Contact Between the Catahoula and Oakville Formations in Grimes County, Texas

Contact Between the Oakville and Catahoula Formations in Grimes County, Texas

A study of the contact between two Tertiary formations, the Catahoula and the Oakville Formations was performed in Grimes County, Texas, near the city of Navasota. Twenty-two borings were drilled in the area to obtain the necessary information. Laboratory methods such as Sand-Silt-Clay analysis, Calcium Carbonate Content analysis, and X-ray analysis of the clays, were used to investigate and describe the cores obtained from borings. Three types of cyclic deposits were found in the cores, a sand cycle, a sand-clay cycle and a clay cycle. A relationship between the units of the cycles and the percentage of calcium carbonate was present in the cores. No abrupt change was noticed in the clay mineral composition of the Oakville and Catahoula Formations, but there was a slow change from one formation to the other.

The dip of the Oakville and Catahoula Formations was found to vary between 35 and 65 feet per mile. This variation is probably due to the nature of their depositional environments. Most of the Catahoula Formation was deposited on a coastal plain of low to moderate relief, and most of the Catahoula Formations detritus was deposited on large flood plains and in the channels of large meandering rivers. The Oakville environment of deposition is one of small braided streams. The climate during the deposition of the Catahoula Formation was humid. The sediment of the Oakville Formation is characterized by calcareous sand size material, and the sediment of the Catahoula Formation is characterized by non-calcareous clay size material. The lithologic units of the Oakville Formation are lenticular and discontinuous. The lithologic units of the Catahoula Formation are not as lenticular and are more continuous than the lithologic units of the Oakville Formation.

The contact between the Oakville and Catahoula Formations is difficult to recognize in some cases. The clay facies of the Oakville, which is very similar to the Catahoula clays, may be in contact with the Catahoula clays. The Oakville clay grades laterally into the typical sand facies of the Oakville Formation. Thus it is possible to map the disconformable erosional contact where the sand facies of the Oakville Formation overlies the Catahoula clays, and it is not possible to map the contact when the Oakville clays overlie the Catahoula clays. The age as generally accepted by geologic professionals of the Oligocene Epoch is from 35 million years BP to 23 million years BP. The Miocene Epoch is from 23 million years BP to 5 million years BP. Therefore, the disconformable erosional contact between the Oakville and Catahoula should be dated at least 23 million years old to15 million years old since the Oakville Formation is generally accepted to be mid-Miocene.




	Contact Between the Catahoula and Oakville Formations in Grimes County, Texas
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	Contact Between the Oakville and Catahoula Formations in Grimes County, Texas A study of the contact between two Tertiary formations, the Catahoula and the Oakville Formations was performed in Grimes County, Texas, near the city of Navasota. Twenty-two borings were drilled in the area to obtain the necessary information. Laboratory methods such as Sand-Silt-Clay analysis, Calcium Carbonate Content analysis, and X-ray analysis of the clays, were used to investigate and describe the cores obtained from borings. Three types of cyclic deposits were found in the cores, a sand cycle, a sand-clay cycle and a clay cycle. A relationship between the units of the cycles and the percentage of calcium carbonate was present in the cores. No abrupt change was noticed in the clay mineral composition of the Oakville and Catahoula Formations, but there was a slow change from one formation to the other. The dip of the Oakville and Catahoula Formations was found to vary between 35 and 65 feet per mile. This variation is probably due to the nature of their depositional environments. Most of the Catahoula Formation was deposited on a coastal plain of low to moderate relief, and most of the Catahoula Formations detritus was deposited on large flood plains and in the channels of large meandering rivers. The Oakville environment of deposition is one of small braided streams. The climate during the deposition of the Catahoula Formation was humid. The sediment of the Oakville Formation is characterized by calcareous sand size material, and the sediment of the Catahoula Formation is characterized by non-calcareous clay size material. The lithologic units of the Oakville Formation are lenticular and discontinuous. The lithologic units of the Catahoula Formation are not as lenticular and are more continuous than the lithologic units of the Oakville Formation. The contact between the Oakville and Catahoula Formations is difficult to recognize in some cases. The clay facies of the Oakville, which is very similar to the Catahoula clays, may be in contact with the Catahoula clays. The Oakville clay grades laterally into the typical sand facies of the Oakville Formation. Thus it is possible to map the disconformable erosional contact where the sand facies of the Oakville Formation overlies the Catahoula clays, and it is not possible to map the contact when the Oakville clays overlie the Catahoula clays. The age as generally accepted by geologic professionals of the Oligocene Epoch is from 35 million years BP to 23 million years BP. The Miocene Epoch is from 23 million years BP to 5 million years BP. Therefore, the disconformable erosional contact between the Oakville and Catahoula should be dated at least 23 million years old to15 million years old since the Oakville Formation is generally accepted to be mid-Miocene.