LAB 6 - Google Docs

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Geology

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Apr 3, 2024

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- . \ \ ‘ \ /\’\\ oWt : : Name: ‘j(\-\j\\’ NN ‘\) : Section: lpm or 3pm (circle one) Lab 6: Sedimentary Rocks Give the texture of each of the following clastic (mineral grains or unidentified fossils or fossil debris), very fine Problem 1: Sedimentary Rock Textures: samples. The following textural terms will apply: debris). bioclastic (made almost entirely of whole grained, or fissile. \_’np@ng'_uing'c_ﬂumimfilbx_‘swcs_zmmlc_s. ‘(S}{ ( { u i : : : =T W Texture(s) Rusty brown {lecks are plant debris. 112 \ \ Y j‘-: p) () ) Look for a fossil. 113 (315 A edoke 0 | ' ARG ) J 116 Problem 2: Seeing the big differences. Put your samples into three groups: Group 1 Group 2 Group 3 100 103 102 - 101 S 4 112 Saees 104 : 116 113 117 \VIEN _ZE\ TPWwv N\~ i@ You have probably already figured out which samples are sandstone and conglomerate. Itis more challenging to distinguish fine-grained limestone or dolostone from shale or mudstone because both are very fine grained and both can contain fossils. Here are some distinguishing clues: 3 * Ifyou break shale, it, being fissile, more irregular, blocky pieces. Muc to be softer than solidly cemented limestone and dolostone. * Ifyou have asilty shale or mudstone, you may see tiny shiny flecks of muscovite. [n some coarse-grained limestones you may see calcite cleavages, but you will not see muscovite flakes. * Ifpresent, silt-sized quartz grains in shale or mudstone will scratch glass if the rock is solid enough to not crumble against the olass. Limestone and dolostone do not scratch glass. breaks into many flat pieces. Limestones break into Istones also form irregular blocky pieces, but they tend

| ' | | but this test is not 1111(‘11(1(‘.({;(; distinguisy, . olostone 2 3 istinguish betwee and d S It is only to be us d to distingu en 3 ks and oth€ $347 e % i . aTance. " -dentical in appearanc \2 : fizz in aciC e Of course, imestone between carbonate roc and dolostone, which otherwise arc limestone ate? : 2 e and conglomerate: a. Which of your three groups consists of sandstone and g ek \ L\ vJ '\ \ 7 ; and mudstone: b. Which group consists of shale \ % \ \ \ (| & \, - 5 A P Nhich gr ¥ <ts of limestone and/or dolostone: c. Which group consists of limestc | - 1k . things sl -estrict your Problem 3: Sedimentary Rock Identification. To make things simple, restrict yo choices to the rock types listed below: R e i SRS E_I_EM; Table 4.4) Chemical/Bioclastic Table 4.5 Conglomerate Micritic Limestone Sandstone (fossils possible) Shale (if fissile) (fossils possible) Bioclastic Limestone Dolostone (fossils possible) __ Mudstone (if not fissile) (fossils possible) |} = Chert = | £ S RN Rock Gypsum S E Rock Salt I Cloal Fxamine sample 100 with a hand lens. It looks like sugar. What type of rock is it? What type of mineral makes up 100% of this rock (apart from occasional rust-colored Fe stains)? b. Sample 101 is what type of rock? on 4} 0lnera T Name the mineral that comprises one of the common clasts. TN s > yOA T ¢ Sample 116. The surfaces of feldspar grains in this type of rock oftenSVEAENSRSRERRECAR down, making it tough to find a vitreous luster or cleavage. The moSEORIORSISERNSN this sample give silvery flashes. What mineral gives these flashes? {\l\uSCO\I\'*fi What type of rock is this? %l Sanl}\sjfovl'( d. The "acid test" is used ONLY to distinguish limestone (rom dolostonesCalciteizzes rapidly in dilute hydrochloric acid (1M HCI) whereas dolomite fizzeS VETNSIONINEIENS

F= a steel ool (o scrape any ] 1y ll)ul)l)llng take pl one from dolostone. k | olten necessar o u \ se ; sample IN order to see together a small pile of powder on a dolostone o . . e o . o "l“L’,lxli to tell lif o ace. The acid test is actually used by In contrast, some people use On samples that ‘ as shale and mu limestone. Mos is then avail lens is a f : the acid test on every sample placed in front of them, even are n G B x ) 3 ‘l ) )\l()llhl) conglomerate or sandstone. Sometimes these rocks as well ds N Contay ’ ) lone contain some carbonate and hence fizz. This does not make them tlack carbonate, and since this acid doesn't react with non-carbonates, it " able to burn hands and eyes and to bleach clothes. A quick look with a hand ]ilm'st(m(-(:S/lf]:,l‘h:)llfi 521\[%‘!‘ way to distinguish ("()ng]nfm-r;m's. sandstones, . : - stones, mudstones, shales, evaporites, and coal. Only use the acid test by ou already know it is either limestone or dolostone. Compare samples 102 and 106. Use a hand lens to see if 106 has a clastic or crystalline texture. Do you see distinct grains or not? a €S hewe WG : /s =} . hie _X( /‘;{Jf\e O”I O < s 8 _»,'v‘ !C, o NS (s Cj|:-‘/ultw'\[ \ AsHNct arnin ¢ LT N ll 2w 1 hrt . . g . d 3 e - 1 1 L 3 s€ the acid test to determine which sample is limestone and which 1s dolostone. 102: |imMeS ¢ oL A 106:4o\0 S “,- You will not need the acid bottle for the rest of the lab because the rest of the carbonate rocks are all limestone. e. Identify the following two common sedimentary rocks: )l-/b' ’ / -~ \ — . . k 4 108: (Just the dark grey or dark brown areas; note fracture and hardness) This rock is “r \ ‘ 4 ~ . L, found as irregular blobs in limestones, dolostones, and chalks. It can be great for making ' stone tools. See Figure 2.4. ‘ “"'\.‘/’:4“\ ) 110: Give both the rock type and the depositional environment (Table 4.2). & . \ AL L > \ (‘fi‘xfi"“h ‘ { : VG i) Nt ¥ ’.T\'\‘\‘\\r'\“ oy f‘)v‘ ‘S *\" Suhmp The next few questions give you an idea of how sedimentary rocks are used to infer the depositional environment in which the rock was formed. There is a whole field of geoloas devoted to such work. Problem 4: Fossils are extremely useful when trying to figure out where a giver deposited. GEOL 1020 (Sedimentology and Stratigraphy) teaches you how to reatu sedimentary rock record so you can figure out whether a given sequence was depOSIEE— river, delta, beach, etc. (Table 4.2 lists some possible depositional environmentSiDE P)('uts a good fossil. Since well-preserved leaves are generally too delicate to SurVINEE into the ocean, fossil leaves indicate a terrestrial environment. Most fossil shells TRt fi

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Te— W N 'lk(' una, bul P 11 rsity shelly faun tiversit) ow-d1y v have 4 | ()I'(l . {iments M ake sec J AL nent (lake logic T€C marine environt yre in §€0 17 e 14 l"' sediments are relatively ¢ - o rocks: a. Identify the following rock A 113: Vit ai > 9 114: b. Sketch one fossil from each sum])lt : - : TRl d in an ancient ocean: (el . . R Lb2) A N :. e c. Which sample was deposited on land and which was deposit 113: Problem 5: Use Table 4.2 and Fig. 4.2 to infer the environment of deposition for the following samples. a. 104: b. 109: Gypsum. M\, > [muc(ufir 'i, < Problem 6: In the field, geologists nibble shale samples in order to see if shales and mudstones are siltstones or claystones. Ifit’s gritty between the teeth, it’s a siltstone. The grains are so tiny in a claystone that you do not feel any grit. I will spare you the fun of chewing on rocks. Instead, compare samples 103 and 112. Look for any tiny silvery reflections of light. These are muscovite flakes. The larger dark grey and reddish/brownish flecks in 112 are fossil plant remains. Based on what you see, which rock has coarser grains and 1s therefore a siltstone? Sample 103 o@ S'\\*S*Gﬂg Sample 112 with a star next to the number has a nice fern stem on it. LT ey ey

® Py e T ', \{ A. Clastic p _Both 1% [\ articles are tr le]g‘c lh(, deposition: ;ms])()rlc(] S]/,( ar o > 5 I'T S np OW Al ]I l(_s i)(l w and deposite J ] o posited by water or wind currents. Using grain I, the stro © ‘ - e strongest to the weakest currents that led to their \O\ / \Q(J / ‘1\1,‘ K’S ample 112, ‘ . ‘1 A 4 . . . . h grain si nd 114, which was deposited under stronger current conditions. grain size and the preservation of the delicate plant materials. b. (.‘omparinq S Consider hot Sample 1142 Problem 8: Identify samples 118 and 119. W 118: e \Lnestond_ 119: CO? U1 of these samples came from just north of Miami, Florida. Did these samples form on land or in the ocean? What is your evidence? O Mar)ee { ex vy thét Oy 20 » ‘./.-. ) - ’ s \e | l’_, Which sample was deposited under higher energy current conditions (i.e., under stronger waves and/or tidal currents)? Explain your reasoning. /’ ALl m & [, V"‘ A2 nAn ",q 4' [ - | 5 e I.' ' L ogv > QfPeshie onoel a Nished 6fu€/4‘5*:) (viren+ Y | r1, S > 5 ] = ,' o~ ” 8 f .:- i » e . o e 5 \' S 3 : o, = olssy FWn Clhes . P -," ' ."‘ i .: Vi ! i : " v B Cooli thic pygeds & lignber ol cbm’v\c U ‘ \‘r‘l"i & § ) ‘{~ “- ., : Problem 9: The waves crashing on a beach continuously stir up beach sand and wash away Although muscovite is very resistant to chemical weathering, its flat, platy carried away by the waves like leaves on the wind. Similarly, plant s) is readily broken up and carried away from the beach. Thus, beach muscovite and plant debris. In contrast, river and delta sands the finer particles. shape allows it to be debris (leaves and twig sands tend to be poor in both often display muscovite and plant debris. Examine samples 100 and 116. Which is more likely to have come (rom a beach @RV RIcH from an ancient delta or river environment? Beach: -’;1‘00 r 116? River/delta: 100 or é 16? )

Problem 10: 5) smple to how the tvpe ol l'|l||" t the pattern in your play outside ['"haw 203 ) Problem 11: Fossils and depositional environments: |he sedimentary rocks ol i \l ielta and ny leposl that include sandstone LMol ['hese were deposited as sediments some 300 million vears 117 ample from on veral thi limentary formations found all across nia and northern West nia. You can find this laver down in Panther Interstate 279. and at vai IS EXPOSUres acros (lu"\n]l‘ﬂl;l[\ {8) n the next page represel ILCrops w.;.w-w’.lmnhul(I.unl»lluu.r Road a. Examine sample 117 and name ll:t‘ exture Ll.ti o« }‘. l-’.[u" i \C o ¥ )Ll d D\ |\t SYo™ LecoV D r non-marine (terrestrial) environmen eSS i \ < : o A - N ¢ presen f O1 In case you are curious, these (ossils are 300 million vears old, Pretty old, eh?

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// /7/ O Block A Rool castse // : //7 Pittsburgh red beds y N V4 ; o // /Y o © o ;’ o o o y // o Caliche nodules // / / /) // // J // — - ._"__ .... /"‘“-—"' Uppcr Sal tsburg Sss borrier \ N N i Morgaontown E and/or | Birmingham . ! block sh c. Sample 1 10 was collected above or below sea level? Sample 117 is from the (ossil root remains. Are the marine:s The Morgantown/1 muscovite. How did sea | sedimentary rock layers ¢ ~ Jirmingham Sandstone lay “Ames Ls” layer shown above. B - Are these terrestrial or marine? eNn | f evel vary to deposit 117 (e (or terrestrial sedimentation? What did sea level do se red beds (red-colored sha a few hundred feet above sample 3 | ontaining root casts, plant debris, 117. Was 110 deposited : ey =T The Pittsburgh red beds contain les) likely to be marine or non- er shown above contains plant debris and across a broad area otherwise dominated by muscovite, and other evidence was deposited? after the Ames Ls v £ 5 B | 200 V'Y a ) 3

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