Sediments recovered from Site 1087 represent a relatively continuous pelagic section down to 430 mbsf spanning the last 9 m.y. The bottom 70 m contains middle Miocene to early Oligocene sediment packages interrupted by at least two major discontinuities. The micropaleontological study was carried out on core-catcher samples from Holes 1087A and 1087C. Additional samples from within the cores were examined to improve the biostratigraphic resolution. A high-resolution biostratigraphy was developed using calcareous nannofossils and planktonic foraminifers. Sedimentation rates range from 2 to 7 cm/k.y. Siliceous microfossils are present in the late Pliocene and Pleistocene only.
Calcareous nannofossils were examined in core-catcher samples from Hole 1087A. Additional samples from within the top six cores of Hole 1087A were studied close to datum events to improve the stratigraphic resolution of the Pleistocene interval. Core-catcher samples from Hole 1087C (Cores 175-1087A-26H through 51X-CC) were examined to resolve the stratigraphy of the bottom 300 m of Site 1087. Calcareous nannofossils are abundant and well preserved throughout the section.
At least three major discontinuities were identified within the bottom 70 m of Site 1087. This disturbed interval contains sediment packages of middle Miocene (Zone NN5; Sample 175-1087C-47X-CC) and Oligocene (Zones NP22–NP24; Sample 175-1087C-50X-CC and 51X-CC) origin. Above this disturbed bottom interval, the nannofossil-derived stratigraphy suggests a continuous sedimentation spanning the Pleistocene to the middle Miocene (Zones NN21–NN10) (Table 2). The following discussion will refer only to this undisturbed section of Site 1087.
Subzone NN21b is missing from the top part of Hole 1087A. The Subzone NN21a/NN20 boundary was identified within Core 175-1087A-1H (between Sample 1H-3, 130 cm, and 1H-CC) at the mean depth of 6.2 mbsf.
This interval of 0.2-m.y. duration terminates at 13.4 mbsf (between Samples 175-1087A-2H-3, 130 cm, and 2H-4, 140 cm), which is the mean depth of the last occurrence (LO) of the Pseudoemiliania lacunosa datum event.
In addition to the zonal boundary events, four biohorizons were identified within this interval. Based on the downcore distribution of these datum events, a rather uniform sedimentation rate is inferred for the Pleistocene and upper part of the late Pliocene of Site 1087 (Fig. 7). The base of Zone NN19 was identified between Samples 175-1087A-6H-CC and 7H-CC at the mean depth of 60.9 mbsf.
Zones NN18 and NN17 were combined because the LOs of both Discoaster pentaradiatus (NN18/NN17 zonal boundary event) and D. surculus (NN17/NN16 zonal boundary) were identified within the same sampling interval (between Samples 175-1087A-8H-CC and 9H-CC; 79.4 mbsf). A refined biostratigraphy based on a higher resolution sampling will be done on shore to precisely constrain the upper boundary of the short-duration Zone NN17 (from 2.45 to 2.55 Ma).
This 1.27-m.y. interval is constrained between 79.4 and 174.14 mbsf and displays the highest sedimentation rates recorded for Site 1087 (7 cm/k.y.). In addition to the zonal boundary events, a bio-horizon dated at 1.83 Ma was identified between Samples 175-1087A-10H-CC and 11H-CC (LO of Discoaster tamalis).
The top of this interval is defined by the LO of Reticulofenestra pseudoumbilica (3.82 Ma), a datum event identified between Samples 175-1087A-18H-CC and 19H-CC. The Zone NN15/NN14 boundary is defined by the LO of Amaurolithus tricorniculatus (4.5 Ma), a datum identified at the mean depth of 193.6 mbsf (Samples 175-1087A-20H-CC through 21H-CC).
These zones were combined because of the sparse occurrence of diagnostic and zonal boundary species of Zone NN13 (Ceratolithus sp.). The first occurrence (FO) of Discoaster asymmetricus, which defines the Zone NN14/NN13 boundary, could not be properly identified because of the combination of coarse sampling resolution and low sedimentation rates (2 cm/k.y.). The base of this interval was found between Samples 175-1087A-22H-CC and 23H-CC (LO of Discoaster quinqueramus; 5.54 Ma).
This 3.06-m.y. interval is defined as the range of D. quinqueramus. The range of Amaurolithus amplificus (LO between Samples 175-1087C-27H-CC and 28X-CC; FO between Samples 30X-CC Miocene
Faunas restricted to late Miocene Zone Mt10 are found in Samples 175-1087A-26H-CC, 175-1087C-29X-CC, and 175-1087C-39X-CC (236–361 mbsf). Zones Mt9 and Mt8 (361–429 mbsf) are undifferentiated. The late Miocene is separated from the middle Miocene by an unconformity between Samples 175-1087C-46X-CC and 47X-CC. This biostratigraphic break is correlative with a sharp lithologic break in the core (see "Lithostratigraphy" section, this chapter). Samples 47X-CC and 48X-CC contain fauna from middle Miocene Zones M6–M7 (429–447 mbsf). There is probably another unconformity between Samples 48X-CC and 49X-CC, because the faunas in Sample 49X-CC are restricted to early Miocene Zone M2 and older. The age estimate is uncertain, however, because reworking occurs in this interval (447–454 mbsf).
Samples 175-1087C-50H-CC through 53H-CC contain fauna restricted to the late Eocene to early Oligocene. There is a significant unconformity between the lower Miocene (Sample 175-1087C-49X-CC) and the upper Eocene/lower Oligocene (Sample 50X-CC) sequences.
The benthic foraminiferal fauna of Site 1087 was studied in the core-catcher samples from Hole 1087A. The benthic foraminifers are abundant throughout Hole 1087A, but as at previous sites in the Cape Basin (Sites 1085 and 1086), there is a very high planktonic to benthic foraminifer ratio. The preservation of the benthic foraminiferal assemblage is good throughout Hole 1087A.
The uppermost core catcher (Sample 175-1087A-1H-CC; 8.21 mbsf) is dominated by Bulimina aculeata, together with Uvigerina hispidocostata (Table 4).
The Pleistocene and the late Pliocene (down to ~160 mbsf) are dominated by Bulimina mexicana, Hoeglundina elegans, and stilo-stomellas (Table 4). Uvigerina peregina is an important component of the fauna in the lowermost Pleistocene and uppermost upper Pliocene sequences. The lowermost upper Pliocene sediment contains Siphotextularia concava.
The lower Pliocene and uppermost upper Miocene sediments recovered from Hole 1087A are strongly dominated by Bolivina subaenarensis, together with Bulimina mexicana, Cibicidoides pachyderma, Ehrenbergina trigona, and Uvigerina auberiana (Table 4). The lowermost core catcher (Sample 175-1087A-27H-CC; 255.15 mbsf) contains a high abundance of Bolivina pseudoplicata (Table 4).
Core-catcher samples from Cores 175-1087A-1H-CC through 27H-CC and 1087C-27H-CC through 39X-CC, 42X-CC, 44X-CC, 46X-CC, 48X-CC, 50X-CC, 52X-CC, and 53X-CC were examined for radiolarians (Table 5). At Hole 1087A, radiolarians are generally rare and show signs of dissolution. Samples 175-1087A-17H-CC through 27H-CC are barren of radiolarians. No radiolarians could be identified from the examined samples from Hole 1087C.
The absence of Axoprunum angelinum indicates that the uppermost samples (175-1087A-1H-CC and 2H-CC) belong to Zone NR1 of Caulet (1991). It was not possible to determine a zone for samples below Sample 2H-CC because of the scarcity or absence of age-diagnostic taxa. The LO of Lamprocyrtis neoheteroporos in Sample 175-1087A-4H-CC probably indicates an age of 1.07 Ma. The FO of Cycladophora davisiana indicates an age of 2.70 Ma for Sample 175-1087A-9H-CC.
The Axoprunum stauraxonium and Ellipsoxiphus attractus groups are common in Samples 175-1087A-1H-CC, 2H-CC, 5H-CC, 6H-CC, 12H-CC, 13H-CC, 14H-CC, 15H-CC, and 16X-CC, indicating low productivity under subtropical warm-water conditions. The radiolarian assemblages that are characterized by common C. davisiana suggest upwelling conditions for Samples 175-1087A-7H-CC and 8H-CC. The presence of an Antarctic species, Cycladophora plio-cenica, in Sample 175-1087A-12H-CC indicates an influence of cooler water.
Core-catcher samples from Holes 1087A (1H-CC through 27H-CC) and 1087C (27H-CC through 53X-CC) were analyzed for their diatom content. Samples were acid-cleaned, rinsed in distilled water, and sieved through a 20- or 63-µm sieve before smear slides were prepared. Diatoms are present (rare to few) in the upper Pliocene sediment only, between Samples 175-1087A-7H-CC (65.71 mbsf) and 13H-CC (122.85 mbsf). As at Site 1085, this interval includes a mixed Thalassiothrix antarctica–rich assemblage (composed of Southern Ocean species and warm oceanic species), with an approximate age of 1.9–2.8 Ma. Diatoms are barren below 122 mbsf at Hole 1087A and in the analyzed portion of Hole 1087C.
Sponge spicules are present only in the Pleistocene and upper Pliocene sediments (from Samples 175-1087A-1H-CC through 18H-CC; 8.21 to 168.44 mbsf); they are particularly abundant in the Pleistocene. Dinoflagellate cysts are common below 213 mbsf (Sample 23H-CC) at Hole 1087A, and between 262 (Sample 29X-CC) and 338 mbsf (37X-CC) at Hole 1087C. The age of the LO of dinoflagellate cysts at Hole 1087A approximates that of Sites 1085 and 1086 (~5.8 Ma), suggesting that both sites were affected by the same oceanographic process simultaneously.