Coral Reef Geology
What is a Reef ?
Wilson Ramirez
Perspective….what is a
reef?
Mariners
Can I hit my keel on it (i.e., shallow)
Biologists
Biologically abundant and diverse
assemblage
Geologists
Biologically built
Wave resistant
Stands above its surroundings
Perspective….what is a
reef?
Canning Basin, Australia
(Devonian)
Mariners
Can I hit my keel on it (i.e., shallow)
Biologists
Biologically abundant and diverse
assemblage
Geologists
Palau, Oceania
Biologically built
Wave resistant
Stands above its surroundings
Canning Basin, Australia
(Devonian)
Isla de Mona, Puerto Rico
A
Geologist’s
Reef
Reef 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 Definition
Stanley (2001)
“Growth of biological framework on modern
shallow reefs is rapid….”
“…it is counterbalanced by highly destructive
(recycling) processes…”
“Reef” definition
 Constructed of material of biological origin
 Rigid structure, owing to either interlocked and in
place framework elements or of reworked
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
Folk (1962) –
biolithites
Dunham (1962) – boundstone ( bound during deposition)
Embry & Klovan (1971)
Tucker & Wright
A Geologic Reef
 Rigid, & wave resistant
 Elevated - affect local
oceanography
 Near sea level?
Let’s put this into a geological perspective…
The reef is "apparent"
i.e., no topography actually occurred in the past
Compression
Compression
Compression
Compression
Compression
Compression
Stratigraphic
Reef (Dunham)
Reef??
& Cementation
Biostrome =Sedimentation
A veneer
of
organisms
with no relief
End
Recolonization
Deposition
Repeat
Stratigraphic reef
An oyster bank is not
wave resistant, but in
time a thick sequence
could result from
upward layered
accumulation.
The reef is "real"
i.e., topography actually did occurred in the past
Compression
Ecological
Reef??
Reef
(Dunham)
Compression
Topography at the time of deposition
Construction/Bioerosion & Sedimentation
Ecologic reef accumulation
Fossil reef with in place structural elements
– Acropora palmata
Built by growth,
Bioerosion, present
Topography
toppling,
encrustation
&
Question: What differences will we see at A versus B?
cementation
A
B
BIOHERM
BIOHERM
e.g., a coral”carpet”
No significant topography
Question: What differences will we see at A versus B?
B
BIOSTROME
A
Biostrome vs. Bioherm
Stratigraphic Reef
Ecologic Reef
Relief
During
No Original Relief
Deposition
How do we get rigid, elevated structures?
Construction
Corals
Other calcifiers
Destruction
Fish
Urchins
Borers
Encrustation
Cementation
Coral Growth
Construction
Encrustation
Boring/Grazing
Toppled
Destruction
Sedimentation
Boring
Sedimentation
Boring/Grazing
Sedimentation
Coral Growth
M. annularisGrazing
Sediment Fill
growth
Encrustation
New Coral
Cementation
Coral
Grazing
Growth
Grazing
Corals Grow
Reefs Accrete (or build)
Sediment production
and redistribution