INTRODUCTION

During Ocean Drilling Program (ODP) Leg 149, a transect of sites (897-901) was drilled across the ocean/continent transition along the western margin of Iberia, a predominantly nonvolcanic passive margin (Fig. 1; Sawyer, Whitmarsh, Klaus, et al., 1994). At these sites, Mesozoic synrift to Cenozoic postrift sedimentary sequences were recovered above a series of basement highs (Fig. 2).

The thickest (~700 m) and most stratigraphically complete sedimentary sequences were recovered at Sites 897 and 900 (Fig. 3; Sawyer, Whitmarsh, Klaus, et al., 1994). The pre-Eocene to Cretaceous sedimentary units are lithologically diverse and include mass-flow deposits at Sites 899 and 897 and Cretaceous serpentinite breccias at Site 899. Oligocene to middle Miocene units at Sites 897-900 consist of interbedded to interlaminated contourites, turbidites, hemipelagites, and pelagites, which are overlain, in turn, by Miocene to Pleistocene turbidite, hemipelagite, and pelagite successions (Fig. 3). The change from predominantly contourite to turbidite sedimentation occurs in the middle Miocene (Fig. 4), concurrent with a compressional phase of regional deformation (Sawyer, Whitmarsh, Klaus, et al., 1994).

In general, the Leg 149 sediments are composed dominantly of terrigenous mud, with a significant calcareous pelagic component, and lesser amounts of sand (Fig. 3). Thin sand laminae occur throughout the Jurassic to Pleistocene successions cored at all five sites, but are most prevalent within the Pliocene and Cretaceous sections at Site 897, within the Pleistocene and Pliocene sections at Site 898, and within the Paleogene and Miocene sections at Site 900. Terrigenous sand, as opposed to bioclastic sand, is most common in the Pleistocene to Pliocene sections at Sites 897 and 898. The composition and provenance of the Jurassic to Pleistocene terrigenous sand is the focus of this paper.

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