Two holes were rotary drilled at Site 1213 on the Southern High of Shatsky Rise. Sediments from the upper Pleistocene to basal Berriasian were recovered overlying a series of diabase sills (see "Lithostratigraphy"). In Hole 1213A, sediments were recovered from the upper Pleistocene to middle Albian. Hole 1213B was cored from the middle Albian. Based on nannofossil and planktonic foraminiferal datums, it was determined that two major unconformities are present in this part of the Shatsky Rise, separating the lower Pliocene-lower Santonian and lower Santonian-lower Cenomanian (see "Sedimentation and Accumulation Rates"). The basal Aptian to Hauterivian interval likely contains an unconformity or highly condensed sequence.
Calcareous nannofossils are generally abundant and moderately to well preserved throughout the sediments of Holes 1213A and 1213B. Neogene planktonic foraminifers are moderately preserved, and abundances are generally low because of selective dissolution and fragmentation, whereas in the Cretaceous sequence, which mainly consists of chert and porcellanite with rare interbedded limestone, planktonic foraminifers are rare and generally poorly preserved.
All core catcher samples were examined, and supplementary samples were used to refine datums and the stratigraphy in and around critical intervals and unconformities. The main calcareous nannofossil and foraminiferal datums are summarized in Tables T5 and T6.
Radiolarians, which are very abundant from the upper Albian to the basal Berriasian or uppermost Tithonian sequence in Hole 1213B, were examined in selected samples to refine the age estimate provided by nannofossils and planktonic foraminifers.
Studies of benthic foraminifers were conducted on core catcher samples from Holes 1213A and 1213B. They are well preserved and common in the Neogene section and moderately preserved and rare to few in abundance in the Cretaceous. Stratigraphic ranges of benthic foraminifers are summarized in Tables T7 and T8. Neogene paleodepth estimates (Fig. F25) are based on the work of Pflum and Frerichs (1976), Woodruff (1985), and van Morkhoven et al. (1986). For the Cretaceous section, estimates are mainly based on Sliter (1977, 1980), Kaiho (1998), and Holbourn et al. (2001), as well as backtracked paleodepth curves from the DSDP and ODP data of Kaiho (1999).
The Neogene section ranges from the upper Pleistocene (Subzone CN14b) to lower Pliocene (Subzone CN10c). This interval appears to be relatively complete and has high sedimentation rates typical of upper Neogene sections on Shatsky Rise. The oldest nannofossil-bearing Neogene sample (Sample 198-1213A-6R-3, 94 cm) is assigned to Subzone CN10c based on the co-occurrence of Amaurolithus delicatus, Ceratolithus rugosus, and Discoaster tamalis. An interval of barren brown clay (interval 198-1213A-6R-4, 94 cm, through Section 6R-CC) overlies the Cretaceous section.
The Cretaceous section ranges from the Santonian (Zone CC15-CC17) to lower Berriasian or uppermost Tithonian (Subzone NJK-C). The Santonian sediments (e.g., Samples 198-1213A-7R-1, 3 cm; 7R-1, 90 cm; and 7R-CC) contain moderately etched nannofossil assemblages, including Lithastrinus grillii. The absence of robust, younger coccoliths, such as Arkhangelskiella cymbiformis and Aspidolithus parcus, allows us to assign this interval to Zones CC15-CC17 (UC11 and UC12). This interval overlies a relatively biostratigraphically complete Cenomanian (Zone UC3) to basal Berriasian or uppermost Tithonian (Subzone NJK-C) section characterized by chert, porcellanite, and chalk that were generally poorly recovered. In many cores, enough chalk was recovered to provide adequate sample material; however, in some cases, sediment had to be scraped from chert pieces. All cores yield nannofossils.
The youngest part of the chert-bearing sequence is Cenomanian (UC3) (Sample 198-1213A-8R-CC) based on the presence of Lithraphidites acutus. A complete lower Cenomanian to lower Aptian succession was recovered through interval 198-1213A-8R-CC to 198-1213B-8R-CC. The lower Cenomanian to upper Albian (Zone NC10) is particularly thick.
An organic-rich interval was recovered in Core 198-1213B-8R, and nannofossil biostratigraphy suggests an early Aptian age within Zone NC6, supporting the correlation of this interval with the OAE1a Selli event. The organic-rich sedimentary rocks are barren of nannofossils, but a carbonate layer from a chert piece high in the core (Sample 198-1213B-8R-1, 3 cm) yields the lowest downhole occurrence (i.e., first occurrence [FO]) of E. floralis, marking the base of Zone NC7 (lower Aptian). The next fossiliferous sample below the barren interval (Sample 198-1213B-9R-1, 17 cm) is tentatively assigned to the lower Barremian, based upon the abundance of Zeugrhabdotus scutula, an acme that is used to define a zone (correlative with Subzones NC5d and NC5e) in the Boreal region (Bown et al., 1998). However, the reliability of this acme zone is untested away from the Boreal area, and the age of the sample could conceivably range from late Hauterivian to Barremian. In any case, there is almost certainly at least one unconformity representing much of the Barremian and perhaps the uppermost Hauterivian. The lack of continuous core in this interval prevents further biostratigraphic refinement.
The first downhole occurrence of C. cuvillieri is observed in Sample 198-1213B-9R-1, 47 cm, and marks the base of Zone NC5 (upper Hauterivian). This species was the only "standard" Neocomian marker taxon recorded in Hole 1213B. The absence of C. oblongata, Lithraphidites bollii, Tubodiscus verenae, and nannoconids greatly hinders the biostratigraphic subdivision of the Neocomian at Site 1213. These absences must be due to paleoecological factors because the nannofossil preservation is moderate to good and species richness remains relatively high throughout. In fact, this section represents one of the best deep-sea nannofossil records for the Neocomian time interval. Nannofossil biostratigraphy thus relied on secondary marker species, and the results should be viewed with caution. Even biostratigraphically useful species that are present tend to be rare and sporadically distributed (e.g., Eiffellithus windii, Umbria granulosa, and Rucinolithus wisei). The last occurrence (LO) of R. wisei (Sample 198-1213B-14R-1, 12 cm) and presence of E. windii (Samples 198-1213B-14R-1, 58 cm, and 14R-1, 148 cm) indicate a Valanginian age (Subzone NK3A). The FO of Tubodiscus spp. (Sample 198-1213B-19R-1, 119 cm) and the occurrence of U. granulosa (Sample 198-1213B-21R-1, 150 cm) indicate a Berriasian age. The FO of Assipetra infracretacea (Sample 198-1213B-26R-1, 15 cm) is a lower Berriasian datum. The presence of C. cuvillieri and Rotelapillus laffittei in the lowermost nannofossil-bearing sample (Sample 198-1213B-27R-1, 38 cm) indicates a correlation with Subzone NJK-C, which ranges across the Jurassic/Cretaceous boundary.
An apparently complete upper Pliocene to Pleistocene nannofossil ooze was recovered in Hole 1213A. Preservation of planktonic foraminifers is generally poor and characterized by selective dissolution and fragmentation. The assemblages in this interval (Zones N22 and N21) (Sections 198-1213A-1H-CC through 5H-CC) are dominated by dissolution-resistant taxa such as Globorotalia inflata, G. tumida, Truncorotalia crassaformis, Sphaeroidinella dehiscens, Sphaeroidinellopsis seminulina, and a few pulleniatinids.
No age determination is made for Sample 198-1213A-6R-CC, which contains rare Neogene (Sphaeroidinellopsis subdehiscens and T. crassaformis) and Albian-Cenomanian (Hedbergella delrioensis, Globigerinelloides bentonensis, and Hedbergella planispira) planktonic foraminifers, together with abundant radiolarians, fish teeth, and common crystals of phillipsite.
Although no keeled species were observed in the small-sized assemblages, an early Santonian age is suggested for Samples 198-1213A-7R-1, 48-50 cm, 7R-1, 85-87 cm, and 198-1213A-7R-CC based on the presence of Heterohelix planata, Heterohelix carinata, and Whiteinella baltica, together with rare Hedbergella holmdelensis, Archaeoglobigerina cretacea, and few schackoinids.
Owing to the poor recovery of the underlying mid to Lower Cretaceous sequence, which consists of chert and porcellanite with interbedded rare chalk, planktonic foraminifers are generally rare and poorly preserved, whereas radiolarians are abundant in most of the studied samples.
Planktonic foraminifers were observed in only a few samples obtained by scraping the relatively soft chalk or limestone from the chert clasts. A few thin sections of the indurated lithologies were also analyzed for planktonic foraminifers. No age-diagnostic species were identified in Sample 198-1213A-8R-CC, which contains rare hedbergellids and schackoinids. Samples 198-1213A-9R-CC and 10H-CC yield a basal Cenomanian assemblage of poorly preserved planktonic foraminifers, including few Hedbergella delrioensis, H. simplex, H. planispira, Costellagerina libyca, G. bentonensis, and rare Praeglobotruncana stephani and Rotalipora globotruncanoides, which permits the identification of the R. globotruncanoides Zone (KS17).
The interval between Samples 198-1213A-12R-1, 15-18 cm, and 15R-1, 6-8 cm, contains rare to common planktonic foraminifers. The species identified are Rotalipora appenninica, Planomalina buxtorfi, H. delrioensis, G. bentonensis, G. ultramicrus, and a possible P. stephani. These taxa indicate the uppermost Albian R. appenninica Zone (KS16).
The presence of a single specimen of Biticinella breggiensis in Sample 198-1213B-2R-CC may indicate the middle-upper Albian B. breggiensis Zone (KS14), in disagreement with the nannofossil datums that indicate an older age (lower Albian) for the same sample.
Rare Ticinella primula together with few H. delrioensis, Ticinella raynaudi, Biticinella praebreggiensis, and G. bentonensis in Samples 198-1213A-21R-1, 148-150 cm, and 198-1213B-3R-CC suggest the T. primula Zone (KS13). A poorly preserved upper Aptian assemblage, including rare Hedbergella trocoidea, Hedbergella maslakovae, "H. delrioensis," and possible Hedbergella infracretacea, was observed in Sample 198-1213B-6R-1, 83-84 cm. These taxa combined with the absence of Ticinella bejaouaensis and Globigerinelloides algerianus allow us to assign this section to the Hedbergella trocoidea Zone (KS9).
No planktonic foraminifers were observed in Cores 198-1213B-7H and 8H, the latter including the lower Aptian Selli equivalent horizon, whereas Sample 198-1213B-9R-1, 17-18 cm, contains a moderately well-preserved planktonic foraminiferal assemblage of Hauterivian age, including few Hedbergella sigali, H. aptica, "H. delrioensis," and rare globigerinelloidids to indicate the Hedbergella sigali-"Hedbergella delrioensis" Zone.
Samples 198-1213B-16R-1, 13-14 cm, and 19R-1, 119-122 cm, contain few radiolarians, some of which are pyritized, together with glauconite, fish teeth, and fish bone. The former sample also contains inoceramid prisms. These features suggest low rates of sedimentation, possibly resulting from current winnowing and/or carbonate dissolution.
Benthic foraminifers were examined in core catcher samples of Holes 1213A and 1213B. They are well preserved and few to common in abundance in the Neogene, but generally poorly preserved and trace to rare in abundance in the Cretaceous.
In Samples 198-1213A-1R-CC through 4R-CC (Pleistocene-Pliocene), benthic assemblages are characterized by abundant uvigerinids (Uvigerina hispida, Uvigerina hispidocostata, and U. senticosa). The abundance of these taxa decreases in Sample 198-1213A-5R-CC, and they are replaced by Anomalinoides globulosus, Cibicidoides wuellerstorfi, Cibicidoides mundulus, Oridorsalis tener, Pullenia bulloides, Pyrgo murrhina, Pyrgo lucernula, and agglutinated species (Eggerella bradyi, Karreriella bradyi, Haplophragmoides spp., and Martinottiella sp.). These benthic assemblages are generally similar to those observed at other sites, except for the dominance of uvigerinids. The abundance of Uvigerina senticosa in Sample 198-1213A-3R-CC indicates deposition at abyssal depths (>2000 m) (Pflum and Frerichs, 1976).
Sample 198-1213A-7R-CC (Santonian-Coniacian) contains common but poorly preserved benthic foraminifers with abundant Aragonia ouezzanensis and Gaudryina pyramidata. These taxa in addition to Oridorsalis umbonatus, one of the characteristic taxa in the Late Cretaceous, indicate deposition within lower bathyal to abyssal depths (1500-3500 m) according to Kaiho (1998, 1999).
In Sample 198-1213A-8R-CC, no benthic foraminifers are present. In Sample 198-1213A-9R-CC (upper Albian-lower Cenomanian), the very rare benthic foraminifers belong to trochospiral calcareous species (Conorotalites aptiensis, Gyroidinoides infracretaceus, Hanzawaia compressa, and Protosangularia albiana). In Sample 198-1213A-21R-1, 0-1 cm, and interval 198-1213B-2R-1, 4-6 cm, through 6R-1, 81-84 cm (Albian-lower Aptian), the benthic assemblages are dominated by abundant trochospiral taxa (P. albiana, Protosangularia cenomaniana, Gyroidinoides globosus, and G.infracretaceus), Dentalina spp., Lenticulina spp., and abundant agglutinated species (Dorothia conula, Dorothia gradata, Gaudryina dividens, Remesella sp., and Tritaxia gaultina). Nodosariids increase in abundance in Sample 198-1213B-6R-1, 81-84 cm. Abundant Hanzawaia sp., diverse nodosariids, and Dorothia praehauteriviana characterize Sample 198-1213B-9R-1, 9-12 cm. Sliter (1977) suggested that Albian benthic assemblages dominated by gavelinellids, gyroidinoidids, and agglutinated genera indicate deposition at middle to lower bathyal water depths (500-1500 m). According to Kaiho (1998, 1999), P. albiana, and P. cenomaniana indicate bathymetric ranges of ~1500-2500 and ~2000-3000 m, respectively. In addition, benthic assemblages in Samples 198-1213B-6R-1, 81-84 cm, and 9R-1, 9-12 cm, are similar to late Albian lower bathyal (1000-2000 m) assemblages of Holbourn et al. (2001), which include diverse nodosariids, rotaliids, and agglutinated taxa with calcareous cement.
In intervals 198-1213B-9R-1, 70-71 cm, to 19R-1, 119-122 cm, benthic assemblages are characterized by diverse nodosariids (Astacolus spp., Dentalina spp., Frondicularia bettenstaedti, Lenticulina spp., Marginulinopsis spp., Psilocitharella spp., Saracenaria triangularis, and Vaginulinopsis spp.) and agglutinated taxa including Marssonella praeoxycona and D. praehauteriviana. According to Sliter (1980), assemblages characterized by nodosariids and larger agglutinated species indicate water depths of <500 m.
Samples 198-1213B-20R-1, 31-33 cm, to 25R-1, 29-49 cm, contain mainly nodosariids, Dentalina spp., and Lenticulina spp. These nodosariid-dominated assemblages are indicative of 100- to 1000-m depths, in agreement with the absence of larger symbiont-bearing foraminifers. The presence of fish debris, glauconite, and prisms of inoceramids in Samples 198-1213B-16R-1, 12-14 cm, 19R-1, 119-122 cm, and 21R-1, 148-150 cm, suggests that the depositional environment was under the influence of strong bottom currents (Sliter, 1977).
In summary, paleodepths of Site 1213 show a deepening trend during the Early Cretaceous. Undated shallow-water limestones (containing rudists and corals) dredged from the Southern High (Sager et al., 1999) suggest that this part of Shatsky Rise was near sea level early in its history (Late? Jurassic) before subsiding to middle or lower bathyal depths by Aptian-Albian time.
The Lower Cretaceous sequence at Site 1213 is rich in radiolarians that can provide useful biostratigraphic information. Radiolarian preservation is typically moderate to poor. However, well-preserved specimens were recovered in samples from Cores 198-1213B-6R, 10R, and 12R. Radiolarian tests are replaced by calcite and a minor amount of pyrite throughout the lower part of the sequence. Rarely, radiolarian tests are filled with silica or calcite and the outer skeleton is dissolved. However, most samples contain specimens with visible diagnostic morphological features.
According to Baumgartner et al. (1995), 10 radiolarian Unitary Association Zones (UAZs) characterize the Lower Cretaceous and can be used for biostratigraphic correlation (see "Biostratigraphy" in the "Explanatory Notes" chapter). Zones UAZ13 to UAZ22, spanning the stratigraphic interval from lower Aptian to lowermost Berriasian, could be identified in Cores 198-1213B-12R through 27R. In addition, Cores 198-1213B-5R and 6R yield a younger assemblage, not formally zoned yet, of late early to late Aptian age. This radiolarian assemblage is informally called the "late early to late Aptian assemblage zone" (see "Sedimentation and Accumulation Rates").
The upper lower Aptian to upper Aptian assemblage zone (Samples 198-1213B-5R-1, 0-3 cm, and 6R-1, 81-84 cm) is characterized by Archaeodictyomitra chalilovi, Anomalinoides simplex, Crucella sp. EJ 1 sensu Erbacher (1994), Eucyrtis micropora, Novixitus(?) daneliani, Thanarla conica, and T. elegantissima sensu Sanfilippo and Riedel (see Baumgartner et al., 1995).
Zone UAZ22 (Sample 198-1213B-8R-1, 45-46 cm) is characterized by Archaeodictyomitra excellens, Cryptamphorella clivosa, Dictyomitra pseudoscalaris sensu Schaaf, Godia lenticulata, Paronaella trifoliacea, Pseudodictyomitra lanceloti, Sethocapsa(?) orca, Sethocapsa simplex, Thanarla elegantissima, and T. pulchra sensu Sanfilippo and Riedel (see Baumgartner et al., 1995), whereas the genus Pantanellium is not present. This assemblage suggests a late Barremian to early Aptian age and possibly is correlative with the upper OAE1a interval because the LO of Pantanellium is restricted to the lower part of the Selli level in the Tethys (Erbacher and Thurow, 1997).
Zone UAZ20 (Samples 198-1213B-10R-1, 21-22 cm, and 12R-1, 9-12 cm) is characterized by Homoeoparonaella peteri, Pseudocrolanium fluegeli, Bernoullius(?) monoceros, Mirifusus dianae minor, S. simplex, S.(?) orca, A. chalilovi, T. elegantissima, T. pulchra, and Podobursa multispina. This assemblage indicates an age of late Hauterivian to early Barremian. Sample 198-1213B-14R-1, 17-19 cm, is assigned to Zone UAZ17 and is of late Valanginian to early Hauterivian age based on the presence of D. pseudoscalaris, Hemicryptocapsa capita, Obesacapsula cetia, Oesacapsula morroensis, T. pulchra, and Wrangellium puga. Zones UAZ15 to UAZ17 could not be differentiated in Sample 198-1213B-15R-1, 15-16 cm. This sample contains Angulobracchia(?) portamanni portamanni, Emiluvia chica decussata, P. squinaboli, S. trachyostraca, and S. vicetina, which suggest an age of late Berriasian to early Hauterivian.
Upper Berriasian-lower Valanginian Zone UAZ15 is recognized in Samples 198-1213B-17R-1, 0-1 cm, 19R-1, 119-122 cm, 20R-1, 31-33 cm, and 22R-1, 58-60 cm, based on the presence of Acanthocircus furiosus, H. feliformis, Jacus(?) italicus, O. bullata, P. squinaboli, S. trachyostraca, S. uterculus sensu Foreman (see Baumgartner et al., 1995), Syringocapsa agolarium, and Thanarla pulchra.
Zones UAZ12 through UAZ14 (Samples 198-1213B-25R-1, 37-40 cm, and 27R-1, 21-22 cm) are characterized by Acanthocircus(?) portamanni portamanni, Archaeodictyomitra apiarium, O. morroensis, P. squinaboli, Paevicingula sphaerica, Pseudodictyomitra carpatica, S. agolarium, and Wrangellium depressum. Sample 198-1213B-25R-1, 37-40 cm, yields distinctive species, including Mirifusus dianae dianae, Napora sp. aff. boneti, and other Mirifusus spp. which characterize Upper Jurassic Zones UAZ10-UAZ12. However, the co-occurrence of M. dianae dianae (Zones UAZ7-UAZ12) and W. depressum (Zones UAZ13-UAZ18) suggests a late Tithonian age. Therefore, it is possible that the lowermost part of Hole 1213B is latest Jurassic in age; however, specimens of M. dianae dianae may also be reworked.