Site 974 is located in the Tyrrhenian Sea on the eastern continental margin of Sardinia (Fig. 1).
Triple advanced hydraulic piston coring (APC) as deeply as possible, followed by extended core barrel (XCB) drilling to total depth, was the strategy employed at this site to ensure recovery of a complete stratigraphic section. Voids and drilling-induced sediment disturbance can occur in APC cores. Drilling three adjacent holes increased the likelihood that any such disturbed intervals or voids in any one core could be reconciled by taking samples from the corresponding interval in one of the other holes.
Only one core (uppermost Pleistocene) was taken in Hole 974A. Hole 974B was cored to a depth of 208.2 mbsf; 22 cores were taken, recovering a stratigraphic sequence ranging from upper Miocene to upper Pleistocene/Holocene. In Holes 974C (22 cores; TD 199.9 mbsf) and 974D (18 cores; TD 170.5 mbsf) cores of lower Pliocene to upper Pleistocene/Holocene sediment were recovered. We examined nannofossils only in the core-catcher samples from Holes 974A, 974C, and 974D. The general biostratigraphy of these holes is summarized in the Leg 161 Initial Reports volume (Comas, Zahn, Klaus et al., 1996). We performed a detailed stratigraphic analysis on samples from Hole 974B.
The zonal assignment of each core is shown in Fig. 3. The distribution and relative abundance of all Neogene nannofossils identified in Hole 974B are shown in Table 2. Neogene cores recovered from Hole 974B contain mostly abundant, well-preserved nannofossils. The only exceptions in the samples examined are in Sections 974B-22X-5 and -CC, where nannofossils are few, and preservation is moderate or poor to moderate. Reworked nannofossils make up a significant portion of the assemblage in this hole and in the other holes investigated. No hiatuses are apparent in the stratigraphic section cored.
The Pliocene/Pleistocene boundary (Subzone NN19A/NN19B boundary) is between Samples 974B-9H-4, 71-72 cm and 9H-6, 25-26 cm, based on the FO of Gephyrocapsa oceanica in 9H-4, 71-72 cm. We were able to use standard marker species (LO Discoaster brouweri, LO D. pentaradiatus, LO D. surculus, LO D. tamalis, LO Reticulofenestra pseudoumbilicus) for the Pliocene zones from NN18 down to the top of Zone NN14 (Fig. 3; Table 2). Because ceratoliths are so rare in these cores, we used the LCO of R. pseudoumbilicus to approximate the NN14/NN15 boundary. The FCO of D. asymmetricus marks the NN13/NN14 boundary. The NN12/NN13 zonal boundary could not be determined. The top of Subzone NN12b occurs in Sample 22X-3, 123-124 cm, based on the LcO of Helicosphaera intermedia. The Miocene/Pliocene boundary occurs in the lower part of NN12b; in this hole the boundary would therefore be between the lowermost part of Section 974B-22X-3 and the uppermost part of 22X-5. Samples 22X-5, 18-19 cm, and 22X-CC contain Coccolithus miopelagicus, Discoaster calcaris, and a single specimen of D. quinqueramus (Section 974B-22X-5), which suggest a NN11 zonal assignment. We have therefore drawn the NN11/NN12 zonal boundary between Sections 974B-22X-5 and 22X-3 (Fig. 3; Table 2). This position also agrees with the boundary assignment based on planktonic foraminifers (Comas, Zahn, Klaus et al., 1996).
A major lithologic change takes place in Section 974B-22X-4, at the biostratigraphically approximated Miocene/Pliocene boundary. Thin, sparsely bioturbated, red to brown, predominantly silty clay beds interspersed with sand and calcareous intervals occur from Section 974B-22X-4 downward to 22X-CC, the bottom of the hole (Comas, Zahn, Klaus, et al., 1996). Above this level the sediments are moderately to intensely burrowed nannofossil clays. This lithologic change probably marks the upward transition from a lacustrine to a normal marine environment. A lacustrine phase (the Lago Mare) is well documented as occurring in the latest Messinian in the Mediterranean region. The brackish- to freshwater lake may also have experienced brief marine incursions before the environment changed to fully marine.
Site 975 is located in a small basin on the Menorca continental rise in the Balearic Sea (Fig. 1). As at Site 974, triple APC and double XCB cores were taken to ensure continuous sediment recovery.
Only one core was taken in Hole 975A (Pleistocene; NN21A). Hole 975B (34 cores; TD 298.98 mbsf) consists of a stratigraphic sequence ranging from uppermost Miocene (NN11) to uppermost Pleistocene/Holocene (NN21B). Sediments in Hole 975C (34 cores; 307.66 mbsf) range from lower Pliocene (Zone NN12) to uppermost Pleistocene/Holocene (NN21B), and Hole 975D (16 cores; TD 157.03 mbsf) from upper Pliocene (NN17) to uppermost Pleistocene/Holocene (NN21B). The biostratigraphy of Holes 975A, 975C, and 975D is based on core-catcher samples only, and is reported in the Leg 161 Initial Reports volume. We performed a detailed stratigraphic analysis on samples from Hole 975B.
Figure 4 shows the zonal assignment of each core. Table 3 gives the distribution and relative abundance of the nannofossil assemblage in Hole 975B.
Neogene nannofossils are common to abundant and mostly well preserved in samples from this hole, except in the lowermost sample collected (161-975B-34X-CC), where nannofossils are few and poorly preserved. We found no hiatuses in the section cored.
Sample 161-975B-13H-CC contains the FO of G. oceanica and thus marks the Pliocene/Pleistocene boundary (Subzones NN19A/NN19B boundary). We used the same biozonal markers as in Hole 974B in this hole from Zone NN18 down to Zone NN13. Again, the NN12/NN13 zonal boundary could not be determined. Recognition of the Zones NN11/NN12 boundary also presented a problem. Lithologically, the open-marine lower Pliocene sediments end rather abruptly downhole in Zone NN12 in Section 975B-33X-2. A thin unit of laminated, possibly intertidal, calcareous silty clay occurs from 975B-33X-2, 131 cm, down to 33X-CC, underlain by gypsum and gypsiferous chalk to the bottom of the hole (Comas, Zahn, Klaus, et al., 1996). Nannofossils suggestive of the upper Miocene (Cryptococcolithus mediaperforatus, Helicosphaera stalis stalis, H.s. ovata, H. orientalis, and Coccolithus miopelagicus) occur in the intertidal calcareous clays in Section 975B-33X-CC in what is apparently a marine intercalation within the gypsum. We have therefore drawn the NN11/NN12 zonal boundary (which approximates the Miocene/Pliocene boundary here) between 975B-33X-CC and 33X-3, 130-131 cm. Sample 975B-33X-3, 130-131 cm, lacks the Miocene markers found below and contains nannofossils typical of Zone NN12 (Table 3). We believe normal open-ocean conditions were re-established by this time. Planktonic foraminifers are all dwarfs below 975B-33X-3, 80-82 cm, and one benthic foraminifer found in 33X-CC is characteristic of a brackish-water environment such as the Lago Mare (Comas, Zahn, Klaus, et al., 1996).
Site 976 is located in the Alboran Sea, about 60 km off southern Spain and about 110 km east of the Strait of Gibraltar (Fig. 1). Site 976 is about 8 km northeast of DSDP Site 121.
Recovery at Hole 976A consisted of one core (Pleistocene/Holocene; NN21B). Hole 976B was dedicated to tectonic objectives. In this hole we APC- and XCB-cored continuously to a depth of 928.7 mbsf, penetrating 660.2 m of a sedimentary sequence (72 cores) ranging from middle Miocene (Serravallian; NN7) to uppermost Pleistocene/Holocene (NN21B), and RCB-cored 268.5 m into pre-middle Miocene metamorphic rocks dominated by gneiss and schist (34 cores). Hole 976C was cored continuously from the uppermost Pleistocene/Holocene (NN21B) to the uppermost Pliocene (NN19A). Four cores were taken in Hole 976D; all were in the upper Pleistocene/Holocene (NN21A-NN21B). Hole 976E was washed down to the lower Pliocene (NN12) at 534.8 mbsf, then RCB cored to the middle Miocene (28 cores). The general biostratigraphy for all five holes, based on core-catcher samples, is given in the Leg 161 Initial Reports volume. The detailed biostratigraphy of Hole 976B is given below.
Figure 5 shows the zonal assignment of each core. Distribution and abundance of all species identified in Hole 976B are given in Table 4.
Cores recovered from Hole 976B contain common to abundant Neogene nannofossils except for intervals from 161-976B-39X-CC to 44X-2, 20-21 cm, from 47X-3, 21-22 cm, to 48X-CC, from 72X-CC to 73X-1, 0-4 cm, and 75R-1, 16-17 cm. Nannofossils are mostly rare to few in these intervals, and two samples (976B-42X-CC and 72X-3, 21-22 cm) are barren. Preservation ranges from moderate to good except in samples taken from Cores 976B-72X, 73X, and 74X, in which preservation is poor. Hiatuses occur in the stratigraphic section, as described below.
The NN19A/NN19B Subzone boundary (Pliocene/Pleistocene boundary) is between Samples 976B-38X-CC and 39X-3, 22-23 cm. The NN18/NN19A zonal boundary is marked by the LO of D. brouweri in Sample 49X-CC (Fig. 5; Table 4). Samples from 976B-49X-CC down to 55X-CC contain a normal, moderately to well-preserved Zone NN18 assemblage. This interval lacks D. pentaradiatus, D. surculus, and D. tamalis, the marker species for Zones NN17 and NN16 (a single specimen, probably reworked, of D. pentaradiatus was found in 52X-CC). The next underlying sample, 976B-56X-1, 18-19 cm, contains D. pentaradiatus, plus R. pseudoumbilicus (common) and Sphenolithus abies, but lacks P. lacunosa and H. sellii. The presence of R. pseudoumbilicus and S. abies, which range no higher than Zone NN15, and the absence of P. lacunosa and H. sellii, which first appear in NN13 (FcO of H. sellii) and range into Zone NN19 indicate Section 976B-56X-1 is in Zone NN12. A hiatus therefore exists between Samples 56X-1, 18-19 cm and 55X-CC, spanning at least Zones NN13 to NN17. Using the time scale in Figure 2, we estimate the duration of this hiatus in the Mediterranean to be at least 2.5 m.y.
The NN11/NN12 (approximate Miocene/Pliocene) zonal boundary is between Samples 976B-61X-7, 71-73 and 61X-CC, based on the LO of Cryptococcolithus mediaperforatus, Reticulofenestra rotaria, and Coccolithus miopelagicus in 61X-CC. Sample 976B-68X-CC contains Reticulofenestra rotaria and Amaurolithus primus, indicating Zone NN11. Discoaster pentaradiatus also occurs in this sample. R. rotaria and A. primus first appear in Zone NN11, and D. pentaradiatus first appears in NN9. Sample 976B-69X-1, 21-22 cm and lower samples lack all three of these species, suggesting a zonal assignment below NN9. D. kugleri has its LO in Sample 976B-71X-4, 21-22 cm. In the absence of Catinaster coalitus, which is not found in the Mediterranean (Rio et al., 1990a), we consider the LO of D. kugleri to approximate the upper boundary of Zone NN7. We therefore assign intervening samples from 976B-71X-3, 21-22 cm to 69X-1, 21-22 cm to Zone NN8. The missing Zones NN9 and NN10 represent a hiatus of at least 2.0 m.y. (Fig. 2). The sporadic co-occurrence of H. walbersdorfensis, D. kugleri, and Calcidiscus macintyrei in the interval from 976B-71X-4, 21-22 cm, to 75R-2, 67-69 cm, indicates that these lowermost cores are still in Zone NN7.
Sediments at the top of Core 976B-75R-1 contain downhole contamination. Scrapings of calcareous material from pebbles in Samples 976B-80X-1, 22 cm, and 80X-1, 124 cm, yielded rare nannofossils that could only be assigned a Miocene age.
Site 977 is located in the eastern Alboran Sea, midway between Spain and Algeria (Fig. 1). The drilling site was spudded in a sediment-filled graben bounded by the Maimonides Ridge to the north and the Yusuf Ridge to the south. The Al-Mansour Seamount lies in the center of the graben, dividing it into two east-west-trending basins. Site 977 is on the south side of Al-Mansour (Fig. 1). Only one hole was drilled at this site during Leg 161 (Hole 977A).
This hole was APC- and XCB-cored continuously to 588.9 mbsf; 62 cores were recovered. An attempt to drill deeper after a bit change failed and the hole was abandoned.
The stratigraphic interval recovered ranges from middle/upper Miocene (NN7-NN11) to uppermost Pleistocene/Holocene (NN21B). Figure 6 shows the zonal assignment of each core. Table 5 gives the abundance and distribution of all species identified in the cores.
Cores recovered from Hole 977A contain common to abundant Neogene nannofossils except for Samples 161-977A-60X-1 (Piece 1) and 60X-CC, which contain few nannofossils. Preservation is good, or moderate to good, in all cores except in the lower Pliocene interval from Samples 977A-56X-CC to 60X-CC, where preservation is moderate or poor.
Gephyrocapsa oceanica makes its FO in Sample 161-977A-29X-1, 65-67 cm, establishing the Subzone NN19A/NN19B (Pliocene/Pleistocene) boundary between Sample 29X-1, 65-67 cm, and Sample 29X-2, 65-67 cm. We recognized the boundaries of Zones NN18, NN17, NN16B, NN16A, NN15, and NN14 using the species markers noted for Holes 974B, 975B, and 976B. A brief hiatus occurs between Samples 52X-6, 19 cm, which contains P. lacunosa and H. sellii, and Sample 52X-6, 23 cm, which lacks these species. The hiatus probably represents the uppermost part of Zone NN13, and perhaps the lower part of Zone NN14. The duration of this hiatus is difficult to estimate, but probably lasted less than 1.0 m.y. (Fig. 2). The stratigraphic interval from 977A-54X-5, 89-91 cm, to 57X-CC contains H. intermedia and lacks upper Miocene forms. We assign this interval to Zone NN12b. Poor recovery from Core 58X to 59X precludes zoning of this interval. Scrapings from the calcareous matrix surrounding pebbles in Samples 977A-60X-1 (Pieces 1, 4) yielded an assemblage containing the Miocene forms H.s. stalis, C. miopelagicus, and Cyclicargolithus floridanus (Table 5), indicating Zones NN7-NN11. The pebbles probably represent a sedimentary gravel unit resulting from erosion caused by the post-Messinian flooding of the western Mediterranean (Tribble et al., 1995). The gravel unit corresponds to the "M" seismic reflector at the Miocene/Pliocene boundary.
Failing our attempt to drill deeper at Site 977, we moved 24 km to the north and spudded Site 978 in the basin on the north side of the Al-Mansour Seamount (Fig. 1).
Rotary coring was intermittent in this single Site 978 hole until 213.0 mbsf, after which coring was continuous to a depth of 694.3 mbsf; 53 cores were recovered. A free-fall funnel (FFF) was then dropped and the bit changed in order to drill deeper in this hole. However, after lowering the new bit, the hole could not be relocated (apparently because the FFF shifted when the old bit was withdrawn), and the site was abandoned.
The sedimentary sequence recovered ranges from upper Miocene Zone NN11) to upper Pleistocene (Zone NN19F). Zonal assignments for each core are shown in Figure 7; abundance and distribution of all nannofossil species are given in Table 6.
Most Neogene samples obtained from Hole 978A contain common to abundant nannofossils, except for intervals in Cores 161-978A-49R, 51R, 52R, and 53R in which nannofossils are "rare" or "few" (Table 6). Nannofossil preservation is moderate or moderate to good in all samples except 46R-CC, where preservation is poor to moderate.
Coring was intermittent down to 213.0 mbsf (lower Pleistocene), after which coring was continuous. The Subzone NN19A/NN19B (Pliocene/Pleistocene) boundary is between Samples 161-978A-4R-1, 6-8 cm, and 4R-1, 64-66 cm. The presence of the usual marker species shows that all Pliocene zones are present (Table 6), with the NN12/NN13 boundary subject to the usual uncertainty. The LOs of H. s. stalis, H. s. ovata, H. orientalis, R. rotaria, C. miopelagicus, and C. mediaperforatus occur in a stepwise fashion from 978A-47R-CC to 45R-CC. We have tentatively placed the NN11/NN12 zonal boundary at the last co-occurrence of H. s. ovata, H. orientalis, and C. miopelagicus in 978A-47R-CC (Fig. 7). The highest upcore occurrence of upper Miocene planktonic foraminifers is also in Core 47R, and the same gravel bed found at the top of the Messinian in Hole 977A occurs in this hole from Sample 978A-46R-1, 0 cm, to 47R-1, 7 cm (Comas, Zahn, Klaus, et al., 1996). Sections 978A-48R-1 through 53R-CC contain low numbers of upper Miocene nannofossils consistent with Zone NN11. Reticulofenestra rotaria is present between 978A-49R-3 and 50-2, suggesting the presence of the R. rotaria Subzone of Theodoridis (1984). Cyclicargolithus floridanus also occurs rarely throughout this interval, but based on the specimens' rarity and preservation state, we consider them to be reworked. Reworked Cretaceous and Paleogene nannofossils are present in greater than usual numbers from Sample 45R-CC downward to the bottom of the hole.
Site 979 is located in the southern Alboran Sea, at the base of the southern flank of the Alboran Ridge (Fig. 1).
This, the only hole drilled at this site, was APC- and XCB-cored to a depth of 583.14 mbsf; 62 cores were recovered. The sedimentary sequence recovered ranges from middle Pliocene (Zone NN16A) to upper Pleistocene/Holocene (Zone NN21B). Zonal assignments for each core are shown in Figure 8; abundance and distribution of all species are given in Table 7.
Neogene samples obtained from Hole 979A contain common to abundant nannofossils, except for Sample 161-979A-50X-CC, in which nannofossils are rare. Preservation ranges from moderate to good. The Subzone NN19A/NN19B (Pliocene/Pleistocene) boundary in this hole occurs between Samples 979A-37X-CC and 38X-3, 20-21 cm. All Pliocene zones from NN18 to NN16A are present, based on recognition of the same marker species used in the previous holes. The hole terminated in Zone NN16A.
A brief NN17 intrazonal hiatus is inferred between 979A-51X-CC and 52X-3, 15-16 cm, based on the LO and co-occurrence of the foraminifer Globorotalia bononiensis and the nannofossil D. pentaradiatus at the same level (476.41 mbsf). Normally the LAD of D. pentaradiatus slightly predates the LAD of G. bononiensis (by about 0.1 m.y.). No other microfossil change is apparent at this level, and no changes in lithology were noted for this level by the shipboard sedimentologists (Comas, Zahn, Klaus, et al., 1996).