Arkaroola Reef: reef builders of the world's best exposed Neoproterozoic interglacial carbonate reef

Dr Maree Corkeron

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

Lyons et al., 2014

Adapted from Spence et al., 2016

Cryogenian Earth system change • Tectonic• Atmospheric• Climatic• Evolutionary

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

Balcanoona Formation

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

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?

Neoproterozoic Adelaide Rift Complex

Arkaroola Reef Geological Setting

Reef facies geometry

Arkaroola reef model

Forereef slope facies association

Large domal stromatolite

Breccia boundstone

encrusting microbial boundstone

Reef Crest facies association Large domal stromatolite

Plus swaley intraclastic grainstoneEncrusing microbial boundstone

? Tungussia indet.Reef Flatfacies association - windward

Columnar andbranching

stromatolites

35 mm

Linella munyallina(tentative identification)

4 cm

? Tungussia etina

Reef Flatfacies association - leeward

Ditgitate stromatolites

Backreef lagoonfacies association

clastic nstone

Cross bedded oolitic & peloidal grainstone

Pseudocolumnar stromatolite

Microbial oolitic boundstone

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

• 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

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

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