by Guy Berthault
CRS Quarterly, Volume 46, Number 4
Spring 2010, pp. 261-269.
Abstract:
Stratigraphy, the basis of geological dating, was founded in the seventeenth century on three principles proposed by Nicolas Steno: superposition, continuity, and original horizontality. Successive observations and experiments show that his stratigraphic model was not in line with experimental data, because it overlooked the major variable factor of sedimentation: the current and its chronological effects. Experiments simulating the formation of sedimentary layers at variable current velocities using different-sized particles show that Steno’s principles apply only to the case of deposition at zero current velocity. Since sedimentary processes affect stratigraphy and geological dating, paleohydraulic conditions must be considered in any stratigraphic analysis. The estimated time of deposition is often the crucial factor in developing a local timescale, and the paleohydraulic approach links deposition to the critical transport velocity of current as determined by particle size. From this velocity, the corresponding transport capacity in units of volume and time is calculated. The time of sedimentation is the quotient obtained from dividing the volume of sedimentary rocks by the transport capacity. A team of Russian sedimentologists have applied this method to geological formations of the Crimean Peninsula and of the Northwest Russian Plateau in the St. Petersburg region. They discovered that the time required for sedimentation was only 0.01% of the corresponding period of the geological timescale. This is at variance with the time required for species to evolve.
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