The lower Murray River's mannum muds: a holocene age lacustrine deposit In a bedrock gorge

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dc.contributor.authorHubble, Ten_AU
dc.contributor.authorDe Carli, Een_AU
dc.contributor.authorClarke, SLen_AU
dc.contributor.authorPenny, Den_AU
dc.contributor.authorHamilton, RJen_AU
dc.contributor.authorPetley, DNen_AU
dc.contributor.authorGadd, PSen_AU
dc.date.accessioned2021-06-10T01:42:53Zen_AU
dc.date.available2021-06-10T01:42:53Zen_AU
dc.date.issued2014-12-12en_AU
dc.date.statistics2021-06-08en_AU
dc.description.abstractMiddle to Late Holocene age, horizontally laminated clays and muds of lacustrine origin predominate the uppermost layers of the valley-fill sequence deposited in the lower Murray River’s bedrock gorge upstream of the set of lakes which separate Australia's largest river system, The Murray-Darling, from its discharge point to the Southern Ocean. The top surface of the Coonambidgal Formation muds is developed at a constant elevation approximately coincident with the Holocene sea-level maximum and the mud deposit thins progressively in thickness upstream from ~30 m to ~10 m over a distance of 150 km due to a gradual, upstream rise in the elevation of the unit's base. Radiocarbon ages for wood and charcoal fragments recovered from two cores indicates the uppermost four to five metres of these muds were deposited after the mid-Holocene sea-level maximum, at below sea-level elevations indicating that the discharge of the Murray-Darling fluvial system was contained and effectively dammed by an obstruction developed downstream of Lake Alexandrina where the present-day river mouth is located. This feature is suspected to be the precursor of the present-day dune and beach-barrier system which occasionally blocks the river mouth and diverts fresh-water flow into the Coorong Wetlands. Muddy sediment from the entire Murray-Darling catchment was effectively trapped in the lower Murray Gorge palaeolake, herein named Lake Mannum, during the mid to late Holocene. High rates of sedimentation (one to two meters per thousand years) produced exquisitely fine-scaled (1 mm to 1 cm) laminations in the upper Coonambidgal Formation. This material has not been disturbed by bioturbation and presents a sediment record with the potential to yield a high-resolution record of the Murray-Darling catchment’s discharge for much of the Holocene. The present-day lower Murray River channel currently presents a meandering but constant planform geometry upstream of Lake Alexandrina that developed as a thalweg incised and entrenched within the Coonambidgal muds, as a somewhat delayed response to the two metre fall in sea-level after the mid-Holocene maximum. The onset of this incision apparently occurred towards the end of the Holocene.en_AU
dc.identifier.citationHubble, T., De Carli, E., Clarke, S. L., Penny, D., Hamilton, R. J., Petley, D. N., & Gadd, P. (2014). The lower Murray River's mannum muds: a holocene age lacustrine deposit In a bedrock gorge. Paper presented at the AGU Fall Meeting, San Francisco, California, 15 to 19 December 2014. Retrieved from: https://agu.confex.com/agu/fm14/meetingapp.cgi/Paper/19975en_AU
dc.identifier.conferenceenddate19 December 2014en_AU
dc.identifier.conferencenameAGU Fall Meetingen_AU
dc.identifier.conferenceplaceSan Francisco, Californiaen_AU
dc.identifier.conferencestartdate15 December 2014en_AU
dc.identifier.otherEP13A-3496en_AU
dc.identifier.urihttps://agu.confex.com/agu/fm14/meetingapp.cgi/Paper/19975en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/10841en_AU
dc.language.isoenen_AU
dc.publisherAmerican Geophysical Union (AGU)en_AU
dc.subjectGeomorphologyen_AU
dc.subjectHydrologyen_AU
dc.subjectSedimentationen_AU
dc.subjectRiversen_AU
dc.subjectOceanographyen_AU
dc.subjectErosionen_AU
dc.subjectWeatheringen_AU
dc.subjectAustraliaen_AU
dc.titleThe lower Murray River's mannum muds: a holocene age lacustrine deposit In a bedrock gorgeen_AU
dc.typeConference Abstracten_AU
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