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The Freeport Rocks, a linear trend of isolated, submerged rock pinnacles about 6 mi offshore from Freeport, Texas, were studied by SCUBA diving, petrographic techniques, and carbon-14 dating. They have been interpreted previously as a relict beach which developed about 30,000 years B.P.
The present study indicates the environment of deposition was an offshore bar or barrier island composed predominantly of reworked material from the underlying Beaumont Formation. Diagenetic features include cementation by low-Mg calcite (in the form of druse and blocky cement) and inversion of aragonite shells to low-Mg calcite. The diagenetic features suggest that the deposit subsequently was exposed subaerially and cemented by low-Mg calcite. Because much of the original shell material was neomorphosed during diagenesis, carbon-14 age determinations may not give the age of the deposit. Thus carbon-14 dates were interpreted in light of the neomorphism and suggest that deposition of the Freeport Rocks was less than 15,857 ± 268 years B.P. This information, combined with data fro various eustatic sea level curves, strongly suggests that the Freeport Rocks were deposited during the still-stand of the transgressing Holocene sea between 7,500 and 8,200 years B.P.
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