Talk:Sedimentary rock
From Wikipedia, the free encyclopedia
 |
Sedimentary rock is part of WikiProject Geology, an attempt at creating a standardized, informative, comprehensive and easy-to-use geology resource. If you would like to participate, you can choose to edit this article, or visit the project page for more information. |
| B | This article has been rated as B-class on the quality scale. |
| High | This article has been rated as High-importance on the importance scale. |
 |
This article has been reviewed by the Version 1.0 Editorial Team. | ||||||||
|
|||||||||
Contents |
[edit] overemphasis of siliciclastic rock
This article seems to be over emphasizing siliciclastic rocks with very little about carbonates, evaporates, etc. Can this be fixed?
[edit] siltstone
yes, it is a bit difficult to understand There are also other classifications of clastic and organic sedimentary rocks, which are not available here. Moreover the pictures are very deficient which create problem in understanding.
[edit] contours of shale and other sedimentary rocks
dear everyone, i'm trying to write about shale and other sedimentary rocks and i just need a few websites or any info available about these sedimentary rocks. any help about where to go to for info would be greatly appreciated. please reply to madewann [at] hotmail [dot] com cheers, W. Mann —Preceding unsigned comment added by User:Madewann (talk • contribs)
this page isnt for asking for help on projects, unless the project in question is the page itself.--58.107.30.145 08:00, 25 October 2007 (UTC)
[edit] shale is deposited clay.
Is clay really a sedementary rock as this article stated before? Isn't shale the sedementary rock type that consists of clays? http://csmres.jmu.edu/geollab/fichter/SedRx/SimpModl.html /Joe Hill —Preceding unsigned comment added by Joe hill (talk • contribs) 10:34, 20 January 2007
- Agreed. Clay minerals are sediments - the lithified product is either shale, mudstone or claystone, the difference is presence or lack of fissility. Vsmith 14:07, 20 January 2007 (UTC)
[edit] Layers
you don't have anything about sedimentary rocks with layers in this article. —The preceding unsigned comment was added by 12.39.96.249 (talk) 19:44, 20 January 2007 (UTC).
[edit] Question
Where is sedimentary rock found?
SEDIMENTARY ROCKS
Sedimentary rocks develop from sediments such as mud or sand in the bottoms of lakes or the ocean that turn to rock. On the map at the right you can see that most folks in the USA live where sedimentary rocks outcrop, if there are any rocks outcropping at all. This is good news for most of us because, on the average, sedimentary rocks are easier to identify than other rock types, plus they sometimes have fossils in them! This means that those of us living where sedimentary rocks outcrop will have a slightly easier time "reading the rocks," and the fossils mean that once we know what kinds of rocks outcrop in our areas, we'll be able to reconstruct what conditions must have prevailed when our rocks were deposited. An important feature of many sedimentary rocks is that they are layered, as shown by the sandstone at the left. Looking at that picture you can visualize that when the parent material (the original sand in this case) was deposited many millions of years ago it was not deposited in a gradual, constant manner. Typically a heavy rain would wash (or wind would blow) a layer of material over an area, then that material would compact, and eventually another rain or wind would deposit another layer over the old layer. Since the old material by now was physically a little different from the new layer, a contact zone between the two layers would exist. Millions of years later when erosion exposed a cross section across the layers, the contact zones would erode at a different rate than the middle of the layers, resulting in such layering as is shown in the picture.
Layering in sedimentary rocks isn't always as obvious as in the picture. Often the layers are much, much thicker and typically they have been distorted -- squeezed into curves or tilted at crazy angles, for instance. Limestone created by the regularly proceeding chemical precipitation of calcium carbonate onto the ocean floor may not show apparent layering at all.
KINDS OF SEDIMENTARY ROCKS Here are the most commonly encountered sedimentary rock types:
Sandstone: basically sand grains cemented together, which may have been deposited as sand dunes, sand bars, or washed into the sea; that's a genuine sandstone rock at the right Shale: composed mostly of tiny clay particles of the kind found in mud, much smaller than sand particles, so shale is smoother than sandstone Conglomerate: composed mostly of rounded, water-worn, cemented-together pebbles much larger than sand grains; the pebbles are usually of quartz Limestone: composed of calcium carbonate (calcite), which may have been chemically precipitated in the sea, or else deposited by living organisms in the sea; often contains fossils of sea life Dolomite: like limestone, except that it has more magnesium in it Coal: As you see at the left, coal is black. It is composed of the remains of plants and animals living millions of years ago. Often you can find fossils in coal such as those in the photo. The bottom chunk of coal, as well as showing two long, slender fossils, displays a yellow crust, which is sulfur. Coal, especially that mined in the eastern US, contains so much sulfur that when it is burned the sulfur in the smoke forms sulfuric acid, which, unless removed by scrubbers at the power plant, contributes greatly to acid rain. Three general categories of coal are recognized. From softest to hardest, they are: lignite; bituminous, and; anthracite. CONCRETIONS Have you ever mixed oil and water, and noticed how droplets of oil joined together to form larger and larger droplets? Something a little like that happens when sand, mud and general muck is deposited, then sits around for millions of years turning to rock. Sometimes inside the sand, mud or muck certain chemicals come together like oil droplets in water, and as the sand, mud or muck turns to rock, so do the chemical concentrations. The result may be that the chemical concentrations become concretions embedded in the rock, such as those shown above exposed in a rock wall.
What is a concretion?
The word "concretion" is a general term used rather loosely for several more or less rounded bodies mainly of non-living origin, occurring in all types and ages of sedimentary rocks. They are different in composition from the surrounding rock material and are generally harder and thus more resistant to weathering, or wearing away, than the surrounding rock.
Concretions are not at all rare in sedimentary rocks. They can form in various ways and not all geologists are in agreement about how they come about, but the way I've just explained them is at least recognized by most as sometimes being a likely scenario.
Concretions can be spherical, flattened, or irregular with lobes arranged in every conceivable way. They can be very small to very large. Spherical ones can be five feet or more in diameter and elongated ones 20 feet or more. Most are measurable in inches, however.
Concretions can have clearly defined outlines or their boundaries can be indistinct. Their surfaces can be rough or smooth. They can be homogeneous, or horizontally layered, or composed of concentric bands. All concretions appear to have grown outward from a center.
One important kind of concretion is the chert concretion, which forms in limestone and dolomite. Limestone and dolomite can dissolve away leaving chert concretions in place because chert, being silica dioxide, doesn't dissolve the way limestone and dolomite do.
FAULTS Especially in roadcuts through sedimentary rocks you can often see faults -- fractures in the earth's crust where one side of the fracture has been displaced relative to the other side. The picture below, taken along US 27 where it crosses the Kentucky River in central Kentucky, shows the location of a major fault in the area's Ordovician limestone.
In the picture, notice the horizontal layering of the rocks on the right side of the picture next to the highway. But notice how the rock layers on the left side are steeply tilted, plunging downward to the right. Here, not only has there been a major displacement of one side of the fault relative to the other, but rocks on one side have been tilted both sideways and at an angle relative to the vertical. A small valley has eroded where the actual fault was, since when the fault occurred the rock's structure was damaged, becoming easier to erode.
GEODES Geodes are a little like concretions, in that they are formed in place, surrounded by rock, and sometimes the rock around them erodes away, leaving them lying about. However, unlike concretions, geodes are hollow, and typically are lined inside with inwardly projecting quartz crystals, like the one shown at the left. A typical geode is about baseball size, but they can range from an inch or less to much more than a foot in diameter. Some rare geodes produce crystals of minerals other than quartz, such as gypsum and calcite.
There is uncertainty as to how geodes are formed.
[edit] QUESTION
I miss information about terms like 'softlimestone' or 'hardlimestone'. I wonder if they can be considered as types of limestone —The preceding unsigned comment was added by 85.85.139.75 (talk) 13:15, 12 March 2007 (UTC).
[edit] "List to prose" tag removed
I'm removing the "List to prose" tag. Wikipedia:Embedded list presents examples of where lists are preferred to prose (!!!), and one of them is logical hierarchies. The bullet list in article Sedimentary presents a hierarchical taxonomy, similar to those used in biology. The alternative presentation would be a phylogram, but: that would be overkill for a simple hierarchy which at present is fairly simple; bullet lists are the most accessible way to present hierarchies, as ALT text in images has limited capabilties (and possibly length) while ASCII art (the most common way of showing phylograms in Wikipedia) is unintelligible to people with severe visual handicaps.Philcha 13:01, 31 August 2007 (UTC)
- I agree. Too often the objection is "satisfied" simply by removing the line breaks or bullets, and rendering a list as text. There are places for lists; the classification in this article is one of them. Kablammo 13:09, 31 August 2007 (UTC)
[edit] names of types of rock
how come the names of sedimentary rocks formed by biogenic methods and precipitates arent listed in the beginning? i dont know them and i would like to find out what they are. 58.107.30.145 09:59, 22 October 2007 (UTC)
- No one has added them yet. If you find them in another source, please consider returning to this article and adding that information here, with the name of the source. Kablammo 12:45, 22 October 2007 (UTC)
Most rocks that are sedimentary rocks are coquina,shale,sandstone,chalk,limestone,micrite limestone,coal,arkose,Quartz sandstone, graywacke,slitstone,and claystone —Preceding unsigned comment added by 69.154.160.104 (talk) 23:42, 6 February 2008 (UTC)
[edit] crystals
Why do sedimentary rocks contain crystals? —Preceding unsigned comment added by 92.2.8.85 (talk) 08:49, 8 June 2008 (UTC)
