Late Neogene Sedimentation Patterns in the Eastern Equatorial Pacific

Abstract

The post-middle Miocene evolution of sedimentary patterns in the eastern equatorial Pacific Ocean has been deduced from a compilation and synthesis of CaCO 3 , opal, and nannofossil assemblage data from 11 sites drilled during Leg 138. Improvements in stratigraphic correlation and time scale development enabled the construction of lithostratigraphic and chronostratigraphic frameworks of exceptional quality. These frameworks, and the high sedimentation rates (often exceeding 4 cm/k.y.) provided a detailed and synoptic paleoceanographic view of a large and highly productive region. The three highlights that emerge are: (1) a middle late Miocene "carbonate crash" (Lyle et al., this volume); (2) a late Miocene-early Pliocene "biogenic bloom"; and (3) an early Pliocene "opal shift". During the carbonate crash, an interval of dissolution extending from-11.2 to 7.5 Ma, CaCO 3 accumulation rates declined to near zero over much of the eastern equatorial Pacific, whereas opal accumulation rates remained substantially unchanged. The crash nadir, near 9.5 Ma, was marked by a brief shoaling of the regional carbonate compensation depth by more than 1400 m. The carbonate crash has been correlated over the entire tropical Pacific Ocean, and has been attributed to tectonically-induced changes in abyssal flow through the Panamanian seaway. The biogenic bloom extended from 6.7 to 4.5 Ma, and was characterized by an overall increase in biogenic accumulation and by a steepening of the latitudinal accumulation gradient toward the equator. The bloom has been observed over a large portion of the global ocean and has been linked to increased productivity. The final highlight, is a distinct and permanent shift in the locus of maximum opal mass accumulation rate at 4.4 Ma. This shift was temporally, and perhaps causally, linked to the final closure of the Panamanian seaway. Before 4.4 Ma, opal accumulation was greatest in the eastern equatorial Pacific Basin (near 0°N, 107°W). Since then, the highest opal fluxes in the equatorial Pacific have occurred in the Galapagos region (near 3°S, 92°W).

Expedition 335 summary

“…This location was formed near the Equator within the equatorial high-productivity zone and initially endured high sedimentation rates (>30 m/m.y.) (e.g., Farrell et al, 1995;Wilson, Teagle, Acton, et al, 2003). Sediment thickness in the region is between 200 and 300 m and is 250 m at Site 1256 (Wilson, Teagle, Acton, et al, 2003).…”

Site 1256

“…(e.g., Farrell et al, 1995;Wilson, Teagle, Acton, et al, 2003). The sediment thickness in the region is between 200 and 300 m and is 250 m at Site 1256 (Wilson, Teagle, Acton, et al, 2003).…”

Controls on carbonate and terrigenous deposition in the incipient Benguela upwelling system during the middle to the late Miocene (ODP Sites 1085 and 1087)

“…Between 12 and 9 Ma, some major drops in CaCO 3 concentration occurred in the central and eastern Pacific Farrel et al, 1995), Ceara Rise (King et al, 1997), and the Caribbean Sea (Roth et al, 2000). So far, deep-water circulation changes, shoaling of the Carbonate Compensation Depth (CCD), and dissolution process were generally believed as possible causes of this so-called "Carbonate Crash" event.…”