Site 1214 lies on the southwest flank of Shatsky Rise at a depth of 3402 m and is a revisitation of Site 306. Rotary coring down to 235.9 mbsf at Site 1214 recovered 15.2 m of sediment and sedimentary rock. The sediment is divided into two lithologic units (Fig. F1). Unit I, extending from 0.0 to 6.9 mbsf, is composed of Holocene to Pleistocene sediments. Unit I recovery was 1.32 m (19%). This unit consists of clayey foraminiferal nannofossil ooze to clayey nannofossil ooze with foraminifers. Unit II consists of chert, lithified, porous, calcareous porcellanite, and minor chalk of late Albian to Hauterivian age. Unit II recovery averaged 7%.
Lithologic Unit I consists of pale to moderate yellowish brown (10YR 6/2 to 10YR 5/4) clayey foraminiferal nannofossil ooze underlain by very pale orange (10YR 8/2) to moderate yellowish brown (10YR 5/4) clayey nannofossil ooze with foraminifers. Carbonate content is 60 to 65 wt%, of which 40%-45% is nannofossils and 20%-25% is foraminifers. Clay content ranges between 25% and 30%, and there are minor percentages of quartz, feldspar, volcanic glass, and Fe oxides. The unit also contains pumice clasts and well-preserved pyrite-filled burrows. Bioturbation is moderate throughout the unit. The boundary between Units I and II corresponds to a Pleistocene to upper Albian unconformity.
Lithologic Unit II consists primarily of fragments (drilling breccia) of chert and porous calcareous porcellanite. Chert usually occurs as irregular-shaped fragments of different colors but is also present as blebs and small stringers in the porcellanite. Porcellanite of various colors (depending on carbonate and clay content) exists as fragments and coatings or inclusions in the chert. Nannofossil claystone, limestone with radiolarians, and nannofossil chalk are present in minor amounts. This unit has been divided into five subunits that are generally based on the color of the chert (Table T2) and changes in the microfossil assemblage composition.
Subunit IIA (interval 198-1214A-2R-1 through 4R-1; 6.9 to 34.5 mbsf) consists of rare to moderate bioturbated, moderate yellowish brown (10YR 5/4) to light olive gray (5Y 6/1) chert and very light gray (N8) to yellowish gray (5Y 8/1) porcellanite. Minor fragments of white (N9) nannofossil chalk are also present. Porcellanite is present as fragments as well as coatings on and inclusions in the chert. Contacts between the chert and porcellanite are irregular and sometimes patchy. Radiolarians (often replaced by calcite) and foraminifers are present in both chert and porcellanite.
In Subunit IIB (interval 198-1214A-5R-1 through 12R-1; 34.5 to 110.7 mbsf) the chert is medium dark gray (N4) and dark gray (N3) to grayish black (N2), whereas the porcellanite is very light gray (N8) to light greenish gray (5GY 8/1). In Sections 198-1214A-11R-1 through 12R-1, the chert color becomes more brownish (brownish gray, 5YR 4/1, to grayish brown, 5YR 3/2), and very light to light greenish gray (5GY 8/1-9/1) limestone with radiolarians is present. Contacts between limestone and chert are gradational, usually with porcellanite in between. Chalk is only present as coatings and inclusions in the chert in this subunit. The degree of bioturbation is rare to moderate. In Section 198-1214A-5R-1, 14 cm, the nannofossil chalk has streaks of purplish gray minerals identified in smear slides as chalcedony. Chalcedony was also found at Site 306 in chert fragments and former radiolarian molds.
The dominant lithology within Subunit IIC (interval 198-1214A-13R-1 through 22R-1; 110.7 to 207.0 mbsf) is medium dark gray (N4), dark gray (N3), brownish gray (5YR 4/1), grayish brown (5YR 3/2), and moderate brown (5YR 3/4) mottled chert, both with and without visible radiolarians. Porcellanite is still present, but it is yellowish gray (5Y 8/1) and very light to light greenish gray (5GY 8/1-9/1) in this subunit. It ranges in composition from porcellanite with radiolarians to nannofossil porcellanite with radiolarians to radiolarian nannofossil porcellanite. Porcellanite forms coatings on or inclusions in chert. White (N9) nannofossil chalk also is present in this subunit as burrow fill and inclusions. Bioturbation is rare to moderate. Downcore in Subunit IIC, the porcellanite begins to exhibit vague, wavy lamination. In some samples, the lamination drapes over small nodules of incipient chert or porcellanite, indicating that compaction occurred during or after the formation of chert. From Core 198-1214A-14R downward, radiolarians occasionally are replaced or infilled with pyrite. In Cores 198-1214A-16R and 18R, pyrite is present as compressed, millimeter-scale microlayers.
Subunit IID (Section 198-1214A-23R-1; 207.0 to 216.6 mbsf) consists mainly of olive black to greenish black (5G 2/1) and dark greenish gray (5G 4/1) claystone to clayey porcellanite. Minor amounts of greenish gray (5G 6/1) to dark greenish gray (5G 4/1) porcellanite with local concentrations of radiolarians are present. The sediment is finely laminated, and darker-colored lamina commonly contain pyrite. Several gray (N5), centimeter-thick horizons, which appear to be altered fine tuffs, are interbedded with the porcellanite and claystone. These layers occur at 48-49, 59-60, 63-64, and 66-67 cm. The contacts between gray layers and the surrounding greenish gray claystone and porcellanite are sharp and horizontal (Fig. F2). The boundary between Subunits IID and IIE is placed at the lower Aptian to Hauterivian unconformity.
The fifth and final subunit recovered at Site 1214, Subunit IIE, extends from Section 198-1214A-24R-1 through Section 25R-1 (216.6 to 235.9 mbsf). The apparent subunit stratigraphy progresses from light greenish gray (5GY 8/1), greenish gray (5GY 61), and yellowish gray (5Y 8/1) porcellanite at the top to brownish gray (5YR 4/1), brownish black (5YR 2/1), and olive-black (5Y 2/4) chert with or without radiolarians. However, drilling disturbance and poor recovery preclude reconstructing the absolute piece-by-piece orientation and stratigraphy. Minor amounts of light greenish gray (5GY 8/1) nannofossil chalk are present in Core 198-1214A-25R. Both chalk and porcellanite are present as coatings on the chert, and the chalk has subhorizontal streaks of pyrite.
Core recovery of Unit I was poor (19%) compared to Site 306, where recovery was 94%. The unit consists of Pleistocene sediments that unconformably overlie upper Albian sediments of Unit II. This unconformity is similar in duration to the major unconformities found at the other relatively deep sites cored during Leg 198. However, the location of Site 1214 (and Site 306) on the flank of a submarine canyon suggests that much of the hiatus is attributable to erosion associated with the cutting of this canyon.
The poor recovery of Unit II was due to abundant chert and porcellanite, resulting in the preferential loss of softer sediments during coring. The primary record of less-indurated carbonate sediments is derived from irregular surfaces and inclusions where it was not completely washed or scraped away. An unconformity is present in Unit II (between Sections 198-1214A-23R-1 and 24R-1), where Barremian sediments are absent. This might be due to deep currents sweeping the flanks of Shatsky Rise or poor recovery. Deposition of Unit II sediment occurred above the CCD, except for Core 198-1214A-23R, based on the presence of carbonate (chalk, calcareous porcellanite, and limestone) throughout the unit.
The goal of returning to DSDP Site 306 to core Site 1214 was to recover Corg-rich sediments corresponding to Cretaceous OAE1a (the Selli-equivalent black shale deposit) at an intermediate paleowater depth between Sites 1207 and 1213. The OAE1a sequence was inferred to have been present at Site 306 (Section 32-306-13-CC) as an interval of grayish olive-green laminated porcellanite with a thin layer of black, carbonaceous, silicified radiolarian claystone. A similar sedimentary sequence was recovered in Core 198-1214A-23R, characterized by primarily greenish gray radiolarian-rich porcellanite and claystone that was burrowed and mottled at the top of the core and then laminated within the middle of the short recovered sequence, followed by an interval of distinctly burrowed claystone and porcellanite below. Pyrite is present as burrow fill throughout the core. Of particular interest is the presence of several gray, centimeter-thick horizons that appear to be altered fine tuffs (198-1214A-23R-1, 48-49, 59-60, 63-64, and 66-67 cm). The contacts between these gray layers and the surrounding greenish gray claystone and porcellanite are sharp and horizontal (Fig. F2).
Abundance of silica-rich lithologies probably reflects high production of siliceous biogenic material, most likely related to the equatorial position of Shatsky Rise during most of the Cretaceous. In Subunit IIC and downcore, radiolarians have in some intervals been replaced by pyrite (Fig. F3). This indicates a more sulfide-rich, reducing environment possibly related to higher productivity.
Porcellanite and chalk in Subunits IIC through IIE are faintly laminated in some intervals. The lamination may have resulted from burrow flattening during sediment burial and compaction. However, some burrows in the cherts have been preserved without being flattened. This can also be seen at Site 1213 and is evidence for relatively early silica cementation.
In Subunit IIA, and to some extent in Subunit IIC, the chert is often brownish, and the porcellanite a more yellowish to olive gray color (Table T2). Chert in Subunits IIB and IIE is more black hued, and porcellanite records different shades of greenish gray. Subunit IID consists of dark greenish gray- to greenish black-colored porcellanite, claystone, and clayey porcellanite. The above color changes are interpreted to be a result of regional, secular redox variations generally related to sedimentation rate. A similar, but very general, secular trend is evident at Sites 306 and 1213 (Fig. F4), although poor-age control and stratigraphic uncertainties render precise intersite correlations difficult. The upper Albian chert and porcellanite recovered are brownish in hue, followed downcore by a shift to greenish black hues in the upper Albian at both sites. Toward the base of the Albian sections and persisting down through the upper Aptian, more oxidizing conditions prevailed based on the reddish brown lithologies. The transition to more greenish black colors occurs in the lower Aptian, and at Site 1214 the inferred reducing conditions persist to the bottom of the cored interval (Hauterivian), whereas at Site 1213, the color changes to reddish brown in the lower part of the Berriasian and remains this way through the bottom of the cored interval.
Significant intervals of early Campanian- to Barremian-aged chert/porcellanite also were recovered at Site 1207, and Santonian- through Valanginian-aged chert/porcellanite at Site 305. Site 1207 downcore color trends are much less pronounced relative to the distinctive trends in chert/porcellanite color found at Sites 1213 and 1214. The less distinct redox-controlled rock color trends at Site 1207 may be related to greater downhole contamination of chert fragments. However, some evidence of a secular trend in redox conditions can be gleaned from the record for comparison with the Southern High of Sites 1213 and 1214 (Fig. F4). General coincidence of lithologic color, and by inference prevailing redox conditions of Sites 1207, 1213, and 1214, occurs in the mid- to lower Cenomanian to upper Albian (oxidizing), the middle portion of the Albian (reducing), the lower Albian to upper Aptian (oxidizing), and the lower Aptian to upper Barremian (reducing).
The changes in regional redox chemistry recorded in the chert and porcellanite intervals may reflect changes in the sedimentation rates (see Fig. F6). Generally higher sedimentation rates correspond to sedimentary intervals that record more reducing conditions (typically greenish black lithologies), whereas slower sedimentation rates permit greater oxidation of the sediments, which thus retain more reddish brown colors induced by the oxidation of Fe oxides. These subtle changes do not necessarily indicate less oxygenated deep water because higher sedimentation rates can drive pore water redox conditions toward the more reducing end-member. In fact, the sedimentation rate-redox condition relationship breaks down at Sites 1207 and 1214. Site 1207 sedimentation rates were constant through the Cretaceous (8.7 m/m.y.), despite significant and somewhat systematic variation in lithologic color throughout the cored interval. At Site 1214, relatively high sedimentation rates of 12.7 m/m.y. characterize the Albian interval, coincident with the broad occurrence of grayish black lithologies. But sedimentation rates within and below the lower Albian are low (<3.7 m/m.y.), despite an interval of grayish black lithology spanning much of the Aptian-aged material recovered. Thus, it is likely that secular changes in prevailing redox conditions were driven by a combination of organic matter flux, overall sedimentation rate, and deepwater oxygen level. However, there may be a hiatus spanning the Barremian and part of the Hauterivian, and the slow sedimentation rates cited above could be artifacts of this missing interval.