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2Physical Properties of Marine SedimentsIn order to correct for slight temperature variationsin the laboratory and to transfer laboratorymeasurements to in situ conditions, usuallytemperature and in situ corrections are applied.Temperature variations mainly affect the porefluid. Corrections to in situ conditions shouldconsider both the influence of reduced temperatureand increased hydrostatic pressure at thesea floor.Porosity and Wet Bulk DensityIn standard sea water of 35‰ salinity densityincreases by maximum 0.3·10 -3 g cm -3 per °C(Siedler and Peters 1986), i.e. by less than 0.1%per °C. Hence, temperature corrections can usuallybe neglected.Differences between laboratory and in-situporosities are less than 0.001% (Hamilton 1971)and can thus be disregarded, too. Sea floor wetbulk densities are slightly higher than the correspondinglaboratory values due to the hydrostaticpressure and the resulting higher density ofthe pore water. For Central Pacific sediments of75 - 85% porosity Hamilton (1971) estimated adensity increase of maximum 0.01 g cm -3 for waterdepths between about 500 - 3000 m and ofmaximum 0.02 g cm -3 for water depths betweenabout 3000 - 6000 m. Thus, corrections to sea floorconditions are usually of minor importance, too.However, for cores of several hundred meter lengththe effect of an increasing lithostatic pressure hasto be taken into account.Electrical ResistivityIf porosities and wet bulk densities are determinedby galvanic resistivity measurements (Sect. 2.2.3)varying sediment temperatures are considered bycomputation of the formation factor (F) (see Eq.2.12). While the resistivity (R s) of the sediment isdetermined by the small hand-held probe (cf. Sect.2.2.3) the resistivity (R f) of the pore fluid is derivedfrom a calibration curve which describes thetemperature (T) - conductivity (c) relation by afourth power law (Siedler and Peters 1986)P-wave velocity and attenuationBell and Shirley (1980) demonstrated that the P-wave velocity of marine sediments increasesalmost linearly by about 3 m s -1 per °C while theattenuation is independent of sediment temperature,similar to the temperature dependence ofsound velocity and attenuation in sea water.Hence, to correct laboratory P-wave velocity measurementsto a reference temperature of 20°CSchultheiss and McPhail’s (1989) equation( T )v20 = vT + 3⋅20 −(2.23)can be applied, with (v 20) = P-wave velocity at20°C (in m s -1 ), (T) = sediment temperature (in °C)and (v T) = P-wave velocity measured at temperature(T) (in m s -1 ).To correct laboratory P-wave velocity measurementsto in situ conditions a modified time-averageequation (Wyllie et al. 1956) can be used(Shipboard Scientific Party 1995)1 1 ⎛⎞⎜ 1 1= + φ ⋅ − ⎟ (2.24)v⎜⎟insituvlab⎝cinsituclab⎠(v lab) and (v in-situ) are the measured laboratory(20°C, 1 at) and the corrected in situ P-wavevelocities, (c lab) and (c in-situ) the sound velocity insea water at laboratory and in situ conditions and(φ) the porosity. If laboratory and sea floorpressure, temperature and salinity are known fromtables or CTD measurements (c lab) and (c in-situ) canbe computed according to Wilson’s (1960)equationc = 1449 . 14+ c + c + c c (2.25)TPS +STP(c T), (c P), (c S) are higher order polynomials whichdescribe the influence of temperature (T), pressure(P) and salinity (S) on sound velocity. (c STP)depends on all three parameters. Completeexpressions for (c T), (c P), (c S), (c STP) can be foundin Wilson (1960). For T = 20°C, P = 1 at and S =0.035 Wilson’s equation results in a sound velocityof 1521 m s -1 .R−12 3f = co+ c1T+ c2T+ c3T+c T44(2.22)The coefficients (c 0) to (c 4) depend on thegeometry of the probe and are determined by aleast square fit to the calibration measurements instandard sea water.68
References2.7 ProblemsProblem 1What is the difference between bulk parametersand acoustic/elastic parameters concerning thedistribution of pore fluid and sediment grains ?Problem 2Which direct and which indirect methods do youknow to determine the porosity and wet bulkdensity of marine sediment, which of both parametersis primarily determined by each method,and how can porosity values be converted todensity values and vice versa ?Problem 3Assume that you have recovered a sediment corein the Antarctic Ocean close to the Polar FrontalZone. The core is composed of an interlayering ofcalcareous and siliceous sediments. You wouldlike to determine the downcore porosity and wetbulk density logs by electrical resitivity measurements.What do you have to consider duringconversion of porosities to wet bulk densities ?Problem 4Which sediment property mainly influences theultrasonic acoustic wave propagation (50 - 500 kHz),and how affects it the P-wave velocity andattenuation in terrigenous and calcareous sediments?Problem 5Which parameter determines the amplitude orstrength of reflection horizons during sedimentechosounding, and which are the two physicalproperties that contribute to it ?ReferencesAki K., Richards P.G., 2002. Quantitative Seismology.University Science Books, 700 ppArchie G.E., 1942. The electrical resistivity log as an aidin determining some reservoir characteristics. Transactionsof the American Institute of Mineralogical,Metalurgical and Petrological Engineering 146: 54-62Barker P.F., Kennett J.P. et al., 1990. Proceedings of theOcean Drilling Program, Scientific Results 113, CollegeStation, TX (Ocean Drilling Program), 1033 ppBell D.W., Shirley D.J., 1980. Temperature variation ofthe acoustical properties of laboratory sediments.Journal of the Acoustical Society of America 68: 227-231Bergmann U., 1996. Interpretation of digital Parasoundechosounder records of the eastern Arctic Ocean onthe basis of sediment physical properties. Rep. onPolar Research, Alfred-Wegener Institute for Polarand Marine Research, Bremerhaven 183: 164 ppBerryman J.G., 1980. Confirmation of Biot’s theory.Applied Physics Letters 37: 382-384Biot M.A., 1956a. Theory of propagation of elasticwaves in a fluid-saturated porous solid. II. Higherfrequency range. Journal of the Acoustical Society ofAmerica 28: 179-191Biot M.A., 1956b. Theory of wave propagation of elasticwaves in a fluid-saturated porous solid. I. Lowfrequencyrange. Journal of the Acoustical Society ofAmerica 28: 168-178Bleil U. et al., 1994. Report and preliminary results ofMeteor cruise M29/2 Montevideo - Rio de Janeiro,15.07. - 08.08.1994. Ber. FB Geow. Univ. Bremen 59:153 ppBlum P., 1997. Physical properties handbook: a guide tothe shipboard measurement of physical properties ofdeep-sea cores. Technical Note 26, Ocean DrillingProgram, College Station, TexasBodwadkar S.V., Reis J.C., 1994. Porosity measurementsof core samples using gamma-ray attenuation.Nuclear Geophysics 8: 61-78Boyce R.E., 1968. Electrical resistivity of modernmarine sediments from the Bering Sea. Journal ofGeophysical Research 73: 4759-4766Boyce R.E., 1973. Appendix I. Physical properties -Methods. In: Edgar NT, Sanders JB et al (eds) InitialReports of the Deep Sea Drilling Project 15, Washington,US Government Printing Office, pp 1115-1127Boyce R.E., 1976. Definitions and laboratory techniquesof compressional sound velocity parameters and wetwatercontent, wet-bulk density, and porosityparameters by gravity and gamma ray attenuationtechniques. In: Schlanger S.O., Jackson E.D. et al(eds) Initial Reports of the Deep Sea Drilling Project33, Washington, US Government Printing Office, pp931-958Breitzke M., Spieß V., 1993. An automated full waveformlogging system for high-resolution P-wave profiles inmarine sediments. Marine Geophysical Researches 15:297-321Breitzke M., Grobe H., Kuhn G., Müller P., 1996. Fullwaveform ultrasonic transmission seismograms - afast new method for the determination of physicaland sedimentological parameters in marine sedimentcores. Journal of Geophysical Research 101: 22123-2214169
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