Procedures in Field Geology

103 Pages·1999·3.717 MB·English

by  Freeman, Tom

Procedures in
FIELD
GEOLOGY
Tom Freeman
Distinguished Teaching ProfessorEmeritus
UniversityofMissouri-Columbia
b
Blackwell
Science

Procedures in
FIELD
GEOLOGY
Tom Freeman
Distinguished Teaching ProfessorEmeritus
UniversityofMissouri-Columbia
b
Blackwell
Science
ii
(c)1999byTomFreeman
BlackwellScience.Inc.
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iii
Preface
Mypurpose in writingthis manual istoprovidea
pocket-size presentation offield procedureswithout
the bulkandcost ofacomprehensivetextbook.
Thefirstpart, Toolsofthe Trade, coversthe
BruntoncompassandJacob'sstaff, the Silva
compass, andtheplanetableandalidade-along
with principlesofmapdirectionand strikeanddip.
Also, I have includedasection on usesofthe
stereographicnetforthosewholackhardwareand
softwarenecessaryforthemanipulationoffield
measurements.
Asecond part, Things toDo, presentsavarietyof
procedurescommonlyundertakeningeologicfield
courses.
Thethird part, ReferenceStuff, provides basic
informationontopographicmaps,trigonometric
solutions, andconventional map patternsand
symbols.
Field proceduresdescribedhereinarethosethat
haveemergedthrough yearsofteaching atour
UniversityofMissouri'sCamp E.B. Branson inthe
Wind RiverMountainsofWyoming. Iwelcome
suggestionsfortheinclusionofadditional proce
dures infutureeditions.
Tom Freeman
Columbia, Missouri

v
c o
N T E N T S
TOOLSOFTHETRADE
TheBruntoncompass 1
Butfirst-two methodsofstating direction 1
Bearing (orquadrant)method 1
Azimuth method2
Brunton anatomy3
Magneticdeclination 4
Magneticdeclinationdefined 4
Adjusting aBruntonformagneticdeclination7
Bewareofmetalobjects! 7
Measuringdirectiontoan object8
UsingaBruntonasaprotractor 11
Measuringverticalangles 12
Review-trigonometryofaright-triangle 14
Solvingformapdistancerepresentedbyslope
angleandslope distance 15
Solvingfordifferencein elevation representedby
slopeangleandslopedistance 15
Solvingfordifferenceinelevation usingsuccesive
eye-heightmeasurements 16
Strikeanddip-definitions 17
Recording strike with the right-hand rule 18
Theotherright-hand rule 18
Theazimuth method ofdescribingthe orientation
ofand inclined plane 19
Measuringstrike-eontactmethod20
Measuringdipmagnitude-contactmethod21
Usingtwooutcropsto measurestrikeanddip22
Measuringtrend and plungeofalineation 24
Measuringthetraceofanoutcrop25
Measuringan inclined stratigraphicsectionwith
aJacob'sstaffand Brunton26
vi
TheSilvacompass28
Weaknessesandstrengths28
Silvaanatomy29
Setting magneticdeclination on a Silva 30
Measuringdirectionwith aSilva 30
Measuringstrikeanddip-contactmethod 31
Plottingdirectionson amapwitha Silva 32
Using a Silvato measurerake (orpitch) 34
Theplanetableandalidade36
Beamanscales, type 1andtype2 36
Alidadeanatomy 37
Setting upthetableandworking on abase map 38
Orientingthetable, focusing, adjustments 39
Reading thevertical arcandvernier40
Stadiadistance 41
Procedure-'runningthe gun' 42
Computing elevationns-forsights44
Computing elevations-backsights 45
Asampleformatfor recording data46
The stereographicnet48
Purpose 48
Preparingastereographicnet50
Planarand linearfeatures 51
Representingan inclined (dipping) pfane 51
Representingan inclined (plunging) line 53
Representingtheplungeofalinefrom its rak€ in
an inclined plane54
Representinga lineformed bytheintersectionof
twoplanes 56
Solvingfororiginalorientation ofstructurally
tiltedcross~beds57
Solvingforstrikeandtruedipwithtwoapparent
dips 61
1
THINGS TO DO
Confrontingan outcrop-pointsto ponder62
Thevalueofreconnaissance 62
The utilityoffield sketches 62
Theimportanceofcontactrelationships 63
Mapping-pace-and-Brunton method 64
Definitionandprocedure 64
Correctingerrorofclosure 66
Triangulating-intersection method 68
Resection method 69
Describingstratigraphicsections-format 70
Lithicdescriptions 70
Geomorphicprofile 71
Constructingageologic roadtraverse 72
Usingcontourmaps-the'rulesofcontours' 74
Constructingacontourmap 76
Constructingatopographicprofile 78
Constructingageologiccross-section 80
Solvingforexaggerateddipwhen thevertical scale
isexaggerated 82
Solvingfortruedipwhen across-section is not
perpendicularto strike 83
REFERENCE STUFF
Landsurveysystem-latitudeand longitude 84
Townshipsand ranges 85
Sectionsand 86
Mapdimensionsandscales 88
Grid north 91
Trigonometricsolutionsofstratigraphicthickness 92
Whereslopeanddipare in oppositedirections 92
Whereslopeanddipare inthe samedirection 93
Lithicpatternsandsymbols 94
Structural mapsymbols 95
2
B
Fig. 1. Thebearing(orquadrant)methodofstating
direction. (A)Fourquadrants-NE, SE,SW,NW-areeast
orwestofnorthorsouth. (B) Thebearingistheangle
turnedeastorwestfromnorthorsouth.