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About 200 compression and heating experiments simulating diagenesis and low-grade metamorphism have been performed on samples of CaCO3 sediments obtained from the banks west of Andros Island in the Bahamas; the mud consists mainly of aragonite needles, 0.1µ by 1µ, and ovoid pellets, about 100µ across. The ranges of conditions and the precisions of the experiments were as follows: pressure P, 1-3,000 bars, ±10%; temperature T, 25°-400°C., ±10%; and time t, 3 hours to 2 months, ±1%. The chemical compositions of the sea water in the mud and the vapor driven off were not determined.
Consolidation is effected by compaction of grains, recrystallization, and by increase of integranular bonding. Pressure of 30 bars causes a compaction of about 20% for a given temperature; at T = 25° C. the density increases from that of the initial mud, 1.7 g/cm3, to a final 2.0 g/cm3; essentially, some of the interstitial water is squeezed out. Heating at T between 100° and 200° C., under P<30 bars, causes an apparently anomalous decrease in density because of an exchange of air for water in the void spaces, and the products remain friable.
Heating at T = 400° C. under low pressure, P<100 bars, for t>1 day, lithifies the mud, apparently during inversion of aragonite to calcite; electron micrographs show coalescence, increasing with time, of the original needles to rounded grains and then to a subhedral, interlocking texture; the product has a compressive strength >100 bars. Higher pressure, P>100 bars, causes increasing breakage of the aragonite needles.
About 30 experiments on aragonitic mud from Kapingamarangi Atoll in the Caroline Islands produced results similar to those obtained on the Bahamas mud. However, in none of 6 experiments performed on deep-sea, coccolithic, calcite ooze from near the Hawaiian Islands could the sample be lithified, even at T = 400° C., P = 1,000 bars, t = 11 days; apparently consolidation of calcite sediment requires the circulation of dissolving water.
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