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Part 2: The geological record |
Sedimentological, mineralogical, chemical and Rb-Sr isotopic studies were made on Fe-smectites (nontronites) from deep sea red clays taken from two cores located 100 km apart in the southern Pacific Ocean. They show that: (1) these sediments are authigenic, (2) they contain variable but few amounts of volcanic-derived chemical components, and (3) they were transported from some place in the ocean and deposited at the present-day site. The transportation, which could occur at different periods, was likely induced by the submarine topography and bottom currents.
These observations necessitate a reconsideration of the traditional concept of sedimentation rate for the red clay facies. Although exhibiting considerable similarities, these sediments may correspond to different stages of a submarine sedimentary cycle. A given horizon can therefore reflect a submarine pedological event, a sudden and massive accumulation, or a very low sedimentation of material formed elsewhere. Genetic information is necessary to determine the local sedimentation rates of red clay, and the inconstancy of the sedimentation prevents any generalization on an ocean-wide scale.
