Table of Contents
- 1 What are the main types of cross-bedding?
- 2 How do you tell the direction of cross-bedding?
- 3 What is the difference between cross-bedding and ripple marks?
- 4 Where are cross-bedding found?
- 5 Are ripple marks caused by sand slumping down a dune face?
- 6 What are the types of cross bedding?
- 7 What is cross bedding in geology?
What are the main types of cross-bedding?
The three types of cross-bedding under this classification are simple, planar, and trough. The lower bounding surfaces are surfaces of nondeposition, planar surfaces of erosion, and curved surfaces of erosion, respectively.
What is cross-bedding in sedimentary rocks?
Cross-beds are the groups of inclined layers, and the sloping layers are known as cross strata. Cross bedding forms on a sloping surface such as ripple marks and dunes, and allows us to interpret that the depositional environment was water or wind.
How do you tell the direction of cross-bedding?
The cross-beds reflect the steep faces of ripples and dunes. These steep faces tilt down-current and thus indicate current flow direction. Cross-beds are commonly curved at the base; this gives a handy way of determining right-side up in complexly deformed rocks.
What is tangential cross-bedding?
In many cases the cross bed angles will shallow in the down-flow direction, giving a tangential contact with the underlying bed. These nearly tangential parts are called bottom sets. Cross beds are described as trough or planar based on their shape along a cross-section perpendicular to the flow direction.
What is the difference between cross-bedding and ripple marks?
RIPPLE MARKS are produced by flowing water or wave action, analogous to cross-bedding (see above), only on a smaller scale (individual layers are at most a few cm thick). The cross-beds or (more accurately) cross-laminae are inclined to the right, thus the water was flowing from left to right.
What can cause cross-bedding?
Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes in a flowing fluid. The fluid flow causes sand grains to saltate up the stoss (upstream) side of the bedform and collect at the peak until the angle of repose is reached.
Where are cross-bedding found?
Cross-bedding can form in any environment in which a fluid flows over a bed with mobile material. It is most common in stream deposits (consisting of sand and gravel), tidal areas, and in aeolian dunes.
Why does cross-bedding happen?
Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes in a flowing fluid. Cross-bedding can form in any environment in which a fluid flows over a bed with mobile material. It is most common in stream deposits (consisting of sand and gravel), tidal areas, and in aeolian dunes.
Are ripple marks caused by sand slumping down a dune face?
Ripple marks are ridges of sediment that form in response to wind blowing along a layer of sediment. The troughs and ridges of fossilized ripple mark in sandstone and siltstones are hardened versions of the short-lived ripples in the loose sand of a modern-day stream, lake, sea, or sand dune.
What does the presence of cross-beds indicate?
Significance. Cross-beds can tell geologists much about what an area was like in ancient times. The direction the beds are dipping indicates paleocurrent, the rough direction of sediment transport. The direction of motion of the cross-beds can show ancient flow or wind directions (called paleocurrents).
What are the types of cross bedding?
The most commonly described types are tabular cross-bedding and trough cross-bedding. Tabular cross-bedding, or planar bedding consists of cross-bedded units that are extensive horizontally relative to the set thickness and that have essentially planar bounding surfaces. Trough cross-bedding, on the other hand,…
What is trough cross bedding?
trough crossbedding. [′trȯf ′krȯs‚bed·iŋ] (geology) A variety of crossbedding in which the lower crossbedding surfaces are smoothly curved, rather than planar.
What is cross bedding in geology?
In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers.