What is a Reef ?What is a Reef ?

Coral Reef Geology

Wilson Ramirez

MarinersCan I hit my keel on it (i.e., shallow)

BiologistsBiologically abundant and diverse assemblage

GeologistsBiologically builtWave resistantStands above its surroundings

Perspective….what is a reef?

MarinersCan I hit my keel on it (i.e., shallow)

BiologistsBiologically abundant and diverse assemblage

GeologistsBiologically builtWave resistantStands above its surroundings

Perspective….what is a reef?Canning Basin, Australia

(Devonian)

Palau, Oceania

Canning Basin, Australia(Devonian)

Isla de Mona, Puerto Rico

AGeologist’s

Reef

Reef DefinitionReef Definition

“the vast majority of of ancient reef deposits are comprised not of in-place, interlocking framework, but rather are loose assemblages with reef-building organisms ‘floating’ in a matrix of reef-derived debris”

Hubbard (1997, p. 43)

Reef DefinitionReef DefinitionStanley (2001)

“Growth of biological framework on modern shallow reefs is rapid….”

“…it is counterbalanced by highly destructive (recycling) processes…”

Constructed of material of biological origin

Rigid structure, owing to either interlocked and in place framework elements or of re worked framework elements bound together by secondary encrustation or cementation

Stands topographically above the surrounding seascape and, therefore, exerts at least local control on oceanographic processes

The majority of the framework elements were formed in an environment similar to the one in which they were ultimately deposited

“Reef” definition

Tucker & WrightTucker & Wright

Folk (1962) – biolithites

Dunham (1962) – boundstone (bound during deposition)

Embry & Klovan (1971)

A Geologic Reef

Rigid, & wave resistant

Elevated - affect local oceanography

Near sea level?

Biostrome = A veneer of organisms with no relief

Let’s put this into a geological perspective…

Sedimentation & CementationRecolonizationRepeatRepeatRepeatRepeatRepeatEnd DepositionEnd Deposition

Compression

CompressionCompressionCompressionCompressionCompressionCompression

Reef??Stratigraphic Reef (Dunham)

The reef is "apparent"i.e., no topography actually occurred in the past

An oyster bank is not wave resistant, but in time a thick sequence could result from upward layered accumulation.

Stratigraphic reef

Construction/Bioerosion & SedimentationConstruction/Bioerosion & SedimentationConstruction/Bioerosion & SedimentationConstruction/Bioerosion & SedimentationConstruction/Bioerosion & SedimentationConstruction/Bioerosion & SedimentationConstruction/Bioerosion & Sedimentation

Topography at the time of deposition

Compression

CompressionReef??Ecological Reef (Dunham)

The reef is "real"i.e., topography actually did occurred in the past

Fossil reef with in place structural elements – Acropora palmata

Ecologic reef accumulation

BIOHERM

Built by growth,Bioerosion,

toppling,encrustation &

cementation

Topography present

BIOHERMAB

Question: What differences will we see at A versus B?

BIOSTROME

e.g., a coral”carpet”

No significant topography

AB

Question: What differences will we see at A versus B?

Biostrome vs. Bioherm

Stratigraphic Reef Ecologic Reef

No Original Relief Relief During Deposition

CoralGrowthGrazingGrazing

New Coral

Grazing

M. annularis growth

Grazing

Boring

Sediment Fill

Coral GrowthBoring/Grazing

Sedimentation

Coral Growth

Boring/GrazingToppled

Sedimentation

EncrustationConstruction

Destruction

Sedimentation

Encrustation

Cementation

How do we get rigid, elevated structures?

ConstructionCoralsOther calcifiers

DestructionFishUrchinsBorers

EncrustationCementation

Corals GrowCorals GrowReefs Accrete (or build)Reefs Accrete (or build)

Sediment productionand redistribution