Hannes Löser

Palaeobiogeographic aspects of Late Barremian to Late Albian coral faunas from Northern Mexico (Sonora) and the southern USA (Arizona, Texas)

The taxonomy of Early Cretaceous shallow marine coral faunas from the Bisbee Basin (northwestern Mexico and Arizona, southwestern USA) and the Comanche Platform (Texas, USA) are compared to each other and to coral associations of the same age around the world. The analysis here employs a large, comprehensive computer database on Mesozoic corals. The database is used to develop a uniform palaeogeographic framework for the comparisons (300 palaeo-provinces are distinguished worldwide for the Cretaceous), and a distance matrix cluster analysis of shared presence is performed on the data to correlate coral faunas both within and outside of the study area. The study is based entirely on coral material recently collected in the field and studied in museum collections. Of the 754 coral samples examined, a total of 160 species is identified from 54 sample locations. This large total number is in contrast to the low to moderate number of species found in each locality, with a maximum number of 28 species from one locality in northwestern Mexico. This demonstrates that coral distribution was controlled by regional (even local) factors. Outside of the sample area, the coral faunas show a strong correlation to central Tethyan faunas, with strongest affinities to that of the Iberian Peninsula, and also to eastern Tethys and western Pacific faunas. This argues against the commonly held concept of a distinct New World coral faunal realm, and is explained by a west-to-east orientation of warm oceanic connections and the close proximity of the land masses during the Early Cretaceous.