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The tidal character of fluvial sediments of the modern Mahakam River delta, Kalimantan, Indonesia
Gastaldo, R.A.; Alleng, G.P.; Huc, A.-Y. (1995). The tidal character of fluvial sediments of the modern Mahakam River delta, Kalimantan, Indonesia, in: Flemming, B.W. et al. (Ed.) Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24: pp. 171-181
In: Flemming, B.W.; Bartholomä, A. (Ed.) (1995). Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24. Blackwell Science: Oxford. ISBN 0-86542-978-2. 358 pp., more
In: Special Publication of the International Association of Sedimentologists. Blackwell: Oxford; London; Edinburgh; Melbourne. ISSN 0141-3600, more

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Keyword
    Marine

Authors  Top 
  • Gastaldo, R.A.
  • Alleng, G.P.
  • Huc, A.-Y.

Abstract
    The Mahakam River delta, Kalimantan, Indonesia, is a low wave-energy, mixed tide- and fluvially controlled delta complex, situated at the eastern edge of the island of Borneo. The medium- to fine-grained terrestrial sediment originates from within a 75000 km² drainage area. It is transported through the equatorial basin and debouches into the Makassar Strait. The Mahakam has two active distributary systems, directed north-east and south-east respectively, with an intervening interdistributary area consisting of a series of tidal channels and former flu vial distributary channels which today are no longer connected to the fluvial regime. A non-random sampling strategy was employed during a vibracoring programme conducted in 1988. The vibracores were collected along two transects: (i) cores from the first transect represent depositional environments within the tide-affected fluvial distributaries; and (ii) cores along the second transect were sampled from sites within the tidal interdistributary area. Sample sites of the distributary channel transect included lateral channel bars, distributary-mouth bars, and delta-front settings. All the sediments recovered from subaqueous sample sites show varying degrees of tidal influence. Mud drapes and couplets of medium-very fine sands and mud are the most commonly encountered sedimentary successions in the active fluvial distributaries, being also characteristic of all tide dominated distributary channels. Sand/mud ratios are variable, ranging from 90: 10 to 30:70. The thickness of clay drapes is also variable. Sedimentary structures include wavy and lenticular bedding composed of asymmetrical ripples and trough cross-stratification. Ripples may be multi-directional within any one core, being inclined upstream, downstream or horizontally disposed. Sand and mud are mixed by bioturbation in the lower delta plain and delta front. Primary sedimentary structures in conjunction with the degree of bioturbation and the presence of phytoclast drapes appear to be useful criteria for the identification of ancient tide-influenced deltaic distributary channels.

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