TROPICAL AMERICAN CORBULIDS: A NEW SOURCE OF PALEOENVIRONMENTAL HISTORY

Oceanographic conditions in tropical American oceans changed dramatically following the closure of the Panama Seaway (PS). Prior to the emergence of the Central American Isthmus, equatorial Atlantic and Pacific water mixed freely. Today, however, the tropical Western Atlantic is generally saline, warm, and nutrient-poor, while the tropical Eastern Pacific is relatively cool and nutrient rich. Despite the overall warming trend in the Western Atlantic, local upwelling remained an important oceanographic phenomenon. Here, we use these previously documented patterns of environmental change to test the effectiveness of corbulid bivalves as recorders of paleoenvironmental history.

We present new corbulid derived, isotopically-based, paleotemperature estimates of pre-PS closure (Miocene) temperatures in the Dominican Republic and southeastern US. In addition, we present stable isotope profiles and paleoenvironmental reconstructions from the Middle Pliocene Pinecrest Beds.

We analyzed δ¹⁸O and δ¹³C from three species of Miocene Bothrocorbula. Each was collected from a different locality: 1) B. synarmostes, Chipola Formation (Miocene: Burdigalian); 2) B. radiatula, Alum Bluff Group (Miocene: Burgdiglian-Langhian); and 3) B. sp. cf. B. viminea, Cercado Formation (Miocene: Tortonian-Messinian). Average δ¹⁸O ranges from all Miocene specimens are similar (0.5‰ to -1.5‰). Minimum temperature estimates range between 19° and 26°C. Average seasonality ranges between 6-8°C, while individual estimates are as great as 12°C.

δ¹⁸O profiles from specimens of B. wilcoxii, Pinecrest Beds (Pliocene: Piacenzian), differ remarkably from Miocene profiles. Average δ¹⁸O values range between 2.3‰ and 0.2‰ and minimum seasonality estimates are between 6-12°C. Analysis of δ¹⁸O and δ¹³C covariation is consistent with seasonal upwelling, and palaeotemperature estimates are relatively cool (~10-20°C).

Our findings are consistent with previous reconstructions of Miocene and Pliocene environments in the western Atlantic. Furthermore, corbulids contain a rich yet untapped source of paleoenvironmental data, especially considering their extremely high abundance in many Neogene deposits from tropical American ocean basins.