A total of 250 m of middle Miocene-lower Eocene sediments and basalt. Calcareous and siliceous microfossils provide a well-defined biostratigraphy in the Miocene and Oligocene (Fig. F11A). Preservation of calcareous microfossils varies considerably through the section, and most assemblages are affected by some degree of dissolution. Planktonic foraminifers and calcareous nannofossils are absent from upper Eocene and upper middle Eocene strata, where stratigraphic subdivision is provided by radiolarian zonation and magnetostratigraphy. Weathered basalt is present below chalk assigned to the upper part of planktonic foraminifer Zone P5 and calcareous nannofossil Subzone CP8b. The volcanic basement is therefore slightly younger than the P/E boundary (~55 Ma) in contrast to the 56-Ma crust expected for this location.
The biostratigraphic results are summarized in Figure F11 and Tables T2, T3, T4, T5, T6, and T7.
Detailed correlation between Holes 1219A and 1219B was achieved using MST data (see "Composite Depths"). This report is, therefore, focused on the biostratigraphy of Hole 1219A. Depth positions and age estimates of biostratigraphic marker events are shown in Table T2.
Cores 199-1219A-1H and 2H are barren of calcareous nannofossils. Below this barren interval, assemblages show poor to moderate preservation. The first downhole occurrence of nannofossils is observed in Section 199-1219A-3H-3, containing a middle Miocene assemblage in which all components except discoasters are completely dissolved. The lower Miocene and Oligocene assemblages contain the best-preserved assemblages. But even these relatively well preserved assemblages are partially altered by dissolution. The Eocene carbonate-bearing sediments show poorly preserved nannofossil assemblages, often with abundant fragments of placoliths. Several barren intervals are observed within the Eocene that severely decreased the number of datums, thus reducing the biostratigraphic resolution. Abundant moderately to poorly preserved assemblages characterized the lowermost Eocene calcareous nannofossil assemblages in Cores 199-1219A-26X and 27X (Zones NP11, NP10, and NP9).
Only middle Miocene discoasters are preserved in Sample 199-1219A-3H-3, 92 cm. Several samples in Section 199-1219A-3H-4 contain assemblages mainly consisting of Discoaster spp., such as Discoaster deflandrei, Discoaster exilis, Discoaster musicus, Discoaster signus, and Discoaster variabilis. Other assemblage components include poorly preserved specimens of abundant Cyclicargolitus floridanus, common Coccolithus pelagicus, and rare Coronocyclus nitescens, Sphenolithus abies, and Sphenolithus heteromorphus, placing Section 199-1219A-3H-4 in Zone NN5 or Zone NN4 (CN4/CN3). The upper half of Core 199-1219A-4H is barren. Nannofossils are present from Sample 199-1219A-4H-4, 90 cm, and downcore. Rare Discoaster druggii, abundant D. deflandrei, rare Triquetrorhabdulus carinatus, and few Orthorhabdus serratus are present in Sample 199-1219A-4H-4, 140 cm, together with other typical lower Miocene species.
The calcareous nannofossils suggest a placement of the O/M boundary in Section 199-1219A-6H-6, where the range of S. delphix was observed. The first occurrence of this species is between Samples 199-1219A-6H-6, 120 cm, and 6H-7, 20 cm (56.97 ± 0.25 mcd) and correlates to Subchron C6Cn.2r (see "Paleomagnetism"). On the Cande and Kent (1995) timescale, an age estimate of 24.28 ± 0.05 Ma is obtained for the base of S. delphix at Site 1219. Conversion to the orbitally tuned timescale of Shackleton et al. (2000), by subtracting 0.9 m.y. from the Cande and Kent (1995) timescale estimate, yields an age of 23.38 Ma for the base of S. delphix. This value is 0.14 m.y. older than the Shackleton et al. (2000) tuned estimate for this datum, which was derived from the eastern South Atlantic (DSDP Site 522) and the western equatorial Atlantic (ODP Sites 926, 928, and 929). Yet the calibration of S. delphix event to the geomagnetic polarity timescale is remarkably consistent in upper Subchron C6Cn.2r from the South Atlantic Ocean to the Mediterranean region (Raffi, 1999) and to the tropical Pacific Ocean (Site 1219).
The interval between the top of Sphenolithus ciperoensis and the top of the abundance peak of Cyclicargolithus abisectus defines the C. abisectus subzone in Bukry's (1973) zonal scheme (CN1a) (Okada and Bukry, 1980). S. ciperoensis has its last occurrence above the abundance peak of C. abisectus in Hole 1219A. This is consistent with results obtained from Site 1218 indicating that Subzone CN1a is obsolete in this part of the tropical Pacific Ocean. Bukry (1973) used the top of Dictyococcites bisectus as an alternative marker for the base of Subzone CN1a. In Hole 1218A, this event is present 21.5 mbsf below the last occurrence of abundant C. abisectus in Subzone CP19a. This stratigraphic interval corresponds to a time interval of ~1.3 m.y. The distance between the top of abundant C. abisectus and the top of D. bisectus is even wider in Hole 1219A (46.1 m), where the latter event is present in lower Zone CP18, ~4.5 m.y. prior to the disappearance of C. abisectus. Taking into account the relatively short geographic distance between Sites 1218 and 1219 (~700 nmi but within 1° of latitude), the time transgressiveness exhibited by D. bisectus suggests that its stratigraphic distribution is influenced by a still unknown paleoecological factor. D. bisectus is, therefore, not suitable for recognition of the base of Subzone CN1a in the tropical Pacific Ocean.
The top and base of S. ciperoensis and Sphenolithus distentus, respectively, are used for subdivision of a good portion of the Oligocene: the top of CP19b, the base of CP19b (base of NP25), the base of CP19a (base of NP24), and the base of CP18 (base of NP25 and base of NP24). These two species are consistently rare members of the Oligocene assemblages at the Leg 199 sites. They are also small (generally 3-5 µm high and 1-2 µm wide), making them difficult to observe in smear slides with dense concentrations of nannofossils. Thus, the low abundance and small size of these biostratigraphic markers hinders accurate determination of their critical evolutionary transitions.
In Hole 1219A, we also determined that the last occurrence of Sphenolithus pseudoradians seems to have a distinct abundance decline preceding its extinction. The extinction occurs in Section 199-1219A-12H-5, in lower Zone CP18. S. distentus evolves just after a bloomlike occurrence of another sphenolith species, Sphenolithus moriformis. This bloomlike occurrence of S. moriformis was observed in Sample 199-1219A-13H-4, 80 cm. Core 199-1219A-13H also holds the first downhole presence of the helicolith Helicosphaera compacta.
D. bisectus exhibits highly variable abundances in Core 199-1219A-15H, from absence in Sample 199-1219A-15H-6, 10 cm, to bloomlike abundances in Sections 199-1219A-15H-3 and 15H-4. Reticulofenestra umbilicus has its last occurrence (NP22/23 and CP16c/CP17 boundaries) in the upper part of Section 199-1219A-15H-6. Ericsonia formosa has its last occurrence (NP21/NP22 and CP16b/CP16c boundaries) in Section 199-1219A-16H-5. Section 199-1219A-17H-2 shows another bloomlike occurrence of Dictyococcites spp., including exceptionally large (>15 µm) specimens of D. bisectus.
Core 199-1219A-17H contains a change in lithology and color, reflecting a shift in the position of the Paleogene CCD. This change occurs within Zone NP21 (CP16a+b) above the extinction of the final Eocene discoasters, which is consistent with the results from Site 1218. Cores 199-1219A-18H and most of 19H are barren of calcareous nannofossils. An interval from Samples 199-1219A-19H-7, 5 cm, through 20H-2, 135 cm, contains nannofossils. Only discoasters are preserved in these two end-member samples, but intervening samples contain a more diverse assemblage, consisting of Chiasmolithus grandis, C. pelagicus, Coccolithus eopelagicus, Dictyococcites hesslandii, D. bisectus, Dictyococcites barbadiensis, Dictyococcites nodifer, Dictyococcites saipanensis, Dictyococcites tanii, Reticulofenestra dictyoda, R. umbilicus, and S. moriformis. The co-occurrence of C. grandis and D. bisectus places this assemblage in Zone NP17 (CP14b).
Another barren interval exists from Samples 199-1219A-20H-3, 90 cm, to 21H-2, 30 cm. Sections 199-1219A-21H-3 through 21H-7 contain middle Eocene assemblages. Dictyococcites spp. are no longer members of these assemblages that contain Discoaster binodosus. The first occurrence of R. umbilicus defines the CP13/CP14a boundary. This boundary is observed in Section 199-1219A-22H-3 using a minimum size of 14 µm for R. umbilicus. The top of Nannotetrina spp. is observed in Sample 199-1219A-22H-CC, which also contains Discoaster bifax, D. binodosus, Discoaster gemmifer, Discoaster septemradiatus, Discoaster wemmelensis, Pseudotriquetrorhabdulus inversus, among other middle Eocene taxa. Bukry (1973) used the evolutionary appearance of both R. umbilicus and D. bifax for recognition of the base of Subzone CP14a. At Site 1219, D. bifax evolves before R. umbilicus when applying the 14-µm minimum size concept for R. umbilicus.
The total range of Nannotetrina fulgens is used for recognition of Zone NP15 (CP13). A few well-developed specimens of this species are observed in lowermost Core 199-1219A-23H and uppermost Core 24H. The lowermost nannofossil-bearing sample here is 199-1219A-24H-4, 100 cm, holding only a sparse discoaster assemblage, including D. gemmifer, D. mirus, D. septemradiatus, and four- to six-rayed Discoaster strictus. This sample is also characterized by obvious Discoaster sublodoensis in the absence of Nannotetrina spp., suggesting a position not far from the NP14/NP15 (CP12b/CP13a) boundary.
The interval from Section 199-1219A-24H-2 to uppermost 26X-1 is barren of calcareous nannofossils.
Sample 199-1219A-26X-1, 40 cm, contains an odd, virtually monospecific assemblage consisting of abundant Tribrachiatus orthostylus, together with a few D. binodosus, Discoaster diastypus, and Discoaster multiradiatus, placing this sample in Zone NP11 (CP9b). The NP10/NP11 (CP9a/CP9b) boundary is observed shortly below, in Section 199-1219A-26X-1. The degree of recrystallization of the Rhomboaster-Tribrachiatus lineage increases downhole, preventing recognition of the base of Tribrachiatus bramlettei and the NP9/NP10 (CP8b/CP9a) boundary. Yet, Tribrachiatus contortus is recognized down to Sample 199-1219A-26X-2, 11 cm, indicating a position within the upper half of Zone NP10. Samples 199-1219A-26X-CC through 27X-CC contain a fairly diverse lowermost Eocene assemblage, including Chiasmolithus bidens, Cruciplacolithus tenuis, D. multiradiatus, Neochiastozygus junctus, Placozygus sigmoides, Prinsius bisulcus, Sphenolithus primus, and Toweius pertusus. Members of the genus Fasciculithus were not observed in any of the samples investigated from the two lowermost cores, indicating a position in upper NP9 (CP8b), which is still within the lowermost Eocene, for Sample 199-1219A-27X-CC.
The initial two cores of radiolarian ooze and clay (lithologic Unit I) were barren of planktonic foraminifers, but, starting in Core 199-1219A-3H, the nannofossil-radiolarian ooze and clay contained planktonic foraminifers of Miocene age. A record of lower Miocene-lower Oligocene planktonic foraminifers was obtained between Cores 199-1219A-3H and 17H (32-150 mbsf). Abundance levels and preservation quality fluctuate considerably during this interval, with preservation optima in the lower Miocene (Zones M4-M2) and the middle part of the Oligocene (Zones P20-P21) when, presumably, the CCD was deepest. The O/M boundary is well resolved in Hole 1219A at ~51 mbsf. In terms of preservation and species abundance, the Miocene and Oligocene assemblages are very similar to those found at Site 1218, although the genus Catapsydra is less common at Site 1219 than at Site 1218. Preservation deteriorates greatly in the lower Oligocene, and the radiolarian oozes of the Eocene-Oligocene through middle Eocene are completely devoid of planktonic foraminifers. Planktonic foraminifers become abundant again in the lower Eocene calcareous chalk overlying basement. This chalk contains poorly to moderately well preserved assemblages, which are assigned to Subzones P6b to upper P5, indicating a younger age (<55.0 Ma) for the crust at this site than was previously estimated by magnetic seafloor anomaly patterns and hotspot reference backtracking. Planktonic foraminifer distributions are listed in Tables T3 and T4. Datum levels of planktonic foraminifers are given in Table T5 and are illustrated in Figure F11.
Planktonic foraminifers can be used to delineate a short lower Miocene sequence. The youngest samples (199-1219A-3H-4, 103-108 cm, through 3H-CC) contain rare specimens of Globoquadrina venezuelana, species belonging to the Globoquadrina tapuriensis-dehiscens group, Paragloborotalia mayeri, Paragloborotalia nana, and Globoquadrina prasaepis. Preservation improves slightly in Samples 199-1219A-3H-CC and 4H-4, 136-140 cm. Also present in these samples are Dentoglobigerina altispira, Dentoglobigerina galavisi, Dentoglobigerina yeguaensis, Globoquadrina dehiscens, and Globoquadrina rohri. Based on the absence of Catapsydrax dissimilis, which is less susceptible to dissolution than most species, these samples are assigned to Zone M4 or younger parts of the Miocene. The first downhole occurrence of C. dissimilis ciperoensis is in Sample 199-1219A-4H-5, 115-120 cm. The subsequent interval, between this sample and 5H-1, 50-55 cm, consistently contains C. dissimilis in the absence of Paragloborotalia kugleri and is thus assigned to the zonal range M2-M3. The boundary between these zones could not be differentiated because of the absence of Globigerinatella insueta.
The highest occurrence of P. kugleri is present in Sample 199-1219A-5H-4, 130-135 cm (40.3 mbsf), and defines the top of Subzone M1b. Samples from this interval (Samples 199-1219A-5H-4, 130-135 cm, to 6H-6, 63-65 cm) contain relatively diverse, moderately well preserved planktonic foraminifers. As in the younger samples, species in the Globoquadrina tripartita and G. dehiscens group are common, with large inflated forms of G. sellii and Globoquadrina tapuriensis being distincitve elements. D. altispira and Dentoglobigerina globulosa are also found frequently. Notably rare from the Site 1219 assemblages, as at Site 1218, are representatives of the Globigerinoides primordius and Globigerinoides triloba groups. The extremely rare occurrence and poor preservation of both species in the Miocene at Site 1218 suggest high susceptibility to dissolution.
The O/M boundary is recognized between Samples 199-1219A-6H-5, 5-7 cm, and 6H-6, 63-65 cm (~51 mbsf), based upon the rare occurrence of P. kugleri. This datum could also be drawn slightly lower (between Samples 199-1219A-6H-6, 63-65 cm, and 6H-CC; ~53 mbsf) based on the occurrence of a single corroded specimen of P. kugleri. The 2-m difference in the placement of the biostratigraphic datum is significant because this event at Site 1219 could be moved from Subchron C6Cn.2r to Chron C6Cr, a difference of ~0.5 Ma in the Cande and Kent (1995) timescale. It will be necessary to conduct much more detailed counts of the distribution of P. kugleri to determine its true first occurrence relative to the Site 1219 magnetostratigraphy. However, we note that the placement of the first occurrence datum of P. kugleri in the middle of Subchron C6Cn.2r agrees closely with the similar correlation at Site 1218.
Berggren et al. (1995) calibrated the appearance of P. kugleri to the base of Subchron C6Cn.2n from Atlantic Ocean DSDP sites. The internal consistency of the position of the base of P. kugleri and the calcareous nannofossil species S. delphix relative to the geomagnetic polarity record appears to suggest that both events in the Pacific are consistent within ~140 k.y. or less of the same events in the Atlantic (see "Calcareous Nannofossils").
Planktonic foraminifer preservation declines in the upper Oligocene compared to the basal Miocene but then improves again just below the Zone P21b/P22 boundary (~73.3 mbsf). Overall species diversity of planktonic foraminifers reaches its highest level (19 species) in the middle of Zone P21b, attesting to the moderate to good preservation of both thin-walled and small-sized species that are ordinarily absent from most other samples at Site 1219. However, even the best-preserved samples still show fragmentation in the <63-µm fraction and corrosion of the walls of dissolution-prone species. The highest occurrence of Paragloborotalia opima opima (marker for the top of Subchron P21b) is very well defined because this species is very abundant just before its extinction level. Accessory species within Subzone P21b include Dentoglobigerina pseudocontinuosa, D. yeguaensis, and tenuitellids such as Tenuitella clemenciae and Tenuitella angustiumbilicata. Species that range across the Zone P21b/P22 boundary include G. tapuriensis, G. tripartita, G. prasaepis, and Globorotaloides suteri. C. dissimilis ciperoensis first becomes a regular constituent below the Zone P21b/P22 boundary at Site 1219, in contrast to its abundance throughout the Miocene and Oligocene at Site 1218.
We are unable to differentiate Zones P21 or P20 owing to the absence of either Globigerina angulisuturalis or Chiloguembelina cubensis at Site 1219. However, the highest occurrence of Turborotalia ampliapertura is present in Sample 199-1219A-12H-CC, 24-30 cm (111.10 mbsf), and identifies the top of Zone P19. A distinct drop in planktonic foraminifer abundance, preservation state, and species richness occurs at ~106 mbsf in Core 199-1219A-17H and renders the last occurrence of T. ampliapertura as a potentially unreliable datum level. Species typical of Zone P19 include dissolution-resistant taxa such as C. dissimilis ciperoensis, G. suteri, P. nana, and P. opima opima.
The first occurrence of P. opima opima could not be determined reliably at Site 1219, owing to intervals of rarity or complete absence of planktonic foraminifers between Samples 199-1219A-14H-2, 53-58 cm (122 mbsf), and 15H-3, 100-105 cm (133.5 mbsf). Single specimens of C. dissimilis, Catapsydrax unicavus, and occasional Subbotina euapertura typify these dissolved assemblages. Planktonic foraminifers are completely absent between Sample 199-1219A-17H-2, 104-106 cm (roughly the level of the E/O boundary according to calcareous nannofossil stratigraphy and magnetostratigraphy), and the top of Core 26X.
The chalk encountered in Cores 199-1219A-26X and 27X contains a moderately to poorly preserved assemblage of lower Eocene planktonic foraminifers. The presence of Morozovella formosa in Sample 199-1219A-26X-CC, 21-24 cm, in the absence of Morozovella aragonensis, suggests that the sample belongs to Subzone P6b. M. formosa was not found in shallower samples from Core 26X, but the continued absence of M. aragonensis and the abundance of Morozovella gracilis, Morozovella subbotinae, Acarinina soldadoensis, Acarinina quetra, and Acarinina coalingensis is typical of Subzone P6b assemblages at other Leg 199 sites.
Sample 199-1219A-27X-1, 19-21 cm, contains Morozovella occlusa and Morozovella acuta, both species that become extinct at the top of Zone P5 (~54.7 Ma). We do not find the zone marker for the upper boundary of Zone P5, Morozovella velascoensis, but we do find several species that make their first appearance at or above the P/E boundary, including Pseudohastigerina wilcoxensis and Chiloguembelina wilcoxensis, both of which also occur in Section 199-1219A-27X-CC. In as much that the bottom of Section 199-1219A-27X-CC recovered weathered basalt, it appears that the seafloor age is very close to, but slightly younger than, the P/E boundary (~55 Ma) and belongs to the middle of Chron C24r, rather than the expected Chron C25n.
Benthic foraminifers are consistently present through the Miocene and Oligocene cores at Site 1219 but are scarce and very poorly preserved through much of the Eocene section. Foraminiferal assemblages consisting of only agglutinated foraminifers are present in Samples 199-1219A-1H-CC through 3H-CC, 17H-CC, 18H-CC, and 24X-CC. The walls of agglutinated forms are well preserved in Samples 199-1219A-1H-CC through 3H-CC but often became fragmented during the sample treatment. Calcareous foraminifers are moderately well preserved in Samples 199-1219A-4H-CC and -5H-CC, but preservation improves rapidly in most of the Miocene and Oligocene. Samples 199-1219A-6H-CC through 16H-CC are well preserved. Preservation of both calcareous and agglutinated foraminifers deteriorates through Eocene Samples 199-1219A-17H-CC through 19H-CC, 21H-CC, 23H-CC through 24H-CC, 26X-CC, and 27X-CC, with most assemblages very poorly preserved. Benthic foraminifers are barren in Samples 199-1219A-20H-CC, 22H-CC, and 25X-CC. The distribution of benthic foraminifers is reported in Table T6.
Miocene benthic assemblages are characterized by Siphonodosaria abyssorum, Oridorsalis umbonatus, Globocassidulina spp., Cibicidoides spp., Pleurostomella spp., and Gyroidinoides spp., all of which are common in bathyal and abyssal depths. Nuttallides umbonifer is rare, but it is consistently present in Miocene Samples 199-1219A-5H-CC and 6H-CC. This species indicates the influences of carbonate-corrosive Antarctic Bottom Water at this site. Epistominella exigua occurs in low abundance in Samples 199-1219A-5H-CC and 6H-CC. The presence of this species indicates a supply of phytodetritus into the deep sea (Nomura, 1995).
Oligocene benthic assemblages are characterized by O. umbonatus, Cibicidoides spp., Globocassidulina spp., Pullenia spp., and various nodosalids and dentalinids. Large specimens of O. umbonatus, Cibicidoides grimsdalei, and Cibicidoides eocaenus are found in Samples 199-1219A-7H-CC through 16H-CC. Both of the Cibicidoides species indicate bathyal to abyssal paleodepths (van Morkhoven et al., 1986). N. umbonifer is rare in Samples 199-1219A-7H-CC through 10H-CC but becomes more common in 10H-CC. The latter sample also contains a number of thin-walled taxa such as Chilostomella sp. and Francesita advena. Astrononion echolsi is found in Sample 199-1219-16H-CC, which is a long-ranging (upper Paleogene-Neogene) species and of little stratigraphic use. It is reported to be particularly common in the Antarctic region (Nomura, 1995). The co-occurrence of A. echolsi and N. umbonifer in Sample 199-1219A-16H-CC indicates the influence of Antarctic Bottom Water at this site in the early Oligocene (Nomura, 1995).
Eocene benthic foraminifers are strongly affected by diagenetic changes, with the test walls of benthic foraminifers often showing the signs of chemical etching. Rare calcareous foraminifers are found in Samples 199-1219A-19H-CC, 21H-CC, and 23H-CC and are also affected by diagenesis.
In order to examine foraminiferal preservation in more detail, test walls of several species in Sample 199-1219A-5H-CC were observed with a polarizing microscope. Observations reveal that the radial texture of E. exigua has been lost and that microscopic crystals have grown on the test surface to give a granular appearance (Fig. F12). The granular texture of O. umbonatus and Globocassidulina sp. has also been destroyed by calcite overgrowth on the walls.
Radiolarians are present in all recovered material except for the deepest core (199-1219A-27X). Preservation and abundances are poor and rare in the first core but are generally good to very good and common to abundant in all other material. The sediments range in age from middle Miocene (Zone RN5) to middle Eocene (Zone RP12).
Core 199-1219A-1H and the upper part of 2H contain a mixed assemblage of species found in Zones RN5 and RN6. However, the samples from Sample 199-1219A-2H-CC and 3H-3, 45-47 cm, can be assigned to middle Miocene Zone RN5 as shown by the evolutionary transition of Dorcadospyris dentata to D. alata. Zone RN4 in the lower Miocene extends to the base of Core 199-1219A-3H, and Zone RN3 is found in Samples 199-1219A-4H-1, 90-92 cm, to 4H-5, 46-48 cm. The boundary between Zones RN4 and RN3 is better defined in Hole 1219B between Samples 199-1219B-2H-2, 45-47 cm, and 2H-3, 45-47 cm. The boundary between Zones RN2 and RN1 is between Samples 199-1219A-5H-4, 45-47 cm, and 5H-5, 45-47 cm.
For radiolarian biostratigraphy, the first occurrence of Crytocapsella tetrapera, which defines the boundary between Zones RN1 and RP22, serves as a good approximation to the O/M boundary (Sanfilippo and Nigrini, 1995). In Hole 1219A, this boundary lies between Samples 199-1219A-6H-1, 45-47 cm (which is also rich in diatoms), and 6H-2, 45-47 cm. As expected, the radiolarian zonal boundary lies somewhat above the first occurrence of S. delphix (between Samples 199-1219A-6H-6, 120 cm, and 6H-7, 20 cm [Subchron C6Cn.2r]) and the first occurrence of P. kugleri (between intervals 199-1219A-6H-5, 5-7 cm, and 6H-6, 63-65 cm [Subchron C6Cn.2r], or between Samples 199-1219A-6H-6, 63-65 cm, and 6H-CC [Subchron C6Cn.2r]). In Hole 1219A, the boundary between Zones RN1 and RP22 lies at the base of Subchron 6CBn.2n, which is in reasonably good agreement with the Chron C6Br level found in Hole 1218A. The boundary between Zones RP22 and RP21 lies between Samples 199-1219A-7H-CC and 8H-1, 43-45 cm, but is better constrained in Hole 1219B between Samples 199-1219B-6H-2, 46-48 cm, and 6H-3, 46-48 cm.
The boundary between the upper Oligocene Zone RP21 and late Oligocene Zone RP20 is formally defined as the evolutionary transition from Tricerospyris triceros to Dorcadospyris ateuchus. However, in Hole 1219A, it was found that these species are rather rare near their transition, and so the first occurrence of Theocyrtis annosa is used instead, placing the boundary between Samples 199-1219A-12H-6, 45-47 cm, and 12H-7, 45-47 cm. Zone RP20 extends to Sample 199-1219A-17H-4, 15-17 cm. Most of the lower Oligocene samples are rich in diatoms.
Zone RP19 crosses the E/O boundary and is present in a relatively short sequence between Samples 199-1219A-17H-5, 32-34 cm, and 17H-CC. The boundary between Zones RP19 and RP18 could not be further constrained by material from Hole 1219B. Zone RP18 is also relatively short extending only to Sample 199-1219A-18H-3, 45-47 cm. Zone RP17 crosses the middle-upper Eocene transition and is present between Samples 199-1219A-18H-4, 45-47 cm, and 19H-4, 45-47 cm. The rest of the recovered material lies within the middle Eocene. Zone RP16 lies between Samples 199-1219A-19H-5, 45-47 cm, and 20H-5, 45-47 cm; Zone RP15, between Samples 20H-6, 45-47 cm, and 22H-3, 46-48 cm; Zone RP14, between Samples 22H-4, 46-48 cm, and 23H-5, 45-47 cm; Zone RP13, between Samples 23H-6, 45-47 cm, and 24H-2, 45-47 cm; and Zone RP12 extends from Samples 24H-3, 45-47 cm, through 25X-CC. The base of Zone RP15 is rich in diatoms. All zonal boundaries from RN5 to RP12 (Sanfilippo and Nigrini, 1998) are recognized (Table T7) and could be placed between successive samples, usually from one core section to the next. First and/or last occurrences of seven species and one evolutionary transition, for which numerical ages have previously been determined in conjunction with paleomagnetic data (see Table T3 in the "Explanatory Notes" chapter), could be placed within 1- to 2-m intervals.