Summary.

The fundamental building blocks of larger-scale, low-frequency (i.e. third-order) depositional sequences within ancient shallow-marine, platform carbonates are high-frequency (meter-scale), shallowing-upward depositional cycles. Depositional subfacies of the Lower Ordovician El Paso Gp in the Franklin Mtns are grouped into small-scale, shallowing-upward cycles (average 8-10 feet thick) ranging from 40,000-75,000 yr in duration. Cycle stacking patterns of cycle type, cycle thickness and subfacies components provide a semi-quantitative representation of systematic shifts in third-order cycles of relative sea-level change. In the Franklin Mtns, two complete El Paso Gp third-order sequences (each approximately 2 myr in duration and 200-450 ft thick) consisting of 115 cycles have been described in detail. In light of the integration of cyclostratigraphy with sequence stratigraphy, it is apparent that high frequency cycles are regarded as the fundamental attribute which best characterizes or describes the vertical and lateral structure of carbonate platforms.

An empirically-based classification of the architecture of platform carbonates is introduced, invoking the “cycle” as an elemental unit of measurement. In this scheme, carbonate systems can be assigned to one of three classes of fundamental architecture with regard to the empirical organization of architectural elements. Drawing an analogy to all natural systems, we classify the behaviour of carbonate systems, as deterministic through chaotic to stochastic, and intepret such differences as a function of secular variation (icehouse vs greenhouse dynamics), tectonic setting and platform geometry. This attempt at an empirical classification de-emphasizes process and origin and places the focus on detectable structure.

Application of statistical routines (runs tests, Durbin-Watson, entropy analysis) to stacks of contiguous platform cycles from the Franklin Mtns suggests long-term (third-order) non-random behaviour. This behaviour is best described as chaotic, wherein third-order sequences provide a stratigraphic example of non-resonant ‘quasi-periodicity'. The utility of fractals as applied to describing the El Paso Gp structure is investigated.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas