Sedimentary structures and bedding styles by wpr1947


									Sedimentary structures and bedding styles.
Please enjoy my rather random assortment of sedimentary structure photos.
More are forthcoming as soon as I organize them!

Click on any image for a full-sized version.

                                               Wedge bedding. Successive stack of erosive-
                                               based channels creates wedge-shaped bedding
                                               cross-sections. Shiguai Formation, Inner
                                               Mongolia, China.

                                               Channelized bedding. Erosive scours that
                                               backfill with sand may give rise to isolated
                                               channelized sandbodies such as this. Mesa
                                               Verde Group, Utah.

                                               Tabular cross-bedding. These steep
                                               foresets are typical of eolian deposition. Late
                                               Jurassic, Liaoning Province, China.
Trough cross-bedding. Trough cross
bedding is produced by the downflow migration
of lunate dunes in both subaqueous and
subaerial environments. Triassic, Hebei
Province, China.

Trough cross-bedding. This unusual view
is of mud-draped gravel foresets cut by a joint
that is oriented parallel to bedding. We are
looking down at a cut-away view of an
originally horizontal surface. The arcuate
surfaces shown were mud drapes on the
downstream sides of gravel lunate dunes.
Hammer handle points downflow. Note also the
wood fragment oriented parallel to flow (just to
the left of the hammer handle), and a second set
of mud-draped forsets that is cut off by the
bottom edge of the photograph.

Wave Ripples. Cross-sectional view of ripple
cross-laminated sandstone, showing bi-
directional cross laminae indicative of a wave
origin. Entrada Formation, Jurassic, San
Rafael Swell, Utah.

Ripple Marks. A pile of eroded, rippled beds
that all contain gorgeous ripple marks. If you
click on nothing else, click to enlarge this one!
Carmel Formation, Utah.
Ripple Marks. Casts of wave ripples on the
base of a sandstone bed. Cretaceous, Hebei
Province, China.

Herrigbone cross-stratification. Bi-
directional cross beds such as these are
indicative of a tidal origin. Curtis Formation,
Jurassic, Utah.

Gilbert Delta foresets. These are composite,
large-scale foresets that indicate depostion into
still water. The height of the foresets indicates
the still water depth. Mecca Formation,

Climbing current ripples. Ripple foresets
that "climb" on the backs of their predecessors
are indicative of waning flow conditions and
rapid sediment fallout, such that sediment drops
out of suspension as fast as it can be molded
into a bedform. Entrada Formation, Jurassic,
Climbing current ripples and convolute
lamination. The result of rapid sediment
fallout is often instability due to liquefaction,
leading to disruption of laminae by water
escape. Such disruption is termed convolute
lamination. Modern Colorado River, Utah.

Graded bedding. Graded bedding results
from a rapid decrease in flow velocity that
causes sediment to drop out of suspension.
Larger particles settle fastest, therefore they
accumulate at the bottom of the bed. Houcheng
Formation, Jurassic, Hebei Province, China.

Graded beds, flame structures. Rapid
sediment fallout from suspension often loads
underlying fine-grained sediment to the point of
failure, causing foundering of the overlying
sediment and formation of structures termed
flames (for obvious reasons!). Permian, Inyo
County, California.

Flame Structure. The flame structures
underlying this thick sandstone bed are
evidence for rapid sand depostion; these
sandstone beds are in fact sublacustrine
turbidites. Cretaceous, Hebei Province, China.
Imbrication. Disk-shaped gravel clasts that
are transported by rolling often "shingle"
themselves to form a fabric termed imbrication.
Individual clasts dip upflow. Current in this
photo is from left to right (click to enlarge!).
Owens Valley, California.

Graded and imbricated bed. OK, now I'm
just getting redundant, but here you are
anyways. Trail Canyon alluvial fan, Death
Valley, California.

HCS? Maybe. Which way is up?

Flute casts. Flutes are caused by erosional
eddies at the base of a turbulent flow. The
deepest scour is on the upstream end of the
flute, and the scours widen and become
shallower downflow. Shiguai Formation, Inner
Mongolia, China.
Gutter casts. Gutter casts are formed by
entrained particles dragging along the base of a
bed and leaving a track in their wake. These
gutters were formed by wood fragments
draggeing along the base of a river bed.
Chengde Formation, Jurassic, Hebei province,

Dessication cracks. Mudcracks can become
very large, which may make them difficult to
recognize in small outcrops. Person for scale.
Jixian Formation, Proterozoic, China.

Dessication cracks. A modern example.
These are up to 1 m deep, and form polygonal
networks that are often difficult to see except
from the air! Panamint Valley, California.
Linguloid Ripples. These mud-draped
ripples are linguloid in form, indicating
shallow, rapid flow within the ripple stability
field. Permian, Inner Mongolia, China.

Debris flow deposit. This type of non-
erosive, unstructured and unsorted bed is
typical of cohesive debris flow deposits. Coffin
Canyon Fan, Death Valley, California.

Debris flow deposit. Oversized clasts
"floating" in a mud-rich matrix are also typical
of such flows. Coffin Canyon Fan, Death
Valley, California.

Slump Deposit. Chaotic deposits such as
these indicate slope failure. Cretaceous, Hebei
province, C

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