UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

BOREHOLE-GRAVITY SURVEYS IN BASIN-FILL DEPOSITS OF

CENTRAL AND SOUTHERN ARIZONA

by

Patrick Tucci, James W. Schmoker, and Stephen L. Bobbins

Open-File Report 82-473

1982

This report is preliminary and has not been reviewed for conformity with

U.S. Geological Survey editorial standards. Any use of trade names is for

descriptive purposes only and does not imply endorsement by the USGS.

INTRODUCTION

The borehole-gravity surveys described here were undertaken as part of

the Southwest Alluvial Basins Study, which is one of a number of U.S.t

Geological Survey planned or ongoing regional aquifer studies. The

objective of the borehole-gravity surveys was to investigate general

relations between density and depth in the basin-fill deposits of central

and southern Arizona. Such deposits form the major aquifers of the region

and store large volumes of ground water.\

Basin-fill deposits penetrated by six wells in Butler Valley, Vekol

Valley, Avra Valley, and the Tucson basin (fig. 1), in central and southern

Arizona, were logged in January, 1980, with the U.S. Geological Survey-

LaCoste and Romberg borehole gravity meter. These cased wells were

originally drilled for water supplies or for aquifer tests.

Subsurface depths in this report are given in feet, in conformance with

common usage and understanding of well data. The multiplying factor to

convert feet to meters in 0.3048.

GEOLOGIC SETTING

The borehole-gravity data described here are .from intermontane basins

(grabens) in or adjacent to the Sonoran Desert section of the Basin and

Range physiographic province (Fenneman, 193D. Mountains (horsts) bounding

the basins consist of igneous, metamorphic, and sedimentary rocks ranging

from Precambrian through Cenozoic in age (Wilson and others, 1969).

31

115

31'108'

I I50 100 KILOMETERS

EXPLANATION

BOUNDARY OF SOUTHWEST ALLUVIAL BASINS STUDY

BUT-1 WELL BUT-1 is well designation

Figure 1.--Locations of wells logged in this study.

The basin-fill deposits, described by Scarborough and Peirce (1976, p.

253) as "the sedimentary group that was deposited in basins created by the

Basin and Range disturbance", are up to about 9,000 ft thick (Eberly andr

Stanley, 1978, p. 938). They consist of gravel, sand, silt, and clay, and

locally include interbedded volcanic rocks and evaporites (Scarborough and

Peirce, 1978). In general, the clastic sediments grade from coarse grained

at basin margins to fine grained in the centers. Basin-fill deposits in

the study area have not been formally named except in the Tucson basin,\

where Davidson (1973) subdivided them into the Tinaja beds of Miocene and

Pliocene age and the Fort Lowell Formation of Pleistocene age.

BOREHOLE-GRAVITY MEASUREMENTS

The U.S. Geological Survey-LaCoste and Romberg borehole gravity meter

(described by McCulloh, LaCoste, and others, 1967; McCulloh, Schoellhamer,

and others, 1967) was used to carry out borehole-gravity surveys in the six

wells located in Figure 1. The borehole gravity meter has a radius of

investigation of tens of feet. Density values derived from

borehole-gravity measurements are not significantly influenced by casing,

borehole rugosity, or formation damage caused by .drilling.

Fundamentals of borehole-gravity logging and data interpretation,

considerations of the effective radius of investigation, and applications

to geologic problems have been discussed by many authors, including Smith

(1950), Goodell and Fay (1964), Howell, Heintz, and Barry (1966), McCulloh

(1966), Healey (1970), Beyer (1971), Jageler (1976), Hearst and McKague

(1976), and Scnraoker (1977a, b, 1978, 1979).

Subsurface gravity stations were located where wire-line or drillers'

logs indicated variations in formation properties. Additional stations

were located between formation breaks to establish details of density

variations. Densities determined from borehole-gravity measurements become

more accurate as vertical station separation increases, so that station

selection involves a tradeoff between stratigraphic detail and density

accuracy (Schmoker, 1978).

Drift control for the borehole-gravity surveys was established by\

station reoccupations; tidal corrections and terrain corrections were

applied to the borehole-gravity data. Principal facts for the

borehole-gravity measurements of this study are tabulated in Tables 1-6.

In the absence of complicating structural factors, the relation between

formation density and measurements of gravity in a borehole is given by

(McCulloh, 1966):

f = 39.124CF- 4g/ ^z) (1)

where J * s t*16 average formation density between two vertically separated

points in the borehole (g/cnr), F is the free-air vertical gradient of

gravity (mgals/ft), Ag is the measured difference in gravity between the

vertically separated points (mgals), and Az is the vertical separation

(ft).

Table 1. Well WKF, Avra Valley

Logged January 19, 1980

Station

12345

6789

10

1112131415

1617181920

2122232425

2627282930

3132

Depth (feet)

19.950.075.1

100.1144.0

194.0245.0286.0326.0365.0

406.0420.0462.0505.0548.0

610.0674.0746.0815.1860.1

910.1970.0

1,030.01,088.01,145.0

1,224.11,285.0

970.0746.0462.0

245.019.9

Greenwich mean time

18:4319:0019:1419:2619:37

19:4920:0120:1520:2920:47

21:0021:1321:2621:3921:50

22:0222:1422:2022:3222:41

22:5022:5623:0823:1823:29

23:3823:4824:0724:2324:42

25:0125:21

Uncorrected g ra vity

(milligals)

2,651.1612,652.5682,653.5622,654.6112,656.493

2,658.5482,660.6962,662.3892,664.0302,665.474

2,666.9602,667.4652,669.0492,670.6142,672.231

2,674.5782,676.9962,679.4862,681.8792,683.432

2,685.1522,687.2242,689.3452,691.3692,693.383

2,696.1512,698.2882,687.2782,679.5552,669.157

2,660.8272,651.287

Tide correction (milligals)

-0.014-.004+ .004+ .010+ .015

+ .020+ .025+ .029+ .032+ .034

+ .035+ .034+ .032+ .030+ .027

+ .023+ .018+ .016+ .010+ .006

+.001-.003-.009-.015-.022-

-.028-.034-.046-.055-.066

-.075-.083

Terrain correction (milligals)

+0.030+ .033+.036+ .040

"' +.047

+ .054+\061+ .067+ .073+ .078

+ .083+ .085+ .090+ .095+ .100

+ .108+ .115+ .123+ .131+.136

+ .142+ .149+ .155+ .162+ .168

+.177+ .183+ .149+ .123+ .090

+.061+ .030

Corrected gravity

(milligals)

2,651.1772,652.5972,653.6022,654.6612,656.555

2,658.6222,660.7822,662.4852,664.1352,665.586

2,667.0782,667.5842,669.1712,670.7392,672.358

2,674.7092,677.1292,679.6252,682.0202,683.574

2,685.2952,687.3702,689.4912,691.5162,693.529

2,696.3002,698.4372,687.3812,679.6232,669.181

2,660.8132,651.234

Table 2. Well MW-2, Avra Valley

Logged January 21, 1980

Station

12345

6789

10

1112131415

1617181920

2122232425 '

262728

Depth (feet)

99.4140.0180.0220.0260.0

300.0333.0365.0408.0460.0

510.0560.0600.1650.0700.0

750.1800.0850.0900.0950.1

1,000.0750.1510.0300.099.4

49.719.999.4

Greenwich mean time

15:5416:1916:2816:3816:48

16:5917:1317:2617:4217:57

18:0818:2318:3218:4418:53

19:0119:1219:2019:2919:38

19:4820:0420:2120:3420:46

20:5421:0321:20

Uncorrected gravity

(milligals)

2,636.6732,638.3892,640.1622,641.8232,643.477

2,645.1472,646.5062,647.9022,649.5362,651.469

2,653.3632,655.2002,656.7262,658.5412,660.336

2,662.0902,663.8582,665.5832,667.2702,668.951

2,670.6132,662.0592,653.3202,645.0962,636.583

2,634.4082,633.0372,636.570

Tide correction (milligals)

-0.084-.090-.091-.091-.091

-.091-.089-.086-.082-.076

-.072-.065-.060-.054-.049

-.044-.037-.032-.027-.021

-.014-.005+ .006+ .013+ .020-

+ .024+ .028+ .036

Terrain correction (milligals)

+0.070+ .081+ .092+ .102+ .113

+ .123+M32+ .140+ .151+ .164

+ .177+ .189+ .199+ .210+ .222

+ .234+ .245+ .257+ .268+ .279

+ .290+ .234+ .177+ .123+ .070

+ .057+ .049+ .070

Corrected gravity

(milligals)

2,636.6592,638.3802,640.1632,641.8342,643.499

2,645.1792,646.5492,647.9572,649.6052,651.557

2,653.4682,655.3242,656.8652,658.6972,660.509

2,662.2802,664.0662,665.8082,667.5112,669.209

2,670.8892,662.2882,653.5032,645.2322,636.673

2,634.4892,633.1142,636.676

Table 3. Well IP-1, Tucson basin Logged January 23, 1980

Station

12345

6789

10

1112131415

1617181920

2122232425

26272829

Depth (feet)

99.9150.0195.0235.0275.0

314.0333.0365.0400.1445.0

489.0518.0560.0603.0650.0

702.0760.0800.0850.0890.1

930.0980.1760.0518.0333.0

99.950.020.099.9

Greenwich mean time

15:5516:0916:2016:2916:42

16:5717:0617:2417:3617:52

18:0818:3318:5319:0719:20

19:3019:4419:5920:0920:18

20:2520:3520:5821:1621:31

21:5022:0122:1622:26

Uncorrected gravity

(milligals)

2,542.7242,544.7942,546.6712,548.3022,549.844

2,551.4042,552.1652,553.3882,554.6452,556.357

2,558.0732,559.1622,560.6912,562.2462,564.078

2,565.9852,568.0322,569.5262,571.2872,572.692

2,574.1512,575.8872,567.9762,559.0822,552.206

2,542.7462,540.6442,539.5242,542.744

Tide correction (milligals)

-0.040-.046-.051-.054-.059

-.064-.066-.070-.072-.074

-.074-.073-.070-.067-.063

-.060-.055-.049-.045-.040

-.037-.032-.020-.010-.001'

+ .010+ .016+ .024+ .030

Terrain correction (milligals)

+0.122+ .138+ .148

., +.154' +.158

+ .161+ .163+ .164+ .165+ .166

+ .167+ .167+ .167+ .167+ .166

+ .165+ .164+ .163+ .162+ .161

+ .161+ .160+ .164+ .167+ .163

+ .122+ .099+ .080+ .122

Corrected gravity

(milligals)

2,542.8062,544.8862,546.7682,548.4022,549.943

2,551.5012,552.2622,553.4822,554.7382,556.449

2,558.1662,559.2562,560.7882,562.3462,564.181

2,566.0902,568.1412,569.6402,571.4042,572.813

2,574.2752,576.0152,568.1202,559.2392,552.368

2,542.8782,540.7592,539.6282,542.896

Table A.~Well BUT-1, Butler Valley Logged January 25, 1980

Station

12345

6789

10

1112131415

1617181920

2122232425 '

2627282930

3132

Depth (feet)

213.9245.0290.0335.0384.0

426.0468.0532.0566.0604.0

651.0690.0740.0796.0847.0

914.0965.0

1,020.01,069.01,118.0

1,165.0914.0690.0651.0426.0

213.9172.0137.092.050.0

20.0213.9

Greenwich mean time

15:5216:0516:1716:2916:41

16:5217:0817:2017:3317:50

18:0118:1218:2018:3018:40

18:4918:5819:0719:1519:23

19:3119:4319:5820:0620:24

20:4120:5921:1321:2621:40

21:5222:05

Uncorrected gravity

(milligals)

2,867.0732,868.3762,870.2202,872.0442,874.003

2,875.6752,877.3062,879.5002,880.8072,882.237

2,883.8622,885.0472,886.8372,888.6862,890.308

2,892.4582,894.0672,895.7972,897.3582,899.010

2,900.7322,892.4592,885.0632,883.7842,875.700

2,867.0602,865.3102,863.9022,861.9252,860.308

2,858.9992,867.024

Tide correction (milligals)

-0.011-.014-.017-.020-.023

-.026-.030-.034-.037-.042

-.045-.048-.051-.053-.056

-.057-.059-.061-.063-.064

-.065-.066-.067-.067-.067-

-.066-.064-.061-.058-.055

-.051-.046

Terrain correction (milligals)

+0.231+ .251+ .279+ .307+ .338

+ .364+ '.389+ .427+ .447+ .469

+ .495+ .517+ .545+ .575+ .602

+ .637+ .664+ .692+ .716+ .740

+ .763+ .637+ .517+ .495+ .364

+ .231+ .204+ .182+ .155+ .132

+ .117+ .231

Corrected gravity

(milligals)

2,867.2932,868.6132,870.4822,872.3312,874.318

2,876.0132,877.6652,879.8932,881.2172,882.664

2,884.2122,885.5132,887.3312,889.2082,890.854

2,893.0382,894.6722,896.4282,898.0112,899.686

2,901.4302,893.0302,885.5132,884.2122,875.997

2,867.2252,865.4502,864.0232,862.0222,860.385

2,859.0652,867.209

Table 5.

Well VEK-5, Vekol Valley Logged January 28, 1980

Station

12345

6789

10

1112131415

1617181920

21222324

Depth (feet)

425.0475.0530.0590.0655.0

720.0760.0830.0900.1956.0

1,020.01,090.01,146.11,206.01,248.0

1,314.01,360.01,443.11,524.01,573.0

1,248.0956.0720.0425.0

Greenwich mean time

22:0022:1522:2722:3622:47

22:5523:0623:1723:2623:35

23:4723:5424:0324:1225:21

24:3324:4324:5125:0025:11

25:3826:0926:2826:56

Uncorrected gravity

(milligals)

2,749.3612,751.0422,752.8582,754.7912,756.916

2,759.0452,760.3412,762.6242,764.9132,766.748

2,768.8272,771.0782,772.8052,774.6552,776.105

2,778.3832,779.8922,782.4812,784.9142,786.532

2,776.1182,766.7072,758.9852,749.285

Tide correction (milligals)

-0.072-.075-.077-.079-.080

-.080-.080-.080-.079-.077

-.075-.073-.070-.067-.063

-.057-.052-.048-.042-.035

-.015+ .010+ .027+ .052

Terrain correction (milligals)

+0.162+ .174+ .189+ .204

"' +.221

+ .237+>. 248+ .265+ .283+ .297

+ .313+ .330+ .344+ .359+ .369

+ .385+ .395+ .415+ .434+ .445

+ .369+ .297+ .237+ .162

Corrected gravity

(milligals)

2,749.4512,751.1412,752.9702,754.9162,757.057

2,759.2022,760.5092,762.8092,765.1172,766.968

2,769.0652,771.3352,773.0792,774.9472,776.411

2,778.7112,780.2352,782.8482,785.3062,786.942

2,776.4722,767.0142,759.2222,749.499

Overnight January 29, 1980

252627282930

3132333435

425.0355.0300.0250.0195.0150.0

100.050.020.0

195.0425.0

16:0616:2216:3917:0417:1517:27

17:3617:4717:5918:1418:28

2,749.4362,747.1032,745.0852,743.2282,741.0862,739.231

2,737.2042,735.2012,734.1422,741.0732,749.391

-.029-.022-.015 .-.006-.002+ .001

+ .003+ .005+ .007+ .008+ .009

+ .162+ .144+ .130+ .117+ .104+ .094

+ .083+ .073+ .067+ .104+ .162

2,749.5692,747.2252,745.2002,743.3392,741.1882,739.326

2,737.2902,735.2792,734.2162,741.1852,749.562

Table 6. Well VEK-2, Vekol ValleyLogged January 30, 1980

Station

12345

6789

10

1112131415

1617181920

2122232425 '

2627282930

3132333435

3637

Depth (feet)

475.0520.0560.0625.0690.0

760.0850.0928,0

1,012.01,100.0

1,154.01,210.01,270.01,325.01,400.0

1,475.01,550.01,620.01,695.01,765.0

1,840.01,900.01,960.01,550.01,210.0

850.0475.0430.5365.0296.0

226.0160.0110.062.020.0

226.0475.0

Greenwich mean time

19:3819:5320:0020:1320:20

20:3120:3920:4920:5621:05

21:1421 : 2221:3121:4021:49

21:5822:0822:1722:2422:30

22:3922:4622:5423:1623:32

23:5124:0624:1824:2924:38

24:4624:5525:0525:1625:24

25:3625:53

Uncorrected gravity

(milligals)

2,690.0462,691.7382,693.2872,695.7662,698.196

2,700.7872,704.2272,707.1902,710.3432,713.729

2,715.8392,718.0292,720.2962,722.3822,725.346

2,728.2072,731.1242,733.8222,736.7102,739.368

2,742.3632,744.6982,747.0742,731.1732,718.082

2,704.3152,690.0912,688.3372,685.5772,682.556

2,679.3642,676.2472,673.8312,671.6272,669.578

2,679.3602,690.116

Tide correction (miliigals)

+0.015+ .011+ .010+ .006+ .004

-.001-.004-.008-.011-.015

-.020-.024-.028-.033-.038

-.042-.048-.052-.056-.059

-.063-.066-.069-.078-.083-

-.087-.089-.090-.090-.089

-.088-.087-.085-.081-.078

-.073-.064

Terrain correction (milligals)

+0.143+ .151+ .158+ .170+ .181

+ .193+'. 208+ .220+ .234+ .247

+ .256+ .264+ .273+ .281+ .293

+ .303+ .314+ .324+ .335+ .345

+ .356+ .364+ .372+ .314+ .264

+ .208+ .143+ .134+ .121+ .107

+ .092+ .077+ .065+ .052+ .041

+ .092+ .143

Corrected gravity

(milligals)

2,690.2042,691.9002,693.4552,695.9422,698.381

2,700.9792,704.4312,707.4022,710.5662,713.961

2,716.0752,718.2692,720.5412,722.6302,725.601

2,728.4682,731.3902,734.0942,736.9892,739.654

2,742.6562,744.9962,747.3772,731.4092,718.263

2,704.4362,690.1952,688.3812,685.6082,682.574

2,679.3682,676.2372,673.8112,671.5982,669.541

2,679.3792,690.195

10

In the study area, the free-air gradient of gravity is slightly

distorted by regional mass anomalies associated with horst (high density)

and graben (low density) structure. In each well surveyed, the theoreticalr

free-air gradient of 0.09406 mgals/ft was corrected for such structure by

modeling the gravity effect of a two-dimensional polygon representing the

estimated regional configuration of the graben in which the well was

located. The magnitude of this correction varied witfr- estimated graben

structure, location of the well within the graben, and well depth, but was\

generally small. The correction lowered the theoretical free-air gradient

by 0.00015 to 0.00079 mgals/ft, resulting in a lowering of calculated

densities (equation 1) of 0.006 to 0.031 g/cm.

DENSITIES OF BASIN-FILL DEPOSITS

Densities of the basin-fill deposits logged in this study, calculated

from borehole-gravity data, are listed in Table 7 and plotted in Figure 2.

3 Densities above the water table range from 1.73 to 2.26 g/cm , and

densities below the water table range from 2.01 to 2.46 g/cm . The

depth-density plots (fig. 2) show density layers, reflecting individual

depositional sequences. In general, densities of the basin fill increase

with depth from the surface to about 800 ft and then remain constant or

even decrease with additional depth, as shown by the plot of average

density versus depth (fig. 3) and the plots of individual wells (fig. 2).

11

.Table 7. Densities of

basin

fill

calculated fr

om borehole-gravity data.

Wel

l IP

-1W

ell

de

pth

, 1,

000

feet

Depth

to

w

ate

r,

316

fee

t

Depth

in

terv

al

(feet)

20-

505

0-

100

10

0-

150

150-

19

51

95

- 23

52

35

- 27

52

75

- 31

43

14

- 33

33

33

- 36

53

65

- 40

0400-

445

445-

489

489-

518

51

8-

560

56

0-

603

60

3-

650

65

0-

702

70

2-

760

76

0-

800

80

0-

850

85

0-

890

89

0-

930

93

0-

980

De

nsity

(gra

ms

pe

r cubic

ce

ntim

ete

r)

2.1

74

1.9

88

2.0

24

2.0

13

2.0

51

2.1

42

2.0

86

2.0

82

2.1

57

2.2

49

2.1

58

2.1

22

2.1

79

2.2

22

2.2

32

2.1

22

2.2

13

2.2

66

2.1

83

2.2

69

2.2

74

2.2

16

2.2

90

Wel

l W

KF

Wel

l d

ep

th,

1,3

02

fee

tD

epth

to

w

ate

r,

365

feet

Depth

in

terv

al

(feet)

20-

505

0-

7575-

100

100-

14

41

44

- 19

41

94

- 24

52

45

- 28

62

86

- 32

63

26

- 36

53

65

- 40

64

06

- 42

0420-

462

462-

505

505-

548

54

8-

610

61

0-

674

67

4-

746

74

6-

815

81

5-

860

86

0-

910

91

0-

970

97

0-1

,03

0-

1,0

30-1

,088

1,0

88-1

,145

1,1

45-1

,224

1,2

24-1

,285

Density

(gra

ms

pe

r cu

bic

centim

ete

r)

1.8

28

2.1

08

2.0

17

1.9

86

2.0

57

2.0

17

2.0

49

2.0

60

2.2

19

2.2

50

2.2

60

2.1

96

2.2

47

2.2

01

2.19

.12.1

95

2.3

18

2.3

18

2.3

23

2.3

27

2.3

19

2.2

91

2.3

08

2.2

92

2.3

04

2.3

01

Wel

l M

W-2

Wel

l d

ep

th,

un

kn

ow

nD

epth

to

w

ate

r,

364

feet

Wel

l obstr

ucte

dat

1,1

00 fe

et

De

pth

in

terv

al

(feet)

20

- 50

50

- 99

99

- 14

01

40

- 18

01

80

- 22

02

20

- 26

02

60

- 30

03

00

- 33

33

33

- 36

53

65

- 40

84

08

- 46

04

60

- 51

05

10

- 56

05

60

- 60

06

00

- 65

06

50

- 70

07

00

- 75

07

50

- 80

08

00

- 85

08

50

- 90

09

00

- 95

0950-1

,000

Density

(gra

ms

pe

r cu

bic

centim

ete

r)

1.8

58

1.9

44

2.0

04

1.9

19

2.0

29

2.0

35

2.0

20

2.0

39

1.9

43

2.1

63

2.1

95

2.1

68

2.2

11

2.1

60

2.2

27

2.2

45

2.2

80

2.2

63

2.3

00

2.3

31

2.3

37

2.3

46

We

ll V

EK

-2W

ell

de

pth

, 2

,04

5 fe

et

Depth

to

w

ate

r,

440

feet

De

pth

in

terv

al

(feet)

20

- 62

62

- 11

01

10

- 16

01

60

- 22

62

26

- 29

62

96

- 36

53

65

- 43

04

30

- 47

54

75

- 52

05

20

- 56

05

60

- 62

56

25

- 69

06

90

- 76

07

60

- 85

08

50

- 92

8928-1

,012

1,0

12-1

,100

1,1

00-1

,154

1,1

54

-1,2

10

1,2

10

-1,2

70

1,2

70

-1,3

25

1,3

25-1

,400

1,4

00-1

,475

1,4

75-1

,550

1,5

50

-1,6

20

1,6

20-1

,695

1,6

95-1

,765

1,7

65-1

,840

1,8

40

-1,9

00

1,9

00

-1,9

60

Density

(gra

ms

pe

r cu

bic

ce

ntim

ete

r)

1.7

34

1.8

46

1.7

52

1.7

94

1.8

58

1.9

30

1.9

94

2.0

55

2.1

75

.2.1

29

2.1

53

2.1

82

2.1

98

2.1

49

2.1

60

2.1

76

2.1

40

2.1

18

2.1

17

2.1

68

2.1

64 '

2.1

00

2.1

54

2.1

26

2.1

39

2.1

40

2.1

60

2.0

84

2.1

24

2.0

97

We

ll V

EK

-5W

ell

de

pth

, 1,9

95

feet

Depth

to

w

ate

r,

345

feet

Wel

l o

bstr

ucte

da

t 1,5

73

feet

De

pth

in

terv

al

(feet)

20

- 50

50

- 10

01

00

- 15

01

50

- 19

51

95

- 25

02

50

- 30

0300-

355

355-

425

425-

475

47

5-

530

53

0-

590

59

0-

655

65

5-

720

72

0-

760

76

0-

830

83

0-

900

90

0-

956

956-1

,020

1,0

20-1

,090

1,0

90

-1,1

46

1,1

46-1

,206

1,2

06

-1,2

48

1,2

48-1

,314

1,3

14-1

,360

1,3

60-1

,443

1,4

43

-1,5

24

1,5

24-1

,573

De

nsity

(gra

ms

pe

r cu

bic

ce

ntim

ete

r)

2.2

64

2.0

76

2.0

57

2.0

31

2.1

20

2.1

94

2.2

09

2.3

40

2.3

25

2.3

49

2.3

81

2.3

61

2.3

59

2.3

71

2.3

64

2.3

62

2.3

54

2.3

68

2.3

81

2.4

34

2.4

30

2.2

86

2.2

86

2.3

54

2.4

20

2.4

61

2.3

44

We

ll B

UT

-1W

ell

depth

, 1,5

20

feet

Depth

to

w

ate

r,

215

feet

Wel

l o

bstr

ucte

dat

1,1

67

fe

et

De

pth

in

terv

al

(feet)

20-

505

0-

9292-

137

13

7-

172

17

2-

214

21

4-

245

245-

290

290-

335

335-

384

384-

426

42

6-

468

46

8-

532

53

2-

566

56

6-

604

604-

651

651-

690

69

0-

' 74

07

40

- 79

6796-

847

847-

914

914-

965

96

5-1

,02

01,0

20-1

,069

1,0

69

-1,1

18

1,1

18-1

,165

De

nsity

(gra

ms

per

cubic

centim

ete

r)

1.9

44

2.1

41

1.9

26

2.0

71

2.0

08

2.0

05

2.0

41

2.0

58

2.0

79

2.0

87

2.1

27

2.3

04

2.1

42

2.1

76

2.3

77

2.3

61

2.2

43

2.3

55

2.4

03

2.3

91

2.4

12

2.4

17

2.4

02

2.3

28

2.2

14

VE

K-2

V

ekol

V

alle

yDE

NSIT

Y LA

YER

u

200

400

UJ

0 9J

600

CO o <

800

uJ

1000

\

K

1200

2T

1 4

nr"

14

0°

r a.

UJ

/"""

"\

1600

1800

2000

i 1

1 1

1 1

11

1|

'-

1',

WAT

ER

1 -

ICV

EI

1 ~

~

',' 1

-

\ 1 -

- ,»

DE

PT

H

1 IN

TE

RV

AL

1

"

r ii ~ i -

- - i1 - i i

i i

i i

i i

Mea

n density

Is

1.8

7

gram

s

cla

y

and

silt,

san

d,

and

gra

ve

l

Mea

n density

Is

2.1

4

gram

sper

cu

bic

ce

ntim

ete

r.

San

dyg

rave

l an

d so

me

silt

VE

K-5

V

ekol

V

alle

y

WAT

ER

LEV

EL

DEPT

INTERVALH

1 I

L

1 _ 1

DE

NS

ITY

LA

YE

R

ANO

D

ES

CR

IPTI

ON

Mea

n density

Is

2.1

4

gram

s p

er

cu

bic

centim

ete

r.

Cle

an

g

rave

lly

sand

Mea

n density

Is

2.3

7

gram

s p

er

cubic

centim

ete

r.

Cle

an

gra

velly

sand

Mea

n density

Is

2.3

6

gram

s p

er

cu

bic

centim

ete

r.

Sllty

sa

nd

, 1

,20

8

to

1,3

50

fe

et;

cem

en

ted

sa

nd

and

gra

vel,

I,.IS

O

to

l,b<

:b fe

et; silly

sa

nd

. 1,5

25

to

1.7

28

feet

BU

T-1

Butler

Va

lley

I 1

1 1

1 1

1

EHPT

M | i

INTERVAL

1 I.

DENS

ITY

LAYIR

ANO

DESCRIPIION

Mean density

is 2.02 grams

per

cubic

cent

imet

er.

Inte

r bedded (.lay

and

grav

elly

silty

sand

Mean density

Is 2.11 gram

per mbic centimeter.

In

sill

y sand

Mean density

Is 2.37 grams

per

cubic

cent

imet

er.

Leme

nted

gravelly,

sllt

y,

and

clay

ey JJ

nd

Mean

de

nsit

y It 2.27 grams

per

cub\c

cent

imet

er.

Grav

elly

sand

?

1.6

1.8

2.0

2.2

1.9

2.1

2.3

2.5

1.9

2.1

2.3

2.5

DENS

ITY,

IN GR

AMS

PER

CUBI

C CE

NTIM

ETER

Figure 2.--Densities of basin fill calculated from borehole-gravity da

ta.

IP-1

Tucs

on basin

DENSITY

LAYE

R

u

UJ <

200

u_ en in o

400

=c |

600

UJ

CO S

800

UJ

u_ 5 10

00rs

zc

f 2i

1200

Q

1400

1111,11

l| j_

1

| _

WAT

ER

|ItV

FL

|

j 1

_

1

DIP

TM! 1

*

INTE

RVAL

! _ 1

1 . 1

1 _

1 1

1 1

1 1

1 I

Mea

n densi

ty

Is

2.07

gr

ams

per

cubi

c ce

ntim

ete

r.

Sand

and

grav

el

and

som

e cl

ay

(Fo

rt l

ow

ell

For

mat

ion)

Mea

n densi

ty

Is

2.17

gr

ams

per

cubi

c ce

ntim

ete

r.

Sand

an

d qr

avel

an

d so

me

clay

(Tln

aja

be

ds)

Mea

n densi

ty

is

2.23

gra

ms

per

cubi

c ce

ntim

ete

r.

Cla

yan

d le

nses

of

sand

and

gr

avel

(T

inaja

be

ds)

?

__

_? ?

1.7

1

.9

2.1

2

.3

WKF

Avra Va

lley

DEPTH

INTE

RVAL :C

I

1 1

1

MW-2

Avra Va

lley

DE

NS

ITY

LA

YE

R

AMD

DE

SC

RIP

TIO

N

Mea

n densi

ty

Is

2.0?

gr

ams

per

cubi

c ce

ntim

ete

r,

inte

rbed

ded

sand

, gra

vel,

cla

y,

and

siH

Mea

n densi

ty

is

2.22

gr

ams

per

cubi

c ce

ntim

ete

r.

Mai

nly

sand

an

d gra

vel,

wea

kly

cem

ente

d

Mea

n densi

ty

is

2.31

gr

ams

per

cubi

c ce

ntim

ete

r.

Mai

nly

sand

an

d gra

vel,

mod

erat

ely

to

stro

ng

ly

cem

ente

d

_ _

_ O

__

O

»J

I i

f

TT

i '

WA

TIR

LE

VE

L

DEPT

H I 1

TERV

AL

1 1

OtNS

ITY

LAYER

AND

DESCRIPTION

Mean

density

Is

I .W gr

a*

per

cubic

centimeter.

Inte

rbed

ded

sand

, gravel,

clay,

and

silt

Mean

de

nsit

y Is

?.IB qr«r

per

rubic

cent

imet

er.

Intorbedded

sand

, grave! ,

clay,

and

SiH; we

akly

cemented.

Clay an

d si It

Incr

ease

wi

th increasing

dept

h

Mean

de

nsit

y is

2.29 gr

ams

per

cubic

cent

imet

er.

Inte

rbed

ded

sand

, gravel,

clay,

and

silt

; moderately

to St

rong

ly ce

ment

ed

_7 7 7

1.7

1.9

2.1

2.3

1.7

1.9

2.1

2.3

DENS

ITY,

IN

GRAMS

PER

CUBIC

CENTIMETER

Figu

re 2. Continued.

UJou_ o:ooQ

_»

3:0

UJCO

1 UJ UJu_

1 1

nrh-

UJ Q

U

100

200

300

400

500

600

700

800

900

1000

1100

1 9nn

J ___ 0 ' 6 I 1 1 1

6

7

_ * 7 ' _

~~ -10 ~

9

- "~^~^ -

-7

- -6

~

-6

Q 6

4

1 1 1 1 1 *\ 3 |

1.7 1.9 2.1 2.3

DENSITY, IN GRAMS PER CUBIC CENTIMETER

2.5

EXPLANATION

7 MEAN DENSITY Numeral, 7, is number of data points used to calculate the mean density. Half the length of the line is the standard error of the sample mean

Figure 3. Mean density of the upper 1,200 feet of basin-fill deposits,

15

Figure 4 compares basin-fill densities measured in this study with

depth-density curves given by other investigators. Curve A is from

borehole-gravity measurements reported by Healey (1970) for the upper 2,000

ft of basin fill in Hot Creek Valley, Nevada. Curve B, modified from Eaton

and others (1972), is based on conventional density-log data from central

Arizona. Curve C is based on well-sample data reported by Mattick and

others (1973) for Cenozoic deposits in the Colorado River delta. Curves A,

B, and C are within the range of densities measured in this study.\

Lateral and vertical changes in grain density, porosity, and water

saturation, which produce changes in the density of basin fill, are a

function of the local geologic history of an area and do not necessarily

correlate from basin to basin or even within a basin (i.e., Avra Valley,

fig. 2). Lacking knowledge of subsurface density in a given basin in the

region, however, curve D of Figure 4 could be used as a first approximation

of the depth-density relation.

16

UJo

O

LU UJ

I

LU Q

200

400

2§ 600 toQ

< 800

1000

1200

1400

1600

1800

2000 j_ _L

1.7 1.9 2.1 2.3

DENSITY, IN GRAMS PER CUBIC CENTIMETER

2.5

EXPLANATION

DENSITY AT MIDPOINT OF INTERVAL -

Well IP-1 o Well VEK-2

Well WKF * well VEK-5

Well MW-2 Well BUT-1

Figure 4. Comparison of the density of basin-fill deposits in parts of Arizona and Nevada. Data for curve A from Healey (1970). Curve B modified from Eaton and others (1972, fig. 11). Data for curve C from Mattick and others (1973, fig. 4). Data for curve D from Figure 3<of this study.

17

POROSITIES OF BASIN-FILL DEPOSITS

Porosity, <£> , was computed for intervals below the water table from the

borehole-gravity density, J , using the equation:

» ioo( - )/( - > (2)

where j5 is the estimated average grain density and J _ is the pore-fluid

density (g/cm ). Pores were assumed to be filled with water of density

3 3 1.00 g/cm ; grain densities of 2.50, 2.65, and 2.80 g/cm were used. The

porosity calculation is quite sensitive to grain density and error in this\

parameter is a major source of porosity uncertainty. A grain density of

3 2.65 g/cm probably best represents the basin fill. Grain densities ofo

2.50 and 2.80 g/cnr are thought to represent upper and lower limits.

Table 8 lists average porosities, calculated from the borehole-gravity

data, of the water-saturated density layers shown in Figure 2. Such data

can be used to estimate volumes of ground water in place.

In some instances, porosity also shows a positive correlation with

hydraulic conductivity and so is related to potential aquifer production.

In Avra Valley (well WKF) , for example, preliminary results of a

three-dimensional mathematical model of the ground-water system indicate

that the density layer between 326 and 67^ ft, with a mean porosity of

about 26 percent, is from two to four times more permeable than the

underlying density layer (67^-1,285 ft) with a mean porosity of about 21

percent (D. R. Pool, U.S. Geological Survey, oral commun., 1980).

18

Table 8. Porosities of basin-fill deposits calculated fromborehole-gravity data.

Well

IP-1

MW-2

WrCF

VEK-2

VEK-5

BUT-1

Depth interval Mean

ft

333-518 518-980

365-600 600-1,000

326-674 674-1,285

475-1,960

355-1,206 1,206-1,573

214-604 604-1,069 1,069-1,165

density g/cm

2.17 2.23

2.18 2.29

2.22 2.31

2.14

2.37 2.36

2.11 2.37 2.27

Average

Grain density

2.50 g/cm3

22 18

21 14

19 13

24

9 9

26 9

15

porosity, percent

Grain density

2.65 g/cm3

\

29 25

28 22

26 21

31

17 18

. 33 17 23

Grain density

3 2.80 g/cm

35 32

34 28

3227

37

24 24

38 24 29

19

Vekol Valley is divided into two parts by a buried ridge of

consolidated rock (Wilson, 1979, p. 8). The mean porosity of the saturated

basin fill is about 18 percent in the northern part (VEK-5) and about 31

percent in the southern part (VEK-2). Aquifer tests and results of a

preliminary model of the ground-water system indicate that basin-fill

deposits in the southern part are two to four times more permeable than

those in the northern part (R. P. Wilson, U.S. Geological Survey, oral

commun., 1980) .\

It must be strongly emphasized that there can be many exceptions to the

positive correlation between porosity and hydraulic conductivity.

Hydraulic conductivity depends on factors such as grain size and grain-size

distribution, pore-throat geometry, fracture density, etc. It is only when

such factors remain approximately constant that increasing porosity

correlates with increasing capacity of the rock to transmit fluid.

20

REFERENCES

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vertical boreholes: Palo Alto, Stanford Univ., Ph.D. thesis, 217 p.r

Davidson, E. S., 1973* Geohydrology and water resources of the Tucson

basin, Arizona: U.S. Geological Survey Water-Supply Paper 1939-E, 81

P.

Eaton, G. P., Peterson, D. L. , and Schumann, H. H., 1972, Geophysical,

geohydrological, and geochemical reconnaissance of the Luke salt body,*

central Arizona: U.S. Geological Survey Professional Paper 753, 28 p.

Eberly, L. D., and Stanley, T. B., Jr., 1978, Cenozoic stratigraphy and

geologic history of southwestern Arizona: Geological Society of

America Bulletin, v. 89, p. 921-940.

Fenneman, N. M., 1931, Physiography of Western United States: New York,

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Goodell, R. R., and Fay, C. H., 1964, Borehole gravity meter and its

application: Geophysics, v. 29, no. 5, p. 774-782.

Healey, D. L., 1970, Calculated in situ bulk densities from subsurface

gravity observations and density logs, Nevada Test Site and Hot Creek

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Hearst, J. R., and McKague, H. L., 1976, Structure elucidation with

borehole gravimetry: Geophysics, v. 41, no. 3, p. 491-505.

Howell, L. G., Heintz, K. 0., and Barry, A., 1966, The development and use

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p. 764-772.

21

Jageler, A. H., 1976, Improved hydrocarbon reservoir evaluation through use

of borehole gravimeter data: Journal Petroleum Technology, v. 28, no.

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Mattick, R. E., Olmsted, F. H., and Zohdy, A. A. R., 1973, Geophysical

studies in the Yuma area, Arizona and California: U.S. Geological

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McCulloh, T. H., 1966, The promise of precise borehole gravimetery in

petroleum exploration and exploitation: U.S. Geological Survey\

Circular 531, 12 p.

McCulloh, T. H., LaCoste, L. J. B., Schoellhamer, J. E., and Pampeyan, E.

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gravimeter system Test results, in Geological Survey research 1967:

U.S. Geological Survey Professional Paper 575-D, p. D101-D112.

Scarborough, R. B., and Peirce, H. W., 1978, Late Cenozoic basins of

Arizona, in New Mexico Geological Society 29th Field Conference, 1978,

Guidebook of Land of Cochise, southeastern Arizona: p. 253-259.

Schmoker, J. W., 1977a, Density variations in a quartz diorite determined

from borehole gravity measurements, San Benito County, California: The

Log Analyst, v. 18, no. 2, p. 32-38.

____ 1977b, A borehole gravity survey to determine density variations in

the Devonian shale sequence of Lincoln County, West Virginia: U.S.

Dept. of Energy, Morgantown Energy Res. Center MERC/CR-77/7, 15 p.

22

__ 1978, Accuracy of borehole gravity data: Geophysics, v. 43, no. 3,

p. 538-542.

1979, Interpretation of borehole gravity surveys in a native-sulfur

deposit, Culberson County, Texas: Economic Geology, v. 74, p.

1462-1470.

Smith, N. J., 1950, The case for gravity data from boreholes: Geophysics,

v. 15, no. 4, p. 605-636.

Wilson, E. D., Moore, R. T., and Cooper, J. R., 1969, Geologic map of\

Arizona: Arizona Bureau of Mines map, scale 1:500,000.

Wilson, R. P., 1979, Availability of ground water on Federal land near the

Ak-Chin Indian Reservation, Arizona a reconnaissance study: U.S.

Geological Survey Open-File Report 79-1165, 36 p.

23