1 / 15

01/0000

Shelf channels provide conduits for the existence of coral reef habitats in the Northern Great Barrier Reef. Andrew D. Heap 1 , Peter T. Harris 2 & Shipboard Party*. 1. Geoscience Australia & Dept. of Geography, Private Box 78, University of Tasmania, Hobart, TAS 7001.

pelham
Download Presentation

01/0000

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Shelf channels provide conduits for the existence of coral reef habitats in the Northern Great Barrier Reef Andrew D. Heap1, Peter T. Harris2 & Shipboard Party* 1. Geoscience Australia & Dept. of Geography, Private Box 78, University of Tasmania, Hobart, TAS 7001 2. Geoscience Australia & Antarctic CRC, Private Box 80, University of Tasmania, Hobart, TAS 7001 01/0000

  2. * Shipboard Party Michael Hughes (Uni. of Sydney) Vicki Passlow (GA) Rick Porter-Smith (GA) Kevin Hooper (James Cook Uni.) Mark Hemer (Uni. of Tasmania) Robin Beaman (Uni. of Tasmania) Jon Stratton (GA) Lyndon O’Grady (GA) Bernadette Heaney (CSIRO) Eric Madsen (CSIRO) Motley Crew

  3. Regional Setting Research Questions • Are modern-day delta processes transporting terrigenous sedimentto the outer Gulf? • Is this process recorded in shelf sediments? • Have these processes influencedthe present northern limit of theGBR? Fly River Delta 120 Mt/a Limited by Terrigenous input

  4. 5 cm Distal Delta Sediment Carbonate Contains Abundant Forams Unconformity Terrigenous Contains Abundant Peat

  5. Late-Quaternary Sea Level Open Marine Highstand Riverine/Estuarine Transgression Constrain transgressive portion of eustatic sea level curve

  6. Distal Delta Sediment Depth (m) Terrigenous sedimenttransport is low Terrigenous sedimentaccumulation ratesare small

  7. Outer Shelf Geomorphology RuggedTopography N N Coral Reefs Sandwaves Channels

  8. 5 cm Outer Shelf Sediment Carbonate-Dominated Marine Deposits Halimeda Banks Channel Floor Channel Bedforms Very poorly-sortedmuddy sand Very poorly-sortedmuddy sand Moderately sortedsand (Consolidated) (Consolidated) Halimeda flakesForaminifers Molluscs Bryozoans Molluscs Foraminifers Gastropods Encrusted shells Mollusc, Foraminifer, and Gastropod Fragments

  9. Channel Formation A North: lateral accretion = River/estuarine channels South: underlying strata truncated = Tidal channels B

  10. Max. bed stress from tides when S.L. at –30-40 m S.L. at these elevations for ~36% for last 150 ka = prolonged time for formation Coral reef surfaces are at –30-40 m Tidal-current Modelling

  11. Sediment –Near bed Phytoplankton – Near Surface Shelf Oceanography

  12. Shelf Water Masses Area A, Inner shelf:high temp/low salinity Area B, Middle shelf: mixed zone Area C, Outer shelf:low temp/high salinity

  13. Delta Sediment Transport Tides Progressive Vector Plot - dominate near-bed currents - directed SW-NE Wind Driven Currents SE Winds = near-bed currents towards NE NW Winds = near-bed currents towards W-SW Mean near-bed current direction towards W-SW

  14. Sediment Transport Model Sediment from Fly River istransported along-shelf ondelta - NE on delta front- SW on distal delta Coral Sea water up-wellsonto shelf via outer shelf channels

  15. Conclusions Significant quantities of terrigenous sediment are not reaching distal delta or outer shelf Cross-shelf channels appear to act as conduits for up-welling of cooler, more saline Cora Sea water Existence of channels on outer shelf and influxes of nutrient-rich water probably have influenced the location of reef habitats to 9° S

More Related