ISSN 2319-8885 Volume.08, Jan-Dec-2019, Pages:434-437 www.ijsetr.com Stratigraphy And Sedimentation of Shinmataung Area, Yesagyo Township, Magway Region, Central Myanmar 1 2 HNIN HTWE HLAING , KO KO GYI 1Dept of Engineering Geology, Mandalay Technological University, Myanmar,Email: [email protected]. 2Dept of Engineering Geology, Pakokku University, Myanmar, Email: [email protected]. Abstract: This paper described the geology and stratigraphy of the Shinmataung area, Yesagyo Township, Magway Region. It includes the study of lithology, sedimentary structures, stratonomic characters and fossil evidences. The main builders of the study area are clastic sedimentary rocks such as sandstone, siltstone and shale of different composition of clastic particles. In accordance with the stratigraphic classification, the rock units of the study area are classified and nominated as Shwezettaw Formation, Padaung Formation and Irrawaddy Formation. Shinmataung is a kind of folded mountain range trending nearly NNW- SSE direction. All strata are dipping towards East with an average inclination angle of 30°. On the basis of faunal content the exposed rocks are ranging in age from Oligocene to Pliocene (38 – 2 million years). This research enlightened the depositional environments of the study area is interpreted as shallow marine tidal environments to fluvial environment. Keywords: Shinmataung, Folded Mountain Range, Sandstone, Siltstone, Shale, Shallow Marine, Fluvial Environment. I. INTRODUCTION II. METHODS OF STUDY This work, geological investigation is mainly concerned This work is mainly occupied on the geological field with the field observation and identification of each rock observation and structural interpretation. Laboratory works units. Bedding thickness, mineral composition, grain sizes, concerned with the petrographic analysis, grain size colour and salient depositional structures are good indicators distribution, primary depositional structural implication and for the interpretation of depositional environments and fossil identification of both megascopic and microscopic geological history of the study area. As the study area is application. Literature survey was also taken thoroughly for situated in the Central Dry Zone and lack of dense the better understanding of the Regional Geologic Setting vegetation cover, the exposed rock layers are observed as and Previous works related to the study area. convenience as possible. The location map of the study is shown in Fig. 1. The main objectives of this work are to A. Regional Geologic Setting draw a geological map and to classify the exposed rocks Geomorphologically, the study area falls in the Central with an emphasis on the lithology, stratigraphy, depositional Cenozoic Belt or Central Low-Land of Myanmar. structures and faunal contents. Tectonically, it lies in the northeastern edge of the Minbu basin. The general structural trend of the area is NNW- SSE. In accordance with the million-scaled Geological Map of Myanmar (1977) Fig 2, Shinmataung is composed essentially of Oligocene sediments (Lower Pegu Group and its equivalents). On the both flanks of Shinmataung range are covered with Mio-Pliocene sediments (Irrawaddy Formation and its equivalents). Khin Maung Htun (1993) proposed that the massive sandstones of Shinmataung are equivalent to Shwezettaw Formation of Early Oligocene and the western side of Shinmataung is covered by the clay or shale dominant unit which is equivalent to Padaung Formation. West and southern parts of the Shinmataung range are covered by volcanic rocks of different composition as the study area lies on the Central Igneous Line of Myanmar (Maung Thein, 2000). Fig 1. Location map of the study area. Copyright @ 2019 IJSETR. All rights reserved. HNIN HTWE HLAING, KO KO GYI extrusion of the Sonetaung olivine basalt flow was probably the last phase of volcanic action in the Shinmataung area (Khin Maung Htun, 1993). Freshly exposed very angular blocks of basalt and its flow patterns indicate that the manifestation of volcanic activities at Sonetaung could possibly be the latest of all eruptions (Ko Ko Gyi, 2012). The present work is the first to describe the stratigraphy of the Shinmataung area. III. STRATIGRAPHY The study area is situated on the north eastern part of the Minbu Basin. This basin is a type of gradually sinking basin filled with clastic sedimentary rocks of enormous thickness. They are mainly shale, siltstone, grit and conglomerate of various compositions. In this paper, the observed rock units are named as Shwezettaw Formation, Padaung Formation and Irrawaddy Formation as an ascending order. The Fig 2. Regional Geological Map of the study (source observed rocks are descrived in this paper with emphasis on Geological map of Myanmar, 1977). the lithology and faunal contents. Structurally, Twindaung, Shinmataung Fig 3 and Popa area A. Shwezettaw Formation are falling in the same line, trending nearly NNW-SSE This unit is composed mainly of yellowish brown, hard direction. According to Maung Thein (2000), renewed and compact sandstone intercalated with pinkish brown volcanism (mainly andesites and basalts) took place along siltstone. This formation is the oldest unit of the study area. the Central Igneous Line, e.g. Mt. Popa and Twindaung. On the basis of lithology it is divided into two sub-units of member rank namely Lower and Upper member. B. Padaung Formation This formation is composed mainly of thin-bdded, grey to light grey shale. This formation is said to have a clay dominant unit with fairly rich fossils of shallow marine environment. This faunal assemblage indicated the middle Oligocene epoch. C. Irrawaddy Formation This formation is composed mainly of coarse-grained, gritty sandstone. The upper part of this formation is overlain by pebbly sandstone, friable sand and silt inter-bedded unit. Silicified fossil woods are the most prominent materials of this unit. In some localities, thick-bedded sandstone interlayered with clay and red ferruginous pebble conglomerates are observed as an indicator of fluvial condition. IV. RESULTS AND NEW FINDING This paper distinctly illustrated and described the lithology Fig3. Picturesque view of Shinmataung range. and stratonomic characteristics of the rock units of the study area. Salient lithologic criteria, beddings, sedimentary B. Previous Works structures and collected fossils are expressed with Pascoe, 1964, stated that some of the volcanic rocks of the photographs, table of stratigraphic sequences and table Shinmataung area are of later age, but some at least are showing the correlation with established units. contemporaneous with the Pegu rocks. The Central Burma Belt may be considered as post-orogenic sediments and the A. Shwezettaw Formation lithologic associations, stratigraphic characters and Lower member of this formation is characterized by buff sedimentary structures indicated that these sediments were to yellowish brown, thick-bedded to massive, medium- to intra-continental mollase (Myint Thein, 1981). Bender, coarse-grained, hard and compact sandstone. Primary 1983, stated that the west zone of “Pegu- Mt. Popa line” sedimentary structures observed are ripple marks, cross- begins south of Kabauk village in the Shinmataung area. bedding, convolute lamination, slump structures, ball and During Miocene to sub- Recent time, five episodes of pillow structures. Upper member is composed essentially of intermittent volcanic activities have been recognized, The thin- to medium-bedded siltstone and purple shale Fig 4. International Journal of Scientific Engineering and Technology Research Volume.08, Jan-Dec-2019, Pages: 434-437 Stratigraphy And Sedimentation of Shinmataung Area, Yesagyo Township, Magway Region, Central Myanmar Hard and compact sandstone layers seldom intercalated with thin shale of this upper member. The well exposed outcrops of this formation are found around the vicinity of Anyardaw village and Taungni Taung Range east of Kabauk village. The well exposed section from Taung U village through three pagoda hill is selected for detailed measurement. The resultant measured thickness of this formation is about 300 meters. Fig 6. Greenish grey shale capped by hard sandstone bed of Padaung Formation. Fossil collected from the Clay dominant portion of Padaung Formation are expressed in Table 1. They are Pelecypods: Taras acclinis sp., Pecten sp., Mactra clathrodon sp., Tellina sp. and Coral: Archohelia vicksburgensis sp. Those fossils indicated the age of the Padaung Formation is Oligocene (38 – 23 m.y.). Fig 4. Thin- to medium- bedded sandstone interbedded Table 1. Collected well preserved fossils of Padaung with buff coloured siltstone of Shwezettaw Formation. Formation B. Padaung Formation The Padaung Formation is composed mainly of light yellowish brown, thinly laminated silty clay intercalated with greenish grey, thick-bedded sandstone Fig 5. The upper part of this formation is designated as greenish grey shale and silty shale with numerous fossils. These shale layers are locally capped by thick-bedded sandstone bed Fig 6. V. STRUCTURAL CONSIDERATION The exposed rocks are mainly clastic sedimentary rocks, In the case of sedimentary rocks, they are derived from the processes of transportation and deposition of debris or rock fragments. Those transported materials are accumulated in the low lying area such as shallow marine tidal environment Fig 5. Light yellowish brown, Massive clay interbedded for Shwezettaw and Padaung Formation. The syn- with greenish grey,