Catuneanu Principles Seq Stratigraphy book[1]
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Catuneanu Principles Seq Stratigraphy book[1]

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and Wightman, 1994; Tandon and Gibling, 1994,
1997). A\u2014calcrete, marking a \u2018subaerial unconformity\u2019 (depositional sequence boundary) within coastal plain
deposits. The carbonate soil implies a semi-arid climatic period, suggesting that lowstands in base level were
relatively more arid than the peat-forming periods that represent the overlying transgressive and highstand
systems tracts; B\u2014close up of calcrete in image A, showing well-developed vertic and nodular fabric; C\u2014
calcrete in image A, with strong nodular texture. Note the non-disrupted nature of the siltstone below; D\u2014
calcrete exposed on wave-cut platform, with strong vertic fabric (scale 50 cm); E\u2014upright tree cast, partially
replaced by carbonate beneath a \u2018lowstand\u2019 calcrete layer. This occurrence suggests that carbonate-rich
groundwaters caused local cementation through conduits below the main soil level; F\u2014close up of carbonate-
cemented tree in image E.
such as texture, color, amount of organic matter, miner-
alogy, cation exchange capacity, and pH (Soil Survey
Staff, 1975, 1998; Fig. 2.14). The main pitfalls of this
approach, when applied to paleosols, are two-fold: 
(1) the taxonomic approach does not emphasize the
importance of hydromorphic soils (i.e., \u2018gleysols\u2019,
common in aggrading fluvial floodplains, defined 
on the basis of soil saturation; Fig. 2.14); and (2) it is
dependent on soil properties, some of which (e.g.,
cation exchange capacity, or amount of organic matter)
are not preserved in paleosols. For these reasons, Mack
et al. (1993) devised a classification specifically for 
paleosols (Fig. 2.14), based on mineralogical and
morphological properties that are preserved as a soil is
transformed to a paleosol. Due to the shift in classifica-
tion criteria, the two systems are not directly equivalent
with respect to some soil/paleosol groups (Fig. 2.14).
From a sequence stratigraphic perspective, paleosols
may provide key evidence for reconstructing the synde-
positional conditions (e.g., high vs. low water table,
accommodation, and sedimentation rates, paleoclimate)
during the accumulation of systems tracts, or about
the temporal significance of stratigraphic hiatuses
associated with sequence-bounding unconformities.
The types of paleosols that may form in relation to the
interplay between surface processes (sedimentation,
erosion) and pedogenesis are illustrated in Fig. 2.15.
Stages of nondeposition and/or erosion, typically
associated with sequence boundaries, result in the
formation of mature paleosols along unconformity
surfaces. Stages of sediment accumulation, typically
FIGURE 2.13 Coastal plain successions showing calcrete horizons
(arrows\u2014depositional sequence boundaries) overlain by red calcic
vertisols (photographs courtesy of M.R. Gibling; Pennsylvanian
Sydney Mines Formation, Sydney Basin, Nova Scotia). The red vertisols
(dryland clastic soils) are interpreted as being formed within the trans-
gressive systems tract under conditions of abundant sediment supply
(Tandon and Gibling, 1997). A\u2014\u2018lowstand\u2019 carbonates (calcrete pale-
osols/sequence boundary \u2013 arrow) pass upward into dryland clastic
soils, probably marking the renewal of clastic supply to the coastal plain
as accommodation is made available by base-level rise; B \u2014 close up of
concave-up, slickensided joints (mukkara structure) in red vertisols of
image A; C\u2014grey coastal-plain siltstones at lower left pass upward in
meter-thick calcrete (arrows). Siltstones immediately below the calcrete
are calcite cemented. Calcrete is overlain by red vertisols and thin splay
sandstones, as sedimentation resumed on the dryland coastal plain,
possibly as transgression allowed sediment storage on the floodplain.
Soil systematics
(Soil Survey Staff,
1975, 1998)
Paleosol systematics
(Mack et al., 1993)
FIGURE 2.14 Comparison between the soil and paleosol classifi-
cation systems of the United States Soil Taxonomy (Soil Survey Staff,
1975, 1998) and Mack et al. (1993). Due to differences in the classifi-
cation criteria, not all soil or paleosol groups have equivalents in
both systems.
associated with the deposition of sequences, result in the
formation of less mature and generally aggrading pale-
osols of compound, composite, or cumulative nature,
whose rates of aggradation match the sedimentation
rates (see Kraus, 1999, for a comprehensive review of
these paleosol types).
Paleosols associated with sequence boundaries are
generally strongly developed and well-drained,
reflecting prolonged stages of sediment cut-off and a
lowered base level (low water table in the nonmarine
portion of the basin; Fig. 2.12). Besides base level,
climate may also leave a strong signature on the nature
of sequence-bounding paleosols (e.g., a drier climate
would promote evaporation and the formation of
calcic paleosols). Base level and climate are not neces-
sarily independent variables, as climatic cycles driven
by orbital forcing (e.g., eccentricity, obliquity, and
precession cycles, with periodicities in a range of tens
to hundreds of thousands of years; Fig. 2.16; Milankovitch,
1930, 1941; Imbrie and Imbrie, 1979; Imbrie, 1985;
Schwarzacher, 1993) are a primary control on sea-level
changes at the temporal scale of Milankovitch cycles.
In such cases, stages of base-level fall may reflect times
of increased climatic aridity (e.g., see Tandon and
Gibling, 1997, for a case study). On the other hand, base-
level changes may also be driven by tectonism, inde-
pendent of climate changes, in which case base-level
cycles may be offset relative to the climatic fluctuations.
A more comprehensive discussion of the relationship
between base-level changes, sea-level changes, tecton-
ism, and climate is provided in Chapter 3.
Irrespective of the primary force behind a falling
base level, the cut-off of sediment supply is an impor-
tant parameter that defines the conditions of formation
of sequence-bounding paleosols. Stages of sediment
cut-off during the depositional history of a basin may
be related to either autogenic or allogenic controls. In
the case of sequence boundaries, the fall in base level
and the sediment cut-off are intimately related, and are
both controlled by allogenic mechanisms. The strati-
graphic hiatus associated with a sequence-bounding
unconformity/paleosol varies greatly with the rank
(importance) of the sequence and the related allogenic
controls, and it is generally in a range of 104 years (for
the higher-frequency Milankovitch cycles) to 105\u2013107
years for the higher-order sequences (Summerfield,
1991; Miall, 2000). Sequence-bounding unconformities
are commonly regional in scale, as opposed to the more
FIGURE 2.15 Interplay of pedogenesis and surface
processes (modified from Morrison, 1978; Bown and
Kraus, 1981; Marriott and Wright, 1993; Kraus, 1999).
Compound, composite and cumulative paleosols occur
within conformable successions, hence within deposi-
tional sequences. \u2018Truncated\u2019 paleosols are associated
with stratigraphic hiatuses, and therefore mark
diastems or unconformities.
Surface processes
Sedimentation (S)
and/or erosion (E)
Sedimentation (S)
Erosion (E)
Pedogenesis (P)
Pedogenesis (P)
E > P:
no paleosol
P > E:
truncated paleosols
S > P:
no soil
no soil
S ~ P:
P > S:
multistory paleosols
solitary paleosols
(±100 - ±413 ka) PRECESSION(±21