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Hot answers tagged sedimentology

46

Yes. In fact, there are sand-dunes in Antarctica [1:15].

18

In a 1983 Journal of Geology paper by Milliman and Meade, "World-Wide Delivery of River Sediment to the Oceans" (link) it is estimated that the world's rivers carry about $13.5\times 10^9$ tonnes of sediment per year. If we assume an average density of $2.5~\rm{g/cm^3}$, this corresponds to a volume of 8.8 cubic kilometers. The total surface area of the ...

17

The cause for this phenomenon is sand and silt moving down an underwater cliff as you guessed. The geography that makes this possible is as follows. The island of Mauritius is located on a giant plateau that was created by seafloor spreading a few million years ago. Most of which is under 8-150 meters of water. Where the waterfall effect occurs there is ...

17

Forming of coastline During the last ice age, the North Sea was dry. When the ice melted sea levels slowly started to rise again and due to tides and currents a barrier of dunes was formed along what approximately is today's coast line. This created an area of land that fell dry during ebb-tide and flooded during high tide (this can still be seen in the '...

14

Jeffrey Ralh of Yale and coauthors published Combined single-grain (U-Th)/He and U/Pb dating of detrital zircons from the Navajo Sandstone, Utah, which concludes that Navajo sandstone originated from the Appalachian Mountains. A review of the article is found here: http://www.geotimes.org/nov03/NN_navajo.html. Rahl et al. propsed that a large river system ...

13

The building material comes from minerals dissolved in the ocean, mainly $\mathrm{Ca}^{2+}$, $\mathrm{Mg}^{2+}$, and $\mathrm{HCO}_3^{–}$, but of course there are all sorts of biochemical details. Most limestone originated as the skeletons of micro- and macro-organisms, such as plankton and coral. The minerals come in turn from the erosion of older rocks (...

12

Sedimentation rate presently varies many orders of magnitude depending on the place you observe. The rate of sedimentation is also different. Some places have continual sedimentation, others have episodic sedimentation events. That is why charts that show changes in sedimentation rate are usually done for individual sedimentary basins, to determine the ...

12

Let's look at this. A very large number of points for one question. First, the solar system. We do not see any hydrocarbons in the inner solar system (Mercury to Mars). This is because in this region of the solar system, dissociation by solar UV rapidly destroys primordial hydrocarbons. This effect is much weaker further out. Oil well 'replenishment' will ...

11

This LiveScience article suggests the areas aren't major: The scant areas that are free of snow and ice make up less than 0.4 percent of the continental land mass. In places there, the wind has built sand dunes. This article by Burton-Johnson et al., 2016 on automated satellite analysis methods, summarized in this DailyMail article, indicates refined ...

10

I think the easy answer comes from the Hawaii Department of Land and Natural Resources: Beaches in Hawaii may be made of 'black sand' derived from the erosion of volcanic rocks, of 'white sand' made by marine organisms, or a mixture of both. On the windward side of the Big Island, for example, black sand beaches are very common. The beach at South Point ...

10

According to page 86 of Exploring the World Ocean: In December 1989, ODP scientists drilled Hole 801C and recovered Jurassic-age rocks and sediments, about 170–165 million years old, from the Pigafetta Basin in the western Pacific, near the Mariana Islands. Sediments of nearly identical age had been found previously from the Deep Sea Drilling ...

10

I think the best option for sediment transport modeling is the Community Sediment Transport Modeling System (CSTMS) package that was developed for ROMS. CSTMS was created by a group of sediment transport modelers lead by the USGS. One of the many benefits is that it is open-source and, thus, free. The model was designed for realistic simulations of processes ...

10

Sandstone bodies in incised valleys can be good hydrocarbon reservoirs. Incised valleys form on the coastal plain and/or continental shelf during a fall in relative sea-level by a combination of fluvial and marine processes (e.g. fluvial erosion, headward erosion). Here's some coastal plain incision by the Orari River in New Zealand — look at those sand ...

9

In simple big picture terms, Sediments were deposited first from the bottom upwards (as you understand). Then the area was uplifted and the river eroded from the top down. Most erosion is from the top down (there are scenarios such as dissolution and caves which are relatively rare exceptions). So here in Texas we find a large amount of the center of the ...

9

When learning to distinguish between siliceous and calcareous samples you should use a handlens. Look for quartz, feldspars or micas. Quartz clasts may be frosted, or you may be able to see conchoidal fracture. Calcite will be very soft compared to both feldspar and quartz, and should fail to scratch copper (or at least not scratch it very well, while a ...

9

The oldest known metasedimentary rocks are about 3.8 billion years old, formed in the Eoarchaean era. 'Metasedimentary' just means they have been metamorphosed, so they started out as sediments. They are found in the Isua Greenstone Belt of southwestern Greenland. You can read about their discovery in Moorbath (2009). Quoting from there: Published zircon ...

9

These features are created by the wind.You will note that the upper left portion has a small dark spot. This is known as Waw al-Namus, or the "Oasis of Mosquitoes." It has a path of material in the same curved manner as the surrounding features you mention. From the link provided below: However, Waw al-Namus and its plume are not the only "wind records" ...

8

The main interest of tephrochronology (i.e. dating sediments using volcanic ash layer) is specifically its instantaneity (relatively to geological timescale of course). It is precisely used for higher-resolution dating. An example would be the Kawakawa/Oruanui tephra from New Zealand which is a good isochronous marker bed at 26.5 ka, spread over 1500km, but ...

8

As Spießbürger also mentions in his answer sedimentation rates are local, and highly depend on sediment supply and accommodation room in the sedimentary basin. Global sedimentation rates are then just an average of all sedimentary basins, and are closely related to global erosion rates, although not necessarily the same depending on the time scales you look ...

8

The technical term for a sedimentary rock that has a lithified fine-grained sediment with larger pieces of rocks suspended in it upon lithification is a conglomerate. The fine-grained interstitial part is called the matrix, and the large pieces suspended in it are called clasts. Clasts can range from gravel- to boulder-size. These are technical terms used by ...

8

Not all sediments are deposited in water, but water is important in the formation of most sedimentary rocks. If we're just thinking about the deposition of the sediment, then we don't necessarily need water. Some counterexamples are: Aeolian sandstones, such as the Lower Permian Rotliegend sandstone of the North Sea. These are deposited by wind, not water. ...

7

Also keep in mind that eluvium and eluvial have a different meaning in soil science. There, it means leaching of soil matter or chemical substances by water. (Usually, after some downward transport, the substances precipitate in an iluvial horizon.)

7

Large parts of Delft3D - including, I think, the sediment transport module - are available in an open source form. The GUI is not currently open source, but (a) Deltares have been offering licences for this for free for academic use; (b) if they are no longer doing this, it is entirely possible to use the software without the GUI. FVCOM also has a sediment ...

7

Not really. Concretions are features of sedimentary rocks almost by definition. Here's my go at a definition; it essentially presupposes a sedimentary rock: Concretions are spatially discrete zones of above-average (compared to the rest of the rock) cementation by authigenic minerals. Common cements include calcite, quartz, siderite, and pyrite. ...

7

Downwelling speeds in the deep water formation areas are likely not significant when compared with the settling speeds of most sediment particles. While deep waters have clearly defined oxygen and nutrient characteristics, it does not seem likely that they can have a particular sedimentary character. The deep water circulation associated with the meridional ...

7

Oolites are limestones that are usually considered as in-organic, although they may have bits of shell/etc in them. These form by the precipitation of calcium carbonate around particles (sand, broken shell, etc) with a process comparable to that of an oyster. Some oolite references: http://www.sandatlas.org/2012/09/oolite/ http://en.wikipedia.org/wiki/...

7

Like Michael, I find your question a little unclear, but the crux of it seems to be this: ... does science have to conclude [that a specimen is] just a rock because the composition is entirely from earth minerals? The answer is an emphatic no. There are lots of non-rocks out there, many of them manufactured by the (alleged) intelligence known as Homo ...

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