Effects of Past Global Change on Life (1995) / Chapter Skim
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Pages 61-63
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From page 61... ...
Even finer resolution for dating and correlation can be obtained by utilizing physical and chemical event deposits/horizons within the same section. Most of the 112 event beds/horizons in the Bridge Creek Limestone are bentonites, trace element, stable isotope, and organic carbon enrichment levels (spikes)
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From page 62... ...
The first geochemical perturbations associated with the C-T extinction interval in this setting occur 880,000 yr below the C-T boundary; the first molluscan extinction event (step) occurs 520,000 yr below the C-T boundary, coeval with initiation of a series of 10 successive trace element enrichment horizons, probably representing an oceanic advection sequence.
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From page 63... ...
The relatively shallow water trace element enrichment layers found to be associated with C-T extinction events in highresolution stratigraphic analysis, probably represent depositional sites of advecting trace elements from deeper ocean sources, situated at and above the oceanic redoxcline between the OMZ and the mixing zone. A third hypothesis for C-T mass extinction, which draws on events described in the two previous hypotheses, focuses on the extraordinary rates and magnitudes of oceanclimate changes associated with the 1.46-m.y.-long C-T boundary interval, and their effects on a global biota narrowly adapted for the most part to the equable greenhouse environments that had been developing throughout the early and middle Cretaceous.
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