Origin of late Pleistocene bryozoan reef mounds; Great Australian Bight

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doi: 10.1306/062303740020
Author(s): James, Noel P.; Feary, David A.; Betzler, Christian; Bone, Yvonne; Holbourn, Ann E.; Li, Qianyu; Machiyama, Hideaki; Simo, J. A. Toni; Surlyk, Finn
Author Affiliation(s): Primary:
Queen's University, Kingston, ON, Canada
Geoscience Australia, Australia
Hamburg University, Federal Republic of Germany
Adelaide University, Australia
Christian-Albrechts University, Federal Republic of Germany
Japan Marine Science and Technology Center, Japan
University of Wisconsin-Madison, United States
University of Copenhagen, Denmark
Volume Title: Journal of Sedimentary Research
Source: Journal of Sedimentary Research, 74(1), p.20-48. Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States. ISSN: 1527-1404
Note: In English. 61 refs.; illus., incl. sects., 4 tables, sketch map
Summary: Bryozoan-rich biogenic mounds grew periodically on the prograding carbonate slope of the central Great Australian Bight throughout Pliocene-Pleistocene time. Cores from three ODP Leg 182 drill sites provide a record of mound growth during the last 300,000 years over a stratigraphic thickness of ∼150 m. These mounds, the first such structures described from the modern ocean, grew between paleodepths of 100 and 240 m; we infer that the upper limit of growth was established by swell wave base, and the lower boundary was fixed by an oligotrophic water mass. Detailed chronostratigraphy, based on radiometric and U-series dating, benthic foraminifer stable-isotope stratigraphy, and planktonic foraminifer abundance ratios, confirms that buildups flourished during glacial lowstands (even-numbered marine isotope stages) but were largely moribund during interglacial highstands and are not extant today. Mound floatstones are compositionally a mixture of in situ bryozoans comprising 96 genera and characterized by fenestrate, flat robust branching, encrusting, nodular-arborescent, and delicate branching growth forms. The packstone matrix comprises autochthonous and allochthonous sand-size bryozoans, benthic and planktonic foraminifers, serpulids, coralline algae, sponge spicules, peloids, and variable glauconite and quartz grains, together with mud-size ostracods, tunicate spicules, bioeroded sponge chips, and coccoliths. Intermound, allochthonous packstone and local grainstone contain similar particles, but they are conspicuously worn, abraded, blackened, and bioeroded. An integrated model of mound accretion during sea-level lowstands begins with delicate branching bryozoan floatstone that increases in bryozoan abundance and diversity upward over a thickness of 5-10 m, culminating in thin intervals of grainstone characterized by reduced diversity and locally abraded fossils. Mound accumulation was relatively rapid (30-67 cm/ky) and locally punctuated by rudstones and firmgrounds. Intermound highstand deposition was comparatively slow (17-25 cm/ky) and typified by meter-scale, fining-upward packages of packstone and grainstone or burrowed packstone, with local firm-grounds overlain by characteristically abraded particles. Mound growth during glacial periods is interpreted to have resulted from increased nutrient supply and enhanced primary productivity. Such elevated trophic resources were both regional and local, and thought to be focused in this area by cessation of Leeuwin Current flow, together with northward movement of the subtropical convergence and related dynamic mixing.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Bryozoa; Carbonate rocks; Cenozoic; Chronostratigraphy; Floatstone; Grainstone; Great Australian Bight; Indian Ocean; Invertebrata; Leg 182; Lithostratigraphy; Mounds; Ocean Drilling Program; Packstone; Pleistocene; Quaternary; Reef builders; Reefs; Rudstone; Sedimentary rocks; Unconformities; Upper Pleistocene
Coordinates: S342330 S331720 E1285500 E1271500
Record ID: 2006010055
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States