At Site 1217, we recovered a 145-m section dominated by pelagic clay, radiolarian ooze, chert, and nannofossil chalk (Fig. F3). Fifty-two meters of middle Eocene-Holocene pelagic clay overlies 80 m of middle Eocene radiolarian clay and chert and 1.1 m of nannofossil chalk. Thirty centimeters of basalt were also recovered at the base of this site.
Three holes were drilled at Site 1217. Recovery in Hole 1217B and Hole 1217C began at 20 and 32 mbsf, respectively. The sedimentary section is divided into four lithologic units on the basis of sedimentary facies. Drilling of Holes 1217B and 1217C was terminated above the chert horizon (Subunit IIB); therefore, this description is largely based on results from Hole 1217A. Lithologic Unit I, Subunit IIA, and Unit III are disturbed by drilling and chert in the upper few centimeters of most cores. Chert in Subunit IIB created numerous flow-ins and other disturbances, resulting in poor recovery throughout this interval.
The sediments of Unit I vary between dark yellowish brown (10YR 4/6) and very dark brown (7.5YR 2.5/2) clay. Zeolitic clay and clay with zeolites are present throughout Unit I, with zeolite and iron oxide content increasing downcore. Sediments are commonly mottled, with bioturbation ranging from slight to moderate. Flow-in occurs within Unit I in Cores 199-1217A-5H (38-43 mbsf) and 199-1217C-3H (45-51 mbsf).
Manganese nodules are present at the top of Hole 1217A. The first downhole appearance of chert occurs in Sections 199-1217A-5H-3, 56 cm; 199-1217B-3H-6, 90 cm; and 199-1217C-3H-2, 116 cm. Below this horizon, black (N1) and brownish black (5YR 2/2) centimeter-sized fragmented chert nodules result in core disturbance. A vitric ash layer is present at Section 199-1217B-3H-3, 96 cm. The distinctive dark yellowish brown (10YR 4/4) to very dark brown (10YR 2/2) color change observed at Site 1215, thought to represent a change in the eolian dust source from China to North America (see "Lithostratigraphy" in the "Site 1215" chapter), was not observed at Site 1217.
Within Unit I is a lower Oligocene dark yellowish brown (10YR 4/4) nannofossil ooze with clay (intervals 199-1217A-4H-2, 36 cm, to 4H-6, 118 cm; 199-1217B-2H-5, 41 cm, to 2H-CC, 10 cm) and not recovered in Hole 1217C. This interval shows heavy bioturbation/mottling. The upper boundary between the nannofossil ooze and the overlying clay is gradational. At the lower contact of the nannofossil ooze in Hole 1217A, there is a prominent (4 cm thick) light gray (10YR 7/1) vitric ash layer (Fig. F4) (interval 199-1217A-4H-6, 50-54 cm) not represented in Hole 1217B. This ash layer has a bioturbated upper contact with the nannofossil ooze and a sharp basal contact with clay. An ash layer was also observed within the nannofossil ooze in Samples 199-1217A-4H-4, 14-15 cm, and 199-1217B-2H-CC.
Unit II is divided into two subunits based upon the lithological components. The base of Subunit IIA was only recovered in Hole 1217A.
Subunit IIA is composed primarily of a very dark brown (7.5YR 2.5/3) radiolarian ooze with clay. Clay content increases downhole, and the lithology grades into a dark brown (7.5YR 3/4) clayey radiolarian ooze in Sections 199-1217A-7H-6, 120 cm, and 199-1217B-7H-2, 30 cm. The ooze is commonly mottled by brownish yellow (10YR 6/8) markings that denote undifferentiated burrows. The upper contact with the Unit I clay is gradational. As in Unit 1, black (N1) chert nodules and fragments result in core disturbance in some intervals. Traces of oxides are present throughout Subunit IIA. A 2-cm-thick, very pale brown (10YR 8/3) vitric ash layer is present in interval 199-1217B-6H-3, 74-76 cm. Centimeter-scale oscillations of strong brown (7.5YR 4/6), dark reddish brown (5YR 3/4), and dark-brown (7.5YR 3/4) banding are present within Cores 199-1217B-6H and 199-1217C-5H and are also represented in the color reflectance data (see "Composite Depths"). However, no significant changes in clay or radiolarian content could be distinguished through smear slide examination.
Notable accessories include a medium gray (N5) 3-cm-sized pumice pebble in interval 199-1217B-8H-3, 135-138 cm (Fig. F5). A thin section of the pumice indicates a glassy, amorphous structure with accessory minerals including plagioclase. Several voids in the thin section contained radiolarian tests and fragments; one species was tentatively identified as Siphocampe acephala (Eocene).
Subunit IIB is differentiated from Subunit IIA by the predominance of chert. Cores 199-1217A-12H to 15X are highly disturbed by the presence of chert, which resulted in poor recovery. The chert is commonly black (N1) and broken into pebble-sized fragments by the drilling process. Angular pebbles and massive chert are present within a dark-brown (7.5YR 3/2) clay slurry. Massive chert in Core 199-1217A-14X showed black (N1) and brownish black (5YR 2/2) banding. The clay is not in situ because of drilling disturbance and in many instances is completely removed.
Beneath the chert horizons, we recovered a thin (1.13-m-thick) very pale brown (10YR 8/3) nannofossil chalk with clay and dolomite that is intercalated with 3- to 6-cm-thick beds of a very dark brown (7.5YR 2.5/2) nannofossil claystone with dolomite and light-gray (10YR 7/2) nannofossil chalk (Fig. F6A). The dolomite crystals are clear, near-perfect rhombs (Fig. F6B). The nature of the contact with the overlying chert and clay is unknown because of poor recovery. The interval is heavily mottled.
Core 199-1217A-17X contains a fine-grained, weathered, ocean-floor basalt with aphanitic texture. Rock fragments are composed of elongate white plagioclase and black pyroxene crystals and black glass. Clay was present with nannofossils, which indicates a late Paleocene age (NP9).
The sedimentary section at Site 1217 records lower Eocene nannofossil chalk overlain by lower-middle Eocene chert. Middle Eocene-Holocene deposition is represented by the overlying clay and radiolarian-ooze lithologies. Radiolarian biostratigraphy indicates that the radiolarian-ooze lithology represents ~8 m.y. of deposition; unlike modern siliceous sediments, this ooze is dominated entirely by radiolarians, not diatoms.
The lower Oligocene nannofossil ooze within Cores 199-1217A-4H and 199-1217B-2H is similar to the nannofossil ooze and chalk recovered at DSDP Site 162 (Fig. F7) (van Andel et al., 1975). Paleodepth calculations suggest seafloor depths >4 km at Site 1217, which helps to constrain the depth of the Oligocene CCD at this time (see Fig. F12 in the "Leg 199 Summary" chapter).