Smear slides were produced from 61 sample intervals of Site 1213. All but four yielded nannofossils; the four barren samples came from an organic-rich interval (OAE1a, see below) in Core 198-1213B-8R. Nannofossil abundance was usually high and preservation consistently moderate to good. The stratigraphic distribution of nannoplankton is shown in Table T1, an age-depth plot in Figure F2, and selected datum events, zonal boundaries, and chronostratigraphic interpretations in Figure F3. The assemblages are largely composed of cosmopolitan species, but there are a number of distinctive features that most likely reflect the position and paleoceanography of the Shatsky Rise area. There are two striking absences from the Lower Cretaceous assemblages: first the total absence of Micrantholithus and second the almost total absence of Nannoconus (trace amounts occur in several upper Albian samples). Both these nannofossil genera are often numerically significant assemblage components, Micrantholithus across a wide range of latitudes and Nannoconus particularly in the western Tethys-proto-Atlantic-Caribbean region (Street and Bown, 2000). Braarudosphaera, a close relative of Micrantholithus and a conspicuous component of many Aptian–Cenomanian epicontinental assemblages, was found in only two upper Albian samples.
Other significant absences or trace occurrences only include Calcicalathina oblongata, Conusphaera mexicana, Conusphaera rothii, Tubodiscus verenae, and Lithraphidites bollii, all Tethyan marker taxa. Eiffellithus primus, Eiffellithus striatus, and Eiffellithus windii are rare and present in only a few samples.
Notable occurrences include the presence of Podorhabdus grassei and Axopodorhabdus cylindratus, not previously recorded above the Tithonian (Upper Jurassic) (Bralower et al., 1989; Bown and Cooper, 1998), the presence of the Tethyan taxa Haqius ellipticus, Umbria granulosa, and Rucinolithus wisei, and the putative high-latitude taxa Stradnerlithus silvaradius and Kokia. Lithraphidites carniolensis is conspicuously abundant throughout.
Nannofossil biostratigraphy of the lowermost cores could not always be achieved by straightforward application of existing biostratigraphic schemes because of the absence or sporadic occurrence of many standard marker species of both Tethyan and Boreal affinity. However, there appears to be a relatively continuous Berriasian–Hauterivian section but an unconformity between the Hauterivian and lower Aptian. Cores 198-1213B-9R through 7R are mid-Cretaceous in age (lower Aptian–Cenomanian) and the nannofossil biostratigraphy is relatively straightforward. The biostratigraphic results are summarized below, and datum and zone details are provided in "Lower to Mid-Cretaceous Biostratigraphy," and Figure F3.
The deepest core (Core 198-1213B-27R) is assigned to Zone NK1 (Berriasian) based on the presence of Helenea chiastia, L. carniolensis, Tubodiscus, and Rotelapillus laffittei. Cores 198-1213B-26R through 16R are correlated with Zone NK2 (Berriasian) based on the presence of the marker species Retecapsa angustiforata and Percivalia fenestrata and supported by first occurrences (FOs) of Assipetra infracretacea and R. wisei. Cores 198-1213B-15R and 14R are assigned to Subzone NK3a (lower Valanginian) based on the FO of Rhagodiscus dekaenelii (see "Lower to Mid-Cretaceous Biostratigraphy"). Interval 198-1213B-13R-1, 5 cm, to 9R-1, 47 cm, falls within Subzones NK3b–NC4b (mid-Valanginian through lower Hauterivian) based on the last occurrence (LO) of R. wisei and the LO of R. dekaenelii. A marked change in nannofossil assemblages in Core 198-1213B-9R indicates a significant stratigraphic gap, incorporating much of Subzone NC4b and all of Zone NC5 (upper lower Hauterivian–uppermost Barremian). Above this there is a relatively straightforward succession of nannofossil marker species (FOs of Hayesites irregularis, Eprolithus floralis, Prediscosphaera columnata, Tranolithus orionatus, Eiffellithus turriseiffelii, and Lithraphidites acutus) that define Zones NC6–NC11 (uppermost Barremian–middle Cenomanian). Not all subzones can be recognized because of missing or anomalous ranges of subzonal markers (see "Lower to Mid-Cretaceous Biostratigraphy"). The organic-rich, noncalcareous sediments recovered in Core 198-1214-8R occur between the FOs of H. irregularis and E. floralis (Zone NC6) and strongly indicate a correlation with the Selli event (OAE1a).
Smear slides were prepared from 38 levels of Site 1214. All but three samples yielded nannofossils; the three barren samples came from an organic-rich interval in Core 198-1214A-23R (OAE1a, see below). Nannofossil abundance was usually high. The stratigraphic distribution of nannoplankton is shown in Table T2, an age-depth plot in Figure F4, and selected datum events, zonal boundaries, and chronstratigraphic interpretations in Figure F3. The assemblages are largely made up of cosmopolitan nannofossil species, but samples from the lowermost cores, 198-1214A-24R and 25R, contain a number of interesting features, specifically, rare occurrences of the typically Tethyan taxa Nannoconus, C. oblongata, L. bollii, and the abundant presence of Micrantholithus.
Much of Hole 1214A (22 of 25 cores) is Aptian–Albian, and the nannofossil biostratigraphy is comparable with that recorded at Sites 1213 and 1207. The lowermost two cores are upper Hauterivian and contain a number of interesting nannofloral elements. Details of the biostratigraphic analysis are given below and summarized in Figure F2.
Interval 198-1214A-25R-1, 22 cm, to 24R-1, 72–75 cm, falls within nannofossil Subzone NC4b based primarily on the co-occurrence of L. bollii and Cruciellipsis cuvillieri and supported by the presence of C. oblongata and Speetonia colligata. This short interval is also notable for the presence of rare nannoconids and very abundant disaggregated Micrantholithus liths; the sediment is essentially a Micrantholithus chalk. Sediments of this age were not recovered at Site 1213, and the older Lower Cretaceous sediments from that site did not yield Nannoconus or Micrantholithus. Sample 198-1214A-24R-1, 46–47 cm, does not contain age-diagnostic species, but the absence of C. oblongata and H. irregularis and the relatively common occurrence of Zeugrhabdotus scutula indicate correlation with Barremian Subzones NC5d–NC5e (see "Lower to Mid-Cretaceous Biostratigraphy"). This part of the section includes a hiatus that comprises much of the Barremian or is extremely condensed.
Site 1214 yielded the same Aptian–Cenomanian zonal succession as Sites 1213 and 1207. Zone NC9 and subzones within Zones NC6 and NC7 were not recognized (see "Lower to Mid-Cretaceous Biostratigraphy").
Organic-rich noncalcareous sediments recovered in Core 198-1214A-23R occur between the FOs of H. irregularis and E. floralis (Zone NC6), strongly indicating a correlation with the Selli event (OAE1a).
Smear slides were prepared from 35 levels of Site 1207. All but two samples yielded nannofossils; the two barren samples came from an organic-rich interval in Core 198-1207B-44R (OAE1a). Nannofossil abundance was usually high. The stratigraphic distribution of nannoplankton is shown in Table T3 an age-depth plot in Figure F5, and selected datum events, zonal boundaries, and chronstratigraphic interpretations in Figure F3. The assemblages are largely made up of cosmopolitan nannofossil species.
Cores 198-1207B-21R through 44R are mid-Cretaceous in age, and the nannofossil biostratigraphy is comparable with that recorded at Sites 1213 and 1214. Details of the biostratigraphic analysis are given below and summarized in Figure F3.
Organic-rich noncalcareous sediments recovered in Core 198-1207B-44R occur between the FOs of H. irregularis and E. floralis (Zone NC6) and strongly indicate a correlation with the Selli event (OAE1a). The lowermost cores, 198-1207B-45R through 49R, lack diagnostic marker taxa but are assigned to Subzones NC5d–NC5e (Barremian) (see "Lower to Mid-Cretaceous Biostratigraphy").
Smear slides were prepared from one core catcher (Section 198-1208A-42X-CC); drilling was terminated at this level due to problems related to abundant chert. The sample yielded a well-preserved, abundant, diverse assemblage (Table T4) that could be assigned to Subzones NC8a–NC9b (middle Albian) based on the presence of T. orionatus and the absence of E. turriseiffelii. The absence of Axopodorhabdus albianus was not used to infer a more refined Subzone NC8a designation because it occurred anomalously high in other more complete sections (Sites 1207, 1214, and 1213).
Smear slides were prepared from four cores (198-1212B-24H through 27H), and samples yielded well-preserved, common to abundant, diverse assemblages (Table T5). The samples are assigned to Subzone NC10a (upper Albian) based on the presence of E. turriseiffelii, H. irregularis, and Gartnerago stenostaurion (see "Lower to Mid-Cretaceous Biostratigraphy" below).