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can destroy primary sedimentary structures on bed
tops and bottoms and obliterate internal structures
e.g. in turbidites. 'Bedding' can be created by di-
agenetic remixing of carbonates (Eder 1971).
Meischner Model and Bouma Model: Zone 1a and
Zone 1b of the Meischner Sequence correspond to Di-
vision A of the Bouma Sequence. Zone 1c exhibits cri-
teria of Division B. Zone 2a and Zone 2b correspond
to Division C. Zone 3 has criteria of Division D of the
Bouma Sequence. The uppermost pelitic Division E of
turbiditic and hemipelagic origin is not included within
the Meischner Sequence. The models are similar, but
exhibit some differences. In comparison with the
Bouma Sequence, Zone 1 of the Meischner sequence
is characterized by ruditic rather than arenitic alloch-
thonous grains. Reverse grading near the base of Zone
1 seems to be more common than in Division A of the
Bouma Sequence. The differentiation of lower plane-
parallel laminated (Division B), middle ripple or con-
volute laminated (Division C), and upper parallel lami-
nated parts (Division D) of the Bouma Sequence is
much less developed in Zone 2 of limestone turbidites.
Fig. 15.18. The Meischner Sequence describing an ideal
'allodapic' limestone turbidite. The turbidite bed is interca-
lated between beds formed by the basinal background sedi-
ment (fine-grained 'pelites', i.e. marls or micrites containing
nektonic and planktonic fossils). The 'pre-phase' (zone 0) is
characterized by micrites or marls with scattered small litho-
clasts and rather large rock fragments. The genesis of the
pre-phase is controversial. Solution and reprecipitation of
carbonate may be important. The contact to the underlying
pelagic zone is sharp. The upper surface of the pre-phase
may be wavy and irregular. The 'main phase' (zone 1) exhib-
its three parts: Part 1a is a distinctly graded limestone with
shallow-water fossils and lithoclasts. Reverse grading and
grain imbrication may occur. Sorting increases upward. Part
1b is a fine-grained micrite. The upper part 1c may be faintly
laminated and includes angular limestone clasts and micrite
pebbles. Zone 2 is a micrite characterized by planar bedding
planes with densely spaced laminations (2a), overlain by a
unit with current ripple lamination (2b), and sometimes also
with convolute bedding. Zone 3 is represented by marls that
may exhibit flaser textures. This zone merges gradually into
the overlying marly or pelagic sediment. Bed thickness is
about 1 m. Bed thickness is high in the near-source proximal
position, and decreases in distal depositional areas. After
Meischner (1964).
Differentiation of turbidites: Turbidites are differ-
entiated into several depositional types:
Proximal turbidites, deposited relatively close to the
source area are massive, relatively weakly graded,
and exhibit only poorly developed tractional struc-
tures and little interbedded pelagic sediment.
Turbidites characterized by the Bouma Sequence ,
have distinct graded bedding, oriented erosion and
fill markings at the base, interbedded pelagic sedi-
ment and a characteristic succession of sedimentary
structures.
Distal turbidites, formed far away from the source
region, are characterized by thin, fine-grained graded
layers, well-developed cross-lamination and absence
of massive intervals and parallel laminations.
Fluxoturbidites: Turbidites can be underlain by beds
characterized by large, very poorly sorted and inversely
graded components forming breccias. These fluxo-
turbidites are overlain by normally graded turbidites.
Fluxoturbidites contribute to a traction carpet, signify-
ing the begin of allochthonous sedimentation in proxi-
mal depositional sites on slope or base-of-slope envi-
ronments (Stanley and Unrug 1972; Sallenger 1979;
Steiger 1981).
Some of the more important characteristics for the
proximality and distality of limestone turbidites are
summarized in Tab. 15.2. Ideally, proximity indicators
work for turbidite sequences deposited only from a
single source by longitudinal sheet flows. In turbidite
fans, turbidites with proximal and distal features may
be juxtaposed. Meandering of turbidity currents may
produce strong deviations from general proximal-dis-
tal patterns. Some of the deviations are caused by dif-
ferences in the sedimentation in deep and large versus
shallow and small basins, point or line sources, and in
the different settling behaviors of carbonate particles
(Sarnthein and Bartolini 1973).
Deep-water source turbidites: Limestone turbidites
with grains derived not from shallow-marine environ-
ments but rather from upper slope or deep-water build-
ups exhibit features known in allodapic limestones, but
also show significant differences when compared with
the Meischner or Bouma Model. Differences involve
the sequence of internal structures and the greater varia-
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