Diatoms are abundant in both greenish gray and olive-gray intervals. Authigenic components are dominated by the presence of glauconite, dolomite, and iron sulfides. Rare, friable nodules, possibly phosphatic, are sometimes disseminated throughout certain intervals. Detailed comparisons between the magnetic susceptibility record generated on the MST and high resolution color reflectance measured with the Minolta spectrophotometer demonstrated complete recovery of the sedimentary sequence down to 140 mcd. Calcareous microfossils show evidence of reworking.
Siliceous microfossils are relatively abundant, well preserved, and show no evidence of reworking.
We tentatively explain this discrepancy as a result of both poor preservation and reworking of calcareous nannofossils. Both calcareous nannofossil and benthic foraminifer assemblages suggest a discontinuity within the sedimentary record at a depth of 120 mbsf. Downcore changes in planktonic foraminifers and diatom assemblages are used as indices of variable surface and subsurface hydrography, as well as proxies for coastal upwelling and fluvial input. Interstitial water profiles record the complete consumption of dissolved sulfate within the uppermost 20 mbsf. In this interval alkalinity and ammonium also increase sharply, recording the degradation of organic matter.