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• bioclastic floatstones with rudists and organic crusts,
and
• oolitic and oncolitic packstones.
The microfacies types formed under low-energy con-
ditions (protected inner ramp) include:
• bioclastic wackestones and packstones with dasy-
clad algae, and
• biopelpackstones and wackestones with benthic
foraminifera.
Highstand Systems Tract:
Again, the transition from
a transgressive systems tract to highstand systems tract
is characterized by major changes in the distribution
of microfacies types. The differentiation of the ramp
into more facies belts is reflected by a significant in-
crease in microfacies diversity. Widely distributed
microfacies types are:
•
inner platform shoals, and deep open-marine basinal
environments.
Facies belts and the distribution of microfacies types
were integrated within a sequence-stratigraphic frame-
work. Sequence boundaries are documented by emer-
sion (paleosols, caliche, vadose cements) or erosional
surfaces connected with changes in lithology and hard-
grounds, and by stratigraphic gaps. Typical sediments
of LSTs are evaporites, claystones with plants, ostra-
cods and oysters, and silt- and sandstones. Relative sea-
level rise is recognizable from the reduction of silici-
clastic influx and the development of inner-platform
marls and coarse bioclastic and oolitic carbonates.
Deep-water TST sediments are represented by marls
and chalks with planktonic foraminifera and ammo-
nites. HSTs are characterized by thick, shallow-sub-
tidal deposits and muddy subtidal and lagoonal car-
bonates.
Note that LST sediments are underrepresented in
this example. Most microfacies types occur both in sedi-
ments formed under TST and HST conditions, but the
diversity of microfacies types increases from TST to
HST.
grainstones and packstones with rudist debris,
•
bioclastic floatstones with rudists,
•
peloidal and bioclastic wackestones and packstones,
•
packstones with benthic foraminifera,
•
fenestral mudstones and dolomites.
The high amount of oolitic microfacies types com-
pared with bioclastic grainstones is interpreted as re-
sult of an increased development of flat, high-energy
areas during the TST, favoring enough accommoda-
tion space for the formation of ooids (see Jenkyns and
Strasser 1995; Pittett et al. 1995). Increasing accom-
modation space supports the formation of ooids in com-
parison with skeletal grains (Schlager et al. 1994).
Basics: Sequence stratigraphy of carbonates (overviews)
Berg, O.R., Woolverton, D.G. (eds., 1985): Seismic stratig-
raphy II. An integrated approach. - American Associa-
tion of Petroleum Geologists, Memoir,
39
, 276 pp.
Bracco Gartner, G.L., Morsilli, M., Schlager, W., Bosellini,
A. (2002): Toe-of-slope of a Cretaceous carbonate plat-
form in outcrop, seismic model and offshore seismic data
(Apulia, Italy). - International Journal of Earth Sciences,
91
, 315-330
Cross, T.A., Lessenger, M.A. (1988): Seismic stratigraphy. -
Annual Reviews of Earth Planetary Science,
16
, 319-354
Emery, D., Myers, K., Bertram, G., Griffith, C., Reynolds,
M.N.T., Richards, M. (1996): Sequence stratigraphy. - In-
ternational Association of Sedimentologists, 297 pp.
Frostick, L., Steel, R. (eds., 1994): Tectonic controls and sig-
natures in sedimentary successions. - International Asso-
ciation of Sedimentologists, 528 pp.
Handford, C.R., Loucks, R. (1993): Carbonate depositional
sequences and system tracts. - In: Loucks, R.G., Sarg,
J.F. (eds.): Carbonate sequence stratigraphy: recent de-
velopments and applications. - American Association of
Petroleum Geologists, Memoir,
57
, 3-41
Harris, P.M., Saller, A.H., Simo, J.A.T. (eds., 1999): Advances
in carbonate sequence stratigraphy: application to reser-
voirs, outcrops and models. - SEPM, Special Publication,
63
, 421 pp.
Lehrmann, D.J., Goldhammer, R.K. (1999): Secular varia-
tion in parasequence and facies stacking patterns of plat-
form carbonates: a guide to the adaption of stacking-pat-
tern analysis in strata of diverse ages and settings. - In:
Harris, P.M., Saller, A.H., Simo, J.A.T. (eds., 1999): Ad-
vances in carbonate sequence stratigraphy: application to
reservoirs, outcrops and models. - SEPM, Special Publi-
cation,
63
, 187-225
Late Cretaceous platform interior carbonates of the
Sinai
Fig. 16.5 shows microfacies and systems tracts of
Turonian shallow-marine platform sediments studied
by Bauer et al. (2002). The Sinai platform extended
over a maximum length of about 200 km and was dif-
ferentiated in the Turonian by a shallow intrashelf ba-
sin. The Sinai platform was drowned during the Early
Turonian. Platform environments recovered in the
Middle Turonian and carbonate platform interior sedi-
ments prevailed until the Late Turonian. From the
Coniacian onward, siliciclastic input from the hinter-
land increased significantly and mixed siliciclastic-car-
bonate deposits accumulated in basins and swells.
The study was focused on the vertical and lateral
microfacies distribution and the relationships between
grain composition and depositional environments based
on the semiquantitative investigation of 450 thin sec-
tions from 20 sections. The latter support shorefaces,
restricted lagoons, shallow subtidal environments and
