Kinematic and geodynamic evolution of the Isthmus of Panamaregion: Implications for Central American Seaway closure

A major topic of debate in earth science and climate science surrounds the timing of closure of the Central American Seaway. While it is clear that the gateway was closed by ca. 2.8 Ma, recent studies based on geological and marine molecular evidence have suggested an earlier closing time of early to mid-Miocene. In this study, we examined the influences of subduction and slab window formation on the time-varying paleoenvironments of the Isthmus of Panama region. We developed detailed reconstructions of the seafloor spreading history in the Panama Basin and incorporated previously published arc block rotations into a revised global plate model. Our reconstructions indicate that the Central American Seaway region has undergone multiple phases of slab window formation and migration, slab detachment, and flat slab subduction since the Oligocene, while kinematically mapped slab windows agree well with slab gaps imaged in seismic tomography. In particular, we found that from the early Miocene, when there is clear evidence for Isthmus of Panama emergence, the region was underlain by a slab window. During the late Miocene, when there is evidence for intermittent arc deepening, and decreased transcontinental migration, we found an increase in subducted slab volumes beneath the Panama arc. Numerical and analogue models and field observations argue that slab windows can induce >1 km of vertical uplift on the overriding plate. We therefore propose that this previously unexplored geodynamic mechanism can explain the variations in Isthmus of Panama emergence, and intermittent shallow-water connections, reconciling alternative lines of evidence for Central American Seaway closure.

Supplemental Material: Kinematic and geodynamic evolution of the Isthmus of Panama region: Implications for Central American Seaway closure

GitHub repository link to plate motion model (GPlates) and slab-tracker Python code, plate reconstruction methodology, and supplementary figures.

Supplemental Material: Kinematic and geodynamic evolution of the Isthmus of Panama region: Implications for Central American Seaway closure

GitHub repository link to plate motion model (GPlates) and slab-tracker Python code, plate reconstruction methodology, and supplementary figures.

Precision in Biostratigraphy: Evidence For a Temporary Flow Reversal in the Central American Seaway During Or After the Oligocene-miocene Transition

The Oligocene-Miocene Transition (OMT) was a time of significant oceanic, climatic, and biotic change, but there is still a great deal we do not understand about its effects, particularly in terms of ocean circulation. The Central American Seaway (CAS) was an important ocean gateway at this time; recent fully coupled modeling results have suggested a possible temporary reversal of surface flow, from westward to eastward, during the OMT. Such a flow reversal would have altered numerous oceanographic properties and the dispersal of marine taxa. Here, we find a mismatch in the timing of the Atlantic vs. Pacific first appearances of the tropical mixed layer planktic foraminifer Paragloborotalia kugleri, a key zonal marker for the OMT. The first appearance ages for P. kugleri from fourteen ocean drilling sites vary from ∼23.2–23.05 Ma in the Pacific to ∼23.05–22.7 Ma in the Atlantic. Key requirements for including a site in this compilation are: 1) sampling resolution; 2) independent non-biostratigraphic chronology, such as magnetostratigraphy or orbital tuning; and 3) a preference for shore-based biostratigraphic analyses rather than shipboard estimates. Although we explore alternative explanations, we conclude that, given the restricted nature of the CAS gateway, timing of dispersal, and results from previous modeling efforts, CAS flow reversal is the most parsimonious explanation for the delayed first appearance of P. kugleri in the Atlantic relative to the Pacific. We suggest that after originating in the tropical Pacific, P. kugleri was initially blocked from dispersal into the Atlantic by westward surface circulation through the CAS during the latest Oligocene. During the OMT, circulation reversed and Pacific surface water flowed through the CAS into the Atlantic, allowing P. kugleri to disperse into the Atlantic. Previously published ocean-climate simulations suggest that the cause of this reversed flow may be related to the progressive constriction of Tethys and opening of the Drake Passage at the time of the OMT, compounded by a short-lived glaciation event in Antarctica and possible change in meridional temperature gradient and prevailing wind patterns in the tropics.