Action Learning Module Information       Close

Competency Statement:

Use plant and animal fossils from well cuttings, cores or outcrops to differentiate rock units, determine the ages of the units, and infer the sedimentary depositional environment.

Learning Objective:

  • Identify the different groups of microfossils used in biostratigraphy.
  • Infer sedimentary depositional environments of sediments based on identification, classification, and occurrences of microfossils.
  • Use microfossils for estimating the ages of rock units.
  • Demonstrate the use of microfossil abundance and diversity charts.
  • Use microfossils to correlate rock units between wells.

Assignment Instruction:

Beta Exploration Inc. is planning a bid for a new block in a basin. As a member of the exploration team, your role is to analyze the biostratigraphic information available from four wells in the area. You will integrate the biostratigraphic analysis with well-logs and seismic profiles near the block.

This exercise begins with biostratigraphic analysis by examination of microfossils. Several groups of microfossils help to estimate the ages of rock units through biostratigraphy and to interpret sedimentary depositional environments.

Biostratigraphic units (biozones) were inferred from first occurrences of microfossils down hole in each well. The ages were assigned using the zonal schemes from the area. The accompanying charts with equivalent zonal schemes will enable you to build a biostratigraphic correlation of the 4 wells.

Microfossil indicators of depositional environments allow interpretation of biofacies changes through the stratigraphic section. You will make a paleoenvironment map of the area.

The integration of biostratigraphy with other geological disciplines, such as geophysics, sedimentology, petrophysics, and geochemistry facilitates sedimentary basin analysis and petroleum exploration. This is essential for planning and developing favorable petroleum prospects.

The Chronostratigraphic chart is from 'Chronostratigraphic equivalence of the palynological zonations for northern South America and Venezuela' (modified from Lorente and others, 1997) and contains ages of stage boundaries (in Ma) according to Haq and others (1987) and Berggren and others (1995).

A chronostratigraphic correlation between the wells using biostratigraphy allows interpretation of maximum flooding surfaces (mfs) in well 4 and their association with important chronostratigraphic species (bioevents) and global sea level curves.

Base map with wells

Base map with wells

Chronostratigraphic chart

Chronostratigraphic chart