A palynological analysis of Upper Jurassic dinoflagellate cysts from the Chihuahua trough and Bisbee basin, northern Mexico and southeastern Arizona
Two Upper Jurassic dinoflagellate cyst assemblages, including 25 genera and 17 species from the La Casita Formation in Cerro Los Panales, Chihuahua, Mexico, and 25 genera and 34 species from the Basin Trail Shale Member of the Crystal Cave Formation in the northeastern Chiricahua Mountains, southeastern Arizona, are defined in this study.^ These dinoflagellate cyst assemblages suggest that an active exchange of dinoflagellate taxa was occurring from the western Tethyan, Boreal, and Euro-Atlantic paleo-oceanographic provinces into the Chihuahua trough and Bisbee basin during Late Jurassic time. These assemblages have direct affinities with dinoflagellate cyst taxa occurring in northwestern Europe, England, and southwestern Atlantic Ocean.^ Concurrent age ranges of key dinoflagellate cysts in the Basin Trail Shale Member suggest marine incursion into the Bisbee basin by Middle Oxfordian time (base of the Tenuisseratum Zone) and extending to the Oxfordian-Kimmeridgian boundary (base of the Baylei Zone). Concurrent age range of dinocysts in the La Casita Formation suggest marine incursion into the region during Early Kimmeridgian time (Baylei Zone through Eudoxus Zone). Shifting shelf conditions during periods of transgressive-regressive sea level changes resulted in fluctuating dinoflagellate cyst populations. Proximate and proximochorate cysts dominate over cavate and chorate forms suggesting proximal to middle neritic zone environments. Upper Jurassic strata in the northeastern Chiricahua Mountains and Cerro Los Panales can be correlated with the Bossier and Haynesville formations and Cotton Valley Group of the United States Gulf Coast and with an unnamed unit and Cat Gap Formation in the Blake-Bahama Basin southwestern Atlantic. These correlations provide an important stratigraphic link between Upper Jurassic stratigraphy of northern Mexico, the United States Gulf Coast, and southwestern Atlantic Ocean. ^
Olmstead, Gary Allen, "A palynological analysis of Upper Jurassic dinoflagellate cysts from the Chihuahua trough and Bisbee basin, northern Mexico and southeastern Arizona" (1998). ETD Collection for University of Texas, El Paso. AAI9832820.