Paper No. 5-2
Presentation Time: 8:00 AM-12:00 PM
FLORIDA WELL REVEALS NEW BASEMENT ORIGINS AND CONNECTIONS TO GONDWANA
The COST No. GE-1 well is located off the east coast of North Florida within the Southeast Georgia Embayment. It extended 13,254 ft (4,040 m) in depth, with cuttings being collected at ten foot intervals. U/Pb dating was performed on zircons extracted from cuttings at intervals from 9,560 ft to 13,230 ft. The cuttings were washed, crushed, and separated using heavy liquids, hand-picked and mounted in epoxy. Samples within 8,630 – 10,870 ft, 8 sample intervals, produced an average of 61 zircons per sample. Samples between 11,250 and 13,130 ft, 3 sample intervals, produced between 1 and 6 zircons. A total of 493 zircons were analyzed by laser ablation on a multi-collector ICP-MS. Zircons < 1000 Ma were <5% discordant and paired with the Pb-208/U-238 age. Zircons >1000 Ma were <10% discordant and paired with the Pb-207/Pb-206 age to evaluate the effects of common Pb. All samples’ ages ranged from 163 Ma to 3287 Ma with concentrations at 522 Ma, 603 Ma, 2087 Ma and 2168 Ma. These groupings suggest this part of the Florida basement has origins in Gondwana. Only three zircons showed ages in the 163- 266 Ma age range. The next youngest age shown is 400 Ma. After 2820 Ma there are 6 zircons with ages between 3084 Ma and 3287 Ma. The COST GE-1 ages give new information on the composition of the Florida Basement. Samples from the Suwannee Terrane (Alachua County, Florida) have concentrations around 576 Ma and 2125 Ma similar to the COST GE-1 samples; however, the COST samples also contain concentrations around 1000 Ma which are not present in the Suwannee Terrane samples. A majority of the ages show a correlation of the Suwannee Terrane and the Bove Basin (West Africa). Containing similar ages from both basins the COST GE-1 well gives insights into the location of the Florida basement and its placement in Gondwana.