Geology Reference
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increase in the number of facies belts (particularly on
ramps) and shallowing-upward successions forming
meter-sized cycles. Often thick-bedded and light-col-
ored. Carbonate mud in lagoons, restricted environ-
ments and tidal flats.
Significant increase in the diversity of microfacies
types and biota as compared with TSTs. Fully marine
biota prevail, exhibiting different associations in dif-
ferent subenvironments. Ooids abundant. Aggregate
grains (Sect. 4.2.7) are common grains of sea-level
highstands carbonates.
lated over distances of more than 100 km and may pro-
vide a chronological framework permitting detailed pa-
leogeographical reconstructions (Strasser 1987).
Differentiating HST and LST in slope and basinal en-
vironments
Carbonate sediment is exported from the platform
to platform flanks. Changes in carbonate production
of the platform may be detected by a quantified analy-
sis of grain composition of platform flanks. These
changes may or may not coincide with stratal geom-
etry and bed surfaces.
Recognizing high-frequency sea-level changes
High-resolution sequence analysis aims to under-
stand short-term depositional processes that took place
on a time scale of some ten thousand to hundred thou-
sand years. These analyses require a bed-per-bed in-
vestigation with respect to facies and depositional en-
vironment, the determination of depositional sequences
(supported by photomosaics; Weidlich and Bernecker
2003), and the identification of sequence boundaries
and maximum flooding surfaces.
Hierarchical stacking of depositional sequences
common in HSTs, and facies changes allow us to de-
fine small-scale, medium-scale and large-scale se-
quences (Strasser et al. 1999). These sequences of
fourth, fifth, and even higher order express the small-
est changes in the environment through facies changes
(e.g. Goodwin and Anderson 1985; Grotzinger 1986;
Strasser 1987). The changes produce relatively thin
shallowing-upward sedimentary successions (para-
sequences) bounded by marine flooding surfaces. These
parasequences exhibit different vertical successions,
depending on their setting in platform, ramp and off-
shore environments. An instructive example from the
Middle Jurassic of Switzerland was described by
Gonzales (1996). Synchronous changes in sea-level are
recorded
• in off-shoal environments by a parasequence with
marl layers at the base of thin upward-shoaling units,
covered by increasingly proximal tempestites;
• in ramp environments by oblique-stratified oolitic
and bioclastic grainstones bounded by marine flood-
ing surfaces; and
• on the platform by marine flooding surfaces over-
lain by coral beds, oncoid beds and platform tempes-
tites deposited under moderate energy conditions,
which are in turn covered by high-energy, oblique-
stratified oolitic grainstones.
Highstand and lowstand shedding
. Sea-level fluc-
tuations affecting the carbonate production in platform
environments are recorded by shallow-marine arago-
nite-rich carbonate material exported to the slope and
into basins. Most sediment is shed during sea-level
highstands (Schlager et al. 1994). Highstand shedding
is triggered by the flat tops of carbonate platforms pro-
viding large production areas that are many times larger
than during lowstands, and by the presence of rimmed
platform margins. Highstand shedding is pronounced
in low-latitude platforms. Evidence of highstand shed-
ding comes from interglacial periods of the Quaternary
of the Bahamas, the Nicaragua Rise in the Caribbean
and the Queensland Shelf. Examples of ancient high-
stand shedding have been described from the Pleis-
tocene back to the Devonian (compare the case study
documented in Sect. 15.7.5.2). Note that the highstand
model is restricted to flat-topped platforms. It does not
apply to carbonate ramps (Betzler et al. 2000; Westphal
et al. 2004).
Shedding is strongly reduced during lowstands by
the very strong reduction or demise of carbonate pro-
duction and the rapid meteoric and marine lithification
preventing erosion of carbonate material (Droxler and
Schlager 1985).
Sediment shed from an exposed platform top (low-
stand) differs from platforms with flooded tops (high-
stand) in the composition of coarse skeletal and non-
skeletal grains. Quantitative compositional analysis of
turbidites and other mass-flow intercalations in slope
and basinal sediments reflect lowstand and highstand
conditions:
•
Highstand shedding
is indicated by the dominance
of non-skeletal grains including abundant ooids, pe-
loids and aggregate grains (grains that require flooded
platform tops for their formation), in association with
specific, shallow-marine platform-interior skeletal
grains. Primarily aragonitic grains dominate.
Such parasequences deposited in response to small-
scale, high-frequency sea-level changes can be corre-
