Sedimentary structures and bedding style (part II)

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.

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, China.

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, China.