Abstract: The Use of Trend and Residual Mapping to Resolve Variations in Sedimentary Facies and to Delineate Pathways for Sand Transport

Anita M. Powers

Trend and residual mapping, most commonly used for structural analysis, can also be used for stratigraphic interpretation. Simple (first order) trend and residual analysis can be used to differentiate sedimentary environments, particularly

in cases where bypass of the middle to outer shelf is suspected.

Trend and residual maps were used to identify sand distribution pathways for the prolific Yegua Formation in Wharton and Jackson Counties, Texas. During sea-level lowstands, Yegua sediments bypassed the broad shelf and were deposited at the shelf edge. Net sand isopach and sand percent maps were used to delineate depocenters in the expanded downdip Yegua and the sandy inner shelf. However, the net sand and sand percent maps lacked the resolution to distinguish highstand deltaic deposition from lowstand incised valley fill where sediment bypass occurred. Trend and residual maps were used to delineate these depositional systems. Deltaic deposition was considered a wedge, with maximum values updip decreasing to zero at the shelf edge. Superimposed upon this wedge were incised valleys. Th deltaic wedge (trend) was subtracted from the net sand data and the resulting anomalous thicks (residual) were interpreted as incised valley fill. The residual maps were used to site strike oriented cross sections to examine stratigraphic details within the sediment transport conduits.

Trend and residual mapping requires a high density of well data to interpret depositional systems. The results, however, are quick and allow for concentration of areas more deserving of rigorous geologic analysis.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994