Smith (1938, p. 945) first described the “Abiquiu Tuff” of north-central New Mexico, as being composed of three units. A basal conglomerate which “grades from unsorted granitic talus to stream-laid gravel, also granitic” underlies a “hard, compact limestone” which is overlain by “true tuff.” Smith (1938, p. 947) also noted the “unique occurrence of a 5-foot bed of flint on the slopes of Cerro Pedernal about 175 feet above the base of the formation” (Fig. 1). Church and Hack (1939, p. 621) further described this “flint” (“usually a pearly white though flecks and stains of red, yellow and black … are common”) and coined the name Pedernal Chert. They reiterated the work of Smith and described all three units, informally, as members,“ but did not attempt detailed petrologic description.

Since then, few workers have studied the stratigraphy, petrology, and provenance of the Abiquiu Formation, which crops out in Rio Arriba and Sandoval Counties in northern New Mexico (Fig. 1). Many workers have summarized and extrapolated Smith's work (Bingler, 1968; Church and Hack, 1939; Galusha and Bick, 1971; Smith and Muehlberger, 1960; Smith and others, 1970). Inconsistencies in published maps of this region have developed due to the lack of detailed petrologic and stratigraphic descriptions. Smith and Muehlberger (1960) compiled the work of previous authors for their “Geologic Map of the Rio Chama Country.” Galusha and Buck (1971) identified paleontologic material within Santa Fe Group outcrops, mistakenly identified as Abiquiu Formation (T. Galusha, 1978, personal commun.) and suggested that the formation is limited to the Espanola basin. Church and Hack (1939), Woodward and Timmer (1979), and Woodward and others (1974, 1976, 1977) have mapped Pedernal Chert and the basal conglomerate as far west as San Pedro Peak and vicinity (Fig. 1). Kelley (1978) shows sediments formerly included in the Los Pinos Formation (Atwood and Mather, 1932; Manley, 1981; Smith and Muehlberger, 1960) as Abiquiu Formation without explanation as to why the map units were changed.

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