Site 1211 is located in lower bathyal (2907 m) water depth on the southern flank of the Southern High of Shatsky Rise. The site is on seismic line TN037-17A (Fig. F29) at the location of DSDP Site 305, which was RCB cored. The drilled sequence at Site 305 contains a relatively thick sequence of Lower Cretaceous chalk and chert, Upper Cretaceous ooze and chert, and Cenozoic ooze (Larson, Moberly et al., 1975). The unindurated part of the sequence at Site 305 was highly disturbed by rotary drilling and the record of the EoceneOligocene transition, the LPTM, and the Cretaceous/Tertiary boundary has been lost. Thus, the triple APC coring strategy for Site 1211 was designed to recover a complete and undisturbed record of the Site 305 sequence.
Site 1211 is the second deepest site in the Upper CretaceousPaleogene part of the Shatsky Rise depth transect. The site is more than 200 m deeper than Site 1212, the next shallowest site, and more than 500 m deeper than Site 1209, the shallowest site. Thus, drilling results from Site 1211 will contribute to broad, leg-based objectives that are aimed at understanding changes in Late Cretaceous and Paleogene ocean circulation at a time of global warmth. Results from Site 305 show that the site is located in a depth range that appears to be rather sensitive to changes in ocean chemistry, particularly carbonate solubility.
Holes 1211A, 1211B, and 1211C were cored with the APC (Table T1). Hole 1211A terminated at 158.9 mbsf at the highest chert layer in the upper Maastrichtian. In Hole 1211B, this chert layer was penetrated with XCB center bit drilling and a total of 169.9 m was cored reaching the lower Maastrichtian. Because there is some recovery of coherent Maastrichtian and Campanian ooze from Site 305, we decided not to spend the time to penetrate multiple chert layers to core the lowermost Maastrichtian and Campanian sequence with APC. Hole 1211C was cored to immediately below the K/T boundary at 138.3 mbsf to fill stratigraphic gaps in the composite sequence constructed from Holes 1211A and 1211B. The lack of overlap between the first two holes resulted from double coring an interval in the upper section of Hole 1211B.Summary of Results
Coring at Site 1211 recovered three lithologic units that have been separated based on sediment composition (Fig. F30). Lithologic Unit I ranges from Holocene to lower Miocene (0 to ~17.3 Ma; 053.4 mbsf) and consists of nannofossil ooze, clayey nannofossil ooze, and nannofossil clay, shades of gray, green, yellow, orange, and brown in color. This unit has a higher clay content than underlying units. Two subunits are distinguished. Subunit IA (Holocene to lower Pliocene; 0 to ~4.8 Ma; 041.4 mbsf) is olive-gray and yellowish gray in color, contains siliceous microfossils and rare ash layers, and often shows a marked decimeter-scale cyclicity. Subunit IB (lower Pliocene to lower Miocene; ~4.8 to ~17.3 Ma; 41.453.4 mbsf) is yellowish orange and grayish orange in color and contains centimeter to decimeter-scale cycles. An unconformity from lower Miocene to upper Oligocene separates lithologic Unit I from Unit II (see "Biostratigraphy" in "Specialty Syntheses"). Lithologic Unit II ranges from upper Oligocene to lower Paleocene (~27 to 65 Ma; 53.38133.80 mbsf) and consists of yellowish brown and dark yellowish brown nannofossil ooze with minor amounts of nannofossil ooze with clay, clayey nannofossil ooze, and clay with nannofossils. A number of minor diastems occur in this interval as indicated by thin, darker horizons. More significant unconformities are found in the middle Eocene (~4045 Ma) and upper Paleocene (~5659 Ma). The unit has a generally higher carbonate content than Unit I. Color reflectance data show decimeter-scale carbonate cyclicity. Lithologic Unit III ranges from upper to lower Maastrichtian (65 to ~70 Ma; 133.8169.9 mbsf) and consists of pale orange nannofossil ooze and chert. The unit has extremely high carbonate contents. One chert layer was penetrated in lithologic Unit III.
The Site 1211 stratigraphic section shows broad similarity to the sections recovered at Sites 1209 and 1210 suggesting, in general, common sedimentation histories. In particular, the critical boundaries, for example the Paleocene/Eocene and Cretaceous/Paleocene boundaries, show a similar sequence of lithologies. However, sedimentation rates throughout the section are generally significantly lower at Site 1211 than at the previous two sites (Fig. F31), and there are additional unconformities and condensed intervals. All of these differences appear to reflect changes in carbonate preservation coincident with the greater water depth.Highlights
The major highlight of coring at Site 1211 is similar to the highlights at Sites 1209 and 1210, namely the recovery of all of the critical intervals, most of which were recovered in all three holes. These include the Eocene/Oligocene boundary, the LPTM, the Cretaceous/Paleocene boundary, and probably the MME. In the first part of this section we describe the general stratigraphy of these intervals. In the absence of detailed data and analysis, however, a discussion of the significance of these events would be broadly similar to Sites 1209 and 1210.
The stratigraphic record at Site 1211 reveals differences from that at Sites 1209 and 1210 that appear to be related to increased water depth. In the second part of this section, we integrate results from the three sites and explores the significance of these differences in the framework of the Shatsky Rise depth transect.Recovery of Critical Events
Sediment recovered at Site 1211 contains the record of the EoceneOligocene transition, the LPTM, the K/T boundary, and possibly the MME. Several of these events were recovered in all three holes. The lithologic record of each of these intervals at Site 1211 appears to be similar to Sites 1209 and 1210, but also to show significant differences.
The EoceneOligocene transition has been recovered in Holes 1211A, 1211B, and 1211C. Cores and reflectance data from the boundary transition show a subtle gradual upward lightening in color, likely as a result of an increase in carbonate content (Fig. F32). This change is evidence for a deepening of the lysocline and CCD. Prominent color cycles in the transition interval suggest an orbital control on dissolution. The amplitude of the reflectance variations is higher than at previously drilled Southern High sites, suggesting greater variation in dissolution intensity at the deeper Site 1211.
The LPTM was recovered in Holes 1211A, 1211B, and 1211C; however, the lithologic record in the three holes is different (Fig. F33), and magnetic susceptibility records are hard to correlate. Part of this problem arises from the fact that the event in Holes 1211A and 1211C was cut by section breaks. In these two holes, the LPTM was recovered in a yellowish brown clayey nannofossil ooze. The contact of this layer with the underlying grayish orange nannofossil ooze is mixed by bioturbation (Fig. F33). The lower part of the clayey nannofossil ooze in Hole 1211A also appears to have been cut by a burrow that contains grayish orange ooze. The clayey nannofossil ooze layer is ~11-cm thick in Hole 1211A and 8-cm thick in Hole 1211C and is overlain abruptly by grayish orange nannofossil ooze. In Hole 1211B, the base of the LPTM corresponds to a sharp change from a pale orange nannofossil ooze to a yellowish brown clayey nannofossil ooze. This color is uniform for 16 cm then grades to a grayish orange over the next ~30 cm. All sediment in the section above the base of the LPTM is darker than below.
Based on lithology and color, it is impossible to correlate between the LPTM in Holes 1211A and 1211C with the event in Hole 1211B. However, biostratigraphy suggests that there is a diastem right above the base of the event in Hole 1211B. Samples from the lower 67 cm of the clay-rich unit in Holes 1211A and 1211C contain the nannolith Fasciculithus in similar abundance to the lower part of the LPTM at Sites 1209 and 1210. Nannofossils in the lower part of the event are also poorly preserved, and abundant calcite blades are seen in samples as at the previous sites. The planktonic foraminifer Morozovella velascoensis, the LO of which defines the top of Zone P5, occurs 33 cm above the base of the event in Hole 1211A and ~24 cm above the base of the event in Hole 1211C. In Hole 1211B, however, Fasciculithus disappears 12 cm above the base of the event and M. velascoensis is absent in a sample 6 cm above the base. The nannolith Discoaster diastypus, the FO of which defines the base of nannofossil Zone CP9, is found 23 cm above the base of the event in Hole 1211B, 34 cm above the base of the event in Hole 1211C, and 10 cm above the base in Hole 1211A, which may have a slight gap at this level (this event is found 2 to 4 m above the base of the event at Sites 1209 and 1210). These preliminary data show the LPTM interval in Holes 1211A and 1211C is correlative with the lowermost 1 cm of the event in Hole 1211B. All three sections are highly condensed compared to records from Sites 1209 and 1210. The condensed nature of the LPTM at Site 1211 suggests that it was in a depth range that was sensitive to carbonate solubility changes across the LPTM.
The K/T boundary stratigraphy at Site 1211 is very similar to that at Sites 1209 and 1210. The boundary succession includes pale orange nannofossil ooze of latest Maastrichtian age (nannofossil Zone CC26) overlain by lowermost Paleocene (foraminiferal Zone P) yellowish orange foraminiferal ooze. This lithology grades upward into a white foraminiferal nannofossil ooze then back into a grayish orange nannofossil ooze. The boundary between the uppermost Maastrichtian and the lowermost Paleocene is clearly bioturbated, and careful sampling of burrows yields planktonic foraminifers dominated by Guembelitria with rare Hedbergella holmdelensis that suggest a possible Zone P0 age. Light brown to amber, spherical particles about 100 from these burrows may be altered tektites.
The MME is likely to have been recovered at Site 1211. Although Inoceramus prisms are not visible in the sediments, they are present in washed residues from Section 198-1211B-17H-CC.Carbonate Record at Site 1211
The Shatsky Rise depth transect was designed to reconstruct the effect of short-term and long-term variations in the lysocline and CCD on the Upper Cretaceous and Paleogene sedimentary record. The total depth range of sites included in this transect is almost 1000 m, from Site 1209 (2387 m) to Site 1208 (3346 m). Site 1208 was clearly below the CCD for a significant part of the early Paleogene and the Maastrichtian, as much of this stratigraphic interval corresponds to an unconformity. Site 1211 (2907 m) is the deepest site in the Shatsky Rise transect with a nearly complete Maastrichtian to Eocene section.
The Site 1211 section shows broad similarities to its shallower neighbors, Sites 1209 and 1210 (2573 m) but is considerably more condensed (Fig. F31). Lower sedimentation rates in the major, continuous parts of the Site 1211 section as well as the longer duration of several hiatuses have reduced the thickness of the stratigraphic column. The major Miocene-Oligocene hiatus is similar in duration at all of the sites, however. This hiatus is thought to represent regionally increased erosion coincident with intensified deep-water flow during the latest Oligocene and early Miocene (see "Site 1207" and "Site 1208" in "Principle Results"). Preliminary biostratigraphy suggests unconformities in the Site 1211 section in the middle Eocene (~4045 Ma) and upper Paleocene (~5659 Ma) that are unique among the Southern High sites or at least much longer in duration than gaps in these intervals at the other sites.
Throughout the Paleogene section at Site 1211 are a number of 5- to 20-cm thick yellow-brown clay rich nannofossil ooze levels that have abundant phillipsite, pyrite, and manganese-coated foraminifers. Carbonate content of these layers reach as low as ~50 wt%. There are approximately 26 such intervals >5 cm in thickness. These levels are thought to result from lengthy seafloor exposure during intervals of intense dissolution when the site was located close to the lysocline/CCD. The late Paleocene to middle Eocene is an interval with a steadily falling but generally shallow CCD in the North Pacific (Rea et al., 1995). Paleodepths of Sites 1209, 1210, and 1211 are thought to be comparable to those of the present day (see "Biostratigraphy" in "Specialty Syntheses"); thus, the unconformities at Site 1211 may be intervals when the CCD shoaled to depths around 2900 m. A few clay-rich intervals in the upper Maastrichtian may also represent short-term lysocline/CCD shoaling events.
Superimposed on this long-term record for CCD variation are short-term (<1 m.y.) events that led to abrupt shoaling of the lysocline/CCD. The two most prominent events are in the mid-Paleocene. The second is at the LPTM. Both of these events are highly condensed compared to Sites 1209 and 1210 as a result of dissolution. For the mid-Paleocene event, dissolution lasted up to 1 m.y. beyond the end of the event.
Color reflectance data from Site 1211 show low-amplitude cyclic variation throughout the Paleogene. The percent total reflectance is usually closely correlated with carbonate content. For much of this interval, carbonate likely reflects the amount of dissolution. This suggests that the intensity of dissolution was controlled by a mechanism that might vary in intensity on orbital timescales. Two possible mechanisms are changing deep-water circulation and surface-water productivity. The cycle record at Site 1211 should allow development of an orbital chronology for the Paleogene section.
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