Geology Reference
In-Depth Information
Fig. 16.22.
Carbonate plat-
forms and reefs.
Global area
covered by carbonate plat-
forms (left) and integrated
reef production at a super-
sequence stratigraphic resolu-
tion (right, data from Kiess-
ling et al. 2000). Error bars
indicate statistical 95% con-
fidence intervals based on to-
tal values, but do not consider
other uncertainties. Reefal
carbonate production varied
more strongly than platform
carbonate production. For
most of the time platform and
reefal production appears to
be decoupled. After Kiessling
et al. (2003).
platforms (see maps of platform distribution in Kiess-
ling et al. 2003).
•
Changes in global carbonate platform areas
do not
vary systematically with climatic fluctuations or with
trends in the availability of shallow shelves at low lati-
tudes.
•
Carbonate platforms usually survive mass extinc-
tion events
owing to their global size and commonly
also to their accumulation rate, which is not signifi-
cantly affected because of the potential of platforms to
balance taxonomic loss by increased non-enzymatic
carbonate production and enhanced production through
surviving taxa.
•
Benthic foraminifera,
which achieved their highest
productivity in pre-Miocene off-reef settings, are im-
portant components of platform carbonates.
• Platform production and reef development were
decoupled over most of the Phanerozoic time
(Kiessling
et al. 2000) although parallel temporal trends exist, as
shown by the increased development of platform-mar-
gin reefs and relatively high platform carbonate pro-
duction (e.g. in the Devonian and Jurassic). The
decoupling is especially evident when the integrated
reef carbonate production is compared with the spatial
extent of carbonate platforms during times of maximal
transgression within Phanerozoic supersequences (Fig.
16.22). Fluctuations in reef production are much more
pronounced than fluctuations in platform size and plat-
form accumulation rates. No significant correlation
exists between changes in reconstructed reefal carbon-
ate production and changes in platform size. Variations
in calcareous non-reefal benthic organisms (e.g. fora-
minifera; Fig. 16.20) are apparently an important con-
trol on changes in carbonate platform production.
• The
evolution of carbonate-secreting biota,
whose
reaction to oceanographic changes is determined by
their genetically fixed ecologic capabilities, is a major
control on platform development and is as important
as sea-level history.
16.7.1.2 Phanerozoic Reef Patterns
Many Phanerozoic reef attributes exhibit significant
temporal trends. The abundance of reefs, preferential
depositional setting, dominant constructional and com-
positional reef types, prevailing reef biota (Sect.
16.2.3.1), and reefal carbonate production related to
reef size and reef debris potential changed markedly
during the Phanerozoic. The following discussion of
some of the reef attributes is based on Kiessling (2002)
and consider the PaleoReef database (Kiessling et al.
1999; Kiessling and Flügel 2002). Note that this data-
base uses a broad reef definition that includes ecologic
reefs, reef mounds and mud mounds (see Sect. 16.2).
Abundance of reefs.
Fig. 16.23 shows the number
of reef sites in the PaleoReef database calculated for
stages. The graph exhibits a strongly fluctuating pat-
tern with a Phanerozoic maximum abundance of reefs
in the Frasnian (Copper 2002 sees the maximum in the
Givetian) and Miocene, and high reef abundance in the
