Abstract

Certain ideas pertaining to baselevel appear to be valid. Among these are the notions: that it is an imaginary surface delimiting the depth of erosion potential (Powell, 1875); that it embodies the concept of balance or equilibrium (Rice, 1897); and that it is a nearly horizontal surface as significant to sedimentation as it is to erosion (Barrell, 1917). Contrary to Barrell, baselevel as a surface is a forceless abstraction which is without control over geological processes; and contrary to Hayes (1899) and Dunbar and Rodgers (1957), the notion of a horizontal baselevel plane gives rise to needless inconsistencies.

Baselevel relates directly to deposition and erosion, which occur only at the lithosphere surface; therefore, the baselevel surface configuration may be conceived only in its relationship to the lithic surface. This and the seemingly valid notions of Powell, Rice, and Barrell permit only a single, abstract, ever-present (worldwide), baselevel “sphere” constantly undulating in response to the ever-changing, erosion and deposition-controlling, supply-energy patterns as they impinge on the lithosphere surface. Baselevel rises above the lithic surface wherever deposition begins and drops beneath it wherever erosion commences, thus making at any place alternate upward and downward transits, and thereby providing a baselevel transit cycle.

The preserved record of the depositional phase of the principal baselevel transit cycles in earth history comprises the major unconformity-bounded sequences. The equally important but nonrecorded parts of the cycle constitute the lacuna, which consists of the hiatus and the degradation vacuity. The degradation vacuity may also be combined with its corresponding sequence to reconstitute the holostrome or original depositional cyclic phase. Significantly, the boundaries separating all of these abstract time-stratigraphic entities are traces of the area-time migration of either the upward or downward transits of baselevel (migration of the intersections of baselevel and the lithosphere surface).

Configurational relationships imply the existence of positive, negative, and neutral aspects of time-stratigraphy.

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