B
BACK-STEPPING
Paul Blanchon
National Autonomous University of Mexico, Cancun,
Mexico
Synonyms
Transgressive reef
Definition
Shallow-reef systems back-step to keep up with rapid relative sea-level rise. Back-stepping involves the demise of
shallow-reef development at one site, and its relocation to
another site further inshore and up-shelf. It is common
during the onlap or retrogradation of tropical carbonate
systems in transgressive systems tracts, and typical of glacial terminations during the Quaternary Ice Age.
Introduction
Reef back-stepping has been widely recognized from the
geological record where it is almost universally interpreted as a result of rapid rise in relative sea level (Smith
and Stearn 1987; Kaufman and Meyers 1988; Ross
1992; Becker et al., 1993; Wendte and Uyeno 2005). Yet
ironically, there has been considerable argument over its
existence and significance in late Pleistocene and Holocene reefs. This largely stems from early assumptions that
healthy reefs could accrete faster than the average rate of
glacio-eustatic sea-level rise (Adey et al., 1978; Schlager
1981). Reef drowning in the strictest sense was therefore
considered uncommon and only ‘incipient drowning’,
where shallow reefs were initially submerged but subsequently recovered when the rise rate declined, was considered likely (Kendall and Schlager 1981). According to this
early view, complete drowning of healthy reefs by
submerging them below the euphotic zone ($100 m)
required exceptional circumstances: either a combination
of regional subsidence and pulsed sea-level rise which
removed the reef from the low-stand euphotic zone, or
more local environmental factors to suppress the accretion
potential of reefs and make them susceptible to drowning
(Adey 1978; Kinsey and Davies 1979; Neumann and
Macintyre 1985; Hallock and Schlager 1986; Vogt 1989;
Hubbard et al., 1997).
Given the impact of global environmental deterioration
on modern reefs, particularly those resulting from greenhouse gas emissions, it is important to clarify arguments
concerning the cause of reef demise and back-stepping.
This is because the processes postulated to have caused
reef demise and back-stepping in the past are very similar
to ones that have been identified as threatening reefs in the
future. In this light, the investigation of reef back-stepping
in the recent past is taking on a new sense of urgency.
Reef back-stepping in stable terranes
The discovery of back-stepping in Quaternary reefs
occurred when Fairbanks (1989) drilled submerged,
postglacial reef terraces off the south coast of Barbados.
His cores showed three back-stepping reefs containing thick
monospecific sequences of the reef-crest coral Acropora
palmata, which has a depth-restricted habitat range of
$5 m (Figure 1). By dating this reef-crest coral, he identified two rapid rises in postglacial sea level termed meltwater
pulse (Mwp) 1a and 1b, but never analyzed the stratigraphy
or recognized the significance of reef back-stepping per se.
That recognition was made by Blanchon and Shaw (1995),
who used elevation differences between the A. palmata
sequences, and their transition into succeeding units, to constrain the rate and magnitude of those rapid-rise events. By
including evidence from other submerged reef crests in the
Caribbean, they also identified a rapid rise (Mwp-1c) in the
early Holocene which caused a third reef back-stepping
David Hopley (ed.), Encyclopedia of Modern Coral Reefs, DOI 10.1007/978-90-481-2639-2,
# Springer Science+Business Media B.V. 2011
BACK-STEPPING
Paul Blanchon
National Autonomous University of Mexico, Cancun,
Mexico
Synonyms
Transgressive reef
Definition
Shallow-reef systems back-step to keep up with rapid relative sea-level rise. Back-stepping involves the demise of
shallow-reef development at one site, and its relocation to
another site further inshore and up-shelf. It is common
during the onlap or retrogradation of tropical carbonate
systems in transgressive systems tracts, and typical of glacial terminations during the Quaternary Ice Age.
Introduction
Reef back-stepping has been widely recognized from the
geological record where it is almost universally interpreted as a result of rapid rise in relative sea level (Smith
and Stearn 1987; Kaufman and Meyers 1988; Ross
1992; Becker et al., 1993; Wendte and Uyeno 2005). Yet
ironically, there has been considerable argument over its
existence and significance in late Pleistocene and Holocene reefs. This largely stems from early assumptions that
healthy reefs could accrete faster than the average rate of
glacio-eustatic sea-level rise (Adey et al., 1978; Schlager
1981). Reef drowning in the strictest sense was therefore
considered uncommon and only ‘incipient drowning’,
where shallow reefs were initially submerged but subsequently recovered when the rise rate declined, was considered likely (Kendall and Schlager 1981). According to this
early view, complete drowning of healthy reefs by
submerging them below the euphotic zone ($100 m)
required exceptional circumstances: either a combination
of regional subsidence and pulsed sea-level rise which
removed the reef from the low-stand euphotic zone, or
more local environmental factors to suppress the accretion
potential of reefs and make them susceptible to drowning
(Adey 1978; Kinsey and Davies 1979; Neumann and
Macintyre 1985; Hallock and Schlager 1986; Vogt 1989;
Hubbard et al., 1997).
Given the impact of global environmental deterioration
on modern reefs, particularly those resulting from greenhouse gas emissions, it is important to clarify arguments
concerning the cause of reef demise and back-stepping.
This is because the processes postulated to have caused
reef demise and back-stepping in the past are very similar
to ones that have been identified as threatening reefs in the
future. In this light, the investigation of reef back-stepping
in the recent past is taking on a new sense of urgency.
Reef back-stepping in stable terranes
The discovery of back-stepping in Quaternary reefs
occurred when Fairbanks (1989) drilled submerged,
postglacial reef terraces off the south coast of Barbados.
His cores showed three back-stepping reefs containing thick
monospecific sequences of the reef-crest coral Acropora
palmata, which has a depth-restricted habitat range of
$5 m (Figure 1). By dating this reef-crest coral, he identified two rapid rises in postglacial sea level termed meltwater
pulse (Mwp) 1a and 1b, but never analyzed the stratigraphy
or recognized the significance of reef back-stepping per se.
That recognition was made by Blanchon and Shaw (1995),
who used elevation differences between the A. palmata
sequences, and their transition into succeeding units, to constrain the rate and magnitude of those rapid-rise events. By
including evidence from other submerged reef crests in the
Caribbean, they also identified a rapid rise (Mwp-1c) in the
early Holocene which caused a third reef back-stepping
David Hopley (ed.), Encyclopedia of Modern Coral Reefs, DOI 10.1007/978-90-481-2639-2,
# Springer Science+Business Media B.V. 2011