Impact of the Late Paleozoic Ice Age from a Paleotropical Carbonate Depositional System (Orogrande Basin, New Mexico, Usa)

Koch, Jesse ¹; Frank, Tracy D.^1
1 Department of Geosciences, University of Nebraska-Lincoln, Lincoln, NE.

Determining the paleotropical response to large-scale polar ice volume fluctuations is challenging because of inherent difficulties in correlating climatological complexities that occur during ice ages. One example is the late Paleozoic ice age (LPIA), and the latest Pennsylvanian-Early Permian tropical carbonate record in the Orogrande Basin provides an excellent opportunity to examine the sequence stratigraphic and paleoclimatological impacts of the LPIA on an ice-distal locality. The goal is to construct a high-resolution sequence stratigraphic framework and correlate major Gondwanan glacial events to stratigraphic changes that occurred in the paleotropics during the LPIA. Field investigations of outcrops from across the basin are allowing for the construction of a sequence stratigraphic framework. Petrographic and stable isotopic analyses of samples collected from logged sections are helping to refine stratigraphic reconstructions of the late Paleozoic strata in the basin. Uppermost Pennsylvanian “Bursumian” strata show a high-frequency cyclical depositional style in a mixed carbonate and clastic system deposited in a shallow subtidal to nearshore environment. These cycles likely record eustatic sea-level changes driven by ice volume fluctuations on Gondwana. Depositional cycles interpreted for Lower Permian strata are similar to the “Bursumian” outcrops in that they were likely controlled by large-scale ice volume fluctuations during the LPIA. However, the magnitude of relative sea-level change inferred for Permian sections is greater than estimates for “Bursumian” strata. The timing and magnitude of inferred sea-level fluctuations are consistent with recently published eustatic reconstructions calling for variations of 50-100 m. Ongoing efforts include the collection of additional outcrop and stable isotopic data, as well as analysis of available subsurface data from the late Paleozoic strata in the Orogrande Basin. These additional stratigraphic data will help to refine our sequence stratigraphic interpretation, which will ultimately be compared to other stratigraphic frameworks from around the world. Furthermore, new evidence emerging from Gondwana suggests the Early Permian was the peak of the LPIA instead of the long held view of a Late Pennsylvanian acme. As a result, this newly constructed sequence stratigraphic framework for the Orogrande Basin will help to better characterize the paleotropical response to the acme of the LPIA.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009