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Geology of Stokes Bay - crossbedding
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Coastal outcrops on the north coast of Kangaroo Island exposes numerous examples of soft sediment and primary structures, such as slump, diapirism, dewatering, ripples, cross-bedding, erosional channels and general loss of layering. These features occur in all three main rock sequences investigated here: the Kanmantoo Group, and the Mt McDonnel and Stokes Bay Formations of the Kangaroo Island Group.
Please park your car at the parking coordinates and walk to GZ. On GZ you can see some nice examples for cross-bedding in the walls of the rock channels of stokes bay.
What does cross-bedding mean?
In geology, the sedimentary structures known as cross-bedding refer to (near) horizontal units that are internally composed of inclined layers. This is a case in geology in which the original deposition layering is tilted, and the tilting is not a result of post-deposition deformation. Cross-beds or "sets" are the groups of inclined layers, and the inclined layers are known as cross strata.
Cross bedding forms during deposition on the inclined surfaces of bed-forms such as ripples and dunes and indicates that the depositional environment contained a flowing medium (typically water or wind). Examples of these bed-forms are ripples, dunes, anti-dunes, sand waves, hummocks, bars and delta slopes. Cross-bedding is widespread in many environments. Environments in which water movement is fast enough and deep enough to develop large-scale bed forms fall into three natural groupings: rivers, tide-dominated coastal and marine settings.
The sandstone of Stokes Bay – a short description
Red-brown to orange arkose. Abundant through cross-bedding, planar and slumped bedding. Thick beds with tabular fore-sets and convoluted bedding.
To claim this earthcache, please send me following answers to my profile:
1.What is the direction of the channel?
2.There are other rock types on this beach. Name the other rock types! Do you have any idea, why the other rock types have no cross-bedding?
3.Some of the sandstone has an orange surface. Why is that?
4.Photos would me nice, but only optional!
(No hints available.)
Last Updated: on 1/27/2018 3:51:02 PM (UTC-08:00) Pacific Time (US & Canada) (11:51 PM GMT)
Coordinates are in the WGS84 datum