Reports: B8

48614-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

The progress that was made during the first year of this grant is in two areas, first is the field work that was accomplished and the second is the digital geologic, GIS database. Undergraduate students were involved in both of these endeavors.

This year was focused on Jamaica. I was fortunate to have Simon Mitchell of the University of the West Indies in Mona as my guide. Simon is the premier geologist in Jamaica, and has extensive field experience of all parts of the island and, in particular, the Cretaceous geology. Simon is also a paleontologist, and recently had a doctoral student finish work on the Cretaceous rocks of the island, including ostracodes. So, Simon knew exactly where to take me to collect for Late Cretaceous ostracodes.

The first field trip was conducted during Thanksgiving week (last full week in November). For this first field trip, I thought it was best to go by myself and check out the conditions, logistics, etc. We spent Nov. 24-26 in the field collecting samples, and the 27th was spent packaging the samples and shipping them to the USA.

The first day was spent in the central part of the island, at the Central Inlier, which is the largest area of Late Cretaceous rocks in Jamaica. Almost all of the samples were collected from the late Maastrichtian Guinea Corn Formation. The second day was at the St. Ann's Great River section near the northern coast in the St Ann's Great River Inlier, which is a highly expanded section of Turonian to late Campanian marine sediments. The third day was spent collecting from the Thomas River Formation (mid-Maastrichtian), the Guinea Corn, and the Peters Hill Limestone (early Campanian). In all, 21 samples were collected. Unfortunately, U.S. Customs destroyed 2 of the samples, thinking they were soil samples. Of the remaining 19 samples, nearly all are richly fossiliferous and contain abundant ostracodes.

The second field trip was during Spring Break (March 24-26 in the field). This time, 2 students accompanied me. One student was Jonathon Riddle, who is our last geology major (the geology major was phased out). The other student was Amanda Moody, who had finished all of the course requirements for a minor in geology. It was a great experience for these students, as they were able to see complex geology, learn from an excellent geologist, and visit a foreign, third-world country. The students were of great assistance in collecting the samples, carrying them in the field, and bringing them back on the airplane. This time, less material was collected for each sample (approximately 2 kg instead of 5), so we could bring them all on the airplane back with us. Fourteen samples were collected on this trip. We focused on areas that had not been visited during the first trip, including Pindar's River in the Central Inlier (more samples of Guinea Corn, but this time in more sandy facies), the Jerusalem Mountain Formation in the Jerusalem Mountain Inlier near the western end of the island, the Woodlands Formation in the Maldon Inlier in northwestern Jamaica, the Shaw Castle Shale at the western end of the island, and the Cretaceous in the Seven Rivers area south of Montego Bay. This second day required that we stay overnight in Montego Bay in the northwestern part of the island. This was excellent, because Simon spent considerable time with us that evening explaining his ideas about the tectonic evolution of Jamaica and the Caribbean.

Almost all of the samples from the Guinea Corn have yielded a very abundant and very distinctive fauna that differs significantly from ostracodes in coeval deposits in the other islands of the Greater Antilles. This indicates that significant faunal barriers existed between these islands that prevented migration. It was discovered that many of the Maastrichtian fossils, including corals, decapods and rudistid bivalves, of Chiapas, Mexico, are similar or identical to those in Jamaica and appear to be endemic to this localities. This distribution has important plate tectonic significance, indicating that Jamaica and the Chiapas region were connected during the Maastrichtian and have since separated. There is, in fact, a mechanism to accomplish this: the Cayman Trough. If the translateral motion along the trough is reversed, there is sufficient motion to bring Jamaica back to the Chiapas region. Therefore, a field trip is now planned for this Thanksgiving to go to Chiapas and collect samples.

The other area of significant development is with regard to the GIS-based geologic map of Jamaica. A student, Courtney Kelly, who is certified in GIS, worked during the Fall and Spring semesters to develop that map. This was a great learning experience for the student because, as we came to discover, there was no digital geologic map of Jamaica, so it had to be constructed from scratch. The first phase of the project was spent trying to locate any digital geologic map of Jamaica, and included Courtney contacting geography faculty at the University of the West Indies. After extensive research, she discovered that no such map existed, so she had to digitize the most recent (1984) geologic map. This effort took considerable time, as each formation was digitized on a separate layer. There are sixty layers of formations and structural features on the map. This digital map will be very useful for publishing and reporting on the results of the investigation.

The efforts for the coming year will include:

1.      the field trip to Chiapas, Mexico; one student will accompany me on that trip;

2.      hire a student who will help me process and pick the samples;

3.      hire another student who will work on the GIS components of the research (the Chiapas geology);

4.      imaging the best specimens on an SEM;

5.      corroborating with colleagues on the taxonomy of the ostracodes;

6.      begin writing the descriptions of the new species

7.      make arrangements to return to Cuba to collect more material that contained ostracodes observed in 2001.