BIOSTRATIGRAPHY: APPLICATION OF THE MARTINI (1971) ZONATION AND ADDITIONAL BIOEVENTS

Two Miocene calcareous nannofossil zonations, Martini (1971) and Okada and Bukry (1980), have been widely adopted for biostratigraphic studies in the North Atlantic. The Okada-Bukry zonal scheme is based on the initial work of Bukry (1971). Using several low-latitude DSDP sites from the Pacific Ocean, Bukry presented a Cenozoic scheme including 10 Miocene zones subdivided into 15 subzones. Bukry (1973, 1975) presented a low-latitude zonal scheme for the Venezuela Basin in the Caribbean Sea that has been applied to most equatorial and subtropical DSDP and ODP sites in the North Atlantic Ocean (e.g., Gartner, 1992: Site 608, 42°N; Olafsson, 1989: Site 667, 4°N; Muza et al., 1987: Site 603, 36°N; Parker et al., 1985: Sites 558, 37°N, 563, 33°N).

It is interesting to note that Jiang and Gartner (1984) used the Martini zonal scheme (for Sites 525-529, 28°S), but introduced some modifications to the original zonal scheme of the early Miocene that follow the zonation of Bukry (1973, 1975).

Most DSDP-ODP biostratigraphic studies from low- to mid-latitude sites (0° to 40°N) have been well dated by using the zonation of Okada and Bukry (1980) or a slightly modified version of the Martini zonation (1971). The general trend for mid-latitude studies is to integrate both zonal schemes. High-latitude studies are usually based on the Martini (1971) zonal units.

Sites from Leg 149 can be zoned using both zonal schemes with some exceptions or modifications, primarily for the lower part of the Miocene. The zonation of Martini (1971) has been selected as the standard for this study. The zonation of Okada and Bukry (1980) is less applicable for both Oligocene (CP17/18) and Miocene (CN 1/2; CN3/4). For the Miocene/Pliocene boundary, the FO of Ceratolithus (zonal marker of CN10a/10b) was applied according to Okada and Bukry's zonal scheme.

Oligocene/Miocene Boundary

The Oligocene/Miocene boundary is placed between the Chattian Stage (late Oligocene) and the Aquitanian Stage (early Miocene). The definition of this boundary using calcareous nannofossils has been long discussed (see IUGS working group on the Paleogene/ Neogene boundary, Steininger, 1994). Several calcareous nannofossils from the Chattian-type locality (Doberg, Germany) described by Martini and Muller (1975) are not observed in the Aquitanian sediments (Saint Jean d'Etampes, France). Pontosphaera enormis is present in the last sample from the Chattian-type section, but has not been reported in the Aquitanian sediment. P. enormis may be useful in determining the Chattian/Aquitanian boundary using calcareous nannofossils. In this study, the LO of this species is correlated with the LOs of S. ciperoensis and R. bisecta bisecta at the top of Zone NP25. According to Steininger (1994), the FO of Sphenolithus capricornutus is the event closest to the boundary and is placed at the top of chronozone C6Cn2r. In Site 898 S. capricornutus is observed in one sample together with S. ciperoensis and P. enormis. The Oligocene/Miocene boundary is defined in Sites 897, 898, 899, and 900 by the LO of S. ciperoensis and secondarily by the LO of P. enormis, and therefore the FO of S. capricornutus is placed in the uppermost Oligocene.

Biohorizons

A succession of bioevents is observed from the upper part of Zone NP21 to the uppermost Miocene Zone NN12. One major hiatus in the lower part of the upper Miocene interrupts the sedimentary record and the sequence of bioevents. Using data from Sites 897, 898, 899, and 900, we propose a synthesis of the major biohorizons based on the earliest/latest occurrence of each taxon. Hole and sample numbers are indicated only for the events used to establish this synthesis. Most of the events described below are listed with sample interval and depth in Table 2, Table 4, Table 6, and Table 8. The following succession of biohorizons has been identified:

FO of Ilselithina fusa

This event is observed at Sites 897, 899, and 900 near the base of the Oligocene. At the beginning of its range, I. fusa is rare, but its characteristic distal spines make this species easily identifiable. The abundance pattern and the range of I. fusa in Hole 900A is shown on Figure 10, together with Z. bijugatus.

Hole 900A: Sample 149-900A-52R-3, 65-66 cm.

LO of Bramletteius serraculoides

The LO of B. serraculoides is observed at Site 897 and at Site 900. At both sites it occurs at the top of Zone NP21, at the extinction level of Ericsonia formosa, and is in good agreement with the distribution given by Backman (1987). The plots of the abundance pattern of the range of B. serraculoides are shown for Sites 897 and 900 (Fig. 3, Fig. 8).

Hole 900A: Sample 149-900A-52R-4, 143-144 cm.

LO of Ericsonia formosa

The decrease in abundance of E. formosa at Sites 897 and 900 (Fig. 3, Fig. 8) is tentatively interpreted as its last true occurrence; this interpretation could be supported by the position of the FO of S. akropodus (see below) and the LO of B. serraculoides, relative to this event.

Hole 900A: Sample 149-900A-52R-4, 143-144 cm.

FO of Sphenolithus akropodus

This species is likely to be similar to the form illustrated by Okada (1990) as Sphenolithus aff. distentus, which range is reported from the top of CP16b to the middle of CP17. According to the distribution of Okada (1990), we use this event to approximate the Zone NP21/ NP22 boundary, both at Sites 897 and 900 (Fig. 3, Fig. 8).

Hole 900A: Sample 149-900A-51R-6, 47-48 cm.

FO of Helicosphaera recta

This helicolith is found to have its FO in the early Oligocene at Sites 899, 897, and 900. In the two latter sites, it occurs together with the FO of S. akropodus, its distribution overlaps the final part of the Reticulofenestra umbilicus range. Previous studies report H. recta from the lower part of Zone NP23 (e.g., Wei and Wise, 1989; Okada, 1990), but it has not been reported in the upper part of Zone NP22. The abundance pattern of the range of H. recta for Hole 900A is shown on Figure 11 with other important helicolith species.

Hole 900A: Sample 149-900A-51R-6, 47-48 cm.

FO of Chiasmolithus altus

This chiasmolith, which is the youngest representative of the genus, has its FO in the early Oligocene at Sites 897, 899, and 900.

Hole 900A: Sample 149-900A-51R-5, 120-121 cm.

FO of Cyclicargolithus abisectus (>10 µm)

This large form of Cyclicargolithus (see Appendix A) is found to occur in the lower Oligocene at Sites 897, 899, and 900. Rio et al. (1990) distinguished C. abisectus by its size larger than 10 µm and they observed its LO close to the LO of S. ciperoensis. The abundance pattern of the range of C. abisectus (>10 µm) for Hole 900A is shown on Figure 12. As reported by Olafsson (1992), large specimens are very rare in the Miocene. The LO of C. abisectus (>10 µm) occurs in Zone NN7, but its last consistent occurrence is recorded at the top of Zone NP25 (end of the regressive phase).

Hole 900A: Sample 149-900A-51-4, 9-10 cm.

FO of Helicosphaera perch-nielseniae

The FO of Helicosphaera perch-nielseniae is observed in the early Oligocene Zone NP22 at Sites 897, 899, and 900. The abundance pattern of the range of H. perch-nielseniae in Hole 900A is shown on Figure 11, along with other helicoliths species.

Hole 900A: Sample 149-900A-51R-4, 9-10 cm.

FO of Reticulofenestra circus

The FO of this new taxon is observed in the lower Oligocene Zone NP22 in Hole 897C.

Hole 897C: Sample 149-897C-50R-1, 85-86 cm.

LO of Isthmolithus recurvus

The LO of this holococcolith occurs at Sites 897, 899, and 900 at the same level or just below the LO of R. umbilicus (Fig. 3, Fig. 8), which is in agreement with the placement of this datum by Premoli Silva et al. (1988) in mid-latitude sections. At the low-latitude Site 522, Backman (1987) reported this event below the LO of E. formosa, but concluded it is a diachronous event. This diachroneity could be explained by a preference of this species for cool water (Wei and Wise, 1990). The abundance pattern of the range of I. recurvus for Hole 900A is shown on Figure 10.

Hole 900A: Sample 149-900A-51R-3, 50-51 cm.

LO of Reticulofenestra umbilicus

It was found in Sites 897, 899, and 900 and marks the Zone NP22/ NP23 boundary (Fig. 3, Fig. 8).

Hole 900A: Sample 149-900A-51R-2, 24-25 cm.

FO of Helicosphaera aff. H. carteri

This medium-sized helicolith (see Appendix A) has its FO in lower Zone NP23, and it is discontinuously distributed up to lower Zone NP24. It is observed at Sites 897 and 900.

Hole 900A: Sample 149-900A-50R-5, 16-17 cm.

LO of Lanternithus minutus

The LO of Lanternithus minutus is observed at Sites 897 and 900 (Fig. 3, Fig. 8) and occurs within Zone NP23.

Hole 900A: Sample 149-900A-50R-3, 129-130 cm.

LO of Reticulofenestra circus

This subcircular Reticulofenestra has a range restricted to the lower Oligocene. Its LO occurs at the same level or close (at Site 897) to that of L. minutus.

Hole 900A: Sample 149-900A-50R-2, 120-121 cm.

LO of Sphenolithus akropodus

This bioevent is observed within Zone NP23 at Sites 897 and 900 (Fig. 3, Fig. 8, Fig. 13). The abundance pattern of the range of S. akropodus for Hole 900A is shown on Figure 13 with other Sphenolithus markers.

Hole 900A: Sample 149-900A-50R-2, 63-64 cm.

LCO of Helicosphaera compacta

The LCO of H. compacta is more easily detectable than its LO. At Sites 897 and 900 (Fig. 3, Fig. 8), this bioevent is observed below the FO of S. ciperoensis. The sharp decrease in abundance of H. compacta for Hole 900A is shown on Figure 10.

Hole 900A: Sample 149-900A-49R-4, 99-100 cm.

FO of Sphenolithus ciperoensis

S. ciperoensis is rare and somewhat discontinuous at its first range. Its FO observed at Sites 897, 899, and 900 defines the base of Zone NP24 (Fig. 3, Fig. 8). The abundance pattern of the range of S. ciperoensis for Hole 900A is shown on Figure 13.

Hole 900A: Sample 149-900A-49R-4, 99-100 cm.

FO of Triquetrorhabdulus carinatus

The FO of T. carinatus occurs in the lower part of Zone NP24 at Sites 897, 899, and 900. T. carinatus has a rare and sporadic occurrence from Zones NP24 to NP25, and is more abundant in Miocene sediments.

Hole 900A: Sample 149-900A-48R-4, 142-143 cm.

LO of Helicosphaera compacta

The LO of Helicosphaera compacta is found in Zone NP24 at Sites 897, 899, and 900 and this data is in accordance with the assignment of H. compacta proposed by Perch-Nielsen (1985). The discrepancy with the LO of this form, reported by Fornaciari et al. (1990) to occur in Zone NP23, could be related to both mid-latitude preference and the difficulty of pinpointing the LO, because of rare abundance of this taxon in its upper range (abundance pattern shown on Fig. 3, Fig. 8, Fig. 10).

Hole 900A: Sample 149-900A-48R-2, 131-132 cm.

FCO of S. ciperoensis

The FCO of S. ciperoensis (shown on Fig. 3, Fig. 8, Fig. 13) is more easily detected than the FO, and is recorded at Sites 897, 899, and 900.

Hole 900A: Sample 149-900A-47R-3, 64-65 cm.

LO of Sphenolithus predistentus

Though the distribution of S. predistentus in its upper range decreases, its LO seems a good alternative marker to approximate the Zone NP24/NP25 boundary (Fig. 3, Fig. 8, Fig. 13) in the eastern Atlantic Ocean, as already suggested for the western Indian Ocean (Fornaciari et al., 1990).

Hole 900A: Sample 149-900A-45R-5, 82-83 cm.

LO of Sphenolithus distentus

At the top of its range, the abundance of S. distentus decreases sharply, and occurrences above this level (Fig. 3, Fig. 8, and Fig. 13) are considered reworked.

Hole 900A: Sample 149-900A-45R-4, 112-133 cm.

FO of Helicosphaera obliqua

The FO of Helicosphaera obliqua is observed in Zone NP25 in Holes 898A, 899B and 900A, and can be useful to recognize the lower part of this Zone. The abundance pattern of the range of H. obliqua for Hole 900A is shown on Figure 11.

Hole 900A: Sample 149-900A-44R-1, 131-132 cm.

LO of Ericsonia sp. 1

This round species of Ericsonia (see Appendix A) is restricted to the Oligocene interval (Fig. 3, Fig. 8, Fig. 10). Its LO is placed between the FOs of H. obliqua and H. truempyi in Zone NP25 and is correlated among Sites 898, 899, and 900. At Site 897, an interval barren of calcareous nannofossils lies above the LO of Ericsonia sp. 1, which precludes precise location of this event.

Hole 900A: Sample 149-900A-43R-2, 80-81 cm.

FO of Sphenolithus delphix

This characteristic form is found only in Holes 897C and 898A. At Site 897 its FO occurs above the LO of S. ciperoensis, whereas at Site 898, it takes place just below the LCO of S. ciperoensis. The latter finding is somewhat in contrast with previous assignment; in Rio et al. (1990), and Gartner (1992), these two sphenoliths do not overlap, which could be explained as a consequence of different methods used to pick out the LO of S. ciperoensis, because, as described above, it is very rare in its upper range.

Hole 898A: Sample 149-898A-29X-2, 117-118 cm.

FO of Helicosphaera truempyi

This helicolith is rare to few in Leg 149 sediments. The FO was observed in the middle part of Zone NP25 (Fig. 5), close to the FO of Sphenolithus umbrellus and the LO of H. bramlettei, and above the LO of Ericsonia sp. 1.

Hole 900A: Sample 149-900A-40R-2, 116-117 cm

LO of Sphenolithus umbrellus

It was recognized in Holes 898A, 899B, and 900A below the LCO of S. ciperoensis, in the upper part of Zone NP25.

Hole 900A: Sample 149-900A-39R-3, 109-110 cm.

FO of Triquetrorhabdulus challengeri

An early morphotype of T. challengeri with three bright ridges first occurs in the upper part of Zone NP25. Though rare at the beginning of its range, T. challengeri becomes more abundant in Zones NN1 and NN2. Specimens observed are well preserved and easily distinguishable from Triquetrorhabdulus carinatus and Triquetrorhabdulus millowii. Its FO is found in Hole 898A at the same level as the LCO of S. ciperoensis.

Hole 898A: Sample 149-898A-29X-1, 103 cm.

LCO of Sphenolithus ciperoensis

This event corresponds to the last consistent occurrence and represents a drop in abundance (Fig. 3, Fig. 8, Fig. 13). It is recognized at Sites 898, 899, and 900. At Site 897 the decrease in abundance is sharp (from 20 to 0 specimens/mm2) and coincides with the LO of S. ciperoensis. At the other sites, the drop in abundance is from about 15 to less than 5 specimens/mm2.

Hole 900A: Sample 149-900A-37R-5, 53-54 cm.

FO of Helicosphaera carteri

H. carteri has a discontinuous, rare occurrence in the upper Oligocene Zone NP25 and its FO is placed above the FO of H. truempyi.

Hole 898A: Sample 149-899B-6X-2, 75 cm.

FO of Tetralithoides symeonidesii

T. symeonidesii has been identified by Theodoridis (1984) in sediments recovered at ODP Sites 219, 231, 372, and 369. Sites 219 and 231 are located in the Indian Ocean, Site 372 is in the Mediterranean Sea, and Site 369 is situated on the continental slope off the Northwest Africa Margin, south of Leg 149 sites. Theodoridis (1984) reported a range from Zones NN2 to NN11. Its earliest occurrence is found in the upper part of Zone NP25 in Hole 898A and 899B. T. symeonidesii occurs rarely and sporadically from Zones NP25 through NN11. Its unique structure, easily identifiable, and its cosmopolitan distribution provide an additional useful marker for the upper part of Zone NP25.

Hole 898A: Sample 149-898A-28X-4, 114cm.

LOs of Sphenolithus ciperoensis, Reticulofenestra bisecta bisecta, and Pontosphaera enormis

S. ciperoensis occurs rarely in the uppermost part of its range, but its LO is consistent within the four sites investigated. The sharp decrease in abundance recorded lower in Zone NP25 has been frequently used in other studies to place the top of Zone NP25. Rare occurrences of S. ciperoensis above this level were frequently attributed to reworked specimens. According to the pattern observed in the Iberia Abyssal Plain, we exclude any possible reworking explanations for the presence of S. ciperoensis up to the LO of R. bisecta bisecta. Martini and Muller (1986) also indicated the reoccurrence of S. ciperoensis in the uppermost Oligocene Zone NP25, and suggested that climatic fluctuations may control the occurrence of S. ciperoensis.

The LO of R. bisecta bisecta is usually at the same level as the LO of S. ciperoensis. Reticulofenestra stavensis and Reticulofenestra bisecta filewiczii are present in the lower Miocene Zone NN1. The LO of P. enormis occurs with the LOs of S. ciperoensis and R. bisecta bisecta at the top of Zone NP25. At the Chattian-type section, Martini and Muller (1975) reported the presence of P. enormis up to the top of the Chattian, and Martini and Muller (1986) place the LO of Pontosphaera enormis at the level of the last reoccurrence of S. ciperoensis.

In accordance with Fornaciari et al. (1993) we use the LO of S. ciperoensis to place the Zone NP25/NN1 boundary, because the LO of H. recta, the original zonal marker of Martini (1971), is recorded in Zone NN2.

Hole 898A: Sample 149-898A-28X-3, 145 cm.

LO of Clausicoccus fenestratus

C. fenestratus occurs throughout the Oligocene and its LO is consistently above the LO of S. ciperoensis. Only forms with an inner bright cycle and a large central area, similar to the drawing of Prins (1979), have their LO in lowermost part of Zone NN1. Clausicoccus obruta, a form with only four perforations, has its LO in Zone NN2. Forms without an inner bright cycle belong to the genus Hughesius (Varol, 1989b), and are found throughout the lower Miocene. The abundance pattern of the ranges of C. fenestratus and Hughesius tasmaniae for Hole 900A are shown on Figure 14, but with different horizontal scales.

Hole 898A: Sample 149-898A-28X-2, 49 cm.

LOs of Sphenolithus delphix and Sphenolithus capricornutus

These two distinct sphenoliths have short ranges from the uppermost Oligocene Zone NP25 to the middle of Zone NN1 (Fig. 5). Although rare and sporadic in their occurrences, these two events are very reliable. Moreover, a very short, characteristic interval contains abundant forms of large S. delphix. This "triradiated" form possesses a very long apical spine and two extremely elongated proximal elements, and it occurs near the top of the range of S. delphix, together with frequent T. carinatus.

Hole 898A: "long triradiated" S. delphix: Sample 149-898A-28X-2, 49 cm.

Hole 898A: Sample 149-898A-28X-1, 99 cm.

FO of Sphenolithus aubryae

S. aubryae is observed from the uppermost part of Zone NN1 to Zone NN3 (Fig. 5) and it first occurs with small forms of Discoaster druggii (<15 µm). According to the original description, D. druggii is a large discoaster (larger than 15 µm). In this study, the base of Zone NN1 is drawn at the first occurrence of D. druggii (>15 µm). Forms similar to S. aubryae were reported, by Rio et al. (1990) from Leg 115 in the Indian Ocean (S. dissimilis-S. belemnos intergrade), ranging from the basal part of Zone NN2 and overlapping the range of S. belemnos. S. aubryae is not considered herein as being an intergrade Sphenolithus, since this form possesses some unique features (see "Appendix A"). S. aubryae was also observed, but not described by M.-P. Aubry (pers. comm., 1994)

Hole 899B: Sample 149-899B-3R-6, 59 cm.

FOs Discoaster druggii and Helicosphaera granulata

The abundance pattern, for Hole 900A, of the ranges of D. druggii (larger and smaller than 15 µm) is shown on Figure 15. D. druggii small is about 12 to 15 µm. At Hole 898A and 900A, small and large D. druggii occur together. At these two latter sites, the sampling resolution at this level is between two to three meters. In Hole 897C and 899B samples are closer, and small specimens of D. druggii are observed one meter below the occurrence of the large form. The FO of H. granulata is recorded with the FO of D. druggii at Hole 898A, and 899B, and few meters above, in the lower basal part of Zone NN2 at Holes 897C and 900A.

Hole 899B: Sample 149-899B-9R-5, 114cm.

FO of Calcidiscus tropicus (<6 µm)

The abundance pattern of the range of C. tropicus (<6 µm) for Hole 900A is shown on Figure 16. This form, easily distinguished by its relative large central opening, has a consistent FO in the lower part of Zone NN2. The FO of this small form of Calcidiscus is a reliable biohorizon, that has been found at the same level at the four sites.

Hole 898A: Sample 149-898A-26X-1, 102cm.

FO of Sphenolithus cometa

This species, easily distinguished from other Sphenolithus (see Appendix A), occurs in the middle part of Zone NN2, and may be helpful to precise the position of the LO of Helicosphaera recta.

Hole 899B: Sample 149-899B-3R-2, 103 cm.

LO of Helicosphaera recta

The abundance pattern of the range of H. recta for Hole 900A is shown on Figure 11. This species, which first occurs in the upper part of Zone NP22, has a consistent range throughout the early Miocene Zone NN1 to the middle of Zone NN2 and its LO is situated at the same level at the four Sites (Fig. 5). Martini and Worsley (1971) reported H. recta (= H. truncata) together with D. druggii in Zone NN2 from sediment recovered from the western equatorial Pacific (DSDP Hole 63-1), but use this taxon as the zonal marker for the top of Zone NP25 (defined in the same publication). Several authors also reported this species in the early Miocene Zones NN1 to NN2 (e.g., Perch-Nielsen, 1977). Gartner (1992) was probably the first to point out the important potential of this marker, and correlate the LO of H. recta with the chronozone C6Bn at DSDP Site 608 in the North Atlantic.

Near the top of its range, the two central openings of H. recta possess a slightly oblique bar, which may make the identification of the LO of H. recta difficult.

Hole 898A: Sample 149-898B-24X-4, 121 cm.

FO of Geminilithella rotula

The abundance pattern of the range of G. rotula for Hole 900A is shown on Figure 16 together with the range of Umbilicosphaera jafari. The FO of G. rotula was used by Theodoridis (1984) as a zonal marker in his Mediterranean biozonal schemes. Theodoridis (1984) defines a Triquetrorhabdulus milowii Zone from the first occurrence of G. rotula to the FO of Sphenolithus heteromorphus (or LO of S. belemnos), and Triquetrorhabdulus martinii Subzone from the FO of G. rotula to the LO of Triquetrorhabdulus carinatus (or FO of Sphenolithus belemnos). At the four Sites from Leg 149, the FO of G. rotula has been found very useful. The distinction of this biohorizon may be difficult because of the presence of large specimens of Umbilicosphaera jafari (= Geminilithella jafari Backman, 1980). Only specimens of G. rotula larger than 5 µm were considered.

Hole 898A: Sample 149-898A-24X-2, 28 cm.

LO of Camuralithus pelliculatus

This species has a consistent occurrence from the upper Oligocene to the upper part of Zone NN2. Its characteristic rim and central area make this marker easily identifiable, and its LO appears to be a good biohorizon. The slightly different position of the LO of C. pelliculatus in the four sites is caused by unfamiliarity in recognizing this new species.

Hole 899B: Sample 149-899B-2R-1, 35 cm.

LO of Ilselithina fusa

The abundance pattern range of I. fusa at Hole 900A is shown on Figure 10. This species has a consistent occurrence from the upper part of Zone NP21 to the upper part of Zone NN2. This biohorizon is used on Figure 9 to correlate the four sites. The LO of I. fusa is recorded above the LO of H. recta, at the level of the FO of G. rotula or slightly above. Gartner (1992) used I. fusa as a marker, and mentions the presence of two morphotypes in lower Miocene sediments from ODP Site 608: one morphotype, present from the Oligocene, with 12 to 14 petals in the basal cycle of elements, and a second one, restricted to the lower Miocene with six elements. The specimens recovered from lower Miocene sediments from Leg 149 have 10 to 14 proximal elements, and are clearly identifiable by their robust distal spine (crown), which has only 5 to 7 elements (see transferred specimen Pl. 12, figs. 22-26).

Hole 899B: Sample 149-899B-1R-2, 104cm.

LO of Helicosphaera euphratis

This large, distinctive helicolith has a consistent LO between the LO of I. fusa and the FO of Reticulofenestra pseudoumbilicus at the four Sites from Leg 149. Although rare near the top of its range, the LO of H. euphratis (large morphotype) is a useful biohorizon in the upper Zone NN2. The abundance pattern range of H. euphratis is shown on Figure 11.

Hole 898A: Sample 149-898A-23X-5, 70 cm.

LO of Sphenolithus conicus

Though S. conicus is rare and sporadic in lower Miocene sediments from Leg 149, the LO of this species is recorded in the upper part of Zone NN2. The placement of this biohorizon is in concordance with the position of the LO of S. conicus documented below the FO of S. belemnos by Gartner (1992). Fornaciari et al. (1990) reported the LO of S. conicus at the level of S. belemnos.

Hole 898A: Sample 149-898A-23X-4, 51 cm.

FO of Reticulofenestra pseudoumbilicus (>7 µm)

Only specimens larger than 7 µm, with an open central area, are included in R. pseudoumbilicus (see Young et al., 1994). Smaller forms are either included in Reticulofenestra minutula or in Reticulofenestra haqii according to the outline and size of the central area (Backman, 1980; Flores, 1989). In the upper part of Zone NN2, Reticulofenestra lockeri becomes less common, and R. minuta increases in size to more than 7 µm. The abundance pattern of the ranges of R. pseudoumbilicus and R. gelida (form with a small opening) for Hole 900A are shown on Figure 17. Sharp first occurrence picks at slightly different levels are observed for both R. pseudoumbilicus and R. gelida and both species show a sporadic occurrence to the upper part of Zone NN5.

Hole 898A: Sample 149-898A-22X-5, 86 cm.

FO of Triquetrorhabdulus serratus

Triquetrorhabdulus serratus occurs at two different levels: first from the upper part of Zone NN2 to the lower part of Zone NN4, and second from Zone NN5 to its LO in Zone NN6.

Hole 900A: Sample 149-900A-25R-5, 37 cm.

FOs of Helicosphaera ampliaperta and Sphenolithus belemnos, and the LO of Triquetrorhabdulus challengeri

The FOs of H. ampliaperta and S. belemnos are observed at the same level in Holes 898A, 899A, and 900A. These events are recorded in the upper part of Zone NN2, just above the FO of T. serratus. The LO of T. challengeri and the FO of H. ampliaperta are recorded together in Hole 897C, and within a short interval in other sites.

Hole 900A: Sample 149-900A-24R-4, 19 cm.

LO of Sphenolithus aubryae

The LO of S. aubryae is recorded within the lower part of the range of S. belemnos.

Hole 898A: Sample 149-898A-22X-4, 35 cm.

LO of Hughesius tasmaniae

The LO of H. tasmaniae near the top of Zone NN2 is consistent between the four sites, and is considered as a good biohorizon. The abundance pattern of the range of this species is shown on Figure 14.

Hole 898A: Sample 149-898A-22X-3, 100cm.

LO of Triquetrorhabdulus carinatus

The LO of T. carinatus occurs just below the LO of S. belemnos at Sites 898 and 900. At Site 897, the interval corresponding to this interval was not recovered. Core 149-897C-32R was lost. At Site 899, the LOs of H. tasmaniae, T. carinatus, and S. belemnos occur in the same sample, and they may indicate the presence of a condensed interval.

Hole 898A: Sample 149-898A-22X-2, 73 cm.

FO of Helicosphaera scissura

This bioevent is observed in the upper part of Zone NN3 at Sites 897, 898, and 900.

Hole 898A: Sample 149-898A-21-CC.

LO of Sphenolithus belemnos

The LO of S. belemnos is shown for Site 900 on Figure 13. The same abundance pattern is observed at the other sites. No overlap between the range of S. heteromorphus and S. belemnos are observed. These two bioevents are close, but always separated by a short interval.

Hole 900A: Sample 149-900A-24R-2, 128 cm.

FO of Sphenolithus heteromorphus

The abundance pattern of the range of S. heteromorphus for Hole 900A is shown on Figure 13 together with the range of S. belemnos.

Hole 900A: Sample 149-900A-24R-2, 61 cm.

LO of Sphenolithus dissimilis

The upper part of the range of Sphenolithus dissimilis has a very short overlap with the lower range of S. heteromorphus.

Hole 900A: Sample 149-900A-23R-6, 83 cm.

FO of Cryptococcolithus mediaperforatus

Small specimens of C. mediaperforatus (<5 µm) are present in Zone NN4. Larger forms occur after the LO of H. ampliaperta in Zone NN5.

Hole 900A: Sample 149-900A-23R-3, 101 cm.

FO of Discoaster moorei

This distinctive species of Discoaster first occurs in the lower part of Zone NN4.

Hole 900A: Sample 149-900A-23R-2, 137 cm.

FO of Calcidiscus premacintyrei (<9 µm)

The FO of C. premacintyrei (<9 µm) is detected in the upper part of Zone NN4. The abundance pattern and the range of C. premacintyrei (smaller and larger than 9 µm) are given on Figure 16 for Hole 900A. A sharp increase of C. premacintyrei is observed in both small and large forms at the end of Zone NN5.

Hole 899B: Sample 149-899B-14R-1, 110 cm.

FO of Discoaster petaliformis and Discoaster exilis

These two distinct forms of discoaster occur together at Sites 898 and 899.

Hole 899B: Sample 149-899B-14R-1, 40 cm.

LOs of Helicosphaera ampliaperta and Triquetrorhabdulus milowii

The LO of these two markers is recorded together in the four sites from Leg 149. The abundance pattern of the range of H. ampliaperta for Site 900 is shown on Figure 11.

Hole 900A: Sample 149-900A-22R-1, 122 cm.

LO of Helicosphaera obliqua

The lower part of Zone NN5 is marked by a short succession of LOs among the genus Helicosphaera. The LO of H. obliqua occurs near the LO of H. ampliaperta at the bottom of Zone NN5 (Fig. 11).

Hole 900A: Sample 149-900A-21R-3, 139cm.

FO of Discoaster musicus

The FO of this distinct Discoaster occurs in the lower part of Zone NN5.

Hole 898A: Sample 149-898A-19X-6, 80 cm.

LO of Helicosphaera perch-nielseniae

This characteristic form of Helicosphaera has its LO in the lower part of Zone NN5 (Fig. 11).

Hole 900A: Sample 149-900A-21R-1, 142cm.

LO of Helicosphaera elongata

This narrow-shaped species is the last Oligocene species of Helicosphaera. Its LO is observed in the middle part of Zone NN5.

Hole 900A: Sample 149-900A-21R-1, 97 cm.

LO of Helicosphaera waltrans

H. waltrans has a short range from Zones NN4 to NN5, and its LO is a very distinct event in the upper part of Zone NN5 in Site 900. 

Hole 900A: Sample 149-900A-20R-2, 91 cm.

LO of Sphenolithus heteromorphus

The LO of Sphenolithus heteromorphus is a useful middle Miocene biohorizon. The abundance pattern of S. heteromorphus for Site 900 (Fig. 13) shows a consistent and frequent occurrence to the top of its range.

Hole 900A: Sample 149-900A-20R-1, 26 cm.

LO of Triquetrorhabdulus serratus

This distinct event is very close to the LO of S. heteromorphus. In Site 900 this event is observed just above it, and in Site 898, a few cm below it.

Hole 900A: Sample 149-900A-19-CC

FO of Triquetrorhabdulus rioi

This species occurs near the base of Zone NN6, and below the FO of Triquetrorhabdulus rugosus.

Hole 898A: Sample 149-898A-19X-1, 106 cm.

FO of Triquetrorhabdulus rugosus

This species is rare at the base of its range. A sharp increase in its abundance is observed few cm above its FO, and defines a distinct biohorizon. The LO of T. rioi is recorded within the lower part of the range of T. rugosus. No overlap occurs between the stratigraphic ranges of T. rugosus and S. heteromorphus.

Hole 897C: Sample 149-897C-29R-1, 126 cm.

LO of Coronocyclus nitescens

Several morphotypes of C. nitescens have been differentiated. The abundance pattern of the ranges of two of these forms, C. nitescens with a thin rim and Coronocyclus with a thin elliptical rim are shown on Figure 14. The elliptical morphotype of C. nitescens has its LO in the lower part of Zone NN6, whereas circular C. nitescens occurs almost to the upper part of Zone NN6. The two plots of the abundance are almost similar from Zones NP25 to NN6.

Hole 897C: Sample 149-897C-28-CC.

FOs of Discoaster cf. D. bollii

The FO of these long-rayed Discoaster bollii (see "Appendix A") is observed in Site 900 with the FO of D. kugleri, and few meters below in Site 898.

Hole 898A: Sample 149-898A-18X-7, 42 cm.

FOs of Discoaster kugleri and Calcidiscus macintyrei (>11 µm)

The abundance pattern of the range of these two markers is shown on Figure 15 and Figure 16. Only large (>11 µm) specimens of Calcidiscus with a close central area are included in C. macintyrei (see "Appendix A").

Hole 898A: Sample 149-898A-18X-5, 53 cm.

LOs of Calcidiscus premacintyrei and Cyclicargolithus abisectus (>10 µm)

The abundance pattern of these two markers is shown respectively on Figure 16 and Figure 12. These events may be correlated with a general decrease in the size of the total assemblage of coccoliths.

Hole 900A: Sample 149-900A-18R-2, 48 cm.

LO of Discoaster kugleri and Cyclicargolithus floridanus (last consistent occurrence)

Both events are recorded together at Site 900. The plots of the abundance pattern of these two species are shown on Figure 12 and Figure 15. Rare, and sporadic C. floridanus are present to the middle Zone NN8.

Hole 900A: Sample 149-900A-17R-2, 89 cm.

FO of Discoaster bollii

The FO of D. bollii is observed in Zone NN8 few meters below the upper Miocene hiatus, and is only recorded at Site 900. At Sites 897, 898, and 899, the lower part of Zone NN8 is missing.

Hole 900A: Sample 149-900A-16R-2, 71 cm.

After a hiatus involving uppermost middle/lower upper Miocene sediments, the following bioevents are observed:

FO of Discoaster quinqueramus var. A

This variety of D. quinqueramus (with a small knob, see "Appendix A") occurs just above the upper Miocene unconformity. The abundance pattern of the range of this species shows a consistent occurrence throughout Zone NN11. According to the abundance pattern of other Discoaster taxa (e.g., D. bellus) observed in Site 900, this event is believed to be close to the base of Zone NN11.

Hole 900A: Sample 149-900A-15R-4, 43 cm.

FO of Discoaster tamalis

Rare to few D. tamalis occurs sporadically from the lower part of Zone NN11 in Site 900. The FO of four-rayed Discoaster brouweri (D. tamalis) is found 40 cm above the FO of Discoaster brouweri with 3 rays. This latter species shows a consistent abundance pattern range through the upper Miocene. A 5-rayed Discoaster brouweri, is also present from the lower part of Zone NN11.

Hole 900A: Sample 149-900A-15R-4, 3 cm.

FCO of Discoaster pentaradiatus

Its FO is reported in the upper part of Zone NN10 (e.g., Gartner, 1992) and has a rare and discontinuous distribution along its lower range. Therefore, the occurrence of few D. pentaradiatus at the beginning of its range in Hole 900A is interpreted as a FCO. Because of the hiatus, the lower part of its range is not recorded.

Hole 900A: Sample 149-900A-15R-3, 30 cm.

FO of Gephyrocapsa sp. (<3.5 µm)

The FO of small Gephyrocapsa sp. has been observed in the lower part of Zone NN11. Though this species has a sporadic occurrence in the upper Miocene, common Gephyrocapsa sp. are recorded in the middle of the lower part of Zone NN11. Gartner (1992) reported the occurrence of small Gephyrocapsa sp. from Site 608 in the North Atlantic near the middle part of Zone NN11.

Hole 900A: Sample 149-900A-14R-7, 44 cm.

LO of Discoaster bellus

The LO of D. bellus is a reliable event in the lower part of Zone NN11. This event occurs slightly above the FCO of D. pentaradiatus.

Hole 900A: Sample 149-900A-14R-7, 44 cm.

FO of Discoaster surculus

The FO of this distinct species is observed in the lower part of Zone NN11. At the beginning of its range in Site 900, few specimens are observed, and the abundance pattern of the range of D. surculus shows a discontinuous occurrence.

Hole 900A: Sample 149-900A-14R-6, 66 cm.

FO of Discoaster asymmetricus

The FO of D. asymmetricus is a late Miocene biohorizon. Though rare at the beginning of its range in Zone NN11, D. asymmetricus is more abundant and shows a consistent occurrence in the uppermost Miocene. This form has been carefully distinguished from other asymmetric 5-rayed Discoaster species (e.g., D. variabilis S ray asymmetric).

Hole 900A: Sample 149-900A-14R-5, 142 cm.

LO of Minylitha convallis

The LO of M. convallis is a distinct event in Site 900, and is used to separate Zone NN11 into a lower and upper part.

Hole 900A: Sample 149-900A-14R-3, 63 cm.

FO of Amaurolithus amplificus

The FOs of Amaurolithus primus, Amaurolithus ninae, Amaurolithus delicatus, and Amaurolithus amplificus are observed in the same sample in Site 900. This is due to the poor recovery of this interval. Only sediments from the core-catcher were recovered.

Hole 900A: Sample 149-900A-13-CC.

LO of Discoaster quinqueramus var. A

The LO of D. quinqueramus var. A. is used in this study to place the Zone NN11/NN12 boundary.

Hole 900A: Sample 149-900A-12-CC.

FO of Helicosphaera sellii

The FO of H. sellii is recorded in the lowermost part of Zone NN12. In Site 900, this bioevent occurs 30 cm above the LO of D. quinqueramus var. A.

Hole 900A: Sample 149-900A-12R-4, 10 cm.

LO of Triquetrorhabdulus rugosus

At Sites 897, 899, and 900, the LO of T. rugosus is observed in the lower part of Zone NN12 (= Zone CN10a of Okada and Bukry's zonal scheme, 1980), above the LO of D. quinqueramus var. A. Though rare, in the upper part of its range, this event is consistent and reliable between Site 897, 899, and 900.

Hole 900A: Sample 149-900A-12R-4, 10 cm.

LO of Discoaster deflandrei

The last consistent occurrence of Discoaster deflandrei is recorded in Hole 900A in Sample 149-900A-18R-1, 78 cm within Zone NN7. Rare specimens of D. deflandrei are observed above Core 149-900A-18R in Zones NN8 and NN11 (Fig. 15, Table 9). Theodoridis (1984) reported this species ranging up to the late Miocene Zone NN11 (= C. pelagicus Zone of Theodoridis, 1984) in land sections from Sicily. The presence of D. deflandrei in upper Miocene sediments is considered as a real event, and its LO is placed in the uppermost Miocene, at the base of Zone NN12.

Hole 900A: Sample 149-900A-12R-2, 106 cm.

LO of Amaurolithus amplificus

The LO of A. amplificus is observed near the bottom of Zone NN12 in Site 900 in the uppermost Miocene within a short interval between the LO of D. quinqueramus var. A, and the FO of Ceratolithus spp. (Sample 149-900A-11R-5, 45 cm). This latter interval corresponds to the Triquetrorhabdulus rugosus Subzone (CN10a) in the zonal scheme of Bukry (1973, 1975).

Hole 900A: Sample 149-900A-12R-1, 112 cm.

LOs of Cryptococcolithus mediaperforatus and Coccolithus miopelagicus (>13 µm)

The LO of C. mediaperforatus (specimens between 6 and 7 µm), observed in Holes 899A and 900A, is recorded in the lower part of Zone NN12. This species is rare near the end of its range, and its LO may be situated in the lowermost part of the Pliocene. More detailed biostratigraphic data and correlation to magnetostratigraphy records of the upper range of C. mediaperforatus are necessary to determine if its LO position is above the Miocene/Pliocene boundary. The abundance pattern range of Coccolithus miopelagicus in Hole 900A is shown on Figure 12, together with the plot of the abundance of C. pelagicus. The presence of rare C. miopelagicus (coccolith length between 13 and 15 µm) is recorded up to the upper part of Zone NN11. At Sites 897, 899, and 900, a decrease in the abundance of C. miopelagicus is observed in the lower part of Zone NN8, and also a marked increase in abundance occurs in the early part of Zone NN11. The presence of C. miopelagicus in Zones NN11 and NN12 is not considered to be due to reworking. The distribution pattern of C. miopelagicus corresponds to the variation of the distribution of Coccolithus pelagicus, and to that of Reworked Cretaceous (Table 9).

It has been reported in other studies (e.g., in NN11 by Gartner, 1992), but never considered as a reliable bioevent. Only the abrupt decrease in abundance observed in NN8 is reported by different studies (e.g., Raffi et al., 1995).

Hole 900A: Sample 149-900A-12R-1, 48 cm.

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