C. Blaine Cecil1,
Frank T. Dulong1,
Sandra G. Neuzil1
(1) U.S. Geological Survey, Reston, VA
Abstract: Sequence stratigraphy and the origin of Pennsylvanian coal beds in North America
Sequence boundaries in Pennsylvanian epeiric deposystems of North America commonly are defined by paleosols. In the United States (U.S.), these paleosols document low stands of sea level and the exceedingly low relief and continental extent of epeiric depositional systems. Characteristics of these paleosols can be used to infer conditions of soil genesis including paleoclimate. In the eastern U.S., coal beds and intensely weathered underlying paleosol/sequence boundaries are indicative of humid to perhumid climates coeval with either low stand or transgressive systems tracts. In the western U.S., coeval paleosol/sequence boundaries are weakly weathered, contain features indicative of aridity, and lack overlying coal. The diminution of coal and the degree of weathering at low-stand sequence boundaries from east to west across the continent indicate that climate rather than relative sea level was the primary control on peat formation. Stratigraphic variation in geochemistry and sediment supply suggest climatic drying and increased seasonality during transgression. When compared to the U.S., climatic conditions in Nova Scotia were reversed when equated to relative sea level. Nova Scotian coal deposits appear to coincide with humid climates during relative high stands; relative low stands are characterized by dry climate paleosols (Gibling, 1999).
Extensive deposits of Holocene peat generally are forming under humid to perhumid conditions. In high latitudes, extensive peat is forming in upland areas independent of relative sea level. Equatorial peat is forming on coastal plains contemporaneously with, but necessarily controlled by, present sea level.
Both Pennsylvanian coal and Holocene peat deposits indicate that extensive deposits of peat tend to form under humid to perhumid climatic conditions. Relative sea level may coincidently correlate with extensive peat formation but is far more important as a mechanism for peat burial and preservation.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana