ABSTRACT: PACs and the Stratigraphic Code: A Reassessment
Jonathan L. Jee
Critical evaluation of the punctuated aggradational cycle (PAC) hypothesis has been limited despite prolific attempts to employ its stratigraphic interpretations. Allegedly, PACs are basin-wide, time-stratigraphic units bounded by synchronous discontinuity surfaces, Walther's Law applies only within PAC, formations (comprising sequences of PACs) are invalid for paleoenvironmental analysis, and diachronous contacts between conformable formations do not exist.
Examination of PAC dogma within the context of the North American Stratigraphic Code reveals criticisms of the formation concept are exaggerated. The formation concept is not exclusively linked to conformable, diachronous relationships, as PAC proponents contend. Pertaining to Waltber's Law, the code recommends that formation contacts honor genetic units, and that formations not straddle significant discontinuities. Time-parallelism of PACs remains an unproven assumption. Lack of objective criteria for identification and correlation is a serious obstacle to application of the PAC hypothesis.
The PAC hypothesis resembles the concepts of formats, genetic units, paracontinuity, and sequence stratigraphy--all of which have precedence. These concepts possess qualities of the PAC hypothesis that are attractive but avoid its many shortcomings and antagonism to the Stratigraphic Code.
As a model of episodic stratigraphic accumulation, the PAC hypothesis is not, as claimed, universally applicable. The narrow perspective through which it views sedimentary processes does more to color than to elucidate our perception of earth history and runs counter to the principle of multiple working hypotheses.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990