Three major types of phosphorites occur off Peru: (1) friable light-colored laminae, including small peloids and nodules, (2) phosphatic sands dominated by peloids, and (3) generally darker, well lithified dense nodules and hard-grounds. The cores recovered during Ocean Drilling Project (ODP) Leg 112 contain all three phosphorite types and allow expansion of the existing information on many aspects of the older Cenozoic to Quaternary sediments of this region. Accordingly, the primary aims of this project are to (1) improve the understanding of oceanographic and sedimentologic factors which control the episodic deposition of phosphorites in the geologic record, and (2) to develop geochemical and isotopic criteria which may distinguish primary properites derived in the original depositional environment, from modified properties, those acquired by the influence of a subsurface saline brine or during later burial diagenesis, or by reworking and concentration through sedimentologic processes. %%% Phosphorites on continental margins are an interesting and potentially economical mineral deposit. This study will examine the controlling factors for the formation of these deposits. Sediments from drill cores on the Peruvian margin will be examined by a variety of geochemical techniques for clues to the climatic influences on formation as well as the post- depositional effects of fluid flow and diagenesis.
