Eocene hydromorphic paleosols: Significance for interpreting ancient floodplain processes
- Univ. of Colorado, Boulder (United States)
Pervasive mottling, iron-oxide nodules, and slickensides indicate that alluvial paleosols of the lower Eocene Willwood Formation in the Elk Creek area of the Bighorn Basin, Wyoming were hydromorphic. Two basic groups of hydromorphic paleosols are present: cumulative, which show evidence for concurrent deposition and pedogenesis, and simple (non-cumulative), which show evidence for a single episode of deposition and pedogenesis. Lithologic packages consisting of vertically stacked simple paleosols and crevasse-splay sandstones alternate with cumulative paleosols. The simple paleosols are weakly developed, indicating rapid deposition with relatively little time for pedogenesis. Cumulative paleosols show greater pedogenic development, indicating significantly longer periods of paleogenic modification and slower, more episodic sediment accumulation. Differences between the simple and cumulative paleosols reflect differences in the deposition of their parent materials. The packages of simple paleosols are similar to avulsion-belt deposits described from the Saskatchewan River, and suggest that avulsion was significant in floodplain construction. The upper parts of cumulative paleosols were formed on true overbank deposits, which accumulated gradually after avulsion and establishment of a new channel. The lower parts of many cumulative paleosols resulted from a prior episode of avulsion deposition and simple soil formation. Because hydromorphy is associated with texture, these different depositional processes influenced lateral variations in hydromorphy of the cumulative paleosols. Paleosols in the Elk Creek area provide a simple means of identifying avulsions. Sediment accumulation rates suggest that avulsions occurred with a regular period of about 20,000 years and may have been induced by climatic cycles.
- OSTI ID:
- 6523263
- Journal Information:
- Journal of Sedimentary Petrology; (United States), Vol. 63:3; ISSN 0022-4472
- Country of Publication:
- United States
- Language:
- English
Similar Records
Time-stratigraphic reconstruction and integration of paleopedologic, sedimentologic, and biotic events (Willwood Formation, lower Eocene, northwest Wyoming, USA)
Relationships of paleosol maturity to autocyclic and allocyclic controls on sediment accumulation rates, Willwood Formation (Lower Eocene), Wyoming, U. S. A
Related Subjects
ALLUVIAL DEPOSITS
DEPOSITION
PETROLOGY
WYOMING
CLIMATE MODELS
CLIMATIC CHANGE
EOCENE EPOCH
GEOLOGIC FORMATIONS
PALEOCLIMATOLOGY
SEDIMENTARY BASINS
SOILS
STRATIGRAPHY
CENOZOIC ERA
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
MATHEMATICAL MODELS
NORTH AMERICA
PALEONTOLOGY
TERTIARY PERIOD
USA
580000* - Geosciences