acoustic impedance, acoustic anisotropy, and ...acoustic anisotropy is 0 to 30% faster parallel to...

48. LABORATORY-DETERMINED SOUND VELOCITY, POROSITY, WET-BULK DENSITY,ACOUSTIC IMPEDANCE, ACOUSTIC ANISOTROPY, AND REFLECTION COEFFICIENTS FOR

CRETACEOUS-JURASSIC TURBIDITE SEQUENCES AT DEEP SEA DRILLING PROJECTSITES 370 AND 416 OFF THE COAST OF MOROCCO1

Robert E. Boyce, Deep Sea Drilling Project, Scripps Institution of Oceanography, La Jolla, California

ABSTRACT

From 661 to 880 m beneath the seafloor at DSDP Sites 370 and 416 are Albian to Barremian claystone with somelimestone, sandstone, and siltstone. Compressional-wave velocities ranged from 1.70 to 4.37 km/s, with an average insitu vertical velocity of 1.93 km/s.

From 880 to 1430 m are Hauterivian to Valanginian turbidites of alternating graded calcareous and quartzose cyclesfrom siltstone or fine sandstone to mudstone. Compressional-wave velocities range from 1.80 to 4.96 km/s with anaverage in situ velocity of 2.61 km/s.

From 1430 to 1624 m are early Valanginian to Tithonian (Kimmeridgian?) turbidites, with alternating quartzose silt-stone grading to mudstone cycles with hard micritic limestone and calcarenite (calciturbidites). Compressional-wavevelocities range from 2.26 to 5.7 km/s, with an average in situ vertical velocity of 3.25 km/s.

Acoustic anisotropy is 0 to 30% faster parallel to bedding in Cretaceous to Tithonian sandstone-siltstone turbiditesin mudstone and minor limestone from 661 to 1624 m below the seafloor. Between 2.0(?) km/s and 4.2(?) km/s, anisot-ropy becomes particularly significant (below 1178 m), where the anisotropy is about +0.4 km/s or greater. The mud-stone, softer sandstone, and softer siltstone tend to have velocities around 2.0 to 2.5 km/s; the cemented sandstone andlimestone cluster around 2.5 km/s to 4.2 km/s; thus the relative percentage anisotropy is greater for lower-velocity li-thologies. Above 4.2(?) km/s, the well-cemented sandstone and limestone tend to have a smaller (less than + 0.4 km/s)absolute anisotropy, and many samples are nearly isotropic.

These physical property data are separated into depth plots for (1) mudstone, (2) siltstone (3) sandstone, (4) marl-stone, and (5) limestone. The mudstone's porosity and wet-bulk density curves versus depth are slightly higher andlower, respectively, than similar porosity and wet-bulk density curves summarized in Hamilton (1976). These differ-ences could be some combination of (1) differences in laboratory methods; (2) age, lithologic, and cementation differ-ences; or (3) overconsolidation created by a geological sequence which has been eroded away.

If the average in situ vertical velocities calculated by Boyce (1980b) for Hole 416A are correct, then the 1.43-s(round-trip) reflector (blue) discussed by Lancelot and Winterer (1980) and Lancelot, Winterer et al. (1980b), wouldcorrelate to about 1500 m in Hole 416A, and not below 1624 m as suggested by Lancelot and Winterer. There appears tobe a significant change in the acoustic character at or around that depth (1500 m) to a more lithified, calcareous, andcemented lithology. This does not prove Lancelot and Winterer (1980) and Lancelot, Winterer et al. (1980b) to be incor-rect, but only suggests another possible interpretation.

INTRODUCTION

This chapter is concerned with the physical propertyrelationships enumerated below, using data measuredon cores recovered from Sites 370 and 416, in the Atlan-tic Ocean off the coast of Morocco (Fig. 1) for the Cre-taceous-Tithonian sandstone, siltstone, mudstone, andminor micritic limestone and calcarenite from 661 to1624 m below the seafloor. The objectives of the chapterare as follows:

1) At Site 416, to study physical properties versusdepth for different lithologic types: (a) mudstone, (b)siltstone, (c) sandstone, (d) marlstone, and (e) limestone.This is important for characterizing the lithology andphysical properties of this area and for making compari-sons to other areas.

2) At Sites 370 and 416, to undertake additional sys-tematic studies of the horizontal and vertical velocity,acoustic anisotropy, porosity, and wet-bulk density of

Hay, W. W., Sibuet, J.-C, et al., Init. Repts. DSDP, 75: Washington (U.S. Govt.Printing Office).

the geologic sequence. This information is valuable forcorrectly interpreting gravity data, seismic reflectiondata, seismic refraction data, and sonobuoy data.

3) At Sites 370 and 416, to attempt to calculate reflec-tion coefficients; and by using in situ interval velocitiescalculated by Boyce (1980b) for the geologic sectionpenetrated at Site 416, to attempt to correlate the acous-tic character of the data obtained from Sites 370 and 416with the 1.43-s (round-trip) reflector (blue) in seismicprofiles discussed by Lancelot, Winterer, et al. (1980b)and Lancelot and Winterer (1980).

DATA, DEFINITIONS, AND METHODSFor Site 416 data, the sediment classification is dis-

cussed in Lancelot, Winterer, et al. (1980a), and de-tailed age-dates and lithologies are discussed in Lance-lot, Winterer, et al. (1980b). Wet-bulk density is definedas the ratio of weight of water-saturated sediment orrock sample to its volume, expressed as g/cm3. Wet-wa-ter content is the ratio of the weight of seawater in thesample to the weight of the saturated sample, and is ex-pressed as a percentage. Porosity is the ratio of the porevolume in a sample to the volume of the saturated sam-

1229

R. E. BOYCE

40° N

35C

30c

25'30° W 25° 20° 15° 10c

Figure 1. Index map showing locations of DSDP Sites 370 and 416.

pie and is also expressed as a percentage. Acoustic im-pedance is defined as the product of the velocity andwet-bulk density, and is expressed as (g 105)/(cm2 s).All the equations, derivations, and techniques are dis-cussed in detail in Boyce (1980a).

With respect to sampling at Site 416, we generallywaited at least 4 hr. after the core had been broughton deck to allow it to reach room temperature. We thencut and removed an undisturbed (visible, undistortedbedding), water-saturated, compressional-sound-velocitysample, about 2.5 cm thick. The sample was carefullysmoothed with a sharp knife or file. Velocities were mea-sured to within ± 2 % accuracy with the HamiltonFrame velocimeter (Boyce, 1980a), perpendicular andparallel to bedding. Immediately afterward, its wet-bulkdensity was measured to within ±2 or 3% precisionwith the Gamma Ray Attenuation Porosity Evaluator(GRAPE) (Evans, 1965) as modified in Boyce (1980a),using special 2-minute gamma-ray counts. Then, thewet-water content of a subsample was determined byweighing the sample both wet and after drying 24 hr. at110°C. The weight of evaporated water was correctedfor salt (45%0) to give the weight of seawater (Boyce,1980a; Hamilton, 1971b). The estimated precision is±2.5% (absolute). Porosity (precision of ±6°7o) is de-termined from the product of the wet-water content andwet-bulk density, divided by the density of the interstitialwater (1.032 g/cm3). The acoustic impedance is ob-tained from the product of the vertical velocity and thewet-bulk density. The laboratory results of Site 416 Cre-taceous-Tithonian sedimentary rocks have been tabu-lated in Table 1.

All data for Site 370 are from Table 1 in Trabant(1978) and will not be tabulated here. Trabant (1978)and Lancelot et al. (1978) discuss their methods and thesediment classification used at Site 370. Detailed litholo-

gies and age-dates for Site 370 data are discussed in de-tail in Lancelot, Seibold, et al. (1978).

Compressional-wave (sound) velocity in isotropic ma-terial has been defined (Wood, 1941; Bullen, 1947; Birch,1961; Hamilton, 1971a, b) as

V =4µ/3\m

Qb(1)

where V is the compressional-wave velocity; ρb is thewet-bulk density in g/cm3 and ρb = ρwΦ + (1 - Φ)çg

(here <f> is the fractional porosity of the sediment orrock, and the subscripts b, g, and w represent the wet-bulk density, grain density, and water density, respective-ly); x is the incompressibility or bulk modulus; and µ isthe shear (rigidity) modulus

Where samples are anisotropic, × and µ may havevarious unique values for the corresponding vertical andhorizontal directions. See Laughton (1957), Carlson andChristensen (1977), Gregory (1977), and Bachman (1979)for a discussion of anisotropy.

Compressional-wave (sound) velocity of sedimentsand rocks has been related to sediment components byWood (1941), Wyllie et al. (1956), Nafe and Drake (1957)and others. Relationships of the Site 416 data to theseequations are discussed in Boyce (1980b). Velocity is re-lated to mineralogical composition, fluid content, watersaturation of pores, temperature, pressure, grain size,texture, cementation, direction with respect to beddingor foliation, and alteration, as summarized by Press(1966). Recently, Hamilton (1976, 1978, 1980) has sum-marized the velocity-density relationships of sedimentand rock of the seafloor for oceanic sediments and sedi-mentary rock.

Acoustic impedance is the product of the verticalvelocity and wet-bulk density. Reflection coefficients

1230

PHYSICAL PROPERTIES AND REFLECTION COEFFICIENTS

Table 1. Data on physical properties, Hole 416A.

Core-Section(interval in cm)

5-1, 30-321, 56-58

6-1, 23-252, 18-202, 140-1503, 16-18

7-1, 33-352, 12-142, 140-1503, 2-4CC, 14-15

8-7, 9-119-1, 146-148

2, 58-603, 145-1474, 125-1274, 140-1506, 11-13

10-1, 13-162,6-82, 30-32

11-1, 2-41, 9-112, 89-914, 140-1505, 135-1376, 77-79

12-1, 10-122, 42-443, 29-313, 86-874, 42-44

13-1, 7-92, 42-443, 28-30

14-1, 5-72, 49-513, 96-984, 62-645, 69-70

15-1, 2-42, 11-133,0-24, 7-85, 133-1356, 55-57

16-1, 2-42, 6-83, 9S-974, 7-8

17-1, 33-351, 86-881, 98-1002, 52-544, 28-30

18-1, 49-502, 25-273,3-54, 2-44, 66-68

19-1, 15-172, 31-333, 11-133, 36-38CC, 18-20

20-1, 6-81, 40-432, 59-612, 70-722, 95-97

21-1, 57-592, 103-1053, 88-904, 46-485, 4-6

22-1,0-22, 22-243, 8-104, 52-544, 57-59

23-1, 2-42, 5-73, 54-554, 13-155, 22-24

24-1, 3-51, 95-972,0-2

Depth inhole(m)

754.30754.56891.23892.68893.95894.16991.83993.12994.45994.52

1102.091178.361178.981181.351182.651182.851184.511185.531186.961187.201194.821194.891197.191200.751202.151203.071204.401206.221207.591208.171209.221213.871215.721217.081223.451225.391227.361228.521230.091232.921234.511235.901237.471240.231240.951242.521244.061246.451247.071252.331252.861252.981254.021256.781261.991263.251264.531266.021266.661271.151272.811274.111274.361278.241277.561277.901279.591279.701279.951290.271292.531293.881294.961296.041299.501301.221302.581304.521304.571309.121310.651312.641313.731315.321318.631319.551320.10

IIBeds

(km/s)

3.8611.8861.897

1.8684.6661.988

2.003

2.5882.4214.3252.4892.330

4.5364.5532.6233.0144.9472.6072.497

2.5022.3574.8362.6023.083

2.7382.3864.4322.2742.4602.6043.8834.3222.3762.3162.4544.5852.4212.7212.1284.5322.1752.6982.4342.4162.0392.5922.3353.6882.1404.6132.4932.7112.5392.5092.0814.0902.3074.1812.6493.2672.3512.4832.9474.2892.5992.8133.4122.6602.4732.7743.7092.2784.4462.5552.4732.6992.7913.6122.3362.7302.224

Compressional-sound velocity

_LBeds

(km/s)

1.7173.4661.7671.767

1.8054.4511.836

1.801

2.6311.8583.8872.3982.176

4.5264.6022.1332.5914.4222.1622.207

2.0852.1304.6862.1752.489

2.2872.0194.5452.0762.0652.2164.0693.5452.2402.0832.0113.8482.2912.3412.0064.4322.0012.1912.1742.0191.9892.1362.0753.2492.0443.8552.0832.2952.1772.0822.0043.5312.1113.7342.2333.2592.1602.1092.5403.8802.2492.3603.1361.8192.0512.3583.036

4.0442.1212.0532.3052.3803.0102.0362.3752.049

Anisotropy

I--L(km/s)

0.3950.1190.130

0.0630.2150.152

0.202

-0.0430.5630.4380.0910.154

0.010-0.049

0.4900.4230.5250.4450.290

0.4170.2270.1500.4270.594

0.4510.367

-0.1130.1980.3950.388

-0.1860.7770.1360.2330.4430.7370.1300.3800.1220.1000.1740.5070.2600.3970.0500.4560.2600.4390.0960.7580.4100.4160.3620.4270.0770.5590.1960.4470.4160.0080.1910.3740.4070.4090.3500.4530.2760.8410.4220.4160.673

0.4020.4340.4200.3940.4110.6020.3000.3550.175

(1-j.yi

11.406.737.36

3.494.838.28

11.22

-1.6330.3011.273.797.08

2.21-1.0622.9716.3311.8720.5813.14

20.0010.663.20

19.6323.87

19.7218.17

-2.499.54

19.1317.51

-4.5721.92

6.0711.1922.0319.155.67

16.236.082.268.70

23.1411.9619.662.51

21.3512.5313.514.70

19.6619.6818.1316.6320.513.84

15.839.28

11.9718.630.258.84

17.7316.0210.5415.5619.198.80

46.23?20.5817.6422.17

9.9420.4620.4617.0917.2720.0014.7314.958.54

Temp.CO25262526

262526

25

2627272727

272727272626.526

2626252525

252626252626252525252525252525252525252425252525252727272525252525252525252525252525252525252626262626262626252525

GRAPE "special"wet-bulk densitya

2-min. count(g/cmJ)D

IBeds

2.100

2.269

2.1522.600

2.439

2.341

2.320

±Beds

1.8012.1022.0522.024

2.576

2.3932.3702.6122.3322.284

2.6352.6012.2632.4692.6532.1672.281

2.2652.3182.6152.3212.191

2.371

2.3142.3982.3452.3762.4692.2062.2072.2792.5202.3192.3182.2952.5242.2142.3422.2872.2622.2812.2782.1982.5482.318

2.3332.2422.3962.392

2.166

2.3272.3222.3682.481

2.3462.3262.5092.3332.3682.5372.2952.5592.331

2.2742.3222.4832.2472.3752.164

Wetwater

contentSalt corr.

(%)

8.2520.5820.8919.2521.243.34

17.8816.2616.10

7.7711.064.48

11.1810.8310.941.951.96

10.877.383.71

10.7611.9712.7711.7411.942.528.42

14.3712.7610.3312.752.36

13.4910.593.423.43

10.2613.17

8.573.59

13.472.14

12.1112.8811.0213.6113.7610.5113.618.70

13.931.01

11.7310.7910.3811.1017.081.36

14.156.28

11.035.92

11.869.075.04

10.309.207.41

10.7211.3310.477.35

12.052.06

10.2311.8210.279.818.14

11.5810.1310.71

Porosityc

(%)

16.8040.9240.97

43.228.34

39.31

33.57

18.0225.4011.3425.2623.97

4.984.94

23.8417.669.54

22.5926.46

25.7726.826.39

18.9430.51

23.73

31.3524.067.878.21

21.9328.16

20.938.07

29.965.28

25.9829.2324.4229.8330.4123.2028.9921.4832.29

25.0937.113.16

32.80

23.1513.99

26.6920.8112.1223.3620.9116.7026.0625.6124.0218.0726.805.11

23.1126.5722.6322.0719.5825.2123.3122.46

Acousticimpedance

(g 105/cm2 s)

3.097.293.633.58

3.79e

11.474.16e

3.88e

6.304.40

10.155.594.97

11.9311.974.826.40

11.734.695.03

4.724.94

12.255.055.45

5.42

4.804.955.209.678.754.944.604.589.705.315.434.60

11.284.435.134.974.574.544.874.568.274.74

4.864.498.465.05

4.837.95e

5.034.906.019.635.26e

5.547.294.564.785.587.705.22

10.344.944.76e

5.245.537.474.575.644.43

Lithologyd

Laminated siltstonePorcellaniteLaminated mudstoneMudstone (dk. grn.)I.W.Laminated siltstoneCalcite cemented sandstoneMarlstone (gyish. grn.)I.W.Mudstone (brn.)Calcite cemented sandstoneLaminated siltstoneMudstone (olv. grn.)Calcite cemented sandstoneSiltstoneMudstone (gyish. grn.)I.W.Calcite cemented sandstoneCalcite cemented sandstoneMudstone (grnish. gy.)Laminated siltstone-sandstoneCalcite cemented sandstoneCalcareous mudstone (gy. olv. grn.)Mudstone (brn. gy.)I.W.Calcareous mudstone (gyish. grn.)Mudstone (brn. gy.)Calcite cemented sandstoneCalcareous mudstone (gyish. grn.)Mudstone (dsky. y. brn.)I.W.Calcareous mudstone (gyish. grn.)Calcareous mudstone (gyish. grn.)Calcite cemented sandstoneMudstone (dsky. y. brn.)Marlstone (gyish. grn.)Mudstone (dsky. y. brn.)Calcite cemented sandstoneCalcite cemented sandstoneSoft sandstone-siltstoneSiltstoneMudstone (gy. olv.)Calcite cemented sandstoneFine-grained sandstoneMarlstone (gy. olv.)Laminated sandstone (gy. olv.)Calcite cemented sandstoneMudstone (dsky. brn.)Mudstone (gy. olv. grn.)Mudstone (dsky. y. brn.)Nannofossil mudstone (dsky. y. grn.)Laminated siltstone (dsky. y. brn.)Nannofossil marlstone (pale grn.)Mudstone (dsky. y. brn.)Calcite cemented sandstoneLaminated mudstone (gy. brn.)Calcite cemented sandstoneMudstone (gyish. brn.)Mudstone (dk. grnish. gy.)Marlstone (gyish. grn.)Calcareous mudstone (gyish. olv.)Laminated mudstone (brn.)SandstoneMudstone (gy. brn.)Calcite cemented sandstoneMudstone (dk. grn. gy.)Calcite cemented sandstoneLaminated siltstoneMudstone (brn.)Calcareous mudstone (dsky. y. grn.)Calcite cemented sandstoneCalcareous mudstone (grn.)Calcareous mudstone (gyish. grn.)SandstoneMudstone (brn.)Mudstone (brn.)Calcareous mudstone (pale grn.)Laminated sandstone (brn.)Laminated siltstoneCalcite cemented sandstoneMudstone (dk. gyish. grn.)Mudstone (dk. brn.)Laminated siltstoneCalcareous mudstone (gy. grn.)Laminated calcite cemented sandstoneMudstone (dk. brn.)Calcareous mudstone (gy. grn.)Laminated siltstone

1231

R. E. BOYCE

Table 1. (Continued).


2, 123-1293, 96-98

25-1, 94-962, 16-182, 123-1253, 20-224,3-55, 113-115

26-1, 72-742,3-43, 34-364, 32-345, 55-57

27-1, 0-22, 39-413, 11-133, 106-107

28-1, 12-142, 59-613, 85-875, 10-126, 2-4

29-1, 52-542, 2-43, 97-994, 103-1055, 51-536, 127-129

30-1, 77-792, 107-1093, 29-314, 147-1495, 104-106

31-1, 14-162, 81-822, 144-1463, 35-373, 95-97

32-1, 21-231, 131-1332,0-22, 100-1043, 71-74

34-1, 12-142, 6-83, 33-354, 24-26

35-1, 35-391, 58-602, 82-843, 0-2

36-1, 16-181, 130-1332, 68-703, 8-103, 29-31

37-2, 2-42, 54-573, 27-294, 17-194, 35-374, 55-574, 70-72

38-1, 10-121, 44-461, 135-1382, 38-412, 44-46

40-1, 33-361, 80-822, 127-1283, 23-253, 48-503, 79-81

41-1, 4-51, 84-873, 107-1094, 110-1135, 8-9

42-1,43-451, 96-982, 110-1133, 58-60

43-1, 35-371, 80-821, 93-952, 36-383, 66-68

Depth inhole(m)

1321.331322.591328.651329.361330.431330.901332.231334.83

1338.731340.541342.021343.751346.701348.591349.811350.761356.321358.291360.051362.301363.721366.221367.221369.671371.231372.211374.471375.971377.771379.491381.171382.241384.741386.911387.541387.951388.551394.311395.411395.601396.601397.811406.921408.361410.131411.541416.751416.981418.721419.401425.561426.701427.581428.481428.691436.521437.041438.271439.671439.851440.051440.201445.101445.441446.351446.881446.941454.831455.301457.271457.731457.981458.291463.941464.741467.971469.501469.981473.731474.261475.901476.881482.751483.201483.331484.261486.06

IIBeds

(km/s)

4.5312.4024.4783.4592.4062.4682.3172.515

2.3622.2542.0972.8092.6574.6153.8562.8872.8744.3762.4232.4932.5014.3072.5182.8232.4332.1932.7912.7153.2392.6552.6812.4973.2422.6434.1892.6263.1423.0672.5722.9843.7783.0533.1442.7242.7664.5943.3572.9752.9305.2573.8203.0993.2443.4283.4563.2042.7614.3262.8033.7853.8823.3563.1803.2772.8364.3003.2773.1623.9993.7023.5804.7054.4604.5323.2054.6923.3734.6355.1613.9513.8823.7373.7023.0213.7813.8443.597


±Beds

(km/s)

3.3732.0264.0913.0212.2462.4602.0842.044

2.0772.209

2.4222.2744.3622.9252.4662.4623.6722.2212.1962.2563.8522.0882.3843.3492.1272.3352.3102.6722.4722.2592.2402.8142.2694.2892.3582.513

2.1122.4903.4382.4752.6832.2702.5444.3032.7712.2622.4404.2932.9942.4582.7663.0143.0772.7492.2153.5692.3323.0033.5802.9762.1132.7542.3683.8222.8872.4943.3863.2912.6994.4023.4664.4742.3944.4012.9094.0385.4842.7473.6483.4323.3382.4763.2523.3623.057

Anisotropy

(km/s)

1.1580.3760.3870.4380.1600.0080.2330.471

0.2850.045

0.3870.3830.2530.9310.4210.4120.7040.2020.2970.2450.4550.4300.439

-0.9160.0660.4560.4050.5670.1830.4220.2570.4280.374

-0.1000.2680.629

0.4600.4940.3400.5780.4610.4540.2220.2910.5860.7130.4900.9640.8260.6410.4780.4140.3790.4550.5460.7570.4710.7820.3020.3801.0670.5230.4680.4780.3900.6680.6130.4110.8810.3030.9940.0580.8110.2910.4640.597

-0.3231.2040.2340.3050.3640.5450.5290.4820.540

(J - X )/ X(%)

34.3318.569.46

14.507.120.33

11.1823.04

13.722.04

15.9816.845.80

31.8317.0716.7319.179.10

13.5210.8611.8120.5918.41

-27.353.10

19.5317.5321.227.40

18.6811.4715.2116.48

-2.3311.3725.03

21.7819.849.89

23.3517.1820.00

8.736.76

21.1531.5220.0822.4627.5926.0817.2813.7412.3216.5524.6521.2120.2026.048.44

12.7750.5018.9919.7612.5113.5126.7818.1012.4932.646.88

28.681.30

33.886.61

15.9514.78

-5.8943.836.418.89

10.9022.0116.2714.3417.66

Temp.CO

2525252525252525

25252525 .262626262525252525252525252525252525252525252525252525252525262626262626262626252525252525252525252525252525252424242424242626262626272625262626262626

GRAPE "special"wet-bulk density8

2-min. count(g/cm3)b

1 •1

Beds Beds

2.635

2.6162.2402.2862.4142.254

2.3792.2202.287

2.2282.3822.5192.6662.4192.3732.1722.5292.4082.3612.3932.5932.3002.3652.3262.2992.4082.277

2.3682.1912.2922.4362.3232.5742.406

2.462 2.3612.3982.3132.3522.3342.3862.4102.3642.4062.5912.4312.3352.3312.5562.521

2.4352.4392.5142.5012.4912.3362.5502.4032.5092.4832.4572.4472.4632.4112.5762.4732.2342.5582.5342.4142.6502.5482.6432.2642.5862.5242.5852.6922.4312.7092.5192.570

2.3862.5342.4812.398

Wetwater

contentSalt corr.

(%)

0.8612.826.598.51

10.3410.0910.4211.5511.406.638.73

14.809.376.552.448.085.047.862.96

10.9512.319.104.82

12.3710.618.977.96

10.649.338.209.328.218.636.66

10.723.138.48

7.9611.856.704.677.474.867.32

8.5110.405.708.012.545.61

10.017.777.014.415.50

11.245.86

10.816.055.056.536.737.038.984.763.565.904.796.727.712.147.752.90

12.424.358.623.201.999.405.364.646.219.294.931.301.30

Porosityc

(%)

2.20

16.7018.4722.9023.6022.76

26.2814.2619.3531.9521.6315.996.30

18.9411.5916.547.25

25.5528.1621.1012.1127.5724.3120.2217.7324.8320.58

21.3917.4319.1715.7224.13

7.8119.77

18.5026.5615.2710.5617.2711.3516.77

21.3724.5012.9018.096.29

13.7023.6218.3617.0810.6913.2825.4414.4825.1714.7112.1515.5515.9616.7820.9811.888.53

12.7711.8716.5018.035.50

19.137.42

27.2510.9021.088.025.19

22.1414.0711.3315.4621.4812.113.133.02

Acousticimpedance

(g 105/cm2 s)

8.89

10.706.775.135.934.70

4.615.054.67e

5.775.73

11.637.085.855.359.295.355.185.399.994.805.647.794.895.625.25

5.854.955.136.855.27

11.045.675.937.35e

4.895.868.025.916.475.376.12

11.156.745.285.69

10.977.555.98e

6.757.587.706.845.179.105.607.538.897.315.176.785.719.857.145.578.668.346.52

11.678.83

11.825.42

11.387.34

10.4314.766.689.888.658.585.91e

8.248.347.33

Litholog

Calcite cemented sandstoneMudstone (olv. gy.)Calcite cemented sandstoneSandstoneLaminated siltstoneCalcareous mudstone (gy. grn.)Mudstone (It. brn. gy.)Mudstone (olv. grn.)Marlstone (gyish. grn.)Mudstone (gyish. red)SandstoneCalcareous mudstone (dk. y. grn.)SandstoneCalcareous mudstone (gyish. grn.)Calcite cemented sandstoneSandstoneCalcareous mudstone (gy. grn.)Calcareous mudstone (gyish. grn.)Calcite cemented sandstoneLaminated siltstone (pale brn.)Mudstone (pale brn.)Mudstone (olv. grn.)Calcite cemented sandstoneMudstone (olv. grn.)Calcareous mudstone (gy. grn.)SandstoneLaminated siltstone (gyish. brn.)Mudstone (brn. gy.)Mudstone (brn.)Calcareous mudstone (gy. grn.)SandstoneMudstone (olv. grn.)Laminated siltstone (brn.)Calcareous mudstone (gy. grn.)Mudstone (pale grn.)Calcareous cemented sandstoneMudstone (brn.)Claystone-siltstone-sandstone (graded bed)Calcareous mudstone (gy. grn.)Mudstone (olv. grn.)Laminated siltstone (brn.)SandstoneMarl (gy. grn.)Calcareous Mudstone (gyish. grn.)Mudstone (dsky. y. brn.)Sandstone-siltstoneCalcite cemented sandstoneCalcareous mudstone (grn. gy.)Laminated mudstone (brn.)Laminated siltstone (brn.)Calcarenite (yish. gy.)Laminated siltstone (olv. gy.)Mudstone (mod. brn.)Calcareous mudstone (gy. olv.)Marly limestone (It. olv. gy.)Laminated siltstone (olv. gy.)Laminated siltstone (olv. gy.)Mudstone (gy. brn.)Calcarenite (grn. gy.); graded bedClaystone (med. brn.)Cross-laminated sandstone-siltstone (brn. & gy.)Limestone (It. olv. gy.)Marlstone (gyish. olv.)Mudstone (brn. gy.)Laminated siltstone (olv. gy.)Claystone (mod. brn.)Calcite cemented sandstone (dsky. y. brn.)Marlstone (pale y. brn.)Mudstone (mod. brn.)Limestone (pale brn.)Laminated siltstone (olv. gy.)Calcareous mudstone (gy. olv.)Calcite cemented sandstone (It. olv. gy.)Laminated calcisiltite (pale brn.)Limestone (pale y. brn.)Mudstone (dsky. y. brn.)Calcarenite (pale y. brn.)Laminated siltstone (dsky. y. brn.)Laminated sandstone (olv. gy.)Calcarenite (It. olv. gy.)Sandstone-siltstone (It. olv. gy.); laminatedLimestone (dk. y. brn.)Calcareous mudstone (gy. red)Calcareous mudstone (mod. brn.)Mudstone (gy. red)Laminated sandstone (olv. gy.)Limestone (pale red)Laminated siltstone (dsky. brn.)

1232


Table 1. (Continued).


44-1, 72-741, 89-911, 143-1452, 104-106

45-1, 13-151, 65-671, 68-702, 72-753, 8-10

46-1, 6-81, 74-761, 82-842,0-22, 20-22

47-1, 11-131, 36-382, 98-100

48-1, 6-91, 52-531, 97-1001, 107-1102, 0-2

49-1, 24-261, 43-462, 18-202, 55-572, 133-135

50-1, 6-81, 18-201,23-251, 133-1352, 82-833, 18-20

51-1, 24-251, 33-342, 24-252, 72-74

52-1, 9-101,31-351, 79-802, 96-983, 16-18

53-1, 0-21, 7-91, 107-1093, 140-142

57-1, 11-131, 36-381, 44-451, 104-1061, 145-147

Depth inhole(m)

1492.621492.791493.331494.451501.331501.851501.881503.421504.281510.661511.341511.421512.101512.301520.111520.361522.481529.561530.021530.471530.571531.001539.341539.531540.781541.151541.931548.661548.781548.831549.931550.921551.781558.241558.331559.741560.221567.491567.711568.191569.861570.561576.801576.871577.871581.201614.611614.861614.941615.541615.95

IIBeds

(km/s)

3.6603.1884.0953.1465.1634.2293.1975.0503.3623.4513.4394.4343.7654.2643.7053.1873.3432.7764.0534.6054.5483.3643.6853.4134.8784.5544.5512.9873.9985.2814.6233.1204.4413.9984.7423.1364.7464.4303.1354.3234.8093.8824.4753.2773.4175.2513.3074.3584.9553.8115.699


_LBeds

(km/s)

3.0662.4373.7512.7874.7304.1702.4295.1651.922?2.9662,9504.2113.1914.0953.3342.4434.4542.2453.7324.8034.3322.9972.9752.6234.5454.4133.7332.4653.6405.2164.3922.6164.1603.6434.6452.4904.5814.2432.3574.1844.7862.9704.4802.6233.0644.8962.5283.9664.5103.1115.532

Anisotropy

I--L(km/s)

0.5940.7510.3440.3590.4330.0590.768

-0.1151.4400.4850.4890.2230.5740.1690.3710.744

-1.1110.5310.321

-0.1980.2160.3670.7100.7900.3330.1410.8180.5220.3580.0650.2310.5040.2810.3550.0970.6460.1650.1870.7780.6390.0230.912

-0.0050.6540.3530.3550.7790.3920.4450.7000.167

(Il--D/-L(%)

19.3730.829.17

12.889.151.41

31.62-2.2374.9216.3516.585.30

17.994.13

11.1230.45

-24.9423.65

8.60-4.12

4.9912.2523.8730.127.333.20

21.9121.18

9.841.255.26

19.276.759.742.09

25.943.604.41

33.013.320.48

30.71-0.1024.9311.527.25

30.819.889.87

22.503.02

Temp.(°C)

262525252525252525262526262626262625262626262525252525262626262626262626262525252525262626262526262525

GRAPE "special"wet-bulk density8

2-min. count(g/cm3)b

I -LBeds Beds

2.4752.3782.6712.4162.6552.4982.2832.6532.5192.5402.5092.6172.4372.6472.5452.4082.6142.3272.5722.6432.5202.4652.4742.3532.6132.674

2.3732.6002.6102.5752.2822.6002.5112.6292.3382.6132.6302.3912.545

2.4782.5392.4352.4422.6812.4292.5552.6292.415

2.717

Wet

watercontent

Salt corr.(%)

4.949.113.108.175.113.996.301.277.945.182.973.373.420.633.389.173.487.352.581.751.127.175.537.012.512.312.208.482.612.172.827.573.104.073.427.591.921.85

11.091.642.394.980.835.815.272.758.022.001.403.120.74

Porosityc

(%)

11.8520.99

8.0219.1313.159.66

13.943.26

19.3812.757.228.558.081.628.34

21.408.81

16.576.434.482.73

17.1313.2615.986.365.99

19.506.585.497.04

16.747.819.908.71

17.204.864.71

25.704.04

11.962.04

13.7112.477.14

18.884.953.577.301.94

Acousticimpedance

(g 105/cm2 s)

7.595.80

10.026.73

12.5610.425.55

13.704.847.537.40

11.027.78

10.848.495.88

11.645.229.60

12.6910.927.397.366.17

11.8811.80

5.859.46

13.6111.315.97

10.829.15

12.215.82

11.9711.165.64

10.65

7.3611.376.387.48

13.136.14

10.1311.867.51

15.03e

Lithology0

Laminated sandstone (olv. gy.)Mudstone (dsky. y. brn.)Limestone (pale y. brn.)Laminated siltstone (dsky. y. brn.)Calcarenite (pale y. brn.)Laminated sandstone (gy. red)Mudstone (mod. brn.)Limestone (pale y. brn.)Laminated siltstone (dsky. y. brn.)Mudstone (mod. brn.)Marlstone (dk. y. brn.)Limestone (pale y. brn.)Laminated sandstone (dk. y. brn.)Limestone (gy. olv.)Laminated sandstone (dk. y. brn.)Mudstone (dsky. brn.)Limestone (pale y. brn.)Mudstone (mod. brn.)Marlstone (dk. y. brn.)Limestone (pale y. brn.)Laminated sandstone (olv. gy.)Laminated siltstone (olv. gy.)Laminated siltstone (dsky. y. brn.)Mudstone (gyish. brn.)Limestone (pale y. brn.)Calcarenite (dk. y. brn.)Laminated sandstone (olv. gy.)Mudstone (gy. olv. grn.)Marlstone (mod. brn.)Calcarenite (pale y. brn.)Limestone (pale y brn.)Laminated siltstone (dsky. y. brn.)Laminated sandstone (olv. gy.)Limestone (pale brn.)Laminated sandstone (It. olv. gy.)Laminated mudstone (dsky. y. brn.)Calcarenite (gy. olv.)Limestone (It. olv. gy.)Mudstone (gy. brn.)Calcarenite (It. olv. gy.)Laminated sandstone (olv. gy.)Laminated siltstone (mod. brn.)Laminated sandstone (gy. olv.)Mudstone (gy. brn.)Laminated siltstone (dsky. y. brn.)Limestone (pale y. brn.)Mudstone (dsky. brn.)Sandstone (It. olv. gy.)Limestone (pale y. brn.)Laminated siltstone (dsky. y. brn.)Calcarenite (pale y. brn.)

a The calculation used the following parametrs: ρ g , ρ g c = 2.7 g/cm3; ρf = 1.025 g/cm3, ρfc = 1.128 g/cm3, µ = 0.1028 cm2/g for Cores 1 through 16, and µ = 0.1024 cm2/g for Cores 17through 57.

b S.I. units are m/s = (km/s) × 1000; kg/m3 = (g/cm3)/103.c Porosity = [salt corrected wet-water content) × (wet-bulk density)] /(density interstitial water); assume salinity = 45% and interstitial water density = l.O32g/cm.d Gray = gy.; green = grn.; brown = brn.; yellow = y.; olive = olv.; light = It.; dark = dk.; moderate = mod.; medium = med.; -ish = -ish (e.g., gyish = grayish); I.W. = interstitial water sample.e Horizontal velocity or density used in the calculation.

(R.C.) from 661 to 1624 m are calculated from the im-pedance data:

R.C. = h ~h + h

(2)

where Io is the upper acoustic impedance and I is thelower impedance value. Reflection coefficients are com-puted very simply by using the upper and lower imped-ance values as they are listed in their tables, and plottingthe reflection coefficient value at the same depth as thelower impedance value. Because of this very simple ap-proach, investigators must be very careful about pre-cisely correlating these reflection coefficients to reflec-tors in the seismic profiles.

RESULTS

The physical property data discussed in this chapterare for the following Cretaceous-Tithonian geologic se-quence at Site 370 and Site 416 (Lancelot, Winterer, etal., 1980b):

1) From 661 to 880 m below the seafloor are Albianto Barremian clay stone with some limestone, sandstone,and siltstone.

2) From 880 to 1430 m are Hauterivian to Valangini-an turbidites of alternating graded calcareous and quartz-ose cycles from siltstone or fine sandstone to mudstone.

1) From 1430 to 1624 m are early Valanginian toTithonian (Kimmeridgian?) turbidites with alternatingquartzose siltstone grading to mudstone cycles with hardmicritic limestone and calcarenite (calciturbidites).

1233

R. E. BOYCE

For the Cretaceous-Tithonian geologic sequence atSites 416 and 370, as discussed above, horizontal com-pressional-wave velocity versus depth below the seaflooris plotted in Figure 2, and vertical compressional-wavevelocity versus depth are shown in Figure 3. From Fig-ure 3 there is an obvious change in acoustic character at~ 1375 and ~ 1475 m.

From 1475 to 1624 m velocities are widely scattered;this is caused by varying amounts of cementation by cal-cium carbonate. Even the relatively lower-velocity mud-stone, in general, appears to have a slightly higher veloc-ity than similar relative low-velocity mudstone above~ 1475 meters. The very high vertical velocities (greaterthan 5.0 km/s) are the micritic limestone, but particu-larly the well-cemented calcarenites below —1473 meters.

The first (going down the hole) high vertical velocity(>5 km/s) layer occurs at ~ 1474 meters, but this is arelatively thin layer and thus it may not create a signifi-cant reflection on the seismic profile. However, it couldbe possible that an important reflector is created as a re-sult of the overall increase in cementation or lithificationof the entire lower geologic sequence from ~ 1474 me-ters and downward. If this is assumed to be possible,

then the actual reflector in the seismic profiles may belower, perhaps at approximately 1500 m or more. Thiswould allow for the proper ideal thickness (about aquarter wave length) needed for a significant reflectinghorizon.

Figure 4 displays reflection coefficients versus depth.It is not particularly helpful as there is such wide varia-tion in all the data; thus it does not appear to be as use-ful as Figure 3 in helping to identify potential seismic re-flectors. However, at about 1460 to 1500 m there aresome variations in velocity which could be a potentialreflector.

Acoustic anisotropy is important for estimating verti-cal velocities (for seismic-reflection profiles) from thehorizontal velocities determined by refraction techniques,and the oblique velocities determined by sonobuoy tech-niques. Acoustic anisotropy in sedimentary rock may becreated by some combination of the following variablesas summarized in Press (1966): (1) alternating layerswith high- or low-velocity materials; (2) tabular miner-als that are aligned with bedding, thus creating fewergaps in a direction parallel to bedding; (3) minerals withacoustic anisotropy, whose high-velocity axis may be

600

700

800

900

1000

E 1100

Ic/> 1200

1300

1400

1500

1600

1

oΔ= DSDP Site 370 (Trabant, 1978)O= DSDP Site 416

Δ

Δ

Δ

Δ Δ

2.5 3.0 3.5 4.0 4.5Horizontal sound velocity (km/s)

5.0 5.5 5.7

Figure 2. Horizontal velocity versus depth for the Cretaceous-Jurassic geologic section at Sites 416 and 370.

1234


600

700

800

900

g 1000

α<D

E 1100

1200

1300

1400

1500

1600

o

ΔΔ

o

Δ= DSDP Site 370 (Trabant, 1978)O=DSDP Site 416

Δ ?Δ

Δ

O

oo.

o

o

1.7 2.0 2.5 3.0 3.5 4.0Vertical sound velocity (km/s)

5.5 5.7

Figure 3. Vertical velocity versus depth for the Cretaceous-Jurassic geologic section at Sites 416 and 370.

aligned with the bedding plane; (4) foliation parallel tobedding, and (5) cementation along certain horizontallayers.

Figure 5 shows acoustic anisotropy for Cretaceous toTithonian sandstone and siltstone turbidites in mudstoneand minor limestone from 661 to L624 m below the sea-floor. In general, acoustic anisotropy of the sedimentaryrocks below 1178 m, which have velocities betweenabout 2.0 and 4.2 km/s, is about 0.4 km/s or more,faster in the horizontal than in the vertical plane. Somesamples have an absolute anisotropy as great as 1.0km/s. The relative acoustic anisotropy ranges from 0to 30%, 5 to 20% being typical. The mudstones whichhave velocities of 2.0 to 3.0 km/s, tend to have the great-est relative anisotropy, as compared with the higher ve-locity (3 to 4.2 km/s) sandstones, siltstones, and lime-stones. Where the sandstone, siltstone, and limestonehave velocities greater than about 4.2 km/s, the acousticanisotropy becomes much less significant, as the sampleis more thoroughly cemented, and many samples areisotropic.

Figures 6 through 15 show the following physicalproperties versus depth for each lithologic type at Hole416A: (1) vertical velocity and horizontal velocity (both

at laboratory temperatures and pressures), (2) acousticanisotropy, (3) porosity, (4) wet-bulk density, and (5)acoustic impedance. Mudstones are presented in Figures6 and 7; siltstones, in Figures 8 and 9; sandstones, inFigures 10 and 11; marlstones, in Figures 12 and 13; andlimestones, in Figures 14 and 15. Some of the calcar-enites in Figures 10 and 11 are equivalent to limestone.Only the Hole 416A data listed in Table 1 are plotted, asthe techniques used at Site 370 are not precisely com-parable to the Site 416 data.

In Figure 7 the wet-bulk density and porosity of themudstones are greater and less, respectively, than simi-lar curves summarized in Hamilton (1976) for oceanicterrigenous sedimentary sequences. The fact that Site416 data are different from Hamilton's could be in partrelated to differences in: (1) methods; (2) differences ingrain-size distribution and mineralogy; (3) differences inthe amount of calcium carbonate cement; (4) age of theSite 416 mudstones (being older, they have had moretime to recrystallize, lithify, and to consolidate to a great-er degree); or (5) overconsolidation of Site 416 mud-stones by a theoretical, previously overlying sedimen-tary sequence which has been eroded away (Hedberg,1936; Hamilton and Menard, 1956; Hamilton, 1959,

1235

R. E. BOYCE

Reflection coefficients

600 r

700 -

800 -

900 -

1000 -

-0.8 -0.6 -0.4 -0.2 +0.2 +0.4 +0.6 +0.8

1100 -

1200 -

1300 -

1400 -

1500 -

1600 -

Δ = DSDP Site 370 (Trabant, 1978)

0 = DSDP Site 416

Figure 4. Reflection coefficient versus depth for the Cretaceous-Ju-rassic geologic section at Sites 416 and 370.

1976, 1980; Margara, 1978). Of these possible causes, 1through 4 are the most probable.

In Figure 7 there is a definite boundary at 1330 mwhere calcareous mudstones have a distinctly lower po-rosity than the overlying unit. Below 1450 m in Figure 6,mudstone acoustic anisotropy is at its greatest, which iswhat one would expect for mudstone as the clayey min-erals become aligned horizontally and samples becomemore fissile (Press, 1966; Bachman, 1978).

Siltstones in Figures 8 and 9 show a distinct boundaryat about 1425 m. The siltstones are relatively uncement-ed above 1425 m, and abundant calcareous cemented silt-stones occur below 1425 m, which have greater velocitiesand greater acoustic anisotropy. Irregular density-po-rosity variations are probably created by different grain-size distribution, grain packing, and different degrees ofcementation.

Sandstone plots in Figures 10 and 11 show an unce-mented sandstone trend and a cemented sandstone trendaround 1200 m depth, with semilithified sandstoneshaving a relatively high acoustic anisotropy. From 1200m down the uncemented sandstone trend becomes morecemented and merges with the cemented sandstone trend(from 1200 to 1600 m). Below 1300 or 1400 m the maxi-mum relative acoustic anisotropy decreases down to1550 m. Below 1550 m, porosity is typically around 5%,sound velocity is very high, and acoustic anisotropy isrelatively small. This is a result of the sandstones be-coming so cemented (particularly the calcarenites) thatthey become more isotropic than the semicemented sand-stone above. At 1420 m is the first high-horizontal-ve-locity-calcarenite (>5.0 km/s). Below 1420 m sand-stones appear to be more cemented.

The calcarenites in Figures 10 and 11 are essential-ly limestones, and they have typically greater velocitiesthan the micritic limestone at the same horizon or depth.This is because they are more recrystallized.

Marlstone velocities in Figure 12 uniformly increasewith increasing depth, but with a possible boundary atabout 1530 m.

Limestone velocity increases and porosity decreas-es with increasing depths in Figures 14 and 15. Many ofthe more cemented and lower porosity limestones havesmaller relative acoustic anisotropies. Porosities hererange from 4 to 18%, which are lower than porositiesof Cretaceous Pacific Ocean pelagic nannofossil-fora-miniferal limestones (Schlanger, Jackson et al., 1976),where identical laboratory methods were used. However,Site 416 limestones are micritic s older, and more deeplyburied; thus they are more recrystallized and probablyshould have a smaller porosity than the nannofossil-for-aminifer types. Site 416 limestone porosities are alsoslightly lower than the limestone porosity-depth plotsummarized by Scholle (1977).

In Situ Reflection Velocity

In general, from 661 to 880 m, the Albian to Barremi-an clay stone, with some limestone, sandstone, and silt-stone, have velocities ranging from 1.70 to 4.37 km/s.According to Boyce (1980b) an in situ average verticalvelocity is estimated to be 1.93 km/s.

From 880 to 1430 m, the Hauterivian to Valanginianturbidites of alternating graded calcareous and quartz-ose cycles from siltstone or fine sandstone to mudstonehave velocities ranging from 1.80 to 4.96 km/s. Boyce(1980b) estimated an in situ average vertical velocity of2.61 km/s.

From 1430 to 1624 m, the early Valanginian to Titho-nian (Kimmeridgian) turbidites with alternating quartz-ose siltstone grading to mudstone cycles with hard mi-

1236


6.0

5.5

5.0

_ 4.5

uI 4.0>o

9)

3.5

3.0

2.5

2.0

1.7

G Sandstone, siltstone, CO3-cemented0 Calcarenite, calcisiltiteO LimestoneΔ Mari, marlstoneO M u d , mudstone, clay, claystone

Solid symbols Site 370Open symbols = Site 416

?O

O

?D

2.0 2.5 3.0 3.5 • 4.0 4.5Horizontal velocity (km/s)

5.0 5.5 5.7

Figure 5. Vertical velocity versus horizontal velocity for the Cretaceous-Jurassic geologic section at Sites 416and 370.

critic limestone and calcarenite (calciturbidites) have ve-locities from 2.26 to 5.7 km/s. According to Boyce(1980b) the unit has an in situ average vertical velocityof 3.25 km/s (see footnote 2). These in situ velocities arebased on logging velocities and laboratory velocities.The results are very subjective, for: (1) the percentagesof each rock type must be known, (2) he (Boyce) mustfill in data where coring data are sparse, (3) log veloci-ties tend to be biased too low, and (4) there is no caliperdata to judge the variability of the sonic log.

If we assume that Boyce's (1980b, Table 6) estimatedin situ velocities and reflection time (round-trip) from 0to 1616 m of 1.50 s are correct,3 then the 1.43-s-reflectordiscussed by Lancelot, Winterer et al. (1980b) wouldcorrelate at about 1500 m in the geologic section at Hole

The text of Boyce (1980b), p. 316, incorrectly lists "3.75 km/s" for the velocity of theTithonian to Valanginian sandstone, siltstone, marlstone, and limestone from 1430 to 1624 m;it should be 3.25 km/s as in Table 6. This also applies to p. 150 in Lancelot, Winterer et al.,1980b.

3 Hole 516 penetrated to 1624 m; however, because of less than 100% recovery andDSDP depth conventions, the deepest velocity measurement is at 1616 m.

416A, where there is a major change in the acousticalcharacter of the sequence at about a quarter wavelengthabove 1500 m (Fig. 3).

Lancelot, Winterer (1980b) believe this 1.43-s reflec-tor is actually below 1624 m at Site 416, based on stack-ing velocities and general geologic knowledge of thearea. They may be correct, for the data here are alsohighly subjective. While these results do not disprovethe conclusions reached by Lancelot, Winterer et al.(1980b), they do offer another possible interpretation toadd to those already discussed in Lancelot, Winterer etal. (1980b) and Lancelot and Winterer (1980) and pointto the difficulty of correlating seismic reflection data todrill hole data. Lancelot and Winterer (1980) interpret-ed the 1.43-s reflector (blue reflector) to represent a Cal-lovian-Oxfordian transgressive phase of more pelagicsediment character. If the blue reflector actually corre-lates to 1500 m in Hole 416A, then the Callovian-Ox-fordian transgressive sedimentary sequence is not repre-sented by this blue reflector, but may occur as a "deep-er" reflector in the seismic section.

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R. E. BOYCE

800

900

1000

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- 1200

a.CD

T3

| 1300C

XI

CΛ 1400

1500

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MudstoneO Brown and red^Gray and greenΔCalcareousD LaminatedSolid symbols = horizontal velocityOpen symbols = vertical velocity

1.7 2.0 2.5 3.0 3.5 4.0 4.5Compressional-wave velocity (km/s)

5.0

O

5.5 0 10 20 30Acoustic

anisotrophy (%)

Figure 6. Mudstone velocities and acoustic anisotropy versus depth for the Cretaceous-Jurassic geologic section at Site 416.

800

900

1000

1100

S 1200

oδ 1300

1400

1500

1600

1700

i i i i i i i

MudstoneO Brown and redΦ Gray and greenΔ CalcareousD Laminated

Hamilton (1976) laboratory

2.0 2.2 2.4 2.6 0 10 20 30 40 50 0 5 10 15Density (g/cm3) Porosity (%) Acoustic impedance (g 105/cm2 s)

Figure 7. Mudstone density, porosity, and acoustic impedance versus depth for the Cretaceous-Jurassicgeologic section at Site 416.

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800

900

1000

1100

£1200•o

Ij> 1300

XJ

1400

1500

1600

1700

-cm

SiltstoneO SiltstoneOCalcisiltiteD Laminated siltstoneSolid symbols = horizontal velocityOpen symbols = vertical velocity

D

m D

JD-O OO

iS>π

D

DD

43.8π

^74?

D


5.0 5.5 0 10 20 30Acoustic

anisotropy (%)

Figure 8. Siltstone velocities and acoustic anisotropy versus depth for the Cretaceous-Jurassic geologic section at Site 416.

800

900

1000

1100

Q.

•§1200

o

1300

1400

1500

1600

1700

SiltstoneO SiltstoneOCalcisiltiteDLaminated siltstone

D D

α D π

oD

o oD

α BBD D

αD

D? α

o

D

D[[

D

D DmD

2.0 2.2 2.4 2.6Density (g/cm3)

0 10 20 30 40 50 0 5 10 15Porosity {%) Acoustic impedance (g I05/cm2 s)

Figure 9. Siltstone density, porosity, and acoustic impedance versus depth for the Cretaceous-Jurassicgeologic section at Site 416.

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R. E. BOYCE

800

900

1000

1100

ρ.1200

SandstoneO SandstoneΔCalcite cemented sandstone<C>CalcareniteD Laminated sandstoneOpen symbols horizontal velocitySolid symbols = vertical velocity

Δ — •

2.0 2.5 3.0 3.5 4.0 4.5Compressional-wave velocity (km/s)

5.0 5.5 0 10 20 30Acoustic

anistrophy (%)

Figure 10. Sandstone velocities and acoustic anisotropy versus depth for the Cretaceous-Jurassic geologic section atSite 416.

800

900

1000

1100

I" 1200Eo

| 1300

1400

1500

1600

SandstoneO SandstoneΔ Calcite cemented sandstoneOCalcareniteD Laminated sandstone

O

O OQ

π

0

2.0 2.2 2.4 2.6Density (g/cm3)

10 20 30 40 50

Porosity (%)0 5 10 15Acoustic impedance (g 10 /cm s)

Figure 11. Sandstone density, porosity, and acoustic impedance versus depth for the Cretaceous-Jurassicgeologic section at Site 416.

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800

900

1000

1100

•f 1200

o

-9 1300

1400

1500

1600

O MarlstoneOpen symbols = horizontal velocitySolid symbols = vertical velocity

O


O

O o

<ò

5.0 5.5 0 10 20 30Acoustic

anisotrophy (%)

Figure 12. Marlstone Velocities and acoustic anisotropy versus depth for the Cretaceous-Jurassic geologic sectionat Site 416.

800

900 -

1600 -

2.2 2.4 2.6Density (g/cm3)

0 10 20 30 40 50 0 5 10 15Porosity (%) Acoustic impedance (g I05/cm2 s)

Figure 13. Marlstone density, porosity, and acoustic impedance versus depth for the Cretaceous-Jurassicgeologic section at Site 416.

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R. E. BOYCE

800

900

1000

1100

1200

-9 1300

1400

1500

1600

O LimestoneSolid symbols = horizontal velocityOpen symbols = vertical velocity

marly

°oo

o

o?


5.0 5.5 0 10 20 30Acoustic

anistropy (%)

Figure 14. Limestone velocities and acoustic anisotropy versus depth for the Cretaceous-Jurassic geologic sectionat Site 416.

800

900

1000

1100

α•8 1200E

1300

1400

1500

1600

O Limestone

O marly O marly marly Q

<HP

o

2.0 2.2 2.4 2.6Density (g/cm3)

0 10 20 30 40 50 0 5 10 15Porosity (%) Acoustic impedance (g 105/cm2 s)

Figure 15. Limestone densities, porosity, and acoustic impedance versus depth for the Cretaceous-Jurassic geologic section at Site 416.

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Comparison to Site 530 Cretaceous Rocks

The oldest sediment recovered at Site 530 is Cenoma-nian. These are younger than any of the Cretaceous-Ju-rassic (Albian to Tithonian) sediments recovered at Sites370 and 416. In addition, data from Sites 370 and 416extend to a much greater depth below the seafloor (1624m vs. 1103 m). Therefore, one would expect these to bemore lithified than sediments at Site 530.

The greater degree of lithification at Sites 370 and416 compared to Site 530 is suggested by comparingmudstone-porosity versus depth curves from each area(Boyce, this volume). At Site 530, Hamilton's (1976)summary curve matches the data very well, while atSites 370 and 416 Hamilton's (1976) mudstone-porositycurve versus depth does not match. Mudstone porositiesat Sites 370 and 416 are less than Hamilton's curve, sug-gesting either (1) different methods; (2) different miner-alogy, grain-size, packing and cementation; (3) or over-consolidation at Sites 370 and 416 by a geologic sectionwhich has now been eroded away. This does not appearto be the case at Site 530, which appears to be normallyconsolidated, and mudstone lithologies and grain sizemay be more similar to those mudstones discussed inHamilton (1976). Velocities of mudstone are generallyhigher at Sites 416 and 370.

Limestone porosities at Site 530 are about 15%,which compares well with limestones at Sites 370 and416. In addition, at Site 530, limestone velocities arewithin the limestone-velocity range at Sites 416 and 370.

Porosities of carbonate-cemented siliclastic sand-stones compare well at both Site 530 and Sites 370/416.Porosities are ~ 10 to ~ 12%. Velocities of carbonate-cemented sandstone of both areas are also similar.

The acoustic anisotropy of the two areas is, however,quite different. The anisotropy at Site 530 is relativelylow compared with all of the data from Sites 370 and416. At Site 530, anisotropy is typically about 0.2 km/s,which is generally similar to anisotropy at other DSDPsites (Bachman, 1978), and it even compares well toSites 370 and 416 above 1178 m. However, below 1178m at Sites 416 and 370, anisotropy is very large (about0.4 km/s or more) where velocities are between 2.2 and4.2 km/s. In part this could be related to a more calcare-ous cementation or to greater lithification at Sites 370and 416. However, the calcareous-cement concept alsoexplains the calcareous mudstones at Site 530, whichhad significantly higher (37%) anisotropies than unce-mented mudstone.

SUMMARY AND CONCLUSIONS

From 661 to 880 m are Albian to Barremian claystonewith some limestone, sandstone, and siltstone. Compres-sional-wave velocities ranged from 1.70 to 4.37 km/s,with an average in situ vertical velocity of 1.93 km/s.

From 880 to 1430 m are Hauterivian to Valanginianturbidites of alternating graded calcareous and quartz-ose cycles from siltstone or fine sandstone to mudstone.Compressional-wave velocities range from 1.80 to 4.96km/s, with an average in situ velocity of 2.61 km/s.

From 1430 to 1624 m are early Valanginian to Titho-nian (Kimmeridgian?) turbidites with alternating quartz-

ose siltstone grading to mudstone cycles with hard mi-crite and calcarenite (calciturbidites). Compressional-wave velocities range from 2.26 to 5.7 km/s, with an av-erage in situ vertical velocity of 3.25 km/s

Acoustic anisotropy is 0 to 30% in the Cretaceous toTithonian sandstone-siltstone turbidites in mudstoneand minor limestone from 661 to 1624 m below the sea-floor. Between 2.0(?) km/s and 4.2(?) km/s, anisotropybecomes particularly significant (below 1178 m), wherethe anisotropy is about +0.4 km/s or greater. Themudstone, softer sandstone, and softer siltstone tend tohave velocities around 2.0 to 2.5 km/s; the cementedsandstone and limestone cluster about 2.5 km/s to 4.2km/s; thus the relative percentage anisotropy is greaterfor the lower-velocity lithologies. Above 4.2(?) km/s,the well-cemented sandstone and limestone tend to havea smaller (less than 0.4 km/s) absolute anisotropy, andmany samples are nearly isotropic. The anisotropy canbe related to some combination of the following: (1)elongated or platy grains, which provide a faster pathhorizontally as a result of there being fewer gaps be-tween minerals, (2) preferred orientation of mineralswhich have an acoustic anisotropy, (3) cementationalong certain horizontal layers, (4) alternating high- andlow-velocity layers, and (5) a larger number of horizon-tal cracks or foliation.

The mudstone's porosity and wet-bulk density curvesversus depth are slightly higher and lower, respectively,for similar porosity and density curves in Hamilton(1976). This could be the result of some combination ofmethods, age, and lithology differences, or overconsoli-dation by an overlying geologic section which has beeneroded away.

Limestone porosities are typically less than Cretaceouslimestones from the Pacific Ocean (Schlanger, Jacksonet al., 1976), where identical methods were used. ThesePacific limestones are the nannofossil foraminifer type,and the limestone from Site 416 is micritic; thus the mi-critic limestone is probably more recrystallized and thuscould perhaps be expected to have a smaller porosity.

If the average in situ vertical velocities calculated byBoyce (1980b) for Hole 416A are correct, then the 1.43-s(round-trip) reflector (blue) discussed by Lancelot andWinterer (1980) and Lancelot, Winterer et al. (1980b)would correlate to about 1500 m in Hole 416A, and notbelow 1624 m as discussed by Lancelot and Winterer(1980c). There does appear to be a significant change inthe acoustic character at or around 1500 m (early Valan-ginian) to a more calcareous and cemented lithology.This investigator only suggests another possible inter-pretation, since this one is based on many assumptionsand is highly subjective.

ACKNOWLEDGMENTS

The author wishes to thank Dr. E. L. Hamilton and Dr. ThomasH. Shipley for reviewing the manuscript.

REFERENCES

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Boyce, R. E., 1980a. Deep Sea Drilling Project Leg 50 laboratory phys-ical-property methods. In Lancelot, Y., Winterer, E. L., et al., In-

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Gregory, A. R., 1977. Aspects of rock physics from laboratory andlog data that are important to seismic interpretation. In Payton, C.H. (Ed.), Seismic Stratigraphy—Applications to HydrocarbonExploration, AAPG Mem., 26:15-46.

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Date of Initial Receipt: December 7, 1981

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acoustic impedance, acoustic anisotropy, and ...acoustic anisotropy is 0 to 30% faster parallel to...

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