Site 1237 (proposed Site NAZCA-17A) was drilled at 16°0.421´S, 76°22.685´W (Shipboard Scientific Party, 2003) on the easternmost flank of Nazca Rise about 140 km off Peru in 3212 m water depth (Fig. F2). Site 1237 overlies oceanic crust with an estimated age of 40–45 Ma based on seafloor magnetic anomalies (Cande and Haxby, 1991). Nazca Rise, a fossil hotspot track with its present-day expression at Easter Island, has moved eastward by ~20° toward the Peru-Chile Trench since 42 Ma. Because thermal subsidence effects are difficult to constrain on this oceanic rise, it is not known how shallow Site 1237 was during its early history. Another complication is extensive deformation and faulting prior to subduction of the Nazca plate beneath Peru; however, benthic foraminiferal assemblages indicate a middle to lower bathyal depth in the late Oligocene (A.E. Holbourn et al., pers. comm. 2005).
Site 1237 is located near the eastern edge of the northward-flowing Peru-Chile Current (a.k.a., the Humboldt Current) that forms the cold eastern boundary current of the South Pacific subtropical gyre. Its modern position is within the productive upwelling system off Peru. In its early history, Site 1237 lay in the oligotrophic subtropical gyre, and therefore biologic production and biogenic sedimentation rates were lower. The present-day water depth of Site 1237 lies in a mixing zone of relatively oxygen rich (nutrient depleted) Circumpolar Deep Water that enters the Peru Basin as bottom water through the Peru-Chile Trench and relatively oxygen depleted (nutrient rich) Pacific Central Water (PCW) (Lonsdale, 1976; Tsuchiya and Talley, 1998) (Fig. F3). Tectonic backtracking to shallower depths suggests that Site 1237 lay within the equivalent of modern PCW during the Oligocene (Shipboard Scientific Party, 2003).