Eocene sediments in Hole 897C (40°50.33'N, 12°28.44'W, water depth = 5315.2 m) were recognized between Samples 149-897C-51R-1, 11-12 cm, and 59R-2, 14-15 cm, and consist mainly of nannofossil chalk, calcareous claystone, claystone, siltstone, and sandstone. Calcareous nannofossils are abundant in most samples; their preservation is either poor or moderate (Table 2, Table 3).
Sample 149-897C-50R-3, 71-72 cm, is considered the first sample below the Eocene/Oligocene boundary, based on the LO of Discoaster barbadiensis and Discoaster saipanensis.
The interval from Samples 149-897C-51R-1, 11-12 cm, through 54R-2, 52-53 cm, is between the FO of the Isthmolithus recurvus and the LO of Discoaster barbadiensis and Discoaster saipanensis and is assigned to the Isthmolithus recurvus Zone (NP19/20, CP15b). The assemblage is dominated by Coccolithus pelagicus, Cyclicargolithus floridanus, Cyclicargolithus formosus, Dictyococcites bisectus, and Zygrhablithus bijugatus.
Samples 149-897C-54R-2, 136-137 cm, to 51R-1, 11-12 cm, are placed in the Chiasmolithus oamaruensis Zone (NP18, CP15a), based on the absence of Isthmolithus recurvus and the occurrence of Chiasmolithus oamaruensis. The last occurrence of Sphenolithus obtusus is in Sample 149-897C-54R-3, 2-3 cm, within this zone. The dominant species are Coccolithus pelagicus, Cribrocentrum reticulatum, Cyclicargolithus floridanus, Cyclicargolithus formosus, Dictyococcites bisectus, Discoaster barbadiensis, and Lanternithus minutus.
Samples 149-897C-55R-1, 74-75 cm, to 55R-3, 75-76 cm, are assigned to the Discoaster saipanensis Zone (NP17, CP14b) based on the absence of both Chiasmolithus oamaruensis and Chiasmolithus solitus. The dominant species are similar to that of Zone NP18.
The Discoaster tani nodifer Zone (NP16) or Discoaster bifax Subzone (CP14a) encompasses the interval from Samples 149-897C-55R-4, 67-68 cm, to 57R-5, 70-71 cm, based on the co-occurrence of Chiasmolithus solitus and Reticulofenestra umbilicus (>14 µm). Rhabdosphaera gladius, used by Martini (1971) to divide Zones NP15 and NP16, was not found is this hole. Therefore, Zones NP15 and NP16 are not distinguishable. The FO of Cribrocentrum reticulatum is observed in Sample 149-897C-57R-2, 128-129 cm.
Okada and Bukry (1981) proposed both the FO of Reticulofenestra umbilicus and the LO of Discoaster bifax to divide Zones CP13 and CP14, but the FO of Discoaster bifax in the Leg 149 sediments (see also Hole 900A) is always earlier than the FO of Reticulofenestra umbilicus. In addition, Discoaster bifax is normally rare and hard to recognize in the Leg 149 sediments. Therefore, as stated previously, I use the FO of Reticulofenestra umbilicus to divide the Zones CP13/14 boundary rather than the FO of Discoaster bifax.
The interval between Samples 149-897C-58R-1, 144-145 cm, and 59R-2, 14-15 cm, is assigned to the Nannotetrina fulgens Zone (NP15 or CP13) based on the FO of Nannotetrina fulgens and the absence of Reticulofenestra umbilicus. The last Chiasmolithus gigas appears in Sample 149-897C-59R-2, 14-15 cm.
Hole 897C was terminated owing to a stuck drill pipe; therefore, Hole 897D (40°50.31'N, 12°28.51'W, water depth = 5315.8 m) was drilled to acquire additional sediment just below the total depth of Hole 897C. The first three cores of Hole 897D are middle Eocene in age and consist mainly of nannofossil claystone and claystone. Calcareous nannofossils are mostly abundant or common in these middle Eocene samples but are normally poorly preserved (Table 4).
Samples 149-897D-1R-1, 146-147 cm, to 3R-2, 47-48 cm, are assigned to the Nannotetrina fulgens Zone (NP15 or CP13) based on the occurrence of Nannotetrina fulgens and the absence of Reticulofenestra umbilicus. The LO of Rhabdosphaera gladius is not an applicable datum owing to the absence of this taxon. Discoaster bifax is present from Samples 149-897D-1R-3, 146-147 cm, to 1R-3, 22-23 cm. The FO of Chiasmolithus gigas is in Sample 149-897D-2R-CC in Zone CP13. The FO of Sphenolithus furcatolithoides is in Sample 149-897D-2R-4, 4-5 cm, which is slightly higher than the FO of Chiasmolithus gigas.
Samples 149-897D-3R-2, 140-141 cm, to 3R-4, 22-23 cm, are assigned to the Discoaster sublodoensis Zone (NP14, CP12b) based on the occurrence of Discoaster sublodoensis and the absence of Nannotetrina fulgens. Few Rhabdosphaera inflata were recognized in this interval. Therefore, according to Okada and Bukry's (1980) zonation scheme, this interval is placed in the Rhabdosphaera inflata Subzone (CP12b).
Only one core (Core 14R) retrieved in Hole 899B (40°46.347'N, 12°16.063'W, water depth = 5291.0 m) belongs to the Eocene (Table 5). Calcareous nannofossils are generally abundant in these samples, and their preservation is moderate. Isthmolithus recurvus, Discoaster barbadiensis, and Discoaster saipanensis are found in all samples from this core, and it is assigned to the Isthmolithus recurvus Zone (NP19/CP15b). The dominant species are Coccolithus pelagicus, Cyclicargolithus floridanus, Coccolithus formosus, and Sphenolithus moriformis.
Hole 900A (46°40.994'N, 11°36.252'W, water depth = 5036.8 m) contains the thickest and most complete Eocene section of the Leg 149 holes (Table 6, Table 7). These sediments consist of nannofossil chalk, nannofossil claystone, claystone, clay siltstone, silt sandstone, and fine sandstone, all of which were deposited as turbidites or contourites. Calcareous nannofossils are generally abundant or common in these samples, and their preservation is moderate or poor.
Sample 149-900A-53R-1, 113-114 cm, is considered the first sample below the Eocene/Oligocene boundary because Discoaster barbadiensis and Discoaster saipanensis were not found in the samples above.
The Isthmolithus recurvus Zone (NP19/20, CP15b) extends from Samples 149-900A-53R-1, 113-114 cm, to 55R-CC, based on the co-occurrence of Discoaster barbadiensis, Discoaster saipanensis, and Isthmolithus recurvus. Nannofossils are moderately preserved. The nannofossil assemblage is dominated by Coccolithus pelagicus, Cyclicargolithus floridanus, Cyclicargolithus formosus, Dictyococcites bisectus, Lanternithus minutus, Sphenolithus moriformis, and Zygrhablithus bijugatus.
Samples 149-900A-56R-1, 37-38 cm, to 57R-4, 31-32 cm, are placed in the Chiasmolithus oamaruensis Zone (NP18, CP15b) based on the occurrence of Chiasmolithus oamaruensis and the absence of Isthmolithus recurvus. The LO of Sphenolithus obtusus is in Sample 149-900A-57R-2, 101-102 cm. Nannofossil assemblages in this zone are moderately preserved, and the dominant species are the same as in NP 19/20. The boundary between the middle Eocene and the upper Eocene is placed between Samples 149-900A-57R-4, 31-32 cm, and 57R-5, 34-35 cm.
Samples 149-900A-57R-5, 34-35 cm, to59R-l, 119-120 cm, are assigned to the Discoaster saipanensis Zone (NP17, CP14b) based on the absence of both Chiasmolithus oamaruensis and Chiasmolithus solitus.
Samples 149-900A-59R-2, 26-27 cm, to 63R-CC, are placed in the Discoaster tani nodifer Zone (NP16) or the Discoaster bifax Subzone (CP14a) based on the co-occurrence of Chiasmolithus solitus and Reticulofenestra umbilicus. Only one specimen of Rhabdosphaera gladius was found in Sample 149-900A-65R-2,48-49 cm (Pl. 2, Fig. 20). The LO of Rhabdosphaera gladius is not used to mark the top of NP15. Instead, the FO of R. umbilicus is used here to mark CP13/14 boundary.
Samples 149-900A-64R-1, 142-143 cm, to 70R-1, 11-12 cm, are assigned to the Nannotetrina fulgens Zone (NP15 or CP13) based on the occurrence of N. fulgens and the absence of Reticulofenestra umbilicus. The other nannofossil events in this interval are the FO of Discoaster bifax in Sample 149-900A-68R-1, 83-84 cm, and the FO of Chiasmolithus gigas in Sample 149-900A-69R-2, 107-108 cm, where the lowest occurrence of Sphenolithus furcatolithoides was found.
Samples 149-900A-70R-2, 48-49 cm, to 74R-2, 46-47 cm, are assigned to the Discoaster sublodoensis Zone (NP14, CP12) based on the occurrence of Discoaster sublodoensis and the absence of Nannotetrina fulgens. The LO of Rhabdosphaera inflata is in Sample 149-900A-70R-2,48-49 cm, just below the boundary between Zones NP14 and NP15. However, the first Rhabdosphaera inflata was found in Sample 149-900A-74R-1, 38-39 cm, just one sample above the first Discoaster lodoensis. Therefore, if the FO of Rhabdosphaera inflata is used to subdivide Zone CP12, then CP12a is represented by only Sample 149-900A-74R-2, 46-47 cm.
The short interval from Samples 149-900A-75R-1, 56-57 cm, to 76R-1, 34-35 cm, is placed in the Discoaster lodoensis Zone (NP12/ 13, CP10-11), based on the occurrence of Discoaster lodoensis and the absence of Discoaster sublodoensis. The FO of Toweius crassus was used by Okada and Bukry (1980) to divide the Tribrachiatus orthostylus (CP10) and Discoaster orthostylus (CP11) Zones. However, Toweius crassus is not present in the Leg 149 sediments; therefore, Zones CP10 and CP11 cannot be distinguished. The dominant species in this interval are Coccolithus pelagicus, Discoaster lodoensis, and Reticulofenestra dictyoda.
A short interval from Samples 149-900A-77R-2, 120-121 cm, to 77R-3, 3-4 cm, is assigned to the combined Tribrachiatus contortus (NP10, CP9a) and Discoaster binodosus Zones (NP11, CP9b), based on the occurrence of Tribrachiatus bramlettei and the absence of Discoaster lodoensis.