Geological Structures of the Kinta Valley Revisited Using Drainage Anomalies

Abstract

More than 50 % of the surface of Kinta Valley is covered by alluvium overlying Paleozoic sequences and Late Triassic granitic intrusions. The alluvium of the valley is thin (mostly less than 30 m thick). Limestone and shale are the dominant lithologies cropping out in the valley, and they have been severely deformed. Unfortunately, these rocks are restricted to small areas of the valley and they are highly weathered, thus making the correlations between outcrops and structural interpretation commonly speculative. In this paper, we make use of drainage pattern anomalies of rivers, streams, and dry thalwegs that commonly reflect subsurface structures or variation of thickness of sediments and may help regional interpretation. Two main anomaly sets have been identified; NE–SW and N–S. These anomalies might reflect slight or large normal faults, and they formed sigmoid-shaped structure after interpolation. Three hypotheses are proposed to illustrate the extensional process in terms of reactivation of faults, transtension, and shear partitioning. Shear partitioning is most likely to occur by distributing the oblique extensional stress into normal faults and strike-slip faults. The valley is shallower and narrower to the north, suggesting more intense shortening than in the southern part. Both shortening by thrust faults and subsequent extension may be rooted in the lower ductile crust beneath the large granitic plutons.