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OBJECTIVE: For the next two days we will examine the stratigraphy and lithofacies of Turanian- and Coniacian-age strata in northwestern New Mexico, on the lands of the Navajo Nation (see location map Figure 6-1). We will focus on the Gallup (shallow marine and coastal plain), Torrivio (predominantly braided-fluvial) and Tocito (estuarine to shallow marine) sandstone formations. An overview of the stratigraphy, lithofacies and hydrocarbon-trapping styles pertaining to these sandstones, in outcrop and from extensive subsurface well-log correlations, is presented in the accompanying paper entitled ‘High- resolution sequence stratigraphy of the Upper Cretaceous Tocito Sandstone…’. A briefer overview is also presented under STOP 1 below. The stratigraphy of the San Juan Basin is summarized in Figures 6-2, 6-3 and 6-4. These are increasingly higher resolution stratigraphic columns, with Figure 6-4, being specifically designed for this field trip. This figure reflects some of the latest ideas on the distribution of significant sequence-stratigraphic surfaces in the Late Turanian and Coniacian parts of the section.

The discussion in the text at each of the field stops is designed to present two somewhat different sequence-stratigraphic interpretations of the rocks; an Exxon (Jones, Van Wagoner and Jennette) and L.S.U. (Nummedal and Riley) interpretation. The reader can draw his/her own conclusions from the observations made at outcrop and in the subsurface (see accompanying papers).

Any person wishing to conduct geological investigations on the Navajo Reservation, including visiting the stops described in this guidebook, must first obtain a permit from the Navajo Nation Minerals Department, P.O. Box 146,

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