5 Rock processes Flashcards
What are sole marks?
Soul marks or flute marks are indentations made by strong currents flowing over mud. the current erodes hollows and other marks into surface of mud. These indentations are filled with sand and then preserved as casts on the base of overlying stand stone units tool marks are produced by the scoring of the underlying made by large particles within the current soul until marks are found along the contact plane between two different lithologies or rock types for example, mudstone and sandstone.
What are mud cracks?
Mud crux form from drying in shrinking of clay, rich settlements in mud. As the sediment dries it, shrinks, causing polygon or shape cracks to form, which often fill with water. Over time with other segments, does preserving the polygon or pattern. Can form in any environment where sediments are wet, then subsequently dried.
What are ripple marks?
Ripple marks are small scale versions of cross beds. They are formed on the top of unconsolidated sediments by currents. Commonly found on stream beds, beaches, and Lake Shores. If ripples are asymmetrical, geologist can determine the Paleocurrent direction, which is the direction that the wind or water is flowing.
What is cross bedding or cross laminations?
This forms when ripples or dunes migrate across the surface, where the deposited. The individual beds form from sediments, moving up and over the wind ward or moving upstream side of a ripple or dune, becoming deposited at an angle or downstream side.
What is graded bedding
Graded bedding are layers of Strata with varying grain sizes and are deposited from slow currents where course fraction settles out. First these beds may vary from less than a centimetre to over a metre thick.
What are sedimentary structures?
Sedimentary structures include graded bedding, cross bedding, ripple marks, and sole marks
Define stromatolites.
Stromatolites are organosedimentary rocks meaning that they are made by physical processes and microorganisms, usually cyanobacteria. These rocks offer some of the earliest evidence for life on earth.
What are evaporites?
Evaporites are chemically precipitated rocks formed from the evaporation of saline water.
Specific conditions are needed for these rocks to form. Form in partly or entirely closed sea or lakes, with absence of plastic settlements, and hot arid climate to allow substantial evaporation.
What are Chemical sedimentary rocks?
Composed of nonclastic sediments formed through biological, or chemical processes or by the extraction of components for material in solutions. Examples include limestones, chert, dolomite, and Gypsum.
What are Clastic sedimentary rocks and examples
Rocks composed of weathered and abraded fragments or clasts. Examples of common clastic, sedimentary rocks include Sandstones, conglomerates, Breccia, shale, mudstone and Clay.
What is meant if a deposit is arenaceous
It means they are composed of cemented or sand like particles between 0.5-2 mm diameter
What does mineral composition say about a rocks deposition environment?
Presence of minerals like feldspars and olivine indicates rapid deposition following erosion as they are unstable on earths surface.
Sediments that accumulate in oxygen rich environments contain ferric iron and are red or yellowish in colour.
Sediments that accumulate in oxygen poor environments contain ferrous iron and are grey or dark blue or green in colour.
What does grain sorting say about a rock?
The more poorly sorted grain sediments are shows deposition close to origin.
Evenly sorted grains indicate the fat transportation of sediments as they have been subject to prolonged wind or water action.
What does grain shape say about a rock?
The more angular a grain is, the closer it is to its deposition environment. A round grain shape means it was exposed to more buffeting and abrasion either by wind or water.
What does grain size say about a rock?
Indicates depositions environment, larger grain size means traveled less, smaller grain size means traveled more being exposed to abrasion.
