HW 5 Geology

Lsastac Sedim ent Name: J•,'-4,~ ... ·r ~cr~~1s · ,._:<;: :.~ • :l ~~ l-- ~~ -- i\ r' ~; -~t-:' -~! ,~., Co . urs'1Sectlon: ________ _ Date: __ _ learning GOAL You will make some c.lascie sediment from an igneous rock. il~3lyze its type. size, and initial roundn, : ss. and rhe n explore what it takes to make an aagular sedimentary grain more round. ;,, .. , f l) Obtain two pieces of grn~te or dioritc. Hold one in each hand a!')d tap them togethet over a piece of pa p er. As you do this, you should notice that you are breaking tiny sedimentary grains from the larger r~k samples. These: broker pieces of rocks and rninerals are called c/asts. 1. Usif1$ a band lens or microscope. observe,the tiny clasfll that )' ou just broke from the larger rock samples. Describe what minerals make up the .clasts and whether tbe · c1asts are fragments of mineral jtair rs, rock fragments 1 or a mix .ture of, bot~. '- ~trr•ft ·~ • 1-L. IAAA.'-< '•s-tr · .A4 Geologists commonly · refer to severaJ different types of c1astk sediment. In the fl 11lowing Usi, circle the name of the type of elastic sediment you just made. rocJastic sedimen.t or tephra \!Olcan ic bombs, lapilli, and ash blasted into tte atmosphere by V•>lcanic eruption _ biodastic en pieces of s~lls, plants, and/or (•ther parts of organ i sms sllicldastic sediment-broken pieces of silicate minenal crys1aJs and/or rocks containing them 3l Roundness is a general,description of how completely the rough edges and points of a clast have been smoothed by banging iJ,to other particles during transP<:>rt (see chart in Fig. A6.1.1). Reexamine your clasts from part and sketch the outline of several of Very angular GRAI N F:OU N D N ESS Subangu4ar Subround ~em. Compared to the-chart, what Figure A 6 . 1 _ 1 :~'""!~••f~()., . 0 V 4-- · ~-~ 4 •. Based on fig. A& 1.2 or a grain~size · scafe (from GeoTools 1 or 2 at the back of yoar manual). list the .Wentworth size classes of the elastic sediment~ yqu made above, ~ ,, ,:;.,:,., ~- 'i 't\'e4 l• roundud ~/I.,,~& Lt., e,4_ nA{ . "'!1.i~ w- . .~ ~ ""' !' . ''•'"'< .!nit" ~•" ;;:,_ · · ... ... •: r~t;i."c! Flgwre A6 .1.2 . ,.. . 0625 mm · :"): iiti\iti~ ~=~ "' ~~ ~l .... : ~ . ~~~

t 1 1 he 11 , c, di,c hargc~ ih load of water and Sl:tlimcnl through the M,~siss,ppi Delta 11110 the (julf ot Mexico. ,\~ ,hown 111 t li c ,;11dll1c ,ma!les in Fig . A6 .1.4. the Mis~issippi Riv er passc~ by La ke Pontchartrain lLP ) and the city of New Orlcan, !NOJ 1m ,i- way 10 the gre at "hirers foot .. delta that exte nd ~ into th e Gulf of Mexico. The detailed view of the hir<h foot delta i, a true-color image acquired u~ing NASA~ J ,anJ:- ,1t 7 ,;1t~ · llitc and ~hu~ , th .;; hrna(I 111::iin channel of the Mi..,w -; -; ippi Ri ve r dis~ :harging water and sediment to more than half a dozen smaller channe l. ~ th at exte nd in many different direc ti ons. The center of t he larger ima ge is around latitude 29. l<i 0 N. longit ud e 89.16W. -------·--·-----·-- .. ______ ..:... __ ·-···- Gulf of. Mexico - 15 km Figure A6 .1.4 On the image in Fig. A6.1.4. write '•D'' tu indicate all of the places where one of these s malkr channels is discharging water and sediment out into the Gulf of Mexico . One example is done for you, marked with a white D n ea r the top of the image.

Activity 6.4 : Sediment from Source to Sin k Name: ----------------- Course/Section: ________ _ Date: _____ _ Learning GOAL You will Investigate sediment formation In Yosemite Valley, California. and consider the evolution in siz.c, shape. and composition as the sediment moves down the Merced River. A u.xlk ar Fig . A6.4.1 . A rockfall from one of the steep granitic walls of Yosemite Valley (A) caused boulders as large as 2 meters in diameter to er.ash down into the forested slope below (8) . Eventually. these sediments might end up in the steep channel of a local stream (C) on their way to the Merced River (D). which flows through the main part of Yosemite Valley. -20 m -9 km Figure A6.4.1 I. Rockfall deposit close to the source area (Photo B). 172 (a) List all of the grain sizes that you see or that are likely to be present in the rockfall deposit shown in photo B (also refer to FiR . 6.2). The lamest sediment 11rain in R i~ annroicimnti-lv 7 m lnno Ir._.. th.- or:iin--:i · n• ,+,"" n,.m,." li<:ti>,1 in S:lo Ii 11; - .... • . • .... .... u -

d 'be the , · g of sedimentary grains in the rockfall deposit'! Use the terms in Fla- 6.16A. (b) How would you escn so r, m (c ) How would you describe the shape of sedimentary grains you can see in the rockfall deposit? Use the terms in Fig. 6. 168 . /1 ~__./-.~'f'~ (d) If the sediments in the rockfall deposit were lithified together as they currently rest, without any further movement ,.f'" .. ..4 .""f"'•A•--•"'+"'"' ...... ,,..t,. ~u, _,,1.-1 - •h•• • ,F"' .... ,? ·- - ·' ··· -- .... :.:... t"-• · ··· - · · -• -"'- - · ~ -- ···· - · · -, .. ._ ...... . ,..., _ _.. _ ...... -J -- ···· 4 -2. '.f.rihu&aryr - mwun ~mt - dn~ - rmm mckfall tlf!!M""it (Photo r.t (a) The large sedimentary grains that can be seen in the stream channel are generally less than ~ 1.5 m in diameter. Judging from the turbulence of the mountain stream, what grain sizes do you expect to be carried (suspended) in the water? ... (b) What grain sizes do you expect to be rolling, sliding, or resting on the bottom of the channel, including those that you can,ee? ..μ.,,_ ~t ~,,., (c) How would you describe the shape of the sedimentary grains you can see in or near this stream channel (Ft,g. 6.168)? ~- 3. River deposits exposed in the eroded bank of the Merced River (Photo D). (a) Li st aJI of the grain sizes that you see or that are likely to be present in the Merced River bank shown in photo D. ~~-/-o~~ (b) How would y ou de sc ribe the sorting of sedimentary grains in the stream banJc? u-<f4 t:f't' /W,') . ( c) How would you describe the shape of se dimentary grains you can s ee in the stream bank ? ~l. 173

Da~ ----- .Name:--------------- course/Section: ---------- Learning CIOAL You will examine photographs of three types of loose sediment, assess grain size, liOrting, roundness, and composition/type, and then infer the sort of environment in wbich the sediment might have originated. ffl,f Complete parts I through 6 for each sample in Fig. A6.5.1. Refer to Flp. 6.15, 6.16, and 6.27 as needed. SampleA A SampleB 1 1111 = 2111111 1. Grain size range in mm: O, O 1 - :2--,..t" 2. Percent of each Wentworth size class: clay: _i._% silt: ..z.:1% 8alld:~,t; % gravel: ~1...% J. Grain sorting (circle): poor moderate 4. Grain roundness (circle): angular 5. Sediment comnosition (circle): precipitated bioclastic pyroclastic 6. Describe how and in what environment this sediment might have fonncd. --a.A-~1 .Mo .. I. Grain size range in mm: 1. - 2 .,.._ " · fercent oi eacn w · emwortn size ciass : clay: __ % silt: __ % sand: / 0 u % gravel.: __ % 3. :,msomn~- ~<r 4. Grain roundness (circle): angular ~ · well rounded 5. Sediment composit"on (circle): precipitated siliciclasf bioclastic pyrocla.-.tic 6. Describe how and in what en~ironment~h ~ iment might have formed. ~~,/\):,"~ SampleC 1. Grain size range in mm: '- - / I) ,... ,.._. 2. Percent of each Wentworth size class: clay: __ % silt:~,% sand: "30 ¼ % gravel:~% 3. sorting (circle): • m~rntP. wP.11 4. Grain roundness (circle): subround well rounded S. Sediment composition (circle): precipitated siliciclastic pyroclastic Ii. - ~~.rihf.~how .»nd in wb:o1t . .-nvirnnn:w.nr th11: 1:t><lil'l1'"nt mioht h:tvt'\ f, rl ~~~.fl.J.,,~~~ Figure A6.5 .1 -~ .... , rt~ REFLECT & DISCUSS Imagine that the sed . . . se iments are rocks. Wh.ich f th . diagnostic ot a spec1t1c ancient environment"! Why'/ 0 e samples do you thmk would be the least ~c ~Ji.~o-u.~~~~ ~t.. kA" .,. -,.,:- en-- ~. s.. ·"~;rt ~. 175

Grand Canyon Outcrop Anal~sis ~nrl lnt-.o .. n .. o .. . ~••nn ....... ,_,. ..... .,..,. ,._, . .... , ............... . ··· A~iVity 6.7 Name: ---------------- Course/Section: ________ _ Date: _____ _ Learning GOAL You will analyze and interpret sedimentary rock from the edge of the Grand Canyon. Ii Analyze the ima~cs in Fig. A6 .7.1, which are from the South Rim of the Gran_d Canyo~ near _Grand Canyon V!llage. _ The edge of the canyon here is formed by a fossiliferous limestone composed of sand-sized da.c;t1c grams. called the Ka1bab LtmeSlone. deposited about 270 million years ago during the Pemiian Period. FlgureA6.7 .1 1. Notice that some of the beds in the outcrop are cross-bedded. Draw an arrow on the picture to show the direction that the water moved here to make this cross beddin~. Refer to FIR, 6.26 as needed. 2. Does this cross bedding indicate a steady flow of air or water. or docs it indicate an oscillating (back :.md forth) flow · ! . (FiS-6.26) fNNL nw+/:/tAL ~044 <M-t ,,,._~ ~ } ~ - ; REFLECT & DISCUSS Describe your ideas about what the environment might have been like here about 270 million &;:::::';•=d~c~ore~~~ o/ ,_/;. ;) ~a..~ ~' 179

Using the Present to Imagine t-~~!~!t;:~'!! . ,_,.._,..,. •V Name : --------------- Course/Section: -------- Date: ____ _ Learn Ing GOAL You will infer characteristics of an ancient environment by comparing present-day seafloor _ sediments · · · I f · ' ly interpreted phenomena m the present with se dimentary rock fonned on an ancient seafloor. This 1s another examp e o usmg easi iv i11is:t1.11c:t c; ... iJc:rn; c: ua irc1:.i c:vc:11i 5 fJICIICI ,..c;J iu tUl.'k, I~ Analyze photographs X and Y in f ig. A6.9.1 of a Kansas rock and the modem-day seafloor near Cape Cod. re spectively. X. Pennsylvanian-age rock from Kansas (290 Myr old) Sand-sized fragments of fossil shells comprise the rock . "f . ;::! . . >.: il' .• lOX close-up < · ~ . :, .· of thin section ,,, . Y. Modern seafloor environment, 40 m deep, -16 km north of Cape Cod, Massachusetts. - Photo includes elastic sediment from the continent, bioclastics, and liviog ocganisms. • 1% gravel • 90% sand • 9% mud Figure A6,9.1 1. How are the modern environment (Photogr.tph Y) and Kansas rock (Photogrnph X) the same? 2, Howy~-:::;nv~•~.::tt:'";,.roc~rer•~i ¾ ;i;:¢r 3. Toda y, this part of Kansas is roJling hills and farm fields. Describe the environment in which the sediment in this rock sam!!!~:DS~ ili~2X~on.;r;7y, -~ Or~ L-t1N~f iJ RE~ss 1 ::;::t~%ttr~o~:. tum ~sed7? .,.._ ..,...ft ..... - ~.,1.,.,.,/. ~""'f'"f t-y."v~ 1 181