Changes

==Time significance of seismic reflections==

==Time significance of seismic reflections==

Using seismic reflection geometries to suggest relative sea level phase requires confidence in the coeval character of seismic reflections. The first downhole occurrence of ''Glob alt (Globoquadrina altispira'', bold arrows) in Figure 4-27 suggests a correlation cross-cutting the seismically imaged clinoforms. If the ''Glob alt'' occurrences are coeval, the seismic reflections are time transgressive.

Using seismic reflection geometries to suggest relative sea level phase requires confidence in the coeval character of seismic reflections. The first downhole occurrence of ''Glob alt (Globoquadrina altispira'', bold arrows) in Figure 4-27 suggests a correlation cross-cutting the seismically imaged clinoforms. If the ''Glob alt'' occurrences are coeval, the seismic reflections are time transgressive.

Note that the first downhole well-cutting sample occurrence of the bioevent ''Glob alt'' is at the interface of outer neritic and upper bathyal biofacies, except in the two southern wells, A446-1 and A267-1, where the first occurrences occur within stratigraphic intervals containing bathyal biofacies. ''Glob alt'' is a planktonic foraminifer normally found associated with open marine faunas and floras interpreted as upper bathyal assemblages. The occurrences of ''Glob alt'' coincident with the first upper bathyal biofacies assemblage suggests a facies-controlled top, depressed below the true extinction top by environmental factors. The two occurrences within upper bathyal biofacies are interpreted as true extinction events. These true extinction events correlate with a seismic reflection, suggesting that specific reflection approximates a time line and can be used to extend the ''Glob alt'' extinction event datum (2.8 Ma) northward toward the basin margin (see .<ref name=ch04r10>Armentrout, J., M., Clement, J., F., 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.</ref>

Note that the first downhole well-cutting sample occurrence of the bioevent ''Glob alt'' is at the interface of outer neritic and upper bathyal biofacies, except in the two southern wells, A446-1 and A267-1, where the first occurrences occur within stratigraphic intervals containing bathyal biofacies. ''Glob alt'' is a planktonic foraminifer normally found associated with open marine faunas and floras interpreted as upper bathyal assemblages. The occurrences of ''Glob alt'' coincident with the first upper bathyal biofacies assemblage suggests a facies-controlled top, depressed below the true extinction top by environmental factors. The two occurrences within upper bathyal biofacies are interpreted as true extinction events. These true extinction events correlate with a seismic reflection, suggesting that specific reflection approximates a time line and can be used to extend the ''Glob alt'' extinction event datum (2.8 Ma) northward toward the basin margin (see .<ref name=ch04r10>Armentrout, J., M., Clement, J., F., 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.</ref>