Print this pageGEOLOGICAL MISCELLANEOUS - 16
RECENT DEPOSITIONAL ENVIRONMENTS AND THE
PRINCIPAL SAND FACIES OF THE NORTHWESTERN
GULF OF MEXICO*
* Appreciation is expressed to Shell Oil Company, AAPG, and Rufus J. LeBlanc, Sr., for their respective efforts, and permission, in regard to publication of this classical report on clastic sediments.
BY
H. A. BERNARD, C. F. MAJOR, AND B. S. PARROTT
The northwestern Gulf of Mexico and adjacent coastal plain together comprise a geological laboratory containing many natural-scale environmental models in which clastic sediments have been and are being deposited. These clastic facies are representative of much of the geologic column.
The characteristics and interrelationships of the sand facies to the other associated facies should provide a basis for a better understanding of the occurrence and prediction of hydrocarbon reservoirs.
The regional framework of sand bodies of related and different environments, as seen in the Recent and late Pleistocene depositional environments of the Gulf Coast area, provides a strategic model which may be employed in the exploration for hydrocarbons. The relationships of the genesis and shape of an individual sand body with its directional features should aid in the tactical search for oil and gas.
The criteria for recognizing these facies are briefly summarized. The combined sequence in sedimentary features, grain size, sorting, fauna, and flora, and also the geometry, associated facies, geological framework, and setting may be used to identify sand bodies similar to those formed in the northwestern Gulf of Mexico.
In many cases, the SP log should be an important tool in determining the generalized sequences in grain size.
In order to employ directional features such as cross bedding and grain orientation in the prediction of a sand trend, it is necessary to have a thorough understanding of the relationships between the directional features and the genesis, geometry, and framework of a similar Recent sand model.
The Recent is a key to the past, for it furnishes the geologist with environmental models with which he can better understand and predict the occurrences and trends of potential hydrocarbon reservoirs. From the study of Recent depositional environments he gains a knowledge of the geometry, sequence, and framework of sedimentary facies which should enable him to better understand older rock facies. In the search for oil and gas, the strategic phase will be furthered by a better understanding of the occurrence of hydrocarbons as related to the framework of older rock facies -the tactical phase, by a knowledge of the relationships between the trends and directional features of individual sands, as determined from the study of Recent environments.
