FILE_0802

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University of Colorado, Boulder *

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Geography

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Feb 20, 2024

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1:43 PM Mon Apr 12 - o . 80% @) Q [€7Ye] [oTe\ VAU (OO N IE:T o o] =Y (oI G YA, Vo UF IR U o TAVZY 1§ VAo ) o] (o] ¢ Te [o 8 Boulde_ @ ll Aa '&) Q ﬂ 5 (’A‘\l\r\l//‘muj ot BN E e Advicue, Gmin; Lab G — Mesozoic Rocks at Dinosaur Ridge For Lab G we will drive to Dinosaur Ridge to examine the characteristics of the rocks and the fossils of Mesozoic age that are exposed there. Our primary objective will be to use the characteristics of those rocks and fossils to reconstruct the changing landscapes of the Denver area throughout the Mesozoic Era. Stop 1 om P !!A wn Stop 1 is a short hike up the road from the place where the van dropped you off, at a display that discusses dinosaur bones visible oy figdl e W (n within the Jurassic-aged Morrison Formation. This rock dates to about 150 million years ago. The scattered bones likely belong to the two famous dinosaurs, Si us and Ap us. The first S us fossil ever found was discovered right here. (o] U‘\Q “)g‘“} L1: L d plot th f Stop 1 on th f Fig. G-1. Label it ‘Stop 1 !(@( e A uestion L1: Locate and plot the position of Stop 1 on the map of Fig. G-1. el it “Stop 1°. D plot the p p p of Fig p (oo 3 #) 6)\ J Question L2: Examine the dinosaur bones at this stop. Your instructor and the interpretive signs will aid you in identifying the bones. a. Are these body fossils or trace fossil‘s. Explain your reasoning. ' P " 'A Sody £ors1U btcaue 15 |29 N ¢ ir U poreidre P~ thehaa 45 b. Identify escribg and sketch two dinosaur bgfires. In youl desc!;ption, make sure you explain how to distinguiz?{l{;l& dinosaur bones from the enc; [ 2 o\ fo~ Nask Hstn do o it7 %_q uestion L3: Classify the rock 1h§ [s Efis’eminosau: bones. Describe the characteristics that led you to this classification. THir o nww Ve, imost «.-ul’ Sanov e ol do tlr ¢ olovpdtion , clarB T | ondk He fediment= gming Walk betweenStop Tand Stop 2 cawt abost- H (oo Sire of -hnaicm SONA R teslicnunt- Observe the rock layers as you walk east, up the road from Stop 1 towards Stop 2, which is at the interpretive sign labeled ‘Brontosaur Gaing, Bulges’. The following question asks you to describe and interpret various aspects of these rocks, which all belong to the Jurassic- aged Morrison Formation. It will probably be most convenient to record your answers to these questions when you reach Stop 2. Question L4: You will see, interbedded with layers of the rock type you identified in Question L3, another rock type. For this rock: 69

1:43 PM Mon Apr 12 - o . 80% @) Q [€7Ye] [oTe\ VAU (OO N IE:T o o] =Y (oI G YA, Vo UF IR U o TAVZY 1§ VAo ) o] (o] ¢ Te [o 8 Boulde_ @ ll Aa '&) Q ﬂ e 4 a Lelarh / seds, a.7 Classify the rock and describe the characteristics that led you to this classification. T _ N ).) THItemf | e mvditone becarke Hil cimi(ar (aomtton | andl W 199 e i+ PN —qraineoh b. Describe the rock’s coloration , T colov OFHA 1ol il it brawy, andk 032 - ifn Ceath a G ved Hnt=\ 2 Md e c. Classify and sketch the contact relationships that exist between layers of this rock type and the rock type of Question L3. Ay 2 A Qviays, Stop 2 e relaBanship seem; poatle| , Woin g e 3 ; © 1V 0 s (et " P‘““"‘ 0\4"1 ) ma (¢ Stop 2 lies at the interpretive sign labeled ‘Brontosaur Bulges’. The rock here belongs to the Morrison Formation of Jurassic age. Canthch - Question L5: Locate and plot the position of Stop 2 on the map of Fig. G-1. Label it ‘Stop 2°. = g Question L6: Measure the attitude (i.e. strike and dip) of the sedimentary layers here (which you did in Lab E, if you’ve done that lab e already). a. Record the attitude you measured for this rock. 10 4 30 digee (wt b. Explain what geologic event must have occurred to produce the rock attitude you measured here. When must this event haye occurred and how can you deduce this timing? . depe = Kb cadkuly affe” depenition 'ri(h‘da‘f'ﬂv 2/ VhOA dw i K HU(\'I‘J c. Between Stops 1 and 2 you have been walking toe east. Using Steno’s Principle of Superposition, in which stratigraphic direction have you been traveling (i.e. up-section, toward younger rocks or down-section, toward older rocks)? How did ., you make this determination? e . Wit (Eing fowaay ¢» Mg H(F iristie cart and i 15 o1 fop et A (B0 e . Question L7: Examine the downwlard bulges in the rock layers that exist at this stop. The signs explain the interpreted cause of these bulges. Evaluate this interpretation and answer the following questions: a. Devise at least one plausible alternative working hypothesis to explain the presence of these bulges. Describe your hypothesis. (aviw] Mg g and ﬂ%“J docn O Ccawee G /\hwr. ™ ay howe e 1 A‘, geo. b. o alternative hypotheses now exist to explain the characteristics of this outcrop. Describe characteristics of the bulges that you would expect to differ between the two working hypotheses. Which of these two hypotheses do you favor? Describe the observed bulge characteristics that have led you to your conclusion. T;M,'/NMM endenu s - He Ylacie/ uy,wmfnil bt i/ cudepnce Ly Cle dmortir t«ypgw.'/-

o N Ay < A Souarian Yy (\M ™ 0eprrhmnl envirsment ios ot “'M'fl yc M |0 (/ et/ Y= . denrsfan \ W '0\)\ c. If we assume that the bulge 1nterpretat10{1l£sc¥1bed on the interpretive signs is the correct one, was the depositional v # environment of the Morrison Formation marine (i.e. in the ocean) or terrestrial (i.e. on land)? /5" Question L8: What is your working hypothesis for the depositional environment of the Morrison Formation? Describe the most sigmificant features of the formation (anywhere from Stop 1 to Stop 2) that led you to this conclusion n@( e v M Fhat are Pregar TAir ainrde f"\°"ﬂ xplain why you favor Ao fle chamays Question L9: What is your wc!rfil‘r‘lgh ".{hesm to explaln the color varlat‘l'(fn W the this hypothesis. T rolor vaviafion is lbreel o~ Fir v olCanic ark 14«‘.1,\ wolcan, « 'HO'C' Stop 3 . . A, With ity tupe ce Ok SO Tl e P oets iy e, g Stop 3 is located a bit farther east along the road, just before it takes a sharp bend to the left. An interpretive sign here is labeled ‘Volcanic Ash’. Here the rock belongs to the Cretaceous-aged Dakota Group (a ‘Group’ is simply a package of related rock formations). The Dakota Group rocks were deposited about 100 million years ago. Question L10: Locate and plot the position of Stop 3 on the map of Fig. G-1. Label it ‘Stop 3. Question L11: In the short walk from Stop 2 to here you have crossed the contact that separates the 150 million-year-old Morrison Formation from the 100 million-year-old Dakota Group. Given the significant age difference between these two formations and the characteristics of the rocks on either side of the contact: a. What type of contact relationship do you conclude exists between these two rock formations (Hint: recall your work on Labs C and E)? Describe the key features that led you to this conclusion. TH VW A divconBormity vilaponbiy jHret v ko Pryical th of-Fine vy ing b. Based on your conclusion in part a), descrlbe any geologic evenfs that you can confidently say did or did not occur in this spot during the time missing between deposition of the Morrison and deposmon of the Dakota (again, recall Lab E). wWaS oy, (_mra Jo o deparivon o cuwing ot e ofF-nising behawn Question L12: Examlrf!:vfie ed ot’ Volcanic ash that is protected by the Plexiglas case aitd then answer the following qu@stions: Mo~Von and\ a. Describe the characteristics of the ash that make it distinctively different from the sedimentary rocks that lie above it and Ooteota - below it. tl W lcanic wh bed VS Dveean \l;qm'{f\ ol wear fle (‘-{o(mnfuj layeer are gre anek e :""“ b

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™he e 'I.(' 47 ke w.y i a ("V‘Vfﬂ)tﬂf Plﬂft b-91-»’\0(&7 Cubdv o) g wolcanic C twas ¢ C T LoUd bt Py, pam cener be couns flut ot not an b . Given what you know about the types of volcanoes that erupt ash, what type of tectonic plate boundary do you susp the source of this ash” Was that plate boundary near or far from Denver" Explain why you answered as you did. VAN o~ r U eve i I+ ash. c. Might this ash layer be useful to a geologist who w1shggt\8 daté the Dakgta Group rocks? Describe why the presence 0 such an ash bed would be useful in this regard and how you would use it for this purpose (Hint: think back to Lab C). Y ; L{l\) Covte Q esg“l)l {13 Examine the segnentary rock that lies above the ash bed and answer the following questions: a. Two types of rock are interbedded here. Classify both rock types and describe the key characteristics of each that revealed their identities. TVt (i) forore 7 andfi-w_ bt cung 0 & it7 4'& what s omel Lerts oS- cetne of ¢ ana(,fu- Aot b. What are the ave% {filc csses otylgfimdual beds for each o?che rock types you classfi' e({l in part 10 ihes c. What are the colors of these two roc}( types" Does the color of either one document a significant attribute of the rock’s depositional environment? If so, describe that attribute and what about the color leads you to that conclusion. Soandstone = |i qm—w‘l T doveer fy 10y ) Pt o OGanil cavieon t+—haus SRt e Thif im tons bWk in Onoyic ¢ ondition . Stop 4 lies around the corner (to the notxzeast) from Stop 3 at an outcrop of orange to tan rock that possesses a distinctive, wavy texture (Fig. 49). This rock, like that of Stop 3, belongs to the Cretaceous Dakota Group (about 100 million-years-old). Question L.14: Locate and plot the position of Stop 4 on the map of Fig. G-1. Label it ‘Stop 4’. Question L15: Examine the wavy rock texture and answer the following questions: a. The wavy-textured bedding features are ripple marks. Which type(s) of ripple marks are they? Draw a sketch that clearly '\'Vf shows the shape of these features in a way that illustrates the ripple type(s) present. Symidm ¢ Avple manes b. Based on the ripple type(s) you identified in part a), what type(s) of current existed here 100 million years ago? Mentally b o, rotate the rocks back to the horizontal and then determine what direction(s) the current(s) flowed in. Express your answer as a compass direction (e.g. North or Southwest). Explain how you arrived at your conclusion. p (eg ). Exp v b ot gveeh %-wcfioﬂa( axent nd T U iy Fam rotin o satia YK oF h (vt <un coun vigoe - 72

Stop 5 Stop 5 is found a short distance down the road (north) from Stop 4 at an interpretive sign marked ‘Trace Fossils’. Question L.16: Locate and plot the position of Stop 5 on the map of Fig. G-1. Label it ‘Stop 5. The interpretive sign at this stop explains that the pockmarked texture on the rock here results from the activities of small worms and crustaceans (invertebrate organisms). Question L17: Examine the pockmarked rock texture and answer the following questions: a. The sign says these are trace fossils. Explain why these are trace fossils and not body fossils. e mebact £srilr be (e Yydeow on ackhvi /hw an acfon | Org anirm. b. Draw a sketch of this texture. As with any scierm? 1c sketch it is very imp at you draw a scale bar on the sketch that allows the reader to comprehend how large the sketched features are. - 12 it 4_\/ ~/Al M Fosilr aw Stop 6 T ot Linuy, fmo ¢ Stop 6 is found a short distance down the road (north) from Stop 5 at an interpretive sign marked ‘Dinosaur Tracks’. eud) \ Question L18: Locate and plot the position of Stop 6 on the map of Fig. G-1. Label it ‘Stop 6’. Question L.19: Examine the spectacular tracks, which were made by two different kinds of dinosaurs. Use your observations and the information contained on the interpretive signs to answer the following questions: a. Are these tracks body fossils or trace fossils? Explain your reasoning. c ol V\"j ) virfer P o M . - w? Thre mebnue F#ivibeone iy Shw fuadku of e dives e o ; b. Draw sketches of both track types texture. Incfude a scale bar on each sk:t?:h. headky W70m|m_ ! Question L20: The larger tracks were made by herbivorous /guanodon dinosaurs. These dinosaurs possessed smaller fore limbs and (a Vo< igger hind limbs. a. Were these dinosaurs walking on two legs or on all fours? How can you tell? THY wie oty on als RouwT becowe fle 7AlL, S quom faugy - ofbmr;u e (ndi (akt trat aBows wodemy on tay Fent g foo. \ ] \§ ‘}‘°Mu:mi"""‘t (A trian e " NB 0T At Lt s

b. In what direction(s) were these dinosaurs moving (e.g. North, Southwest, etc.)? c. Do you suspect that these dinosaurs traveled alone or in herds? On what evidence do you base your conclusion? ™y g bably Mou(td 1 heds beawee i looers lite tue if g aoundan e« of face, Question L21: The smaller, thinner tracks were made by carniverous Ornithomimus dinosaurs. These dinosaurs, which were about the size of a modern ostrich, possessed smaller fore limbs and bigger hind limbs. a. Were these dinosaurs walking on two legs or on all fours? How can you tell? uo (7 be cane M fiL« «Fthnoe dmues g consishmt b. In what direction(s) were these dinosaurs moving (e.g. North, Southwest, etc.)? a",d ofo /uf'CV)C(n’e. c. Do you suspect that these dinosaurs traveled alone or in herds? On what evidence do you base your conclusion? VWY prevedly honfed Gla~r berowe fige aT jUt & cocpic VA d. Given the track spacing and the size of the animal, do you believe these animals were walking or rur%ing? How can you tell? THY ~ve probably vumnir be (et iz alavge dutara bekre,, . . Acn \C . . Question L22: Given the presence of these dinosaur tracks, was the depositional environment of" the Dakota Group rocks marine or terrestrial? Explain your answer. T/(— s +Cf‘r(r.lv'~a( Pt Came .\»y).(_;\. am-;ﬂd r o lamd Pnimal s, Stop 7 Stop 7 lies a short distance farther north down the road from Stop 6, at an interpretive sign labeled ‘Mangrove Swamp’. Question L23: Locate and plot the position of Stop 7 on the map of Fig. G-1. Label it ‘Stop 7’. Question L24: The linear indentations near the base of the rock are fossil logs that have been interpreted as mangroves. a. Are these body fossils or trace fossils? Explain your answer. | with indiCattr WI'OM] body Forrils Ve (ure Yhe imageis a g wapciion o b. Given what you kno¥ about mangroves today, was the depositional environment for this rock marine or terrestrial? aohv'ly The cavwrvneun t vawdrierfia (- 74

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crowodily mditae d Ingilal climake dar Cone aF’W-mepy Pafuc c. Although they are not readily visible, tracks attributed to crocodiles have been found in the rock here. What does this discovery suggest about the climate of this area 100 million years ago, when this rock was deposited? Another feature of the rock here is a series of vertical grooves that paleontologists have recently interpreted as having been made by male dinosaurs doing courtship displays around the nests of females. Modern nesting birds, which are descendants of dinosaurs, perform similar displays. It is this modern bird behavior that led the paleontologists to this conclusion — another example of how geoscientists use the present as the key to interpreting the past. Question L25: All of the rocks you have observed between Stop 3 and here belong to the Dakota Group, which was deposited about 100 million years ago. Considering all of your observations at these stops, describe your working hypothesis for the depositional environment of the Dakota Group rocks. Paint as detailed a picture of that environment as you can, including anything you can say about the paleogeography, paleoclimate, and paleoecology. Describe the key observations that support your conclusions. m(_,,”,‘(_ri«\dila.if e envipovinpdag Jerverhiatl becae e dine awz h'\'{o—\hmp() Pndt Hr lv:g-' @l climafe ) beved onfle e gun p=ce, sbows Cidence of- ferverhsul Clvva, Stop 8 lies a short distance farther north down the road from Stop 7, at an interpretive sign labeled ‘Western Interior Seaway’. The 7 . rock here belongs to the Cretaceous-aged Benton Formation, which directly overlies the Dakota Group with no significant time gap way Stop 8 between the deposition of the two. l71ze MG fop Question L.26: Locate and plot the position of Stop 8 on the map of Fig. G-1. Label it ‘Stop 8. Iy ’olrw tidter Question L.27: Examine the rock of the Benton Formation and answer the following questions: mrfhf- a. What rock type is this? as wellt. b. What is the average bedding thickness of individual beds? Based on this thickness, how much sediment was available during each individual depositional episode? Tt leovs like GYok a fvol (o voltr ro bhaud o ) e ~ayse vdda-\e ( c. What color is this rock (to determine the color it is important to examine a fresh surface, as weathering alters the rock ( 7k color)? What significant attribute of the depositional environment is revealed by this color? ey by (g bl A b A goncd ouerfirm i e came Adayiis Guy- T S pnvay, SCdiment Although no fossils are present in this outcrop, fossils from a number of species have been discovered elsewhere in the formation.J Qe, These include fish, giant clams (/noceramus) and marine reptiles (Plesiosaurs). b o € Coc 2 tre daet O an, 75 nid (ol

Question L28: Considering both rock and fossil characteristics, what is your working hypothesis for the depositional environment of the Benton Formation? Paint as detailed a picture of that environment as you can, including anything you can say about the paleogeography, current energy, and paleooceanography. Describe the key observations that support your conclusions. e depnsifonal enironnunt- 1 pebably on o Corbmentnl Joye becavie tre blax ShAl{ deposition OUMI ntle OKy qen Aminitwn™ ZonC - T dove e Crhal(e D N Cdtes Qnoyia, wMitn oy i donc of 0qunic cavion (- °chza-f’"4‘f"‘4fiko,; Un Mot ana L. 177 The Dakota Group rocks record the depositional environment of the Denver area about 100 million years ago. Because no gap in time (i.e. no unconformity) exists between the Dakota and the overlying Benton Formation rocks, the Benton records the changes in that dﬂl’t environment that occurred shortly after 100 million years ago. i One factor that strongly influences changes in depositional environment at a given spot is a change in sea level. Geologists refer to a ( oA~ sea level rise over time as a fransgression. If sea level drops over time it is called a regression. * Question L.29: Do the rocks of the Dakota and Benton allow you to trace a transgression or a regression that occurred in the Denver area during the Cretaceous? If so, which one occurred and how can you tell? M ner et M Davela . cunct Voenfon atiow wrhs Trute @ AT G Lhion Y (une (N3 ‘fhrv\,ﬂvo\.\mu WU Apequlher W Uh (T bregh wohky patk othe S of e Daustt Gevapo’, i/ (e dle dep=tio '

TOPO! map printed on 10/15/10 from "Untitled.tpo" WGSB4 105°1100° W N 004768 i el o~ ed with: ‘WGsE4 1051100 W il N00v.68 TNVMN o 1015110 000 005 010 0.15 0.20 025 0.30 035 040 0.45 050 miss ! o NATIONAL GEOGRAPHIC 77 Figure G-1

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