Introduction
Stenon was the founder of stratigraphy. It was in 1667 that he introduced in his work Canis Calchariae the postulate: layers of sub-soil are ‘strata’ of ancient successive ‘sediments’. From this partial interpretation, Stenon drew three initial principles of stratigraphy formulated in his work Prodromus (1669).
(1) Principle of superposition
At the time when one of the high stratum formed, the stratum underneath it had already acquired a solid consistency. At the time when any stratum formed, the superincumbent material was entirely fluid, and due to this fact at the time when the lowest stratum formed, none of the superior strata existed.
(2) Principle of continuity
Strata owe their existence to sediments in a fluid. At the time when any stratum formed, either it was circumscribed on its sides by another solid body, or else it ran round the globe of the earth.
(3) Principle of original horizontality
At the time when any stratum formed, its lower surface, as also the surfaces of its sides, corresponded with the surfaces of the subjacent body, and lateral bodies, but its upper surface was (then) parallel to the horizon, as far as it was possible.
The sedimentological model corresponding to these three principles is, therefore, the following. In a fluid covering the Earth, except for emerged land, a precipitate deposits strata after strata, covering all the submerged Earth [ANIMATION 1]. After the deposition of each stratum, the sedimentation is interrupted for the time it takes for the stratum to acquire a solid consistence. The stratum being contained between two parallel planes indicates that the sedimentation rate of the precipitate is uniform around the submerged Earth.
Animation 1 (no sound)
Stenon’s assertion relies solely upon observation of stratified rocks and the superposition of strata, independently of data from the sedimentological process. This process is composed of three phases: erosion, transport and deposition of sediments, the liquid current being the vector of transport. Stenon’s stratigraphy only took account the third phase of sedimentology, i.e., the deposition, assuming implicitly a nil velocity of current.
Fig. 1 : Grand Canyon in North Arizona,an example of stratification>>> Problems