Walther's Law, Climate Change, and Upper Paleozoic Cyclostratigraphy

SOREGHAN, GERILYN S.,

Walther's Law states that facies that form coevally in laterally contiguous environments will be superposed vertically. Sedimentary geologists routinely apply this concept to vertical successions of strata to interpret depositional facies and reconstruct paleogeographic and sequence stratigraphic scenarios. Walther's Law "works" because sedimentary environments migrate laterally in response to relative baselevel change. The application of Walther's Law, however, may be problematic in strata that have been influenced by significant and geologically rapid climate change. This type of climate change may be typical of times in earth's history characterized by continental glaciation, such as the Quaternary and the late Paleozoic. During such times, abrupt and significant climate fluctuations may have caused depositional environments to change fundamentally, rather than migrate laterally, resulting in a stratigraphic succession wherein depositional facies vertically superposed rarely coexisted laterally.

Upper Pennsylvanian cycles of the Southwestern U.S. include proxy paleoclimatic indicators that suggest that paleoequatorial climate fluctuated between semiarid and subhumid conditions during glacial and interglacial extremes, respectively. Although glacioeustasy was the primary control on baselevel change recorded in these strata, climate significantly impacted siliciclastic sediment flux in both nonmarine and marine systems. Accordingly, the influence of climate change is most pronounced in lithologically mixed (e.g., carbonate-eolian and/or carbonate-fluviodeltaic) cycles and may help explain the preponderance of such cycles in Pennsylvanian strata. In cases of such rapid and significant climate change, indiscriminate use of Walther's Law for facies and/or paleogeographic interpretations may lead to erroneous conclusions.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.