patches of deep-water coral further down-slope. Behind
the barrier, the lagoon is dominated by skeletal sand interspersed by patch reefs, and passes laterally into coral
thickets of the fringing reef (terrace VIIa). This doublereef complex is dissected by the Kwangam Gorge, where
the fringing reef is seen to pass beneath the lagoon floor
into the barrier (Bloom et al., 1974). The gorge also
exposes an erosion surface $20 m below the barrier crest
sloping gently for some 30 m into the lagoon, but it shows
no evidence of subaerial exposure (Stein et al., 1993).
Although laterally discontinuous, this erosion surface
was interpreted as separating the two reef units and indicating that the barrier reef disconformably overlies the
fringing-reef unit (Chappell and Veeh, 1978). Part of this
interpretation was clearly based on different alpha spectrometric U-series ages that were reported early on from the
two reef-crests by Veeh and Chappell (1970) and Bloom
et al. (1974). But recent dating using more precise and
better screened U-series ages has failed to replicate these
early results, and has also identified significant age
inversions down the barrier-reef slope where no evidence
of stratigraphic discontinuity exists (Stein et al., 1993).
A similar erosion surface was observed to divide reef
units in the Sazum River gorge, a further 10 km to the
northwest (Aharon et al., 1980; Aharon and Chappell,
1986). At this location, a 30 m barrier-reef section
erosively overlies a 70 m thick reefal unit that was implicitly assumed to be a seaward extension of the fringing-reef
unit (Figure 2). However, this underlying reefal unit was
also encountered in “Aladdin’s Cave” located some
90 m below the barrier crest close to the Kwangam gorge
(Esat et al., 1999). A shallow head-coral assemblage
found in the walls and floor of the cave imply that this
underlying reef unit is an early transgressive reef that
accreted vertically in response to the deglacial SL rise, as
has also been illustrated for the Holocene reef terrace
(Chappell and Polach, 1991; Ota and Chappell, 1999).
Corals from this cave returned seven isotopically acceptable
230
Th ages of between 125.6 and 133.7 ka (i.e.,
a 7.2 ka true-age variation). These were averaged by Esat
et al. (1999) to assign an age of 130 ka to the cave reef
(ignoring a reliable age of 115 ka), and then compared to
an average of 134 ka assigned to the barrier crest from four
corals dated by Stein et al. (1993), (again ignoring four
significantly younger ages also reported by those authors).
By comparing the average age and elevation of these two
coral groups, Esat et al. (1999) claimed that SL fell rapidly, at least 70 m from the 134 ka barrier-crest group to
the cave group, and then rose rapidly, at least 85 m from
the 130 ka cave group, with both the fall and the rise
occurring within the 4 ka difference between groups.
Unfortunately, the validity of this comparison is questionable given that it ignores younger ages from the cave site
as well as those from the barrier-crest site reported by
Stein et al. (1993). It is much more likely that these stratigraphic age inversions reflect true-age variability (Scholz
and Mangini, 2007) and that the cave is simply the oldest
part of terrace VII which accreted vertically as SL rose.
It is clear from the foregoing, that the interpretation of
LIG reef architecture in the Huon Peninsula has been
obfuscated by various attempts to obtain a terrace chronology. The fundamental problem has been that unreliable
U-series age determinations, which clearly fail any test
of stratigraphic consistency, have driven the analysis of
the stratigraphy itself, rather than the other way round.
This has led to disconformities being inferred between
stratigraphically inverted ages, or inverted ages simply
being ignored, rather than acknowledging that many dates
have large true-age variabilities and that more than 50% of
those with “reliable” isotopic signatures have discordant
231
Pa ages (Scholz and Mangini, 2007). As a result, SL
histories determined from these inadequate data are premature, especially interpretations of extreme excursions
based on ages alone (Esat et al., 1999).
Furthermore, and as noted by Pandolfi and Chappell
(1994, p. 138), widely spaced stratigraphic sections are
merely “one-dimensional sloping profiles of threedimensional reef structures” and say little about stratigraphic architecture, which has been poorly documented
in the area. And what little stratigraphic detail has emerged
has been over-interpreted. Erosion surfaces which lack
evidence of subaerial exposure are clearly difficult to
interpret in the absence of supportive contextural data,
given that they can be produced by processes other than
SL fall. Likewise, it is premature to apply a keep-up model
of interglacial reef development in the absence of internal
facies geometries from either the LIG or Holocene terraces. Even the Holocene reef structure, which has been
described from a long bore-hole (Chappell and Polach,
1991), lacks a taxonomy to species level and thus identification of coral zonation (biofacies) data, making interpretation of SL history or reef response difficult to
substantiate (cf. Chappell and Polach, 1976).
Red Sea
The Red Sea is an active continental rift system related to
the development of a spreading center between the African and Arabian plate. Dynamic interplay between rift tectonics, halokinetic faulting, volcanism, climate, and SL
variation during the Quaternary has produced a complex
stratigraphy where abrupt facies changes between river
alluvium, alluvial fans, reef, lagoon, Salina, and beach
units, make it difficult to correlate between areas and
unequivocally separate tectonic from eustatic SL events
(Plaziat et al., 1995). This complexity, together with
incomplete exposure and limited uplift of LIG deposits,
makes it a difficult area to investigate either interglacial
duration or highstand character. Nevertheless, several
investigations of reef development during the LIG have
been reported from the Egyptian and Eritrean coasts of
the Red Sea.
Along the coast of Eritrea, an uplifted and tilted LIG
reef sequence near Abdur shows two main stages of shallow-reef development (Walter et al., 2000; Bruggemann
et al., 2004). The lower unit is composed of fringing-reef
626
LAST INTERGLACIAL AND REEF DEVELOPMENT
the barrier, the lagoon is dominated by skeletal sand interspersed by patch reefs, and passes laterally into coral
thickets of the fringing reef (terrace VIIa). This doublereef complex is dissected by the Kwangam Gorge, where
the fringing reef is seen to pass beneath the lagoon floor
into the barrier (Bloom et al., 1974). The gorge also
exposes an erosion surface $20 m below the barrier crest
sloping gently for some 30 m into the lagoon, but it shows
no evidence of subaerial exposure (Stein et al., 1993).
Although laterally discontinuous, this erosion surface
was interpreted as separating the two reef units and indicating that the barrier reef disconformably overlies the
fringing-reef unit (Chappell and Veeh, 1978). Part of this
interpretation was clearly based on different alpha spectrometric U-series ages that were reported early on from the
two reef-crests by Veeh and Chappell (1970) and Bloom
et al. (1974). But recent dating using more precise and
better screened U-series ages has failed to replicate these
early results, and has also identified significant age
inversions down the barrier-reef slope where no evidence
of stratigraphic discontinuity exists (Stein et al., 1993).
A similar erosion surface was observed to divide reef
units in the Sazum River gorge, a further 10 km to the
northwest (Aharon et al., 1980; Aharon and Chappell,
1986). At this location, a 30 m barrier-reef section
erosively overlies a 70 m thick reefal unit that was implicitly assumed to be a seaward extension of the fringing-reef
unit (Figure 2). However, this underlying reefal unit was
also encountered in “Aladdin’s Cave” located some
90 m below the barrier crest close to the Kwangam gorge
(Esat et al., 1999). A shallow head-coral assemblage
found in the walls and floor of the cave imply that this
underlying reef unit is an early transgressive reef that
accreted vertically in response to the deglacial SL rise, as
has also been illustrated for the Holocene reef terrace
(Chappell and Polach, 1991; Ota and Chappell, 1999).
Corals from this cave returned seven isotopically acceptable
230
Th ages of between 125.6 and 133.7 ka (i.e.,
a 7.2 ka true-age variation). These were averaged by Esat
et al. (1999) to assign an age of 130 ka to the cave reef
(ignoring a reliable age of 115 ka), and then compared to
an average of 134 ka assigned to the barrier crest from four
corals dated by Stein et al. (1993), (again ignoring four
significantly younger ages also reported by those authors).
By comparing the average age and elevation of these two
coral groups, Esat et al. (1999) claimed that SL fell rapidly, at least 70 m from the 134 ka barrier-crest group to
the cave group, and then rose rapidly, at least 85 m from
the 130 ka cave group, with both the fall and the rise
occurring within the 4 ka difference between groups.
Unfortunately, the validity of this comparison is questionable given that it ignores younger ages from the cave site
as well as those from the barrier-crest site reported by
Stein et al. (1993). It is much more likely that these stratigraphic age inversions reflect true-age variability (Scholz
and Mangini, 2007) and that the cave is simply the oldest
part of terrace VII which accreted vertically as SL rose.
It is clear from the foregoing, that the interpretation of
LIG reef architecture in the Huon Peninsula has been
obfuscated by various attempts to obtain a terrace chronology. The fundamental problem has been that unreliable
U-series age determinations, which clearly fail any test
of stratigraphic consistency, have driven the analysis of
the stratigraphy itself, rather than the other way round.
This has led to disconformities being inferred between
stratigraphically inverted ages, or inverted ages simply
being ignored, rather than acknowledging that many dates
have large true-age variabilities and that more than 50% of
those with “reliable” isotopic signatures have discordant
231
Pa ages (Scholz and Mangini, 2007). As a result, SL
histories determined from these inadequate data are premature, especially interpretations of extreme excursions
based on ages alone (Esat et al., 1999).
Furthermore, and as noted by Pandolfi and Chappell
(1994, p. 138), widely spaced stratigraphic sections are
merely “one-dimensional sloping profiles of threedimensional reef structures” and say little about stratigraphic architecture, which has been poorly documented
in the area. And what little stratigraphic detail has emerged
has been over-interpreted. Erosion surfaces which lack
evidence of subaerial exposure are clearly difficult to
interpret in the absence of supportive contextural data,
given that they can be produced by processes other than
SL fall. Likewise, it is premature to apply a keep-up model
of interglacial reef development in the absence of internal
facies geometries from either the LIG or Holocene terraces. Even the Holocene reef structure, which has been
described from a long bore-hole (Chappell and Polach,
1991), lacks a taxonomy to species level and thus identification of coral zonation (biofacies) data, making interpretation of SL history or reef response difficult to
substantiate (cf. Chappell and Polach, 1976).
Red Sea
The Red Sea is an active continental rift system related to
the development of a spreading center between the African and Arabian plate. Dynamic interplay between rift tectonics, halokinetic faulting, volcanism, climate, and SL
variation during the Quaternary has produced a complex
stratigraphy where abrupt facies changes between river
alluvium, alluvial fans, reef, lagoon, Salina, and beach
units, make it difficult to correlate between areas and
unequivocally separate tectonic from eustatic SL events
(Plaziat et al., 1995). This complexity, together with
incomplete exposure and limited uplift of LIG deposits,
makes it a difficult area to investigate either interglacial
duration or highstand character. Nevertheless, several
investigations of reef development during the LIG have
been reported from the Egyptian and Eritrean coasts of
the Red Sea.
Along the coast of Eritrea, an uplifted and tilted LIG
reef sequence near Abdur shows two main stages of shallow-reef development (Walter et al., 2000; Bruggemann
et al., 2004). The lower unit is composed of fringing-reef
626
LAST INTERGLACIAL AND REEF DEVELOPMENT