Quaternary bryozoan reef mounds in cool-water, upper slope environments; Great Australian Bight

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doi: 10.1130/0091-7613(2000)28<647:QBRMIC>2.0.CO;2
Author(s): James, Noel P.; Feary, David A.; Surlyk, Finn; Simo, J. A. Toni; Betzler, Christian; Holbourn, Ann E.; Li, Qianyu; Matsuda, Hiroki; Machiyama, Hideaki; Brooks, Gregg R.; Andres, Miriam S.; Hine, Albert C.; Malone, Mitchell J.
Ocean Drilling Program, Leg 182, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
Queen's University, Kingston, ON, Canada
Australian Geological Survey Organization, Australia
University of Copenhagen, Denmark
University of Wisconsin, United States
Johann Wolfgang Goethe-Universität, Federal Republic of Germany
Kiel University, Federal Republic of Germany
University of Adelaide, Australia
Kumamoto University, Japan
Japan Marine Science and Technology Center, Japan
Eckerd College, United States
ETH-Zentrum, Switzerland
University of South Florida, United States
Texas A&M University, United States
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 28(7), p.647-650. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. 25 refs.; illus., incl. 1 table, sketch maps
Summary: Bryozoan reef mounds are common features in the geological record, occurring within mid-ramp, slope paleoenvironments, especially in Paleozoic carbonate successions, but until now have not been recorded from the modern ocean. Recent scientific drilling in the Great Australian Bight (Ocean Drilling Program Leg 182) has confirmed the existence of shallow subsurface bryozoan reef mounds in modern water depths of 200-350 m. These structures have as much as 65 m of synoptic relief, and occur both as single mounds and as mound complexes. They are unlithified, have a floatstone texture, and are rich in delicate branching, encrusting and/or nodular-arborescent, flat-robust branching, fenestrate, and articulated zooidal bryozoan growth forms. The muddy matrix is composed of foraminifers, serpulids, fecal pellets, irregular bioclasts, sponge spicules, and calcareous nannofossils. The 14C accelerator mass spectrometry dates of 26.6-35.1 ka indicate that the most recent mounds, the tops of which are 7-10 m below the modern seafloor, flourished during the last glacial lowstand but perished during transgressive sea-level rise. This history reflects changing oceanographic current patterns; strong upwelling during lowstands, and reduced upwelling and lowered trophic resources during highstands. Large specimens of benthic foraminifers restricted to the mounds confirm overall mesotrophic growth conditions. The mounds are similar in geometry, scale, general composition, and paleoenvironments to older structures, but lack obvious microbial influence and extensive synsedimentary cementation. Such differences reflect either short-term local conditions or long-term temporal changes in ocean chemistry and biology.
Year of Publication: 2000
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Absolute age; Algae; Biogenic structures; Bioherms; Bryozoa; C-14; Carbon; Carbonate sediments; Cenozoic; Continental slope; Dates; Fecal pellets; Foraminifera; Glacial environment; Glaciomarine environment; Great Australian Bight; Indian Ocean; Inner slope; Interglacial environment; Invertebrata; Isotopes; Leg 182; Marine environment; Marine sediments; Morphology; Nannofossils; ODP Site 1129; ODP Site 1131; Ocean Drilling Program; Paleo-oceanography; Paleocurrents; Paleoecology; Plantae; Pleistocene; Polychaetia; Porifera; Protista; Quaternary; Radioactive isotopes; Reef builders; Reef environment; Sea-level changes; Sedimentary structures; Sediments; Serpulidae; Shallow-water environment; Slope environment; Spicules; Trophic analysis; Upper Pleistocene; Vermes
Coordinates: S333000 S331000 E1283000 E1283000
Record ID: 2000056023
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States