Practice English Speaking&Listening with: 77) Full Field Project

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(Opening music)

Welcome back geology fans! I suggest you pull up Google Earth and

explore the area around the town of Morrison, Colorado to enhance today's

experience, kind of play along. My goal is to map out this area to get a cross-section

along this A to A' transect, and then interpret the geologic history of this

place. As I do my preliminary investigations, I note there is a good

road cut exposure at Bear Creek Avenue which I can start with to get a local

stratigraphic column. Of course, in my preliminary internet investigations I

found this stratigraphic column already produced for the Morrison area, so that

should be a big help. I can see that there's a north-south trend to the grain

of the rocks, that the beds seem to be dipping to the east and that

differential erosion is creating a series of north-south trending ridges

and valleys. The cross section transect line from A to A' was chosen to cut

across this grain, perpendicular to the various beds. I go to the National

Geologic Map Database, find my area, and copy the topographic map for my intended

map area, take that into Photoshop, turn it into a black and white base map,

print it on cardboard paper, and make a couple of copies just in case. While at

the National Geologic Map Database, we'll also grab the satellite image, which I

could also get from Google Earth, but I also want to get the geologic map for

the area from the National Geologic Map Database. I'm giving myself two days to

get the fieldwork for this project done, so I need to do as much preparation work

as possible. On reconnaissance missions previously, I have flown drones over this

area and so have a good sense of the lay of the land, and where I can walk and

where I can't walk, and where the probable formation boundaries might be,

and good exposures. And though I can get a sense of the topographic profile of our

transect line from the drone data, we'll get a topographic profile to start our

cross section the old-fashioned way with a topographic map, paper, and pencil, or

Google Earth as explained in episode 11. I have a few blank sheets to make my own

strat column, and have gotten all my equipment together. I'm ready to

head out, and my plan is to get the strat column done the first day and with any

remaining time start following contacts to look for any structures present, or

this distinct ridge to look for any folding or faulting patterns. On my

second day, I will walk my transect from A to A' and take as many

measurements along that line as possible, and then hit any locations of interest,

and walk out any uncertain contacts. From the material online, I know that I will

be skipping the Idaho Springs Gneiss at the bottom, and starting my exploration

in the Fountain Formation red bed sediments, and going up through the Lyons

and then the Lykins formation. So let's get out there. On the ground the Fountain

Formation is a very distinctive poorly sorted conglomerate-sandstone-siltstone

mix, and I don't see good exposure to make a good strat column so I am

starting the strat column at the base of the Lyons formation. But recent rock fall

has blocked me from getting directly to the rock face of this section so I'll begin

with strike and dip measurements on both sides of this fenced area, and getting

rather consistent values we will assume this area is also at that attitude. And

you better believe I am putting this down in my field notebook, and on my map.

Now it's time for the Jacob Staff, which we remember to tilt in the direction and

angle of dip of these beds, which we know from research and observation are

sedimentary layers. We start at the base of the Lyons as close as we can get in

and sight 1.5 metres up section. Note where that is because we're gonna place

the base of the Jacob staff there in a moment,

but note this 1.5 meters section of the Lyons and start describing it in detail

on the strat column. And then repeat, and this will get tedious and so here's what

I got as a result of a few hours of work. The Fountain Formation is a poorly

sorted mix of conglomerate, coarse to fine sandstone, and even this dark siltstone.

It is cemented with hematite, which gives its red color all the way through.

This allows us to say it is highly oxidized. It has rounded clasts and

cross-bedded channel forms. Our most likely environment for this is an

alluvial fan exposed to the air and variable flow from nearby mountains.

Color changing from red to a more buff tan to yellow colors lets us know we cross

the boundary somewhere in here. We'll try to narrow that down later. But now in the

Lyons, which is mostly sandstone but has conglomerate in sections. Some parts are

uniform fine sand indicating a possible aeolian, that is windblown, environment.

Other parts with coarser and more variable sands or full-on conglomerates

are clearly streamflow deposits. In both the stream flow and the aeolian deposits,

we're seeing some cross-bedding. Again we change color going from the Lyons to the

Lykins Formation, but now back to the reds, but in the Lykins much finer red

material than Fountain had. Lykins shows chicken-wire structure of gypsum

deposits that have dissolved out, and very thin repeated layers that arch

upward into dome shapes, and these effervesce with hydrochloric acid.

Stromatolites do all that, and so we feel the Lykins is probably a shallow

brackish, that is very salty, bay that hosted stromatolites. I find a nice place

to break for lunch, and then when ready I walk this contact between the Lyons

and Lykins, and confirm no major deformation beyond the tilted beds. Then

I walk back out along this contact between the Fountain and Lyons measuring

all the way, being sure to put all this in my field notebook and on my map, and

hey! Here's an exposure of the contact between the Fountain and Lyons. Well with

that and seeing this blob as Lyons over here I feel I can put this contact on my

map right now, and even provide some color. So next day out I start at the A

end of my transect, and start heading towards A'. I will need to be

careful around the cliff edge created at the base of the Lyons Formation. I need

to wander off my transect line to get over this cliff,

but can collect enough data around there to be confident. I must be careful

in these Lyons layers as we saw cross- bedding. I am focusing on bounding

surfaces to get the true strike and dip of the layers, but we'll take some cross-

bed measurements as well. I recognize where I am by certain features such as

the iron concretion nodules I saw at this level back on the road cut. I

crossed the formation boundary I walked along the day before and find the strike

and dip are basically the same on either side, so even though it's hard to put my

finger exactly on the boundary here to measure, we infer it's in this area with

this attitude. We know we cross the boundary when we go from tan buff yellow

sandstone/conglomerate to red fine sand- silt and even dirty limestone, and can

project from the road cut where this boundary must be. And here we reach the

end of our transect. We've investigated before and know there's a shale down in

that valley, with very similar structure to all the beds we just crossed. I find a

nice place for lunch less likely to have ticks, and notice that my spot has some

very interesting anhydrite stromatolitic material in the Lykins. May

be some kind of an ancient seasonal record from the warm wet times, and cold

dry times. And nice little stromatolite. Might have to collect these samples and

take them back to the lab and get them cut, and teaching samples. During lunch I

put in all those contact leader lines on my cross-section where I think I've

located them. After lunch I take a little more time to try to find those contacts

exactly, and not just put the dashed lines of "I guess" on our map. I might grab

a few more joint cross bed and bedding measurements to get a good coverage on

the map. I don't need a bunch of the same measurements in one tight area. Better to

get a few in every area. When feeling I have good coverage, I sit down on this

nice high spot where I can view everything, and try to finish my map. I'm

keen to note that the beds are dipping fairly steeply to the east, and the

drainage is to the east, and so we have some interesting V shapes

down the valleys in our field area pointing to the east. Coloring the map

in fully can be done later tonight over a beer, as that doesn't take so much time

as just patience. If I need to visit some location again to finish the map, I try

to get that done, and then walk back to the car along this ridge to get a good

view of the site from either side. Depending on the season, I may have a

cooler of juice packs waiting for me. I should probably head back to base camp

and start making dinner, or off to the restaurant after perhaps having the

courtesy of getting cleaned up for the public, but the rest of that night should

be spent finishing your map and your cross section while it is still fresh on

your mind. And this wasn't the hardest map to do so let's make it a little more

professional using Adobe Illustrator. Let me go into this a little bit more depth,

so open up Adobe Illustrator, and we're going to call this Morrison Map and just

accept those dimensions. I guess if I had more time I'd probably make that 8"x11"

dimension, but we're going to import the aerial photo that I've been playing with

so far, and I want to enlarge it, but don't just grab a corner and start

enlarging because you can completely screw up all the dimensions on your

aerial photo. So hold down shift, and then enlarge and get it on that edge, and then

I shift and enlarge, and you will have your map enlarged and in proportion. So

what we're gonna do here is make another layer, and I'm gonna make this next layer

the title. And we'll speed this up just a little bit. We're going to put in

the name of the location, the name of the person doing it, the date of the map when

it was made, and any other pertinent information you might have. And with our

title properly centered and everything spaced out right, we will now go on to

make the actual layers of the three layers: the Fountain, the Lyons, and the

Lykins on our map. So we're gonna make a new layer, and label this one "layers", but

we're not going to just make the layers directly in this layer. We're gonna make a sub-

layer. This will become clear why we're doing this later on. So the first sub-

layer I'm going to call the Fountain for the Fountain Formation. With the Fountain

layer selected I'm going to use the pen tool here, and I know this whole left

side is Fountain. Now, we're going to start from one side of our map and move

towards the other. You can go from right to left or left to right, but you'll

understand the logic of this here towards the end. So the Fountain/Lyons

contact goes right through here and across this area. So we're very careful

making the exact contact between Lyons and Fountain as we found in the field. And

then we're gonna close that off, and we are, like with our other maps, going to

make the Fountain a red color. And there you are. Now I'm going to make

another layer, but it's a sub-layer again, and this sub-layer will be the sub-layer

for the Lyons Formation. And use that pen tool again over there to draw out where

you saw the Lyon/Lykins contact. And the Lyons/Lykins contact was a little more

affected by the drainages here so rule of V's. We're seeing the contact dip

downstream on these stream channels as we go across them, so we have to be a

little more careful as we're drawing out the Lyons/Lykins contact. Now when you

get to the end of this Lyons/Lykins contact, and come back to close the loop

so that you have an enclosed . . . we're gonna make it yellow in this case for Lyons. I

don't really care about the left side. I'm going to just put it way back here so

it's overlapping on to the Fountain. We're going to make that one yellow as we

did on our map, nice bright yellow. And I don't care about that left side because

I can drag the Lyons under the Fountain, and there, the Fountain where I very

carefully made the contact is now the left side contact of this new sub-layer

that I made, the Lyons. So we have to make one last sub-layer and label that the

Lykins, and the Lykins is going to be drawn in a

similar way. We're going to use the pen tool to basically follow this tree line,

is where the Lykins and the Ralston Creek Shale, which we did not take our

time to map in this particular project, but that contact goes right along that

tree line basically with a little effects from the drainages again. As with

our Lyons formation, we don't really care about the left side, so we're going to be

a little sloppy and be as quick as possible here. Just nail it across and

close the loop, and again we can just move the Lykins underneath. Now why do

we make these sub-layers into the big "layers" here? Well if I start just

selecting the "layers" (big upper layer), and have that activated, I can go to

opacity, or transparency, and I can start to make it transparent so I can see my

aerial underneath. But it makes everything transparent without causing

you to see the yellow under the red or the green under the yellow, because

they're all sub layers within that group that got made transparent. And that's why

we did it that way. And you saw why we went from left to right so that we could

be a little quicker, sloppier, on that one side where we didn't have to be so

careful. Speed this last part up. We of course need to make a key and so we're

going to have a key. We're going to make little boxes which you can just copy and

paste again so that they're the exact same size, and well lined up. You make the

key for the Fountain, the Lyons, and Lykins, and so you're going to color

those boxes appropriately, and use the text tool to write in their names. Use

the line tool to draw in our North arrow, and get that nice and pretty with an N

for north. And then I did pace this area over here

on the road, and know it's exactly 0.1 Km,

I have to correct that it says 1 K,m dear it's 0.1 Km

across there, and so we can make our scale bar if we move it down and put our

0.1 Km marker on there. And now we have our map in

Illustrator very professionally done. It looks very pretty. You can import that

into any other document, and so that's a nice tool to have under your belt. I also

write up a quick summary of the formations, they're interpreted

environments, the interpreted geologic history for this area; alluvial fans of

an ancient mountain range gave way to rivers and dunes as the land eroded down

and seas rose up, and then we went completely underwater in a shallowish

brackish bay with evaporite deposition and stromatolite fossils. But I'm going

to do a much greater coverage for the Colorado Front Range in coming episodes

so I'll leave that for there. But I hope that gives you a general idea of how you

might approach the mapping and data recording of a basic field site. When we

come back next time, we'll look at some of the smartphone apps that are out

there that might help you in all these steps we've talked about so far, and more,

here on Earth Explorations.

The Description of 77) Full Field Project