Gregory C Nadon¹

(1) Ohio University, Athens, OH

ABSTRACT: Eustatic and Tectonic Bias in Climate Inferences From Shallow Marine and Nonmarine Sediments During Ice House Periods

The facies architecture of foreland basin sediments reflects the combined influence of eustasy, tectonics, and climate. The climate signal is generally inferred from vertical changes in specific facies such as coal, freshwater limestone, and, to a lesser degree, in the types of paleosols present. The climate signal should be most apparent in facies patterns during Ice House intervals of Earth history, however, only a portion of the potential signal is preserved. Sea level rise allows burial and preservation of sediments of the transgressive and early highstand systems tracts. Incised fluvial channels or valleys and the contemporaneous soil profiles formed on the interfleuves represent the late highstand deposits. Therefore, the facies most commonly used to infer climate commonly represent the same small fraction of each eustatic cycle.

Interpreting the climate signal from facies patterns is further compromised by variations in deposition and preservation resulting from changes in the magnitude of eustasy and subsidence. Vertical changes in the presence or absence of coal, freshwater limestones and, redbeds can be produced by variations in the magnitude of the eustatic signal. Variations in the amount of tectonic subsidence, which ultimately determines how much sediment is preserved, also dictates the vertical and lateral juxtaposition of facies within a basin. Simultaneous changes in both variables can produce a variety of facies patterns that could be interpreted as a change in climate. The result is that a climate signal from Ice House sediments cannot be inferred solely from changes in shallow marine and nonmarine facies patterns.

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