widespread reef development than present, and reefs not
only extended further into coastal lowlands but significantly expanded their latitudinal range (Kendrick et al.,
1991; Greenstein and Pandolfi, 2008; McCulloch and
Mortimer, 2008). The elevation and age of fossil reefcrests from tectonically stable terrains in several areas of
the world indicate that the sea level was 3 m higher than
the present by $125 ka and peaked at 6 m sometime thereafter (Stirling et al., 1998; Blanchon et al., 2009).
Reef development during the LIG has played
a particularly important role in understanding the causes
of climate and sea-level oscillations during glacial–interglacial cycles. First, the absolute timing and duration of
reef development has been used to test the Milankovitch
theory of orbital forcing, which holds that variation in
northern-hemisphere summer insolation drives ice-sheet
growth and decay as reflected in SL records (Hays et al.,
1976). Second, the age and elevation of fossil reef-crests
allow the reconstruction of a high-resolution record of
ice-volume and sea level during the highstand, and thus
provides an analog for ice-sheet stability in the present
interglacial under sustained, greenhouse-gas induced
global warming.
Reef development in uplifted terrains
Reef development in uplifted areas can potentially provide
an assessment of the timing of postglacial sea-level rise (or
glacial termination) and the duration of the interglacial
but, due to the tectonic overprint and the possibility of
coseismic displacement, it is difficult to infer anything
about the detailed SL behavior or the absolute elevation
reached during the highstand.
Barbados
Pleistocene reef terraces on Barbados have been extensively dated by various methods since the late 1960s,
and 15 separate terraces have been identified which represent an episodic record of reef development from 640 to
60 ka (Broecker et al., 1968; Mesolella et al., 1969; James
et al., 1971; Matthews, 1973; Bender et al., 1979). The
continuous uplift of the island at rates of up to 0.53 mm/
year has produced terraces that record the last six or seven
interglacial SL highstands, corresponding to MIS 5–17
(Shackleton and Matthews, 1977; Fairbanks and Matthews, 1978; Taylor and Mann, 1991; Speed and Cheng,
2004).
Early reconnaissance mapping by Mesolella and
coworkers discovered that many of the interglacial terraces on Barbados displayed a regular, depth-related facies
sequence consisting of a deep head-coral zone which
passed vertically into thickets of branching Acropora
cervicornis, and then into the more robust A. palmata in
the reef-crest zone (Mesolella, 1968; Mesolella et al.,
1970). As seen in Figure 1, the elevations of these coral
assemblages on the terrace surfaces are very similar to
the depth-zonation on mid-twentieth century Jamaican
reefs (Mesolella, 1967). In his analysis of the terraces,
Mesolella also observed reefs with two main types of
facies sequences: those with over-thickened reef-crest
units, and those with a shallowing-up sequence which
started in deep head corals and finished in reef-crest or
rear-zone facies (Mesolella et al., 1970). The first
sequence he attributed to a keep-up response to rising
SL, and the second to a prograding response to a semistable SL. Based on known rates of SL rise, uplift, and reef
growth, he speculated that reefs did not initiate on Barbados until later stages of the transgression, when the rise
slowed and approximated accretion rates of the reefs (see
Mesolella et al., 1970, Fig. 16). He postulated that this late
transgressive stage of reef development was initially characterized by vertical accretion of facies producing an overthickened sequence, and then to progradation as relative
stillstand conditions prevailed.
The fundamental problem with this keep-up and prograde model was that Mesollela was uncertain as to what
facies lay at the base of the terraces because shallow
road-cuts provided no exposure. He postulated that reef
bases may have started either as a pioneering assemblage
of deep-water corals that built up into a climax reef-crest
community, or initiated with a full zonation that responded
directly to SL rise. Furthermore, he acknowledged that his
model could not account for certain morphological anomalies in the LIG reef terrace. For example, a reef terrace on
the south coast is split into two sub-terraces which are both
rimmed by facies containing the reef-crest coral
A. palmata (Figure 1). Subsequently, Ku et al. (1990)
interpreted the lower terrace, informally known as the
“Maxwell Hill” sub-terrace, as a reef-crest-lagoon unit
and suggested that this division might represent stratigraphic evidence of a double highstand (Figure 1). Upon
dating, however, he could not detect any significant age
difference between the two sub-terraces. More recently,
Schellmann and Radtke (2004) redated these two subterraces using electron spin resonance and claimed significant age differences between terraces, with the upper
terrace being older (128 ka) than the lower (118 ka).
Unfortunately, there are problems with the analysis of
Schellmann and Radtke (2004). First, the terrace ages
have analytical errors as large as their age differences,
and the age ranges for each terrace overlap to such an
extent that the new age designations are effectively meaningless. Second, no facies analysis of the lower sub-terrace
was presented to support the claim that it was a reef-crestlagoon system (as suggested by Ku et al. [1990]). And
third, it ignored a detailed facies analysis by Blanchon
and Eisenhauer (2001), which confirmed that a true reefcrest facies was absent from the lower Maxwell Hill
subterrace (Figure 1). In fact, these new facies data
showed that the two sub-terraces combined have a facies
zonation that is consistent with a single-reef system, with
the upper sub-terrace encompassing the rear zone and
a high-energy reef-crest facies, and the lower sub-terrace
the reef-front A. cervicornis facies and a peripheral ridge
of inter-grown thickets of A. palmata and A. cervicornis
(Blanchon and Eisenhauer, 2001). That A. palmata is
622
LAST INTERGLACIAL AND REEF DEVELOPMENT
only extended further into coastal lowlands but significantly expanded their latitudinal range (Kendrick et al.,
1991; Greenstein and Pandolfi, 2008; McCulloch and
Mortimer, 2008). The elevation and age of fossil reefcrests from tectonically stable terrains in several areas of
the world indicate that the sea level was 3 m higher than
the present by $125 ka and peaked at 6 m sometime thereafter (Stirling et al., 1998; Blanchon et al., 2009).
Reef development during the LIG has played
a particularly important role in understanding the causes
of climate and sea-level oscillations during glacial–interglacial cycles. First, the absolute timing and duration of
reef development has been used to test the Milankovitch
theory of orbital forcing, which holds that variation in
northern-hemisphere summer insolation drives ice-sheet
growth and decay as reflected in SL records (Hays et al.,
1976). Second, the age and elevation of fossil reef-crests
allow the reconstruction of a high-resolution record of
ice-volume and sea level during the highstand, and thus
provides an analog for ice-sheet stability in the present
interglacial under sustained, greenhouse-gas induced
global warming.
Reef development in uplifted terrains
Reef development in uplifted areas can potentially provide
an assessment of the timing of postglacial sea-level rise (or
glacial termination) and the duration of the interglacial
but, due to the tectonic overprint and the possibility of
coseismic displacement, it is difficult to infer anything
about the detailed SL behavior or the absolute elevation
reached during the highstand.
Barbados
Pleistocene reef terraces on Barbados have been extensively dated by various methods since the late 1960s,
and 15 separate terraces have been identified which represent an episodic record of reef development from 640 to
60 ka (Broecker et al., 1968; Mesolella et al., 1969; James
et al., 1971; Matthews, 1973; Bender et al., 1979). The
continuous uplift of the island at rates of up to 0.53 mm/
year has produced terraces that record the last six or seven
interglacial SL highstands, corresponding to MIS 5–17
(Shackleton and Matthews, 1977; Fairbanks and Matthews, 1978; Taylor and Mann, 1991; Speed and Cheng,
2004).
Early reconnaissance mapping by Mesolella and
coworkers discovered that many of the interglacial terraces on Barbados displayed a regular, depth-related facies
sequence consisting of a deep head-coral zone which
passed vertically into thickets of branching Acropora
cervicornis, and then into the more robust A. palmata in
the reef-crest zone (Mesolella, 1968; Mesolella et al.,
1970). As seen in Figure 1, the elevations of these coral
assemblages on the terrace surfaces are very similar to
the depth-zonation on mid-twentieth century Jamaican
reefs (Mesolella, 1967). In his analysis of the terraces,
Mesolella also observed reefs with two main types of
facies sequences: those with over-thickened reef-crest
units, and those with a shallowing-up sequence which
started in deep head corals and finished in reef-crest or
rear-zone facies (Mesolella et al., 1970). The first
sequence he attributed to a keep-up response to rising
SL, and the second to a prograding response to a semistable SL. Based on known rates of SL rise, uplift, and reef
growth, he speculated that reefs did not initiate on Barbados until later stages of the transgression, when the rise
slowed and approximated accretion rates of the reefs (see
Mesolella et al., 1970, Fig. 16). He postulated that this late
transgressive stage of reef development was initially characterized by vertical accretion of facies producing an overthickened sequence, and then to progradation as relative
stillstand conditions prevailed.
The fundamental problem with this keep-up and prograde model was that Mesollela was uncertain as to what
facies lay at the base of the terraces because shallow
road-cuts provided no exposure. He postulated that reef
bases may have started either as a pioneering assemblage
of deep-water corals that built up into a climax reef-crest
community, or initiated with a full zonation that responded
directly to SL rise. Furthermore, he acknowledged that his
model could not account for certain morphological anomalies in the LIG reef terrace. For example, a reef terrace on
the south coast is split into two sub-terraces which are both
rimmed by facies containing the reef-crest coral
A. palmata (Figure 1). Subsequently, Ku et al. (1990)
interpreted the lower terrace, informally known as the
“Maxwell Hill” sub-terrace, as a reef-crest-lagoon unit
and suggested that this division might represent stratigraphic evidence of a double highstand (Figure 1). Upon
dating, however, he could not detect any significant age
difference between the two sub-terraces. More recently,
Schellmann and Radtke (2004) redated these two subterraces using electron spin resonance and claimed significant age differences between terraces, with the upper
terrace being older (128 ka) than the lower (118 ka).
Unfortunately, there are problems with the analysis of
Schellmann and Radtke (2004). First, the terrace ages
have analytical errors as large as their age differences,
and the age ranges for each terrace overlap to such an
extent that the new age designations are effectively meaningless. Second, no facies analysis of the lower sub-terrace
was presented to support the claim that it was a reef-crestlagoon system (as suggested by Ku et al. [1990]). And
third, it ignored a detailed facies analysis by Blanchon
and Eisenhauer (2001), which confirmed that a true reefcrest facies was absent from the lower Maxwell Hill
subterrace (Figure 1). In fact, these new facies data
showed that the two sub-terraces combined have a facies
zonation that is consistent with a single-reef system, with
the upper sub-terrace encompassing the rear zone and
a high-energy reef-crest facies, and the lower sub-terrace
the reef-front A. cervicornis facies and a peripheral ridge
of inter-grown thickets of A. palmata and A. cervicornis
(Blanchon and Eisenhauer, 2001). That A. palmata is
622
LAST INTERGLACIAL AND REEF DEVELOPMENT