dr maree corkeron - energymining.sa.gov.au€¦ · microbially mediated ppt conventional...
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Arkaroola Reef: reef builders of the world's best exposed Neoproterozoic interglacial carbonate reef
Dr Maree Corkeron
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http://space-telescopes-news.blogspot.com.au/2010/03/cryogenian.htmlNASA
Two intervals of global-scale glaciation
Cryogenian Earth Marinoan >639 - 635.5 MaSturtian ~716 - ~658 Ma
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Lyons et al., 2014
Adapted from Spence et al., 2016
Cryogenian Earth system change • Tectonic• Atmospheric• Climatic• Evolutionary
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Reef builders & reef ecology evolved from Proterozoic to Phanerozoic
Ediacaran stromatolite reef
Cambrian archaeocyathid reef
Devonian stromatoporioid
reef
Modern scleractinian
coral reef
Sibbling, 1999
Reefs through time preserve complex organic ecosystems
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Balcanoona Formation
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Stromatolite Buildingorgano-sedimentary structures,
cyanobacteria (plus archaea, prokaryote & eukaryote microbiota)
1. Trapping and binding
2. Microbially mediated ppt
Conventional
Contemporary
on filament surface
replacing organic matter
On & in complex organic framework
Webb and Kamber, 2011
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What controls their morphology?
1. Environment?• Hydrology• Water chemistry; e.g. alkalinity, redox profile• Water depth/light• Other facies
2. Microbial consortia in stromatolite community?• Cyanobacteria, archaea, algae• Does morphology represent a ‘taxonomic’ entity?
What are the drivers of stromatolite morphology – environment versus
evolution?
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Neoproterozoic Adelaide Rift Complex
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Arkaroola Reef Geological Setting
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Reef facies geometry
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Arkaroola reef model
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Forereef slope facies association
Large domal stromatolite
Breccia boundstone
encrusting microbial boundstone
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Reef Crest facies association Large domal stromatolite
Plus swaley intraclastic grainstoneEncrusing microbial boundstone
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? Tungussia indet.Reef Flatfacies association - windward
Columnar andbranching
stromatolites
35 mm
Linella munyallina(tentative identification)
4 cm
? Tungussia etina
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Reef Flatfacies association - leeward
Ditgitate stromatolites
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Backreef lagoonfacies association
clastic nstone
Cross bedded oolitic & peloidal grainstone
Pseudocolumnar stromatolite
Microbial oolitic boundstone
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Reef fabrics – element of reef building communities
Baff
lest
ones Modifies hydrology
Allows settling
Accumulates & cements mobile grains
Fram
esto
nes
Stabilises
Supports
Cements and traps grains
Bind
ston
es Satabilises and binds
Cements
Produces micrite & intraclasts
Microbial boundstone facies• encrusting• Breccia binding• bedded• Swaley intraclastic
grainstone
Large domalstromatolite (new form)
Columnar, branching, digitate stromatolitesLinella munyallina? Tungussia etina?Omachtenia new formUnidientified forms
after Embry & Klovan (1971) classification
PHAN
ERO
ZOIC
REEF
S
CRYO
GEN
IAN
ARK
ARO
OLA
REE
F
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• Stromatolites occur in a range of forms across the reef
• Respond to reef sub-environments
• Different forms reflect different roles in reef dynamics
• Analogous to contemporary coral reefs geomorphology,
• biological response to environmental drivers but in a distinct prokaryote ecosystem.
• Biotic resilience after global glacial event
Artwork by Lisa Pyers
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The Arkaroola reef gives a unique window into the role of stromatolites as Precambrian reef framework bioconstructors and geomorphological engineers.
Preservation, accessibility and spectacular exposure attest to their world-class geological and evolutionary value
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Thanks for your attention
Acknowledgements
Kath Grey (Geol. Survey of Western Australia)Heidi Allen (Geol. Survey of Western Australia)James Smith (Qld Health/QUT)Paul Slezak (James Cook University/University College Dublin)Annette George (University of Western AustraliaFrance Champenoise (University of Western Australia)Marg and Doug Sprigg (Arkaroola)Lisa Pyers