Distribution of Recent Foraminifera Off West Coast of Central America

Abstract

A survey was made of the foraminiferal distribution in the sediments off the west coast of Central America, between depths of 6 and 6,270 feet. Thirty-six samples were examined from areas off Acapulco, off the Gulf of Fonseca, and from the Gulf of Panama. A few of the samples represent intervening areas. The composite frequency distribution of Foraminifera is plotted against changes in depth, temperature, and salinity. Faunal zones are recognized as follows. Inner Shelf fauna (0-150 feet): Elphidium spp., miliolids, Nonionella basispinata, streblus spp. Outer Shelf fauna (151-400 feet): Discorbis panamensis, Planulina ornata, Uvigerina (striate species). Upper Bathyal fauna (401-2,000 feet): Bolivina acuminata, Bolivina seminuda vars., Epistominella bradyana. Middle Bathyal fauna (2,001-4,000 feet): Bolivina spp., Bolivinita minuta, Bulimina affinis, Bulimina spinifera, Buliminella exilis tenuata, Cassidulina delicata,Chilostomella ovoidea, Uvigerina peregrina, Valvulineria inaequalis. Lower Bathyal fauna (4,001-6,270 feet): Bulimina clava, Cassidulinoides tenuis, Pullenia bulloides, Pyrgo murrhina, Uvigerina proboscidea, Valvulineria araucana, Virgulina nodosa. Associated offshore trends include: (1) increase in number of species away from shore; (2) increase in foraminiferal number out to the upper bathyal zone and a decrease beyond; (3) greatest abundance of plankton in the outer shelf zone; (4) and abundant Radiolaria and diatoms below depths of 4,000 feet.