Questions tagged [sedimentology]

Sedimentology encompasses the study of modern sediments such as sand, mud, and clay, and the processes that result in their deposition.

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1answer
325 views

What is the maximum grain size of a sediment that can be point counted using a standard thin section?

Point counting is an extremely useful tool for determining the composition of a clastic sedimentary rock. It is also very useful in provenance studies to determine the sediment source of a sedimentary ...
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Waves on sandy beach separating differently-sized rocks?

I recently went to a beach, and I noticed that the sand seemed to have a few distinct regions. I'm wondering what would cause this, and how it works. One region is the part of the beach which is ...
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What factors bring sand into or out of the beach?

I like to walk my dog along a beach, but in medium to high tide, there is no beach at all, as the water reaches the bluffs. The thing is, the height of the sand seems to vary drastically as well. ...
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Specific Chemical Composition of Nero Marquina Marble

I'm looking to understand the chemical composition of the Spanish Nero Marquina Stone. Specifically, are the white veins of different composition than the black? We are design studio pursuing work in ...
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What is the earliest sedimentation we know of?

Did large-scale sedimentation occur in any great amount during or soon after the Hadean/Archean period? Or did it only start later, because of the intense geological activity?
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No sedimentation without water?

I just found a video on sedimentary rock formation, and to my surprise, it stated that this only could occur in water! I always thought that any layer of matter, if buried deep underneath more matter, ...
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540 views

Is Desert Sandstone a chemical sedimentary rock?

I gather that chemical sedimentary rocks are formed when minerals in solution are supersaturated and therefore they precipitate out. I also understand that desert sandstone is formed as Iron Oxide ...
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0answers
399 views

What does a negative value for the inclusive graphic standard deviation mean?

I'm calculating the inclusive graphic standard deviation for sediment from a cumulative frequency graph, with this formula: But when I plug in the numbers, I get a negative value, because my ranges ...
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What do you call boulders of non sedimentary rock that were lithified into sandstone?

I'm convinced there is a word for this. I was in the Hoodoos at Writing on Stone this weekend and kept noticing what looked like reddish quartzite boulders laying around in the sand, or sometimes ...
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Are all natural diamonds made of organic carbon material?

I've read that diamonds are created at a depth of about 180 km. By volcanic activity it comes above. But did plants and trees of 300 million years ago sink so deep? Or is it possible that inorganic ...
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How far upstream would severe sea level rise (1m) noticably affect a large river?

The projection for sea level rise due to global warming seem to hover about 1m by 2100, let's use this figure. How far upstream would this noticably affect a large river, e.g. the Rhine? I think it ...
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295 views

A simple formulation to calculate the sequence and rate of salt precipitation in a brine?

Is there a simple formulation to estimate the rate of salt precipitation in a brine given its ion concentrations and the evaporation rate? For example: if we know the concentrations of Cl−, Na+, Mg2+...
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Why pro-gradation occurs along coastal environments?

I am currently studying the deposition process in coastal environments and I came across a point which I do not understand concerning grading of grain size. According to "Petroleum Geology by North F....
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How are natural specimens, such as ‘Moqui Marbles’, distinguished from man-made artifacts?

If a particular type of rock specimen is found throughout Earth and is made entirely of natural minerals, but the individual specimens differ minutely from another in size and shape and look to be ...
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Why is coal classified as a sedimentary rock?

Something just clicked in my head today. Rocks, by the definition I was taught, are composed of minerals which in turn are by definition not organic, so they are or were not alive. However. Coal, ...
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Does dirt compact itself over time? If so, how does this happen?

If I were to bury something 10 feet (~3 metres) underground, with loose soil on top, would the ground naturally compact itself over time, until whatever I had buried has dirt tightly pressing against ...
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How to model bed load transport in channels of non-rectangular cross sections

All the formulas presented in the relevant technical literature refer to channels of rectangular cross section — the formulas assume a constant depth of flow right across the channel section. I need ...
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741 views

where are the thickest limestone layers on earth ? (CaCO3)

What is the maximum thickness of limestone layers on earth? (Limestone or any other biochemical sedimentary rocks, for example chalk or coral reefs.)
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Hydrocarbon potential in Ganges Brahmaputra delta

According to Curray (1991): Total sediment thickness beneath the [Ganges–Brahmaputra delta] southeast of the hingezone exceeds 16 km... Considering a normal geothermal gradient and data for oil ...
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Incised valleys and hydrocarbon potential

The Wikipedia page on sequence stratigraphy states: Sandstone bodies associated with incised valleys are good hydrocarbon reservoirs. Can anyone elaborate on this statement and the reason behind ...
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Software for sediment transport modeling

I am doing a paper about coastal processes and I was told that I should include a sediment transport modeling to further examine my geophysical findings. I was reading in the net and found that ...
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Sand on the beaches of Kanyakumari, India

I recently visited the southern tip of India (State of Tamil Nadu) - it is called Kanyakumari. The beach was beautiful and one thing that struck me was that the sand was multicolored. The local legend ...
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How do we use oxygen isotopes as temperature proxy?

As far as I know scientists use oxygen isotope 16 to 18 ratio in air trapped in glaciers (or in old foraminiftera shells) as proxy for temperature in the past. I know that $\ce{^18O}$ is heavier, and ...
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What is the oldest sediment?

Sedimentary rocks in Akilia or at Hudson Bay have been proposed as the oldest in the world. My question is not related to rocks, but rather to sediment while still forming sedimentary deposits but ...
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What are the non-anthropogenic causes of The Netherlands' low elevation?

A large area of The Netherlands is below sea level. There are two non-anthropogenic reasons that I can think of: Compaction of delta sediments that lie below the country, A side effect of the ...
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333 views

What are the mechanisms maintaining the Dune of Pilat?

The Dune of Pilat (Dune du Pilat) is the tallest dune in Europe. The dune has been around for at least centuries. Where is the sediment coming from? Why is the dune so tall?
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What is the difference between eluvium and alluvium?

I was reading about kimberlite on Wikipedia and it mentioned eluvium. I've heard of alluvium, alluvial fans, alluvial deposits, etc. However, when I looked up eluvium, it sounded exactly like alluvium....
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What is limestone made of?

I know that it is calcium carbonate (CaCO3). I also know that these are the dead bodies of microorganisms. My question is, where do they procure the building material? The limestone seems to cover ...
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Have meteorites been found in the oldest sedimentary rocks?

Dropstones sometimes occur in sedimentary rocks. These are foreign rocks and boulders that happened to "drop" into a sediment and were fossilised when the sediment was lithified. (source: Michael C. ...
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How does the sand appear on Hawaiian beaches

It's quite surprising to me that there's only one beach with black sand on Hawaii (maybe not exactly one beach, but it's only a very small fraction). The concern is, if the whole Hawaii is volcanic, ...
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490 views

Formation of limestone without living organisms?

Limestones are formed mostly from skeletal fragments of marine organisms. However, calcium carbonate dissolves naturally in water, so the living organisms are not the only source of it in water. Is ...
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Determining a rock age using volcanic ash layer

I wanted to know if volcanic ash deposits found in the geologic record are most useful in correlating the age of rock layers if the volcanic ash was distributed over a large area during a short period ...
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Identifying sedimentary rocks in hand specimen

I'm currently learning how to identify rocks in hand specimen. The initial classification into igneous, metamorphic, and sedimentary is mostly ok, but I'm having a problem with further identifying ...
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Does the Great Pacific Garbage Patch increase sedimentation rates over the patch?

As in, does the debris in the patch area eventually sink? And if so, could sedimentation measurements over these regions provide a more fine-scaled measure of environmental conditions than ...
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161 views

Sediment layer chronology

In the new Cosmos series, Neil DeGrass Tyson in explaining different ways the age of the world has been determined, shows how sedimentary layers at the Grand Canyon are a fossil record of a lot of the ...
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How does the meridional overturning circulation affect sedimentation rates in the North Atlantic?

There's a lot of downwelling in the region. Does this increase sedimentation rates?
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Formation of flint & chert in limestones/chalk

Chert and flint are commonly found in chalky deposits (and have obvious importance in human history as tools). What are the processes of diagenesis of these silica-rich nodules in otherwise silica-...
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What is responsible for the underwater waterfall illusion of Mauritius Island?

From an aerial view just off the island of Mauritius, there is what appears be an underwater waterfall. The picture below illustrates this visual phenomenon: The image can also be seen from the ...
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Barite and Acantharians

Acantharians are planktonic protists (abundant in today oceans), sister-group to polycystine Radiolarians, that have the particularity of biomineralizing complex skeletons in strontium sulfate SrSO4 (...
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Can concretions form in non-sedimentary rocks?

Most modern works (e.g. Nichols 2009; Allaby & Allaby 1999) seem to restrict the definition of ‘concretion’ specifically to formations in sedimentary rocks. I have recently come across a taxonomy ...
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Biogenic origin of authigenic zeolites

Bohrmann et al. 1989 advanced the idea that the silicate phase from some clinoptilolites come from the diagenetic degradation of biogenic opal (from radiolarians in that case but presumably also other ...
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How have global sedimentation rates changed over the last billion years?

Do we have a graph of how sedimentation rates changed over time?