Lab 7

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Portland Community College *

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Course

201

Subject

Geology

Date

Apr 3, 2024

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pdf

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Uploaded by JudgeClover13449

I • Exercise J _ Geo/o . • ,g,c Maps (8 points). Geologic maps sh • · at the surface • .A ,~;::ie distribution of rock fonnations faults and other structural features exposed age of the rock units 11 acc~mpanies the map to defin; the s~bols and colors used to indicate th e geolooic • J.v 1 any unportant t f · d ' m 0 ... maps. Refer t th . aspec so a region's geologic history can be determine uo Note that the legend ac:om e geo!ogic map 0 ~ Michigan to answer the following questions. hnportant: at the top. Pan}'lng the map 1s arranged in order from oldest to the bottom to youngeSt I. Where are th . e Youngest rocks d · • · ) expose 1n this area? What is their age (geologic period)? ( 1 point 11'1 ljO~+cwt---\w Lll?pct Y'Qtn. in -tt-u, p~1lvru,iio.n aria!, W ¼ r 4tAi bt\7(/ • .• t. · v I - 2 - Where are the oldest G 9f O'Ulp kJ \.1 Mt• ()kQAfQ.Vlf. . rocks exposed 1n this area? What is their age (geologic period)? (1 point) o\dt&r Yncks cwt -\-Vu 'lttwcx\\f\ ~t.s 'n p Y t llU'Yl b llh /tqe . 3 • S::idy th e patterns made by the rock units in the southern peninsula of Michigan. What major s ctural feature is shown? Provide reason(s) to support your answer. Hint: note the spatial3. ou!crop pattern and the age relationship between different units ( as shown by the map legend). ( 1 pomt) Tu.<_ W\Ll·\c( S1YlAL1V\Vo.l /fwt-lwL \s tk b&\Sln ~) llltrLAi -\t'U_/ v-o rJcs 1n ~)-tAL {)JIL(!J>\ MOvL L °"- cJr ccilir j u1Vl,un,--h--i (, ,w~ if v) _ lAfi~ ld o~lf rocts 1 lYL -(-iv_ OvVlJ oldif VVU!~ 4. Note the outcrop pattern of Silurian and Devonian rocks in northwest Indiana. What major structural feature is present in this area? How can you tell? Hint: note the spatial outcrop pattern and the age relationship between different units (as shown by the map legend). (1 point) ~~d< ~l ~vie e.;rL~t- 1~ Otflh c1Jvv- -rtu_ tJl ci« vu Ll<- f s ~- tJ\1 ~e#v~ VOGk=_CJV) w()tV\_ f{ , Ph ·cal Geology GEO 201 lorys! Maps and StrUctures Lab 7: Geo ig,c Page3of JO

f on in this area? How can you tell? Hint: remeinb fthe defonna I • t 1 h th er Wh t • th oldest possible age o . k units were honzon a w en ey were deposited 5. a 1s e . tall ty · the roe . ) , the principle of original honzo~ w~re deposited. ( 1 pomt 1lf 1..f .'!\.. • ,,... anddeformedsometimeaftert ey lJ he 'ft,\t \JvvOvlWwv ~nct ' \Vu, O\W~ °'-~ \jl/OJJ. V\(AF»1 -\tu \)\A .t ct • eY\ ClL~ Sc> · 1{ \,M)WIJ W~\/ vJ~ ovf~l~ °' f\-tV \)'ti\\ VT/vi- -J I • (\ v' OllvV\ '.) q_ ')<) vw l l l(/'/\ ' Use the geologic map of the Grand Canyon to answ er the following questions. . h C 1 do River had not created the Grand 6. What rock unit would be exposed at the surface if t e o ora th this unit? (1 point) Canyon? Are the rocks exposed within the Canyon older or younger an - • 1iN_, (GdGS ,\- ()JI A_ {;'2(1od NM r'1 , l\ '-(__, I · 1, ( · 1 CD,hAj<M (>Nl(__ J\i4v,l,lvtd vOut':,, .Z-·',,JL' c:-,1 ct+- &\A;Y fC\U W r,\,\,lc_\ p le vrJ JL 7. Locate the Bright Angel Fault (in the southeast portion of the map area). Is the fault dip flat (gentle) or steep? How can you tell? Hint: a gently dipping fault or contact will follow the surface topography, while a steeply dipping fault or contact cuts across (shows no relationship to) the surface topography. (I point) f\;0. ~IA[{-- J{ p (\ Jt {,lp NJlf1l, OJv\& f; l. S dtu +t> -t ¼ t Gic !μ\,Jul\ WlLl ~d tdfW\ '/\Vlfr .11cYW J .' . f' 8. What is the general dip of the rock units in the Grand Canyon area? How can t 11 _U\(fl<-d701\. Hint: examine the relationship between surface contour lines (thin gray lines)youd eh? (I point) between rock layers (thin black lines). an t e contacts 1k wl &t' f. '1~ MuVI{_ f9-t,U4L~ co~ i~s VWJlL 6W\Pvl l k,& ex,f -k i1AJ, flfa~ ik.uLt ·We Ccvttl,\ l-f1 GEO 201 Physical Geology Page 4 oifJO Lab 7: Geologic Maps and Structures

Exercise 2 - Drawing a Geologic Cross Section (8 points) Geologi,c cross sections are often included with geologic maps. A geologic cross section is a vertical slice through the earth showing the arrangement of rock units and their associated contacts underground and providing a more complete picture of the local geology. The geologic map on th e next page shows the distribution of various sedimentary rock layers where they outcrop at the surface. The line from A to B cuts perpendicular to the strike of the bedding and is an ideal place to make a cross-section revealing the geologic structure of the area. A geologic cross-section is made the same way you make a topographic profile: • Align the edge of a piece of scrap paper with the line A - B on the geologic map. At each pla~e where a geologic contact crosses the line A - B, make a tick mark. Label the different rock units on each side of the tick. • Use your piece of scratch paper to transfer the locations of contacts and names for the different rock units to the top (surface) of your cross section represented by the line A-B. • Note that the strikes and dips of the contacts at the surface are shown on the map. Use a protractor to draw in the dip angle of the contacts at the surface on your cross section. The dip needs to drawn in the correct direction and at the correct angle with the surface (represented by the horizontal line A - B). Important: the dips shown on the map were measured at the surface where the contacts between the rock layers were visible. We cannot assume that the dip angle remains constant beneath the surface. Use your protractor to draw only a short line representing the dip direction and angle. Start at the surface and extend only a short distance underground. • Notice that some formations crop out in more than one area of the map. You will need to make a reasonable interpretation about how the different outcrops of the same formation are connected beneath the surface and how the dip of their contacts change below the surface to accommodate outcrops of the same layer in different areas of the map. You may also find it helpful to draw dashed lines above the ground surface of your cross section, representing the portion of the geologic structure that has been eroded away, to help you visualize how different outcrops of the same layer are related. After completing your cross section, answer these questions: (4 points for cross section) 9. What type(s) of geologic structure(s) are shown? Be specific and explain your answer. (1 point) \\f..L 5'{'(\A,{)wr U ())ft ~~"\~Vl/L. -l OJAt\c ¼ V\tL ~-\e. Of-~ tf ~-e)1 1'vl ¾ . c~vrf'e,( ~v1d. of c0/r . . v& ~s . \ V\.. --r v~ L..(._vvN- y o-Y'\ . ri~ hf- l 0. What 1s the YOUNGEST umt shown 1n this area? Explain your reasorung. (1 point) • ~t);YJ(Y'A:ru ~ye, It ls Ct~ lA U a,f ~- h~~h_S, ?E 1 · . (1 . 11. What is the OLDEST urut s own 1n t 1s area. xp ain your reasoning. point) ClNMIL- \~ - ¾ -{, ai~~ kJeCl,lAAR ,r ,~ b<,,L(Jw Wl l~¥ . 12 _ Considering the depositional environment_ of different types of ~edimentary rocks, does this sequence record a relative sea level rise or relative sea level fall? Explain your answer. ( 1 point) I+ ~s (A Vlf,,t Or}WvL l-vviL I I I fee~lK i\A,t ~Olf O n~0 o£t, IN&j-1uV hod,N._cS GEO 201 Physical Geology 0\.,, V\;c} _ t\ltD vvtJL,JdVte,, Page 5 of I O Lab J: Gp~;~t:res D\N1' w\MM fu feet {~ I fut/,

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~I Map: I Black Shale A J Lime- I Sand- I Evaporites stone I stone 70 If- 52 II- 35 28- I Sandstone I Limestone Bfack Shale Chalk 25-l 224 164 Black Shale Limestone r35 ~59 -------+--·------~--- ·---t-----------------------+--------------- B J J · --------------------+-----------------------+----------------------- · --- · ---------+---------- I Cross Section: A s~nJJYll, rf l 6~0 ~15'd ~V()f · 7 3_f6d LA~ ---- 6S GEO 201 Physical Geology Lab 7: Geologic Maps and Stroctures /' ., / ,, c/Ji) I / / ( (Q d Page 6 of 10 e,~(~ /- -

I . Ma 's Peak (19 points) Exercise 3 - Geologic Cross Sectton of ry three rock units that outcrop . the Mary's Peak area. There are . are localized on th~ upper The next page shows a ge~logic map of he field trip. Intrusive rocks (Tl~ is artly responsible for on Mary's Peak, all ofwhich_we sa~ on t these intrusive rocks to ~rosion . pa se uence of ocean part of Mary's Peak; the relative resi st ance of_ 1 t River Volcanic Senes (Tsr) ts q d can be seen the topographic relief of Mary's Pe~- The Si e z saw exposed in the ~uarry' a~ uence of ridge basalts, including the fine pillow basalts we The Tyee Formation (T~) ts a seq bol throughout much of the Coast Range of weS t em Or~~on. The capital T 1n the map sym • d turb1d1te sequences. · · old) marine sandstones and mudstones deposite as_ . (b tween 2 and 66 milhon years • for these rock units indicates that they are Tertiary in age e . ding sediments (Tt) flat or steep? 13. Is the contact betwee~ the intrusive rocks (T1) and the s:ot: surface contours, then the contact How can you tell? Hint: If the contact more or less follo h 1 cation of the contact has no is flat. If the contact cuts across the surface contours -: t e O 1 oint) relationship with the surface topography- then the contact is steep. ( P I \j\,L Cwv1TA-CA \ ".-\- \rtlOvUk --¥1'.,L f l.eS \V\ r;.xu.JAS }liu, \ rAA.~u & t1v\.,t:e_A- l1t,,vie, \p -H""~N\. Lt? 0 ~\o 0) \r('C,_vi"tcn1--l-ott~ 1 • 14. Does this type of cb'ntact m\ike.,.,the'intrusion a dike or sill? Explain your answer ( point). t+- cv~o C\ oill ~to -t'k tross -c~ ~-r T s rw~ll.{,,I te --(k 6'>1,fYlMJ'lcl,i;~ (w.J-er.P 15. What type of fault is the Mary's Peak fault? How can you tell? Hint: Use the map symbols to determine the direction the fault dips. This allows identification of the hanging-wall and footwall sides of the fault, which along with the relative movement across the fault shown on the map allows us to determine the type of fault. <t pointL\Ws \ S Cl V\O\fv\f\.ovl {~t -ftN__ ~'4 \J\JC\ l l is \of M~ cl-0\AJV\ \J s. cl9r"'8 Wf. 16. Study the dips along and near the line A-A'. What type of fold is present here? Explain your answer. Sketch the general shape of the fold in the space below (1 point). -1 s- ~- 0-Vlt -\k ol deJ-t oV'- bcJW)W\ GW\~ rnlwW \r)&Sed1-r CU-tr\ t.A- CM-l q,lf{\,8 +tu- ~d · tlid s-iJ hr ! 1\ \ J.' _fr !l rs: .p,t d., A' - - ---------- I ' .1 1 I '\ i ,;~ ", ,, '}hl -----/ \ "- l \.,' "' '-, ~- --. il \ ' •,-, ~- GEO 201 Physica'i'Geology ""' - ......... ,__ _ 1 - La.b 7: Geologic Maps and Structure~ ....... _ \... _______ _ s, JVtL, lM,t ,_ - 1 l A

r however its direction of dip is not The relative motion on the Corvallis fault is shown on th e map, shown. . h direction (towards A or towards A') 17. If the Corvallis fault is a steeply dipping normal fault, whic must it dip? Explain your answer. (1 point) tas -ft-.e A I ~c.4f er) 1\1\L ½ H ckfs -tovl~l ftvwlt,. . . 1,r \¥S {A, s\aP c},J r l 11 d thrust fault) which dtrect1on 18. If the Corvallis fault is a gently dipping reverse fault (a so ca e ' r~\IU/k l t, . . . Mak~ cross-sections along the A-A' line by interpreting the 1nfonnation shown o~ this map. In the first cross-section, draw the Corvallis fault as a steeply dipping normal fault, and 1n the second cross-section draw the Corvallis fault as a gently dipping reverse fault (also called a_thrust fault). The topographic profiles have already been made for you. Follow these steps: (12 points for cross sections) First, transfer all available information from the map to the profiles: • Make short marks on the profile line showing the location of contacts between rock units. • Label the rock type (Ti, Tsr, Tt) seen at the surface along your profile between your marks. • Draw in the Mary's Peak Fault through each profile with the correct direction and angle of dip as shown on the map. Use a protractor. Add in arrows showing the relative movement along the fault. • Locate the dips closest to the line A-A' and mark their location on the profiles. Use a protractor to draw the dip direction and angle on the profile by making short lines on the profile to represent where these dips were measured. Next, draw in the contacts between rock types beneath the surface based on what is seen at the surface (the information shown on the map that you have reproduced on your profiles). You will find it helpful to draw in what would be above the surface (had it not been removed by erosion) using dashed lines. Use your answers to questions 13-18 to help you draw the cross section. Page 9 of 10 GEO 201 Physical Geology Lab 7: Geologic Maps and Structures I t I j ..,.-:1f_

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, ---- - snW'it~m A A /L Corvallis Fault== Normal Mary's '\{_ ~~ak A ,...-GI l1 i I 1' //, ----- I l r---_ __ I 0 Mary's Corvallis Fault= Reverse 1J::, P~ak / · i1A\ A ,-Ltl, u \t6y t;~ A' Elevation (ft) 4000 3000 2000 1000 Sea level -1000 -2000 A' Elevation (ft) 4000 u 11 · --0 __ - __,..,_ Corva 1s ------ tit 3000 2000 1000 Sea level -1000 -2000 19. Although we did not see evidence for the relative age of the Tyee Formation (Tt) and intrusive rocks (Ti) on the field trip (all we could say was that both are younger than the pillow basalts (Tsr)), your cross sections reveal the cross cutting relationships between Tt and Ti, and therefore the relative age relationship between them. Which is younger, Tt or Ti? Explain your answer (1 pt). {,; i S lvi'[lll{S1\l-t Otl1ld \d 7'/,/(13/-}( k CUt~-t:- ti \S ~{,, ,'.lV} Jvft~ r~YV\~ ~r 1t ~d, GEO 201 Physical Geology Page JO of JO Lah 7: Geologic Maps and Structures ) )

Lab 7

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