Microfossils, paleoenvironments and biostratigraphy of the Mal Paso Formation (Cretaceous, upper Albian), State of Guerrero, Mexico

microfossils from an outcrop of the coral reef and rudist-bearing calcareous upper member of the mal paso formation just north of chumbítaro, state of michoacán, mexico, indicate a deepening trend and transition from nearshore through outer shelf depositional environments upward through the sampled stratigraphic interval. the microbiota is mostly composed of species of calcareous algae and foraminifera. the identified calcareous algae are: pseudolithothamnium album pfender, 1936; cayeuxia kurdistanensis elliott, 1957; acicularia americana konishi and epis, 1962; and dissocladella sp. cf. d. savitriae rama rao and pia, 1936. the species of foraminifera are: nezzazata sp. cf. n. isabellae arnaud-vanneau and sliter, 1995; buccicrenata subgoodlandensis (vanderpool, 1933); cuneolina parva henson, 1948; pseudolituonella sp.; praechrysalidina sp.; and rotalipora appenninica (renz, 1936). in addition, a species of stromatoporoid is illustrated and an indeterminate tube-shaped calcitic microorganism is described as an incertae sedis. from the base of the section upward, four biofacies are defined by the co-occurrences of these taxa: a benthic foraminiferal assemblage, a coral assemblage, a caprinid - dasycladacean assemblage, and a coral - miliolid assemblage. this report documents the first detailed examination of the microbiota of the calcareous upper member of the mal paso formation. data from this analysis of the microbiota supplement earlier paleoenvironmental interpretations based on studies of macrofossils, mainly scleractinian corals, rudists, and other mollusks, and carbonate facies relationships. the combined stratigraphic ranges of the microfossil species identified from this measured section of the mal paso formation support an age determination of late albian. the occurrence of rotalipora appenninica (renz, 1936), a planktic foraminiferan, in the uppermost portion of the exposed stratigraphic section is especially significant because its presence indicates a mar