Palaeogeography, Palaeoclimatology, Palaeoecology
Palaeoclimate across the Late Pennsylvanian–Early Permian tropical palaeolatitudes: A review of climate indicators, their distribution, and relation to palaeophysiographic climate factors
Introduction
The Late Pennsylvanian–Early Permian was an interval of geological and climatological transition. This interval includes early tectonic post-assembly of the supercontinent Pangaea (Ziegler et al., 1979) which resulted in construction of a wide (~ 1000 km) and long (5000–7000 km) east–west oriented equatorial Central Pangaean Mountain (CPM) chain of poorly known elevation (Ziegler et al., 1997), both of which (Pangaean assembly and orogenesis) may have contributed toward reorganization of global atmospheric circulation systems into the so-called megamonsoon (Kutzbach and Gallimore, 1989, Dubiel et al., 1991, Parrish, 1993). This interval is also characterized by build-up and ablation of perhaps the most expansive continental ice sheets of the Phanerozoic (e.g., Frakes et al., 1992, Isbell et al., 2003). These ice sheets apparently waxed and waned, resulting in sea-level oscillation and large-scale changes in the distribution of land and sea (e.g., Heckel, 1977, Heckel, 1986, Heckel, 1990, Ramsbottom, 1979, Busch and Rollins, 1984, Ross and Ross, 1985, Veevers and Powell, 1987, Soreghan, 1994a, Yang, 1996, Rankey, 1997, Olszewski and Patzkowsky, 2003). In addition, geochemical evidence indicates large variations in the concentration of atmospheric CO2 during Pennsylvanian and Early Permian time (Montañez et al., 2007). All of these climate factors were operative within an ~ 40–60 million year interval of northward tectonic drift that might also have affected the regional and temporal record of palaeoclimate indicators in tropical Pangaean basins.
The Late Pennsylvanian–Early Permian interval was also a period of tremendous low-latitude environmental change. Palaeoclimate indicators, including records of the temporal and spatial occurrence of coal, laterite, bauxite, Vertisols, calcrete, eolianite, evaporite, and flora, indicate that large regions of near-equatorial Pangaea experienced significant drying over this interval. For example, palaeoclimate indicators of humid tropical climates, such as coal, laterite, and bauxite are common in Pennsylvanian strata, but are virtually non-existent and replaced by indicators of dry climate, such as calcrete and evaporite, in Lower Permian strata of western and central Pangaea (e.g., Mack and James, 1986, Patzkowsy et al., 1991, Kessler et al., 2001, Gibbs et al., 2002, Tabor and Montañez, 2004, Schneider et al., 2006, Tabor et al., in press). The transition from relatively humid to arid climate was rapid in western equatorial Pangaea (Tabor and Montañez, 2004, Montañez et al., 2007, Tabor et al., in press), whereas the transition was protracted over much longer time-scales in central Pangaea (Schneider et al., 2006, Roscher and Schneider, 2006), and on the eastern tropical island blocks palaeoclimate indicators of humidity continued to be deposited through the Late Pennsylvanian and Early Permian (Ikonnikov, 1984, Gibbs et al., 2002, Rees et al., 2002, Yang et al., 2005).
How, and to what extent, did specific tectonic and global climate factors shape palaeoclimate in low-latitude Pangaea? To address this question, we review palaeoclimate indicators from the latest Pennsylvanian (Serpukhovian–Ghzelian) through Earliest Permian (Asselian–Cisuralian) low latitudes of Pangaea. From these palaeoclimate indicators, we develop a regional characterization of climate evolution at stage level, review detailed intrabasinal palaeoclimate reconstructions across low-latitude Pangaea, and evaluate this history in the context of previously proposed explanations for Late Palaeozoic climate change.
Section snippets
Time frame
This contribution focuses upon evidence for atmospheric circulation and climate dynamics preserved in Upper Pennsylvanian (Serpukhovian–Gzhelian) and Lower Permian (Asselian–Cisuralian) terrestrial rocks (Fig. 1). Plate reconstructions (Fig. 2) and palaeoclimate indicators (Fig. 3) used herein are based on a compilation of palaeomagnetic data and palaeogeographic distributions of sedimentological and palaeontological climate indicators (evaporite, coal, eolianite, etc.; Scotese et al., 1999,
General long term trends
Several different global-scale compilations of climate-sensitive sedimentary lithotypes, mineralogical assemblages, and fossil plant types have been used to reconstruct palaeoenvironmental and palaeoclimatic conditions across Pangaea, and to infer the evolution of palaeoatmospheric circulation, from their spatial and temporal distribution (Nairn and Smithwick, 1976, Parrish et al., 1982, Phillips and Peppers, 1984, Rowley et al., 1985, Ziegler et al., 1987, Ziegler et al., 2003, Scotese and
Factors of tropical climate variation
What factors controlled tropical climate in equatorial Pangaea? To answer this, we can draw upon nearly thirty years of scientific investigation into the climate of Pangaea (e.g., Parrish, 1982, Parrish, 1993, Parrish, 1998, Parrish and Peterson, 1988, Kutzbach and Gallimore, 1989, Witzke, 1990, Ziegler, 1990, Dubiel et al., 1991, Crowley and Baum, 1992, Kutzbach et al., 1993, Crowley et al., 1993, Otto-Bliesner, 1993, Otto-Bliesner, 1996, Otto-Bliesner, 1998, Otto-Bliesner, 2003, Kutzbach, 1994
Summary
Several conclusions may be drawn from our analysis of the temporal and spatial distribution of climate factors, and the various hypotheses that have been proposed to explain Pangaean climate evolution:
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Late Pennsylvanian–Early Permian climate evolution, as recorded by lithological indicators, was complex and is unlikely to have a single explanation. Moreover, the stratigraphic record demonstrates climate change at multiple temporal scales that were unlikely to have a single, common cause. In
Acknowledgements
This work is supported by NSF-EAR 0617250, NSF-EAR 0545654, and NSF-EAR 0447381 to Tabor and NSF-EAR-0544760 to Poulsen. Thanks to Lynn Soreghan, Judy Parrish, Steven Driese, Blaine Cecil, and Bette Otto-Bliessner for constructive reviews that significantly improved the quality of this manuscript. The authors would like to thank Isabel P. Montañez, William DiMichele, Crayton J. Yapp, Alfred Ziegler, Ronald Blakey, David Rowley, Judy Parrish, Christopher R. Scotese, Tracy Frank, Chris Fielding,
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