The sedimentary section at Site 1221 consists of 156 m of pelagic sediment dominated by Eocene radiolarian ooze and chert, which overlie lower Eocene to uppermost Paleocene chalks. Intervals containing both the E/O boundary and P/E boundary were recovered. The lithologic descriptions are primarily based on Holes 1221A and 1221C because they contained most of the recovered material from the site. The section at Site 1221 is divided into four lithologic units on the basis of sedimentary facies (Fig. F3). Unit I is a thin (1.12 m) clay and radiolarian ooze of early Oligocene and younger age. Unit II contains 6.28 m of nannofossil ooze and diatom ooze of early Oligocene age. Unit III comprises a 143.10-m-thick sequence of upper and middle Eocene age of radiolarian ooze resting on chert. Unit IV is a 5.50-m-thick sequence that is dominated by nannofossil chalk with clay of late Paleocene-early Eocene age and contains the P/E boundary. Unit V is represented by basalt fragments recovered at the base of the section.
Unit I is composed of 1.12 m of brown to yellowish brown (10YR 4/3 to 10YR 4/4) radiolarian ooze with clay; abundant black (10YR 2/1) mottling is also present. This unit may reflect an erosional lag and contains an admixture of diatoms, Fe-Mn oxides, and opaque minerals. This unit was not recovered in Hole 1221A due to overpenetration.
Unit II contains interbedded nannofossil and diatom oozes with varying amounts of radiolarians, clay, and volcanic glass. Interbedding is present on the scale of tens of centimeters with gradational boundaries between lithologies. The nannofossil ooze ranges in color from dark yellowish brown (10YR 4/4) to yellowish brown (10YR 5/4); the diatom ooze ranges from yellowish brown (10YR 5/4) to dark brown (10YR 3/3). Large (~5 cm) very pale brown (10YR 8/2 and 10YR 8/3) mottles are common. The drilling disturbance at the top of the cores from this site affects the continuity of the upper portion of Unit II as well as the sediments of Unit I.
Unit III is siliceous in character and is divided into two subunits based on lithology. Subunit IIIA is radiolarian ooze and radiolarian ooze with clay, and Subunit IIIB is dominated by chert.
Subunit IIIA contains a 104.7-m sequence dominated by dark brown radiolarian ooze with lighter-colored mottles. The uppermost 4 m of Subunit IIIA is dominated by a dark brown (10YR 3/3) to very dark brown (7.5YR 2.5/2) zeolitic clay that contains radiolarians, Fe-Mn oxides, and opaques. Colors of the radiolarian ooze range from very dark brown (7.5YR 2.5/3) to strong brown (7.5YR 4/6). The mottles are usually very pale brown (10YR 8/3) to light brown (7.5YR 6/4), although occasionally darker mottles are present. Intervals of dark brown (10YR 3/3) zeolitic clay are present within the radiolarian ooze. Mn nodules, pumice, and a one centimeter-sized fish tooth (Section 199-1221A-6H-1, 14 cm) are also present.
Recovery of Subunit IIIB was poor in all holes and consists of chert fragments and drilling breccia. The chert is generally black (N1), and larger fragments often exhibit banding ranging from dark yellowish brown (10YR 4/4) to white (10YR 8/1); the banding is interpreted as flattened burrows and mottles later replaced by silica.
Unit IV is dominated by calcareous and nannofossil chalk and contains an interval of zeolitic clay with dramatic color variations (Fig. F4). The upper portion of the unit contains very pale brown (10YR 8/2 to 10YR 7/3) to light reddish brown (5YR 6/4) calcareous chalk with nannofossils and clay and dark yellowish brown (10YR 4/4) nannofossil chalk. The middle portion of the unit is a zeolitic clay exhibiting extensive color banding with millimeter- to centimeter-scale laminations and layering. The lower portion of the unit contains a very pale brown (10YR 7/4 and 10YR 8/4) to brown (10YR 4/3) calcareous chalk. Some chert fragments and occasional microfaulting were observed in Unit IV.
The P/E boundary lies within Unit IV (see "Biostratigraphy"), and was recovered twice (intervals 199-1221C-11X-3, 50-90 cm, and 199-1221D-4X-2, 70-125 cm). The two intervals are very similar, with the interval in Hole 1221D appearing slightly expanded relative to that in Hole 1221C and exhibiting more disturbance (i.e., microfaults in interval 199-1221D-4X-2, 80-86 cm, and folded laminations in intervals 199-1221D-4X-2, 17-26 and 54-56 cm). A detailed lithologic stratigraphy of these two P/E boundary intervals is presented in Figure F4 and summarized below.
The first temporal occurrence of Eocene benthic foraminifers is at 50 cm in Section 199-1221C-11X-3 (see "Benthic Foraminifers" in "Biostratigraphy") in the transition between a very pale brown (10YR 7/4) to yellowish brown (10YR 5/4) calcareous chalk. A similar lithologic transition occurs in Section 199-1221D-4X-2 at 70.5 cm; however, no biostratigraphic samples were taken from Hole 1221D. This chalk is strongly bioturbated, as evidenced by common light brown (10YR 7/3) burrows and mottles.
Below the chalk is a zeolitic clay interval (intervals 199-1221C-11X-3, 59-69 cm, and 199-1221D-4X-2, 79-96.5 cm), which darkens downcore from reddish yellow (5YR 6/6) to dark brown (10YR 2/2). The downcore decrease of light yellowish brown (10YR 6/4) burrows indicates that bioturbation is strong at the top of the clay and moderate toward the bottom; laminations of color, if not in lithology, are observed in intervals 199-1221C-11X-3, 65-68 cm, and 199-1221D-4X-2, 84-87 cm.
Beneath the zeolitic clay interval lies a narrow band of clay (intervals 199-1221C-11X-3, 69-71.5 cm, and 199-1221D-4X-2, 96.5-97.5 cm), which is dark reddish brown (5YR 2.5/2) to black (10YR 2/1). It is generally structureless, with faint dark mottling present in the top of the clay in Hole 1221C.
Underlying the clay is another zeolitic clay (intervals 199-1221C-11X-3, 71.5-90 cm, and 199-1221D-4X-2, 97.5-126 cm), which lightens downcore from dark brown (5YR 2.5/2 and 10YR 2/2) to light brown (10YR 6/4 and 10YR 6/6). Common to minor mottling and burrowing is present in the upper portion of the zeolitic clay; the lower portion is generally homogeneous in appearance. A prominent yellowish red (5YR 5/6) horizon is present near the top of this zeolitic clay (Sections 199-1221C-11X-3, 74.5-76.5 cm, and 199-1221D-4X-2, 101.5-106 cm). This yellowish red color band is very similar to one described in the same stratigraphic position at Site 1220.
The last temporal occurrence of Paleocene benthic foraminifers is at the base of this zeolitic clay (Sections 199-1221C-11X-3, 90 cm, and 199-1221D-4X-2, 126 cm), where it gradually changes to a calcareous chalk over a span of several centimeters. This lowermost chalk interval is very pale brown (10YR 7/4 and 10YR 6/4) and exhibits moderate bioturbation in the form of light colored burrows.
Two 3-cm-sized fragments of partially weathered basalt were recovered at the bottom of Hole 1221D. The basalts are fine grained and phaneritic.
At Site 1221, Paleocene seafloor basalt is overlain by 156 m of pelagic sediment. The lowermost sedimentary unit, Unit IV, contains a dramatically colored P/E boundary interval consisting of reddish yellow zeolitic clay beneath a black, oxide-rich clay. The clay layers are present within calcareous and nannofossil chalks. The color variation is the result of changes in mineralogy and geochemistry (see "P/E Boundary" in "Geochemistry"). The sequence is remarkably similar to the P/E boundary interval obtained 206 km to the south, at Site 1220 (see Fig. F30 in the "Leg Summary" chapter).
The Eocene siliceous sediments of Unit III, radiolarian ooze overlying chert, dominate the lithology of Site 1221. This section of siliceous material is comparable to the radiolarian oozes, cherts, and radiolarites drilled at other sites (e.g., Sites 1216-1220) and may represent a broad zone of low-latitude biological productivity during the middle and late Eocene.
The E/O boundary interval was also recovered near the top of the sediment section at Site 1221. It is present as a gradational transition from siliceous (Unit III) to carbonate sedimentation (Unit II), similar to that observed elsewhere in the region (e.g., Sites 1218, 1219, and 1220). The transition from Eocene siliceous sediments to Oligocene carbonates reflects a deepening of the CCD during the Oligocene (van Andel et al., 1975).
The thin cover of sediments overlying the E/O boundary interval is probably the result of some combination of sediment removal by abyssal processes and declining sedimentation rates as this site moved northward on the Pacific plate during the later Oligocene and Neogene.