Recent Advances in Upper Jurassic (Kimmeridgian - Tithonian) Ammonite Biostratigraphy of North-Central Mexico Based on Recently Collected Ammonite Assemblages

摘要

The analysis of recently collected ammonite assemblages from type and new sections in central and eastern Mexico allows improvement of Upper Jurassic (Kimmeridgian-Tithonian) biostratigraphy and biochronostratigraphic correlations. The Schneidia, lower Idoceras without Sutneria, upper Idoceras with Sutneria, Taramelliceras-Aulacostephanus, Coryceras-Procraspedites assemblages, and the interval zone with Lingulaticras, are all useful in subdividing Kimmeridgian deposits. The precise identification of the Kimmeridgian-Tithonian boundary is difficult, but the upper Beckeri Zone and part of the Hybonotum Zone can be recognized on the basis of Hybonoticeras. The Usseliceras-Franconits, Parastreblits-Torquatisphinctes, and Andiceras-Kossmatia assemblages characterize stratigraphic intervals in overlying Lower Tithonian deposits. More research is necessary to determine precisely Upper Tithonian ammonite assemblages in central and eastern Mexico. A revision of traditional and recent biostratigraphic interpretations is provided on the basis of the new material collected in situ bed-by-bed.