Syllabus & General Information
GEOL 4120/6120 (Field Geology)
GEOL 4121/6121 (Advanced Field Geology)
Georgia State University
William J. Fritz, and Robert C. Thomas
2. Geology in the Field
2. Geological Field Techniques
of theoretical concepts
Field camp provides a unique opportunity to actually see many types of rocks and geologic features that have only been discussed in books. During field camp students can see glacial systems, identify rocks in field context, observe ancient volcanic systems, use fossils in mapping, see and use a wide variety of sedimentary and deformation structures, observe and map many types of geomorphology.
to Read a Map
Geologists who understand the interpretative nature of maps can make much better use of published maps. Even though you may never again be in the position of having to map in the field, if you continue a career in geology you will surely make use of maps. Maps provide the fundamental data for environmental work, hydrogeology, site selection, etc. The goal of field camp is to help you make better use of this material. You can be assured that after field camp you will never again look at a published map in the same way!
During camp students will be asked to perform under a variety of weather conditions. Often students think that it is “too hot, too wet, too cold, too windy, too dry and on and on” to do field work. The reality is that field conditions are never ideal and field geologists always wish for better conditions. The trick is to develop the ability to perform no matter what the conditions. This takes training and is a major tack to be accomplished at field camp. Students who have learned to get out map every day for a month or more can be assured of having the ability to perform most field-oriented tasks.
Other field skills necessary to any study include: note taking, sample collection, measurement of geologic structures, sample labelling, and locating sites on a topographic base map. Field mapping teaches these skills in a superb manner. The important thing to remember is that these skills will be useful in many more situations that just field mapping. Field camp will give you a great set of skills that will be useful in most geotechnical, environmental or geological related jobs, or in starting work on a thesis if you choose graduate school. Even if you choose to continue work or study in a strictly laboratory setting, field camp will give you a much better appreciation for the field context of the samples that you are working on.
Because field camp consists of both group and independent projects, the standards of academic honesty may not be readily apparent to some students. Following are guidelines and rules designed to eliminate the possibility of inadvertently being accused of “cheating” on a project. Past experience suggests that even though published maps, maps of former students, and maps of students enrolled in field camp at other universities exist, these are of only limited value to field camp students. Without a firm grasp of mapping principles and personal work in the field area it is nearly impossible to make use of published materials. Nonetheless, it is expected that unless specifically allowed by the faculty, students will not use (1) previously published materials covering the map areas or (2) someone else’s unpublished map covering the map areas. Students found using materials not handed out or otherwise expressly approved for that project risk receiving a failing grade on at least that project, possibly for the entire course.
naturally worried about the final outcome of their grade because of this
intentionally rigorous approach. However, this is taken into account in
two ways when assigning grades.
Furthermore, grades are not based on a “curve” and you are not in competition with other students in the course. Faculty have no preconceived notion as to how many students will earn a certain grade. If all students in a particular year perform at an “A” level all will receive A’s. Each student is thus only competing against herself. You must improve steadily throughout field camp.
Field camp is a course, not a test. It is not expected that you know how to map before field camp starts. Past years have shown that students with previous mapping experience have little advantage over those who have never mapped. The important criterion for determining your grade is performance on the final projects during the last 10 days of camp. Also, remember that mapping and comments on your maps are a learning exercise. Grades are given not as harsh punishment but as a learning tool designed to show you where you need improvement.
Material to be Handed in for Each Mapping Project:
(1) Geologic map: Each project will require a geologic map. The map must have a title and the mapper’s name, inked contacts, fold and fault symbols, strike and dip symbols, stations pinholed and inked on back, formation symbols inked, and lightly colored using appropriate color scheme. All writing on the front or back of the map should be oriented the same way so as to be read with north to the top. Lines of cross section should be inked and labeled on the map. The map will be graded for both geologic content and neatness.
A common failing is to provide too few strikes and dips. Strike and dip may be taken anywhere and need not coincide with a station. The most common problems with producing a neat map are: 1) colors that are too heavy and uneven, and 2) inked lines that are too thick and uneven. Ballpoint pens do not produce acceptable results. Use a high-quality drafting pen (rapidograph) and practice on the back or edge of the map to be sure the ink does not bleed on the basemap. Be sure that the pen makes a very dark (but thin) black line.
A map is produced in the field – not in the office. Use office time to ink, color, and spruce up the appearance of the map. The map that you use in the field is the one you turn in. You will not be allowed to transfer from the field map to a new map, so you must protect your map in the field from weather, abrasion, or other deteriorating agents.
(2) Cross sections: Generally 1 to 3 structural cross sections will be required for each mapping project. These sections often are used to gauge your understanding of the three-dimensional nature of the rock units. As much time, care, and thought should go into producing the cross section as into the map itself. Indeed, fully ¾ of your office time should be spent on the cross sections, from conceptualization to actual production. The cross section(s) is far more important than a beautiful legend, for example.
Cross sections should have boxed lines and should extend no deeper than to include the oldest rocks seen in the map area; generally this will be about 1,000’-1,500’ for the Dillon area. Label points A, A’ etc. to correspond with the geologic map.
The cross section should not be vertically exaggerated and should be at the same scale as the map. Do not extend lines or contacts above the topography. If lines extending up into the air are needed to obtain the proper scale and relationship they should be done in light pencil and erased completely prior to turn in. Units in the cross section should be labeled and colored to match the geologic map.
The units should be colored with the inked symbol for the appropriate formation . Do not include patterned lithologic symbols (sandstone, limestone, shale, etc.) as in a measured section.
Typical problems with drawing cross sections are: 1) making the sections too deep and 2) changing the thickness of a bed. Generally the section should be drawn no deeper than to show the oldest unit exposed in the map area. For stratified sedimentary rocks assume that the true thickness of the bed or map unit remains constant throughout each map area and in the cross sections. Structural problems (and poor grades) occur when the unit changes thickness.
(3) Field notes: Field notes should be handed in when requested. Field notes should be numbered to correspond with the station numbers on the map. Sufficient detail must be included for each station to defend the interpretation of that unit, fault, strike and dip or other information. These need not be lengthy. The notes are used to supplement the map and should provide the supporting detail for the information presented on the map.
(4) Legend: Each map and project should included a legend of all symbols used for that project. The legend should contain only those symbols actually used on the map. Stratigraphic units should be a colored box with the symbol for the formation included within the box. Units should be placed in stratigraphic order from old at the base to young at the top. Show ages to the left of the column. A complete and concise description must be given for each unit. Non-stratified rock (e.g. intrusive or high grade crystalline metamorphic rock) should go in a separate column.
(5) Other: Often a short geologic history, description of the map area, or defense of a field problem will be required as part of the project. These should include reference to the map and should cite field evidence at specific locations to support your statements.
(6) Stratigraphic column: About midway through the course, you will have seen all stratigraphic units in the field area. After this time, you will be required to draft and hand in a stratigraphic column for the Dillon area of southwestern Montana. The information for the stratigraphic column will come from your field notes. It is thus important when first describing a new stratigraphic unit to estimate stratigraphic thickness, note detail of bedding and sedimentary structures, detail of lithology and composition and lateral and vertical variation within the unit. Other information such as color, resistance to weathering, vegetation cover, fossils, etc. should be included where appropriate.
GEOLOGIC MAP SYMBOLS
Lithologic and Stratigraphic Symbols
Qal Quaternary alluvium (mapped only as the flat floodplain along modern rivers & streams)
Qp Quaternary pediment surfaces and associated deposits
Qaf Quaternary alluvial fan deposits (recognized by fan-shaped landforms)
Qls Quaternary landslide deposits (recognized by scarp, hummocky land form and sharp toe; usually developed in Tertiary volcanics)
Qg Quaternary glacial deposits undifferentiated
Qgl glacial lacustrine (recognized by modern lakes and flat swampy modern meadows)
Qgt glacial till - use dotted line to indicate position of moraines (recognized by erratic boulders and hummocky topography)
Qgo glacial outwash (recognized by very flat surfaces or terraces above base level of modern streams)
Nvb Neogene basalt, includes the 6.0 +/- 0.1 Ma Timber Hill basalt
Nvr Rhyolite - mostly pyroclastic flow, fall and surge deposits
Tsbh Big Hole River Member
Tsa Anderson Ranch Member
Sweetwater Creek Member
Tr Tertiary (Paleogene) Renova Formation
Tdv Tertiary Dillon Volcanics undifferentiated (Mostly Paleogene - 52-30 Ma)
Tdvb basalt (Paleogene)
Tdva andesite (Paleogene)
rhyolite, includes pyroclastic flow deposits and lava flows
KTb Cretaceous/Tertiary Beaverhead Formation/Group. Contains limestone angular conglomerate/breccia in a red sandstone matrix, red sandstone and siltstone, quartzite cobble comglomerate with red sandstone
KTi Late Cretaceous/Early Tertiary intrusive rock (70-140 Ma) associated with the Pioneer and Boulder Batholiths. Generally mapped by lithology, a - andesite, g - granite, r - rhyolite
Kcsc Cretaceous Cold Spring Creek Volcanics (white & pink tuffs, dark fragmental volcanicbreccia)
Kb Cretaceous Blackleaf Formation undifferentiated
Kbv Upper volcaniclastic/shale member of the Blackleaf Fm (valley former)
Kblc Lower clastic member (includes Kblsh & Kbuc of Dyman) of the Blackleaf Fm
Kkg Gastropod Limestone Member
Kkuc Upper Clastic (Shale) Member (valley former -- red shale with ribs of sandstone)
Kkm Middle Limestone Member
Lower Clastic (Sandstone) Member (ribs of ss & congl. with
red shale valleys)
Jurassic Morrison Formation
TR d Triassic Dinwoody Formation - undifferentiated
TR du upper bedded carbonate member
du lower shale member
Pp Permian Phosphoria Formation (includes Mead Peak Phosphatic Shale, Rex Chert, Park
Retort Phosphatic Oil Shale, Shedhorn Sandstone)
Pennsylvanian/Permian Quadrant Sandstone (Quartzite)
MIPa Mississippian/Pennsylvanian Amsden Formation
Mbs Mississippian Big Snowy Formation/Group
Mm Mississippian Madison Group undifferentiated
Mmm Mission Canyon Limestone
Dt Devonian Three Forks Shale
Devonian Jefferson Dolomite
Ch Cambrian Hasmark Dolomite
Cw Cambrian Wolsey Shale
Cambrian Flathead Sandstone
pCu Precambrian crystalline basement rocks undifferentiated. These are generally mapped using lowercase letters that designate lithologic units. g - granite, gn - gneiss, mg - mafic gneiss, m - marble, as - amphibolite schist, sh - schist, etc.; pick letters appropriate for rock type and area being mapped.
and Dip Symbols (black):
Geologic Field Notes
Notes recorded in the field provide a record of observation for future use of the note taker and other geologists. Often field notes are kept on permanent file by government survey and industry and provide a legal record of data collected in the field. At field camp notes should be used to fill in the details and refresh the memory of the note taker. Without notes it is not possible remember all of the outcrops, road cuts and samples collected in a days work. The notes should be concise, legible, systematic and descriptive. Each page should have a date and general location. Specific notes should be tied to specific locations such as numbered stations on a base map. The name of the base map and/or aerial photograph should always be included in the notes.
Notebooks should be permanent, not loose leaf and should be written in with a waterproof medium such as pencil or waterproof ink. Ballpoint pens are not acceptable. You should never make erasures in a field notebook or skip pages. Corrections should be made by striking out errors.
Drawings, cross-sections and sketches are some of the most useful material included in a field notebook. Each sketch should have a north arrow or other means of orienting the drawing. A scale bar or comment on scale should be included in each drawing.
Note taking procedures vary according to the purpose of the project and individual style and preference. However, all good field notes follow a system worked out in advance. This system or checklist can be pasted into the notebook and reviewed at each station so as not to forget to include pertinent information. The following checklist indicates items which might be recorded at a station. In practice most details are recorded only for stations at which a new formation or lithology is encountered, or where a special feature is noted (e.g. minor folds or particularly well preserved fossils). Terms like “similar to Sta. 7” are convenient time savers. It is often desirable to include notes and comments on the geology between specific stations by writing “SLO” (since last observation) and summarizing.
2. Strike and dip of bedding, foliation, or joints. Be sure to separate each of the three types of surfaces and use the appropriate symbol. It is useful to plot these by symbol in the margin of your notebook beside the station number and using north as the top of the notebook page. Be sure to both sate and indicate if the beds are overturned and indicate your criteria for this determination.
b) Primary structures: bed thickness, cross-bedding, ripple marks, flow banding, columnar joints, compositional variation, grain or crystal size.
c) Deformational structures: fault surfaces, slickenside striae, drag folds, rock cleavage, lineation.
5. Sample number if collected. All samples should be assigned a sample number based on some predetermined scheme. Some people prefer to use their initials followed by year and a continuous list of numbers for that year. Others prefer to use a three-letter designator for each locality e.g. WJF-91-310 for the 310th sample collected by Fritz during 1991 or FPG-91-21 might be the 21st sample collected in 1991 at Frying Pan Gulch. In either case, all samples should be numbered following a scheme that is explain in your notebook. To avoid confusion the same number should never be used more than once!
6. Miscellaneous comments: fossils, nature of contacts (buried, sharp, gradational), interpretations and suggestions for future testing of hypotheses.
Sketch: Include cross-section, outcrop and hand specimen sale
4 July 1998
Armstead Anticline, Beaverhead County, Montana. Map area located 2 miles north of the Clark Canyon Reservoir and West of I-15 on the Armstead 7.5’ quadrangle. Station numbers pinned and circled on the base map.
Sta. 42. Flathead Sandstone Cf 15’ exposed N15W, 50E
Brown to tan weathering, cliff forming outcrop; elsewhere has brush covered sandy soil with hard sandstone fragments.
Thick beds (3-5’) except for 1’ shale and 3’ slabby, hematitic, glauconitic sandstone near top of exposure. Exposure cross-bedded at base.
Fresh rock: Hard well-indurated ss, light gray with specks and spots of limonite stain (from weathered glauconite??). Dominantly coarse-grained, subrounded, fairly well-sorted; visible porosity; silica cement. 95% quartz and 5% glauconite and heavy minerals except for 20+% glauconite, partly altered to hematite in upper 3’ of exposure; green fine-grained micaceous clay shale in a 1’ zone in middle of outcrop.
Samples: AA-93-05 of basal cross-bedded sandstone; AA-93-06 of clay shale, location as shown in cross section.
Comments: Green shale appears identical to that seen in the lowest Wolsey Shale.
Contacts: Upper contact with Cw sharp and well-exposed. Lower contact with pCu covered; however, granitic gneiss crops out 35-50’ to the west.
SLO traversed 3/4 mile to the north parallel to the ridge of Flathead SS of Sta 42. Followed a small gully east of the ridge that appears to be eroded into the Wolsey Shale. Beds to the north appear to wrap eastward into the nose of a fold.
Sta 43. Cf as per Sta 42 except 3-5’ thicker and basal cross bedding less well developed. N5E, 75E
C. Other Information:
REGULATIONS FOR WESTERN MONTANA COLLEGE AND THE DORMS
WESTERN MONTANA COLLEGE OF THE UNIVERSITY OF MONTANA RIGHTS:
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