Allocycle symmetry in the hierarchic structure of the Upper Silurian Tonoloway Formation

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5879080

Chadwick, W J; Goodwin, P W ^[1]

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1. Temple Univ., Philadelphia, PA (United States). Dept. of Geology

The basal Third-Order cycle of the Upper Silurian Tonoloway Formation at Pinto, Maryland reveals asymmetry at different levels within a genetic hierarchy of cycles consistent with the Milankovitch Model of orbital forcing. The Tonoloway Formation itself is the upper portion of a Second-Order Super Sequence (10 my duration) which includes the underlying Wills Creek Formation. Approximately 230 meters of Tonoloway pertidal and shallow shelf facies can be divided into 3 Third-Order cycles (1.6--2.0 my Eccentricity) whose asymmetry is expressed in the relative depths of its 4 Fourth-Order cycles (400 ky Eccentricity). For example, within the basal Third-Order cycle, the deepest, most open facies occur in the 2nd Fourth-Order cycle. Each Fourth-Order cycle is, in turn, highly asymmetric, its deepest facies occurring in the first of its 4 Fifth-Order cycles (100ky Eccentricity). The remaining 3 Fifth-Order cycles contain generally shallower facies terminating in the shallowest facies of the last Fifth-Order cycle. Each Fifth-Order cycle, consisting of 5 Sixth-Order cycles (when complete), is also strongly asymmetric; the deepest facies occur in the second Sixth-Order cycle. Finally, each Sixth-Order cycle of PAC (20ky Precession) is a shallowing-upward, sharply bounded cycle frequently containing a sharp surface separating its upper shallower facies from its lower deeper facies. Comparison of the symmetries of each order in the Tonoloway hierarchy with the symmetries of other hierarchic sequences should help to distinguish the relative roles of tectonism and Milankovitch eustasy in producing this important diagnostic stratigraphic property.

• OSTI ID: 5879080
• Report Number(s): CONF-9303211--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGIC STRATA
GEOLOGIC STRUCTURES
GEOLOGY
MARYLAND
NORTH AMERICA
PALEOZOIC ERA
SILURIAN PERIOD
STRATIFICATION
STRATIGRAPHY
USA