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ABSTRACT

Structural geology courses at Wheaton College innortheastern Illinois conclude with a three-weekgeologic mapping simulation. It is preferable to haveclass participants learn basic mapping skills in the field.However, time and geographic constraints are such thatthe Geology Department now resorts to an indoorexercise as a prelude to the required summer field camp.

The Geology Department’s large basement lab spaceprovides a flexible environment to create an artificialfield area. Books, color coded to a set of distinctive handspecimens, are distributed throughout the room inpatterns representing geologic-suite outcrops. These inturn correspond to a diversity of tectonic terranes. Booksare oriented so as to portray structural information.Structural and petrologic data enable the students tosynthesize a geologic map, cross sections, annotatedgeologic column, and ultimately, a report of in-vestigation with historical narrative. Several years’experience indicates that the simulations meet or surpassexpectations. Participants enjoy the puzzle-likechallenge and integration of concepts. Those who havecompleted the exercise are typically more confident andable to synthesize data during actual field work thanthose who have not.

Keywords: structrual geology; education-laboratory

INTRODUCTION

Geology majors receive their undergraduate degreesfrom schools located throughout all regions of the U.S.and Canada. Most programs still require a very similarcluster of core courses and experiences. This courseworkshould include field exercises incorporating observationof geologic materials in “units”, their interrelationships,structures and other important features. It is crucial thatstudents learn through practice that in situ observationsare the primary basis of good geological interpretation.Cultivating the ability to interpret field data is anessential component in all areas of our science.

For various reasons, certain regions of NorthAmerica, such as northern Illinois, are less endowed thanothers with respect to field opportunities. There arebroad areas of urban or suburban development that havegreatly modified the land and obscured many naturalattributes. Vegetative cover as well as pavement concealnatural landforms. Other places, especially those withlittle topographic relief commonly display minimalbedrock exposure and geologic variety. Unfortunatelyfor those of us in northern Illinois, this area is cursed byover development, a soil/vegetation veneer of variable

thickness, and a rather monotonous landscape of gentleglacial features. In order to escape the monotony andwitness a good diversity of geologic activity, we musttravel a few to several hours away. The academic yearand unfavorable weather also limit our ability toadequately practice field investigation. We do have asummer field program at Wheaton College’s ScienceStation in the Black Hills, conduct a Spring Break fieldtrip to the southeastern U.S. most years and incorporate atwo- to three-day field trip into each majors’ course. Thisis still not satisfactory. Without moving the campus toanother geologically blessed part of the country, we areat a disadvantage.

Many years ago I heard the description of an indoor“field” exercise designed by Bill Blackburn when hetaught petrology at the University of Kentucky. Bill usedan arrangement of rock samples distributed about a labroom to mimic actual field relationships. More recently,Dillon and others (2000) describe a rock garden used tosimulate geologic relationships for freshmen and visitorsat their institution. There have undoubtedly been othersuch creative projects devised by geology professorsthrough the years. My desperation to provide a betterbackground for students in the structural geology courseled me to design an exercise and evaluate itseffectiveness on an initial group of fifteen majors asguinea pigs.

OBJECTIVES

Although the mapping exercise has become a part of thestructural geology class at Wheaton College, it isorganized to integrate different geoscience disciplines. Itcould just as easily be assigned as a final project in anadvanced historical geology course or in GeneralPetrology.

My design is intended to present all major rock typesin expected tectonic-suite associations. The patterns of“outcrop” associations are meant to represent geologicprovinces or terranes from oceanic basin to activecontinental-margin and a hypothetical selection ofpreserved environments further inland. Implied contactrelationships and representations of minor structures aredistributed to reveal the geometry of large-scale features,ala Pumpelly’s Rule (the concept that smaller micro- andoutcrop, macro-scale structures mimic the orientation ofthose too large for direct observation). Moderatelysophisticated interpretations are expected from studentscompleting upper-level undergraduate courses.

Evaluation of a student’s performance in the exercisecould serve as one form of comprehensive exam or partof a larger one. Are our students actually learning thesynthetic integration of geologic data in order to solveproblems? Can they derive good feasible workingmodels?

Greenberg - Indoor Field Study for Structural Geology Course 575

INDOOR FIELD STUDY FOR STRUCTURAL GEOLOGY COURSE

Jeffrey K. Greenberg Department of Geology and Environmental Science, Wheaton College,

Wheaton, IL 60187, [email protected]

576 Journal of Geoscience Education, v. 50, n. 5, November, 2002, p. 575-582

Figure 1. Photos of the basement “field” area. a) wooden box used to display hand samples keyed to book

colors; b) student standing amid several oriented book “outcrops”; c) two State of the World volumes

(horizontal sedimentary units) unconformably overlying near-vertical geochemistry book (tilted

metasedimentary rock); d) stratigraphic sequence of rift-related units represented by horizontal stack of

books on table.

FINAL PRODUCTS

Students labor to complete the exercise in five parts: 1)their geologic map of the “region”, 2) two or moreperpendicular cross sections, 3) an annotated geologiccolumn based on suite interpretations, 4) hand specimendescriptions of all units with pertinent tectonicobservations (for example, type of metamorphism orsedimentary environment), and 5) a report ofinvestigation (RI) including a possible historicalnarrative. I outline specifications for the products, suchas standard symbology, colors for lithologies, map scale(1m=100km, 1:100,000 usually) and exactly what topicsin what order must be addressed in the RI.Standardization requires discipline. It also teachesfamiliarity with realistic mapping conventions.

EXERCISE COMPONENTS AND LAYOUT AT

WHEATON COLLEGE

The larger the available area for the exercise, the morecreative we instructors can be without crowding theplanted “outcrops”. I use books which are color coded torepresent bedrock exposures. These are keyed to a set ofgood representative hand samples (Figure 1a). I providea cheat sheet of hints and additional information aboutthe rocks to aid in the interpretation (Figure 2). Helpfulinformation may include chemical data, fossil content,unconformable relationships, geophysical maps/re-lationships (if students have covered the topic) andindicator minerals, if not obvious. Compasses are usedfor determination of orientation data on the booksurfaces.

Our department has a large, approximately 19m by12m lab area appropriately located in the building’sbasement. There are shelving units along one long sidewall, rock saws against the other long wall, work tablesin the room’s center and desks at the far end wall (Figure3a). These furnishings and several lab stools allow thecustom positioning of books (Figure 1b,d). Bookorientations, flat-on-surface, tilted or vertical representbedding, attitude of dikes/sills or some form of foliation.Books can be juxtaposed to help show cross-cutting andunconformable relationships (Figure 1c). Their relativeelevations (short versus tall stool, for example) may aidstratigraphic interpretation. I also use State of the Worldvolumes published by the Worldwatch Institute as goodindicators of in or out of sequence units. This series ofpublications is imprinted on spine and front cover withlarge dates for each year. They are particularly useful indepicting thrust sheets where units may repeat or be outof sequence. The display area containing the handsamples (Figure 3a) is kept in the same room as thesimulation, which makes it easier to continuouslycompare coded books to rocks.

EXERCISE PROCEDURE

Over a two- to three-week period, students follow aprogression of steps in project completion. First theyproduce a rock guide by describing the samplesprovided for each unit. Next, a regional base-map of ourbasement is carefully prepared using a meter stick ortape for proper scaling. The location of eachbook/outcrop is plotted on the base map. After checkingthe map for accuracy, participants measure the bookattitudes and record each site with a structural symbol.At this point, maps as raw data are pondered to yieldfeasible interpretations of geological relationships.Students are not to share information, but they shouldseek the advice of the instructor or Teaching Assistant tosee if their observations are valid and if theirinterpretations are consistent with the evidence. Initially,I allowed collaboration among class members. Unfort-unately, there was a strong tendency among the lessconfident and ambitious students to rely on colleaguesfor interpretations. Even after warning about how suchbehavior subverted the exercise, there was still too muchreliance on borrowing. We do encourage team-workcollaboration during actual field camp projects. Even so,supervisors must be diligent in overseeing teamdynamics.

The “final” exercise map progresses through two ormore versions. The ultimate time of inking in the contactsmay be rather stressful for some and require ouradditional encouragement (just like field camp). By thispoint, each participant should be able to make aconvincing argument for their overall perspective as wellas for the nature of individual contacts.

The geological report is probably best prepared rightafter the map. This step mentally solidifies therelationships among rock units and establishes anhistorical/tectonic context. I provide some state surveyand USGS reports as examples of possible formats to beemulated (Rogers, 1952; Henika, 1971; Scott 1974; Scottand others, 1976; Bartholomew, 1981). The map andreport then contribute all the detail needed for thecompletion of cross sections and the geologic column.

BEST MODEL THUS FAR

The mapping exercise has been assigned three times overthe last eight years because Structural Geology is taughtin alternate years. It has undergone revision with eachsubsequent effort to eliminate previous weaknesses. Thecurrent “geo-world” of my creation begins in the south,nearest the room’s door with island-arc volcanic rocks,graywackes, and somewhat deformed orogenic in-trusives (granodiorite, tonalite, etc.). This package isadjacent to a linear belt of deformed oceanic materials,including rather obvious blueschists, then greenstones,serpentinites, cherts, and peridotites, all representingophiolitic units and a suture zone. I hope to stimulate the



Figure 2. Handout providing the participants with book color/specimen code plus hints.

impression of accretion of the package onto a continentalcratonic block immediately north. A sequence ofmetamorphic units is situated obliquely to the suture,trending northwest. I have varied the polarity ofmetamorphic intensity from higher to lower the firsttime with a reversal of that order more recently. Onepossible interpretation is that the collisional marginexhibits a build up in thermal intensity away from thesuture and toward an orogenic core zone. The samplesprovided for reference are distinctly Barrovian in theirkey-mineral assemblages. A nice mylonite zone can alsobe added into the higher-grade facies. Here, the use oflarge porphyroblasts and ductile-shear features with orwithout accompanying thin sections aids interpretation.

To the west of the metamorphic terranes, there is anexpanse of horizontal sedimentary units, some indicatedby book orientation as unconformably overlyingdeformed and metamorphosed rock. The uppermostsedimentary units are poorly consolidated, weaklyindurated clastics. This hopefully conveys a sense oftheir youthful character. In the northwest the lowersedimentary units are thrust northward toward a blockof old migmatitic gneisses with ages provided. The


Figure 3. Basement lab details taken directly from

student notebook entries: a)floor plan including loci

for oriented books, encircled ‘s’ symbols are stools;

b)outcrop locations and numbers with annotated

orientations; c) structure-symbol sketch produced on

a grid system


Figure 4. Selection of some better geologic maps, cross sections and tectonic interpretations.

gneisses are in turn intruded by near-vertical basalticdikes of reported age.

The region’s east and northeast are dominated bytwo large fold structures and a graben. One fold isconstructed as an asymmetric anticline with overturnedlimb. Tilted books are held in correct position with smallangle-cut pieces of wood or rock (Figure 1b). The otherfold is delineated such as to imply an eroded intrusivedome cored by an anorogenic porphyry. Thesedimentary cover is converted to obvious contactmetamorphosed lithologies, skarn and tactite adjacent tothe intrusion, but it is just an impure carbonate rockfarther from the contact. The variable character of thiscarbonate unit in the domed sequence strongly suggeststhe forceful intrusion of a hot porphyry. The rift-grabenfeature is small and incorporates a good sequence forinterpretation of depositional environment. Within andon the edge of the graben are redbeds, evaporites,silicified wood and reddish sandstone bearing tinyfootprints. All this is intended to generate the impressionof terrestrial rift development. The second time theexercise was conducted, I included alkali basalts(chemical data provided) at the edge of rifted sequenceand tholeiitic basalts within the graben.

PROBLEMS AND REQUIREMENTS

In a new undertaking of his scope, it is a good instructor’spolicy to hope for the best but expect the worst fromstudents and lab design. Our unrealistic expectations canbe a major problem. Student performance on the firsttrial of the exercise provided me with excellent feedback.My initial instructions were too vague, hand specimenswere not optimal, more concentrated lab time andenabling supervision were needed and the variation instudent background was too great. Now I seek to haveevery participant complete prerequisites of Physical andHistorical Geology and Petrology before taking Struct-ural Geology, with this exercise as the culmination. Wehave no separate course beyond Structural thatemphasizes tectonic synthesis.

I have remedied the more obvious weaknesses in theexercise thus far. Lab set up does require a substantiallylarge area that can remain undisturbed by other activitiesfor extended time. A variety of sites to pose books (floor,tables, stools, shelves, etc.) is most helpful. Also neededare good characteristic rock samples and a lot of books(not usually a problem for academic types). It is best tohave several sets of volumes of the same color, forexample in series like encyclopedias or special papersand memoirs of the Mineralogical Society of America,American Geophysical Union, the Benchmark collections,State of the World, SEPM, etc. Journal publications mayhave desirable qualities of common color and sequentialnumbering, but most of these are too flexible to representorientation data.

OUTCOMES

I am pleased. Each subsequent offering of the mappingproject has shown improved results, yet even the firsteffort must be considered a success. This is after muchgrumbling and expressions of shock that I would expectmajors to know so much. They struggle to get started andtend to lean on each other too much at the beginning. Idemand that they resist the temptation to constantly seektheir labmates’ counsel; it often just spreads ignorance.This means that I must be careful in making myselfavailable to help, particularly to draw from them theknowledge that is already there but dormant. Soon afterinitiation there comes the “ah ha!” moments of surpriseddiscovery. They are edified and gain confidence in therealization of successful detective work. I then mustprovide the strokes of “well done” as feedback. By theexercise end, after two to three weeks of toil, they presentthe fruits of the project and unanimously declare theexperience to be a ‘5’ out of a possible 5 on classevaluations. Even the less enthusiastic or talentedstudents show good evidence of learning. The betterstudents have generated some amazingly good mapsand reports (Figure 4). Following the project experience,summer field-course mapping requires less of mysupervision of majors than in years before the exercise.

I do wish that there were more objective measuresavailable to gauge the success of this assignment. Myimpressions are the only ones of longitudinalsignificance, but like those of the students, they aresubjective and anecdotal. As for specific benefits to thestudents, I see these as multiple. Mentioned above is thefunction of easing majors into their summer fieldexperience. I must additionally reiterate the integratedaspect of the exercise, requiring an instrumentalistunderstanding of various geological disciplines.Participants may feel that memorizing the names,characteristics and geologic significance of diversemineral species in Mineralogy class is busy work. Thesame could be said for index fossils in HistoricalGeology. They see that their negative impression iswrong. I consider this or similar efforts to synthesizediverse data as far superior measures-in-themselves thanthe now defunct geology-specific GRE exam.

FINAL NOTE ON OPTIONS

I have avoided getting too elaborate with the challengefacing majors in the map area. However, for otherschools where undergrads have more room for electivecourses in their program or for graduate classes, theremight be some intriguing modifications. Subtleties ofinterpretation can be derived from thin sections or fossilevidence. Contrived elevation variation in books mightmodel stratigraphic complexities. For example, outcropbooks might be placed on the floor, at lower stool level,and higher upon tables. This could represent


stratigraphic variation with depth as observed from hillsides or drilling data. Results would yieldthree-dimensional interpretation and be depicted byfence diagrams.

ACKNOWLEDGEMENTS

I give Bill Blackburn credit for the general concept. Mygreatest inspiration comes from the students themselves.Their honest feedback has been essential in refining awild idea into a fruitful learning experience. The reviewsof Martin Miller, John Stimac, and Terry Pavlis aregreatly appreciated in helping get the idea to others.

REFERENCES

Bartholomew, M.J., 1981, Geology of the Roanoak andStrewartsville Quadrangles, VA: Virginia Division ofMineral Resources, Pub. 34, 23p.+ geologic map,1:24,000.

Dillon, D.L., S.R. Hicock, R.A. Secco, and C.J. Tsujita,2000, A geologic rock garden as an artificial mapping

area for teaching and outreach: Journal ofGeoscience Education, v. 48, p. 24-29.

Henika, W.S., 1971, Geology of the Bassett Quadrangle,VA: Virginia Division of Mineral Resources, Reportof Investigations 26, 43p. + geologic map, 1:24,000.

Rodgers, J., Geology of the Athens Quadrangle, TN: U.S.Geological Survey Geological Quadrangle Series,Map GQ-19, 1:24,000.

Scott, G.R., R.B. Taylor, R.C. Epis, nd R.A. Wobus, 1976,Geology Map of the Pueblo 10 X 20 Quadrangle,south-central Colorado: U.S. Geological SurveyMiscellaneous Field Studies Series, MF-775, 2 sheets,1:187,500.

Scott, R.B., 1974, The Bedrock Geology of the SouthburyQuadrangle: Connecticut Geological SurveyQuadrangle Report #30, 63p. + geologic map,1:24,000.


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