A MECO RAIN FOREST/MANGROVE COMMUNITY FROM LAREDO, TEXAS

Deep sea drill cores bearing marine microfossils have provided the primary evidence for the Middle Eocene Climate Optimum (MECO). The MECO occurred during the early Bartonian Stage, 40 million years ago and lasted up to 600,000 years. The MECO began in Chron 18r and peaked during Chron 18n. Planktonic forams from zone P13 and nannoplankton from the upper half of NP16 are found in MECO deep sea cores. Records of MECO-age continental communities are rare. The late middle Eocene Casa Blanca community (TMM vertebrate locality 42486) is an exception as the stratigraphic layer it came from lies 32 meters above the Turritella cortezi zone in the Laredo Formation at Laredo, Texas. The T. cortezi zone allows biostratigraphic correlation between the middle portion of the Laredo Formation in northeastern Mexico and Laredo, Texas, and the Hurricane Lentil in the Landrum Member of the Cook Mountain Formation at Alabama Ferry on the Trinity River. Cook Mountain Formation planktonic forams come from zone P13 and its nannoplankton come from the upper half of zone NP16 indicating the Hurricane Lentil and the Casa Blanca fossils were deposited during the MECO event. Paleomagnetic analysis of a 30 meter-long core drilled near the Lake Casa Blanca spillway indicates that the Casa Blanca community remains were deposited during Chron 18n, approximately eight meters above the reversal from Chron 18r. The Casa Blanca community indicates the local climate supported coastal mangroves living adjacent to a lowland tropical rain forest and was home to a diverse tropical vertebrate community including the perissodactyls Amynodon advenus, Epihippus cf. E. gracilis & Notiotitanops mississippiensis. Rodents include Microeutypomys karenae, Pauromys simplex, Microparamys sp., & Mytonomys new sp. Primates include Mahgarita cf. M. stevensi, Mytonius new sp. and two unidentified omomyids. Plus an additional 20 mammal species. The aquatic community includes Crassostrea amichel, sharks & rays, Pterosphenus schucherti, plus crocodilians and turtles.