Effects of Past Global Change on Life (1995) / Chapter Skim
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paleobiological, geochemical, and sedimentological studies provide a global perspective of the rates, patterns, causes, and consequences of the C-T mass extinction interval. In the Western Interior Basin of North America (Figure 3.2)
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Kauffman (1984b) integrated diverse late Cenomanian molluscan data from detailed stratigraphic sections to demonstrate that the C-T extinction occurred as a series of 51 FIGURE 3.2 Paleogeographic map of the Western Interior Basin of North America during the Cenomanian-Turonian boundary interval, showing the extent of the interior epicontinental seaway (defined by bold lines enclosing sedimentary rock symbols)
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From page 52... ...
first group of molluscan extinction events within a zone of Ir and other trace element enrichment (Figures 3.3 and 3.4) (Kauffman, 1988b, Figure 3.2)
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and Wright and Kennedy (1981~. Whereas these studies have not been directed specifically at mass extinction phenomena, they do show similarly distributed, stepwise disappearance of late Cenomanian macrofossils.
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have recently completed a high-resolution, integrated stratigraphic analysis for the C-T boundary interval in the Magdalena Basin region, and have shown by graphic correlation nearly identical geochemical fluctuations (stable isotopes, trace elements including Ir, organic carbon) , in the same stratigraphic order as found in Europe and North America, suggesting oceanic sources for these chemical perturbations.
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From page 55... ...
5 T T T T 7 iii 111 T T T T T T ~ T ' · , = ~ tr 1' · · ~ ~ ~ = ~ = _~ 1 i_ 1 1 1 1 ~ 2.5 ~ T ~T ~__ _~ ~ = T T T T; __ T T T T ' ~i' ~ __ ~_ _a~ ~ o 1 1 1 1 1. 1 1 TOTAL VALUES ~ KEY: ~ = CLIMATE CYCLE TOPS = BENTONITES -- - = MAJOR BIOEVENTS D= DURATION OF EVENT AGE, OR CYCLE-BOUNDED INTERVAL 55 Ammonito zones Calculatod and40 Ar-39Ar ages time scalo (Obradovich basod on = 1993)
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From page 56... ...
In particular, the first five mass extinction steps are coincident with iridium and other noble metal trace element excursions, suggesting a cause-effect relationship. Further, the entire C-T mass extinction record in the Western Interior of North America and elsewhere occurs within the 1.2-m.y.-long stratigraphic interval of extraordinarily rapid, large-scale, fluctuations in 6~3C' 6~80' Core, CaCO3, and trace elements.
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From page 57... ...
(1987, 1990, 1993) have cautiously suggested that the enriched late Cenomanian trace element suite, including Ir, was probably derived from oceanic sources (e.g., mantle outgassing during rapid CenomanianTuronian plate rearrangements, and/or from the last phases of outgassing of the Pacific superplume; Larson, 199 la,b)
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