Early Cretaceous Sedimentation and Tectonics in Southeastern Arizona: ABSTRACT

Abstract

Sedimentary strata of Aptian to Albian age are widespread in southeastern Arizona, southwestern New Mexico, and northern Mexico. These rocks comprise a transgressive/regressive marine/nonmarine basinal sequence, locally over 3,000 m thick, of sandstone, shale, limestone, and conglomerate mapped as the Bisbee Group. In general, the nonmarine lower third of the sequence is composed of coarse clastic alluvial fan and basin-fill deposits of local origin and rests unconformably on rocks of Jurassic to Precambrian age. These syntectonic sediments were deposited during regional southwest-northeast extension where local fault-block uplifts bounded by northwest-trending normal faults created a basin-and-range paleogeography with isolated clastic-filled basins and mountain ranges r mmed by alluvial fans. The marine and marginal-marine shales and limestones of the middle third are restricted to the southeastern part of the region and represent the northwestern end of a shallow marine sea (Bisbee Sea) which advanced northwestward across northeast Mexico from the Jurassic rift basins of the Gulf of Mexico. Shallow-water platform carbonates were deposited over a wide area, with coral-algal-rudist patch reefs localized over paleo-structural highs. The upper part of the Bisbee Group is the regressive facies of this sea and is composed primarily of nonmarine deltaic (fan delta), lacustrine and fluvial sandstones, and siltstones. This facies reconstruction suggests that differential vertical displacements along northwest-trending normal faults controlled the regional variations in thickness, lithology, and grain size in the Bisbee Group. End_of_Article - Last_Page 549------------