National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)

Chapter: HIGH-RESOLUTION APPROACH TO DOCUMENTING ANCIENT ENVIRONMENTAL CHANGE

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Suggested Citation:"HIGH-RESOLUTION APPROACH TO DOCUMENTING ANCIENT ENVIRONMENTAL CHANGE." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
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Page 49

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GLOBAL CHANGE LEADING TO BIODIVERSITY CRISIS IN A GREENHOUSE WORLD: THE CENOMANIAN-TURONIAN 49 (CRETACEOUS) MASS EXTINCTION HIGH-RESOLUTION APPROACH TO DOCUMENTING ANCIENT ENVIRONMENTAL CHANGE Quaternary analyses of global environmental changes, and biological responses to them, are conducted at scales of years (varves) to tens of thousands of years with nearly continuously represented data (Figure 3.1), commonly sampled at the 1- to 10-cm stratigraphic scale. Excellent preservation of original sedimentological, geochemical, and paleobiological materials allows integrated environmental and ecological analyses through small increments of time. These analyses reveal the dynamics and mechanisms of global change at several scales (e.g., Thompson, 1991; Webb, 1991). However, claims that older stratigraphic data sets are not completely enough preserved or highly enough resolved to contribute significantly to global change research and predictive modeling, are rejected. High-resolution event stratigraphic methodology (Kauffman, 1988a; Kauffman et al., 1991) provides interdisciplinary data, at 100- to >1000-yr Quaternary scales, for Phanerozoic strata. Figure 3.1 A comparison between the resolution of Quaternary data and time scales used in global change studies, and that possible from high-resolution Cretaceous paleoenvironmental studies in fine-grained marine facies. Quaternary data taken from Oeschger and Arquit (1991): Lower field of small black circles represent CO 2 values obtained from centimeter-scale (100- to 200-yr) intervals in ice cores at Byrd Station, Antarctica; the thin line graph above it connects δ18O values from the same core and sample set. The triangles connected by a heavy dashed or solid line and superimposed on the Quaternary data set represent a typical high-resolution, centimeter-scale (1000- yr) sample interval for middle Cretaceous global change and mass extinction research, applied to the same data set. Note that all major climate trends shown by high-resolution Quaternary data are also shown by the data set representing Cretaceous sample intervals, and only the smallest fluctuations are lost between the 100-yr and 1000- yr scales. Rock accumulation rates (RARs) for marine strata, which may preserve the most continuous and diverse record of Phanerozoic environmental changes, range from <1 cm/1000 yr (basinal fine-grained facies) to >1 m/1000 yr (e.g., in coarse- grained turbiditic, slope fan, shoreface, foreshore, and estuarine channel facies). Whereas more rapidly deposited strata allow finer stratigraphic time divisions to be sampled easily, these facies commonly reflect episodic high-energy sedimentation events separated by erosive intervals and do not preserve a long, continuous record of environmental change. More slowly but more continuously deposited basinal marine and lacustrine sequences characterized by shales, mudstones, and biogenic pelagic or hemipelagic facies provide the best Phanerozoic record of global change at scales comparable to long-term Quaternary records. Such data do exist and have been gathered largely through the application of methods inherent in high-resolution event stratigraphy (HIRES: Kauffman, 1988a; Kauffman et al., 1991). HIRES focuses the analysis of stratigraphic sections on the centimeter-scale in search of event and cyclic stratification (see papers in Einsele et al., 1991). These events are expressed as physically unique surfaces or thin intervals; as short-term geochemical excursions from background values; as short-term evolutionary and ecological phenomena; and as depositional cycle and hemicycle boundaries, all with regional to interregional extent. Thus, stratigraphic deviations from background patterns are emphasized, and data from various disciplines are integrated into holistic interpretations of these depositional events. Initially, these data comprise a working chronostratigraphy for regional correlations at very high levels of resolution (days to hundreds of years per event surface or thin stratigraphic interval, typically spaced at intervals hundreds to thousands of years apart; Kauffman, 1988a). The correlation potential for HIRES exceeds that of the best biozonation, geochronology, or magnetostratigraphy (Kauffman et al., 1991). Ultimately, a diverse, high-resolution physical, chemical, biological, and cyclostratigraphic data base collected continuously over a significant interval of Phanerozoic time will enhance integrated analysis of dynamic changes in regional to global environments, and biological responses

Next: THE CENOMANIAN-TURONIAN (C-T) MASS EXTINCTION - AN ANCIENT GLOBAL BIODIVERSITY CRISIS IN A CHAOTIC GREENHOUSE WORLD »
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What can we expect as global change progresses? Will there be thresholds that trigger sudden shifts in environmental conditions—or that cause catastrophic destruction of life?

Effects of Past Global Change on Life explores what earth scientists are learning about the impact of large-scale environmental changes on ancient life—and how these findings may help us resolve today's environmental controversies.

Leading authorities discuss historical climate trends and what can be learned from the mass extinctions and other critical periods about the rise and fall of plant and animal species in response to global change. The volume develops a picture of how environmental change has closed some evolutionary doors while opening others—including profound effects on the early members of the human family.

An expert panel offers specific recommendations on expanding research and improving investigative tools—and targets historical periods and geological and biological patterns with the most promise of shedding light on future developments.

This readable and informative book will be of special interest to professionals in the earth sciences and the environmental community as well as concerned policymakers.

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