The four holes drilled at Site 1221 yielded a sequence of lower Oligocene-lower Eocene radiolarian clay and ooze and a condensed (~16 m) section of upper Paleocene-lower Eocene nannofossil ooze and chalk. Radiolarian and nannofossil biostratigraphy indicate the presence of the E/O boundary in Cores 199-1221A-1H, 199-1221B-2H, and 199-1221C-1H. However, the exact placement of this boundary at Site 1221 cannot be constrained because of the absence of planktonic foraminifers, upon which the E/O boundary is defined. Calcareous microfossils are completely absent in the siliceous sediments between ~8 and ~96 mcd, and biostratigraphic control through this interval is provided entirely by radiolarians. The carbonate content of sediments increases in the basal 17 m of Site 1221, and nannofossil and planktonic foraminiferal biostratigraphy allow basic zonation of a condensed sequence of lower Eocene nannofossil ooze and chert. Section 199-1221C-11X-3 contains an interval of colorful strata, the base of which, as at Site 1220, corresponds to the extinction of Paleocene benthic foraminifers and, therefore, the P/E boundary. Preservation of calcareous microfossils improves below the P/E boundary, and planktonic foraminifers and nannofossils allow a detailed zonation of upper Paleocene nannofossil ooze and clay, which constitutes the short section recovered in Core 199-1221C-12X. The biostratigraphic results are summarized in Figure F5 and in Tables T2 and T3.
The uppermost carbonate-bearing sediment in the mudline core of Hole 1221B contains abundant nannofossils showing poor preservation. Sample 199-1221B-1H-1, 127 cm, taken immediately below the overlying radiolarian ooze, contains a low-diversity assemblage belonging to Zone CP17 (lower NP23) of the lower Oligocene, which includes Coccolithus pelagicus, Cyclicargolithus floridanus, Dictyoccites bisectus, Dictyoccoccites hesslandii, Discoaster deflandrei, Discoaster nodifer, Discoaster tanii, and Sphenolithus moriformis. Samples from Section 199-1221B-1H-2 contain apical parts of lower Oligocene sphenoliths, presumably originating from Sphenolithus predistentus and Sphenolithus tribulosus. The last occurrence of Reticulofenestra umbilicus is constrained within a 49 cm interval in Section 199-1221B-1H-2 (Table T2), which defines the CP16c/CP17 (NP22/NP23) boundary. Exceptionally large specimens of D. bisectus (up to 18 µm) are present in Sample 199-1221B-1H-CC.
The CP16c/CP17 boundary is also observed in Hole 1221A, between Samples 199-1221A-1H-3, 3 cm, and 1H-3, 40 cm. The CP16c/CP16a+b (NP21/22 boundary; defined by the top of Ericsonia formosa) is observed between Samples 199-1221A-1H-5, 70 cm, and 1H-6, 40 cm. Calcareous nannofossils in Core 199-1221A-1H are badly dissolved. Isolated, circular, and elliptical distal shield rims that are nonbirefringent between crossed nicols are observed from below the extinction level of E. formosa. These rim ghosts are considered to originate from E. formosa (circular) and C. pelagicus (elliptical). Only elliptical distal shield rims are observed above the assigned range of E. formosa, and these rim ghosts undoubtedly originate from C. pelagicus, supporting the proposed placement of the top of E. formosa and the CP16c/CP16a+b boundary despite the strongly dissolved assemblages in the critical interval.
Subzone CP16a+b (NP21) is recognized through Sample 199-1221A-1H-6, 100 cm. Sample 199-1221A-1H-1, 110 cm, is barren of calcareous nannofossils. The E/O boundary is formally defined by the extinction of the planktonic foraminifer genus Hantkenina. But planktonic foraminifers are completely dissolved throughout Core 199-1221A-1H. The exact placement of the E/O boundary at Site 1221, therefore, will remain unresolved, perhaps until the problem can be addressed by analysis of nannofossil stable isotopes.
Eocene radiolarian ooze prevails from Sample 199-1221A-1H-1, 110 cm, through Sample 199-1221C-10X-CC. Several samples were investigated from the core catcher of Core 199-1221C-10X-CC. This core has a total recovery of 27 cm, with chert pieces overlying nannofossil ooze. A smear slide, made from ooze stuck to a piece of chert, yielded mixed lower Eocene assemblages representing Subzones CP9b (NP11) and CP9a (NP10), with common Rhomboaster spp., Tribrachiatus contortus, Tribrachiatus orthostylus, Discoaster diastypus, Discoaster multiradiatus, and lower Eocene placoliths.
Sample 199-1221C-10X-CC, 14 cm, from the ooze underlying the cherts continues an assemblage from the lowermost part of Subzone CP9a (NP10), judging from the presence of both rare Tribrachiatus bramlettei and forms transitional between Rhomboaster spp. and Tribrachiatus spp. Secondary calcite overgrowth blurs the morphological details in the evolution of the Rhomboaster-Tribrachiatus lineage in virtually all lower Eocene samples investigated from Leg 199 sediments, including those from Site 1221. Sample 199-1221C-11X-1, 20 cm, contains an assemblage from Zone CP8 (upper NP9), implying that the base of Zone CP9 (NP10) falls in the gap between Cores 199-1221C-10X and 11X.
The Benthic Extinction Event (BEE) and, thus, the P/E boundary is located in Sample 199-1221C-11X-3, 91 cm. The pattern of nannofossil abundance and preservation in the colorful strata immediately overlying the P/E boundary layer is similar to the corresponding interval at Site 1220. A 30-cm barren interval, or one with only rare nannofossils, is present between Samples 199-1221C-11X-3, 60 cm, and 11X-3, 90 cm. The fasciculiths disappear between Samples 199-1221C-11X-2, 97 cm, and 11X-2, 110 cm, ~1.4 m above the benthic foraminfer extinction. The assemblages are poorly preserved below the boundary. Preservation improves above the colorful strata in Section 199-1221C-11X-3.
Core 199-1221C-12X consists of 72 cm of sediment in Section 199-1221C-12X-1 and 8 cm of sediment in the core catcher. Fasciculiths are common to abundant and diverse throughout Core 199-1221C-12X. Preservation is otherwise poor throughout the samples investigated from Section 199-1221C-12X-1, corresponding closely to preservation category 3 of Bukry (1973); "Majority of specimens strongly etched. Many major structures removed. Many centerless specimens and fragmented specimens of questionable identity; low-diversity assemblage."
The base of both D. multiradiatus (defines the base of Subzone CP8a/NP9) and Discoaster nobilis (defines the base of Zone CP7) are present between Samples 199-1221C-12X-1, 18 cm, and 12X-1, 32 cm, which probably indicates strong condensation or a short hiatus in the carbonate-free dark brown sediment between these two samples. Ray numbers of D. multiradiatus are higher here than in younger (Eocene) populations. The large (>9 µm) Ericsonia robusta is common together with D. multiradiatus in the upper part of Section 199-1221C-12X-1 and disappears in the core gap between Cores 199-1221C-11X and 12X. Discoaster okadai is observed in Sample 199-1221C-12X-1, 40 cm.
Sample 199-1221C-12X-CC shows a marked improvement in preservation compared to the overlying samples in Core 199-1221A-12X and contains a diverse assemblage representing Zone CP6 (NP8) of the upper Paleocene. These taxa include Bomolithus elegans, Chiasmolithus bidens, Coccolithus pelagicus, Cruciplacolithus frequens, Cruciplacolithus latipons, Discoaster mohleri, Ellipsolithus macellus, E. robusta, Ericsonia spp. (see Bralower and Mutterlose, 1995; plate 4, figs. 9 and 10), Fasciculithus involutus, Fascicultihus tympaniformis, Fasciculithus ulii, Heliolithus riedelii, Neochiastozygus spp., Prinsius bisulcus, Sphenolithus primus, Toweius eminens, Toweius pertusus, and Zygodiscus plectopons. Isolated rims and rim fragments are abundant in this core catcher sample.
Sample 199-1221C-12X-CC represents sediment resting immediately on the underlying basalt. This sample has an age range between 56.5 and 57.3 Ma, being older than the first occurrence of D. nobilis and younger than the first occurrence of H. riedelii.
The ~152 m of radiolarian clay, radiolarian ooze, and chert recovered at Site 1221 is completely barren of planktonic foraminifers. As at Site 1220, planktonic foraminifers are sporadically present in the upper Paleocene-lower Eocene nannofossil ooze and chalk sequence overlying basaltic basement in Holes 1221C and 1221D. As a result of extremely low recovery, variable states of foraminiferal preservation, and limited sampling through this critical interval (mainly core catcher samples), planktonic foraminiferal biostratigraphic zonation was confined to the Paleocene-Eocene portion of the site.
Sample 199-1221C-10X-CC contained highly dissolved planktonic assemblages characterized by solution-resistant forms such as Acarinina coalingensis, Acarinina soldadoensis, and Morozovella aequa. These species indicate a Zone P5-P6 age, which is in agreement with the nannofossil Zone NP10 assignment for this sample. A highly dissolved planktonic foraminifer assemblage was also recovered from Core 199-1221C-11X and contains only A. soldadoensis. The BEE has been placed at 154.31 mbsf and suggests that Sample 199-1221C-11X-CC is of latest Paleocene age. Sample 199-1221C-12X-CC contains a moderately well preserved and diverse assemblage of Paleocene planktonic foraminifers. Species present in this sample include A. coalingensis, A. soldadoensis, Acarinina nitida, Morozovella mckannai, M. aequa, Morozovella velascoensis, Morozovella acuta, Morozovella angulata, Igorina albeari, Globanomalina pseudomenardii, Globanomalina ovalis, Subbotina triangularis, Subbotina patagonica, and Subbotina velascoensis. Based on the presence of G. pseudomenardii, M. aequa, and A. soldadoensis, we assign this sample to Subzone P4c. Sample 199-1221D-4X-CC contains only traces of A. coalingensis and cf. Tenuitella spp.
A suite of small-volume samples (~1 cm3) from Section 199-1221C-11X-3 was obtained by scraping the surface of the core with glass microscope slides. These samples are heavily contaminated with plastic fragments derived from sawing through the core liner during core splitting. Planktonic foraminifers are very rare in the scrape samples, consisting only of pieces of acarininids and extremely small specimens of four chambered cf. Tenuitella spp. No traces of the P/E boundary "excusion taxa" that are present at Site 1220 were found. However, these sample residues are extremely small and it is possible that larger volumes of sediment may yield greater numbers of planktonic foraminifers.
Benthic foraminiferal assemblages from the early Oligocene and most parts of the Eocene at Site 1221 consist of agglutinated species. Samples 199-1221A-1H-CC, 2H-CC, 3H-CC, 5H-CC, 8H-CC, and 10H-CC contain Recurvoides sp. Ammodiscus sp., Ammovertellina sp., Thalmannammina sp., and Spiroplectammina spectabilis. Preservation of these species is poor, and most specimens show signs of damage. Elongate tests of Bathysiphon sp., Rhizammina sp., and Archimerismus? sp. are usually fragmented. These assemblages indicate abyssal paleodepths.
Calcareous foraminiferal assemblages are present in Samples 199-1221C-10X-CC through 12X-CC. These assemblages are moderately well preserved, but the presence of small calcite microcrystals on the surfaces of the tests indicates some diagenetic alteration. Sample 199-1221C-10X-CC is characterized by a high abundance of Nuttallides truempyi and Abyssamina quadrata. Also present are Anomalinoides spissiformis, Globocassidulina globosa, small pleurostomellids, and stilostomellids. This assemblage is also characterized by low species diversity, which is suggestive of the early Eocene (Tjalsma and Lohmann, 1983). In contrast, high diversity assemblages are found in Samples 199-1221C-11X-CC and 12X-CC. These assemblages contain the Velasco-type species such as Gavelinella beccariiformis, Bulimina midwayensis, Gyroidinoides globosus, Pullenia coryelli, Nuttallinella florealis, Anomalinoides praeacuta, Aragonia velascoensis, Neoeponides hillebrandti, Neoflabellina semireticulata, and Dorothia trochoides, indicating a Paleocene age and placement of the P/E boundary above Sample 199-1221C-11X-CC.
Ten samples scraped from the surface of Section 199-1221C-11X-3 were analyzed to precisely locate the P/E boundary. The foraminiferal assemblages in Samples 199-1221C-11X-3, 23-31 cm; 11X-3, 31-38 cm; 11X-3, 38-45 cm; and 11X-3, 45-53 cm, are composed mainly of A. quadrata, Nuttalides truempyi, and G. globosa. The high abundance of these species is diagnostic of the early Eocene (Tjalsma and Lohmann, 1983). Benthic foraminifers are rare and very poorly preserved in Samples 199-1221C-11X-3, 53-60 cm; 11X-3, 60-68 cm; and 11X-3, 68-76 cm. However, the main constituents of the assemblage are recognizable and are similar to the assemblage above these samples. Sample 199-1221C-11X-3, 76-83 cm, is barren of benthic foraminifers. Sample 199-1221C-11X-3, 83-91 cm, contains a few poorly preserved specimens of N. truempyi and A. spissiformis praeacuta. Samples 199-1221C-11X-3, 91-98 cm, and 11X-3, 98-106 cm, are characterized by A. velascoensis, Gyroidinoides globosus, and G. beccariiformis, which constitute the Velasco-type assemblage. The P/E boundary is probably present near 154.31 mbsf (Section 199-1221C-11X-3, 91 cm), using the BEE as criterion for boundary definition (see "P/E Boundary" in "Biostratigraphy" in the "Explanatory Notes" chapter).
A continuous sequence of radiolarian-bearing sediments, ranging in age from earliest Oligocene to early middle Eocene (Zone RP11), was recovered from Hole 1221A. Poorly recovered chert horizons in Cores 199-1221C-8X and 9X are barren of radiolarians. However, a small amount of radiolarian ooze in Sample 199-1221C-10X-CC contains radiolarians indicative of Zone RP7. Cores 199-1221C-11X and 12X are barren of radiolarians. With the exception of Core 199-1221A-1H and the upper sections of 2H, the radiolarian fauna is abundant and well preserved. Radiolarian zonal assignments are presented in Table T3.
Despite considerable reworking of middle Eocene forms, numerous diatoms, and some ash, it was possible to place the RP20/RP19 zonal boundary between Samples 199-1221A-1H-5, 45-47 cm, and 1H-6, 45-47 cm. Using data from Hole 1221B it is possible to further constrain this boundary and place it between Samples 199-1221A-1H-5, 45-47 cm, and 199-1221B-2H-3, 22-24 cm. Zone RP19 spans the E/O boundary. A combination of reworking and poor preservation made it equally difficult to place the boundary between Zones RP19 and RP18. However, by removing poorly preserved samples from consideration, using data from Hole 1221B, and integrating information from the magnetostratigraphic record (see "Paleomagnetism"), the RP19/RP18 boundary can be placed between Samples 199-1221A-1H-6, 45-47 cm, and 199-1221B-2H-4, 7-9 cm.
Subsequent zonal boundaries are clearly defined because of an increase in preservation of the radiolarians below the E/O boundary. The Eocene sediments maintained a uniformly brown color with a sugarlike texture. Although not abundant, the first occurrence of Calocyclas bandyca clearly defines the Zone RP18 and Zone RP17 boundary between Samples 199-1221A-2H-7, 43-45 cm, and 2H-CC. The RP17 and RP16 zonal boundary is equally well defined by the first occurrence of Cryptocarpium azyx between Samples 199-1221A-3H-3, 46-48 cm, and 3H-4, 46-48 cm. The series of middle Eocene zones defined by the evolution of species belonging to the genus Podocyrtis are all present and contain a rich and abundant faunal assemblage. The RP16/RP15 zonal boundary lies between Samples 199-1221A-4H-5, 45-47 cm, and 4H-6, 45-47 cm; the RP15/RP14 boundary is between Samples 199-1221A-6H-3, 45 cm, and 6H-4, 45 cm; the RP14/RP13 boundary is between Samples 199-1221A-7H-6, 45-47 cm, and 7H-CC; and the RP13/RP12 boundary is between Samples 199-1221A-9H-1, 45-47 cm, and 9H-2, 45-47 cm. The first occurrence of Sethochytris triconiscus is a useful and easily recognizable datum within Zone RP14. The earliest clearly defined boundary is between Zones RP12 and RP11 between Samples 199-1221A-11H-6, 45-47 cm, and 11H-7, 45-47 cm, and between Sections 199-1221C-4H-CC and 5H-CC. The lowermost Zone RP11 assemblages are found in Samples 199-1221A-12H-CC and 199-1221C-6X-CC.
An older assemblage, found only in Hole 1221C and belonging to Zone RP7, was recovered. Radiolarian Zone RP7 spans the lower/middle Eocene boundary. In Section 199-1221C-10X-CC, a small amount of the typically brown sugarlike sediment was found between the overlying chert and underlying calcareous material belonging to nannofossil Zone NP10. The fauna is well preserved and abundant.
Table T3 summarizes newly determined zonal boundary ages calibrated using the paleomagnetic reversals from Site 1220. Figure F6 compares the calculated ages with those estimated by Sanfilippo and Nigrini (1998; SN98) (see "Radiolarian Zonal Scheme and Taxonomy" in "Biostratigraphy" in the "Explanatory Notes" chapter). The age estimates of Sanfilippo and Nigrini (1998) are based on an unpublished catalog and chart constructed from a reexamination of all Paleogene low- and middle-latitude Deep Sea Drilling Project/Ocean Drilling Program sites from Legs 1-135 where there is a recognizable radiolarian fauna. The published information was reevaluated using current uniform species concepts and integrated, where possible, with published nannofossil and paleomagnetic data. Sanfilippo and Nigrini (1998) cautioned that their chronology of Paleogene radiolarian zonal boundary events is, at best, a good approximation. However, tested against a direct paleomagnetic record it can be seen that the estimates are fairly accurate. The largest discrepancies are present at the Zone RP15/RP14 boundary with a Site 1220 age that is 1.89 m.y. older than the SN98 age (from Sanfilippo and Nigrini, 1998). The fact that this boundary is defined by the evolutionary transition of Podocyrtis mitra to P. chalara rather than a more objective morphological first or last occurrence may account for some of this discrepancy. There is also a relatively large discrepancy for the boundary between Zones RP12 and RP11, where the SN98 age is 1.61 m.y. older than the Site 1220 age. In this case, the paleomagnetic record is not well constrained in Site 1220. The Site 1220 age for the boundary between Zones RP16 and RP15 is 1.32 m.y. older than the SN98 age. The RP15/16 boundary event is marked by the first occurrence of Podocyrtis goetheana, which is easily recognizable but not particularly abundant in the Site 1221 material.