Geology Reference
In-Depth Information
Fig. 14.7
Bedding patterns of purported internal tide deposits,
compiled by He et al. (
2008
) . (
a
) inverse to normally graded
sandstone/siltstone exhibiting bi-directional cross-stratifi cation.
(
b
) inverse to normally-graded sandstone with bi-directional
cross-stratifi cation. (
c
) Normally graded sandstone with bi-
directional cross-stratifi cation. (
d
) Same as (
c
) but with large-scale
cross-stratifi cation (unidirectional) at the base. (
e
) Thickening
then thinning upward succession of sand-mud couplets. The
sand exhibits bi-directional cross-stratifi cation. (
f
) Bioclastic
or oolitic limestone, commonly with bi-directional cross-
stratifi cation
(Laird
1972
), the Cretaceous of the Ontong-Java Plateau
(Klein
1975
) , the Cretaceous Rosario Formation,
Mexico (this study), the Cretaceous Wheeler Gorge
conglomerate, California, U.S.A. (this study), the
Eocene-Oligocene Annot Formation, SW France
(Shanmugam
2003
), the Eocene Torrey submarine can-
yon, California, U.S.A. (May et al.
1983
) , the Miocene
Salir Formation, SW Turkey (Hayward
1984
) , and the
Pliocene of the deep-water Krishna-Godavari Basin,
India (Shanmugam et al.
2009
) . A few of these deposits
are described in more detail below.
Zhenzhong and Eriksson (
1991
) presented a rela-
tively shallow (<200 m water deep) submarine canyon-
confi ned part of the Ordovician Bays Formation, where
they interpreted sedimentary structures consistent with
deposition from bi-directional currents as the deposits
of internal tides. This interpretation is based on several
40-75 cm thick intervals of well-sorted, very-fi ne
grained, cross-laminated sandstone with bidirectional
paleocurrent orientations (foresets inclined both up
and down-canyon), two of which exhibit inverse to
normal grading, and a thin (10-13 cm), normally-
graded interval that contains unidirectional ripple
cross-lamination which dip up-canyon. These 'internal
tide deposits' are interbedded with dark shales and
normally-graded, poorly sorted beds interpreted to be
of turbidite origin. Deposited under less than 200 m
of water, however, this setting could have experienced
a major contribution from the surface tides, and
therefore the relative contribution of surface to internal
tidal currents is unresolved.
Zhenzhong et al. (
1998
) interpreted a 30 m thick
section of thinly interbedded fi ne-grained sandstone
and mudstone of the Upper Ordovician Yankou
Formation (China) as tidal rhythmites deposited in an
unchannelized upper continental-slope setting, although
they present neither a clear understanding of the paleo-
bathymetry nor any rigorous test of tidal origin (e.g.
harmonic analysis). These deposits are arranged into
20-100 cm thick intervals of thickening then thinning
upward couplets of very-fi ne to fi ne-grained sandstone
and mudstone (Fig.
14.7e
). The couplets vary in thick-
ness from 1 to 2 cm at the base and top of a succession
to 3-7 cm thick in the middle. The sandstones are coars-
est in the middle of a succession. The sandstones exhibit
bidirectional paleocurrent directions, foresets dipping
up and down the slope, and contain abundant lenticular,
wavy, and fl aser bedding. Subsequently quite a lot of
work on internal tide deposits in outcrop and well-bores
has been done in China, primarily by Chinese scientists
at Yangtze University (Chengxin et al.
2005
; Gao et al.
1997
; He and Gao
1999
; He et al.
2008
; He et al.
2007
) .
This group of researchers has recognized four main
types of sedimentary facies associations they think are
characteristic of internal tidal deposits: (1) inverse to
normally-graded successions with bidirectional cross-
lamination (up and down-channel dipping) (Fig.
14.7a, b
),
(2) normally graded successions with bidirectional
