Late Quaternary and Holocene sediments from the Santa Barbara Basin have been analyzed using back-scattered electron imaging (BSEI) techniques to identify the origins of laminae and document intra- and interannual ocean/climate variability over the last glacial cycle. Laminae observed in X-ray radiography and BSEI are entirely defined by variations in the relative abundance and grain size of biogenic and terrigenous components. There is no evidence to suggest that bacterial mat mediation may have played a role in lamina formation. The simplest lamination type comprises silt-rich, silt-poor couplets that originate from seasonal variation in the supply of silt to the basin. The second lamination type contains an additional lamina of diatom ooze to form terrigenous-sediment diatomaceous triplets. The thicker diatom ooze laminae commonly exhibit a vertical succession of diatom floras, which represents intra-annual variation in productivity. The variation in thickness and assemblage of diatom ooze laminae is probably a function of the amount of diatom flux, which is controlled by upwelling-driven primary productivity in the basin. Laminated sediments deposited during cooler periods generally contain thicker diatom ooze laminae, consistent with more vigorousregional circulation and increased upwelling.

Date of initial receipt: 29 August 1994
Date of acceptance: 20 March 1995

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