Mathematics – Logic
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmgp23a..06e&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #GP23A-06
Mathematics
Logic
1525 Paleomagnetism Applied To Tectonics (Regional, Global), 8149 Planetary Tectonics (5475), 8157 Plate Motions: Past (3040), 9619 Precambrian
Scientific paper
The foremost answer to the above question is that high-precision global biostratigraphy extends only to Early Cambrian time. A more challenging issue concerns paleomagnetic data from the Ediacaran (proposed terminal Proterozoic period) and earliest Cambrian intervals: each paleocontinent's apparent polar wander path shows a large spread in poles, intriguingly distributed around a great circle (excepting Baltica, see below), and implying rates of paleolatitude translation or rotation far exceeding typical values from the Cenozoic. Oscillatory true polar wander (TPW) has been proposed to explain these great-circle distributions, but as more data are gathered the number of required episodes increases steadily. Another mechanism to explain such jumpy datasets is a persistently nonaxial geomagnetic field, with greatly amplified paleosecular variation; however, such an interpretation is unattractive to many geodynamicists. A third approach to explain the anomalous data is to discount them altogether; this is unsatisfactory because some of the most reliable results (e.g., Grenville dykes B component and Bunyeroo Formation pole) must be discarded in order to simplify the paths. We propose a new technique for Ediacaran-Cambrian continental reconstruction, which uses these intriguing great circle pole paths regardless of how they were generated. Each paleocontinent's path yields a best-fit great circle and corresponding pole. In the TPW interpretation, that pole describes the long-lived, common (equatorial) axis to the oscillatory rotations. Given that age constraints on the poles is generally so poor, we may reconstruct each continent to this axis with azimuthal freedom. This is topologically identical to the longitudinal degeneracy of standard paleomagnetic reconstructions, but in the case of TPW uncertainties in positions along the great circle represent uncertainties in paleolatitudes, hence climate zones. Analysis of the global Ediacaran-Cambrian paleomagnetic database indicates that all reconstructed Gondwanaland fragments share the same great circle except Arabia, whose circle is offset slightly indicating late rotations during Pan-African accretion. Iapetus can be made wide or narrow, but the latter paleogeography is preferred according to the age of Appalachian rift successions. Siberia remains on the equator, near the pole to its great circle of paleomagnetic results. Baltica is the poorest constrained of any Ediacaran-Cambrian continent: no existing paleogeographic model, with or without TPW, can readily explain its highly divergent paleomagnetic poles.
Evans Daniel A.
Maloof Adam C.
Raub Timothy D.
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