ABSTRACT

Study of the Freeport Rocks, a linear trend of isolated, submerged rock pinnacles about 6 miles offshore from Freeport, Texas, was conducted through the use of SCUBA diving, petrographic studies, and carbon-14 dating. The Freeport Rocks have previously been interpreted as a relict beach line developed about 30,000 years B.P. The present study determined that the environment of deposition was that of an offshore bar or barrier island which was composed of predominantly reworked material from the underlying Beaumont Formation. Diagenetic features found in the samples are cementation by low-Mg calcite cement (in the form of druse and blocky cement) and inversion of aragonite shells to low-Mg calcite. The diagenetic features indicate that this bar deposit was subsequently subaerially exposed and cemented by low-Mg calcite. Because much of the original shell material was neomorphosed during diagenesis, carbon-14 age determinations can not be accepted blindly. The ages obtained by carbon-14 dating were interpreted in light of the neomorphism and indicate that the age of deposition of the Freeport Rocks was less than 15,857± 268 years B.P. When this information is combined with the information from various eustatic sea level curves, it shows that the Freeport Rocks must have been deposited during the stillstand of the transgressing Holocene sea between 7,500 and 8,200 years B.P.