GIS INTERPOLATION OF STRATIGRAPHIC CONTACT DATA TO RECONSTRUCT PALEOGEOGRAPHY: DERIVING A PALEOLANDSCAPE MODEL FOR THE BASE OF THE ZUNI SEQUENCE AND SUBSEQUENT CRETACEOUS ISLANDS IN CENTRAL TEXAS

This research uses raster GIS technology to interpolate paleogeographic digital terrain models in south central Texas. High-resolution geological maps (1:24,000 and 1:31,600 scale) were digitized. Paleosurface modeling focused on three key stratigraphic boundaries at and just above the base of the Zuni sequence. Stratigraphic contact traces between these surfaces were converted to three dimensional data by extracting elevation values from 28 m digital elevation models. Paleo-digital elevation models (PDEM) were interpolated using a Kreiging method based upon 12 nearest points along contact traces and their elevation values. The interpolated PDEMs have estimated vertical root mean square and standard error within 5 m, roughly the same as the published accuracy of modern DEMs. Thickness maps were verified by using measured section data. The paleotopography at the base of the Zuni Sequence was comparable in total relief and slope as the modern topography of the study area. The Hensel Fm is locally absent on interfluves of Paleozoic rock that constitute about 7.5% of the study area. The Glen Rose Fm is also predicted to have been locally absent, indicating terrestrial exposure as islands that persisted throughout the deposition of this marine unit. These islands shifted up dip (northwest) relative the Paleozoic interfluves, but still account for about 7.5% of the total interpolated grid cells. The interfluves during the Hensel deposition may preserve well developed paleosols because these features were never scoured by Cretaceous fluvial systems, exposed to the atmosphere longer, and eventually buried by subsequent low-energy marine sediments. In at least two separate areas the Glen Rose Fm laterally terminates on islands of Pre-Cretaceous rocks. This study demonstrates how raster GIS modeling can be used with stratigraphic and paleogeographic studies to spatially interpolate known data into buried, obscured or missing areas. The implications for GIS modeling in paleogeographic studies include, but are not limited to, identifying terrestrial habitats, refining depositional models, and interpolating geologic surfaces for petroleum exploration.