A Geophysical Investigation of a Possible Astrobleme in Southwestern Michigan

Western Michigan University ScholarWorks at WMU

Master's Theses Graduate College

4-1984

Suhas L. Ghatge

Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses

Part of the Geophysics and Seismology Commons

Recommended Citation Ghatge, Suhas L., "A Geophysical Investigation of a Possible Astrobleme in Southwestern Michigan" (1984). Master's Theses. 1498. https://scholarworks.wmich.edu/masters_theses/1498

This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. A GEOPHYSICAL INVESTIGATION OF A POSSIBLE ASTROBLEME IN SOUTHWESTERN MICHIGAN

Suhas L. Ghatge

A Thesis Submitted to the Faculty of The Graduate College in Partial Fulfillment of the requirements for the Degree of Master of Science Department of Geology

Western Michigan University Kalamazoo, Michigan April 1984

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A GEOPHYSICAL INVESTIGATION OF A POSSIBLE ASTROBLEME IN SOUTHWESTERN MICHIGAN

Suhas L. Ghatge, M.S.

Western Michigan U n iv ers ity , 1984

A circular pattern to the oil production in Calvin Township,

Cass County, Michigan, absence o f about 1200 fe e t of Ordovician sediments

and uplift indicated by a deep drill hole in the center of the productive

area and absence o f anomalies on the regional g ra vity and magnetic maps

led to detailed gravity and magnetic surveys over this structure to

delineate it and provide information regarding its genesis.

The Bouguer g ra v ity and magnetic anomaly maps show no anomaly

associated w ith the s tru ctu re. The 28-m ile wavelength second harmonic

residual gravity and magnetic maps show linear features in the area.

Two dimensional gravity modeling of the NNW-SSE trending linear feature

over the area of circular production is interpreted as upthrusting

involving the basement rocks. The NNW-SSE trending Jefferson fie ld

appears to be truncated by NE-SW trending faults.

The lack of a circular gravity anomaly and the lack of direct

geologic evidence in support of the impact origin leaves the question

of genesis open.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

This p roject would not have been possible without the funds from

the Western Michigan University Graduate College Research Grants and the

support of Dr. William Sauck who organized and developed many of the

ideas in this investigation. I would like to thank him for his help.

I would also like to thank Dr. Straw, Dr. Grace and Dr. Harrison for

ideas, recommendations and inform ation. I am also thankful to Mr.

Florencio Mata of Hosking Geophysical for suggesting this problem and

Mr. Ron DeHaas o f Michigan Petroleum Geologists Inc. and Mr. Robert

Mannes of Mannes Oil Corp. for providing some geologic and geophysical

inform ation. Special thanks are extended to Mr. Douglas Daniels of

the Michigan Department of Natural Resources fo r providing time fo r

discussions and for making available geological information on the area.

Thanks are also extended to the Department of Geology, Albion College,

fo r providing th e ir Magnetometer and to the Computer Center a t Western

Michigan U niversity fo r the computer time.

Last, but not the least, I would like to express my deepest

appreciation and thanks to my wife Gauri who helped me in my data

collection and during the process of writing this report. Her care

and patience were important and vital during all aspects of the survey.

Suhas L. Ghatge

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INFORMATION TO USERS

This reproduction was made from a copy of a document sent to us for microfilming. While the most advanced technology has been used to photograph and reproduce this document, the quality of the reproduction is heavily dependent upon the quality of the material submitted.

The following explanation of techniques is provided to help clarify markings or notations which may appear on this reproduction.

1.The sign or “target” for pages apparently lacking from the document photographed is “Missing Page(s)”. If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting through an image and duplicating adjacent pages to assure complete continuity.

2. When an image on the film is obliterated with a round black mark, it is an indication of either blurred copy because of movement during exposure, duplicate copy, or copyrighted materials that should not have been filmed. For blurred pages, a good image of the page can be found in the adjacent frame. If copyrighted materials were deleted, a target note will appear listing the pages in the adjacent frame.

3. When a map, drawing or chart, etc., is part of the material being photographed, a definite method of “sectioning” the material has been followed. It is customary to begin filming at the upper left hand corner of a large sheet and to continue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again—beginning below the first row and continuing on until complete.

4. For illustrations that cannot be satisfactorily reproduced by xerographic means, photographic prints can be purchased at additional cost and inserted into your xerographic copy. These prints are available upon request from the Dissertations Customer Services Department.

5. Some pages in any document may have indistinct print. In all cases the best available copy has been filmed.

University Mfcitffilms International 300 N. Zeeb Road Ann Arbor, Ml 48106

GHATGE, SUHAS LAXMAN

A GEOPHYSICAL INVESTIGATION OF A POSSIBLE ASTROBLEME IN SOUTHWESTERN MICHIGAN

WESTERN MICHIGAN UNIVERSITY M.S. 1984

University Microfilms

International 300 N. Zeeb Road. Ann Arbor, MI 48106

In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark V ■

1. Glossy photographs or pages _____

2. Colored illustrations, paper or print _____

3. Photographs with dark background _____

4. Illustrations are poor copy ______

5. Pages with black marks, not original copy ______

6. Print shows through as there is text on both sides of page _____

7. Indistinct, broken or small print on several pages.

8. Print exceeds margin requirements

9. Tightly bound copy with print lost in spine _____

10. Computer printout pages with indistinct print

11. Page(s) ______lacking when material received, and not available from school or author.

12. Page(s) ______seem to be missing in numbering only as text follows.

13. Two pages numbered ______. Text follows.

14. Curling and wrinkled pages _____

15. Other______

University Microfilms International

ACKNOWLEDGEMENTS ...... i i

LIST OF FIGURES...... v

LIST OF PLATES...... vi

Chapter

I . INTRODUCTION ...... 1

Objective ...... 1

Location ...... 7

Physiography ...... 7

Approach ...... 7

I I . GEOLOGY...... 9

Regional Geology ...... 9

Local G eo lo g y ...... 15

I I I . GRAVITY AND MAGNETIC SURVEYS OVER ASTROBLEMES ...... 17

IV. FIELD METHODS...... 27

Gravity Survey ...... 27

Magnetic Survey ...... 28

V. DATA REDUCTION AND PLOTTING...... 30

Gravity Data Reduction ...... 30

Magnetic Data Reduction ...... 31

Data P lo t t in g ...... 32

i i i

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter

VI. INTERPRETATION...... 33

Data A nalysis ...... 33

Map Interpretation ...... 34

Gravity Modeling ...... 39

V II. CONCLUSION...... 44

APPENDICES

A. GRAVITY MODELING PROGRAM ...... 47

B. GRAVITY DATA...... 67

BIBLIOGRAPHY ...... 71

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

Figure Page

1. Location Map of the Survey Area ...... 2

2. Oil Field Location Map of Calvin Township, Cass County, Michigan ...... 3

3. Bouguer G ravity Anomaly Map of the Southern Peninsula of Michigan ...... 5

4. Total Magnetic Intensity Map of the Southern Peninsula of Michigan ...... 6

5. Structure in the Vicinity of the Michigan B asin ...... 10

6 . Strati graphic Succession in M ichigan ...... 11

7. Basement Surface Configuration Map of the Southern Peninsula of Michigan ...... 13

8 . Interpreted Regional Basement Lithology, Southern Peninsula o f Michigan ...... 14

9. A. Bouguer Anomaly Map, Gosses B lu ff, A u s tra lia ...... 18

B. Residual Anomaly Map, Gosses B lu ff, A u s tra lia ...... 18

10. A. Total Magnetic Intensity Anomalies, Ries, Germany .... 20

B. Residual Gravity Field, Ries, Germany ...... 20

11. Bouguer Anomaly Map, Flynn Creek C rater, Tennessee ...... 24

12. Total Intensity Magnetic Anomaly Map, Flynn Creek C rater, Tennessee ...... 25

13. Borehole Section Across the Structure in Calvin Twp ...... 4]

14. Residual Gravity Profile A-A' and 2-D Gravity Upthrust Model Profile ...... 43

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF PLATES

Plate

I. Bouguer Gravity Anomaly Map, South-central Cass County, Michigan

II. Total Magnetic Intensity Anomaly Map of South-central Cass Co., Michigan

III. F irs t Harmonic Residual Gravity Map, Wavelength = 16 Miles; South-central Cass Co., Michigan

IV. F irs t Harmonic Residual Gravity Map, Wavelength = 28 Miles; South-central Cass Co., Michigan

V. Second Harmonic Residual Gravity Map, Wavelength = 28 Miles; South-central Cass Co., Michigan

VI. Second Harmonic Trend Surface G ravity Map, Wavelength = 28 Miles; South-central Cass Co., Michigan

VII. F irs t Harmonic Residual G ravity Map, Wavelength = 42 Miles; South-central Cass Co., Michigan

VIII. Residual Magnetic Map; South-central Cass Co., Michigan

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I

INTRODUCTION

Objective

The discovery of oil in the Traverse limestone of Middle Devonian

age in the Calvin Township, Cass County o f Michigan (F ig . 1 ), led to

the development of the Calvin-28 oil field located in sections 27, 28,

29, 32, 33 and 34, T14W,R7S of Cass County, Michigan. The production was

found to be in a circular pattern with a diameter 1.5 miles which led to

the drilling of deep holes in the center and on the edge of the circular

producing area (Fig. 2). In the deep hole at the center o f the produc

tion (Hawkes-Adams 1-28) there is an indication from the well logs of

the absence of about 1200 feet of Ordovician sediments as a result of

uplift and erosion during Late Ordovician time. Lawson 1-28, the deep

hole on the edge of the production, is 0.75 miles northeast of the

Hawkes-Adams 1-28. The Lawson 1-28 cut a t lea s t two thrust fa u lts that

duplicate portions of the Trenton and Black River Formations. The

Utica Shale was not encountered and the dips are very disoriented

below the faults as indicated by dipmeter log. The Hawkes-Adams 1-28

deep te s t did not encounter the sequence from the Upper Munising

Formation to the Utica Shale (DeHaas, personal communication, 1983).

DeHaas suggested that the Eau Claire was uplifted over 1400 feet

probably due to a large thrust fault. He described the structure as

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2

CASS

Lagrange Penn

Jefferson Calvin

Ontwa Mason

Figure 1. Location map of the survey area.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -9 - o '/«. PEW . M l l i Heiass • n t ± 1 1 >

2s 3! 2 1 ¥

I 4 w o l w e l w e l c a le a t i o ■ ■ JACKSON

c - 0 Gas Loc £ D$■ r ) © ■ U lJ o 7 2 2 2 CEO TE^ CEO Oroharowsi i Mitchem _ rAVETT^ ° Baker Gordon MANNES Kirkdorfsf SCO.TECH 2047 T O T ir^ j Swanson E* » T ® 3 * 6 /! i/ A 2 o & © ' Bums > * » £ » Mamt Burns Bums ^ M ANH ^ G E O T ^ MANNES MANNES Crohoweweki Horaon U w * ^ 01 /f ® / t HALLWEU MANNER 1 r ✓

3 A ©2 I © 6© 1 m an n er Low son Low ski TOTIMg Totimo 7s I4w o o S S l 21 o ©1 4 - * 2 0 I Orach c7i Orach * o Hawks M A H N ^ Bnvdtr Havka HAU.WELL Lawsdn MANNES MANNES FAVETT^ -# -# # ] 2 VIN 1 *

02 o v © 1 # C C AL mannes Hawks Adams MANNES MANNES BOWSCf Adams Horns Bowers FAVETTE FAtCTTC 6«tfh i GEO 1 ° ' rf © * r 1- 3o 6© 4 ©

Smith ^ Rraaar AdQoa wotta GEO.Tt^ Bowars C C O .T^ r r t 4 4 © re E I V o © FATE FATE * © CO LAK FAtET a , Smith Smilh /S m ith I ^ smith 0 0 19 2 “I ... 2 . 0 J UNI J R ally CAST Sartfc fAtETTJ ^ S S I (from Oil § Gas News.) CP Rally EAST A © ® 2 ‘ © e Oordon EAST fATETTC Me M Me e OMNI Wood © © - I f . " MANNES h Bouto^cw MANNES C arlisle HABRIS wood HAAftlS 4 - NATIVE E. m annes ° Wood 4 Figure 2. Oil Field location map of Calvin twp., Cass Co., Michigan, 50 50 t* V 19 0 * o (SANMCI McKes K ontiefh Gifrbt OMNI CM. NAT. ^Carlisle V Al P 1 OMNI

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. being similar to cryptoexplosive structures in midcontinental United

States. The Kentland structure in Indiana (Gutschick, 1971), the

Versailles structure (Black, 1964), Jeptha Knob (Seeger, 1966) in

Kentucky, the Glasford structure in Illin o is (Buschbach and Ryan, 1963)

and the Serpent Mound structure in Ohio (Bucher, 1963) are some mid

continent features that have been referred to as cryptoexplosive struc

tures. The Lawson 1-28 has an Ordovician section which according to

DeHaas (personal communication, 1983) is s im ila r to that exposed a t the

Kentland structure in Indiana and the Glasford structure, Illinois,

which have been considered to be possible astroblernes.

Seismic surveys have been conducted in Cass County, but the confi

dential nature of these investigations has resulted in a paucity of

published information on the applicability of seismic methods to

delineate the location and structure of the production. Florencio

Mata (personal communication, 1982) described the structure responsible

for the production as being probably due to the presence of a possible

astrobleme o f Upper Ordovician age which could account fo r the absence

of about 1200 fe e t o f Lower Ordovician sediments and the central u p lif t

of the subsequent sediments. Seismic sections across the area were

described by him as being similar to those across structures in the

Williston Basin that have been considered to be astroblernes (Sawatzky,

1975).

The above information and the absence o f anomalies in the area

on the Regional Bouguer Gravity Anomay and Total Magnetic In te n s ity

Anomaly Maps of the Southern Peninsula of Michigan (Figures 3 and 4)

prepared by Hinze and M erritt (1969) and Hinze et al_., (1971) gave the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5

■»- /4it.rs Contour Int. • lmi'lliga

Figure 3. Bouguer Gravity Anomaly Map of the Southern Peninsula of Michigan (from Hinze et al.,1971)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 MU*S ONTARIO *0 iwaBa|l 2 TOTAL MAONCttC IN flN JIfT MAP !•«•««• !•«•««• n tltftl H >MWH Oia*J SOUTHERN P IM H 3 U L A OP MICHIGAN Peninsula of Michigan(from Hinze et al.,1971).

wl m « m l l l Wm f t m

I** Figure 4. Total Magnetic Intensity Map of the Southern Reproduced with permission ofthe copyright owner. Further reproduction prohibited without permission. 7

necessary impetus for conducting detailed gravity and magnetic investi

gations in the area.

Location

The area under investigation includes portions of the Penn, Calvin,

P orter, Jefferson, Mason and Ontwa Townships in Cass County o f South

western Michigan (Fig. 1). The study area is about 12 miles by 14 miles,

and lie s between la titu d e 41° 451N and 41° 561N and longitude 85° 49'W

and 86 ° 6 'W. It is covered by portions of the Vandalia and Cassopolis

quadrangles, 15-minute series, Michigan-Indiana (USGS Maps).

Physiography

The area has numerous lakes and swamps w ith r e lie f mainly due to

the uneven disposition of the glacial material forming a rolling sur

face, smooth rounded slopes, knobs and ridges of sand and gravel. This

is characteristic of topography in glaciated areas. The elevation

ranges from 700 fe e t to 1100 fe e t. The northwestern part o f the area

is relatively flat and under agricultural cultivation.

Approach

The gravity observations in the field were carried out using the

Worden Prospector gravimeter and the field data was corrected with

la titu d e and elevation factors to determine the Bouguer g ravity

anomalies. Sea-level was assumed as the datum, the density used as

2.67 gm/cc and the formula used as the In tern atio n al Gravity Formula

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of 1930. The Bouguer g ra v ity anomalies were analyzed using Double

Fourier Series to remove the regional and obtain residual gravity values.

The Bouguer g ra vity values from 178 stations were analyzed fo r residual

values.

Magnetic field observations were taken at 159 stations using two

Geometries Proton Precession Magnetometers (Model G816). One magneto

meter was used as the mobile field unit while the other was used as the

stationary base station unit to correct the field data for the diurnal

variations to obtain total magnetic field intensities. Pipelines, well

casings, fences and other ferromagnetics were avoided as much as

possible.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I I

GEOLOGY

Regional Geology

The Michigan Basin is located in the midwestern portion of the

large North American craton. The structural basin is surrounded by

major geologic features which define the basin framework (Cohee and

Landes, 1958). The Precambrian rocks of the Lake Superior Syncline

form the northern boundary o f the basin. The Wisconsin Arch forms the

western boundary, the Kankakee Arch in Indiana and the Findlay Arch in

northwestern Ohio form the southern boundary and the Algonquin Axis,

probably fa u lt co ntrolled (F ish er, 1969), forms the Eastern boundary

of the basin (Fig. 5).

The sedimentary rocks of the basin dip in a northeasterly direction

toward the center of the structural basin at a rate of 25 to 60 feet per

mile (Ells, 1969). The Paleozoic rocks in southwestern Michigan

(F ig . 6 ) comprise of a th ick sequence which includes Cambrian sand

stone sequence, a carbonate, sand and evaporite sequence o f Lower

Ordovician to Middle Devonian age, an Upper Devonian-Mississipian

sequence of sandstone, carbonate, anhydrite and shale.

The dominant trend in major folds and faults in the Michigan Basin

is NW-SE (Newcombe, 1933; P irtle, 1932). This NW-SE trend direction

was confirmed by the regional gravity and magnetic data of Hinze and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MAJOR STRUCTURAL TRENDS SOUTHERN PENINSULA ANO VICINITY

ANTICLINE SYNCLINE

FAULT GRENVILLE FRONT

LAKE SUPERIOR SCALE w 20 20 AO MILES

N / /! ‘ yS. T»'.0 • ■7'

CHATHAM SAG

INDIANA

INDIANA-OHld PLATFORM

Figure 5..v— Structure in the Vicinity of the Michigan Basin. (from Ells, 1969)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11

STRATIGRAPHIC SUCCESSION IN MICHIGAN

PALEOZOIC THROUGH IECZST nHSTOONt NOMlNOAnjRI IRA SYSTEM SERIES STAGE AKIMf MKMUAN M9MTMMT Of COWUVATSO*) IwOwllIlW ill RWlM W * A.Hm M Op——» 8 QUATERNARY HmroCTHi O r WA o I» m I w « 8 »«e*eClww EIIIKUaEACE NOMENCLATURE OUTCROP NOMENC1ATURE lOOtJTMIICIlAmC •OCK-JT*AT*0AAfHtC f o r m a t io n m e m b e r g r o u p

SERIES GROUP f o r m a t io n OOMNAHT imooct INFORMAL TERMS

ITIAnCAWHC W nO N MOUUA IBM)

ew otu n o M e w ti

PPtAHOEVdNfgR

zsm «s™

crxan im* u n o n n v a

IASSiuahdi IASS BLAMM

EXPLANATION

U~hMP^ rfiRTT H*aJK CAlAJtACT M l

»«H«M

•svoAa

ruMCUom EUM CXJ Q«^

IT. OUMXJJI u n v jttu x

Figure 6. Stratigraphic succession in Michigan.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and Merritt (1969). A basement control has been suggested for the

faults and folds in the basin (Cohee & Landes, 1958; Hinze, 1963;

Hinze & M erritt, 1969).

Based on the 19 poorly d is trib u te d basement d r ill holes and depths

interpreted from a total magnetic intensity map, Hinze and Merritt

(1969) depicted the basement surface configuration (F ig . 7 ). The Pre-

cambrian basement surface was depicted by Hinze and M e rritt (1969) as

a uniform and oval depression, with a maximum depth of 15,000 feet below

sea level near the center of Bay County. Figure 8 depicts the inter

preted regional basement lith o lo g y in the southern peninsula of

Michigan (Kellogg, 1971). The few existing drillholes penetrated

granite, granite gneiss, granite regolith, mafic gneiss and some

metasediments. The mid-Michigan anomaly on the g ravity anomaly map

(Fig. 3) prepared by Hinze et aj_. (1971) is probably due to mafic

rocks. The anomaly has also been in terp reted as having its source

in a Keweenawan paleorift zone expressed locally as a basalt trough,

and generally as a disturbance of the deep crustal layers by intrusion

and upwarp (Hinze & M erritt, 1969). Hinze et a_L (1971) suggested

th a t the broad negative g ra vity anomaly associated with the basin

re fle c ts the lower density o f the sedimentary rocks in comparison to

the underlying basement rocks and th a t the g ra v ity anomalies derived

from bedrock topography and sedimentary structures such as reefs and

fracture zones have short wavelengths and positive and negative ampli

tudes of less than 1 mi 11igaT and commonly less than 0.5 m illigals.

The magnetic anomalies are primarily the effect of gross basin

co nfiguration, basement topography and intrabasement lith o lo g ic

variations (Hinze et al., 1971).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 6 *0 0 ' 8 5 *0 0 ' 8 4 °0 0 ' 83 *00'

4 3*3 0 3 0 0 0 ABASEMENT DRILL HOLE • BASEMENT MAGNETIC DEPTH ©BASEMENT MAGNETIC DEPTH WHICH EXCEEDS CONTOUR VALUE BY 10% OR MORE "=ioooo;

•/

+ 4 4 * 0 0

' - I 5 0 0 0 * '-i400opL+— -1 3 0 0 0 - ^ooo'I^-n&oo - 10000-

8 0 0 0 + 9 0 0 0 * -7 0 0 0

V •

- 4 0 0 0

8 5 * 0 0 ’ 0 10 20 SCALE 0 0 * 0 Datum Sea Level Contour Interval 1000 feet

Figure 7. Basement surface configuration map of the Southern Peninsula of Michigan (from -.Hinze § Merritt, 1969)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MAFIC V0LCANIC3 BASEMENT PROVINCE MAP MAFIC EX THUS IVES SCALE ANO IN - metavolcanics , metasediments TnUSIVES 20 MILES AND GNEISSES 3 0 3

+ 4 3 *0 0

4 8 * 00* +

EXTRU- SIVES, / METASEDIMENTS MAFIC IN - METAVOLCANICS TRUSIVES, AND GNEISSES NEISSES/ AND / META- / EOIMENTS + 4 4 *0 0

4 4 * 0 0 * +

METAVOLCANICS

MAFIC GNEISSESy ^

MAFIC INTRUSIVES, | GNEISSES ANO GRANULITE

4 3 * 0 0 ' + MAr C GRANITE, FELSIC AND INTRUSIVES MAFIC GNEISSES, EX A N D E X T R U TRUSIVES AND GIVES AND ETASEDIMENTS \ MAFIC a J s n e is s e s

+ 4 2 *0 0

42 * 0 0 * +

+ 8 2 *3 0 86*30 8 3 *3 0 8 4 *3 0 8 3 *3 0 ' PREDOMINANT E23 PENOKEAN (I.8-I.88.Y.) Q KEWEENAWAN(I.03-I.I3BY.) STRUCTURAL TREND r r q CENTRAL (1.2 —1,3 BY) S ORENVILLE ( 0 .8 - I . I B.Y.)

Figure 8. — Basement Province Map of the Southern Peninsula of Michigan, (from Kellogg, 1971)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Local Geology

The area under investigation is a portion of the southwestern

flank of the Michigan basin. The Paleozoic sequence overlying the Pre-

cambrian basement consists of the Mt. Simon Sandstone, the Eau Claire,

the Dresbach, the Franconian and Trempealeau Formations of Cambrian age

the Praire du Chien Group, St. Peter Sandstone, Black River Group,

Trenton Group and Cincinnatian Series of Ordovician age; the Cataract

Group and Clinton Formation, Niagaran Series, Salina Series and Bass

Island Groups of Silurian age; Sylvania Sandstone, Detroit River Group,

Dundee Limestone, Traverse Limestone and Traverse Formation of Devonian

age and the bedrock subcropping under the glacial d r ift is the Antrim

Shale or the Ellsworth Shale of early Mississippian age (Fig. 6). The

regional dips in the area range from 19 feet per mile for the Traverse

Formation to 48 feet per mile for the Niagaran Series in a 14.5 mile

long section from section 35 of Jefferson Township to section 26 of

Volinia Township of Cass County, Michigan (Doug Daniels, personal

communication, 1983). The Utica Shale, Trenton, Black River,

Praire du Chien, Upper Trempealeau and Upper Munising formations were

not encountered in the Hawkes-Adams 1-28 in section 28 of the Calvin

Township. Rocks of the Cincinnatian Series directly overlay the

Cambrian Trempealeau Formation. The entire sequence appears to

have been uplifted. The Lawson 1-28 in section 28 of the Calvin

Township encountered two thrust faults and the Black River Formation

has been duplicated due to this faulting. The Utica Shale is missing.

The dips below the faults, indicated by dipmeter log, are highly irreg

ular ranging from 10 to 70 degrees towards the east and northeast with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. fracturing and fragmentation (DeHaas, personal communication, 1983).

The Gordon Smith 1-20 deep well in section 20, Calvin Township, encoun

tered an unusually thick Glenwood-St. Peter Sandstone sequence and the

Trempealeau-Praire du Chien sequence appears to be missing (DeHaas,

personal communication, 1983). The Jefferson fie ld which is to the

west of the Calvin Field in Jefferson Township has a NNW-SSE trend to

the production which is probably fau lt controlled. Newcombe (1933)

and Hinze and M erritt (1969) have noted this trend direction in the

Michigan Basin. Other deep wells in the area show a normal sequence

of Paleozoic sediments in the area with dips toward the Basin depocenter

in Midland County.

The Precambrian basement in the area is probably granite gneiss

and metasediments (Fig. 8 ) as determined from deep holes and magnetic

and gravity maps (Kellogg, 1971). Depth determinations carried out by

Kellogg (1971) on the basis of magnetic data show that the average depth

to basement in Cass County ranges from 3495 feet to 3740 feet below

mean sea-level. He determined the depths from the straight slope

methods and Peters' half slope method. The nearest basement d r i l l

hole is in section 10, Berrien County, and i t encountered the Pre

cambrian metasediments at a depth of 3800 feet below sea-level. The

basement configuration map (Fig. 7) shows the generalized depth of the

basement for the region.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I I I

GRAVITY AND MAGNETIC SURVEYS OVER ASTROBLEMES

The term astrobleme, from the Greek roots meaning 'star wound',

refers to ancient scars le f t in the earth's crust by meteorites

(Dietz, 1968). McCall (1977, 1979), French and Short (1968), Silver

and Schultz (1982) and Middlehurst and Kuiper (1963) have edited and

commented on various publications concerning possible Astroblemes or

cryptoexplosion structures in the world. McCall (1977, 1979) has

classified cryptoexplosive structures-astroblernes on the basis of

evidence or proof of their genesis. McCall (1979) has cited unique

indicators of impact explosions: shatter cones, the high pressure

polymorphs of silica, coesite and stishovite, shock lamellations,

diaplectic glasses, impactites and impact melts and breccias.

A number of these astroblemes have been geophysically investigated.

The results of the gravity and magnetic studies of some of these crypto

explosion structures-astrobiernes are described below. These structures

are of class IV A of McCall (1979) where these structures are either

deeply eroded or buried or complex and do not display an immediately

apparent physiographic form of meteorite craters. All are possible

meteorite impact-explosion structures and display some form of shock

metamorphism or brecciation.

The Bouguer gravity map of the Gosses Bluff impact structure

(Fig. 9A) in Australia shows low values. The residual gravity map

(Fig. 9B) indicates a residual gravity low, circular and centered on

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oo aV ,3 ,3 r . i (b) a n w B nrtd Baoar ♦ Ban (from (from Milton et al.,1972) (a) lit fll I f b)Residual Anomaly map, Gosses Bluff, Australia. /// \ Figure 9. Figure 9. aJBouguer Anomalymap, Gosses Bluff, Australia. Z 3 *M

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19

the Bluff. The fir s t regional aeromagnetic survey showed no anomaly

for Gosses Bluff. A la te r survey, however, showed a local anomaly of

-75 gammas and a detailed ground magnetic survey at the base of the

south wall of the B luff reveal two anomalies (Milton et aj_., 1972).

The Bouguer anomaly map around Lake Lappajarvi Basin in Finland

indicates a negative anomaly of 5 to 10 mi H i gals over the basin which

is 10 to 17 miles diameter. The presence of shock-induced deformations,

transformations and fusion indicate that this feature is due to meteoric

impact sometime between Precambrian and Pleistocene times (Engelhardt,

1972), probably late Cretaceous age according to Grieve (1982).

The Ries structure, southern Germany, has a diameter of 24 k ilo

meters and with a centrosymmetrical residual negative gravity anomaly

that is thought to be due to fillin g of the crater by breccias and

Mesozoic sediments (Fig. 10A). The total intensity of geomagnetic

fie ld near Ries shows moderate negative anomalies due to the presence

of suevite in the sediments (Fib. 10B). The Ries structure has been

dated as upper Tortonian age (late Miocene) (Dennis, 1971).

The Steinheim Basin, Germany, has a diameter of 2.2 miles and

slight negative gravity anomaly that is due to the presence of sedi

ments, breccias and brecciated bedrock in the center part of the

feature. The magnetic fie ld shows a small positive anomaly 2 miles

south-southeast of the center. This structure has a central u p lift.

The topography, central u p lift with shatter cones and breccias indicate

an impact origin at about the same age as the Ries structure, that is,

late Miocene (Engelhardt, 1972).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ro o krts’l WO WOfl«rzOStK3W WO

•CH01MOCW •CH01MOCW O OCMNCCN “!o5~ ulQQ (b) Q|90 0190 Contour Contour interval:1 gamma, 10*24* II (from Dennis, Dennis, (from 1971).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Popigay meteorite crater, U.S.S.R., shows negative gravita

tional and magnetic anomalies caused by the lower density of shattered

and re-fused rocks and their weak magnetization. The feature has a

central uplift, explosion breccia, suevite, and shatter cones which

indicate an impact origin during the Neogene (Miocene) age (Masaytis et

al.., 1971).

The negative gravity anomaly field in the Deep Bay Crater of

Saskatchewan, Canada, with a diameter of 8.5 miles shows deformation

of the rocks underlying waters of Deep Bay in the form of intense

fracturing and fragmentation (Innes, 1964; Innes et aj_., 1964). The

negative anomaly forms a circular pattern concentric with the feature

with amplitude of gravity variation of about 20 mi 11igals near the

center of the bay. The Aeromagnetic map of the Geological Survey of

Canada shows small and uniform variation in intensity over the central

portion of the crater not exceeding 190 gammas with uniform gradients

no larger than 50 gammas as compared to the surroundings (Beals et a l.,

1963). The date of formation of the crater is indicated at 100 + 50 M

years (Grieve, 1982).

Magnetic fie ld anomalies of low intensity in the 18-mile diameter

Carswell structure in Canada are characteristic of impact craters due

to blanketing effect of brecciated and highly shocked material under

lying the crater floors. The greatest magnetic disturbance is in te r

preted as an indication of central uplift. The gravity map shows a

negative gravity anomaly and is described as due to a dolomite ring.

The higher gravity anomalies in the center are due to the central

u p lift of the uneroded impact breccia (Innes, 1964).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22

The Lake Wanapitei structure, Canada, probably formed in late

Paleozoic or Mesozoic time and is described as showing a relatively

uniform featureless magnetic fie ld . The Bouguer gravity anomaly map

indicates a local, circular gravity depression of about 15 mi 11igals

(Dence & Popelar, 1972). Grieve (1982) gave the age of the crater at

37 + 2 M years.

The gravity interpretation in the Sudbury area, Canada, has failed

to produce evidence in support of the meteorite impact hypothesis for

the origin of the Sudbury structure because the features associated with

this structure are not well preserved and i t cannot be properly studied.

The residual gravity map shows a nearly circular anomaly over the Sudbury

structure and the regional magnetic map shows an oval positive anomaly

(Popelar, 1972).

Gravity observations of the Brent Crater, Canada (Beals et a l.,

1963; Millman et al_., 1960), and Holleford Crater of Precambrian age in

Canada (Beals, 1960; Beals et al_., 19.63) indicate the presence of c ir

cular negative gravity anomalies associated with both these craters.

These anomalies have been interpreted as being due to sediments fillin g

the craters and the presence of crushed and fragmented rock due to

meteorite impact and explosion (Innes, 1961). The aeromagnetic survey

over Brent Crater shows marked contrast between intensities observed

within and outside the rim of the crater. An aeromagnetic survey over

the Holleford crater shows uniform variation of contours indicating

absence of an anomaly (Beals et al_., 1963).

A gravity survey over the Nicholson Lake area of Canada shows a

disturbance of the gravity field at Nicholson Lake. Removal of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23

regional’ gave an approximately circular negative residual anomaly with

a central low of 7.5 milligals (Dence et aJL » 1968).

Gravity surveys over the Clearwater Lakes (Dence et al_., 1965) and

West Hawk Lake crater (Dence et , 1968) in Canada indicate negative

anomalies of the kind expected for craters underlain by large volumes

of breccia and shattered rock.

No closed gravity anomalies (Fig. 11) and no large magnetic anomalies

(Fig. 12) are associated with the Flynn Creek Crater, Tennessee. I t was

probably formed during the Devonian period and has a diameter of 2.2

miles with a large central h ill, highly deformed rim strata and a breccia

lens within the crater (Roddy, 1968).

The Wells Creek structure, Tennessee, was formed in Late Mississipian

or Early Pennsylvanian age. I t has been described as showing regional

gravity lows trending down both the east and the west sides of the structure

and regional gravity highs bound the structure to the north and the south

with a small central gravity high that is due to a central uplift of more

than 2500 feet (Stearns et al_., 1968).

The Versailles structure in Kentucky has a diameter of about 1 mile

and gravity and magnetic surveys of i t show no anomalies. Apparently

there are no anomalous densities or magnetizations associated with this

structure indicating that basement rocks are not involved in the defor

mation (Seeger, 1972).

The gravity survey over the Kentland structure, Indiana, shows an

encircling outer positive anomaly interpreted as a ring anticline with

an inner negative anomaly due to a ring syncline and a central positive

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24

40'

Gainesboro

36* 20' 36* 20 ' Flynns Liclv

o, -

2 km.

2 me

36* 10' 36* 10' 8 5 *4 5 ' 40 ' 8 5 * 3 5 ' Contour interval: 1 milligal.

Figure 11. Bouguer Anomaly Map, Flynn Creek Crater, Tennessee(from Roddy, 1968).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25

65 *45 ' 4 0 ' 8 5 ° 3 5 ‘

3 6 *2 0 '

oF lynns Lick y

200

3 mi

4 km.

4 0 ' Contour interval: 25 gammas.

Figure 12. Total Intensity Magnetic Anomaly Map, Flynn Creek Crater, Tennessee. (from Roddy, 1968)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26

anomaly over the central u p lift, this is used to interpret basement

u p lift of 2000 to 3000 feet and hence involvement of the basement rocks

in the structure. Because there is no significant magnetic anomaly

directly associated with the structure, it is interpreted as a basement

u p lift rather than an igneous intrusion (Tudor, 1971). Shock meta-

morphic structures and shatter cones have been observed at Kentland

(Gutschick, 1971).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER IV

FIELD METHODS

The Gravity Survey

The Worden Prospector gravimeter capable of being read to the

nearest .01 mi 11igal (1 mi 11igal = 0.001 cm/sec ) was used in this

study. The gravimeter is capable of measuring variations as minute as

one unit in 100,000,000 of the earth's total gravity field.

Survey Procedure

Gravity readings were taken along all available roads at approxi

mately 1-mile intervals. Coverage was extended at the center of the

area of interest by using gravity readings at 1/4-mile intervals.

Accuracy of the gravimeter readings was maintained by taking repeated

observations at each station until duplication was obtained within 0.2

scale divisions. The calibration constant of the Worden gravimeter of

0.09706 m illigal/division was used throughout the survey. Survey

stations were established at selected benchmarks, spot elevations at

road intersections or section boundaries. Station elevations were

taken from USGS topographic maps (Cassopolis and Vandalia Quadrangles)

and the local station elevations were interpolated from the topographic

maps having 10-foot contour intervals. Interpolation error is estimated

to be + 1 foot relative to the contour lines. However, USGS map

. 27

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28

specifications normally suggest that at least 90% of the elevations

interpolated from the contour lines shall be correct within one-half

the contour interval. The primary base station established by the

Michigan State University is 4 miles due west of Cassapolis on the

Pokagon Highway at the -intersection with Old Mills Road on the northern

edge of the road. The observed gravity at this station is 980284.18

mi 11igals and the elevation is 920 feet.

Magnetic Survey

Instrumentation

Two Geometries Proton Precession Magnetometers (Model G816) were

used in this survey. The instrument is accurate within + 1 gamma over

a range of 20,000 to 90,000 gammas and measures the total intensity of

the earth's magnetic fie ld . One was used as a fie ld or mobile magneto

meter and the other the base magnetometer. Usage was kept the same

throughout the survey.

Survey Procedure

The general location of most magnetic stations coincide with the

gravity stations. The magnetic stations were located so as to be free

from magnetic effects of steel fences, pipelines, iron and steel struc

tures, etc. Whenever a site free from extraneous magnetic fields

was unavailable near a gravity station, another station was located.

At each station three readings were taken at a separation of 5 feet

with the third reading taken at a right angle offset or L pattern.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29

This method was used to aid in the evaluation of magnetic effects of

surface formations and to check for any surface disturbances. I f three

readings did not check within 20 gammas, more readings were taken at

5-foot intervals until the desired consistency was obtained. In cases

where the inconsistency persisted, the station was abandoned.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER V

DATA REDUCTION AND PLOTTING

Gravity Data Reduction

Data reduction was performed us.ing a gravity reduction program

to calculate the Bouguer gravity anomalies. Secondary base stations were

established on Calvin Center Road at various road intersections by loops

tying them with the primary base station. The gravimeter readings at

each station were converted to observed gravity by fir s t correcting

for instrumental d r ift from base station readings repeated every 2 hours.

Then the difference between base station and fie ld station were multi

plied by the meter constant (0.09706) and added to the base station

observed gravity to obtain the station observed gravity.

For latitude corrections, the station coordinates were taken from

the topographic sheets. The margin of error in latitude was + 0.025

min. The theoretical gravity at sea-level at each station was deter

mined from the International Gravity Formula of 1930 which is G =

978049 (1 + 0.0052884 SIN 2 () - 0.0000059 SIN2 (2*)) gals where G

is the sea-level gravity at latitude . The free-air correction compen

sates for the normal vertical gradient of gravity by applying a correc

tion factor to the difference in elevation between the station and a

reference datum, in this case the sea-level. The mass correction

accounts for the gravity acceleration due to a mass of material between

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sea-level and station elevation. The effect of the elevation of the

station above sea-level is determined by calculating the free-air and

Bouguer reductions. The free-air effect is 0.09406 milligals/foot.

The Bouguer correction factor is 0.01277*Sigma m illigals/foot where

Sigma is the mean density of the included rock mass. The Bouguer

correction is applied in the opposite sense to fre e -a ir, that is , i t

is subtracted when the station is above the datum plane and vice versa

(Dobrin, 1976; Telford et , 1976). A density of 2.67 gm/cc was used

in these corrections.

The terrain*correction accounts for the deviation of topography

from a horizontal surface. Terrain corrections were not calculated for

this survey due to the gentle topography.

The Bouguer gravity anomaly was calculated using the corrections

given above. The equation (Dobrin, 1976) used in the calculations is:

Bouguer gravity anomaly = observed gravity - theoretical sea-level

gravity + free-air correction - Bouguer correction.

Magnetic Data Reduction

The magnetic data were corrected to take into account the daily

variations of the earth's magnetic field. These variations or drift in

magnetic fie ld called diurnal variations were obtained by taking repeated

readings at the base station at 3-minute intervals. The base station

was located at the public access site on the western bank of Paradise

Lake in section 3 of Calvin Township of Cass County, Michigan. The

station readings were corrected to an arbitrary base fie ld of 58,000

gammas. This was done by subtracting the total fie ld at the base

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32

station from the base fie ld (58,000 gammas) and the result was added to

the total field of the station.

Data Plotting

The Bouguer gravity anomalies and the total magnetic fie ld data

were plotted on the California Computer Products (CALCOMP) 906 Drum

Plotter, using the Fortran Computer Program MAPNUM.FOR written by Dr.

William Sauck, Department of Geology, Western Michigan University. The

plot shows the station location and gravity or magnetic value at that

station. The data were then manually contoured and the Bouguer Anomaly

Map (Plate I) and the Total Magnetic Intensity Map (Plate II) of

south-central Cass County was produced.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER VI

INTERPRETATION

Data Analysis

Gravity Data

The Bouguer gravity anomalies were analyzed using the Double Fourier

Series Analysis Fortran Program (James, 1966). This program computed

the residual values for the gravity data by subtracting the computed

values from the observed Bouguer anomalies. The computed gravity values

were computed using Double Fourier series of the fir s t harmonic with

wavelengths of 16, 28 and 42 miles. These values were used as they are

equal or larger than the dimensions of the control area. Otherwise

there is a repetition of trends outside the control area. James (1966)

suggested that i f there was some periodicity on data the wavelength may

be estimated and multiplied by successive integers and the program run

using a variety of fundamental wavelengths choosing from them on the

basis of the reduction in sum of squares due to removal of the trend.

Residuals were also calculated with wavelength of 28 miles for the second

harmonic. The second harmonic surface with 28 miles fundamental wave

length was the best trend surface f i t (98.5%). The f ir s t harmonic

surface with wavelength of 16 miles gave a trend surface f i t of about

88 % to the observed Bouguer surface. The fir s t harmonic surfaces with

wavelengths of 28 and 42 miles gave fits of 95.8% and 96.7%, respectively,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34

to the observed Bouguer surface. The second harmonic gravity trend

surface with 28-mile wavelength (Plate VI) has the best f i t to the

Bouguer surface and hence probably best describes the regional for the

area under investigation. The residual values were then plotted and

contoured as mentioned earlier to give residual gravity maps with d iffe r

ent wavelengths and harmonics (Plates I I I to V II).

Magnetic Data

The total magnetic intensity data were analyzed using the Double

Fourier Series Analysis program like the gravity data using the second

harmonics with fundamental wavelength of 28 miles. The residual values

obtained were plotted using the CALCOMP plotter and hand contoured to

produce the residual magnetic map (Plate V III).

Map Interpretation

A representation of geologic conditions may be provided by gravity

and magnetic anomaly maps. These maps illu s tra te the difference between

observed and theoretical values of a force fie ld caused by horizontal

or lateral variations in physical properties of the underlying rock

formations. The physical property is density in the case of the gravity

maps, and magnetic susceptibility and remanent magnetism in the case of

the magnetic maps. The sum of a ll departures from the horizontally

homogeneous earth conditions gives the anomaly values. Hinze et a l.

(.1971) suggested that short wavelengths and low amplitude anomalies

in the Michigan Basin are caused by the density contrasts within the

glacial d r ift and long wavelength anomalies of variable amplitude are

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. produced by regional facies changes within the sediments, deep crustal

or upper mantle density contrasts, and variable thickness of crustal

layers. Bedrock topography and sedimentary structures have short wave

length and positive or negative amplitude gravity anomalies typically

less than 1 mi H i gal. Relief of the basement surface produces gravity

anomalies of varying wavelength and amplitude. Intra-basement lithologic

variations produce the largest amplitude anomalies (Hinze et aj_., 1971).

Magnetic anomalies produced by basement lithology are more pro

nounced than in the case of gravity. Hinze ejt al_. (1971) suggested that

the magnetic effect of basement topography is an order of magnitude less

than the effect of basement lithology. According to these authors the

major gravity and magnetic anomalies within the Michigan Basin are pro

duced by variations in the intrabasement lithologies.

The Bouguer gravity anomaly map for south-central Cass County (Plate I)

shows mainly the gravity due to a regional source which has long wave

length. This map, contoured at 1 mi 11igal intervals, does not show any

local anomaly closures, probably because of the strong regional feature

which dominates. The contours in this map are similar to the contours

for the area on the Regional Bouguer Gravity Anomaly Map of the Southern

Peninsula of Michigan (Fig. 3). The absence of closures on this map

could possibly indicate the lack of involvement of the basement in the

structure under investigation. However, the lower density of the Mt. Simon

Sandstone may be opposing some of the basement effects. Because of the

presence of a strong regional anomaly, various attempts were made to

remove i t so that local residual anomalies could be studied. Residual

values are the component of gravity having a local source and shorter

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36

wavelength (Dobrin, 1976). The fir s t harmonic residual gravity map

with wavelength of 16 miles (Plate I I I ) and 88 % fit shows a circular to

subcircular negative anomaly surrounding a central positive. The central

positive is located around section 31 of Calvin Township and has a magni

tude of 2.2 m illigals. An annular gravity low surrounds this high and

positive residuals occur to the north and the east. This is similar to

anomalies expected over astroblemes but the regional from which the

residual was obtained is a poor f i t to the data. Hence, this circular

feature is an a rtifa c t of the processing, a result of trying to force-

f i t a small wavelength to the regional. The eastern positive anomaly

is also present on the other residual maps and coincides with a positive

magnetic anomaly. Some of the higher negative or positive values along

the edges may be due to edge effects.

The f ir s t harmonic residual gravity anomaly maps (Plates IV & V II)

with wavelengths of 28 and 42 miles appear to be similar in configuration.

This is because the trend surface representing the regional are similar

and the reduction of the sum of squares are very close. These residual

maps and the second harmonic residual anomaly map with wavelength of 28

miles (Plate V) show four gravity highs and six gravity lows bounded by

linear features. A linear negative anomaly in Ontwa Township may be

due to an edge effect as this becomes a positive in the second harmonic

residual gravity map using wavelength of 28 miles (Plate V). These

positive and negative anomalies are generally separated by linear

trending gradients. A linear feature appears to be trending N-S

near the eastern edge of the central positive and negative gravity

anomalies (Plates IV & V II). But this trend is NNW-SSE in the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37

second harmonic residual map with wavelength of 28 miles (Plate V)

whose trend surface (Plate VI) probably best represents the regional

gravity contours. Other linear features (discontinuities) trend NW-SE

and NE-SW conforming with the general trend of anticlines and faults

in the Michigan Basin (Newcombe, 1933; P irtle , 1932; and Hinze &

Merritt, 1969). The Jefferson field in Jefferson Township has a NNW-

SSE trend which is in close proximity to a linear trend in the residual

gravity maps. This trend is pronounced in the 28-mile wavelength

second harmonic residual map (Plate V). The Jefferson field appears

to be truncated on the north and south by NE-SW trending linear features.

In the center of the study area just north of the central positive there

is a small linear feature trending E-W which appears to cause displace

ment between the negative anomaly in the north and positive anomaly to

the south of the feature.

The high positive residual anomaly observed in the southeastern

portion of the area represented by the fir s t harmonic residual gravity

maps (Plates I I I , IV & V II) appears to have been shifted by about a mile

to the west on the second harmonic residual map with wavelength of 28

miles (Plate V).

The central positive gravity anomaly is not associated with the

anomalous Hawkes-Adams deep test but is about 2 miles to the west of

the well. There is a linear-trending feature over the Hawkes-Adams

and Lawson deep tests which has a NNW-SSE trend, indicating a possible

faulted area which might account for the uplifted sediments in the

Hawkes-Adams deep test. The structural map on top of the traverse

limestone in Calvin Township also suggests that the structural high

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38

is 1 mile west of the Hawkes-Adams test. The Lawson deep test encoun

tered two faults and steeply dipping beds below the faults.

The total fie ld magnetic intensity map (Plate I I ) shows one high

positive anomaly towards the southeastern corner of the map in sections 31

and 32 of north Porter Township. This anomaly is also observed on the

regional magnetic map of the southern peninsula of Michigan (Fig. 4).

This anomaly coincides with the gravity high observed in the residual

gravity maps of the area (Plates I I I , IV, V & V II) , thus suggesting an

intrabasement lithologic variation. No anomalous closures are observed

over the area of known structural deformation. The variation in con

tours is also smooth. NNW-SSE trending linear features are observed on

the magnetic residual map (Plate V III) east and west of the area of

interest coinciding with the trends in the same direction observed on

the residual gravity map (Plate V).

The linear features and anomalies are probably caused by a horst-

graben type of structure in the area. The positive anomalies indicate

the horsts and the negative anomalies the grabens which are bounded by

faults trending NNW-SSE, NW-SE, E-W and NE-SW as indicated by the linear

features on the residual gravity map (Plate V). Such horst and graben

type of feature has been observed in astroblernes like the Wells Creek

structure in Tennessee as described by Stearns et al_., (1968). The

negative residual gravity anomaly in sections 19, 20, 29 and 30 in

Calvin Township in the center of the map (Plate V) may be due to the

abnormally thick Glenwood-St. Peter Sandstone which was encountered in the

Gordon Smith 1-20 deep test.

Two possible hypotheses to explain the cause of the u p lift and

faulting are:

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39

1. The u p lift may have been a result of either delayed isostatic

adjustment or prompt rebound due to meteoric impact. Older faults may

have been rejuvenated by the impact to produce the horst-graben feature

and the general rectilin ear fault block pattern of the area; and

2. The area could have been a focal point of regional stress.

The presence of parallel left lateral strike-slip faults causing

shearing within the central block could have resulted in upthrusting

as explained by Lees (1954) and Quennell (1957) for the faults and folds

near the Dead Sea. Lowell (1972) experimented with Clay and produced

strike-slip movement with a component of shortening across the fault zone.

A zone of en-echelon fractures were formed at a small angle to displace

ment but the material moving up out of the fault zone formed a welt

bounded by thrusts on both sides and a series of en-echelon folds.

Gravity Modeling

The low density o f the Mt. Simon Sandstone overlying the Precambrian

basement could be masking the uplifted denser Precambrian basement, and

thus reducing the Bouguer gravity anomaly to the small values observed.

Modeling was done in an attempt to determine the cause of the positive

anomaly and the NNW-SSE trending linear feature on the residual gravity

map (Plate V). Three-dimensional vertical cylinder and two-dimensional

fault models were used to model the profile A-A' obtained from the second

harmonic residual gravity values using wavelength of 28 miles (Plate V).

The density values for the layers were obtained from the bulk

density logs of the Hawkes-Adams and Lawson deep tests. The P'recam-

brian basement was assumed to have a density of 2.7 gm/cc, the Eau

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40

Claire a density of 2.55 gm/cc, the Mt. Simon a density of 2.45 gm/cc

and the other overlying sediments were assigned a density of 2.67 gm/cc

which is an average density for these sediments as per the logs.

The modeling was started from the top of the Eau Claire as the

significant lateral density variations were downward from this forma

tion. Each formation was modeled separately and a composite anomaly

was added to account for the total effect. The model gravity values

were calculated by Fortran programs (Appendix A) using the formulas

in Telford et al_., (1976).

The vertical cylinder with diameter 2 miles model showed a negative

gravity effect over the cylinder which was not the observed response.

Different density contrasts were used to attempt a match but to no avail.

Hence the vertical-cylinder model was discarded. The thicknesses and

depths of the layers in the cylinder were taken from the well logs of

the Hawkes-Adams 1-28 deep test and those of the Lawson 1-28 deep hole

were used to represent the normal section (Fig. 13).

The normal fault model showed a small positive anomaly with a

steep negative slope which was again not the observed effect.

The thrust-fault model was prepared after studying the geologic

cross section of the deep holes between Hawkes-Adams 1-28, Lawson 1-28,

the Gemberling 1-36 and Haldeman 1-31 in Calvin Township (Fig. 13). The

depths to the top of each faulted layer were taken from the well logs.

The model was prepared using fault plane dips of 30 degrees and 45 degrees

towards the southwest. The models clearly showed steeply descending

gravity values towards the east and'high gravity values to the west

which was the observed effect. The 45 degree upthrust fault matches

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

1-31 1-31 E Haldeman ______B l . R v . Trenton G dinV-~-T Cinn. Utica Niag. "PDC.?_ - - 1-36

Gemberling 1 ------______

~f -\

Pres. Pres. _ _ Franc. Eau Claire PDC PDC Tremp| B l . Rv|: Cinn. Cinn. “ Utica? — — Niag. ■ — — ■ 4-Mt. Simon 4-Mt. ^ C l i n t o n - * - + . I . Trent/j h 1 9 =T t ‘ v r r

Hawkes- Hawkes- Lawson =*1 mile =*1 Adams 1-28 1-28 Mt. Mt. Simon Eau Eau Claite C^inn._ Tremp. Michigan. i = 1 r 0

•\> * r 1*

_ - _ = 1 _____ Scale: Eon. 7 * 1m F n n PDC Utica Cinn. Cinn. | Trenton _B_lack_ Riv. _B_lack_

_ _ I _ _ _XianI __ _ N i a £ . 1-26

' ' * Kaminski 2600' 2200 2400' 2000 1600' 1200 10001 800 ' 800 600 1 W 1 600 ■ ■ - 1800' - - 1400’ - ' w 2800' w r O CD Figure 13. Figure Borehole 13. Section across the structure in Calvin twp., Cass Co., cd CD S CD a c/> CD CD +-> iH •p n -C ■H m

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. more closely the residual gravity profile (Fig. 14). Hence the NNW-SSE

trending linear feature may well be a thrust fault involving the base

ment in the u p lift. The other linear features may also represent faults,

either thrust or normal, causing a horst-graben type of structure in the

area. There are apparently strike-slip cross faults truncating the

horst-graben feature and thus lim iting them in their strike extent.

The result is an assemblage of fau lt blocks which are roughly equi-

dimensional prisms.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. J j C

2.45 2.45 g/cc 2.55 g/cc 2.55 2.67 2.67 g/cc densities Model + A ’ * * Model Profile ^ ^ Residual Profile ______------4 * Precambrian Mt. Mt. Simon Hawkes-Adams 1 GlcfTTH Precambrian Eau Eau Mt. Mt. Simon MSL 5280* -0.4 •H •H Figure 14. Figure 14. Residual Gravity Profile A-A1 and Gravity 2-D Upthrust Model Profile.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER VII

CONCLUSIONS

Due to the lack of core samples from the deeper parts of the

section, there is a lack of direct geologic evidence such as shatter

cones, brecciation, presence of coesite, e tc ., to support an impact

origin for this feature. The interpretation of the genesis of the

u p lift and the absence of Ordovician sediments is inconclusive from the

gravity and magnetic surveys. Thrust faulting in the central u p lift

and erosion of the sediments has been observed in most proven astro-'

blernes or impact craters. The presence of shock metamorphism and

brecciation have also been observed in a ll astroblemes. Astroblemes

that have been investigated by gravity and magnetic methods have shown

circular negative gravity anomalies with a central positive gravity

anomaly i f a central u p lift is present. Magnetic anomalies are rarely

associated with known astroblemes. Most astroblemes that have a c ir

cular negative gravity anomaly are near-surface features or have not

been deeply eroded. Structures like the Flynn Creek Crater in Tennessee

do not have any gravity anomaly closures associated with the structure

even at the level of 1 mi H i gal on the Bouguer gravity map like the

structure studied in this project. As there was no significant circular

Bouguer gravity anomaly associated with the Cass County structure,

residual values were calculated. The circular-subcircular anomaly with a

central positive anomaly observed on the fir s t harmonic residual gravity

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45

map with wavelength of 16 miles may not represent the actual geology as

the trend surface produced by this wavelength does not represent the

regional. A NNW-SSE trending linear feature with a positive closure to

its w es t was observed on the f ir s t harmonic residual gravity maps with

wavelengths of 28 and 42 miles. I t can also be seen on the second har

monic residual map with wavelength of 28 miles. The other linear features

which bound the positive gravity anomaly trend E-W, NW-SE and NE-SW may

also be faults. The NNW-SSE trending Jefferson fie ld appears to be trun

cated by NE-SW trending strike-slip faults. A residual gravity positive

is located in the southeast section of the area and which is coincident

with a magnetic high which could be interpreted as being effects of

variations in basement lithology.

Two- and three-dimensional modeling was performed to try to match

the residual profile across the NNW-SSE trending linear feature over the

circular production area observed on the second harmonic residual map

with wavelength of 28 miles. The thrust-fault, normal-fault and the

vertical-cylinder models were used and the best f i t obtained was from

the thrust-fault model which shows the steep slope northeast of a high

positive similar to that of the gravity profile. The vertical-cylinder

and normal-fault models did not match the residual profile. Hence the

u p lift could be due to a thrust fau lt involving the Precambrian basement.

The fau lt could have been active until the Late Ordovician and the up

lifte d sediments could have been eventually eroded away. The Hawkes-

Adams and Lawson deep tests in section 28 of Calvin Township could be

on the flanks of the uplifted portion and the center of the uplifted

portion is 1 mile to the west.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The genesis of the u p lift s t ill remains a question, as there is no

magnetic anomaly associated with the uplift. A central gravity posi

tive, representing the central uplift, and linear trending features,

representing faults, are present on the second harmonic residual gravity

map with fundamental wavelength of 28 miles, probably forming horst-

graben type of structures similar to structures in proven astroblemes.

Another possible hypothesis to explain the u p lift and faulting is that

parallel left-lateral strike-slip faults could cause shears within a

central block to produce upthrusts. With the lack of conclusive

geologic evidence in support of the impact theory, the structure should

be called a crypto-explosion structure until more evidence is available.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A

GRAVITY MODELING PROGRAM

PROGRAM GRMOD3 c ------C THIS PROGRAM (ON FILE GRMOD8. FORC2003C/20 030 3 ) CALLS A VARIETY OF C SUBROUTINES WRITTEN BY STUDENTS OF GL562 CLASS/ (WMU/ FALL/ C 1 9 8 3). THESE SUBROUTINES CALCULATE A GRAVITY PROFILE OVER VARIGUS C 2-0 AND 3 - D BODIES. THE PARAMETERS AND GRAVITY ARRAY ARE PASSED BAC- C TO THE MAIN PROGRAM/ WHERE THEY ARE DISPLAYED ON THE LINE PRINTER. C ALL LINEAR DIMENSIONS ARE IN FEET. DIP ANGLES ARE MEASURED CCW C ABOUT THE CENTER POINT ( 2 6 ) . C MAIN PROGRAM WRITTEN BY W.A. SAUCK FOR DEC1099/ OCT./ 1983. c ------REAL GRAV(51)/ TITLE(16)/LENG/XI( 20)/21 (20) COMMON F IG ( 5 1 /2 5 ) DATA DASH/VERT/ DOT/PL US/ BLANK/ AST/RATI 0 / '- '/ '! '/ '. '/ '+ '/ ' '/ + '*'/1 .666666667/ OPEN(UNIT = 6/ DEVICE='OSK'/ FILE='GRVMO0.0 AT', PROTECTION="155) 10 WRITE(5/1000) 1000 FORMAT(2X/'ENTER: 1 FOR SPHERE/'/1 5 X/' 5 FOR DIPPING SHEET/' + ///1QX/'2 FOR DIPPING ROD/'/10X/'6 FOR HORIZ. THIN SHEET/' + ///1QX/'3 FOR HORIZ. R0D/'/1lX/'7 FOR THICK PRISM/'/// + 10X/ '4 FOR THICK VERT. CYL./'5X/'8 FOR DIPPING FAULT.' + / / / 1 0 X / ' 9 TO TOGGLE TABULAR OUTPUT ON/OFF' / 5 X/ ' - 9 TO STOP') RSAD(5/11Q0/ERR=10) ITYPE 1100 FORMAT(I) IF(ITYPc.LE.C) GO TO 999 IF (IT Y P E .G T . 9) GO TO 10 IF(ITYPE.LT.9) GO TO 15 IF(ITAB) 12/12/13 12 IT A B= 1 GO TO 10 13 IT A8 = 0 GO TO 10 15 WRITEC5/1200) 1200 F0RMAT(2X/'ENTER UP TO 80 CHARACTERS OF TITLE') READ(5/13Q0) TITLE 1300 F0RMAT(16A5) c gNO OF MAIN PROGRAM INPUT. ERASE SUBSURFACE CROSS-SECTION. 30 DO 25 1=1/51 DO 25 J = 1 /25 25 FIG(I/J)=BLANK WRITE(6/1310) TITLE 1310 FORMAT('1'/2CX/16A5) GO TO(100/200/300/40C/500/600/700/800)/ITYPE

100 CALL SPHERE(DEPTH/RADIUS/DENS/DX/GRAV)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48

XINCH=DX*6. WRITE(6/1400) DEPTH/RAOIUS/DENS/XINCH 1 4 0 0 F0RM ATC5X/'DEPTH TO CENTER OF S P H E R E *'/ F 7 . 1 / ' / RAD IUS= ' / F 7 . 1 / + '/ DENSITY CONTRAST*'/F5.2/'/ SCALE:1"*'/F7.1/' FT.') C— NOTE USE OF TRUNCATION FOR CONVERSION TO INTEGER/' NEXT 3 LINES/ ETC. 110 IDEP=0.5 + DEPTH*RATIO/DX IRA0X=0.5 + RADIUS/DX IRADZ=0»5 + RATIO*RADIUS/DX IFCIDEP.GT.24) GO TO 120 I= 2 5 - ID E P FIGC26/I)=PLUS IFCRAOIUS.LT.DX) GO TO 900 J= 26-IR A D X FIG(J /I)=0ASH J =26+IR A 0X FIGCJ/I)=DASH I= I+ IR A D Z FIG(26/I)=VERT I=I~IRADZ*2 IFCI.LT.1) GO TO 900 FIG C 2 6 / I ) = VERT GO TO 900

120 FIGC26/1)=AST GO TO 900

200 CALL DIPRODCDEPTH/RADIUS/LENGTH/DIP/DENS/DX/GRAV) XINCH=0X*6. WRITEC6/1500)DEPTH/RADIUS/LENGTH/DIP/DENS/XINCH 1500 FORMATC5X/'DEPTH TO TOP OF ROD = ' / F7.1/'/ RADIUS='/F7.1/ + '/ LENGTH-*'/F7.1/'/ DI P= ' / F 6 .1 / ' / DENSITY CONTRAST*' + F5.2/'/ SCALE:1"='/F7.1/' FT.') 1X0=26 210 I0EP=0.5 + DEPTH*RATIO/DX IFCIDEP.GT.24) GO TO 240 DBOT=OEPTH+LENG*SINCCIP*0.01745329) IB0T=Q.5 + DBOT*RATIO/DX DO 220 I=IDEP/25 IS U B = I CALL DIAGCDIP/ IX/ FX/ ISUB) REM=FX~IX IFCREM.LE.0.25) GO TO 216 IFCREM.GE.0.75) GO TO 215 GO TO 220 215 IX=IX+1 216 II=IXO-IX IFCII.LT.1 .OR. II .GT. 51) GO TO 225 F IG C H /25-I) = AST 220 CONTINUE 225 GO TO 900 C------BODY BELOW 30TTCM OF FIGURE ------240 CALL DIAGC D IP / I X / FX/ IDEP) II=IX0-CFX+0.5) FIGCII/1)=AST GO TO 900

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49

GO TC 900

300 CALL HORRODCDSPTH/RADIUS/LENG/Y/OENS/DX/GRAV) XINCH=DX*6. LENG=LENG*2. WRITEC6,1600)DEPTH,RADIUS,LENG/Y/CENS/XINCH 1 600 FORMATC5X,'DEPTH TO CENTER = ' , F 7. 1 , ' , RA 01US= ' / F7 .1 / + ' , L E N G T H = ',F 7 .1 ,'/ Y OF F S ET= ' / F7 . 1 , / , 5 X , + 'DENSITY CONTRAST=',F5.2,', SCALE:1"=',F7 .1, ' FT.') GO TO 110 c ------400 CALL VERCYL(DEPTH,RACIUS,LENG,OENS,OX,GRAV) DB=DEPTH+LENG XINCH=DX*6. WRITEC6,1700)DEPTH/RAOIUS,OB,CENS/XINCH 1700 FORMAT(5X/'OEPTH TO TOP= ' ,F7 .1/'/ RADIUS=',F7.1, + ', DEPTH TC BOTTOM*',F7.1///5X,'DENSITY CONTRAST= ',F5.2, + ', SCALE:1"=',F7.1,' FT.') I0EP=0.5 + DEPTH*RATIC/OX IRADX=0.5 +RAOIUS/OX 13OT = C . 5 + D3*RATI0/DX I= 2 5 -ID E P J=26-IRADX K =25-IB 0T L=26+IRADX IF ( IDE P.GT.24) GO TO 420 IF(K.LT.0)K=1 DO 410 M=K/I FIGCJ/M)=OASH 410 FIG(L/M)=OASH IFCK.EQ.1) GO TO 420 00 415 M = J,L FIG(M/I)=VERT 415 FIG(M,K)=VERT GO TO 900 420 00 422 M = J/ L 422 FIGCM/1)=AST GO TO 900

500 CALL CSHEETCCEPTH/THICIC/LENG/OIP/CENS/OX/GRAV) XINCH=DX*6. WRITE (6 /1 8 0 0 ) DEPTH,THICK,LENG/OIP,DENS,XINCH 1 800 FORMAT<5X,'DEPTH TO TCP= ' / F7.1 /'/ THICKNESS='/ + F 7 .1 / ' / LENGTH=' ,F7.1, '/ DIP= ' /F6.1 / ' / DENSITY CONTRASTS, + F 5 . 2/'/ SCALE:1" = '/ F7.1/' FT.') IDEP=0.5 + DEPTH*RATIO/DX CALL CIAGCOIP/IX/FX/ICEP) 1X0=26 + X GO TO 210

600 CALL HSHEETCDEPTH/THICK/LENG/CENS/DX/GRAV) XINCH = DX *6 . WRITE (6/1900) DEPTH,THICK/LENG/DENS/XINCH 1900 FORMAT(5X,'0EPTH TO CENTER= '/F7.1,', THICKNESS= ',F7.1, + '/ LENGTH='/F7.1,', DENSITY CONTRAST='/F5.2/

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced c C o o o - C - C 02 OMT2,YU OTU I O FL GVO.OAT') GRVMOD. FILE ON IS OUTPUT FORMAT(2X,'YCUR 3002 05 OMT11 ,'I',6,'GA',//,51(10X/I3/F10.3,/)) ) / , 3 . 0 1 F / 3 I / X 0 1 ( 1 5 , / / , GRAV' ' 6X, , ' X, ' I 2 1 , / / FORMAT(1H1, 3 00 5 08 OMT2,ETR 1 O EUN O EU CX, 1 / / / ' MENU/ TO RETURN TO 1 FORMAT(2X,'ENTER: 3008 ------04 OMT 2F) FORMAT( 3004 ------03 OMT2,ETR PINL IIU AD AIU SAE AUS / ' VALUES SCALE MAXIMUM AND MINIMUM OPTIONAL FORMAT<2X,'ENTER 3003 01 OMT2/TE ETA 1 GA VLE AE HW BELOW',// W O L E B SHOWN ARE VALUES GRAV 14 CENTRAL FORMAT(2X/'THE 3001 10 OMT5,DPH O IH S0S=',F7.1,', DPH O ' TO DEPTH , ' , 1 . 7 S F S10 = , ' RIGHT TO FORMAT(5X,'DEPTH 2100 9 WRI 5, 2) 02 0 ,3 (5 E IT R W 999 2 WRI 53003) 0 0 (5/3 E IT R W 920 1 WRITEC5/3003) W 910 0 WRT(/01)( I, 1 ) = /32 9 1 (I), V A R G ) ( RITE(5/3001 W 900 0 CL FAULT(DEPTH1/DEPTH3/THICK/DIP/DENS/DX/GRAV) CALL 800 CONTINUE 725 ' O END') TO '3 + ' T CLUAE NTE POIE F AE T SAMEY OF P E, ' PROFILE , ANOTHER / , 1 CALCULATE 0 TOX, '2 + 'O PLOT. , ' ASS RP T FL ETR SCALE ENTIRE FILL TO GRAPH CAUSES T.') . O S L P E O YOUR R E WITH ,'Z X /,4 'RANGE / .' T O L + P 'FOR + 14F6.2,//, ENTER: 0 O OTNE 1 O TR OVER') START TO 1 CONTINUE, TO 0 : R E T N 'E , X ,2 / / , 2 . 6 F 4 1 + F7.1/'/ DNIY OTAT='/F5 CL: 1" = / ' 5CALE: / ' / 2 5. F / CONTRAST ' = DENSITY ') . T F ' / F7 1 . / ' / 1 . 7 + F + /LEFT $I0E=',F7.1/'/ TIKES'/F7.1///5X ='/ ' P= 1 0 ' X, 5 / / / 1 . 7 F / THICKNESS=' / ' / 1 . 7 F , ' = E 0 I $ T F E /'L + -- IDEP=DEPTH*RATIO/DX SD O RPTTV CLS O IG RM FUT FGR DRAWING ) 5 ,2 FIGURE 1 COMMON(5 FIG "FAULT" FROM DIAG TO CALLS REPETITIVE FOR USED URUIE TI(ET,ETATDPR I OXIW) X,ISW /O TIO ETDIA(DEPTH,VERT,AST,DIP,RA G SUBROUTINE S “1 RW HRZ IE RM AL T LF EG O FIGURE. OF EDGE LEFT TO EDGE. FAULT FROM RIGHT TO LINE FAULT HORIZ FROM DRAWS LINE 1 HORIZ DRAWS “ ISW +1 ISW ------END STOP NGC , ) 9 9 9 , 5 1 , 0 1 ( 0 T GO AD(/10 NGO (5/1100) D EA R TE( 3005) RV(I),I=1,1) ,51 1 = I , ) GRAV I , ( I ( ) 5 0 0 ,3 (6 E IT R W AL RP(RV51/GMIN/GMAX) 1 GRAPH(GRAV,5 CALL AL T A( , , , P, O, /-1) X ,D IO T A ,R IP T,D S T,A R E 4,V H T P E (C IA ETD G CALL F(TAB. O) O O 920 TO GO ) .O Q .E B A (IT IF O O 30 TOGO AD(/04ERR=0) GMIN/GMAX =900) R R (5/3004,E D EA R AL TIC PT / RTAS/ P/ I/ /+1) X TI0/D A /R IP ST/D T/A ER 2/V TH EP ETDIACC G CALL F(NO T1) O O 910 TO GO ) LT.1 NGO. ( IF AL A( VERT, DI RATI 0X,1) ,-1 X ,0 I0 T A ,R 900 IP ,D TO T GO S ,A T R E /V 3 H T P E (D IA D / T + E X G /D 1) I0 T CALL A /R P A(DEPTH1/VERT/AST/Cl GET01 CALL E D(5/1100/ER90 NGO ERR=900) / 0 0 1 1 READ / 5 ( 0EPTH4=0EPTH3+THICK DEPTH2=0EPTrt1+THICK RT< DEPTH1/DEPTH3/THICK,DIP/DENS,XINCH ) 0 0 1 2 , WRITE<6 XINCH=DX*6 . XINCH=DX*6 O O 900 TOGO ED EUT T B POTD N IE PRINTER. LINE ON PLOTTED BE TO RESULTS SEND RVE CLUAE POIE GV CAC T RESTART. TO CHANCE GIVE PROFILE) CALCULATED PREVIEW

G( 1= T S ,1)=A (M IG F RN OTOA OTU TABLE. OUTPUT OPTIONAL PRINT

------

------— - - — -

------

“ - - — 50

+ SCALE:1,,= '/F7.1/' FT.') IDEP=0.5 + OEPTH*RATIO/OX IHTHIK=0.5 + THICK*RATIO/(2.*0X) ILEN=0.5 + LENG/DX IFdLEN.GT.25) ILEN=25 IX=26 + ILEN IFdDEP.GT.24) GO TO 620 IT=25-IDEP+IHTHIK IB=25-IDEP-IHTHIK DO 610 M = 2 6 ✓ IX FIG(M/IT)=VERT 610 FIG(M/IE)=VERT DO 615 M = I3 /IT IFdLEN.LT.25) FIG(IX,M)=DASH 615 FIG(26/M)=DASH GO TO 900 620 DO 630 M=26dX 630 FIG(M/1)=AST GO TO 900

700 CALL PRISM (DEPTH/-DEPTH2,WIDTH,DIP/DENS/DX/GRAV) XINCH=DX*6. WRITEC6,2000)0EPTH,DEPTH2,WIDTH,DIP,DSNS,XINCH 2000 FORMAT(5X, 'DEPTH TO TOP =' , F8.1 ,', DEPTH TO 30TT0M=', + F8.1/'/ WICTH=',F3.1,', DIP=',F6.1,/,5X,'DENSITY CONTRAST + , F 5 . 2/ ' , SCALE: 1 " = ' , F 8 . 1 , ' F T . ' ) IDEP=DEPTH*RATIO/DX I= 2 5 -ID E P IOEP2=DcPTH2*RATIO/DX IWIDE=WIDTH/OX IFCIDEP.GT.24) GO TO 720 CALL OIAG(DIP,IX,FX,IDSP) IX L = 26~ IX IF(IXL.LT.I) GO TO 711 IXR=IXL+IWIDE DO 710 M=IXL,IXR IFCM.LT.1 .OR. M .GT. 51) GO TO 710 FIG(M,I)=VERT 710 CONTINUE 711 IF ( I0 E P 2 .G T .2 4 ) GO TC 720 CALL DIAG(DIP,IX,FX,IDEP2) I= 2 5 -ID E ? 2 IX L = 2 6 -IX IXR=IXL+IWIOE DO 715 M = IX L,IXR IF (M.LT.1 .OR. M.GT.51) GO TO 715 FIGCM,I)=V5RT 715 CONTINUE GO TO 900 720 CALL OIAG(DIP,IX,FX,25.) IX L = 2 6 -IX IXR=IXL+IWIDE C------— 30TTCM EDGE CF DRAWING OR CROSS-SECTION ------DO 725 M = IX L ,IX R IF (M .LT. 1 .OR. M.GT.5DG0 TC 725

QAIN 0A TLOD — TELFORD 2 . A/ A0 EQUATION —

52 53

c s - THE STATION SPACING c D - THE DENSITY CONTRAST c G - ARRAY CONTAINING THE CALCULATED STATION GRAVITY c DA 2 - DENSITY CONTRAST * RAD. OF SPHERE * * 3 / A CONSTANT c Z2 - OEPTH TO THE CENTER CF THE SPHERE SQUARED c X THE DISTANCE FROM THE POINT IMMEDIATELY ABOVE THE CEN c I / J ~ ARRAY INDICES

C * * * * DECLARATIONS * * * *

REAL Z/ A /X/O /G (51) /D A 3 /Z2/S INTEGER I/J

c INPUT PARAMETERS

5 WRITEC5/100) 100 FORMAT( / / ' '/'W HAT IS OEPTH TO CENTER OF SPHERE------> ' / $ ) READ(5/101/ERR=5)Z 101 FORMAT CF) IF (Z.LT .1 .) GO TO 5

6 WRITE(5/110) 110 FORMAT?//' '/'W H A T IS THE RACIUS CF THE SPHERE------> ' / $ ) READ(5/101/ERR=6)A IF?A.LT.1.) GO TO 6 IF(Z.GE.A) GO TO 7 WRITEC5/115) 115 F0RMATC2X/'ERROR! RADIUS GREATER THAN DEPTH') GO TO 5

7 WRITEC5/120) 120 FORMAT?//' '/'WHAT IS THE STATION SPACING------> ' / 3 ) READ?5/101/ERR=7)S IF?S.LT.0.001) S=A/5.

S WRITE?5/130) 130 FORMAT?//' '/'W HAT IS THE DENSITY CONTRAST------> ' / $ ) READ?5/101/ERR=S)0

C CALCULATION CF CONSTANTS

DA 3=0* ? A ** 3 . ) Z2 = Z ** 2. J=26 X = 0. 0

C LOAD ARRAY G

DO 1C I = 26/51 G ? I ) = 8.53E-3*?DA3/(Z2*??1.0+?**1.5))> G ? J) =G ?I ) X = X + S J=J-1 10 CONTINUE RETURN

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54

END

C /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/'w '

SUBROUTINE DIPROD

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55

C XNUM1 TEMPORARY VARIABLE FOR EQUATION C XNUM2 C XDEN1 C XDEN2 C TERM1 " " " " C TERM2 C XTERM VALUE OF EQUATION AT 'X ' C CONST CONSTANT MULTIPLIER C C INTEGER I LOOP INDEX COUNTER C J STATION NUMBER COUNTER C C REAL G(51)/ALPHA/ALRAO/AREA/R/Z/SIGMA/L/X/DELX REAL XNUM1/XNUM2/XDEN1/XDEN2/TERM1/TERM2/XTERM/CONST INTEGER I / J C c ------C C READ IN DATA FROM OPERATOR C WRITE(5/50 0) 500 FORMAT(' '/////10X/'TYPE IN VALUES FOR THE FOLLOWING:'////) C 1 WRITEC5/510) 510 FORMAT(' '/'E N T E R :RCD DIPANGLE (ALPHA) IN DEGREES: ' / $ ) READ(5/700/ERR=1) ALPHA C CHECK FOR ANGLE BETWEEN 0 -1 3 0 DEG. IF ( ( ALPHA.LE.0 .0 ).OR.(ALPHA.GE.130))G0T01 C C 2 WRITE(5/520) 520 FORMAT(' '/'E N T E R :R 0 C RADIUS (R) INFEET: '/S ) READ(5/700/ERR=2)R C CHECK FOR NEGETIVE RADIUS IF ( R .L E .Q .O ) G0T02 C C 3 WRITE(5/530) 530 FORMAT(' ' / ' ENTER:DEPTH TO TCP OF ROD (Z) IN FEET: '/$) READ(5/700/5RR=3)Z C 4 WRITE(5/540) 540 FORMAT( ' ' / ' ENTER: DENSITY CONTRAST (SIGMA): '/ $ ) READ(5/700/ERR=4)SIGMA C 5 1 WRITE (5 /5 5 0 ) 550 FORMAT( ' '/'E N T E R ROD LENGTH (L) IN FEET: */S ) READ(5/700/ERR=5)L C CHECK FOR NEGATIVE ROD LENGTH IF(L.LE.O.O)GOT05 C C 6 WRITE(5/560) 560 FORMAT( ' ' / ' ENTER: STAT ION SPACING (DELX) IN FEET: '/ $ )

56 57

RETURN END c/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/w

SUBROUTINE HCRROO ( Z / R/ L / Y / RHC/ DX/ G) C THE GRAVITY effEC T OF A BURIED HORIZONTAL ROC C FROM EQUATION 2 .4 2A / TELFORD ------C C WRITTEN BY J. PORTER AND MARK CALDWELL / OCT./ 1 983/ WMU C THIS SUBROUTINE WILL CALCULATE THE VERTICAL COMPONENT OF C GRAVITY OVER A BURIED HORIZONTAL ROD. THE ROD IS C ASSUMED TO BE PARALLEL TO THE Y-AXIS AND CENTEREO C UNDER THE X-AXIS AT A DEPTH Z. THE USER MAY SPECIFY C LENGTH/ RADIUS/ DENSITY CONTRAST ANO DEPTH OF BURIAL C OF THE ROD. BY INPUTTING SPECIFIED VALUES FOR X AND Y C IN FEET/ THE USER MAY GENERATE THE PREDICTED GRAVITY C EFFECT AT ANY POINT CN THE SURFACE. DISTANCES ARE IN C FEET AND G IS IN MGALS. C C *********vARIA 3LE DICTIONARY******************* C C K1=G*PI=CONSTANT=6.387 EXP -3 C R=RAOIUS OF ROD C RHO = DE NSIT Y CONTRAST C Z=DEPTH TO CENTER OF BURIED ROD

C Y = HORIZONTAL DISTANCE (PARALLEL) FROM CENTER OF ROD C L = L ENGTH OF ROD C DX=STATION SPACING C C G=OUTPUT=VERTICAL COMPONENT OF GRAVITY ( MGAL) C c c *****************VARIA3LE DECLARATION************* C REAL R/RH0/Z/DX/Y/L/G(51)/K1/K2/K3/X INTEGER I/M EPS = 1 .0 E -4 C C ENTER THE PARAMETERS C 20 WRITE(5/200) 200 FORMAT(' '/ 'T Y P E A VALUE FOR Y / (Y=C 3 LEFT END OF ROD) > READ(5/900/5RR=20)Y 30 W R IT E (5/800) 800 FORMAT(' '/'T Y P E A VALUE FOR THE RADIUS OF THE ROO ------> */S ) REA0(5/900/ERR=30)R IF(R.LE.0.00001) GO TC 30 50 WRITEC5/300) 300 FORMATC '/'TYPE A VALUE FOR Z > '/S) READ(5/900/ERR=50)Z IF ( Z .L T .O ) GO TO 50 IF(Z.LT.R) GO TO 50

------'/$) $ / ' > 58 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced c c CLUAE RA GRAV(X) ARRAY CALCULATE C ------r> o o o 0 TEMP(I/J)=A*((0.5*C(J))-(0.125*C(J)**3*P(2))+(C.0625*C(J)**5*P(4)) ) 4 ( P * 5 * * ) J ( C * 5 2 6 0 . C X ( + ) = ) X 2 ( P + * 3 D * * ) X J ( C * 5 2 1 . 0 ( - ) ) J ( C * 5 . 0 ( ( * 500 A = ) J / I ( P M E T 400 0 TM(1/ 1 TEMP( 300 ------6 FRAT(' '' DLA ') X DELTA : R E T N '/'E FORMA ' ( T 160 5 FRAC /ENTER: LENGTH') : R E T N '/'E FORMATC 150 3 FRA(' '' DPH O C O CYLINDER') OF TCP TO DEPTH : R E T N '/'E ' FORMAT( 130 4 FRMT(' /ENTER: EST CONTRAST') DENSITY : FOR R E T MAT N '/'E ( ' 140 2 FORMAT(F) 120 1 FRAC /ENTER: RADIUS') : R E T N '/'E FORMATC 110 0 CONTINUE 20 0 CONTINUE 10 5 RT(5/160) 1 / 5 WRITE( 15 4 TE(5/150) E IT R W 14 ITE(5/140) R W 13 2 RT( 130) 0 3 /1 WRITE(5 12 1 WRITEC5/110) 11 -(0.0390625*C(J)**7*P(6))) ) ) 6 ( P * 7 * * ) J ( C * 5 2 6 0 9 3 0 . 0 ( - + (0.125*3(J)**4*P(4))+(0.0625*E(J)**6*P(6))) ) ) 6 ( P * 6 * * ) J ( E * 5 2 6 0 . 0 ( + ) ) 4 ( P * 4 * * ) J ( 3 * 5 2 1 . 0 ( + 8(2)/C(2) 2 ( C / ) 2 ( 8 + : OSAT AU 2*(PI)*R*SIGMA ) I P ( * 2 VALUE CONSTANT A: RV GAIY EFFECT GRAVITY GRAV: : OAIN LN X AXIS X ALONG LOCATION X: O O 500 TOGO AD S(J). R) G T 300 TO GO ) .R E .L ) J ( S .AND. ) J ( S . E L . ) J ( Z ( F I 25 1 3 . - 2 * * ) J ( U * 5 2 6 5 . 6 + 4 * * ) J ( U * 5 7 8 6 . 9 1 - 6 * * ) J ( U * 5 7 3 4 . 4 1 = ) 6 ( P J) ( S / R = C ) J ( 5 7 3 . + 2 * * ) J ( U * 5 7 . 3 “ 4 * * ) J ( U * 5 7 3 . 4 = ) 4 ( P ( =U( ) (J U P(1 )= 5 . 0 - 2 * * ) J ( U * . 5 1 = ) 2 ( P 5 . 0 )/R * J ( * ) S ) J 2 )= ( * (J * /S B ) ) J J ( ( Z Z = + ) J 2 ( * * U X ( = ) J ( S O 0 1=26/51 10 DO X = 277*R*SIGMA 1 0 0 A=0. LT.0. DX=R/5. ) 1 0 0 .0 0 . T .L X D ( F I READ( 5 / 1 20/ERR=11 )R 20/ERR=11 1 / 5 READ( QAIN O LRE . TLOD E. .5 ) 2.45B EQ. (TELFORD/ X. LARGE FOR EQUATION / ) 2 ( U / ) 2 ( S / ) 2 ( Z / ) 2 / 1 5 ( P M E T / ) 1 5 ( V A R G / ) 6 ( P / G / L / A M G I S / R REAL QAIN O SAL O SAL . TLOD E 2.45A) EG (TELFORD/ R. SMALL OR X SMALL FOR EQUATION READ(5/120/ERR=15)DX (/2/ =14)L R R 0(5/120/E A E R ED(5/120/ERR / 0 = 2 1 13)SIGMA READ / 5 ( 51 ERR=12Z( ) (1 2)Z 1 = R R /E 0 (5/12 D A E R RVI=EP(1/ I2) (I/2 P M S T - ) /1 1 ( GRAV(I)=TEMP O 0 1=26/51 30 DO X = 0. 0 F Z(J) G. ) O O 400 TO GO R) .GT. ) J (Z IF ( F( G. .N. .T Z( O O 400 TO GO ) ) (J Z R.GT. .AND. R GT. ) .(S J IF ( O 0 /2 1 = J 20 DO ) Z1 + L + Z(1) Z ( 2)= F(L. O. O O 14 TO GO ) .O .O E .L L ( IF FCIGT. 52-) (I) V A R G -I)= 2 (5 V A R G ) 6 .2 T I.G C IF

* A = ) J

- ) ) 2 ( P * 2 * * ) J ( 8 * 5 . 0 ( + ) ) 1 ( F * ) J ( B - . 1 ( (

DECLARATIONS

------

30 CONTINUE RETURN END

C /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\V \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/w

SUBROUTINE DSHEET(DEPTH,THICK,LENG^DIP,DENS,CX,GRAV) c c * * * * * * * * * * * * 0 SHEET SUBROUTINE DESCRIPTION * * * * * * * * * * * * c c USES EQUATION 2 .4 6A , TELFORO ------c WRITTEN BY R. LEVISKA AND J. ZAPATA, OCT., 1983 FOR GL562 c THIS SUBROUTINE WILL CALCULATE 51 DIFFERENT GRAVITY VALUES c FOR A THIN DIPPING SHEET. ALL INPUTS WILL BE IN DEGREES c AND FEET. LISTED ARE THE FOLLOWING PARAMETERS: c c DEPTH - DEPTH OF BODY FROM SURFACE c THICK “ THICKNESS OF BODY c LENG - LENGTH OF BOCY c DENS - DENSITY CONTRAST c DX - CHANGE IN HORIZONTAL DISTANCE c

REAL DEPTH,THICK,LENG,DIP,DENS,DX,X, X A ,B ,C ,D ,0 1 ,D 2 ,E ,L ,G R A V (51 ) INTEGER N DATA RAD/0.01745329/ 10 WRITE(5,140Q) 1400 FORMAT(1H ,29HPLEASE ENTER DEPTH,THICK,LENG) READC5,1500,ERR=10) DEPTH, THICK, LENG 1500 FORMAT(3F) IF (DEPTH .LE. O.C) GO TO 10 IF (THICK .LE. O.C) GO TO 10 IF(LENG .LE. 0.0) GO TO 10 CONTINUE 20 W RITE(5,16 00) 1600 FORMAT <1H ,25HPLEASE ENTER DIP AND DENS) REAO(5,1700,ERR=20) CIP, OENS 1700 FORMAT (2F) IF (DIP .LT. 0.0 .OR. DIP .GT. 180.0) GO TO 20 CONTINUE 30 WRITE(5,1800) 1300 FORM AT(1H ,15HPLEASE ENTER OX) READ(5,1900,ERR=30) DX 1900 FORMAT(F) C C IF USER ENTERS 0 OR A NEGATIVE VALUE FOR OX C THEN THE PROGRAM WILL PROVIDE DX C IF (DX .GT. 0.0) GO TO 2100 OX = ((3.Q/2.G)*LENG)/25.0 2100 CONTINUE X = -26.*D X

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DO 51 N=1/51/1 A = 0.004C7*0ENS*THICK 3=((DfcPTH+LENG+SIN(DIP*RAD))**2+(X+LENG*COSCDIP*RAD))**2)/ X (X**2+0£PTH**2) C = 0.5*SIN(CIP*RAD)*AL0G10(3> D1=CDEPTH*SIN(DIP*RAD)+LENG+(X)*COS(DIP*RAD)) D2 = (CX)*SIh(DIP*RAO)“DEPTH*COS(DIP*RAD)) D = ATANCD1/D2) E=ATAN((DEPTH*SIN(DIP*RAD)+(X)*COSCDIP*RAO))/ X ((X)*SIN(DIP*RAD)“DEPTH*COS(DIP* R A D))) L = COS(DIP*RAD)*(0 - E) GRAV(N)=A*(C“ L) X=X+0X 51 CONTINUE RETURN END

C/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

C AUTHORS: DAVE COOK , ANN NEVERO C SUBROUTINE HSHEET C C USES EQUATION 2 .4 7 A , TELFORD ------C THIS FORTRAN PROGRAM CALCULATES THE GRAVITY EFFECT OF C A HORIZONTAL THIN SHEET OF VARIABLE LENGTH AND GIVEN THICKNESS C C VARIABLE DICTIONARY C C REAL Z-VERTICAL DEPTH TO CENTER OF SHEET OR SLAB C T-SLAB THICKNESS C SIGMA-OENSITY CONTRAST C DX-DISTANCE BETWEEN POINTS C X-OISTANCE FROM ZERO PT.CLENGTH IN FT.Q C L-LENGTH OF THE SHEET [FEET]/' MEASUREO TO RIGHT FROM ORIS C G < ) “ GRAVITY AT A GIVEN PT. C C INTEGER PNT-THE PT. IN QUESTION C I-LOCATION OF POINT ON X C SUBROUTINE HSHEET (Z/T/-L/SIGMA/OX/-G) C REAL Z/T,SIGMA,DX,X,G<51>,PI,L INTEGER PNT/I C C IN IT IA L IZ E VARIABLES C PNT = -25 PI = 3.1415927 1 = 0 C C INPUT THE DEPTH C 10 WRITE (5 ,1 0 0 ) 100 FORMAT(2X, 'WHAT IS THE DEPTH TO CENTER OF SHEET?')

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62

READ (5/200/ERR = 10) Z

200 FORMAT( F) 20 WRITE ( 5 /3 0 0 ) 300 FORMAT (2X/'WHAT IS THE SLAB THICKNESS?') READ (5/200/ERR = 20) T IF (Z.GT.2. 0*T) GO TC 400 WRITE (5 /3 5 0 ) 350 FORMAT (2X/'ERRR! OEPTH < 2* THICKNESS!') GO TO 10 400 WRITE ( 5 /5 0 0 ) 500 FORMAT (2X/'WHAT IS THE DENSITY CONTRAST?') READ (5/2 0 0 /E R R = 40C) SIGMA 30 WRITE (5 /6 0 0 ) 600 FORMAT (2X/'WHAT IS THE X-LENGTH OF THE SHEET') READ (5/200/ERR = 30) L 40 WRITE ( 5 /7 0 0 ) 700 FORMAT(2X/'WHAT IS THE OISTANCE BETWEEN POINTS?') READ (5/200/ERR = 40) DX IF (DX.LT.0.0001) DX = 2.0*Z/25.0 50 IF (PNT.GT.25) GO TO 70 X = PNT*DX 1 = 1 + 1 PNT = PNT + 1 G(I)=0.0C4O7*SIGMA*T*(ATAN((L-X)/Z)+ATAN(X/Z) ) GO TO 50 70 RETURN END

c/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

SUBROUTINE PRISM (3T/D8/B/ALPHA/DS/DX/G RAV) C*** GEOLOGY 562-GRAVITY AND MAGNETICS. C AUTHORS: DEMETRE VALINORAS & WILLIAM MORSE. C * ** THIS SUBROUTINE CALCULATES THE THEOROTICAL GRAVITY C FOR A CENTRAL STATION AND 25 STATIONS ON EITHER SIDE C OF THE CENTRAL STATION. C USESEQUATION 2 .4 9 A / TELFORD------C THE VARIABLES ARE DECLARED EXPLICITLY ONLY IF THEY C ARE SIGNIFICANT. THEY ARE NOT DECLARED BUT USED C IM PLICITLY IF THEY ARE ONLY INTERMEDIATE OR CONTROL C VARIABLES. A LIST OF THE VARIABLES FOLLOWS: C DT: DEPTH TO THE TOP OF THE PRISM C • DBS DEPTH TO THE BOTTOM OF THE PROSM. C B: WIDTH OF THE PRISM C ALPHA: ANGLE OF DIP CF THE PRISM. (MEASURED CCW) C OS: DENSITY CONTRAST OF THE PRISM C DX: STATION SPACING ON THE SURFACE. IF A VALUE C OF 0 .0 0 0 1 OR LESS IS INPUT THEN THE SPACING C IS CALCULATED ACCORDING TO: DX=3/6 C P I: THE CONSTANT P I. C ALPHAR: ALPHA IN RADIANS. C X ( 51 ) : ARRAY CONT A IN IGN THE STATIONDISTANCES FROM C THE CENTRAL STATION. NEGATIVE DISTANCES ARE C TO THE LEFT OF THE CENTRAL STATION/ POSITIVE

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63

C TO THE RIGHT. DISTANCES ARE IN FEET. C GR AV < 51 ): ARRAY WITH THE CORRECTIONS FOR EACH STATION. c THE REST OF THE VARIABLES ARE SELF EXPLANATORY. INTEGER I REAL DT/D3/8/ALPHA/DS/0X/PIxALPHAR/X(51)/ GR A V <51)/ SINArCCSA,SIN2A/C0TA,C0NST DATA PI/3.1415926536/

10 WRIT E(5✓1000) 1000 F O R M A T (//2 X ,'IN P U T DEPTH TO TOP & BOTTOM OF PR IS M :'S ) READC5/1005,ERR=10) 0T,D3 1005 FORMAT(2F) 11 WRITE(5✓1010) 1010 FORMATC/,2Xx'INPUT WIDTH OF PRISM & ANGLE OF C IP :'S > R E A 0(5 /1 005 ,E R R = 11) S,ALPHA 15 WRITE(5,1015> 1015 FORMAT(//2Xr'INPUT DENSITY CONTRAST S DELTA X:'$) READ(5/1005*ERR =15) CS/DX

1700 IF(DX.LT.0.QC01) DX=B/6.

ALPHAR=PI*ALPHA/180. SINA=SIN(ALPHAR) COSA=COS(ALPHAR) SIN2A=SINA**2 COTA=COSA/SINA CONST=O.OO407*DS 0 8 2 = 0 3 **2 DT 2 = 0T ** 2

DO 1200 1=1^51 X(I)=

FR1=(D32+CX FR3=(QS2+

G1=X (I)*SIN2A*0.5*L0G1+B*SIN2A*0.5*L0G2 G2=X

GRAV(I)=C0NST*(G1~G2+G3-G4) 1200 CONTINUE

RETURN END

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64

C C SU3R0UTINE FAULT c a u t h o r ; s a if u l b a h r i baharom c GEOPHYSICS 542 GRAVITY AND MAGNETIC METHODS c

C c THIS IS A SUBROUTINE TO CALCULATE THE GRAVITY EFFECT c OF A FAULT AT VARIOUS POINTS.THE INFORMATION NEEDED c TO DO THIS ARE : c 1) THE THICKNESS OF THE 3EO c 2) THE DEPTH TO THE RIGHT SIDE c 3) THE DEPTH TO THE LEFT SIDE c 4) THE ANGLE OF DIP OF THE FAULT (MEASURED CCW FROM L5F' c 5) THE AVERAGE DENSITY OF THE ROCK c 6) THE INCREMENT OESIRED FOR THE X-AXIS c THE ROUTINE IS BASED ON EQUATION 2.51A OF TELFORD ------c

C C DECLARATION CF VARIABLES SUBROUTINE FAULT ( Z1 / Z3 / THIK / DIP / D EN S / DX / GR A V) REAL 8/Q1/Q2/Q3/Q4/Y1/Y2/Y3/Y4/F1/F2/F3/F4/PI/X/Z2/Z4 REAL GRAVC51) INTEGER I DATA PI/RAD/3 . 1415926/0.01 745329/

C C INPUT OF DATA:THICKNESS/DEPTH TO RIGHT SIDE/DEPTH TO THE C LEFT S ID 5 /0 IP ANGLE/ AVERAGE DENSITY C AND THE X-AXIS INCREMENT. C 5 WRITE (5 /1 0 ) 10 FORMAT(2X/'ENTER THICKNESS/ DEPTH TO RIGHT SIDE/ DEPTH TO + LEFT S ID E ')

READ (5/20/ERR=5) THIK/Z1/Z3 20 FORMAT(3F) IFCTHIK.LT. (O.OD)GO TO 5 IFCZ1.LT.(O.C1))GO TO 5 IF C Z 3 .L T .C O .0 1 ) )G0 TO 5

25 WRITE (5 /3 0 ) 30 F0RMATC2X,'ENTER DIP ANGLE/AVERAGE DENS IT Y / X-INCREME NT')

READ (5/40/ERR=25) CIP/DENS/DX 40 FORMAT(3F) IF(OIP.LT.(0.00001>)G0 TO 25 IFCDIP.GT.(180.0))GO TO 25 ROIP = DIP * RAD

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65

IF (DX.LT.(0.000001)) DX = 23 / 5.0 Z2 = Z1 + THIK Z4 = Z3 + THIK C

C C C LOOP FOR CALCULATING THE GRAVITY VALUES AT VARIOUS POINTS C 50 I = 1/51 X • ( I - 26 ) * CX IF ( I . EQ . 26 ) GO TO 45 B = ( PI / 2. - ROIP ) Q1 = A TAN ( X / Z1 + SIN(B)/COS(5) ) Q2 = AT AN ( X / Z 2 + SIN<3)/COS(3) ) Q3 = ATAN < X / Z 3 + SIN<3)/COS(B) ) Q4 = ATAN C X / Z 4 + SIN(B)/COS(B) ) Y1 = ( Q1 - 3 ) Y2 ( Q2 - B ) Y3 = ( Q3 - B ) Y 4 = ( Q4 - 3 ) F1 Y1 * ( COS ( Y1 ) / SIN (Y1)) - AL0G10> F 2 = Y 2 * ( COS < Y 2) / SIN (Y 2) ) “ AL0G10(ABS(SIN(Y2))) F3 Y3 * ( COS < Y 3) / SIN ( Y3) ) - AL0G10(ABS(SIN(Y3))) F4 = Y4 * ( COS C Y4) / SIN ( Y4) ) - AL0G10(ABS(SIN(Y4)))

GRAV(I)=0.00407*DENS*(PI*THIK+X* + (COS (B))**2*(F2-F1-F4+F3)) 45 IF (ABS(X) .LT.0.00001)GRAV(I )=0.004G7*DENS*PI*THIK C------SUBTRACT THE BACKGROUND CONSTANT GRAV DUE TO THE ENTIRE S L A 5. GRAV(I)=GRAV (I) - C.01277 * OENS * THIK 50 CONTINUE RETURN END

c/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

SUBROUTINE GRAPH(Y/N/ AMIN / AMAX) C WRITTEN BY W. A. SAUCK/ U. OP ARIZONA/ 1969. C— MODIFIED FOR WMU DEC1099 IN OCT./ 1983. C— PLOTS VALUES OF Y FOR EACH OF N VALUES OF X. (N) IS SIZE OF Y ARRAY. C— SUBROUTINE CALCULATES MIN AND MAX VALUES OF Y UNLESS THEY ARE C— SUPPLIED AS NON-ZERO VALUES BY CALLING ROUTINE. DIMENSION Y ( 511/ CHAR(81> COMMON F IG C 51/25) DATA BLANK/PL /A S T /D 0T/1H /1 H + /1 H * /1 H . / 200 FORMAT(53X/*GRAVITY ANCMALY'/1 7X/5(1 OX/ F10 .4 )/34X/1 H:/ 14(19X/1H:)) 300 F0RMAT(6X/22 ( ' ...... ')) 400 FORMAT (' . ' / 25A1 / ' . . '/3 1 A1 / 1 H .) IFCAMIN.NE.O..AND.AMAX.NE.O.) GO TO 11 YMIN = Y (1) YMAX = Y (1) DO 10 I=1/N IF(YMIN.LT.Y (I)) GO TO 5

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66

YMIN = Y ( I ) GO TO 10 5 IF(YMAX.GT.Y(I ))GO TO 10 YMAX=Y(I) 10 CONTINUE IF(ABSCAMIN). LE.0 .0000CC1) GO TO 12 11 YMIN = AMIN 12 IF(A3S(AMAX).LE.O.0OOOCG1) GO TO 14 13 YMAX = AMAX 14 YRANGE = YMAX-YMIN SF=30./YRANGE Y1Q = YMIN+YRANGE/ 4. Y2Q = YMIN+YRANGE/2 . YTQ = YMIN + . 75 *YRANGS WRITE (6/200) YMIN/Y1G/Y2Q/YTQ/YMAX WRITE (6 /3 0 0 ) DO 20 IJ= 1/N DO 15 K=1/81 15 CHAR(K) = BLANK IF(IJ-(IJ/3)*3)152,151/152 151 CHAR( 2 1 ) = QOT CHAR( 4 1 ) =DQT CHAR(61)=D0T C— NEXT 5 STMNTS PUT VERTICAL LINES AT UNIFORM INTERVALS GIVEN ON C— NEXT CARD. 152 IFCIJ-(IJ/18)*18) 13/16/13 16 CHAR( 1 )=PL DO 17 K=1 / 7 1 / 1 C CHAR( K) = DOT 17 CHARCK+5) = PL 18 I=(Y(IJ)-YMIN)*SF+1.5 C— NEXT 2 CARDS ALLOW + OR - 100 PERCENT ERROR IN ESTIMATING C— AMIN AND AMAX. IFCI.GT.81) 1=1-30 IF(I.LT.1 ) 1=1+80 19 CHAR( I ) = AST 20 WRITE (6 /4 0 0 ) ( F IG <1J / I I ) / I I = 1/25 ) / CHAR WRITEC6/300) RETURN END

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B

GRAVITY DATA

BOUG.AN STN. LATITUDE LONGITUDE ELEV. OSS• GRAV. FR.AIR

8 7 4 1 3 ’ : 2 ? 7 l 82 " a 41 5 3 .8 3 35~56Too’ 36375 9 8 0 2 7 6 7 6 6 5 -21 .2 0 8 A 41 5 3 .3 3 85 5 6 .0 0 8 6 8 .0 9 8 0 2 7 6 .6 4 0 8 .3 8 8 -21 .135 A 41 5 3 .8 3 85 5 6 . OC 8 6 8 .0 9 3 0 2 7 6 .6 6 2 8 .4 1 0 8 .1 0 6 - 2 1 . 5 9 1 AE1 41 5 3 .8 0 85 5 5 .1 3 871 .0 9 8 0 2 7 6 .0 3 2 - 2 1 . 2 0 0 AE 2 41 5 3 .8 8 85 5 4 .8 3 8 7 7 .0 9 8 0 2 7 6 .1 8 4 8 .7 0 2 8.8 71 - 2 1 . 2 3 6 AE3 41 5 3 .5 5 85 5 3 .6 8 8 8 3 .0 9 8 0 2 7 5 .2 9 4 1 0 .0 4 9 - 2 1 . 0 8 1 AE 4 41 5 3 .5 3 85 5 3 .0 8 9 1 3 .0 9 8 0 2 7 3 .6 1 9 1 0 .3 5 9 - 2 0 . 9 4 1 AE 5 41 5 3 .6 0 85 5 2 .5 0 9 1 8 .0 9 8 0 2 7 3 .5 6 5 . 1 0 . 4 2 4 - 2 0 . 9 1 0 AE6 41 5 3 .8 5 85 5 2 .5 0 9 1 9 .0 9 8 0 2 7 3 .9 0 9 - 2 0 . 3 4 9 AE7 41 5 3 .8 3 85 5 2 .0 0 9 2 6 .0 9 8 0 2 7 3 .5 2 1 1 0 .7 2 4 1 0 .6 3 5 - 2 0 . 6 3 1 AES 41 5 3 .3 0 35 5 2 .0 0 9 1 7 .0 9 8 0 2 7 3 .4 8 5 - 2 0 . 9 3 2 AN1 41 5 4 .6 8 85 5 6 .0 0 8 7 0 .0 9 8 0 2 7 8 .0 6 6 8 .7 3 1 9 .3 3 5 - 2 0 . 5 6 7 AN10 41 5 5 .1 0 85 5 4 .8 5 8 7 7 .0 9 8 0 2 7 8 .6 4 0 8 .6 4 8 - 2 0 . 6 0 6 AN11 41 5 4 .6 8 85 5 4 .8 5 8 5 8 .0 9 8 0 2 7 9 .1 1 2 - 2 0 . 9 1 8 AN12 41 5 4 .2 5 85 5 4 .8 3 381 .0 9 8 0 2 7 6 .7 7 7 9 .1 2 0 1 0 .4 8 3 - 2 0 . 5 7 8 AN13 41 5 4 .1 5 85 5 2 .5 0 911 .0 9 8 0 2 7 5 .1 7 0 - 2 0 . 7 4 6 AN2 41 5 5 .1 0 85 5 6 .0 0 8 9 0 .0 9 S 0 2 7 7 . 681 9 .6 0 0 - 2 0 . 6 4 3 AN3 41 5 5 .1 0 85 5 7 .1 5 331 .0 9 8 0 2 7 8 .3 2 3 9 .3 9 6 9 .5 6 7 - 2 0 . 8 1 2 AN4 41 5 5 .1 0 85 5 8 .3 0 89'1 . 0 9 8 0 2 7 7 .5 5 5 9 .6 2 4 -21 .1 3 0 AN5 41 5 5 .5 5 85 5 8 .3 0 9 0 2 .0 9 8 0 2 7 7 .2 5 1 1 0 .1 4 3 - 2 0 .2 7 1 AN6 41 5 5 .5 5 85 5 7 .1 5 8 9 2 .0 9 8 0 2 7 8 .7 1 0 - 2 0 . 4 8 1 AN7 41 5 5 .5 5 35 5 6 .5 0 8 9 3 .0 9 8 0 2 7 8 .4 4 0 9 .9 6 7 - 2 0 . 2 3 0 AN8 41 5 5 .5 3 85 5 4 .2 5 8 8 7 .0 9 8 0 2 7 8 .9 7 0 9 .9 6 3 - 2 0 . 0 2 3 AN9 41 5 5 .5 5 85 5 4 .8 5 8 7 8 .0 9 8 0 2 7 9 .7 9 7 9 .9 1 3 -2 1 .8 1 7 AW1 41 5 3 .8 3 85 5 8.2 8 8 7 5 .0 9 3 0 2 7 5 .6 1 0 3 .0 1 7 8 .3 1 9 - 2 2 . 4 3 5 AW2 41 5 3 .8 5 86 0 .6 5 9 0 2 .0 9 8 0 2 7 3 .4 0 4 -21 .8 5 7 B 41 5 3.0 0 85 5 6 .0 0 3 5 4 .0 9 8 0 2 7 5 .5 9 0 7 .2 6 1 -21 .8 6 5 3 41 5 3 .0 0 35 5 6 .0 0 8 5 4 .0 9 8 0 2 7 5 .5 8 2 7 .2 5 3 - 2 1 . 8 1 3 B 41 5 3 .0 0 85 5 6 .0 0 8 5 4 .0 9 8 0 2 7 5 .6 2 9 7 .3 0 0 - 2 0 . 9 6 4 BE1 41 5 3 .1 8 85 5 5 .1 0 8 6 3 .0 9 8 0 2 7 6 .2 1 2 8 .4 6 1 -2 1 .5 2 8 3£2 41 5 2 .9 5 85 5 3 .6 8 881 .0 9 8 0 2 7 4 .2 2 5 8.511 BE3 41 5 2 .9 0 85 5 2 .8 5 9 1 3 .0 9 8 0 2 7 2 .4 5 6 9 .3 2 6 -21 .303 -21 .272 BE4 41 5 2 .9 0 85 5 2 .5 0 9 1 5 .0 9 8 0 2 7 2 .3 6 8 9 .9 2 6 - 2 0 . 9 2 2 3E5 41 5 2 .9 0 85 5 2 .0 0 9 1 8 .0 9 3 0 2 7 2 .5 3 8 1 0 .3 7 8 BU1 41 5 2 .9 8 85 57.1 5 8 6 3 .0 9 8 0 2 7 4 .6 5 5 7 .2 0 3 - 2 2 . 2 2 2 - 2 2 . 7 3 2 BW 2 41 5 2 .9 8 85 5 8 .3 0 8 6 5 .0 9 8 0 2 7 3 .9 7 5 6 .7 11 - 2 3 . 2 6 6 BW3 41 5 3 .0 0 86 0 .6 5 8 9 2 .0 9 8 0 2 7 1 .9 0 2 7 .1 4 7 3W4 41 5 3 .0 0 86 1 .8 0 8 9 2 .0 9 8 0 2 7 2 .2 2 1 7 .4 6 6 - 2 2 . 9 4 8 - 2 3 . 3 6 4 C 41 5 1 .6 5 85 5 6 .0 5 8 6 8 .0 9 8 0 2 7 1 .2 2 5 6 .2 3 1 - 2 3 . 0 3 6 C • 41 5 1 .6 5 85 5 6 .0 5 8 6 8 .0 9 3 0 2 7 1 .5 5 3 6 .5 6 0 c 41 51 .65 85 5 6 .0 5 8 6 3 .0 9 8 0 2 7 1 .5 7 4 6 .5 81 - 2 3 . 0 1 4 - 2 3 . 2 1 5 CE1 41 5 1 .6 5 85 5 5 .1 5 8 9 7 .0 9 8 0 2 6 9 .6 3 5 7. 369 - 2 2 . 8 8 6 CE2 41 5 1 .6 3 85 5 4 .5 8 8 9 3 .0 9 8 0 2 7 0 .1 7 5 7 .5 6 2 - 2 2 . 4 0 8 CE3 41 51 .6 3 85 5 4 .0 0 8 8 9 .0 9 8 0 2 7 0 .8 9 3 7 .9 0 3

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68

-22.173 CE4 41 51 .60 85 52.85 848 .0 980273.541 6.740 -20.580 CE5 41 51.15 85 51 .10 910.C 980270.742 10.447 -20.303 CE6 41 51 .60 85 51.10 913.0 980271 . 51 3 10.826 -22.424 CN 41 52.28 85 56.00 854.0 980273.946 6.694 -22.262 CN1 41 52.28 85 55.13 862.0 980273.628 7.129 -22.494 CN 2 41 52.25 85 54.00 904.0 980270.833 8.329 -22.040 CN3 41 52.25 85 52.83 901 .0 980271.467 8.681 CN4 41 52.03 85 51.10 920.0 980271.450 10.780 -20.588 -22.899 CNW1 41 52.33 85 57.33 849.0 980273.846 6.049 CNW2 41 52.68 85 58.90 862.0 980273.719 6.621 -22.770 -23.344 CNW3 41 52.60 86 0.05 871 .0 980272.485 6.354 CNW4 41 52.60 86 0.60 884.0 930271.533 6.625 -23.516 CNW5 41 52.1 5 86 1 .00 856.0 980272.132 5.263 -23.923 CN W6 41 51 .28 86 1.75 864.0 980269.089 4.271 -25.187 CNW7 41 51 .33 86 0.30 832.0 930271.570 3.669 -24.699 CNWS 41 52.15 86 C .05 862.0 980271.940 5.636 -2 3.755 CS1 41 51.20 35 56.05 339.0 980271.733 4.685 -23.922 CS10 41 49.50 85 58.38 846.0 980266.621 .2.772 -26.073 CS11 41 49.05 85 58.40 841 .0 980265.835 2.188 -26.487 CS12 41 48.43 35 58.40 813.0 980265.506 0.151 -27.569 CS2 41 50.30 85 56.05 924.0 98C263.673 5.964 -25.541 CS 3 41 49.45 85 56.08 911 .0 980261.911 4.251 -26.810 CS A 41 49.50 85 57.53 880.0 980264.736 4.085 -25.919 CS5 41 49.25 85 56.68 900.0 9S0261.670 3.274 -27.412 CS6 41 49.45 85 56.68 900.0 980263.179 4.484 -26.202 CS7 41 5C.33 85 57.20 937.0 980263.320 6.789 -25.159 CSS 41 51 .20 85 58.35 842.0 980272.104 5.338 -23.371 CS 9 41 50.33 85 50.35 895.0 980265.141 4.659 -25.857 CW1 41 51.70 85 '57.15 839.0 980272.395 4.598 -24 .009 CM2 41 51.70 85 58.33 831 .0 980273.312 4.763 -23.571 D 41 50.80 85 56.05 880.0 980267.654 5.060 -24.945 0 41 50.80 85 56.05 880.0 980267.864 5. 270 -24.735 D 41 5G.30 85 56.05 880.0 980267.896 5.301 -24.704 DE1 41 50.55 85 54.90 914.0 930265.479 6.456 -24.708 DE2 41 50.53 35 53.73 924.0 980266.107 8.055 -23.450 DE 3 41 50.53 85 52.85 935.0 980266.222 9.204 -22.676 -25.078 DW1 41 50.78 85 57.13 904.0 980266.052 5.745 DM 2 41 5G.80 85 58.35 851 .0 980269.471 4.148 -24.867 DM3 41 50.78 85 59.40 842.0 930269.944 3.806 -24.903 E 41 49.90 85 56.05 943.0 980261.402 6.079 -26.073 E 41 49.90 85 56.05 943.0 980261.420 6.097 -26.056 E 41 49.90 85 56.05 943.0 980261.468 6.145 -26.008 E 41 49.90 85 56.05 943.0 980261.537 6.214 -25.939 EE 1 41 49.90 85 54.90 936.0 930262.346 6.364 -25.550 EE1 41 49.90 85 54.90 936.0 980262.497 6.516 -25.398 EE 2 41 49.90 85 53.75 911.0 980265.351 7.018 -24.044 EE 2 41 49.90 85 53.75 911 .0 980265.292 6.959 -24.102 -22.364 EE3 41 49.90 85 52.85 897.0 930267.869 8.220 EE3 41 49.90 85 52.85 897.0 980267.991 8.342 -22.242 EE A 41 49.20 85 51.98 357.0 980270.798 8.431 -20.790 EES 41 49.85 85 50.88 872.0 980272.657 10.730 -19.001 E56 41 49.85 85 50.30 862.0 980274.043 11.176 -18.215 EE7 41 49.85 85 49.15 921 .0 980270.457 13.139 -18.264 ESE1 41 49.43 85 54.93 908.0 980263.067 5.154 -25.805 ES52 41 49.43 85 53.75 888.0 980265.318 6.024 -24.253

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69

ESE3 41 49.43 85 52.58 895 0 980263.166 9.030 -21 .486 EW1 41 49.90 85 56.63 955 0 980260.532 6.383 -26.174 EW1 41 49.90 3556.63 955 0 980260.621 6.427 -26.135 EW10 41 49.90 85 56.35 936 0 980261.729 5.747 -26.167 EW11 41 49.90 85 56.95 945 0 980261.395 6.260 -25.961 EW12 41 49.90 35 57.50 910 0 980263.438 5.012 -26.016 EW1 3 41 49.90 85 58.30 912 0 980262.979 4.696 -26.399 EW14 41 49.90 85 53.63 875 0 930265.407 3.613 -26.221 EW15 41 49.90 85 59.20 828 0 980268.500 2.285 -25 .946 EW16 41 49.70 85 59.00 850 0 980265.934 2.162 -26.819 EW17 41 49.50 8 5 59.00 847 0 980267.212 3.457 -25 .422 EW18 41 49.30 85 59.00 822 0 930267.756 1.948 -26.079 EW1 9 41 49.08 85 58.75 840 0 980266.200 2.414 -26.226 EW2 41 49.90 85 57.20 915 0 980263.304 5.347 -25.351 EW2 41 49.90 85 57.20 915 0 980263.138 5.230 -25.967 EW20 41 49.05 85 58.15 342 0 980265.328 1.774 -26.934 EW21 41 49.05 85 57.65 882 0 930262.932 3.141 -26.932 EW22 41 49.28 85 58.40 355 0 980265.403 2.729 -26.423 EW23 41 49.70 85 58.40 880 0 980264.273 3.323 -26.681 EW24 41 49.70 85 56.65 930 0 980261.320 5.573 -26.136 EW25 41 49.70 85 56.05 910 0 980262.793 4.665 -26.362 EW26 41 48.83 85 56.08 874 0 980262.771 2.556 -27.244 EW27 41 49.25 85 56.05 905 0 930261.748 3.822 -27.035 EW3 41 49.90 35 57.80 919 0 980262.959 5.379 -25.955 EW3 41 49.90 85 57.80 919 0 980262.968 5.388 -25.946 EW4 41 49.90 85 58.35 393 0 980263.820 4.227 -26.392 EU4 41 49.90 85 58.35 898 0 980263.881 4.287 -26.331 EW5 41 49.90 85 58.95 862 0 980266.104 3.163 -26.228 EW5 41 49.90 85 58.95 862 0 980266.127 3.1 86 -26.205 EW6 41 49.90 85 59.38 816 0 980269.335 1.991 -25.831 EM6 41 49.90 85 59.38 816 0 980269.365 2.021 -25.801 EW7 41 50.35 86 0.33 806 0 980270.313 1.437 -26 .045 EWS 41 5C.43 86 1.80 836 0 980269.190 2.935 -25.570 EW9 41 49.83 86 1 .80 828 0 980267.830 1 .795 -26.436 F 41 48.60 85 56.10 867 0 980262.694 2.165 -27.396 F 41 48.60 85 56.10 867 0 980262.749 2.220 -27.341 F 41 48.60 85 56.10 367 0 980262.904 2.375 -27.186 F 41 48.60 85 56.10 867 0 980262.557 2.027 -27.534 F 41 48.60 35 56.10 867 0 980262.811 2.281 -27.280 -26.740 FE1 41 48.60 85 54.90 879 0 980262.631 3.23C FE2 41 48.60 85 53.75 888 0 980264.319 5.766 -24.512 FF3 41 48.60 85 52.80 897 0 980265.915 8.203 -22.376 FE4 41 48.60 85 51 .95 878 0 980268.171 8.677 -21 .259 FE5 41 48.55 85 50.83 871 0 980269.512 9.434 -20.264 FE 6 41 48.55 85 50.05 775 0 980277.257 8.149 -18.275 -27.434 FW1 41 48.33 85 56.70 883 0 980262.041 2.673 FW2 41 49.05 85 57.53 371 0 980263.935 3.159 -26.533 FW3 41 49.05 85 57.95 864 0 980264.130 2.646 -26.813 FW.4 41 49.08 85 59.00 303 0 980267.545 0.273 -27.101 FW5 41 49.08 86 0.05 807 0 980267.002 0.111 -27.404 FW6 41 49.05 36 1.75 817 0 980266.635 0.729 -27.127 G 41 48.15 85 56.13 853 0 980262.598 1.425 -27.659 G 41 48.15 85 56.13 853 0 980262.643 1.470 -27.614 G 41 48.15 85 56.13 853 0 980262.729 1.557 -27.527 G 41 48.15 35 56.13 853 0 980262.547 1.374 -27.710

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70

-27.788 GE1 A1 48.15 85 54.98 891 0 980260.190 2.592 -25.202 GE2 A1 48.10 85 53.80 882 0 980263.240 4. 870 -22.941 GE3 A1 49.10 85 52.00 884 0 980266.377 7.200 -25.727 GSE1 A1 47.70 85 53.80 887 0 980261.818 4.51 6 -28.239 GSW1 A1 47.85 85 57.25 823 0 980263.068 -0.008 -28.518 GSW2 41 47.75 85 58.43 £44 0 980261.681 0.259 -28.434 GSU3 A1 47.75 85 54.45 804 0 980264.164 - 1.021 -29.462 H 41 47.30 85 56.15 374 0 930258.266 0.338 -29.288 H 41 47.30 85 56.15 874 0 980258.439 0.512 H A1 47.30 85 56.15 874 0 980258.325 0.397 -29.402 -28.614 HE1 A1 47.23 85 55.00 878 0 980258.344 1.322 -21.053 HE 2 41 47.25 85 50.85 314 0 980270.198 6.701 -29.265 HW1 41 47.30 85 57.00 848 0 930260.021 -0.352 -29.644 HW2 41 47.28 85 58.45 336 0 980260.333 -1=140 -28.492 HW3 41 47.35 86 0.63 324 0 980262.309 -0.396 -28.693 HVI4 41 47.53 86 1 .50 812 0 930263.097 -1.007 -29.492 I 41 46.85 85 56.15 850 0 980259.002 -0.511 -29.509 I 41 46.85 85 56.15 850 0 980258.985 -0.527 -29.093 IE1 41 46.83 85 55.00 848 0 980259.491 -0.180 1 .366 -26.865 IE2 41 46.80 85 53.85 823 0 98G262.873 -29.454 IW1 41 46.85 85 57.00 846 0 980259.280 -0.608 IW 2 41 46.88 85 58.45 825 0 980260.401 -1.507 -29.636 -29.505 IW3 41 46.90 86 0.50 816 0 980261.103 -1 .683 -29.569 IMA 41 46.90 36 0.65 814 0 980261.158 -1.815 -29.422 IW5 41 46.90 86 1.30 814 0 980261.306 -1 .668 J 41 46.15 85 56.15 802 0 980260.594 -2.388 -29.733 -29.769 J 41 46.15 85 56.15 302 0 980260.558 -2.424 JE 1 41 46.20 85 55.00 803 0 980261.198 -1.764 -29.143 JNW1 41 46.60 35 58.45 816 0 980260 = 269 -2.069 -29.892 -28.009 JSE1 41 45.95 85 53.88 782 0 930263.219 -1.346 JSE2 41 45.95 85 52.33 791 c 980266.424 2.706 -24.264 -21.553 JSE3 41 45.90 85 5C.88 787 0 930269.299 5.280 JW1 41 46.10 85 57.40 802 0 980259.792 -3.114 -30.459 -30.830 JW 2 41 46.00 35 58.50 303 0 980259.212 -3.451 JW3 41 46.03 36 0.05 797 0 980259.193 -4.079 -31 .254 JWA 41 46.00 86 1 .20 805 0 980259.312 -3.163 -30.610 K1 41 53.03 86 5.30 857 0 980275.544 7.452 -21.768 K1 G 41 50.38 86 4.10 861 0 980267=957 4.203 -25.153 -24.747 K1 1 41 51 .25 86 2.95 873 0 980263.645 5.189 K1 2 41 51 .70 86 2.95 869 0 980270.485 5.511 -24.119 K13 41 52.58 86 2.95 870 0 980273.452 7.257 -22.407 K1 A 41 53.03 86 2.98 884 0 980273.992 8.440 -21 .700 -21.266 K15 41 53.85 86 2.98 866 0 980276.731 8.261 K1 6 41 54 = 63 86 3.15 851 0 980279.698 8.576 -20.439 K17 41 54 = 70 86 5.23 820 0 980281.872 7.804 -20.155 K18 41 53.35 86 5.20 825 0 930280.158 7.331 -20.298 K1 9 41 53.78 86 6.00 796 0 980281.480 6.531 -20.609 K2 41 51.25 86 5.25 869 0 980270.223 5.921 -23.708 K3 41 50.40 86 5.25 873 0 980267.706 5.051 -24.715 KA 41 49.10 86 5.28 856 0 980265.481 3.171 -26.015 K5 41 46.95 86 3.00 801 0 980262.093 -2.179 -29.490 -23.134 K6 41 47.85 86 3.00 815 0 980263.953 -0.346 K7 41 49.08 86 2.70 831 0 980265.966 1.333 -27.001 -26.496 K8 41 49.55 86 3.15 351 0 980265.973 2.520 K9 41 5C.33 86 2.50 845 0 980268.323 3.069 -25.742

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BIBLIOGRAPHY

Beals, C. S. A probable meteorite crater of Precambrian age at Holleford, Ontario. Pub. Pom. Obs. (Ottawa), 1960, 24(6), 117-142.

Beals, C. S., Innes, M. J. S., & Rottenberg, J. A. Fossil meteorite craters: The solar system. In B. M. Middlehurst & G. P. Kuiper (Eds.), The Moon, Meteorites and Comets, Vol. 4. Chicago, IL: University of Chicago Press, 1963. Pp. 235-284.

Black, D. F. B. Cryptoexplosion structure near Versai'Hes, Kentucky. U.S. Geol. Surv. Prof. Paper 501B, 1964. Pp. 9-12.

Bucher, W. H. Cryptoexplosion structures caused from within or without the earth (Astroblemes or Gleoblemes?). Am. J. Sc., 1963, 261, 567-649.

Buschbach, T. C., & Ryan, Robert. Ordovician explosion structure at Glasford, Illinois. AAPG Bull. , 1963, 47(12), 2015-2022.

Cohee, G. V ., & Landes, K. K. Oil in the Michigan Basin. In L. G. Weeks (Ed.), Habitat of Oil, Vol. 42, Amer. Assoc. Petrol. Geol., 1958. Pp. 473-493.

Daniels, D. L. Personal Communication, May 1983.

DeHaas, R. J. Personal Communication, Nov. 1983.

Dence, M. R ., Innes, M. J. S ., & Robertson, P, B. Recentgeological and geophysical studies o f the Canadian craters. In B, M. French & N. M. Short (Eds.), Shock Metamorphism of Natural M aterials. Baltimore, MD: Mono Book Corp., 1968. P. 339.

Dence, M. R., Innes, M. J. S., & Baals, C. S. On the probable meteorite origin of the Clearwater Lakes, Quebec. Royal Astron. Soc. Canada J . , 1965, 59, 13-22.

Dence, M. R ., & Popelar, J. Evidence fo r an impact origin for Lake Wanapitei, Ontario. Geol. Assoc. Canada Spec. Paper 10, 1972.

Dennis, J. G. Ries structure, southern Germany. A review. J. Geophys. Res., 1971, 76, 5394-5406.

Dietz, R. S. Shatter cones in cryptoexplosion structures. In B. M. French & N. M. Short (Eds.), Shock Metamorphism of Natural M aterials. Baltimore, MD: Mono Book Corp., 1968. Pp. 267-285.

Dobrin, M. B. Introduction to Geophysical Prospecting, 3rd ed. New York: McGraw-Hill, 1976. P. 630.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72

Ells, G. D. Architecture of the Michigan Basin. In Stonehouse (Ed.), Studies of the Precambrian of the Michigan Basin. Mich. Basin Geol. Soc. Ann. Excursion, 1969. Pp. 60-88.

Enge'lhardt, W. Von. Impact structures in Europe. In G. J. H. McCall (Ed.), Astroblemes - Cryptoexplosion Structures, Vol. 50. Strouds burg, PA: Dowden, Hutchinson & Ross, Inc., 1979, and Internat. Geol. Congr., 24th Proc., 1972, 1_5, 90-111.

Fisher, J. H. Early paleozoic history of the Michigan Basin. In H. B. Stonehouse (Ed.), Mich. Basin Geol. Soc. Ann. Excursion, 1969. Pp. 89-93.

French, B. M., & Short, N. M. Shock Metair.orphism of Natural Materials. Baltimore, MD: Mono Book Corp., 1968.

Grieve, R. A. F. The record of impact on earth: Implications for a major cretaceous te rtia ry impact event. Geol. Soc. Am. Spec. Paper 190, 1982.

Gutschick, R. C. Geologyof the Kentland impact structural anomaly, northwestern Indiana. FieldGuide for Nat. Assoc. Geol. Teachers, East-Central Sec., 1971.

Geometries, 1979. Operating Manual: Model G 816, Portable Proton Magnetometer. Sunnyvale, CA. 1979.

Heiskanen, W. A., & Vening Meinesz, F. A. The Earth and Its Gravity Field. New York: McGraw-Hill, 1958. P. 470.

Hinze, W. R. Regional gravity and magnetic anomaly maps of the southern peninsula of Michigan. Mich. Geol. Surv., Rept. Inv. 1, 1963, P. 26.

Hinze, W. J ., & M erritt, D. W. Basement rocksof southern peninsula of Michigan. In H. B. Stonehouse (Ed.), Mich. Basin Geol. Soc. Guidebook, Studies of the Precambrian of Michigan, 1969, Pp. 28-59.

Hinze, W. J ., M erritt, D. W., & Kellogg, R. L. Gravity and aeromagnetic anomaly maps of the southern peninsula of Michigan. Mich. Geol. Surv. Rep. Inv. 14, 1971, P. 16.

Innes, M. J. S. The use of gravity methods to study the underground structure and the impact energy of meteorite craters. J. Geophys. Res., 1961, 66, 2235.

Innes, M. J. S., Recent advances in meteorite crater research at the Dominion Observatory, Ottawa, Canada, Meteoritics, 1964, 2, 219-241.

Innes, M. J. S., Pearson, W. J ., & Geuer, J. W. The Deep Bay crater. Pub. Dorn. Obs. (Ottawa), 1964, 31_(2), 39.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73

James, W. R. Fortran IV program using double fo u rier series for surface fitting of irregularly spaced data. Computer Contr. 5, State Geol. Surv., Univ. Kansas, 1966B.

Kellogg, R. L. An Aeromagnetic Investigation of the Southern Peninsula of Michigan. Ph.D. Thesis, Michigan State University. 1971.

Lowell, J. D. Spitsbergen tertiary orogenic belt and the Spitsbergen fracture zone. Bull. Geol. Soc. Amer., 1972, Vol. 83.

Masaytis, V. L ., Mikhaylov, M. V., & Selivanovskaya, T. V. The Popigay meteorite crater. Internat. Geol. Rev., 1971, J4, 327-331. In G. J. H. McCall (Ed.), Astroblernes - cryptoexplosion structures. Benchmark Papers in Geology, Vol. 50, 1979. Stroudsburg, PA: Dowden, Hutchinson & Ross, In c ., 1979.

Mata, F ., Jr. Personal Communication. July 1982.

McCall, G. J. H. (Ed.), Astroblemes - cryptoexplosion structures. Benchmark Papers in Geology, Vol. 50, 1979.

Merritt, D. W. A Gravitational Investigation of the Scipio Oil Field in H illsdale County, Michigan, with a Related Study for Obtaining a Variable Elevation Factor. Ph.D. Thesis, Michigan State University. 1968.

Middlehurst, B. M., & Kuiper, G. P. (Eds.), The solar system. The Moon, Meteorites, and Comets, Vol. IV. Chicago, IL: University of Chicago Press, 1963. PV 810.

Millman, P. M., Liberty, B. A., Clark, J. F., Williams, D. L., & Innes, M. J. S. The Brent Crater. Pub. Dorn. Obs. (Ottawa), 1960, 24, 1-43.

Milton, D. J., Barlow, B. C., Brett, R., Brown, A. R., Glikson, A. Y., Manwaring, E. A ., Moss, F. J ., Sedmik, E. C ., Van Son, J ., and Young, G. A. Gosses Bluff impact structure. Australia Science, 1972, 175, 1199-1207.

Newcombe, R. B. Oil and gas fields of Michigan. Mich. Geol. Survey Pub. 38, 1933.

Pirtle, G. W. Michigan structural basin and its relationship to surrounding areas. AAPG Bull. , 1932, J_6, 145-152.

Popelar, J. Gravity interpretation of Sudbury area. Geol. Soc. of Canada, Spec. Paper 10, 1972, Pp. 103-115.

Quennell, A. M. The structural and geomorphic evolution of the dead sea r i f t . Geol. Soc. London Proc., No. 1544, 1957, Pp. 14-20.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Roddy, D. J. The Glynn Creek crater, Tennessee. In B. M. Brench & N. M. Short (Eds.), Shock Metamorphism of Natural Materials, Baltimore, MD: Mono Book Corp., 1968, P. 291.

Sawatzky, H. B. Astroblernes in the Williston Basin. Amer. Assoc. Petrol. Geol., 1975, 59(4), 694-710.

Seeger, C. R. Origin of the Jeptha Knob Structure. Ph.D. Thesis, University of Pittsburg, 1966.

Seeger, C. R. Geophysical investigation of the Versailles, Kentucky Astrobleme. GSA Bull., 1972, 8^, 3515-3518.

Sharma, R. G., & Biswas, S. K. A portable proton precession magneto meter. Geophysical Prospecting, 1966, 292.

Silver, L. T ., & Schultz, P. H. Geological implications of impacts of large asteroids and comets on the earth. Geol. Soc. Amer., Spec. Paper 190, 1982.

Stearns, R. G., Wilson, Jr., C. W., Tiedemann, H. A., Wilcox, J. T., & Marsh, P. S. The Wells Creek structure, Tennessee. In B. M. French & N. M. Short (Eds.), Shock Metamorphism of Natural Materials, Baltimore, MD: Mono Book Corp., 1968, P. 291.

Telford, W. M., Geldart, L. P., Sheriff, R. E., and Keys, D. A. Applied Geophysics, Cambridge, England: Cambridge University Press, 1976.

Tudor, D. S. A Geophysical Study of the Kent!and Disturbed Area. Ph.D. Thesis, Indiana University, 1971, P. 111.

SOUTH-CENTRAL CASS COUN

2. 5-0

■

tfvvnruw 1 1 ■Q2j

PI ATE

NQMALY MAP, 1 scale il mile

COUNTY, MICHIGAN EXPLANATION Contour Interval: I *0 mllllgol © MSU Network Bos© Station Instrument: Worden Prospector I.G.F. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 to July 2? NT Station Location Oil Field

r 9

\ c

ZS-o

P L AT-E— I

scale il mile

EXPLANATION Contour Interval: I *0 mllllgal 0 MSU Network Base Station Instrument: Worden Prospector 1.6. F. 1930 Density: 2 .6 7 g m /c c Survey Date: Jan. 1933 to July 1983 -Station Location foil Field

BjJ 16

3 0

32 3 433

S o

20 23

8 6° ' 0 0‘

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mss Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Y./

TOTAL MAGNETIC INTENSITY A

SOUTH-CENTRAL CASS COUNTY

CASSA POLIS I R G E

SOloO

A Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE

N TY ANOMALY MAPs

scale .Imile

COUNTY, MICHIGAN. EXPLANATION Contour interval; 2 5 gammas 0 Base Station Instrument. Proton Precession Magnetometer (Geometries G-816) Survey Date: July 1983 to Aug. E

Declination-. 1-8° Inclination: 71° F

J-14 .L

EXPLANATION Contour interval: 2 5 gammas 0 Base Station Instrument. Proton Precession Magnetometer (Geometries G-816) Survey Date: July 1983 to Aug. 1983

Oil Field o° ? 35 Declination-. 1-8° Inclination: 71° y— f

F 14 ■(-

Reproduced with permission of the copyright owner. Further reproduction prohibited wi without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further' re p ro ^ 7 p r^ ~ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FIRST HARMONIC RESIDUAL GRAVIT

16 M IL E S ; SOUTH-CENTRAL CAS

CASSA >0L|S

POKAHOH

m M M m m m m

x Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iV IT Y MAP. WAVELENGTH- scale 3I n

EXPLANATION

Contour Interval: 0 • 5 p © MSU Network Baso Instrument: Worden Pro; I.G.F. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 Station Location Oil Field

h 17 fUJ

‘J . • v 'v . rfL r" jNfM i

scale al mile

EXPLANATION Contour Interval: 0*5m llllg als 0 MSU Network Base Station Instrument: Worden Prospector IGF. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 to July 1983 Station Location lO il Field

■'■•"Y y . '. ; - v v th permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a-o

1*1+ 3:

3 2 3 3 y 34

8 6°* 0 0*

Reproduced with permission of the copyrigni owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. j u n o

32. 33 34 [5 f \ L f i K f

- 1-0 20 24

/i MAP. WAVELENGTH2 28 MILES scale al mile

EXPLANATION S COUNTY, MICHIGAN Contour Interval 0 -2 5 mllllgfl © MSU NeHvorli Boos Static' instrument; Worden Prospect^ IGF. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 to v 4 - Station Location ■ Oil Field

r 9

UJ 16

^ 0 2 ©

LFSBase & ho» scale =al mile

EXPLANATION Contour Interval:0 2 5 tnllllgals 0 MSU Network Base Station Instrument: Worden Prospector I.G.F. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1963 to July 1983 -+- Station Location H I Oil Field

jJ 16

5] Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SECOND HARMONIC RESIDUAL GRAVITY

MILES; SOUTH-CENTRAL CASS

C a SSA >01.13

pottnc a t) h m v .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RAVITY MAP, WAVELENGTH: 28 scoler Oc n l mils MICHIGAN. k, CASS COUNTY, EXPLANATION Contour lnterval:Q-£5 tnlltf © MSU Network Baoo Stc Instrument: Worden Prospej IG F . 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 to •+• Station Location N 0 1 Field

W i:»\ VM-V rfvvj'*jyv>vxv/.v. Pv / w . V .v ' . . V w i W l

i8 scaler Oc= si mile

EXPLANATION Contour lnterval:0*25 mllllgals © MSU Network Base Station Instrument; Worden Prospector 1.6. F. 1930 Densltv: 2 .6 7 am/cc

-4- Station Location ]Oil Field

iJ 16

_o-2b

- 0 - 7 5

-•5;«

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. E2SB Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SECOND HARMONIC TREND SURFACE

LENGTH = 28 MILES; SOUTH-CENTRAL

MICHIGAN.

3 l i tM/rf fAOf®

- 2 ^ o

F E o __n±

+ 3 4 •- WVA Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE VI

FACE GRAVITY MAP WAVE- I scale zs\ mile ITRAL CASS COUNTY, EXPLANATION Contour Interval: I -0 mllllgals © MSU Network Bose Station Instrument: Worden Prospector I.G.F. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 to July Station Location Oil Field

- 2

- ZS O * I- |9

mmw M

AT E -V -l

scale Oc 3I mile

EXPLANATION Contour Interval: I -0 mllllgals 0 MSU Network Base Station Instrument; Worden Prospsctor I.G.F. 1930 Density: 2 .6 7 gm/cc Survey Date: Jan. 1983 to July 1983 Station Location fOil Field

H 4 -F -I- 17 / IjJ

' ... 1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. — ...... — ■— — t ^ — i ^ — — am — BMM Miwiiii!iiwfnfiiaEiisaiBaii!i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26-0 30

32 33

S'O

- 3

20 23

8 6° ' 0 0

s&sawi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 28

■ 32 33 , ' W

2423 20

iii* %?(4 i s

s»! Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. J

FIRST HARMONIC RESIDUAL GRAVITY

42 MILES; SOUTH-CENTRAL CAS

CASSA

. fPKrtse/'

- 0*2 5

JL_S

BSB Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N GRAVITY MAP, WAVELENGTH* scole il mile

' EXPLANATION AL CASS COUNTY, MICHIGAN Contour Interval: 0 *5 mllllgals (B MSU NetworK Base Station Instrument: Worden Prospector IGF. 1930 Density: 2 .67 gm/cc Survey Dote: Jan. 1983 to Jul -t- Stotion Location n P i j O i l Field

31V * * *

r \

)

N ■ i 1

scole Oc al mile

' EXPLANATION Contour Interval: 0 * 5 mllllgals 0 MSU Network Base Station Instrument: Worden Prospector IGF. 1930 Density: 2.67 gm/cc Survey Date: Jan, 1983 to July 1983 Station Location ® | O i l Field

^0-25

0-73 rmission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^ 0 *5

0 -7 3

f.kfy

3 ISJ

y-^mgwwwpiwmiiw Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. R E S ID U A L MAGNETIC M A P , S

C ASSA POL 15 I

V & ys& ss& ;

MICHIGAN. EXPLANATION Contour Interval: 25 gammas ® Base Station Instrument. Proton Precession Magnetometer (Geometries 6-816) Survey Date: July 1983 to Aug. 1983. Oil Field

Declination*. 1*8° Inclination.* 71° 7 — F

< m m

m m , L7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. y

PLATE VIII

scale .Imile

EXPLANATION Contour Interval: 25 gammas 0 Base Station Instrument-. Proton Precession Magnetometer (Geometries G-816) Survey Date: July 1983 to Aug. 1983. Oil Field

Declination'. 1-8° Inclination: 71®

If*

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ESSEHSfflMSa Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. */» H Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.