Breaking Walther's Law: ABSTRACT

Abstract

Walther's law of facies cannot be meaningfully applied to explain major facies transitions in the Helderberg Group of New York. Correct application of the law requires that superimposed facies accumulated conformably, that is those facies and facies areas can be superimposed primarily which can be observed beside each other at the present time. Application of the law to the Helderberg Group fails on the conformable constraint. The Helderberg Group consists entirely of punctuated aggradational cycles (PACs), shallowing-upward cycles (1-5 m thick) separated by isochronous surfaces of marked facies discontinuity. The facies changes across these surfaces indicate that they were produced by abrupt relative sea level rises. Analysis of facies within any pair of successiv PACs indicates that each sea level rise disrupted the environmental spectrum associated with the deposition of the underlying PAC and established a disconnected new environmental pattern in which deposition of the overlying PAC was initiated. Therefore, facies changes analogous to those occurring across PAC boundaries cannot be found in contiguous modern environments. It is possible to meet Walther's strict criterion of conformity, and thus correctly apply his law, only for vertical facies transitions within PACs. The law cannot be applied to thicker rock sequences such as the Helderberg Group, represented by several formations and major facies, because they consist entirely of PACs and thus contain many paleo-environmental discontinuities. We conclude that stratigraphers, as a conseque ce of assuming the paradigm of stratigraphic gradualism, have failed to recognize the significance of these discontinuities and therefore have been breaking Walther's law. One of the consequences of adopting a new paradigm of episodic accumulation may be that stratigraphers will apply Walther's law in the manner that Walther apparently intended, as an actualistic rule for interpreting conformable vertical sequences. End_of_Article - Last_Page 234------------