geo303 lab9 geologic maps

variation related to dip of strata

-for any dip shallower than 90 degrees, outcrop width is larger than true bed thickness. -for verticle bed, outcrop width = true thickness

geologic provinces of texas

1. llano uplift 2. north central 3. edwards plateau 4. trans-pecos 5. high plains 6. gulf coastal plain

What is the relationship between map width and true thickness of a vertical layer?

If a bed is verticle then the map width and true thickness are equal.

How does the letter symbol for a formation express the age of a formation? Use a specific example.

The letter symbolizes the geologic time period it orginated. ex. Kbu stands for Buda Limestone that originated in the Cretaceous period which is symbolized with a K

define the terms true thickness and map width

True thickness and map width correlate with each other. The map width is how wide or narrow the section of a map is that is representing the true thickness or actual size of a geologic cross section.

5. If beds dip downstream more steeply than the channel

V points downstream

1. for horizontal beds

V points upstream

3. bed dips downstream less steeply than the channel

V points upstream. V is narrower than the contour lines

4. bed dips into the hill slope

V points upstream. V is wider than the countour lines

what is a geologic formation?

a discrete, mappable rock unit typically indicated on a geological map by: -a unique color or fill pattern on the map -a map notation indicating its name and age

depositional contact

between adjacent sedimentary strata, lava flows, etc., or their metamorphic equivalents

igneous intrusive contact

between host rocks and an invading igneous body

fault contact

between rock units that have strike-slip or dip-slip displacement

2. for vertical beds

contacts are straight, regardless of topography

geologic map of texas

dashed line that shows where ancient N America used to end but cenozoic sediments deposited by texas rivers much up gulf coastal plain. -north west of line is precambrian granitic continental crust -south east is basaltic oceanic crust. -balcones fault zone developed along this ancient zone of weakness.

broader outcrop pattern

gentle slope

geologic contacts

interfaces between adjacent rock units (formations) shown as lines on geologic maps. geologic contacts between unfolded horizontal strata follow contour lines.

presence of fold

may be indicated with mirrored repetition of beds

omission of beds

may indicate an unconformity or fault

geologic map

show the outcrop patterns of rock bodies (formations) and geologic structures (faults, folds) on the land surface.

narrower outcrop pattern

steep slope

outcrop width

the angle at which a bed intersects the land surface affects the width of its outcrop pattern on the map. 1. variation related to slope of the land surface 2. variation related to dip of strata

Rule of Vs

the pattern created where a bed crops out in a stream channel allows up to determine the dip of the bed. 5 cases.