Exposure, drowning, and missed beats'': Shelf-edge sequence stratigraphy, Middle Ordovician non-cycle carbonates, east Tennessee
- Univ. of Tennessee, Knoxville, TN (United States). Dept. of Geological Sciences
Stratigraphic sequences in a Middle Ordovician platform interior carbonate succession can be correlated to the shelf-edge. Surfaces of subaerial exposure are correlated among seven stratigraphic sections, 4 at on-shelf positions and 3 at or near the shelf-edge. This analysis of carbonate facies geometry is based on outcrop observation, analysis of thin-sections, and consideration of water-depth curves. In platform successions, most sequences are bounded by exposure surfaces, but in more continuously subtidal areas, period of shallowing and drowning are discerned in bathymetric curves based on multiple lines of evidence. Cephalopod-rich limestone beds that overlie subtidal limestones and contain black, iron-manganese oxide rich sediment and pavements provide additional evidence for drowning followed by condensed sedimentation. These non-cyclic carbonates have 4th order sequences that are grouped into 3rd order sequences based on the occurrence of pronounced and less pronounced exposure surfaces. For example, 7 pronounced surfaces of subaerial exposure define six 3rd order sequences at on-shelf positions at Thorn Hill, TN. Within the lower four 3rd order sequences, 19 less pronounced surfaces occur with a total of 23 surfaces recognized in about 400 m. These less pronounced surfaces define 4th order sequences that are correlative across the shelf. Within these 3rd and 4th order sequences, 5th order packages occur. Fifth order sequences are not correlative across the shelf or from the shelf to the shelf-edge and many are probably the result of lateral environmental migration. Stratigraphic sequences define shallowing-upward packages and are used to construct Fischer plots, substituting sequences for cycles. The modified Fischer plots show that some sequences are missing. Sequences are missed in 3 ways: Sea-level stays below the shelf edge even though sea level is oscillating; Tectonic uplift exposes the shelf until subsidence allows submergence; and During drowning.
- OSTI ID:
- 6111719
- Report Number(s):
- CONF-9304188-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:4; Conference: 42. annual Geological Society of America (GSA) Southeastern Section meeting, Tallahassee, FL (United States), 1-2 Apr 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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