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Figure 5. Continued. (B) Time-structure map of top Oli- gocene unconformity (MB2). The overall structure is similar to that of MB); however, the number of faults cutting MB2 in the Cuu Long Basin is significantly decreased compared with the number in the acoustic basement, constraining the main phase of active rifting in the basin to the early Tertiary (approximately Oligocene). Continued.
Son Basin. These high-amplitude reflections are interpreted as carbonate buildups. Middle to late Miocene carbonate complexes have been penetrated by exploratory wells drilled in the structural highs in the eastern Nam Con Son Basin (Matthews et al., 1997; Dien et al., 1998). The Mia 1 well also encountered about 200 m of Miocene carbonates.
Very few faults intersect MB3 in the Cuu Long Basin, indicating almost complete cessation of tectonic
movement in the Cuu Long Basin before the late Miocene. Some northeast-trending and north-trending faults, however, cut MB3 in the Nam Con Son Basin, suggesting continued rifting and extension. These faults, however, are more or less restricted near the Con Son swell and in the eastern Nam Con Son Basin, suggesting a significant decrease in faulting during the late Miocene. The displacement of these faults in the southwestern Nam Con Son Basin is less than 0.15 s
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