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.

Sedimentary structures and bedding style (part I)

another picture of sedimentary structure and bedding style:

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.

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, California.

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, Utah.

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.

Sedimentary Structures

some kinds of sedimentary structures:

1. Deformational Structures

- Load cast: are rounded or bulbous protrusions formed during compaction. Where these grooves and depressions become filled with sediment, especially if the surface is mud, the marks may be preserved.

- Convolute Bedding: appears as highly contorted, folded and disrupted layers.

- flame structure: deformed clay or silt laminations with curved, pointed ends that project into the overlying bed and resemble a flame blown in the wind.

2. Current Flow Structures

- Parallel Lamination : (where the upper and lower contacts are approximately parallel) can result from

• settling from suspension
• deposition in a low energy environment
• laminar flow (water flowing in a planar way)

- Ripple Marks : formed when the current flow energy increases.

- Cross Bedding : continuous erosion of the stoss side of the ripples and deposition on the leeward side causes

- Graded Bedding: As sediment is carried from a high energy environment into a low-energy environment, the heaviest particles will be the first to settle out, followed by progressively lighter and lighter particles.

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3)organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris. Pictures and brief descriptions of some common sedimentary rock types are shown below.

Breccia

Breccia is a clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragments. The spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds the rock together. The specimen shown above is about two inches (five centimeters) across.

Chert

Chert is a microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO₂). It occurs as nodules and concretionary masses and less frequently as a layered deposit. It breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons. The specimen shown above is about two inches (five centimeters) across.

Coal

Coal is an organic sedimentary rock that forms mainly from plant debris. The plant debris usually accumulates in a swamp environment. Coal is combustible and is often mined for use as a fuel. The specimen shown above is about two inches (five centimeters) across.

Conglomerate

Conglomerate is a clastic sedimentary rock that contains large (greater then two millimeters in diameter) rounded particles. The space between the pebbles is generally filled with smaller particles and/or a chemical cement that binds the rock together. The specimen shown above is about two inches (five centimeters) across.

Iron Ore

Iron Ore is a chemical sedimentary rock that forms when iron and oxygen (and sometimes other substances) combine in solution and deposit as a sediment. Hematite (shown above) is the most common sedimentary iron ore mineral. The specimen shown above is about two inches (five centimeters) across.

Limestone

Limestone is a rock that is composed primarily of calcium carbonate. It can form organically from the accumulation of shell, coral, algal and fecal debris. It can also form chemically from the precipitation of calcium carbonate from lake or ocean water. Limestone is used in many ways. Some of the most common are: production of cement, crushed stone and acid neutralization. The specimen shown above is about two inches (five centimeters) across.

Rock Salt

Rock Salt is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is also known by the mineral name "halite". It is rarely found at Earth's surface, except in areas of very arid climate. It is often mined for use in the chemical industry or for use as a winter highway treatment. Some halite is processed for use as a seasoning for food. The specimen shown above is about two inches (five centimeters) across.

Sandstone

Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains and deltas. The specimen shown above is about two inches (five centimeters) across.

Shale

Shale is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces. The specimen shown above is about two inches (five centimeters) across.

Siltstone

Sedimentary Rocks Picture Gallery of the Most Common Rock Types Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3)organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris. Pictures and brief descriptions of some common sedimentary rock types are shown below. Share| Sedimentary Rock Types Menu Breccia Chert Coal Conglomerate Iron Ore Limestone Rock Salt Sandstone Shale Siltstone Breccia Breccia is a clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragments. The spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds the rock together. The specimen shown above is about two inches (five centimeters) across.Return to Top Chert Chert is a microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO2). It occurs as nodules and concretionary masses and less frequently as a layered deposit. It breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons. The specimen shown above is about two inches (five centimeters) across.Return to Top Coal Coal is an organic sedimentary rock that forms mainly from plant debris. The plant debris usually accumulates in a swamp environment. Coal is combustible and is often mined for use as a fuel. The specimen shown above is about two inches (five centimeters) across.Return to Top Conglomerate Conglomerate is a clastic sedimentary rock that contains large (greater then two millimeters in diameter) rounded particles. The space between the pebbles is generally filled with smaller particles and/or a chemical cement that binds the rock together. The specimen shown above is about two inches (five centimeters) across.Return to Top Iron Ore Iron Ore is a chemical sedimentary rock that forms when iron and oxygen (and sometimes other substances) combine in solution and deposit as a sediment. Hematite (shown above) is the most common sedimentary iron ore mineral. The specimen shown above is about two inches (five centimeters) across.Return to Top Limestone Limestone is a rock that is composed primarily of calcium carbonate. It can form organically from the accumulation of shell, coral, algal and fecal debris. It can also form chemically from the precipitation of calcium carbonate from lake or ocean water. Limestone is used in many ways. Some of the most common are: production of cement, crushed stone and acid neutralization. The specimen shown above is about two inches (five centimeters) across.Return to Top Rock Salt Rock Salt is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is also known by the mineral name "halite". It is rarely found at Earth's surface, except in areas of very arid climate. It is often mined for use in the chemical industry or for use as a winter highway treatment. Some halite is processed for use as a seasoning for food. The specimen shown above is about two inches (five centimeters) across.Return to Top Sandstone Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains and deltas. The specimen shown above is about two inches (five centimeters) across.Return to Top Shale Shale is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces. The specimen shown above is about two inches (five centimeters) across.Return to Top Siltstone Siltstone is a clastic sedimentary rock that forms from silt-size (between 1/256 and 1/16 millimeter diameter) weathering debris. The specimen shown above is about two inches (five centimeters) across.