A FORAMINIFERA AND GASTROPOD ASSEMBLAGE FROM THE MAL PASO FORMATION IN THE CHUMBÍTARO REGION, GUERRERO, SOUTH MEXICO: BIOSTRATIGRAPHICAL, PALEOECOLOGICAL AND PALEOBIOGEOGRAPHICAL SIGNIFICANCE
The upper part of the clastic lower member contains abundant gastropods including Mesoglauconia (M.) burnsi (Stanton), Gymnentone (G.) paluxiensis (Stanton), Gymnentone (G.) zebra (Stanton), Pyrazus (Echinobathra) valeriae (Verneuil and Loriere), Natica alcibari Coquand, Natica ervyna d’Orbigny, Natica gasullae Coquand, Tylostoma globosum Sharpe, Tylostoma ovatum Sharpe, Polyptyxiella dayi (Blanckerhorn), and Diptyxis luttickei (Blanckerhorn).
The upper member is a packstone, wackestone textured-limestone that contains an abundant foraminiferal association mostly composed of Orbitolina (Mesorbitolina) texana (Roemer), Orbitolina (Mesorbitolina) subconcava Leymerie, a few specimens of Coskinolinoides texanus Keijzer, and small textularids and miliolids.
Based on the stratigraphic range of the species Orbitolina (Mesorbitolina) texana (Roemer) assigned an early Albian age to this part of the sequence. The orbitolinid larger foraminifera are excellent markers for correlation of the lower and mid-Cretaceous platforms.
The limestone texture and the orbitolinid larger benthic assemblage suggest a shallow-water tropical deposit. Orbitolina (Mesorbitolina) texana (Roemer) is regarded as a Tethysian species which is useful for paleobiogeographic reconstructions.
Among gastropods the following species were identified: Tylostoma princeps White, Eunerinea azteca (Alencaster), Eunerinea pauli (Coquand), Diptyxis luttickei (Blanckerhorn), Aptyxiella boehmi (Blanckerhorn), Polyptyxiella dayi (Blanckerhorn), Multiptyxis prefleuriaui (Delpey), Peruviniella dolium (Roemer), and Trochacteon (Neocylindrites) cumminsi Stanton.
The gastropod community inhabited a warm shallow-water environment adapted to such different habits as epifaunal on firm bottom or semi-infaunal. They also have Tethysian affinities.