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Surface Geology

Competency Statement:

Identify geologic units and structural elements on a surface geologic map. Demonstrate the use of geologic cross sections to tie these surface features into the subsurface.

Learning Objective:

  • Demonstrate ability to read surface geologic maps.
  • Understand various geologic cross-section preparation techniques and factors to evaluate the relationship between the surface geology and the subsurface geology.
  • Locate a particular rock unit and define the geographic distribution of that rock unit on a surface geology map.
  • Use outcrop descriptions from a stratigraphic column to interpret rock units on a geologic map.

Assignment Instruction:

As a Geologist in the New Ventures Team for Beta Exploration, Inc., your assignment is to evaluate new hydrocarbon exploration opportunities in the Eastern Venezuela Basin (see Location Map). Use the surface geologic map, geologic cross section and stratigraphic column provided in References and Field Data to interpret the surface geology and tie it into the subsurface. This information will aid in understanding the stratigraphy, structure, and petroleum system.

The studied area is located at the southern flank of the eastern Serrania del Interior (see Location Map). The surface geologic map shows the geographic distribution of the Cretaceous sedimentary rocks that outcrop in the area. The map was drawn using outcrop information, topography, and aerial photography.

The Cretaceous stratigraphic section consists of the Barremian to Albian age Barranquin, Garcia and El Cantil Formations and the Campanian age San Antonio Formation:

The Barranquin Formation consists of coarse grained quartz sandstones, siltstones and shales of fluvial-deltaic environments that interbed with fossiliferous limestone towards the top.

The Garcia Formation represents a rapid deepening of the environments, as well as deposition of 90 meters of dark, calcareous, highly fossiliferous shales.

The El Cantil Formation is characterized by a shallowing trend of marine limestones and sandstones with carbonaceous shales.

The San Antonio Formation is in fault contact with the Barranquin, Garcia and El Cantil Formations in the southern geologic map area.

Geologic cross section A-B presents the stratigraphic and structural configuration of the Early Cretaceous Formations on a west to east topographic profile across northern geologic map area.

The characteristic shaly and fossiliferous lithology of the Garcia Formation represents the maximum marine transgression for the Early Cretaceous of Eastern Venezuela and is a potential source rock. The stratigraphic column is located east of Pico Garcia where the type section of the Garcia Formation outcrops in a continuous manner (see Geologic Map).

Location Map for Eastern Venezuela Basin and Serrania del Interior range

 Relative location map Venezuela Eastern Basin