Changes

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>

This type of bioevent analysis is essential when identifying chronostratigraphically useful bioevents and demonstrating that seismic reflections approximate time lines.<ref name=ch04r71>Mitchum, R., M., Jr., Vail, P., R., Sangree, J., B., 1977, Stratigraphic interpretation of seismic reflection patterns in depositional sequences, in Payton, C., E., ed., Seismic Stratigraphy—Applications to Hydrocarbon Exploration: AAPG Memoir 26, p. 117–143.</ref>

This type of bioevent analysis is essential when identifying chronostratigraphically useful bioevents and demonstrating that seismic reflections approximate time lines.<ref name=ch04r71>Mitchum, R., M., Jr., Vail, P., R., Sangree, J., B., 1977, [http://archives.datapages.com/data/specpubs/seismic1/data/a165/a165/0001/0100/0117.htm Stratigraphic interpretation of seismic reflection patterns in depositional sequences], in Payton, C., E., ed., Seismic Stratigraphy—Applications to Hydrocarbon Exploration: [http://store.aapg.org/detail.aspx?id=1157 AAPG Memoir 26], p. 117–143.</ref>

==See also==

==See also==