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doi:10.2204/iodp.proc.320321.105.2010

Lithostratigraphy

At Site U1333, Eocene seafloor basalt is overlain by ~183 m of pelagic sediments that are divided into four major lithologic units (Fig. F4). Lithostratigraphic Unit I is ~7 m thick and contains an alternating sequence of clay, clayey radiolarian ooze, radiolarian clay, clayey nannofossil ooze, and nannofossil ooze of early Miocene age (see "Biostratigraphy" and "Paleomagnetism"). These sediments overlie ~112 m of alternating very pale brown nannofossil ooze and yellowish brown nannofossil ooze with radiolarians of early Miocene to latest Eocene age (Unit II). Unit III consists of ~60 m of clayey radiolarian ooze and clayey nannofossil ooze, nannofossil radiolarian ooze, nannofossil ooze, radiolarian nannofossil ooze, and porcellanite of latest Eocene to middle Eocene age. Unit III is divided into two subunits (IIIa and IIIb) based on the occurrence of porcellanite (Subunit IIIb only). At the base of Hole U1333A a thin (~3.3 m thick) unit of nannofossil ooze and foraminifer-bearing limestone (Unit IV) overlies basalt of middle Eocene age (Unit V). Lithologic unit and subunit boundaries are also defined by differences in physical property data series. Lithologic differences, based on visual core descriptions and smear slide and thin section analysis (Table T2; Fig. F4; see "Site U1333 smear slides" in "Core descriptions"), are primarily attributable to varying distributions of biogenic components (e.g., nannofossils and radiolarians) and clay-sized lithogenic material. Lithologic descriptions are largely based on sediments recovered in Hole U1333A, supplemented with observations from Holes U1333B and U1333C.

Unit I

Intervals: 320-U1333A-1H-1, 0 cm, through 1H-3, 135 cm; 320-U1333B-1H-1, 0 cm, through at least 1H-CC, 18 cm (base not recovered); 320-U1333C-1H-1, 0 cm, through 2H-3, 40 cm

Depths: Hole U1333A = 0.0–4.35 m CSF; Hole U1333B = 0.0–7.66 m CSF; Hole U1333C = 0.0–5.00 m CSF

Age: early Miocene

Lithology: clay, clayey radiolarian ooze, radiolarian clay, clayey nannofossil ooze, and nannofossil ooze

The major lithologies in Unit I are dark brown (10YR 3/3) clay, dark brown (10YR 3/3) clayey radiolarian ooze, dark yellowish brown (10YR 4/4) radiolarian clay, dark brown (10YR 3/3) clayey nannofossil ooze, and very pale brown (10YR 7/3) to light yellowish brown (10YR 6/4) nannofossil ooze. Sometimes clay occurs with nannofossils and radiolarians, whereas both clayey radiolarian ooze and radiolarian clay occur with nannofossils. Both clayey nannofossil ooze and nannofossil ooze occur with radiolarians and clay. Unit I is characterized by a downhole alternation of dark brown clayey radiolarian ooze with nannofossils and very pale brown nannofossil ooze. Bioturbation intensity is minor in these sediments. Typically, Unit I is marked by higher magnetic susceptibility values, lower gamma ray attenuation (GRA) bulk densities, lower L* reflectance (lightness), and lower CaCO₃ content than Unit II (Fig. F4; see "Physical properties" and "Geochemistry"). The boundary between Unit I and underlying Unit II is defined by a downhole transition in lithology to an absence of clay as a major component.

Unit II

Intervals: 320-U1333A-1H-3, 135 cm, through 13X-4, 150 cm; 320-U1333B-3H-CC, 18 cm, through 13H-6, 55 cm; 320-U1333C-2H-3, 40 cm, through at least 14H-CC, 22 cm (base not recovered)

Depths: Hole U1333A = 4.35–116.30 m CSF; Hole U1333B = 7.66–120.25 m CSF; Hole U1333C = 5.00–117.57 m CSF

Age: early Miocene to late Eocene

Lithology: nannofossil ooze

Unit II is dominated by white (10YR 8/1) to very pale brown (10YR 7/3 and 10YR 8/2) to light yellowish brown (10YR 6/4) and yellowish brown (10YR 5/4) nannofossil ooze. Within the major lithology, alternations of predominantly very pale brown (10YR 8/2 to 10YR 7/4) nannofossil ooze and yellowish brown (10YR 5/4) nannofossil ooze with radiolarians occur in the uppermost part of the sequence (Cores 320-U1333A-2H through 4H). These sediments are deposited immediately above an alternating sequence of white (10YR 8/1), light gray (10YR 7/2), and very pale brown (10YR 7/3) nannofossil ooze (Cores 320-U1333A-4H through 13H). At the base of Unit II, white nannofossil ooze shows increasing alternation with very pale brown (10YR 8/2) nannofossil ooze with diatoms and with very pale brown (10YR 7/4) nannofossil ooze with diatoms and radiolarians. Bioturbation intensity is typically minor to nonvisible within Unit II. Baseline magnetic susceptibility values are generally low in Unit II with greatest amplitude of variability in the uppermost part (Cores 320-U1333A-2H through 4H). GRA bulk density, L*, and CaCO₃ values are all high in Unit II relative to Unit I with significant variations in the uppermost part (Fig. F4; see "Physical properties"). The pronounced variability of physical property data in these sediments occurs in association with alternations of very pale brown (10YR 7/4) nannofossil ooze and yellowish brown (10YR 5/4) nannofossil ooze with radiolarians. Pumice clasts (0.5–2 cm) are occasionally found in Unit II. Thin section analysis indicates fine volcanic glass (shards typically 10–500 µm in diameter) with vesicules and plagioclase as a minor component (crystal size = 50–100 µm in diameter; Sample 320-U1333A-3H-6, 148–149 cm) (Fig. F5; see "Site U1333 smear slides" in "Core descriptions"). Pumice clast margins and some vesicules and pores are filled with nannofossil ooze. The boundary between Unit II and underlying Unit III is defined by the occurrence of clay as major component in the lithology in Unit III.

Unit III

Intervals: 320-U1333A-13X-4, 150 cm, through 20X-2, 82 cm; 320-U1333B-13H-6, 55 cm, through at least 20X-CC, 0 cm (boundary not recovered); 320-U1333C-14H-CC, 22 cm, through at least 23X-CC, 7 cm (boundary not recovered)

Depths: Hole U1333A = 116.30–179.92 m CSF; Hole U1333B = 120.25–178.17 m CSF; Hole U1333C = 117.57–172.87 m CSF

Age: late Eocene to middle Eocene

Lithology: clayey radiolarian ooze, clayey nannofossil ooze, nannofossil radiolarian ooze, nannofossil ooze, radiolarian nannofossil ooze, radiolarian ooze, nannofossil ooze, and porcellanite

The major lithologies in Unit III are dark yellowish brown (10YR 4/4) to very dark grayish brown (10YR 3/2) clayey radiolarian ooze, dark brown (10YR 3/3) clayey nannofossil ooze, very pale brown (10YR 7/3) to brown (10YR 5/3) nannofossil ooze, dark brown (10YR 3/3) nannofossil radiolarian ooze, grayish brown (10YR 5/2) to light yellowish brown (10YR 6/4) nannofossil ooze, pale brown (10YR 6/3) to brown (10YR 4/3 and 10YR 5/3) to yellowish brown (10YR 5/4) radiolarian nannofossil ooze, and brown (10YR 4/3) to dark brown (10YR 3/3) radiolarian ooze and porcellanite. In general, downhole changes in physical properties (magnetic susceptibility, GRA bulk density, and L*) correspond to changes in CaCO₃ content within Unit III (see Fig. F4). The Subunit IIIa/IIIb boundary is defined by the uppermost occurrence of porcellanite. The Unit III/IV boundary is defined by the uppermost occurrence of nannofossil ooze and limestone.

Subunit IIIa

Intervals: 320-U1333A-13X-4, 150 cm, through 19X-1, 10 cm; 320-U1333B-13H-6, 55 cm, through at least 18H-CC, 22 cm (boundary not recovered); 320-U1333C-14H-CC, 22 cm, through at least 22X-CC, 9 cm (boundary not recovered)

Depths: Hole U1333A = 116.30–168.10 m CSF; Hole U1333B = 120.25–162.94 m CSF; Hole U1333C = 117.57–163.29 m CSF

Age: late Eocene to middle Eocene

Lithology: clayey radiolarian ooze, nannofossil radiolarian ooze, radiolarian nannofossil ooze, radiolarian ooze, and nannofossil ooze

Subunit IIIa is distinguished from Subunit IIIb by the absence of porcellanite in Subunit IIIa. The major lithologies in Subunit IIIa are dark yellowish brown (10YR 4/4) to very dark grayish brown (10YR 3/2) clayey radiolarian ooze, very pale brown (10YR 7/3) to light yellowish brown (10YR 6/4) and brown (10YR 5/3) to grayish brown (10YR 5/2) nannofossil ooze, dark brown (10YR 3/3) nannofossil radiolarian ooze, pale brown (10YR 6/3) to brown (10YR 4/3 and 10YR 5/3) to yellowish brown (10YR 5/4) radiolarian nannofossil ooze, and brown (10YR 4/3) to dark brown (10YR 3/3) radiolarian ooze. Sometimes clayey radiolarian ooze occurs with nannofossils, nannofossil radiolarian ooze and radiolarian nannofossil ooze occur with clay, radiolarian ooze occurs with clay and nannofossils, and nannofossil ooze occurs with diatoms and radiolarians. On a decimeter to meter scale, three types of alternations are common:

1. Brown to pale brown radiolarian nannofossil ooze and brown to dark brown nannofossil radiolarian ooze,

2. Very dark grayish brown clayey radiolarian ooze and yellowish brown nannofossil radiolarian ooze, and

3. Very dark grayish brown clayey radiolarian ooze and brown clayey radiolarian ooze.

Bioturbation is moderate to intense in these sediments. GRA bulk density, L*, and CaCO₃ content show high-amplitude variations, with lowest values in Sections 320-U1333A-15X-4 through 16X-5 (Fig. F4; see "Physical properties"). Generally, magnetic susceptibility values in Subunit IIIa are ~30 x 10^–5 SI higher than in Unit II (Fig. F4; see "Physical properties"). Microfaults occur in intervals 320-U1333A-18X-4, 80–87 cm, and 320-U1333B-18H-3, 26–28 cm, within stiff light yellowish brown (10YR 6/4) nannofossil ooze with radiolarians and dark yellowish brown (10YR 4/4) clayey radiolarian ooze. The boundary to underlying Subunit IIIb is defined by the uppermost occurrence of porcellanite.

Subunit IIIb

Intervals: 320-U1333A-19X-1, 10 cm, through 20X-2, 82 cm; 320-U1333B-19X-1, 0 cm, through at least 20X-CC, 0 cm (boundary not recovered); 320-U1333C-22X-CC, 9 cm, through at least 23X-CC, 7 cm (boundary not recovered)

Depths: Hole U1333A = 168.10–179.92 m CSF; Hole U1333B = 162.7–178.17 m CSF; Hole U1333C = 163.29–172.87 m CSF

Age: middle Eocene

Lithology: nannofossil ooze, radiolarian ooze, clayey nannofossil ooze, clayey radiolarian ooze, and porcellanite

Subunit IIIb is distinguished from Subunit IIa by the presence of porcellanite. The dominant lithologies in Subunit IIIb are yellowish brown (10YR 5/4) to brown (10YR 4/3) nannofossil ooze, dark brown (10YR 3/3) clayey nannofossil ooze, brown (10YR 3/3) radiolarian ooze, and brown porcellanite. Sometimes nannofossil ooze occurs with clay and radiolarians, radiolarian ooze occurs with clay, and clayey radiolarian ooze occurs with nannofossils. Bioturbation intensity in these sediments is minor. GRA bulk density, L*, CaCO₃ content, and magnetic susceptibility all increase downhole across the Subunit IIIb/Unit IV boundary. The boundary between Unit III and underlying Unit IV is defined by the uppermost occurrence of nannofossil ooze and limestone.

Unit IV

Intervals: 320-U1333A-20X-2, 82 cm, through at least 21X-CC, 0 cm (boundary not recovered); 320-U1333B-20X-CC, 0 cm, through at least 20X-CC, 17 cm (boundary not recovered); 320-U1333C-23X-CC, 7 cm, through at least 24X-CC, 16 cm (boundary not recovered)

Depths: Hole U1333A = 179.92–181.60 CSF; Hole U1333B = 178.17–178.34 CSF; Hole U1333C = 172.87–176.16 m CSF

Age: middle Eocene

Lithology: nannofossil ooze, limestone

The dominant lithology in Unit IV is white (10YR 8/1) to light gray (10YR 7/2) limestone with green flecks and very pale brown (10YR 7/4 and 10YR 8/2) nannofossil ooze. A small basalt fragment in Sample 320-U1333A-21X-CC, 2–5 cm, is found above an 11 cm thick white limestone with green flecks. GRA bulk density, L*, and CaCO₃ content are marked by lower values compared to Subunit IIIb (Fig. F4; see "Physical properties").

Unit V

Intervals: 320-U1333A-21X-CC, 0 cm, through at least 22X-CC, 5 cm (boundary not recovered); 320-U1333B-20X-CC, 17 cm, through at least 20X-CC, 40 cm (boundary not recovered); 320-U1333C-24X-CC, 16 cm, through at least 24X-CC, 38 cm (boundary not recovered)

Depths: Hole U1333A = 181.60–182.65 CSF; Hole U1333B = 178.34–178.57 m CSF; Hole U1333C = 176.16–176.38 m CSF

Age: middle Eocene

Lithology: basalt and breccia of limestone and basalt

Fine-grained fresh basalt fragments were recovered at the base of each hole drilled at Site U1333. A breccia of limestone and basalt was recovered in Section 320-U1333A-21X-CC.

Sediments across the Oligocene–Miocene transition

A complete record of the Oligocene–Miocene transition was recovered at Site U1333 (Fig. F6). In Hole U1333B the Oligocene–Miocene transition is captured in a single core (Core 320-U1333B-3H). The Oligocene/Miocene boundary is defined by the first occurrence of planktonic foraminifer Paragloborotalia kugleri (see "Biostratigraphy"). Both this datum and the last occurrence of the nannofossil datum S. delphix are observed in Core 320-U1333A-2H (see "Biostratigraphy"). The sediments across the Oligocene–Miocene transition at Site U1333 are marked by an alternating sequence of very pale brown (10YR 8/3 to 10YR 7/3) nannofossil ooze and yellowish brown (10YR 5/4) nannofossil ooze with radiolarians to brown (10YR 4/3) radiolarian nannofossil ooze with clay (Figs. F4, F6; see "Site U1333 smear slides" in "Core descriptions"). Holes U1333B and U1333C are marked by correlative variations of magnetic susceptibility (see "Physical properties;" Figs. F4, F6). An excellent magnetostratigraphy is available for Site U1333 (Fig. F6; see "Magnetostratigraphy"). In Hole U1333B the Oligocene–Miocene transition corresponds to magnetic Subchrons C6Cn.2n to C6Cn.3n. Section 320-U1333A-2H-5 is characterized by an interval of drilling disturbance (flow-in), obscuring the magnetic susceptibility signal.

Sediments across the Eocene–Oligocene transition

An Eocene–Oligocene transition was recovered in all three holes drilled at Site U1333 (Figs. F4, F7). The absence of the planktonic foraminifer biostratigraphic marker (Hantkenina) means that the Eocene/Oligocene boundary cannot be formally identified at Site U1333 (see "Biostratigraphy"). Radiolarian and nannofossil bio- and magnetostratigraphy provide excellent age control, however, indicating that the Eocene/Oligocene boundary falls between the base of Chron 13n and the Biozone RP20/RP19 boundary (within Cores 320-U1333C-14H and 320-U1333B-13H and between Cores 320-U1333A-12X and 13X) (Fig. F7).

The lithostratigraphy of the Eocene–Oligocene transition is well captured in all three holes at Site U1333, and in Holes U1333B and U1333C it falls within a single APC core. In Core 320-U1333B-13H a downhole transition takes place from white (10YR 8/1) to very pale brown (10YR 7/3) nannofossil ooze to alternations of very pale brown (10YR 7/4) nannofossil ooze with radiolarians (and between 5% and 10% diatoms) and yellowish brown (10YR 5/4) radiolarian ooze and finally to alternations of brown (10YR 5/3) radiolarian nannofossil ooze with clay and (10YR 4/2) dark grayish brown clayey radiolarian ooze (Figs. F5, F7). Thus, the Eocene–Oligocene transition is marked by a distinct stepwise color change from very pale brown nannofossil ooze to alternations of darker radiolarian nannofossil ooze and clayey radiolarian ooze. Associated pronounced downhole stepwise increases occur in magnetic susceptibility, a*, and b*, together with pronounced downhole decreases in GRA bulk density, L*, and CaCO₃ content (see "Physical properties;" Figs. F4, F7). These lithostratigraphic results for the Eocene–Oligocene transition at Site U1333 are broadly consistent with those obtained from Sites U1331 and U1332 and multiple sites drilled during ODP Leg 199, in particular with those of Site 1218 (Shipboard Scientific Party, 2002a, 2002b).

Porcellanite layers

Multiple distinct dark brown (10YR 3/3) to dark yellowish brown (10YR 4/4) porcellanite intervals occur in Subunit IIIb in all holes at Site U1333 interbedded with nannofossil ooze of Eocene age (calcareous nannofossil Zone NP15) (Figs. F4, F8; see "Site U1333 smear slides" in "Core descriptions"). Five porcellanite layers occur in Sections 320-U1333A-19X-4 (173.60–173.91 m CSF) and 320-U1333B-19X-1 (162.70–163.73 m CSF) with a typical thickness of 3 to 8 cm. Porcellanite fragments recovered in Sections 320-U1333C-19X-CC (169.45–169.84 m CSF) and 22X-CC (163.50–163.59 m CSF) are interpreted as drilling disturbance associated with penetration of similar layers (see "Site U1333 smear slides" in "Core descriptions").

Summary

At Site U1333, Eocene seafloor basalt (Unit V) is overlain by 183 m of pelagic sediments that are divided into four major lithologic units (I–IV), and Unit III is divided into two subunits. Site U1333 sediments are dominated by nannofossil and radiolarian ooze with varying amounts of clay and can be correlated with Site 1218 using biostratigraphic, magnetostratigraphic, and cyclostratigraphic (magnetic susceptibility and GRA density) results (see "Stratigraphic correlation and composite section"). Basal limestone and nannofossil ooze (Unit IV) of middle Eocene age is overlain by a clayey radiolarian ooze, clayey nannofossil ooze, and porcellanite, also of middle Eocene age. The immediately overlying sediments are dominated by alternations of clayey radiolarian ooze, nannofossil radiolarian ooze, radiolarian nannofossil ooze, radiolarian ooze, and nannofossil ooze of middle to late Eocene age. In turn, these sediments are overlain by alternating sequences of predominantly white and very pale brown nannofossil ooze, as well as yellowish brown nannofossil ooze with radiolarians of early Oligocene through early Miocene age. The uppermost sediments at Site U1333 comprise an alternating sequence of clay, clayey radiolarian ooze, radiolarian clay, clayey nannofossil ooze, and nannofossil ooze of early Miocene age.

Multiple distinct porcellanite layers were found at Site U1333 interbedded with nannofossil ooze of Eocene age. The Oligocene–Miocene transition at Site U1333 is marked by an alternating sequence of very pale brown nannofossil ooze and yellowish brown nannofossil ooze with radiolarians through brown radiolarian nannofossil ooze with clay. The Eocene–Oligocene transition at Site U1333 is marked by a distinct downhole color change from pale nannofossil ooze with radiolarians to alternations of brown radiolarian nannofossil ooze with clay and dark grayish brown clayey radiolarian ooze. A transition from Eocene siliceous sedimentation to Oligocene carbonate deposition is also observed in sediments from several other sites in the equatorial Pacific Ocean (e.g., ODP Sites 1218 and 1219 and DSDP Sites 161 and 162).

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