elephantower wrote:Heavyhitter, your not living up to your name
um idk what crossproducts are but it certainly does involve vectors (the way I did it).
75.6 degrees -- did you switch digits? :/
and
98.5 degrees
. I'm sure that the strike isn't 0 from inspection; how exactly did you get that?
I did this quickly, and rounded carelessly, so my numbers could be off.
EDIT: Read about crossproducts: if I understand them that would give the strike; how would you get the dip?
The problem you gave was a three-point problem right? So I just drew the points and figured out where each elevation value was (900, 800, 700 etc). Then I connected the elevation points to get the structural contours and used a protractor to measure the angle, which I got was almost vertical, which is how I got a strike of 0 degrees. Not sure why the dip is off though This is my first year doing this event so I don't really know what I'm doing.
elephantower wrote:Also, that question was aimed at 2nd year geomappers, so maybe I should do a separate one for the young 'uns .
Here's one that's somewhat difficult, but requires little prior knowledge and should develop necessary spatial analysis skills.
The image above shows an outcrop of quartzite in sedimentary rock, plotted onto a topographic map by an intrepid observer. Does the quartzite form a fold? How can you tell from the map? If it forms a fold, is it an antiform or a synform? Also, if there is a fold, is it an anticline or a syncline? Keep in mind that the fold may not be pointing straight up.
This index of, well, index fossils should help you figure out the relative ages of the rock (Hint: older fossil = older rock) http://pubs.usgs.gov/gip/geotime/fossils.html
This picture would probably be a fold because it is V-shaped, indicative of a slanted antiform?? (not sure). Because the trilobite fossil is very old compared to the other fossil, the newest rock layer is inside the fold, meaning the fold is a syncline.
Re: GeoLogic Mapping C
Posted: October 10th, 2014, 6:47 pm
by elephantower
It is indeed a syncline, but it isn't an antiform.
Imagine yourself standing in the canyon looking up at the canyon side where the fold is exposed.
Also, if you measured dip direction, that would be pretty close to 0 (8 degrees, I believe?). Try using the 3-point equation and see if you get the same result (to avoid measurement error).
Re: GeoLogic Mapping C
Posted: December 17th, 2014, 8:44 am
by bernard
Reviving this marathon with a question!
A topographic map is in 1:24,000 scale. How far does 1 inch on the map represent?
Re: GeoLogic Mapping C
Posted: December 21st, 2014, 6:11 pm
by elephantower
24000 inches??
Re: GeoLogic Mapping C
Posted: December 26th, 2014, 1:26 pm
by bernard
elephantower wrote:
24000 inches??
Yes, correct! Your turn to ask a question.
Re: GeoLogic Mapping C
Posted: December 26th, 2014, 10:19 pm
by elephantower
What is Bowen's Reaction Series?
Re: GeoLogic Mapping C
Posted: February 21st, 2015, 11:16 am
by boomvroomshroom
Describes what different types of minerals crystallize from different temperatures of magma. Can be used to help predict how complex the silicate structure is, and thus if they will weather faster. Typically minerals at the top are characteristic of mafic (dark, low-silica content) igneous rock.
Re: GeoLogic Mapping C
Posted: February 23rd, 2015, 5:00 pm
by Magikarpmaster629
It's been a few days, I'll revive this.
A strata is layered
.....Cs/Oc/Dc.....
What is the unconformity?
Re: GeoLogic Mapping C
Posted: February 23rd, 2015, 8:54 pm
by boomvroomshroom
but if they're all horizontal sedimentary layers, then it must be a disconformity?
Re: GeoLogic Mapping C
Posted: February 24th, 2015, 7:46 pm
by Magikarpmaster629
Disconformity is right, but not for the reason I was looking for. The letters mark geologic periods, and there is a gap in time between the Ordovician (Oc) and the Devonian (Dc). Because of the gap in time, there must have been a period of time during the Silurian (between Ordovician and Devonian) where there was no deposition and much erosion, making it a disconformity. I should have made that clearer, sorry.
This is my first year doing this event so I don't really know what I'm doing. 
.
