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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 930

Last Page: 930

Title: Reflection of Topography on Pre-Cretaceous Unconformity Through Overlying Section in Central Alberta: ABSTRACT

Author(s): Douglas E. Glass

Article Type: Meeting abstract


Topographic highs and lows on the pre-Cretaceous unconformity of central Alberta are reflected as irregularities in the structure of overlying formations. In some places, the effects of large highs and lows can be seen directly on structure maps of the Cretaceous formations. For example, the Leduc reef chain, which itself is up to 1,000 ft (305 m) below the unconformity, causes anomalies in the structure of all overlying formations. The effect of the Leduc reef chain can even be seen in the present-day topographic surface through approximately 6,000 ft (1,829 m) of overlying sediment from almost every geologic environment. In many places, however, the irregularities on the unconformity are small and their effects are masked by the regional dip of the Alberta basin. They a so become more diffuse on the upper formations.

Trend surface analysis on the structure of the overlying formations removes the regional trend from the data so that the more subtle highs and lows can be recognized. They can be seen, not only as differences between positive and negative residuals, but also as relative highs and lows within areas of positive and negative residuals.

Advantages of using residual maps of the structure of Cretaceous formations to locate highs and lows on the pre--Cretaceous unconformity include: (1) showing that some structural and stratigraphic traps are a direct result of irregularities on the unconformity; and (2) illustrating tht despite limited well control to the unconformity, highs and lows can be mapped using the more numerous shallow-well formation top values.

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Copyright 1997 American Association of Petroleum Geologists