymium (Nd) isotope signatures of microscopic fish teeth/debris and detrital fractions in deep sea sediments reflect the Nd-isotope composition of bottom waters in the region they were deposited. Subsequently, this Nd can be used as a water mass tracer for paleo-circulation. While this proxy has been widely applied to deep sea sediment cores and even the CAS closure story, its application to samples from outcrops of marine strata that are now aerially exposed is not as well established, particularly in the tropics. Here, we investigate the potential for marine sediments from the seaway itself to preserve water mass Nd signatures that may help to further elucidate the shoaling history of the CAS.

This investigation was facilitated by a field expedition to a number of geographically distinct localities in the Azuero Peninsula, Panama in June of 2015. During the expedition, several outcrops of marine stratigraphic successions were described for the first time and corresponding in-situ deep marine, hemipelagic sandstone, and turbiditic conglomeratic sediments were collected. The isolation of fish microfossils from these sediments and analysis of rare earth element compositions and Nd-isotopic ratios within them enables a direct comparison to those from other exposures across Panama and deep marine signatures from the Pacific and Caribbean. This comparison should further allow determination of the origins of the Nd signal recorded in Azuero, as well as whether or not the specimens may be used as a peri-continental complement to circulation reconstructions from deep sea sediments and thus provide a more accurate depiction of the depth of the isthmus during the Cenozoic.