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The AAPG/Datapages Combined Publications Database
West Texas Geological Society
Abstract
Chaos in El Paso?
Abstract
The Lower Ordovician El Paso Group contains several “third-order” depositional sequences
which consist of higher-frequency “fifth-order” depositional
cycles
. Cycle stacking patterns of cycle type, cycle thickness and subfacies components provide a semi-quantitative representation of systematic shifts in third-order
cycles
of accommodation. In the Franklin Mtns, two complete El Paso Group third-order
sequences
(each approximately 2 myr in duration and 200-450 ft thick) have been described in detail by Goldhammer et al (1993). 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.
In this study, 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 “behaviour” 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 geo-statistical routines (runs tests, Durbin-Watson) 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 Group structure is investigated.
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