Abstract

• The Mann anticline occupies the northern part of the NNW-SSE trending first line of anticline structures known as Minbu-Htaukshabin-Tagaing-Chaungtha structural line which develops on the east flank of Salin Basin. It expresses on surface as anelongated, asymmetrical north plunging fault related anticline where Irrawaddian, Kyaukkok, Pyawbwe, Okhmintaung and Padaung formations as core were exposed and the northern plunging area of which is mainly covered by alluvium and Irrawaddians. Present study revisited the interpretations of gravity and dense seismic data and well to well correlations, as a result proposes a new light on the development and evolution of Mann anticline. From the gravity data it can be assumed that the northward plunge continues in the subsurface up to the latitude 20° 18′ about 8 miles from outcrop area; the anticline is intersected by two longitudinal faults, one on the western and the other on the east limb, and there exist a E-W transverse fault at latitude 20° 15′. The seismic images of the anticline suggest that Mann anticline is a strike slip fault related inversion anticline of positive flower shape bounded by west hading high angle fault zone on the east limb and syn-inversion antithetic faults on the west. The anticline is broad with gentle flanks in the north and the core of the anticline nose narrows to the south with steepening flanks. The structural analysis of the seismic data led to the conclusion that two phases of structuration took place in Minbu area. The first phase was E-W compression in Late Oligocene and formed proto Mann anticline with a NNW-SSE trending oblique longitudinal normal fault along the crestal portion. The second phase is the dextral strike slip faulting initiated from Pliocene and continues to recent which caused inversion of the existing structures resulted in current positive flower shape configuration of Mann anticline. Over 600 wells were drilled on the Mann anticline to date and the well to well correlations confirmed existence of cross and oblique normal faults and longitudinal reverse faults which have effective sealing potential and compartmentalizing the anticline into numerous oil pools. The Sabwet Chaung indicated by gravity low anomaly is a zone of high angle conjugate normal faults dipping towards each other and separated Mann anticline from Htaukshabin Anticline. It may possibly has an active strike slip component and forming a passage through which the clay intermingled with water and gas seeps to the surface as small mud volcanoes at Nagapwet Taung.