Early Eocene micromammals in the San Jose Formation, San Juan Basin, New Mexico.

摘要

The San Jose Formation mammal assemblages are composed of two local faunas--the Almagre and Largo local faunas, which are from the Regina and Tapicitos Members, respectively. Intensive screenwashing of sediments from five fossil localities in the Regina Member yielded more than 5000 mammal specimens, most of which are small mammal teeth. Study of these micromammals and review of previously collected specimens recorded 31 taxa that are first known in the San Jose faunas, including two new species. These new findings expand the San Jose faunas up to 105 species, of which 97 species comprise the Almagre local fauna, and 28 species make up the Largo faunal assemblage. The sciuravid rodent Knightomys reginensis of Flanagan, 1986 was considered invalid, and a new species Knightomys sp. nov. was established to accommodate a part of the specimens referred to the former.; Twenty-eight previously measured sections primarily in the Regina Member were correlated, and known fossil localities in the Regina Member were put into a stratigraphic framework. Five fossil horizons (H-1 through H-5) in the Regina Member were recognized.; Faunal analysis and statistics of the San Jose faunas suggest that the Largo assemblage, even though much smaller, is similar in general faunal composition to the Almagre fauna. A late Graybullian age is assigned to these two San Jose faunas based on faunal comparison with the standard Wasatchian faunas from Wyoming, and the strata producing these faunas are considered equivalent to the Bunophorus Interval Zone in the Bighorn Basin of Wyoming.; The sedimentary and tectonic history of the Laramide San Juan Basin is also studied based on compilation and synthesis of comprehensive data achieved by previous workers. Stratigraphic relations, sediment-dispersal patterns and depositional environments identified for the terrestrial sequence accumulated in the Laramide San Juan Basin indicate that tectonics imparted a significant control on the basin subsidence and sedimentary history. Stratigraphic geometries and structural characteristics of the terrestrial formations within the San Juan Basin indicate that two of the three previously proposed major pulses of the Laramide deformation were recorded by San Juan Basin deposition.