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Mixed Siliciclastic-Skeletal Carbonate Lagoon Sediments from a High Volcanic Island, Viti Levu, Fiji, Southwest Pacific

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Title: Mixed Siliciclastic-Skeletal Carbonate Lagoon Sediments from a High Volcanic Island, Viti Levu, Fiji, Southwest Pacific
Authors: Gussmann, Oliver A.
Smith, Abigail M.
Issue Date: Apr 2002
Publisher: University of Hawai'i Press
Citation: Gussmann OA, Smith AM. 2002. Mixed siliciclastic-skeletal carbonate lagoon sediments from a high volcanic island, Viti Levu, Fiji, southwest Pacific. Pac Sci 56(2): 169-189.
Abstract: Modem sedimentation in the Navua-Suva Lagoon, southeastern Viti
Levu, Fiji, derives from both allochthonous siliciclastics and autochthonous
marine carbonates. Sediments are characterized by a high insoluble load, small
grain size, a wide range of textures, and a high degree of mixing. The distribution
of the two facies (skeletal-dominated muddy sandy gravel and skeletalbearing
very fine sand to mud) is controlled by both the shallow-marine
carbonate sediment productivity and sediment supply and dispersal processes
from siliciclastic point sources across a narrow lagoon. Mollusks and Halimeda
dominate the gravel fraction of the skeletal grains. Sediment budget estimates
indicate that 97% of the siliciclastic supply bypasses the lagoon. Some 0.2 Mt/yr
is accumulating in the lagoon, not yet enough to inhibit potential carbonate
production (~0.1 Mt/yr) by a interreefal benthos that is at least somewhat
sediment-tolerant. Contemporary allochthonous siliciclastic and autochthonous
skeletal carbonate sedimentation in the lagoon results in true syndepositional (in
situ) mixing. The central high volcanic island mass in a tropical setting produces
the geomorphological (high topographic relief, narrow shelf), environmental
(high rainfall), and ecological (shallow benthic area) conditions that lead to
carbonate-siliciclastic mixing in lagoons along adjacent, mostly carbonate, coasts
of oceanic islands, a high volcanic island mass effect. We propose that tropical in
situ mixing of carbonate and siliciclastic sediments is more common in high
volcanic island settings than previously appreciated. Such islands are thus excellent
testing grounds for the study of carbonate-siliciclastic interactions. Their
special characteristics highlight the need for better understanding of coastal
physical processes of tropical Pacific high volcanic islands.
ISSN: 0030-8870
Appears in Collections:Pacific Science Volume 56, Number 2, 2002

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