Questions tagged [geology]

The science comprising the study of the rocks Earth is composed of, and the processes by which they change. Some subfields of geology are petrology, mineralogy, and geophysics.

Filter by
Sorted by
Tagged with
2
votes
1answer
31 views

What would a rock thin section look like without any polarizers?

I'm interested in knowing what features can still be discerned. I've been struggling find any image of a thin section of a rock under a regular light microscope, or a petrographic microscope with the ...
3
votes
1answer
98 views

“Obicular” structures in basalts

I found spherical or globular structures, structures in basalts of a greenstone belt which underwent alteration and deformation. However, in thin section, these structures have undeformed pyroxene and ...
6
votes
3answers
2k views

How was Nastapoka arc formed?

As wikipedia says, the Nastapoka arc is a geological feature located on the southeastern shore of Hudson Bay, Canada. (Other description with picture at the Royal Astronomical Society of Canada) No ...
3
votes
1answer
115 views

Can a braided fluvial create thick relatively continuous siltstone beds?

I am attempting to interpret an outcrop I went to. I suggested it was created by a braided fluvial. The one thing I cannot explain are prominent alternating siltstone beds with the sandstone beds. ...
3
votes
1answer
63 views

What was the Earth's continent's positions 10000 years ago, or 11700 years ago, AKA when the late Pleistocene epoch was coming to an end?

In many articles online, geologists and geographers have described and depicted the theorized locations of all our continental plates with great detail and illustration, providing pictures, time-lapse ...
3
votes
1answer
48 views

Are the precious metals (silver, gold, platinum) present everywhere throughout the Earth's crust at least in the trace quantities?

Do some rocks, soils, sands or waters exist that contain fewer than one atom of gold per cubic meter or tonne of their mass?
8
votes
1answer
2k views

What is the white coating “patina” we often see on deposited chalcedony/agate?

Me and some of my friends were wondering what exactly is the white coating we can see on chalcedony that has been deposited by a river during quartenary (and so the original material is damaged and ...
2
votes
2answers
91 views

Can an igneous rock have a Vp of less than 1000 m/s and need blasting to excavate?

I have run a 60 m refraction seismic line on a mountain summit. The environment was noisy (wind would be the principal agent) and quite difficult to pick first arrivals. It resulted in 800 m/s. A ...
13
votes
1answer
964 views

What causes “hydrocarbons” to take the form of petroleum versus natural gas?

"Hydrocarbons" are found in geological formations consisting of strata or layers of rocks. Specifically, they are formed from decomposed organic material (that contains carbon), that bonds with ...
18
votes
3answers
16k views

What caused the bend in the Emperor/Hawaii chain of islands, 45 million years ago?

What caused the bend in the Emperor/Hawaii chain of islands, 45 million years ago? Has there been any updates to this mystery I am unaware of? Are there any new theories that could potentially ...
0
votes
0answers
64 views

Geo-Spherical shape of Earth

I know that the best possible approximation of the shape of earth is an oblate sphere. But people also call it as geo-spherical shape of the Earth. What is the meaning of geospherical shape? Does this ...
12
votes
2answers
542 views

What's it like inside a natural gas cavern on Earth?

I suppose natural gas underground caverns on Earth have substantial volume and gas is in gaseous form there. As such I wonder how it would look like inside such cavern (with artificial light of ...
4
votes
0answers
65 views

How do you choose appropriate parameters for a lowpass filter when filtering a Bouguer anomaly?

I am trying to filter my Bouguer anomaly data to remove the short wavelength features. I have created a lowpass filter to achieve this, but I am wondering how I can more objectively choose my cutoff ...
4
votes
1answer
172 views

where are the poles of rotation of the tectonic plates located?

Euler's "fixed point" theorem ... can be stated as: The most general displacement of a rigid body over the surface of a sphere can be regarded as a rotation about a suitable axis which passes ...
4
votes
1answer
202 views

Why would CaO be more finely spread than K2O in Granodiorite?

I recently interpreted some XRF data on samples of a granodiorite which were classified under three different types of physical characteristics: very little, mild and significant levels of weathering. ...
7
votes
4answers
519 views

Round structure in southern United States

Assuming here might be someone who knows something about this, I wanted to ask what is behind this round structure I have spotted today on Google Earth: There seems to be a large (~200 km), nearly ...
0
votes
0answers
39 views

Estimations of time to turn a beach rock into this?

[ROUND BEACH STONECan anyone help determine how long it would have taken to turn this rock into the ball it is now? heavy density .Found on the South Coast here in the UK near Lyme Regis (Jurassic ...
0
votes
0answers
18 views

How all of the files listed as stream (st) could be used or listed as traces (tr) in obspy (python)?

PPSD (seismic background noise) I list all of my files, basically as components (H1, H2, and V), as streas as follows: import os from obspy import read from obspy.signal import PPSD import ...
2
votes
1answer
62 views

Earth's interior heat ratio between pressure and atomic decay

What is our current understanding between the ratio of Earth's interior heat between the downward pressure and atomic decay?
0
votes
1answer
45 views

Where can I find broadband seismic reflection data?

or what type of companies should I contact to ask for the data? This data would be produced from Seismic Vibroseis survey trucks which are mostly used to locate oil and gas. I doubt most oil and gas ...
5
votes
0answers
94 views

Has a scientific consensus been reached concerning the formation of the Grand Canyon?

new student of Oceanography here! I'm studying Earth Science right now, and I found conflicting reporting re: the formation of the Grand Canyon; whether it was formed singularly by the Colorado ...
4
votes
1answer
103 views

Why isn't Iberia a tectonic plate?

I usually read that Iberia is a subplate, while India is a plate. But it was a plate at the beginning of the Alpine Orogeny: Source: wikimedia.org Description: Tectonic map of southern ...
2
votes
1answer
33 views

Storing borehole interval data (logs) in netcdf

I have a number of datasets that describe geological properties as intervals down a borehole (e.g. unit codes, sample results) In a database, or a flat ASCII file, I would describe these with a ...
5
votes
4answers
76 views

Sources or strategies for stone identification

I have a bunch of semi-precious stones here, but I am not very learned in geology etc and I would like to have some way to know what kind of stones they are. As far as I understand question about ...
6
votes
2answers
480 views

Are old geophysics textbooks useful?

I have had much success with old textbooks in mathematics. Generally, for any branch of mathematics that I (as a non-mathematician) would like to learn or re-learn, I can buy a classic textbook from ...
5
votes
2answers
89 views

Has there ever been a case where we have found what appears to be a prehistoric fossil but have no way of dating it?

I find that when ever I learn of a new fossil, the age of said fossil is always mentioned. This perplexes me given how intuitively rare it seems to have radioactive material to date a formation. I ...
4
votes
1answer
74 views

Waves in very thin layer

Elastic waves in the earth are described by the elastodynamic equations \begin{align} \rho \frac{\partial^2 u}{\partial t^2} &= (2 \mu + \lambda) \frac{\partial^2 u}{\partial x^2} + \mu \left( ...
3
votes
2answers
5k views

What's the difference between a crater and a vent? [closed]

Crater is above a vent whereas a vent is below it. All the best....
0
votes
1answer
64 views

Have fossils ever been found in the asphalt lakes of Trinidad and Venezuela?

La Brea tar pits in California are the result of ancient oil seepages and famous for the fossils of extinct animals which were trapped in the tar. The asphalt lakes in Trinidad and Venezuela are also ...
2
votes
0answers
181 views

How Big Were the Siberian Traps ORIGINALLY?

252 million years ago, Siberia was subject to a mass series of flood basalt eruptions, creating a large igneous province called the Siberian Traps. Today, it measures three million square miles in ...
2
votes
0answers
74 views

Where and how big was Sicily between 5 and 1 Ma ago?

Sicily is a geologically complex island which seems to have been extensively studied geologically and from a tectonically point of view. There are an overwhelming number of papers dealing with the ...
4
votes
1answer
56 views

Luis Alvarez's K-T Impactor Calculation

I am trying to perform the calculation that Luis Alvarez used to establish the size of the K-T impactor. I used the following information: Assume that the clay layer with iridium was uniformly ...
8
votes
2answers
657 views

Why are South African mountains short and flat?

I drove through South Africa from Cape Town to Mozambique and noticed that almost all heights and mountains were no higher than approx 200-400 meters and had a flat top, just like the iconic Table ...
15
votes
3answers
3k views

Is there any evidence for higher air pressures in the geological past?

I was curious about how the Earth's overall air pressure has varied over time, and tried to take a look around the internet. However, Google pops up a lot of sites with questionable science proposing ...
0
votes
0answers
35 views

What are the favourable conditions for the formation of porphyry copper deposits?

Favourable condition for the formation of porphyry copper deposits is : 1. Extremely low oxygen fugacity in initial magma 2. High water content in initial magma 3. Crystallization of magama at deep ...
3
votes
1answer
75 views

What ore minerals are likely to be found in a thin section like this? What can we deduce from the structure?

The following image is of polished sample of mineral-rich rock. There are two major portions we can see that is ore minerals and rest the grayish material is gangue. The photo was taken with an ore ...
2
votes
1answer
74 views

Can we separate a sandy, clayey & salt layer on basis of their rheological properties?

Since, given enough compaction, salt is able to behave like a fluid & buoyant too if it's overlain by a higher density rock (it could be fine grained clay or a sandy sequence). But in another case,...
6
votes
2answers
1k views

Why do the earth sciences use mega-annum instead of mega-year?

I've noticed that geology and related fields use mega-annum (Ma) instead of mega-year (Myr) as the unit for 1 million years. Why is that? Is an "annum" different from a "year" in geology?
4
votes
1answer
77 views

How are stratigraphic limits defined before the Phanerozoic?

International Commission on Stratigraphy defines the limits of geological ages and they create this chart: Click on image for full view. Acording to Wikipedia: The standard stratigraphic ...
2
votes
0answers
25 views

Faster shale velocities in deviated wells

I am currently working with sonic measurements in the wells and there is an observation, that velocities are faster in shales over the deviated parts of the well. So, when the relative dip between the ...
2
votes
2answers
65 views

What are the key elements defining the separation between Jurassic and Cretaceous?

We have one mass extinction that seperates Trias from Jurassic, roughly huge volcanims over a long period of time, and Pangea starting to divide. Another mass extinction that marks the end of ...
36
votes
3answers
7k views

Does gravity increase the closer to the core you get?

Or does the mantle and crust above you counteract the increase at one point and it actually decreases?
1
vote
2answers
123 views

Centripetal Force Perfect Ball and Water

I made a question in WolrdBuilding as I was directed to. There a user said that with a perfect ball all water would pool to the equator because of centripetal force. What I do not understand is how ...
5
votes
2answers
81 views

Do we know what the rigid mantle looks like?

The rigid mantle, which is hard and lies above the asthenosphere, is separated from the "crust" that we can see and touch by the Mohorovičić discontinuity. Wikipedia provides an image of what may once ...
2
votes
2answers
114 views

Introduction to Geology Books

I am a high school student who is thinking about going to university for Geological Sciences. I've had an interest in rocks and such since I was little, but I want to get an idea of what studying ...
6
votes
0answers
39 views

Are there any known global effects of the Mediterranean sea evaporation and refilling?

This is a broad subject I realize, but I'm looking for specific geologically observed answers of global effects elsewhere, between about 5.96 and 5.33 million years ago when the Mediterranean sea was ...
12
votes
0answers
366 views

What is the global distribution of oil filled geodes?

In a general 40 mile radius of Keokuk, Iowa many sedimentary geodes can be found. They are abundant in the Warsaw Formation with the type section at Geode Glenn in Warsaw, Illinois. In one specific ...
7
votes
2answers
424 views

How are chenier ridges and strand plains formed at wave dominated coastlines?

In the attached image, we can see chenier ridges and strand plains. How are they formed and what is the involvement of rip and longshore currents in their formation?
3
votes
2answers
98 views

What is the difference between mobile & molten rock?

In the book Fundamentals of Geomorphology (Routledge Fundamentals of Physical Geography) by Richard John Huggett there is a sentence " Intruded rocks, which must be mobile but not necessarily molten,...
6
votes
6answers
18k views

Cause for round holes in stones

I picked up this stone form a beach on the south coast of England (lancing). How is it possible it has such round holes? Plenty of stones looked similar.

1
2 3 4 5
13