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Proximal features of thick-bedded sandstones in Eocene flysch sequence, Rih area, Chin State, Myanmar
- The Eocene flysch sequence, Rih area, Chin State, includes a number of thick-bedded, generally non-graded or poorly graded sandstones as well as normal graded sandstones (turbidites), laminated siltstones, conglomerates, and shales. Most of the thick beds occur in composite units up to 60 m or so thick, within which there is interfingering and inter-grading with thinner sandstones, and frequent amalgamation of beds. The composite units are separated by siltstone sequences, and in some cases at least appear to be large lenses. They are interpreted as being mainly channel deposits in submarine fan complex.Many of the thick beds are either structureless throughout or have only a thin division of flat lamination (with parting lineation) near the top, followed in some cases by ripple mark. Some beds, however, show unusual wavy lamination or “dish structure” beneath the flat lamination, and this in turn may be underlain by bioturbated sand/siltstone. Trace fossils of Scoliciaplana, Scoliciaprisca, Granularia, Spriophycus, Cosmorhaphe, and Chondritesare well developed. Narrow vein-like de-watering channels (elutriation columns) occur in the wavy-laminated division of some beds.The thick beds from a gradational series with the normal graded beds, and apparently represent the over-thickened basal parts of such beds, i.e., they are lateral variants of the normal turbidites. Similar beds called “sandy high-density turbidity current deposits” by Lowe (1982) also appear to be proximal turbidites. The origin of the wavy lamination and dish and pillar structures are deposited by the direct sedimentation of a coarse-grained high-density suspension.
Khin Khin Lin
- Universities Research Journal