Paleoclimate studies for controversial continental paleogeographies: The application of spherical geodesic grids and climate models to Gondwana's Devonian apparent polar wander path

Abstract

Paleomagnetic data acquired in the last 10 to 15 years have failed to clearly delineate the Devonian apparent polar wander (APW) path for Gondwana. Consequently, many paleogeographers and paleomagnetists have turned to paleoclimate data to assist in locating Gondwana. Paleoclimate data have been used to either support proposed paleomagnetic-based positions for Gondwana or to independently position the continent. Both of these approaches have problems, including how paleoclimate data are handled and the assumption of a zonal climate system. Several improvements of these approaches are proposed in this study. First, paleoclimate data were grouped into occurrences using a spherical geodesic grid system when statistical manipulations were to be performed. The use of occurrences reduces errors caused by variations in sampling resolution and post-depositional processes. Grid cells in the spherical geodesic grid systems are near-equal area and shape. A comparison between spherical geodesic grid systems with other grid systems showed that the spherical geodesic grids were the most stable grid system if used in combination with a technique called rotational minimization, which finds the fewest possible occurrences for a given data set. Second, two techniques commonly used in paleogeographic studies were modified and a third technique was introduced. The first two techniques, called the palepole zonality method and the modified pole-finder method, were designed to rate proposed pole positions for Gondwana using latitude-distribution models for paleoclimate data. The final method, the parametric climate-model method, uses a conceptual climate model to predict the climate of the continent, which was compared to regional climate inference models. The results of these techniques when applied to Gondwana suggested that the continent moved little during the Devonian: the pole moved from west-central Gondwana in the Early Devonian to the northwest or to the east by the Carboniferous. The results also show, however, that all of these techniques are limited in their ability to pick a single position for Gondwana. Consequently, the best path identified by these methods cannot be assumed to be correct and confirming paleomagnetic data are still required.