Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

A detailed systematic study of samples from the Pliocene of the Saline Basin, Veracruz, Mexico, shows characteristic ostracode assemblages fro the Encanto, Lower and Upper Concepcion, and Agueguexquite strata. The remaining units, Filisola, Paraje Solo and Cedral, did not contain ostracodes. Ninety species belonging to 53 genera are determined and described. The ostracode assemblages of the studied units indicate a general upward shallowing trend during the Pliocene. The Encanto strata, constituting the oldest unit (N 19 or upper N 18), are characterized by Ambocythere spp., Argilloecia posterotruncata Bold, Bradleya normani (Brady), Krithe trinidadensis Bold, and Parakrithe spp. indicating a middle to upper bathyal environment. The Lower and Upper Concepcion beds (N 20) can be recognized by the presence of Actinocythereis vineyardensis (Cushman), Touroconcha lapidiscola Hartmann and the abundance of Hulingsina sp. 1, Henryhowella ex. gr. asperrima (Reuss) and Puriana spp. Encanto species persisting in the Lower Concepcion beds indicate an upper bathyal to outer neritic environment. The Upper Concepcion beds lack these species but instead possess abundant Cyprideis and Perissocytheridea spp., Basslerites? sp., Cytherura wardensis Howe and Brown and Loxoconcha sp. A Hazel. This assemblage indicates an outer to middle shelf environment. The Filisola and Paraje Solo samples were barren of ostracodes. Their foraminiferal and molluscan fauna indicates nearshore and brackish environments. The Paraje Solo may be in part contemporaneous to the Agueguexquite. The Agueguexquite strata contain the youngest (middle N 20), most abundant, and diverse fauna, indicating an inner neritic environment of deposition. They represent a local marine transgression of short duration in the northern part of the basin. By upper Agueguexquite time brackish and continental conditions had returned. A Q-mode cluster analysis utilizing Ward's method on species proportions divided the Agueguexquite and Upper Concepcion samples in two main clusters, each one subdivided into two groups representing slightly different environments. Because of their low abundance only one Encanto and 3 Lower Concepcion samples were used in the clustering. They form generally independent groups. No apparent diversity trends were found.

Pages

271

Share

COinS