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The Great Barrier Reef; the chronological record from a new borehole

Colin J. R. Braithwaite, Helene Dalmasso, Mabs A. Gilmour, Douglas D. Harkness, Gideon M. Henderson, R. Lin F. Kay, Dick Kroon, Lucien F. Montaggioni and Paul A. Wilson
The Great Barrier Reef; the chronological record from a new borehole
Journal of Sedimentary Research (March 2004) 74 (2): 298-310


A new borehole, 210 mbsf (meters below sea floor) deep, drilled in Ribbon Reef 5 on the Great Barrier Reef off Cooktown, NE Australia, reveals a shallowing-upwards succession, the younger part of which is punctuated by a series of erosion surfaces. Nine depositional units have been defined by lithological changes and are numbered sequentially from the base of the hole upwards. Aminostratigraphy, magnetostratigraphy, radiocarbon dating, uranium series dating, and modeling together with strontium ratios have been applied in an attempt to establish a chronology of accumulation. Carbonate deposition began about 770 ka ago in a relatively deep-water slope environment and is represented by a series of debris flows. Lithoclasts within these rocks, indicate that older limestones already existed in the area. Subsequent accretion involved the downslope accumulation of grainstones and wackestones, sometimes cross-laminated, characterized by intervals with abundant rhodoliths and scattered, probably reworked, corals. Four units at the base of the hole reflect deposition that probably began during isotope stage 16 and continued through stage 15 from about 770 to about 564 ka. Unit 5 probably extended to stage 11 (about 400 ka), and unit 6 to stage 9 ( approximately 330 ka). Typical reefal associations of corals and calcareous algae were established in this area only above depths of about 100 m in the borehole, units 5-4. The succession is apparently unbroken to an erosion surface at 36 mbsf indicating subaerial emergence. The lack of evidence of emergence below this surface reflects progressive accretion or progradation or both. Two younger erosion surfaces define further periods of lowered sea level. Unit 7 is attributed to deposition during isotope stage 7, but erosion during stage 8 resulted in the preservation of only 8 m of unit 7 limestones. Unit 8 is correlated with stage 5 ( approximately 125 ka), and unit 9 is interpreted as Holocene (post 7,700 ka). The limited thicknesses of units 7, 8, and 9 are considered to reflect erosion. The progressive shallowing brought the depositional surface within the zone exposed during lowstands, and there is no sedimentological evidence that aggradation was restricted by a lack of accommodation.

ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 74
Serial Issue: 2
Title: The Great Barrier Reef; the chronological record from a new borehole
Affiliation: University of Glasgow, Division of Earth Sciences, United Kingdom
Pages: 298-310
Published: 200403
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 43
Accession Number: 2004-039118
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
S16°36'59" - S16°36'58", E149°36'02" - E149°36'03"
Secondary Affiliation: Universite de Provence, FRA, FranceOpen University Milton Keynes, GBR, United KingdomScottish Universities Environmental Research Centre, GBR, United KingdomUniversity of Oxford, GBR, United KingdomNatural Environment Research Council, GBR, United KingdomVrije Universiteit Amsterdam, NLD, NetherlandsUniversity of Southampton, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200411
Program Name: ODPOcean Drilling Program
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