Abstract: Integration of Sedimentology, Paleontology, and Structural Geology in Petroleum Exploration, Rocky Mountain Region

Mitchell W. Reynolds

Petroleum exploration in the Rocky Mountain region has advanced from the early recognition of structural traps having surface expression to identification of subtle buried stratigraphic and structural traps by means of the progressive integration and application of sedimentology, paleontology, and structural geology.

Principles of sedimentology in combination with a growing collection of stratigraphic observations are applied to define geometries of rock bodies and to provide a basis for interpreting environments of deposition and for reconstructing topography that influenced not only sedimentation but also the migration and accumulation of petroleum in depositional basins. From such interpretations, facies changes are being predicted by combined subsurface geologic and geophysical techniques. Examples from detrital-clastic strata of Cretaceous age in Wyoming and from Paleozoic carbonate rocks of Montana and the Dakotas illustrate applications of the principles.

Paleontology first provided a relative framework by which strata and geologic events during Phanerozoic time could be correlated from place to place. Refinement of that time framework, using a variety of fossil taxa, now permits more precise correlation of rock units and recognition of geologic events of shorter duration than previously possible. Combined with sedimentation, paleontology has helped establish environments of deposition, paleoclimates, hiatuses, and datum surfaces by which depositional topography can be recognized. Paleontologic data keyed to radiometric ages have extended application of an absolute chronology to sedimentary basins, with the result that rates of deposition, erosion, subsidence, uplift, transgression, and regression can be established. The stratigraphic aleontology of macrofossils, microfossils, and trace fossils in Cretaceous and Tertiary rocks provides an excellent example of the contribution of paleontology to exploration in the Rocky Mountain region.

Surface mapping and seismic surveys have delineated structures and structural styles in the Rocky Mountains. Mechanics of development of the structures are better understood through the application of deformation theory and model studies. Paleontology and radiometric age determinations have contributed to structural studies by refining knowledge of the time and rate of structural movements. Examples from Paleozoic and Mesozoic strata in the southern and central Rockies demonstrate that structural movements have been recurrent and have affected sedimentation at several scales. Resulting facies variations or thickness changes have strongly influenced petroleum generation, migration, and accumulation.

Continued integration and application of the disciplines will ensure that frontier areas will be explored successfully and producing areas developed fully in the decades ahead.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA