Coarse Components in Surface Sediments of the Panama Basin, Eastern Equatorial Pacific.

摘要

The abundance and distribution of biogenic, terrigenous, and volcanic particles in the Panama Basin are markedly dependent on bottom topography and dissolution of calcite in the deeper parts of the basin. Of the coarse fraction (> 62 micrometers), foraminiferal tests and acidic volcanic glass shards are concentrated on the Cocos and Carnegie Ridges as lag deposits. Foraminiferal fragments found on these ridge flanks and on the Malpelo Ridge are caused by the winnowing of bottom currents and by dissolution of calcite with increasing depth. The hydrodynamically light radiolarian skeletons are concentrated by bottom currents in the basin adjacent to the ridges. The foraminiferal calcite compensation depth in the basin is 3,400 m. This relatively shallow depth is probably a consequence of the high biologic productivity in the cold, nutrient-rich surface waters over the basin. The pattern of productivity, however, is not reflected in the pattern of biogenic sediments. Acidic volcanic glass appears to have been carried into the basin form Costa Rica, Colombia, and Ecuador by easterly winds at altitudes of 1,500-6,000 m. Basaltic shards from the Galapagos Islands have been dispersed only over short distances to the west. Terrigenous sand-sized material is found on the edge of the continental shelf, where associated glauconite points to a relict origin, and along the northern Cocos Ridge, where contour currents may act as the dispersal mechanism. (Author)