Site 1214 is located at 3402 m water depth on the southern flank of the Southern High of Shatsky Rise. The site is at the location of DSDP Site 306 (Larson, Moberly, et al., 1975). At Site 306, we penetrated 475 m of sedimentary rocks with RCB drilling but only continuously cored from 207.5 m to total depth. Most of the upper section (28 to 207.5 mbsf) was alternately cored and washed at ~9-m intervals. The recovery was approximately 7%. The recovered sedimentary rocks, mainly calcareous porcellanite and chert with minor nannofossil chalk and ooze are late Albian to early Berriasian in age, covered by about 9 m of Holocene siliceous foraminifer-bearing nannofossil ooze.
According to the coring record from Site 306 (Larson, Moberly, et al., 1975), the uppermost Cretaceous sediments lie between Reflectors R1 and R2 of Sliter and Brown (1993). Reflector R1 (Cenomanian/Turonian boundary) crops out a few kilometers northeast of Site 306. Reflector R2 of Barremian/Aptian boundary age corresponds to the top of the porcellanite, chert, and shale section at Site 306 that rests on basement. The interval between R1 and R2 consists of chalk, chert, and porcellanite.
Site 1214 lies in the middle of the mid-Cretaceous portion of the Shatsky Rise depth transect between Site 1207 (3101 m) and Site 1213 (3883 m). The objective at Site 1214 was to recover a more complete and continuous record of the Site 306 sequence. As part of the Shatsky Rise mid-Cretaceous depth transect, drilling at Site 1214 addresses a number of leg-related objectives concerning ocean circulation and environmental change in an interval of global warmth.Summary of Results
Hole 1214A was cored with RCB drilling terminating at 235.9 mbsf in the Hauterivian (Table T1). Average recovery of 7% was equivalent to Site 306. The sedimentary section has been divided into units based on composition and color. Lithologic Unit I (Holocene to Pleistocene; 0.06.9 mbsf) consists of very pale yellowish brown to moderate yellowish brown clayey foraminiferal nannofossil ooze and very pale to moderate yellowish brown clayey nannofossil ooze with foraminifers. Subunit IIA (late Albian; 6.934.5 mbsf) is composed of moderate yellowish brown to light olive-gray chert and very light gray to yellowish gray porcellanite, with minor white nannofossil chalk. Medium dark gray, dark gray to grayish black chert, and very light gray to light greenish gray porcellanite is grouped in Subunit IIB (late Albian to early Albian; 34.5110.7 mbsf). Very light to light greenish gray limestone with radiolarians is a minor lithology in this subunit. Subunit IIC (early Albian to late Aptian; 110.7207.0 mbsf) contains medium dark gray, dark gray, brownish gray, grayish brown and moderate brown chert, and yellowish gray, very light to light greenish gray porcellanite. Olive-black, greenish black and dark greenish gray claystone to clayey porcellanite is placed in Subunit IID (early Aptian; 207.0216.6 mbsf). Finally, Subunit IIE comprises brownish gray, brownish black, and olive-black chert and light greenish gray, greenish gray, and yellowish gray porcellanite (Hauterivian; 216.6235.9 mbsf). Throughout the section, porcellanite and limestone have variable amounts of radiolarians and nannofossils. Most of the ages were obtained from chalk adhered to the sides of chert nodules. This sediment indicates the soft and relatively unaltered nature of the unrecovered intervals.Highlights
The results of coring at Site 1214 provide important information on the stratigraphy of the mid-Cretaceous section on Shatsky Rise. The interpreted stratigraphy of Site 1214 are different from the stratigraphy of Site 306 from Larson, Moberly, et al. (1975) and Sliter (1992). One possibility for this difference is that Site 1214 is actually located at a distance from Site 306 given the imprecision of the coordinates of the latter site. A second possibility is that the biostratigraphy of Site 306 was carried out almost exclusively using planktonic foraminifers, whereas that of Site 1214 included nannofossils and radiolarians.
Site 1214 has an expanded Albian section, approximately 180 m in thickness, compared to 120130 m at Site 1213. One possible reason for this disparity is that the latter site is located at greater water depth and thus subject to greater dissolution. More significantly, the stratigraphy of Site 1214 confirms that much of the Barremian corresponds to a regional unconformity on the southern part of Shatsky Rise. In both locations, lower upper Hauterivian sedimentary rocks are found in the core below lower Aptian horizons. At Site 1213, one sample at the top of Core 198-1213B-9R contained neither Aptian nor Hauterivian markers. Even with this uncertainty, combined data from Site 1213 and 1214 suggest that a significant hiatus occurred during much of the Barremian and at least part of the upper Hauterivian. The reason for this unconformity is currently unclear. This interval was present at Site 1207, which was some 800 m shallower than Site 1213 at that time; thus, a temporary change in the CCD could have led to the hiatus. However, the Barremian in most parts of the ocean, including the Pacific, is generally regarded as an interval when the CCD was relatively deep (i.e., Thierstein, 1979). Alternatively, it is possibly that this interval corresponded to an erosional event that removed sediment from the flanks of the southern high and not from the top of the northern high.
The lower Aptian section in Hole 1214A (Section 198-1214R-23R-1) contains olive-black, greenish black, and dark greenish gray claystone to clayey porcellanite. Both of these lithologies are laminated in places indicating low-oxygen conditions on the seafloor. Corg contents are low (<0.5 wt%) in the greenish gray lithologies. Four thin, discrete bentonite or tuff layers are observed within pieces of porcellanite. A sample from a piece of olive-black claystone toward the top of Section 198-1214R-23R-1 contains 1.4% Corg. Characterization of the organic matter from this sample indicates it is algal and bacterial in origin, similar to lower Aptian, highly carbonaceous lithologies from Sites 1207 and 1213 (see "Geochemistry" in "Specialty Syntheses"). This interval lies in nannofossil Zone NC6, between the FOs of Eprolithus floralis and Hayesites irregularis. Most of the sedimentary rocks in Section 198-1214R-23R-1 are noncalcareous but contain abundant radiolarians in discrete layers. Diagnostic radiolarian faunas in these levels are similar to assemblages observed in the Livello Selli in the Cismon core from the southern Alps of Italy (Premoli Silva et al., 1999) and in horizons bounding organic-rich intervals in the lower Aptian at Site 1213 (see "Biostratigraphy" in "Specialty Syntheses"). Thus, combined biostratigraphic and lithostratigraphic evidence suggests that the olive-black claystone comes from within the general OAE1a interval, but certainly not from near the peak of the event as did samples with much higher Corg contents from Sites 1207 and 1213.
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