Geology Reference
In-Depth Information
supply (Fig.
21.22
), which is compatible with various
existing sequence stratigraphic models (For a detailed
review of sequence stratigraphic principles and models
see Miall
1997
; Schlager
2005
; Catuneanu
2006
;
Catuneanu et al.
2009
) .
A depositional sequence can be subdivided into
systems tracts (linkage of contemporaneous deposi-
tional systems) as defi ned by Brown and Fisher (
1977
) ,
which are defi ned on the basis of parasequence stack-
ing patterns, position within the sequence and types of
bounding surfaces (Van Wagoner et al.
1988,
1990
) . A
depositional sequence may consist of up to four types
of systems tracts depending on the shape of base-level
curve, type of depositional system, basinal setting, and
post depositional erosion at the sequence boundary
(e.g. Catuneanu
2006
; Catuneanu et al.
2009
) . These
packages include lowstand, transgressive, highstand
and falling stage systems tracts (Fig.
21.22
).
The lowstand systems tract (LST) overlies the
sequence boundary and comprises normal regressive
sediments deposits after the onset of relative sea level
rise. The transgressive systems tract (TST) lies between
the transgressive surface (ts) above the LST or it over-
lies the sequence boundary and is capped by maximum
fl ooding surface (mfs). It forms when the rate of rise
exceeds the rate of deposition, displays a deepening-
upward facies trend and a characteristic retrograda-
tional parasequence stacking pattern. The highstand
systems tract (HST) forms during the late stage of
base-level rise, when the rate of deposition exceeds the
rate of accommodation being created (shoreline normal
regression). HST deposits underlie the FSST or the
sequence boundary and are characterized by shallow-
ing-upward facies trend displaying aggradational to
progradational parasequence stacking pattern. The
falling stage systems tract (FSST) includes the strata
deposited during base-level fall (forced regression)
and underlies the sequence boundary.
Carbonate platforms produce sediment during peri-
ods of base-level rise mainly during transgressive and
highstand stages of a base-level curve. During falling
stage and lowstand sea level rise, the entire platform
or the platform interior is exposed to karstifi cation
and calichie (calcrete) development in humid and dry
climates, respectively, forming a pronounced subaerial
unconformity. Therefore, FSST-LST packages are nor-
mally absent and the sequence boundary commonly is
capped by transgressive systems tract of the overlying
sequence. In a carbonate ramp setting of a passive
Fig. 21.21
(
a
) Brownish gray lagoonal deposits (
right
) grading
into
light brown
intertidal and supratidal deposits. Note the
abrupt upper contact (
dashed line
) with the overlying lagoonal
deposit (the
encircled tree
is about 3 m tall); Lower Miocene
middle member of the Asmari Formation in the Mish Mountain,
Zagros Mountain range, southwest Iran. (
b
)
Dark gray
biotur-
bated lime mudstone (subtidal lagoon facies) overlies, with an
erosional contact, a
yellow
dolomudstone (tidal fl at facies)
indicating transgression over a tidal fl at cycle cap; Lower
Triassic lower member of the Elika Formation in the central
Alborz Mountains, northern Iran
and Goldhammer
1999
) and represent a depositional
sequence. A depositional sequence as defi ned by
Mitchum et al. (
1977
) is a stratigraphic unit composed
of a relatively conformable succession of genetically
related strata bounded by unconformities (Fig.
21.20
)
or their correlative conformities. Catuneanu et al.
(
2009
) recommended using the term 'stratigraphic
sequence', a sedimentary succession deposited during
a full cycle of change in accommodation or sediment
