Global Paleogeography of the Earliest Reservoirs: How Much We Do Not Know, and Why
Tim Raub1, Joseph Kirschvink1, and David Evans2
1Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA
2Geology and Geophysics, Yale University, New Haven, CA
Almost 30 years after the widespread recognition of late Precambrian, severe ("Snowball Earth") glaciation, there is still no reliable global paleogeography for that age. As of 2007, only three continental blocks are well-constrained ca. 635 Ma: cratonic Australia, Brazil's Amazon craton, and those Neoproterozoic parts of Arabia intimately associated with Cryogenian-Ediacaran basins in present-day Oman.
This paleogeographic ambiguity continues throughout Ediacaran time and into, at least, the middle Cambrian, spanning deposition of economically significant northern African and middle Eastern reservoirs and prospects.
The source of this paleogeographic uncertainty is not simply lack of paleomagnetic effort or quality. It rather reflects an underlying complexity to Earth's geomagnetic field or geodynamic state. An explanation which brings most existing paleomagnetic data from all continents into coherence invokes multiple, fast episodes of true polar wander (TPW) spanning the last half of the Neoproterozoic Era and possibly continuing well into the Paleozoic Era as well.
TPW is a geophysically well-understood process, and it is observed at measurable (but minor) rates by modern satellites. Multiple, fast episodes of TPW in the Neoproterozoic-Cambrian would exert first-order controls on global sequence stratigraphy and loci of organic carbon burial. In order to apply TPW-predicted sea level and carbon burial patterns to a global paleogeography at this time, one of two paleomagnetic conditions must be satisfied. Either 1) only precisely-dated paleomagnetic poles of nearly identical age may be used to establish relative positions of continents, or 2) only continents with a handful of reliable paleomagnetic poles spanning Neoproterozoic-Cambrian time may be inserted into a global paleogeographic reconstruction based on a novel method using "spinner diagrams."
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