Biostratigraphic control at Site 1215 was provided by shipboard analyses of benthic and planktonic foraminifers and calcareous nannofossils. Siliceous microfossils were not encountered in the sediments retrieved from Site 1215. Red-clay facies characterized the uppermost part of the sequence, in which the fossil content is reduced to ichthyoliths. The underlying calcareous fauna and flora in lithologic Units II and III (see "Unit II" in "Lithostratigraphy") indicate the presence of a near complete succession of lower Eocene and upper Paleocene assemblages from Zone NP12 to NP8.
Two holes were cored at Site 1215, recovering red clays of unknown Cenozoic age (Unit I) and underlying late Paleocene and early Eocene nannofossil clay (Unit II) (see "Lithostratigraphy"). A maximum penetration of 82.8 m was reached in Hole 1215B (Fig. F4). In the CaCO3-bearing sediments (Unit II), nannofossil assemblages are all strongly affected by dissolution, resulting in fragmentation and/or loss of many characteristic morphological features such as central areas in placolith and zygodisc assemblages. Dissolution has largely prevented secondary calcite overgrowth of critical groups in lower Paleogene biostratigraphy, such as the Rhomboaster-Tribrachiatus lineage and discoasters, whose features are commonly obscured by secondary calcite overgrowths in less dissolved assemblages.
The calcareous nannofossil-bearing section recovered at Site 1215 encompasses the interval from the lower Eocene Zone NP12 (CP10) to the upper Paleocene Zone NP8 (CP7). The distribution of calcareous nannofossil datums is given in Table T2.
The youngest nannofossil assemblage encountered contained age diagnostic forms such as Discoaster lodoensis (5-7 rays) and Tribrachiatus orthostylus (indicating Zone NP12) from Sample 199-1215A-4H-5, 67 cm, to 4H-6, 66 cm. The latter sample showed evolutionary early variants of D. lodoensis. Other typical Zone NP12 assemblage components are Chiasmolithus solitus, Coccolithus pelagicus, Discoaster barbadiensis, Discoaster binodosus, Discoaster falcatus (8-10 rays), Sphenolithus moriformis, Sphenolithus radians, and Toweius spp.
The transition from red clays to carbonate-bearing sediments in Core 199-1215A-4H is complicated by a short interval showing reversed stratigraphic order. Three samples investigated from Section 199-1215A-4H-4 (taken at the 83-, 110-, and 145-cm levels) are characterized by the absence of D. lodoensis and the presence of T. orthostylus, indicating Zone NP11 (CP9b). Sample 199-1215A-4H-4, 137 cm, however, contained rare D. lodoensis, suggesting that the transition sediment from the red clays to the carbonate-bearing sediments is, in part, a reworking product of Zone NP11-age sediments.
The NP10/NP11 (CP9a/CP9b) boundary was observed in the upper half of Section 199-1215A-5H-5, where the crossover in abundance between Tribrachiatus contortus and T. orthostylus is present. The evolutionary transition from Sphenolithus anarrhopus to S. radians was observed between Samples 199-1215A-5H-2, 80 cm, and 5H-1, 80 cm. Discoaster diastypus appeared between Samples 199-1215A-6H-1, 119 cm, and 6H-2, 122 cm. These two samples also contain the transition from Tribrachiatus bramlettei to T. contortus. The first occurrence of T. bramlettei was observed between Samples 199-1215A-6H-5, 85 cm, and 6H-CC, marking the NP9/NP10 boundary. The former sample showed rare T. bramlettei together with Rhomboaster spp. and evolutionary intermediate forms.
Core 199-1215A-7H only recovered two chert pieces. In Core 199-1215A-8H, sediments are highly disturbed (see "Lithostratigraphy"). Flow-in occurred from the top of the core through Section 199-1215A-8H-3, 121 cm, and the nannofossil assemblages, observed in scattered samples from this interval, showed a mixing of NP11 to NP9 assemblages. In samples from Sections 199-1215A-8H-4 to 8H-6, partially dissolved assemblages belonging to the lower part of Zone NP9 were observed, with common Discoaster multiradiatus and abundant Fasciculithus spp. (e.g., Fasciculithus schaubii, Fasciculithus richardii, Fasciculithus involutus, and Fasciculithus tympaniformis).
Despite the strong dissolution of the nannofossil assemblage in Core 199-1215A-9H, it was possible to place the NP8/NP9 boundary, defined by the first occurrence of D. multiradiatus, between Samples 199-1215A-9H-5, 30 cm, and 9H-5, 70 cm. The lowermost fossiliferous Sample, 199-1215A-9H-6, 10 cm, taken from metalliferous sediments in Unit III, contains few, poorly preserved nannofossils. Discoaster mohleri, Discoaster okadai, and Ericsonia robusta are present in that sample, indicating Zone NP8.
Sample 199-1215B-10H-CC belongs to Zone NP9, with common D. multiradiatus, common Fascicultihus spp., common Toweius eminens, and few Ellipsolithus macellus and Ericsonia subpertusa.
Planktonic foraminifers in Hole 1215A cores are highly affected by dissolution; therefore, their biostratigraphic utility is limited. At best, samples contain reasonably diverse (~12 species), poorly to moderately well preserved tropical assemblages of early Eocene-late Paleocene planktonic foraminifers, whereas in other samples planktonic forms are completely absent or only the most dissolution resistant species remain (Table T3). Our plan was to focus our efforts on producing a planktonic foraminifer biostratigraphy for Hole 1215A only, and to this end we selected one sample per section from the lightest-colored samples, which we assumed had the highest carbonate content. However, the core catcher samples from Hole 1215B turned out to have considerably better preservation than nearly all of the intervals sampled in Hole 1215A, so our analysis includes data from both holes.
Planktonic foraminifers were absent from a sample of water and mud collected from the core top that was dominated by radiolarians. The dark-brown clays of lithologic Unit I (0-25.8 mbsf, Hole 1215A) are also barren of planktonic foraminifers (Fig. F4). Planktonic species are recognizable from Sample 199-1215A-4H-6, 64-66 cm, in the clayey nannofossil ooze of Unit II, following the color change from dark to lighter brown sediments below Sample 199-1215A-4H-5, 120-122 cm (27.40 mbsf). Preservation is generally poor and assemblages are heavily affected by dissolution. Therefore, only broad zonal ranges could be assigned (Fig. F4).
Samples 199-1215A-4H-7, 46-48 cm, 4H-CC, and 5H-1, 12-14 cm, contain heavily encrusted and rather poorly preserved representatives of the genus Acarinina, including Acarinina soldadoensis, Acarinina nitida, Acarinina coalingensis, and Globanomalina pseudoimitata, indicating a broad late Paleocene-early Eocene age (Zones P4c-P7). Also present in these, and all subsequent planktonic foraminifer-containing samples, is a small (63 to 125 µm), unidentified four-chambered species (referred to here as cf. Tenuitella sp.), which possesses an umbilical-extraumbilical aperture and a relatively high spire. This form appears to have a delicate wall, possibly microperforate, yet the species persists even when all other elements of the planktonic assemblage have dissolved.
Preservation improves downhole in the middle-lower part of Core 199-1215A-5H, resulting in slightly more diverse assemblages indicative of an early Eocene age. In addition to the acarninids listed above, various species belonging to the genus Morozovella are present in these samples, including Morozovella gracilis, Morozovella formosa, Morozovella aequa and Morozovella subbotinae, Morozovella marginodentata, and Morozovella lensiformis. Occasional specimens of Chiloguembelina wilcoxensis, Subbotina praecentralis, and Subbotina sp. were also recorded. Because of differential preservation and sporadic occurrence of morozovellids, only broad zonal ranges can be assigned. Samples 199-1215A-4H-CC through 5H-CC are placed in the zonal range P7-P6b based on the presence of M. formosa. Samples from the middle of Cores 199-1215A-5H through 9H also contain M. aequa, and these suggest a slightly older zonal range between Zones P6b and P5.
Core catcher samples from Cores 199-1215B-4H through 8H contain slightly better preserved assemblages than those from Hole 1215A. The top of Zone P5 lies in the core gap between Cores 199-1215B-5H and 7H (47.86-52.57 mbsf), as suggested by the presence of M. acuta in Samples 199-1215B-7H-CC and 8H-CC, whereas the overlying Sample 199-1215B-5H-CC has M. formosa and M. lensiformis. We have not identified any samples indicative of Subzone P6a but cannot determine whether there is an unconformity in the section or merely the dissolution of marker species.
Samples from Section 199-1215A-9H-1, 70-72 cm, through 9H-CC (60.4-69.1 mbsf) contain mainly benthic foraminifers with a few heavily encrusted planktonic specimens of Globanomalina pseudoimitata and are consistent with the late Paleocene age determined from calcareous nannofossils and benthic foraminifers.
Benthic foraminifers were analyzed mainly in core catcher samples from Holes 1215A and 1215B (Table T4). Three additional samples (199-1215A-8H-1, 90.5-92.5 cm; 8H-3, 50.5-52.5 cm; and 8H-4, 13.5-15.5 cm) were analyzed to constrain the level of the P/E boundary BEE. Benthic foraminifers are abundant and generally moderately well preserved, except for samples from Sections 199-1215A-1H-CC through 3H-CC, 9H-CC, and 199-1215B-1H-CC through 8H-CC, all of which are barren. The benthic foraminifers present are characterized by hyaline calcareous tests. Agglutinated forms are rare. The distribution of benthic species is presented in Table T4. The highest stratigraphic occurrence of the Velasco-type benthic foraminifers, which are the characteristic deepwater benthic forms of the Paleocene (Van Morkhoven et al., 1986), is shown in Figure F4.
Benthic foraminiferal assemblages from Samples 199-1215A-4H-CC through 6H-CC are characterized by lower diversities than other samples, and Nuttallides truempyi, Abyssamina inflata, and Abyssamina poagi account for up to 70% of the total assemblage. Cibicidoides species are commonly present, but they are small in size. A high abundance of abysamminid species suggests a 3000- to 5000-m paleodepth, according to Tjalsma and Lohmann (1983). The assemblages characterized by lower diversity and predominance of Nuttallides truempyi represent the early Eocene assemblage of the benthic fauna. Sample 199-1215A-8H-CC contains much of the Velasco-type assemblage, such as Aragonina velascoensis, Gyroidinoides globosus, Pullenia coryelli, and Gavelinella beccariiformis, which are common in upper Maastrichtian to Paleocene sediments. Thus, this sample can be assigned a Paleocene age. Of these species, A. velascoensis and P. coryelli are considered to have a lower bathyal to abyssal depth habitat (Van Morkhoven et al., 1986). Neoeponides hillebrandti and Anomalinoides praeacuta are deeper elements among the assemblage (Tjalsma and Lohmann, 1983). These lines of evidence suggest that the Paleocene and Eocene fauna grew in lowermost bathyal and abyssal depths.
The main composition of the benthic foraminifer assemblages from Hole 1215B are similar to those from Hole 1215A. However, benthic foraminifers are rare in Sample 199-1215B-5H-CC, which contains a high abundance of planktonic foraminifers. The planktonic to benthic foraminifer ratio of this sample is ~54:1. It is assumed that this high ratio is not a direct result of paleodepth but may be attributed to dissolution of benthic foraminifers. The Paleocene assemblage of Sample 199-1215B-8H-CC is more diverse in comparison with that of Sample 199-1215A-8H-CC and contains Osangularis velascoensis and agglutinated species such as Tritaxia globulifera, Spiroplectammina jarvisi, as well as Dorothia trochaoides. These species are also included in the Velasco-type fauna and indicate lowermost bathyal and abyssal depths.
The BEE was observed between Samples 199-1215A-8H-3, 50.5-52.5 cm, and 8H- 4, 13.5-15.5 cm. The Velasco-type foraminifers (such as Pullenia coryelli, Aragonina velacoensis, Gavelinella beccariiformis, and Gyroidinoides globosus) are common and indicate that the assemblage predates the extinction event. Roughly 30% of the Velasco-type assemblage became extinct at this site. The assemblage after the extinction is dominated by Nuttallides truempyi (46% of the total assemblage vs. 14% before the BEE). Diversity continues to decline between Samples 199-1215A-8H- 3, 50.5-52.5 cm, and 8H-1, 90.5-92.5 cm.
It is noted that the Paleocene foraminiferal walls are particularly well preserved, in contrast to the early Eocene foraminifers. Optical wall texture of the Paleocene Abyssamina quadrata shows clear crystal boundaries, whereas that of the Eocene A. quadrata shows slightly recrystallized boundaries (Fig. F5).