Abstract

Remote sensing methods are of great value in assessing the stratigraphy and geologic structure of inaccessible terrains, especially where lithologic contrasts are marked. In this paper, we show that such techniques can be successfully applied to a massive carbonate unit, the Reed Dolomite, exposed in the Waucoba Mountain, Blanco Mountain, and Mount Barcroft quadrangles of east-central California. Airborne NS-001, satellite Landsat TM, and SPOT panchromatic imagery combined with conventional geologic mapping were employed to demonstrate that observed spectral variations on false-color images were caused by subtle compositional variations of the dolomite. Based on reflectance differences and field investigations, six discrete bedding units were recognized in exposures of the Reed Dolomite. From lower to upper, they are (1) very coarse grained, granular, gray, pisolitic, blocky dolomite; (2) medium-grained, white, oolitic, massive dolomite; (3) fine- to coarse-grained, light-gray, oolitic, massive crystalline dolomite and rare interbedded rusty quartzarenite; (4) medium-fine-grained, cross-stratified, locally ocherous brown, interlayered quartzarenite, tan siltstone, and sandy dolomite; (5) fine-grained, thin-bedded, sparsely oolitic, buff dolomite; and (6) fine-grained, fissile, dull white dolomite. Subunit 4 and underlying subunit 3 appear to interfinger, with subunit 4 representing a more proximal shelf facies. In the southeast corner of the mapped area, subunit 4 is present and subunit 3 is absent, with the situation reversed along the western and northern portions of the range. Subunit 5 thins to a feather edge on the north near the Barcroft Granodiorite. Thickness variations of the different Reed stratigraphic entities in the eastern and northern White-Inyo Range may reflect attenuation caused by granitoid intrusion, as well as original stratigraphic variations. The broad expanse of Reed Dolomite directly northeast of the Sage Hen Flat pluton is due to north-south-trending folds. Details of the White-Inyo anticlinorium are now better resolved in the central portion of the range where previously undetected folds, faults, and homoclinal sections are revealed in false-color imagery of the macroscopically featureless Reed Dolomite. Thickness trends and facies boundaries for the newly recognized subunits trend north-south or north-northeast throughout the study area, locally reflecting the gentle west-northwest continental shelf paleoslope of the passive margin of western North America during latest Precambrian-Early Cambrian. This study is important to petroleum geologists because it demonstrates that detailed stratigraphy and structure can be determined using remote sensing techniques in semiarid regions where massive, indistinct carbonate units crop out. In some cases, no single processing method allows spectral discrimination of all lithostratigraphic entities; furthermore, the spectral characteristics of a specific unit have been shown to vary even within a single image. Hence, our work underscores the site-specific limitations of individual multispectral methods and illustrates why a combination of diverse methods needs to be employed. Finally, geologic lessons learned within the study area may be extrapolated to similar terrains elsewhere within the Basin and Range province.

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