Coring of Hole 1067A (40°40.950´N, 11°35.750´W, water depth = 5020.9 m) began 648 meters below seafloor (mbsf), and Eocene sediments were recognized between Samples 173-1067A-1R-1, 34-36 cm, and 13R-1, 30-31 cm (Fig. F1). The stratigraphic distribution of nannofossils is indicated in Table T1. Key biohorizons are listed in Table T2, along with their sample interval and average depth. These sediments consist mainly of grayish green calcareous siltstones, grayish green nannofossil claystones, and moderate brown claystones. Calcareous nannofossils are abundant in most samples. Their preservation is generally good to moderate, grading to poor downhole, and is facies controlled.
Samples 173-1067A-1R-1, 34-36 cm, through 1R-CC, 21-23 cm, are middle Eocene in age and belong to the Discoaster bifax Zone (CP14a/NP16), based on the FO of D. bifax. Reticulofenestra umbilica is also used by Okada and Bukry (1980) to mark the beginning of this zone. This marker is not employed in this study, as R. umbilica appears sporadically and Reticulofenestra samodurovii has been shown to grade into R. umbilica, with size being conventionally used to separate the two species (Perch-Nielsen, 1985). Common assemblage nannofossils in this zone are Chiasmolithus solitus, Coccolithus pelagicus, Discoaster barbadiensis, Girgisia gammation, Reticulofenestra dictyoda, R. samodurovii, and Sphenolithus moriformis. The nannofossils are abundant and well to moderately preserved.
The Nannotetrina quadrata Zone (CP13/NP15) of Okada and Bukry (1980) is broken into three subzones. The Birkelundia staurion "gap" Subzone (CP13c) is demarcated by the LO of Chiasmolithus gigas and the absence of D. bifax and R. umbilica. This subzone occurs from Samples 173-1067A-2R-1, 121-122 cm, through 2R-CC, 13-16 cm. This subzone contains common nannofossils represented by Coccolithus formosus, C. pelagicus, G. gammation, R. dictyoda, Sphenolithus furcatolithoides, S. moriformis, and Sphenolithus radians, which are moderately preserved. The C. gigas Subzone (CP13b) occurs from Samples 173-1067A-3R-1, 34-35 cm, to 5R-3, 8-9 cm, and is marked by the presence of C. gigas. This subzone contains several poorly preserved and barren intervals that occur in siltstone and claystone layers. Sample 173-1067A-5R-3, 48-49 cm, is the first sample in the Discoaster strictus Subzone (CP13a) of Okada and Bukry (1980). This interval is marked by the absence of C. gigas and the FO of Nannotetrina fulgens (N. quadrata of other authors). The FO of N. fulgens is difficult to pinpoint because of the overgrowth of most specimens. Some authors use the FO of the Nannotetrina genus to mark the beginning of Subzone CP13a (Perch-Nielsen, 1985), but this genus appears ~6 m below the LO of Rhabdosphaera inflata in Hole 1067A. This study uses the last appearance of few specimens of R. inflata to mark the bottom of Subzone CP13a. Rare R. inflata specimens observed above Sample 173-1067A-7R-2, 32-33 cm, are considered reworked.
The Rhabdosphaera inflata Subzone (CP12b) begins with Sample 173-1067A-7R-3, 32-33 cm, and continues through Sample 173-1067A-8R-4, 30-31 cm. This subzone is marked by the occurrence of R. inflata. Nannofossils are moderately preserved throughout this interval and are represented by C. pelagicus, Discoaster barbadensis, Discoaster deflandrei, Discoaster tanii, R. dictyoda, S. moriformis, and Zygrhablithus bijugatus. The Discoaster kuepperi Subzone (CP12a) is marked by the absence of R. inflata and the presence of D. sublodoensis and begins with Sample 173-1067A-8R-CC, 23-25 cm. Nannofossils are commonly present and poorly preserved throughout this interval, which is characterized by the presence of C. pelagicus, D. barbadensis, R. dictyoda, and Z. bijugatus. The middle/early Eocene boundary is placed between Samples 173-1067A-9R-3, 37-38 cm, and 9R-3, 121-122 cm, based on the FO of D. sublodoensis.
The Discoaster lodoensis Zone (CP11/NP13) extends from Sample 173-1067A-9R-3, 121-122 cm, through 11R-1, 36-37 cm. The boundary between Zones CP11/CP10 (NP13/NP12) in this study is based on the LO of Tribrachiatus orthostylus, as C. crassus cannot be identified because of poor preservation. C. pelagicus, D. barbadensis, and D. lodoensis dominate this moderately preserved assemblage.
The T. orthostylus Zone (CP10/NP12) begins with Sample 173-1067A-11R-1, 119-120 cm, and continues through Sample 173-1067A-11R-2, 121-122 cm. This short interval contains moderately preserved common nannofossils represented by C. pelagicus, S. moriformis, and T. orthostylus.
Sample 173-1067A-11R-3, 40-41 cm, begins the Discoaster binodosus Subzone (CP9b/NP11). This "gap" zone is marked by the absence of D. lodoensis and Tribrachiatus contortus. Nannofossils are common and moderately to poorly preserved, and there are two barren intervals. Common nannofossils in this interval are C. pelagicus, D. barbadensis, D. deflandrei, S. moriformis, and T. orthostylus. Sample 173-1067A-12R-CC, 10-12 cm, contains the first T. orthostylus and no T. contortus and is the last sample in Subzone CP9b.
Subzone CP9a (Okada and Bukry, 1980) is marked by the presence of D. diastypus and T. contortus, and the corresponding Zone NP10 (Martini, 1971) is marked by the FO of T. bramlettei. These events are not synchronous (Berggren et al., 1995), all occurring slightly before the currently drawn Paleocene/Eocene boundary. Because of preservational constraints and the scarcity of both Tribrachiatus markers, this study bases the beginning of the Eocene epoch and the bottom of Zones CP9a/NP10 on the FO of D. diastypus, even though a solid magnetochronologic age for the FO of D. diastypus has not been recorded (Berggren et al., 1995). Ladner and Wise (Chap. 5, this volume) have also adopted this definition. The lowermost Eocene zone is represented by three samples from Samples 173-1067A-12R-CC, 25-27 cm, to 13R-1, 30-31 cm. Nannofossils are abundant and moderately preserved, although one interval of grayish brown clay is barren. The nannofossil assemblage shows poor diversity, being dominated by D. diastypus, C. pelagicus, and S. moriformis.
Coring of Hole 1068A (40°40.955´N, 11°36.720´W, water depth = 5043.9 m) began at 711.3 mbsf (Fig. F1) and contains Eocene sediments between Samples 173-1068A-1R-1, 35-36 cm, and 8R-3, 7-8 cm. Calcareous nannofossils are abundant and moderately preserved throughout the grayish green calcareous siltstones, light gray-green nannofossil chalks, and greenish gray calcareous claystones of this interval and are listed in Table T3. Moderately to poorly preserved calcareous nannofossils are found in the moderately brown claystones and greenish gray calcareous sandy siltstones, which are occasionally barren of calcareous nannofossils. Key biohorizons, their sample interval, and their average depths are listed in Table T4.
Sample 173-1068A-1R-1, 35-36 cm, is considered the first sample in the middle Eocene D. sublodoensis Zone (CP12/NP14). Okada and Bukry (1980) broke this zone into two subzones (CP12a and CP12b) based on the FO of R. inflata. Based on the occurrence of R. inflata, Samples 173-1068A-1R-1, 35-36 cm, through 1R-6, 36-37 cm, represent the R. inflata Subzone CP12b. Samples 173-1068A-1R-CC through 5R-2, 35-36 cm, represent the D. kuepperi Subzone CP12a, based on the FO of D. sublodoensis and the absence of R. inflata. The nannofossil assemblages are moderately well preserved and are dominated by C. formosus, C. pelagicus, D. barbadensis, D. deflandrei, R. dictyoda, S. moriformis, and Z. bijugatus. The middle/lower Eocene boundary is placed between Sample 173-1068A-5R-1, 121-122 cm, and 5R-2, 35-36 cm, based on the FO of D. sublodoensis. The D. lodoensis "gap" Zone (CP11/NP13) begins with Sample 173-1068A-5R-2, 35-36 cm, based on the absence of D. sublodoensis and T. orthostylus. The FO of C. crassus could not be determined in these samples because of overgrowth and dissolution.
Sample 173-1068A-6R-3, 121-122 cm, marks the beginning of the T. orthostylus Zone (CP10/NP12) based on the presence of T. orthostylus. This zone is represented by five samples, three of which are barren claystones.
Sample 173-1068A-6R-6, 38-39 cm, begins the D. binodosus "gap" Zone (NP11/CP9b), based on the absence of D. lodoensis and T. contortus. The nannofossil assemblage is moderately well preserved and dominated by C. formosus, C. pelagicus, D. barbadensis, D. kuepperi, T. orthostylus, and Z. bijugatus.
The T. contortus Zone (CP9a/NP10) extends from Sample 173-1068A-6R-CC, 23-25 cm, through 8R-3, 7-8 cm, based on the presence of D. diastypus. The FO of T. bramlettei or T. contortus did not prove to be reliable markers because they are commonly overgrown and difficult to separate from Rhomboaster cuspis (Wei and Zhong, 1996). The nannofossil assemblage is poorly preserved to barren in sandstones and claystones of this zone, which is dominated by C. pelagicus, D. barbadensis, D. diastypus, D. multiradiatus, Toweius magnicrassus, T. orthostylus, and Z. bijugatus. The Paleocene/Eocene boundary is drawn between Samples 173-1068A-8R-3, 7-8 cm, and 8R-4, 44-45 cm, based on the FO of D. diastypus.
Coring of Hole 1069A (40°42.612´N, 11°46.633´W, water depth = 5074.8 m) began at 718.8 mbsf and recovered 147 m of sediment overlying metasedimentary rocks (Fig. F1). Eocene sediments were recognized in Samples 173-1069A-1R-1, 3-5 cm, through 7R-4, 61-63 cm, and are listed in Table T5. Calcareous nannofossils are abundant and moderately well preserved in these sediments. Preservation again is facies controlled, with poor preservation of nannofossils in the moderately brown clays and improved preservation in the greenish gray nannofossil claystones and greenish gray sandy siltstones. Preservation also declines downsection. Table T6 lists sample intervals and average depths of key nannofossil biohorizons.
Sample 173-1069A-1R-1, 3-5 cm, is considered the first sample in the middle Eocene based on the occurrence of R. inflata (Subzone CP12b). The interval between Samples 173-1069A-1R-CC and 5R-2, 29-30 cm, contains no R. inflata and is assigned to the D. sublodoensis (NP14) Zone or the D. kuepperi Subzone (CP12a). C. pelagicus, D. barbadensis, D. kuepperi, D. tanii, G. gammation, R. dictyoda, S. radians, and Z. bijugatus dominate the assemblage. The boundary between the middle and early Eocene is placed between Samples 173-1069A-5R-2, 29-30 cm, and 5R-CC, 1-2 cm.
The early Eocene D. lodoensis Zone (CP11/NP13) extends from Samples 173-1069A-5R-2-CC, 1-2 cm, to 5R-2-CC, 14-17 cm. Difficulties exist in discerning the CP11 D. lodoensis Zone defined by Okada and Bukry (1980) by the FO of C. crassus, which could not be determined in these samples because of overgrowth and dissolution of the nannofossils. Instead, the datums marking the NP13 "gap" Zone of Martini (1971), defined by the LO of T. orthostylus and FO of D. sublodoensis, were used.
Sample 173-1069A-6R-1, 4-5 cm, is the first sample of the T. orthostylus Zone (CP10/NP12), based on the FO of D. lodoensis. The assemblage is dominated by C. formosus, C. pelagicus, D. barbadensis, D. lodoensis, S. radians, T. orthostylus, and Z. bijugatus.
Sample 173-1069A-6R-5, 87-88 cm, is the first sample of the D. binodosus "gap" Zone (CP9b/NP11), based on the absence of T. contortus and D. lodoensis. Preservation of nannofossil assemblages in this zone shows a rapid change to poor preservation compared with previous zones with moderate preservation. The assemblage is dominated by C. pelagicus, D. barbadensis, D. binodosus, D. diastypus, T. bramlettei, and T. orthostylus.
Sample 173-1069A-7R-1, 147-150 cm, is the first sample belonging to the T. contortus Zone (CP9a/NP10), based on the FO of D. diastypus. No nannofossils were found from Samples 173-1069A-7R-2, 33-35 cm, through 7R-4, 61-63 cm. These samples are considered to be early Eocene in age, based on the absence of D. diastypus, T. bramlettei, and T. contortus in Sample 173-1069A-7R-5, 1-3 cm, marking the beginning of upper Paleocene sediments (Ladner and Wise, Chap. 5, this volume).
The thickest, most complete Eocene section recovered during ODP Leg 149 (Fig. F1) was at Hole 900A (46°40.994´N, 11°36.252´W, water depth = 5036.8 m). The dominant lithology in the Eocene section is upward-darkening turbidite sequences (Shipboard Scientific Party, 1994). The Eocene calcareous biostratigraphy of Hole 900A was previously described by Liu (1996). Her original smear slides have been reexamined using the species and boundary definitions of this study to facilitate a comparison with the zonal schemes established for Holes 1067A, 1068A, and 1069A. Early to middle Eocene sediments complimentary to those drilled at Leg 173 sites were found in Samples 149-900A-64R-2, 100-101 cm, to 77R-3, 3-4 cm. Calcareous nannofossils are abundant and moderately to poorly preserved in the hemipelagic and pelagic sediments deposited above the CCD. Minor modifications to Liu's (1996) biostratigraphy are summarized in Table T7, which lists sample intervals and average depths of key nannofossil biohorizons, as defined in this study.
During DSDP Leg 47B, one site was drilled (40°57.6´N, 10°43.1´W) on the southern flank of the Vigo Seamount (Fig. F1) in 1976. The original nannofossil biostratigraphy was completed by Blechschmidt (1979), who loosely applied the zonation of Martini (1971). Samples located between Blechschmidt-assigned zonal boundaries were analyzed to further constrain these boundaries and to look for key Okada and Bukry (1980) and Martini (1971) markers that were not originally recorded. Samples 47B-398D-35R-7, 30-31 cm, to 23R-1, 25-26 cm, contain lower to middle Eocene sediments complementary to those recovered in Holes 1067A, 1068A, and 1069A. Calcareous nannofossils were abundant and moderately preserved throughout this interval. C. gigas was found in only one sample, and Subzone CP13b could not be identified. Refinement of Blechschmidt's biostratigraphy is summarized in Table T8, which lists sample intervals and average depths of key nannofossil biohorizons.
Stratigraphic correlations between Holes 1067A, 1068A, 1069A, 900A, and 398D are presented in Figure F4. Zonal boundary lines are drawn on the FOs and LOs of key biohorizons (Fig. F3).