Sediments recovered from Site 1079 represent a relatively continuous hemipelagic section spanning the last ~700 k.y. of the Pleistocene. The calcareous micropaleontological study was carried out on core-catcher samples from Hole 1079A. Additional samples from within the cores were examined for calcareous nannofossil biostratigraphy. Diatoms, silicoflagellates, and radiolarians are absent.
Calcareous nannofossils were studied in core-catcher samples from Hole 1079A. Additional samples from within the cores were examined close to datum events to improve the stratigraphic resolution. Preservation of nannofossil specimens is good to very good. The overall abundance ranges from very abundant to abundant throughout the entire section. Reworked specimens (Neogene) are rare to common in Cores 175-1079A-10H through 13H.
The nannofossil-based biostratigraphy (Table 2; Fig. 8) indicates that Site 1079 terminated within the upper part of Zone NN19. Based on the oldest identified datum (last occurrence [LO] of Small Gephyrocapsa acme sensu Weaver [1993]) and paleomagnetic evidence (see "Paleomagnetism" section, this chapter), the bottom age of Hole 1079A is estimated at 0.7 ± 0.05 Ma. Within the sampling resolution, the sedimentation appears continuous throughout the entire section. Sedimentation rates show a step-like pattern, with a maximum of 40 cm/k.y. within Zone NN21a (i.e., from the top of isotope Stage 5 [~0.09 Ma] to the middle part of isotope Stage 8 [0.26 Ma]). This maximum value agrees with the one recorded within the same stratigraphic interval (60 cm/k.y.) in the nearby shallower Site 1078.
The first occurrence of the Emiliania huxleyi acme, which defines the Zone NN21b/NN21a boundary, was recognized between Samples 175-1079A-3H-3, 130 cm, and 3H-CC. This datum event is near-synchronous with a planktonic foraminiferal datum event (LO of Globorotalia tumida flexuosa, 0.07 Ma) found within Core 175-1079A-3H. Sedimentation rate within this top interval is >23 cm/k.y.
This stratigraphic interval spans most of the section at Site 1079. The LO of the Gephyrocapsa caribbeanica acme (Weaver, 1993), which marks the Zone NN21a/NN20 boundary, was identified between Samples 175-1079A-10H-5, 80 cm, and 10H-CC.
As documented at Sites 1077, 1076, and 1075, this interval spanning 0.2 m.y. from mid-isotope Stage 8 to mid-isotope Stage 12 is constrained within a narrow depth range (~10 m). The Zone NN21a/NN20 boundary was identified within the lower part of Core 175-1079A-11H.
The LO of the Small Gephyrocapsa acme (Weaver, 1993), the only identified datum event within this bottom interval, was found between Samples 175-1079A-12H-CC and 13H-2, 140 cm.
Planktonic foraminifers are common in the upper six cores, but abundance levels fall to few in Cores 175-1079A-7H-CC, 9H-CC, and 10H-CC and to trace levels in Sample 14H-CC. The low abundance in Sample 175-1079A-14H-CC is attributed to dissolution, but the other intervals may have lower abundances caused by dilution from increased terrigenous input.
Near this site, the cold surface Benguela Current and the warm, southward-flowing surface Angola Current converge, and downcore variations should reflect the change in the position of the Angola-Benguela Front. The uppermost assemblage at Hole 1079A (5.3 mbsf) is dominated by high abundances of Orbulina universa, Globigerinoides sacculifer, Globigerinella siphonifera, and Neogloboquad-rina pachyderma (dextral) (Table 3). Other species that are present but not abundant are Globigerinoides ruber (pink and white), Globigerina bulloides, Globorotalia crassaformis, Neogloboquadrina dutertrei, Neogloboquadrina pachyderma (sinistral), Globorotalia inflata, and Pulleniatina obliquiloculata (Table 3).
Globorotalia tumida flexuosa is present in Samples 175-1079A-3H-CC, 4H-CC, and 12H-CC and constrains the age to no younger than 0.07 Ma. This is in agreement with the calcareous nannofossil biostratigraphy.
The change in fauna downcore is similar to the change at Site 1078. In Sample 175-1079A-8H-CC (72.5 mbsf) and below, N. pachyderma is abundant, but above this level, it is only present in the uppermost assemblage (5.3 mbsf) at high abundances (Table 3). Samples 175-1079A-2H-CC through 7H-CC are dominated by G. ruber, G. sacculifer, and G. bulloides, indicating a change to warmer surface-water conditions (Table 3). This change in fauna from abundant N. pachyderma to abundant G. ruber apparently occurs at the same stratigraphic level as at Site 1078, near 0.25 Ma. G. crassaformis is abundant in Samples 175-1079A-6H-CC and 12H-CC. The species is associated with the Equatorial Undercurrent (Bé and Tolderlund, 1971) and may represent greater southern penetration of this current in the past.
The benthic foraminifers are well preserved and abundant in all core catchers from Hole 1079A, except for Sample 175-1079A-14H-CC, which is barren. The diversity is relatively low, as at the nearby, slightly shallower Site 1078. Most of the samples are dominated by Bolivina sp. 1 and Bolivina sp. 2. Additional contribution comes from Bulimina exilis, Cassidulina leavigata, and the Praeglobobulimina/Globobulimina group (Table 4; Fig. 9). Variations in the relative abundance occur but do not show any significant changes that can be attributed to major environmental changes. Hyalinea balthica shows a single large peak in Sample 175-1079A-3H-CC (27%), and Uvigerina auberiana peaks in Sample 175-1079A-13H-CC (32%). The absence of benthic foraminifers in Sample 14H-CC (121.02 mbsf) may be of local character because samples above and below this depth at Hole 1079B (Sample 175-1079B-13H-CC [118.72 mbsf] and Sample 14H-CC [128.23 mbsf]) have abundant benthic foraminifers.
As at Site 1078, the dominance of Bolivina sp. 1 and Bolivina sp. 2 and the overall low faunal diversity suggest low oxygen concentrations at the seafloor (see "Biostratigraphy and Sedimentation Rates" section, "Site 1078" chapter, this volume). The average contribution of Bolivina sp. 1 and Bolivina sp. 2, is, however, somewhat lower at Site 1079 (~60%) than at Site 1078 (~85%), which may reflect less severe oxygen depletion at the seafloor at the former.
Core-catcher samples from Holes 1079A, 1078B, and 1079C were analyzed for their diatom and radiolarian contents. Samples were prepared as smear slides (for diatoms) and acid-cleaned (for both microfossil groups). The treated samples were washed with distilled water and sieved through 20-µm, 38-µm, or 63-µm sieves. Diatoms and radiolarians are absent in almost all core-catcher samples. Trace amounts are found in Samples 175-1079A-1H-CC, 4H-CC, and 6H-CC.