PATTERNS OF DISPLACEMENT ALONG BOUNDARY FAULTS: IMPLICATION FOR BASIN EVOLUTION IN NAKHON BASIN, GULF OF THAILAND

Abstract

Nakhon basin is located in the western portion of the Gulf of Thailand. The northern part of the basin is oriented NW-SE and the southern part is oriented N-S. The rifting started in  Eocene?/Early Oligocene along NW-SE oriented faults. According to displacement-distance (D-d) profiles, the Western Boundary fault displays three individual fault segments and Eastern Boundary fault displays two segments. These are also indicated by the distinct strikes of fault segments, the abrupt decrease in throw and strata thickness from depocenters to their tips and the location of transverse anticline. Sedimentation was controlled by main Western Boundary fault and Eastern Boundary fault until Late Oligocene. Thermal subsidence may play role during Early Miocene to Middle Miocene. Inversion anticlines were observed along Eastern Boundary fault of the northern part of the Basin. This local feature is interpreted as being caused by compression at the tip of the oblique-striking fault segments due to oblique extension with a dextral left stepping compression. Extensional fault systems in study area were influenced in a number of ways by oblique pre-existing fabrics as indicated by oblique orientation of intrabasinal faults and zigzag pattern of regional faults. This influence of preexisting fabric is associated with Three Pagoda Fault zone which is cross cutting the study area.