organisms in various abundances were wide spread in
Gondwana, Laurussia, Armorica, Kazakhstan, China, and
in the Panthalassa Ocean.
After climate cooling in the Mid-Carboniferous, corals
did not contribute to reef formation any more. In the tropics and subtropics various calcareous algae (tubular
algae, phylloid green algae and red algae) and chaetetid
sponges contributed to the formation of three basic types.
In somewhat more temperate waters pelmatozoans, bryozoans, brachiopods, and microbial communities were the
main contributors to the formation of reefal/reef like structures (Wahlman, 2002).
In the latest Carboniferous period, following a short
global warming, reefs of the tropical Tethyan realm consisted of calcareous algae and calcareous sponges, whereas
in subtropical to temperate waters Palaeoaplysina mounds
occurred in shallow settings and bryozoan-Tubiphytes reefs
in deeper settings (Wahlman, 2002).
Bibliography
Aretz, M., and Vachard, D., 2007. Carboniferous: Introduction. In
Vennin, E., Aretz, M., Boulvain, F., and Munnecke, A. (eds.),
Facies from Palaeozoic Reefs and Bioaccumulations. Mémoires
du Musée d´histoire Naturelle de Paris, 198, pp. 227–230.
Wahlman, G. P., 2002. Upper Carboniferous – Lower Permian
(Bashkirian–Kungarian) mounds and reefs. In Kiessling, W.,
Flügel, E., and Golonka, J. (eds.), Phanerozoic Reef Patterns.
SEPM. Special Publications, 72, pp. 271–338.
Webb, G. E., 2002. Latest Devonian and Early Carboniferous
reefs: depressed reef building after the middle Paleozoic
collapse. In Kiessling, W., Flügel, E., and Golonka, J. (eds.),
Phanerozoic Reef Patterns. SEPM. Special Publications, 72,
pp. 239–269.
Cross-references
Algae-Macro
Atolls
Barrier Reef (Ribbon Reef )
Binding Organisms
Climate Change and Coral Reefs
Corals: Biology, Skeletal Deposition, and Reef-Building
Devonian Reef Complexes of the Canning Basin
Sea Level Change and Its Effect on Reef Growth
Sponges
CAY FORMATION
Peter Flood
University of New England, NSW, Armidale, Australia
Definition
A cay (sometimes spelled key or quay) is a small, low elevation island composed of coral reef detritus of rubble or
shingle and/or sand sized materials that have accumulated
on the reef top surface.
Formation
Cays are formed when ocean waves and tidal currents
transport loose sediment across the reef top surface to
a depositional node where concentration occurs and the
sedimentary pile rises above the high tide (Hopley, 1981;
Gourlay, 1988). Over time soil and vegetation may
develop on the cay surface. This process is assisted by
the presence of extensive sea bird populations and their
associated guano deposition, which acts as a fertilizer for
the developing vegetation.
There is a basic division of cays into windward shingle
cays and leeward sand cays or mixed shingle/sand cays
depending on the surface area and size of the associated
reef top.
Stoddart and Steers (1977) seminal study of cays and
the subsequent study by Stoddart et al. (1978), showed
that cays on reefs of the Great Barrier Reef vary from
small ephemeral sand patches emerging only at low
tide to variable sizes of vegetated sand and shingle or
mixed sand/shingle cays to the complex low wooded
islands which are characterized by variable development
of mangrove vegetation (McLean and Stoddart, 1978;
Stoddart, 1965, 1969). The classification scheme of
Stoddart and Steers (1977) is applicable throughout
the various reef provinces (Indian Ocean, Maldives,
Indonesia, Central Pacific Ocean, Fiji, Samoa, Polynesia,
atolls; Atlantic Ocean, Caribbean, etc). One variant of
the mixed sand/shingle cay type are called motus. This
variety, unlike the sand-shingle cays that are molded by
wave refraction, lie on unbroken reefs on atoll rims. They
are formed by the deposition of shingle on the windward
edge as storm boulder ridges. Such ridges serve as an
anchor to further leeward deposition of sand-sized sediment (Nunn, 1994). Dickinson (2001; 2009) suggests that
many of the Pacific Ocean motus are in fact “pinned” to
the elevated abandoned reef flat which developed during
higher-than-present sea levels during the mid-Holocene
period.
Hopley et al. (2007, p.364, Fig. 10.16) have provided
a summary of the attributes and frequency of reef types
and cays on the Great Barrier Reef Province.
The cays are subjected to a range of physical, biological, and chemical variables that influence the morphological development (Flood, 1977, 1980, 1981, 1986;
Umbgrove, 1947; Hopley, 1982, 1997; Chivas et al.,
1986). Once the cay extends above the limit of high tide
the wind action commences and the dry sands of the upper
beach are transported inland to form dunes. This wind
action produces an asymmetrical cross profile of the cay
with a higher elevation on the windward side. Dunes of
up to three meters elevation are not uncommon. Once colonized by pioneer vegetation and the presence of nesting
colonies of sea birds, the humic and fertility content of
the soil increases and larger vegetation such as shrubs
and trees commence to grow. In addition, once the cay
reaches a critical size, a fresh and/or brackish lens may
become established towards the center of the cay.
CAY FORMATION
191
Gondwana, Laurussia, Armorica, Kazakhstan, China, and
in the Panthalassa Ocean.
After climate cooling in the Mid-Carboniferous, corals
did not contribute to reef formation any more. In the tropics and subtropics various calcareous algae (tubular
algae, phylloid green algae and red algae) and chaetetid
sponges contributed to the formation of three basic types.
In somewhat more temperate waters pelmatozoans, bryozoans, brachiopods, and microbial communities were the
main contributors to the formation of reefal/reef like structures (Wahlman, 2002).
In the latest Carboniferous period, following a short
global warming, reefs of the tropical Tethyan realm consisted of calcareous algae and calcareous sponges, whereas
in subtropical to temperate waters Palaeoaplysina mounds
occurred in shallow settings and bryozoan-Tubiphytes reefs
in deeper settings (Wahlman, 2002).
Bibliography
Aretz, M., and Vachard, D., 2007. Carboniferous: Introduction. In
Vennin, E., Aretz, M., Boulvain, F., and Munnecke, A. (eds.),
Facies from Palaeozoic Reefs and Bioaccumulations. Mémoires
du Musée d´histoire Naturelle de Paris, 198, pp. 227–230.
Wahlman, G. P., 2002. Upper Carboniferous – Lower Permian
(Bashkirian–Kungarian) mounds and reefs. In Kiessling, W.,
Flügel, E., and Golonka, J. (eds.), Phanerozoic Reef Patterns.
SEPM. Special Publications, 72, pp. 271–338.
Webb, G. E., 2002. Latest Devonian and Early Carboniferous
reefs: depressed reef building after the middle Paleozoic
collapse. In Kiessling, W., Flügel, E., and Golonka, J. (eds.),
Phanerozoic Reef Patterns. SEPM. Special Publications, 72,
pp. 239–269.
Cross-references
Algae-Macro
Atolls
Barrier Reef (Ribbon Reef )
Binding Organisms
Climate Change and Coral Reefs
Corals: Biology, Skeletal Deposition, and Reef-Building
Devonian Reef Complexes of the Canning Basin
Sea Level Change and Its Effect on Reef Growth
Sponges
CAY FORMATION
Peter Flood
University of New England, NSW, Armidale, Australia
Definition
A cay (sometimes spelled key or quay) is a small, low elevation island composed of coral reef detritus of rubble or
shingle and/or sand sized materials that have accumulated
on the reef top surface.
Formation
Cays are formed when ocean waves and tidal currents
transport loose sediment across the reef top surface to
a depositional node where concentration occurs and the
sedimentary pile rises above the high tide (Hopley, 1981;
Gourlay, 1988). Over time soil and vegetation may
develop on the cay surface. This process is assisted by
the presence of extensive sea bird populations and their
associated guano deposition, which acts as a fertilizer for
the developing vegetation.
There is a basic division of cays into windward shingle
cays and leeward sand cays or mixed shingle/sand cays
depending on the surface area and size of the associated
reef top.
Stoddart and Steers (1977) seminal study of cays and
the subsequent study by Stoddart et al. (1978), showed
that cays on reefs of the Great Barrier Reef vary from
small ephemeral sand patches emerging only at low
tide to variable sizes of vegetated sand and shingle or
mixed sand/shingle cays to the complex low wooded
islands which are characterized by variable development
of mangrove vegetation (McLean and Stoddart, 1978;
Stoddart, 1965, 1969). The classification scheme of
Stoddart and Steers (1977) is applicable throughout
the various reef provinces (Indian Ocean, Maldives,
Indonesia, Central Pacific Ocean, Fiji, Samoa, Polynesia,
atolls; Atlantic Ocean, Caribbean, etc). One variant of
the mixed sand/shingle cay type are called motus. This
variety, unlike the sand-shingle cays that are molded by
wave refraction, lie on unbroken reefs on atoll rims. They
are formed by the deposition of shingle on the windward
edge as storm boulder ridges. Such ridges serve as an
anchor to further leeward deposition of sand-sized sediment (Nunn, 1994). Dickinson (2001; 2009) suggests that
many of the Pacific Ocean motus are in fact “pinned” to
the elevated abandoned reef flat which developed during
higher-than-present sea levels during the mid-Holocene
period.
Hopley et al. (2007, p.364, Fig. 10.16) have provided
a summary of the attributes and frequency of reef types
and cays on the Great Barrier Reef Province.
The cays are subjected to a range of physical, biological, and chemical variables that influence the morphological development (Flood, 1977, 1980, 1981, 1986;
Umbgrove, 1947; Hopley, 1982, 1997; Chivas et al.,
1986). Once the cay extends above the limit of high tide
the wind action commences and the dry sands of the upper
beach are transported inland to form dunes. This wind
action produces an asymmetrical cross profile of the cay
with a higher elevation on the windward side. Dunes of
up to three meters elevation are not uncommon. Once colonized by pioneer vegetation and the presence of nesting
colonies of sea birds, the humic and fertility content of
the soil increases and larger vegetation such as shrubs
and trees commence to grow. In addition, once the cay
reaches a critical size, a fresh and/or brackish lens may
become established towards the center of the cay.
CAY FORMATION
191