310
Chapter 7 Sequences, Minor Cycles, and Event Stratigraphy
a PROXIMAL
DISTAL
SS
SEO "" ACC
SEO < ACC
~
."
I .
LONG-TERM
COMPOSITE SL-CURVE,
PARASEQU ENCES
~---- 'L---ER + BYP NEW _...::JL _ ~
_________ P ....... _,.gp~~T
Q
:c:;r - -- - - .==---~-~
SUB,
-__
~
/ \ --------1 5U6 ' >5U6,
e
f
9
d
CHRONOTHICKNESS.
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STRATIGRAPHY
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w
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d
w
CI:
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RELATIVE FALL
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Fig. 7.9. Model of parasequenee formation in
embayments, shallow seas, and somewhat deeper
water. a Cross seetion of basin margin. b,c Superposition of a sinusoidal high-frequeney and low-amplitude eustatie sea-Ievel fluetuation onto a seeond sinusoidal sea-level eurve of lower frequeney but greater
amplitude. SUB, SED, SLF, ACC rates of subsidence, sediment buildup, relative sea-Ievel fall, and
gain or loss of aeeommodation spaee. SS sediment
supply. Long-term it is always: max. SLF d Short time intervals in whieh SLF>SUB.
e Chronostratigraphie sequenee in proximal position
,
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,
. -- -..
RISING
3RD ORDER SL
. ~~~~~'~I~G+ .
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DING I
I
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I
,
where SS and SED::::: ACC (low-frequeney eurve).
Stratigraphie gaps are mostly longer than shown in d
beeause of rapid SED. Phases of low SED (reworking, winnowing), deepening and shallowing. f Thiekness of aetual sediment buildup with erosional uneonformities ete. Subseetions of long-term SLF are
thinner than those of SLR. g Sediment buildup in
more distal position (temporally ACC>SED) where
eroded and bypassed material from proximal loeations aeeumulates as prograding or baekstepping sediment bodies