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Fig. 21.19 ( a ) Interlayered light green - to reddish brown lami-
nated argillaceous dolomudstone/dolomitic shale and reddish
brown and fi ne- to very fi ne-grained lithic sandstone from the
Middle Cambrian member 2 of the Mila Formation, eastern
Alborz Mountains, northern Iran. ( b ) Close up view of a part of
( a ) showing the laminated shale/dolomite and the capping sand-
stone facies (Lens cap diameter is 5.5 cm). The laminated shale-
carbonate facies contain hopper halite casts and has no subaerial
exposure features interpreted as a lowstand coastal salina pond
deposit. ( c ) Cast of hopper halite crystals mentioned in ( b ).
( d ) A laminated supper mature quartz arenite bed overlies
and underlies, with abrupt contacts, a fenestral dolomudstone
(supratidal facies) forming a pure carbonate and pure silici-
clastic double cycle (Y. Lasemi et al. 2008 ); base of the trans-
gressive systems tract in the Lower Triassic Sorkh Shale
Formation, south of the Tabas failed rift basin, east central Iran
21.6.1.2 Allocyclicity
In many ancient carbonate tidalites, cyclicity has been
interpreted based on Milankovitch-band periodic cli-
mate changes (e.g. Goldhammer et al. 1987 ; Koerschner
and Read 1989 ; Goldhammer et al. 1993 ; Strasser et al.
1999 ; Preto et al. 2004 ). In the Milankovitch orbital
forcing model, three parameters including precession,
obliquity and eccentricity could generate high frequency
eustatic sea level cycles with approximate durations
of 20,000, 41,000 and 100,000 years, respectively.
Evidence for Milankovitch-band periodic eustatic sea
level changes in the stratigraphic record include lateral
continuity of cycles on a regional and interregional
scale, 5:1 grouping of 5th-order small-scale cycles to
form larger 4th-order cycles of 100,000 years duration,
and high frequency subtidal cycles with karstic or cal-
ichie soil caps (e.g. Goldhammer et al. 1987 ; Koerschner
and Read 1989 ; Preto et al. 2004 ) . Allocyclicity is
strong during icehouse periods due to higher-amplitude
relative sea level changes (Lehrmann and Goldhammer
1999 ; Burgess 2006 ) .
Subsidence due to high-frequency extensional fault
movements (“yo-yo” and “yo” tectonics) can also create
accommodation space for the formation of stacked
peritidal cycles (Hardie 1986 ; Hardie et al. 1991 ;
De Benedictis et al. 2007 ; Bosence et al. 2009 ) .
According to Bosence et al. ( 2009 ) , the cycles form
due to fi lling of accommodation created by episodic
rapid downwarping followed by slow subsidence in
the hanging wall and graben sites (“yo” tectonics) and
concurrent rapid uplift and slow subsidence in the
footwall sites (“yo-yo” tectonics). The most common
cycle type is asymmetric shallowing-upward, but sym-
metric deepening then shallowing-upward, asymmetric
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