Mawdin Fm

Irrawaddy River Delta, type section at Mawdin, Pagoda Point (15° 57′ N, 94° 15′ E) (Than Tun et al. 1973). [Original Publication: Barber, A. J., Khin Zaw & Crow, M. J. (eds) 2017. Myanmar: Geology, Resources and Tectonics. Geological Society, London, Memoirs, 48, 219–260]

[Figure: Map showing location of sub-basins of the Central Myanmar Basin (after Myint Thein and M. Maung 2017)]

Clayey sandstone. This Fm, interspersed with exotic blocks, is generally made up of strongly deformed and folded very hard shales, intercalated with sandy beds, well-bedded sandstones, thinly bedded siltstones, some grits beds and thin tuffaceous sandstone beds. It is locally divided into basal, middle and upper parts, based upon lithological features. Lower part has a basal conglomerate 1–2 m (4–6 ft) thick, grey brown to chocolate brown, hard, bedded to cross-bedded, poorly sorted, sub-angular to subrounded clasts, composed of serpentinite, basalt, reworked pebbles of quartz, sandstone and hard shale pebbles in a sandy matrix. This is followed by ash-grey light brown sandstones, hard, well-bedded, medium to coarse grained, poorly sorted, sub-angular to subrounded clasts, composed of quartz 20%, feldspar 30%, rock fragments 40% in a silty matrix, and intercalated with thin sand and shale beds. Shale beds are ash grey, orange brown, very hard and thinly laminated. Middle part is developed as thick-bedded sandstone sequences, gradually passing into an alternating sequence of shale, tuff and dark grey limestone lenses. Upper part is well exposed in the type section, and consists of hard to very hard light ash-grey to dark brown shale beds, intercalated with gritty sandstones, sandstones, siltstones and some tuff-bearing sandstone beds. It is of thickness 2620 m (8600 ft).

This Fm is laterally widespread, deposited in a predominantly deep-water environment of submarine fans, spreading into abyssal mud in the Late Eocene.