--> ABSTRACT: Chaos and order: How predictable are the character and extent of lake strata?, by Kevin M. Bohacs, Alan R. Carroll, and Jack E. Neal; #90906(2001)

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Kevin M. Bohacs1, Alan R. Carroll2, Jack E. Neal1

(1) ExxonMobil Upstream Research Co, Houston, TX
(2) UW-Madison, Madison, WI

ABSTRACT: Chaos and order: How predictable are the character and extent of lake strata?

Observations of modern and ancient lake systems reveal minimal relations among lake size, stratal character, and measured or inferred climate or tectonic setting. Lake systems do, however, commonly display quasi-periodic behavior at several scales, from parasequence to sequence-set and beyond that support constrained stratigraphic predictions at several scales (exemplified by the three lake-basin types: Overfilled, Balanced-fill, Underfilled).

Complex and nonlinear relations among forcing functions, system response, and stratal record in lake dynamical systems causes unresolvable difficulties in both forward and reverse modeling based on paleoclimate or tectonics. Thus one can interpret (non-uniquely) a paleoclimate for a given interval of lake strata, but cannot infer that a major change in the record is due necessarily to a major change in climate, absent external independant evidence. For example, a change to a more freshwater system may be due to increased precipitation, or decreased evaporation, or decreased basin subsidence, or lowering of outflow sill, or stream capture due to landscape evolution, stream piracy, or tectonics, or through various combinations of these factors.

Ultimately, these considerations indicate the improbability of predicting details at higher resolutions. Prediction within a given lower-order scale (parasequence, sequence, sequence set), however, can be fairly robust, allowing accurate interpolation and extrapolation of stratal and play-element distribution. Transitions among scales are extremely difficult to forecast.

Successful prediction therefore must concentrate on developing models over appropriate scales, each with their own key factors: from continent/basin-cycle (=tectonic setting and subsidence history) through basin/sequence-set (=climate+tectonics+basin history), to local sequence/parasequence (=sediment+water supply relative to potential accommodation) scales.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado