Reports: B848614-B8: Tectonic Evolution of the Caribbean Basin and Gulf of Mexico: Constraints from the Paleobiogeography of Greater Antillean Late Cretaceous Ostracodes

Terry Markham Puckett, University of North Alabama

This is the final report for the ACS-PRF grant entitled, “Paleobiogeography of Greater Antillean Late Cretaceous Ostracodes: Implications for the Evolution of the Earth-Life System in the Caribbean Basin and Gulf of Mexico.” This is year four of the grant, which had been extended an extra year because there were funds left over at the end of year three.

During the course of this research program, five students were hired to take part in essentially all aspects of the research, from collecting the samples in the field to washing the samples, picking and cleaning specimens, and preparing maps for publication. These students include Courtney Kelley, a geography major who digitized the geologic map of Jamaica; Bradley Arnett, who was our last geology major and assisted me in the field in Mexico and spent a great amount of time washing and picking the samples; Gable Palmer, a geography major who assisted in plotting the sample localities for the geologic map of Jamaica and started digitizing parts of the geologic map of Cuba; Robert Evan Smith, a geography major who digitized part of the Cuba geologic map; and Amy Jordan, who worked for me for a year washing and picking the samples from Cuba. Two other students, Jonathon Riddle and Amanda Moody, who were geology majors and minors, respectively, assisted me with field work in Jamaica. All of these students except one have now graduated. These students received a total of $16,236 stipend for their assistance.

Much of the micropaleontological work conducted during this research is very labor intensive, requiring many hours of washing the samples, often repeatedly, and picking them. Samples that contained well-preserved microfossils were picked in their entirely, or at least the entire samples were scanned and the best specimens were picked. This often resulted in many picked specimens from which information such as species’ variability, sexual dimorphism, and ontogeny could be observed. For the Jamaican samples, for example, more than 5000 specimens were picked. For these reasons, many of the results of the research are still being prepared for publication.

The time spent on the project this year was largely focused on two tasks: preparing a manuscript describing the new species from Jamaica and picking the specimens from the samples from Cuba. The manuscript of the Jamaican samples has gone very well. I decided to collaborate with a colleague from France, Jean-Paul Colin, on the ostracode descriptions. Jean-Paul is one of the leading researchers on Cretaceous ostracodes, and has been publishing on them since the 1970’s, so his input was very valuable. After extensive discussions on the taxonomy and classification, we finally named and described twenty-five new species and three new genera of ostracodes, essentially all from the latest Cretaceous. Simon Mitchell, my guide in Jamaica, collaborated on the section on geology and stratigraphy of Jamaica. The manuscript turned out to be more than 100 pages of text, plus sixteen plates, and will hopefully be published as a supplement (special issue) of the journal Micropaleontology. Both of the anonymous reviews have been completed and were quite favorable. The final version of the manuscript was accepted for publication on September 26, 2012. As mentioned in previous reports, one of the most significant results of the study of the Jamaican ostracodes is that they are similar to a fauna collected from the Maastrichtian Ocozocoautla Formation of Chiapas, southern Mexico. With these observations, in addition to those of the paleobiogeographic distribution of large benthic foraminifera, rudist bivalves and corals, indicates that Jamaica was attached to southern Mexico during the Late Cretaceous, only moving relatively to the east since the early Eocene. These are the kinds of observations for which the grant was originally sought.

Data collected from Jamaica also helped in the preparation of a manuscript that was published in Micropaleontology.This paper demonstrated that, while many ostracodes are similar externally, some groups display systematic differences in muscle scar patterns that correlate to geography. In other words, study of the muscle scar patterns can lead to improved recognition of genera and more refined uses in plate tectonic reconstructions. A talk was presented at the Southeastern Section of the Geological Society of America meeting in Asheville, NC this past spring, and an abstract on the new ostracodes has been accepted for the GSA Annual Meeting in the Charlotte this fall. In all of the publications, acknowledgement was given to ACS-PRF for funding the research.

The samples collected from Cuba turned out to be very difficult in terms of washing and of the lack of abundance and quality of preservation. Many of the samples turned out to be barren and several of the samples required special treatment to break them down. This treatment was that of Lirer (2000, A new technique for retrieving calcareous microfossils from lithified lime deposits: Micropaleontology, v. 46, no. 4, p. 365-369), which involves soaking the sample overnight in glacial acetic acid, sieving the sample, then cleaning in an ultrasonic bath for several hours. This treatment worked very well for the sample from the Peñalver Formation, from which many ostracodes were picked. The last of the samples bearing ostracodes will be picked within the next few weeks. In the meantime, my guide from Cuba, Leidy Peñate Menéndez, will be coming the University of North Alabama to use the scanning electron microscope to image the planktonic foraminifera collected from the same samples as those for the ostracodes. The commonality of the samples ensures that the ostracode samples will be assigned directly to specific planktonic foraminiferal zone. The images of both the planktonic foraminifera and the ostracodes will hopefully enable two manuscripts to be prepared, one in English focusing on the ostracodes and another, possibly in Spanish, focusing on the foraminiferal biostratigraphy.

The American Chemical Society-Petroleum Research Fund is sincerely thanked for funding this research program.