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Maubin, Myanmar

Licht A.,University of Arizona | Licht A.,University of Lorraine | Licht A.,CNRS Institute of Paleoprimatology, Human Paleontoly: Evolution and Paleoenvironments | Reisberg L.,University of Lorraine | And 3 more authors.
Basin Research | Year: 2016

Located at the southern edge of the eastern Himalayan syntaxis, the Central Myanmar Basin (CMB) is divided into several Tertiary sub-basins that have been almost continuously filled since the Indo-Asia collision. They are currently drained by the Irrawaddy River, which flows down the eastern Tibetan Plateau and the Sino-Burman Ranges. Tracing sediment provenance from the CMB is thus critical for reconstructing the past denudation of the Himalayan-Tibetan orogen; it is especially relevant since a popular drainage scenario involves the capture of the Tsangpo drainage system in Tibet by a precursor to the Irrawaddy River. Here, we document the provenance of sediment samples from the Minbu Sub-Basin at the southern edge of the CMB, which is traversed by the modern stream of the Irrawaddy River. Samples ranging in age from middle Eocene to Pleistocene were investigated using Nd isotopes, trace element geochemistry and sandstone modal compositions. Our data provide no evidence of a dramatic provenance shift; however, sandstone petrography, trace element ratios and isotopic values display long-term trends indicating a gradual decrease of the volcanic input and its replacement by a dominant supply from the Burmese basement. These trends are interpreted to reflect the progressive denudation of the Andean-type volcanic arc that extended onto the Burmese margin, along the flank of the modern Sino-Burman Ranges, where most of the post-collisional deformation of central Myanmar is located. Though our results do not exclude an ephemeral or diluted contribution from a past Tsangpo-Irrawaddy connection, sedimentation rates suggest that this hypothesis is unlikely before the development of a stable Tsangpo-Brahmaputra River in the Miocene. These results thus suggest that the central Myanmar drainage basin has remained restricted to the Sino-Burman Ranges since the beginning of the India-Asia collision. © 2016 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists. Source

Licht A.,CNRS Institute of Paleoprimatology, Human Paleontoly: Evolution and Paleoenvironments | Licht A.,University of Lorraine | France-Lanord C.,University of Lorraine | Reisberg L.,University of Lorraine | And 3 more authors.
Journal of the Geological Society | Year: 2013

Strain resulting from the collision of India with Asia has caused fundamental changes to Asian drainage patterns, but the timing and nature of these changes are poorly understood. One frequently proposed hypothesis involves the connection of the palaeo Tsangpo drainage to a precursor to the Irrawaddy River of central Myanmar in the Palaeogene. To test this hypothesis, we studied the provenance of Palaeogene fluvioclastic sedimentary rocks that crop out in central Myanmar, namely the Late Middle Eocene-Early Oligocene Pondaung and Yaw Formations. Isotopic analysis on bulk-rock and petrographic data indicate a primary magmatic arc source, and a secondary source composed of recycled, metamorphosed basement material. Although the exact location of both sources is hardly distinguishable because Burmese and Tibetan provinces share common lithological features, the presence of low-grade metamorphic fragments, the heterogeneity in Sr-Nd isotopic values of bulk sediments and westward-directed palaeoflow orientations indicate a proximal source area located on the eastern Asian margin. Central Myanmar was the locus of westward-prograding deltas opening into the Indian Ocean, supplied by the unroofing of an Andean-type cordillera that extended along the Burmese margin. We found no evidence to support a palaeo Tsangpo-Irrawaddy River, at least during the Late Eocene. © 2013 The Geological Society of London. Source

Licht A.,CNRS Institute of Paleoprimatology, Human Paleontoly: Evolution and Paleoenvironments | Licht A.,French National Center for Scientific Research | Cojan I.,MINES ParisTech | Caner L.,French National Center for Scientific Research | And 3 more authors.
Sedimentology | Year: 2014

This study examines the lateral distribution of hydromorphy in the fine-grained alluvial deposits of the Eocene Pondaung Formation, central Myanmar. Through detailed outcrop analysis and using a combined sedimentological and pedological approach, this study proposes a reconstruction of Pondaung overbank floodplain palaeoenvironments. The variations of hydromorphic features in the different overbank sub-environments are then discussed and used to build a model of hydromorphic variability in alluvial deposits. Two main architectural associations with distinctive lithofacies and pedogenic features were identified, corresponding to different sub-environments: heterolithic deposits and extensive mudstone successions. The heterolithic deposits display variegated fine-grained lithofacies and contain poorly developed palaeosols with gley and vertic features, which are interpreted to reflect a seasonal wetlands landscape, developed in actively aggrading avulsion belts. Extensive mudstone successions with Vertisols that locally exhibit mukkara-style pseudogley features are interpreted to represent a distal open-forested environment. The palaeosols of both sub-environments display dense local hydromorphic variations they are also characterized by a gradual shift from gley-dominated to pseudogley-dominated features with increasing distance from the avulsion belt. The clay-dominated lithology of the floodplain parent material, which forms numerous subsurface permeability barriers, is shown to have acted as a fundamental control in limiting water-table dynamics in coarse-grained parts of the succession, thereby favouring hydromorphic variability. Palaeosol sequences of the Pondaung Formation contrast with the soil-landscape associations described in other studies and provide an alternative model with which to account for the hydromorphic variability in poorly drained, alluvial soils. The model proposed as an outcome of this study demonstrates that hydromorphic variations can be dramatic in floodplains where permeability barriers are numerous. Further, the model stresses the importance of undertaking detailed lateral palaeosol analyses prior to making interpretations regarding hydromorphic variability. © 2013 International Association of Sedimentologists. Source

Licht A.,CNRS Institute of Paleoprimatology, Human Paleontoly: Evolution and Paleoenvironments | Licht A.,French National Center for Scientific Research | Boura A.,University Pierre and Marie Curie | De Franceschi D.,CNRS Center for Research on Palaeobiodiversity and Palaeoenvironments | And 3 more authors.
Review of Palaeobotany and Palynology | Year: 2014

Twelve species of fossil wood were identified from silicified specimens collected in the late middle Eocene Pondaung Formation, Myanmar. These species display affinities with modern Fabaceae, Moraceae, Combretaceae, Sapindaceae, Malvaceae, Dipterocarpaceae and Theaceae. They include five new species of the fossil genera Ficoxylon (F. mogaungense sp. nov.), Sapindoxylon (S. burmense sp. nov.), Bombacoxylon (B. pondaungense sp. nov.), Shoreoxylon (S. panganense sp. nov.) and Schimoxylon (S. benderi sp. nov.). This material represents the oldest record of fossil dipterocarps so far reported outside the Indian subcontinent. It reflects different ecotones of a dry dipterocarp forest, with coastal, riparian, and inland elements. The Burmese fossil assemblage further contrasts with the common idea that lowland rainforests were widespread in Southeast Asia during the Eocene. It suggests that the climate in the proto-Bengal Bay was more seasonal than previously thought. This confirms that early Dipterocarpaceae were adapted to seasonally dry climates, despite the modern prevalence of warm humid tropical species. © 2013 Elsevier B.V. Source

Yamaguchi T.,Kochi University | Suzuki H.,Otani University | Soe A.-N.,Defence Services Academy | Htike T.,Shwebo University | And 2 more authors.
Zootaxa | Year: 2015

The ostracode genus Bicornucythere (Ostracoda, Crustacea) is abundant in modern-day eutrophic marine bays, and is widely distributed in estuaries and inner bays throughout East Asia, including in China, Korea, Japan, and the Russian Far East. The evolutionary history of Bicornucythere is poorly understood. Here, we report on a new species of Bicornucythere (Bicornucythere concentrica sp. nov.) from the upper Eocene Yaw Formation in the Central Myanmar Basin. The oldest previously known Bicornucythere taxon, Bicornucythere secedens, was reported from lower Miocene strata in India, although a molecular phylogeny suggests that the genus first appeared in the Late Cretaceous. Bicornucythere concentrica sp. nov. is at least 10.9 million years older than the earliest known B. secedens. The new species occurs with Ammonia subgranulosa, a benthic foraminifer, an association that is representative of brackish water conditions in modern Asian bays. Our findings indicate that extant genera have inhabited Asian bays since the late Eocene. The paleobiogeography of Bicornucythere indicates that the taxon was dispersed onto Indian coasts during the collision between the Indian and Eurasian plates. Copyright © 2015 Magnolia Press. Source

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