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Tertiary evolution of Caribbean vegetation in the context of geologic and nearshore marine events

Estimates of SST (sea surface temperature) during the Cenozoic are complicated by uncertainty as to the presence, extent, and effect of glaciers in the Paleogene, and by an emerging re-evaluation of the accuracy of foraminifera  to precisely record changes in equatorial ocean water temperatures in the Neogene, especially at the last glacial maximum (18,000 years B.P.). If Paleogene marine temperatures were as warm as at present, Early Tertiary floras deposited at the ocean-continent interface should record vegetation comparable in ecological import to that of the present. The middle (?) to Late Eocene Gatuncillo flora from Panama (9° N latitude) is similar to the modern vegetation along the north (Atlantic) coast of southern Central America. This argues for the presence of limited glaciers, probably on Antarctica, to account for the increasing 18O in the marine waters. Assuming that any cooling of low latitude SST’s in the late-glacial extended into early glacial times, at least to some extent, Neogene floras should reflect these cooler conditions. The Middle Pliocene (N20; 4-5 Ma) Paraje Solo palynoflora from coastal southeastern Mexico (~18° N latitude) suggests a MAT (mean annual temperature) at least 2°-3°C cooler than at present. The cause(s) likely involved continued decline in CO2 concentration, threshold changes in ocean water circulation, upwelling, deposition just prior to closure of the Isthmus of Panama (~3.5-2.5 Ma) which strengthened poleward transport of ocean heat, and also orbitally induced global lowering of temperatures. The temperature change suggested by the Middle Pliocene Paraje Solo palynofloral is about mid-way between the calculated ~5° C cooling by 18,000 yrs B.P., based on the 18O/16O ratios and strontium evidence from Barbados corals, and the CLIMAP (Climate Long-range Investigation and Mapping Program) estimated of stable equatorial SST about as warm as at present.