Siliceous microfossils (radiolarians, diatoms, and silicoflagellates) are common and generally well preserved in lithostratigraphic Units I and II at Site 1179 (see "Sedimentology"). They are absent from the red pelagic clays (lithostratigraphic Unit III) and generally poorly preserved (recrystallized) in the cherts (lithostratigraphic Unit IV). Numerous radiolarian datums can be identified, and upper Miocene to upper Pleistocene sediments can be assigned to established radiolarian zones, providing good biostratigraphic resolution (Fig. F24). Two species are identifiable in a single chert sample near the basaltic basement, providing an Early Cretaceous age for the oldest sediments at this site.
The only core-catcher sample that contains calcareous microfossils (calcareous nannofossils and planktonic and benthic foraminifers) is Sample 191-1179B-4H-CC (36.02 mbsf). The foraminifers are not biostratigraphically useful, but calcareous nannofossils provide an early Quaternary age for this sample. There is no explanation at this time for the preservation of calcareous microfossils in this sample and in several other samples within cores of late Pliocene to early Pleistocene age where routine inorganic geochemical analysis and palynological processing identified anomalously high CaCO3 contents (Table T2). Agglutinated foraminifers are present in some upper Miocene to upper Pliocene samples, and the presence of the finely agglutinated taxon Spirosigmoilinella compressa constrains the interval from 229.77 to 181.94 mbsf to the middle to late Miocene. No calcareous nannofossils or foraminifers were found in lithostratigraphic Units III or IV.
Terrestrial spores and pollen and marine dinocysts and acritarchs are present and moderately to well preserved in all samples examined in the upper ~144 m of lithostratigraphic Unit I. All of these samples are of late Pliocene to late Pleistocene age except for the lowermost palynomorph-bearing sample examined, Sample 191-1179C-11H-CC (143.84 mbsf), which is of late early Pliocene age. All other sediments in lithostratigraphic Unit I and all of lithostratigraphic Units II, III, and IV are barren of palynomorphs. A number of dinocyst datums can be identified, providing good stratigraphic resolution in sediments of late Pliocene to Pleistocene age. Terrestrial palynomorphs (pollen and spores) are most abundant in sediments of Pleistocene age, where they sometimes outnumber dinocysts, and in those upper Pliocene sediments with anomalously high CaCO3 content (see Table T2).
The depths at which we drilled (below the CCD) make it almost impossible for nannofossils to be preserved in the sediment. Samples 191-1179B-1H-CC through 6H-CC were examined. Samples 1H-CC through 3H-CC are barren of nannofossils. Sample 4H-CC contains a small assemblage of nannofossils. These are Coccolithus pelagicus, small Gephyrocapsa (<5 µm), large Gephyrocapsa (>5 µm), Emiliania huxleyi, and Pseudoemiliania lacunosa. This assemblage can be assigned to Zone NN19 using the Martini zonation and late Subzone CN13b using the Okada and Bukry zonation. An early Pleistocene age is indicated by the absence of Discoaster brouweri. The presence of E. huxleyi is considered contamination of the sample because its first occurrence (FO) is at the beginning of Zone NN21. Cores 191-1179B-5H and 6H are barren of nannofossils.
Samples 191-1179C-2H-CC through 27X-CC are barren of calcareous nannofossils. Calcium carbonate content measurements in some intervals record CaCO3 peaks that could indicate the presence of nannofossils (see Table T2). Sample 191-1179C-6H-4, 90 cm, was made into a smear slide because of a peak in the carbonate concentration of >1 wt%. Nannofossils are present in this sample, but the assemblage may be the result of contamination because it is the same assemblage as Sample 191-1179B-4H-CC, some 60 m above Sample 191-1179C-6H-4, 90 cm. Further investigation is required.
In Hole 1179D, Cores 191-1179D-1R through 10R recovered chert using the RCB. Recovery was poor, and no interbedded soft sediment was recovered. Samples were taken at various intervals where indurated sediment was in contact with the chert layers in Hole 1179D. These were Samples 191-1179D-4R-1, 25 cm; 6R-1, 40 cm; 6R-1, 60 cm; and 7R-1, 60 cm. Unfortunately, these samples are barren of nannofossils.
All core-catcher samples were examined for foraminifers. Only Sample 191-1179B-4H-CC contains calcareous fossils. The washed residues from the core catchers contain very well-preserved and unbroken radiolarians, diatoms, and sponge spicules. Sample 191-1179B-4H-CC contains a well-preserved planktonic foraminiferal fauna with common Neogloboquadrina pachyderma (mainly sinistral), Globorotalia inflata, Globigerina bulloides, Globigerinoides ruber, and Orbulina universa, together with a few specimens of the benthic species Cibicides sp. and Astrononion stelligerum.
The first downcore appearance of a small number of poorly preserved agglutinated foraminifers was observed in Sample 191-1179C-7H-CC, where fragments of Pseudonodosaria sp. are recognized together with an increase in diatoms. A few fragments of Rhabdammina sp. were observed in the subsequent core catchers down to Sample 191-1179C-18H-CC. The largest number of agglutinated foraminifers (30 and 23 specimens per 25 cm3) was found in Samples 191-1179C-19H-CC and 20H-CC, which contain moderately preserved Pseudonodosaria sp. and very well preserved Spirosigmoilinella compressa. A few S. compressa were also found in Samples 191-1179C-15H-CC and 17H-CC, giving an age of middle to late Miocene for Samples 191-1179C-15H-CC through 20H-CC.
Fish teeth were observed in Samples 191-1179C-19H-CC, and bryozoa were observed in Samples 191-1179C-20H-CC, 21H-CC, and 22H-CC. Samples 191-1179C-23H-CC, 24H-CC, 25X-CC and 191-1179D-1R-CC are barren, and in Sample 191-1179C-26X-CC, only a few radiolarians were observed.
Palynomorphs are moderately to well preserved in the upper part of lithostratigraphic Unit I (0 to ~144 mbsf), but all samples examined below Sample 191-1179C-11H-CC are essentially barren (Fig. F25). Dinocyst concentrations are generally low, ranging from fewer than a hundred to several hundred cysts per cubic centimeter in sediments of late early Pliocene to late Pleistocene age (143.84-0.92 mbsf). Terrestrial palynomorph (pollen and spores) concentrations are also generally low, ranging from a few hundred to several hundred grains per cubic centimeter in the Pliocene section, but are generally higher in the Pleistocene section (especially in the upper ~55 mbsf), where they may exceed a thousand grains per cubic centimeter.
Samples 191-1179B-1H-1, 92-94 cm (0.92 mbsf), through 6H-CC (55.2 mbsf) are assigned to the Pleistocene. The dinocyst genus Brigantedinium and Picea pollen are common to abundant in Samples 191-1179B-1H-1, 92-94 cm (0.92 mbsf), 191-1179A-1H-CC (9.87 mbsf), and 191-1179B-5H-2, 39-43 cm (38.01 mbsf). The cool surface water and continental climates recorded by the abundance of these palynomorphs suggest that these sediments were deposited during a glacial interval. Warmer sea-surface and continental conditions, and thus presumably interglacial conditions, are recorded in Samples 191-1179B-3H-4, 90-94 cm (22.62 mbsf), 4H-3, 44-48 cm (30.06 mbsf), 4H-CC (36.02 mbsf), and 6H-CC (55.2 mbsf) by thermophilous dinocyst taxa such as Impagidinium aculeatum, Impagidinium sphaericum, and Impagidinium strialatum, together with various Spiniferites spp. Pinus pollen is abundant in these samples, and angiosperm pollen is common. Tsuga is also common in some Pleistocene samples interpreted as interglacial. Picea is rare in these samples, which is consistent with the warmer conditions recorded by the dinocysts.
Sample 191-1179C-3H-CC (67.70 mbsf) is assigned an early Pleistocene age (older than 1.3 Ma) based on the common presence of Operculodinium israelianum together with long-ranging taxa such as Brigantedinium spp., Bitectatodinium tepikiense, and various species of Impagidinium.
Sample 191-1179C-5H-CC (86.93 mbsf) is late Pliocene in age, based on the presence of rare Spiniferites cf. pseudofurcatus and Impagidinium japonicum together with Operculodinium eirikianum. Long-ranging taxa such as Operculodinium centrocarpum and I. strialatum are also common.
Late Neogene dinocysts, such as Operculodinium janduchenei and Habibacysta tectata, are consistently present in Samples 191-1179C-6H-4, 90-94 cm (92.22 mbsf), through 11H-CC (143.84 mbsf). The presence of few Corrudinium harlandii in Samples 191-1179C-9H-CC (124.84 mbsf) and 8H-CC (115.62 mbsf) and of rare Hystrichokolpoma sp. 1 of Mudie (1987) in Sample 191-1179C-8H-CC constrains this interval to late Miocene to late Pliocene age. A number of long-ranging dinocysts are common over this interval, including I. aculeatum, I. strialatum, Selenopemphix nephroides, O. israelianum, B. tepikiense, and various species of Spiniferites. Pollen assemblages in Pliocene samples are very similar to the Pleistocene section, with a variety of gymnosperm and angiosperm (e.g., Carya, Betula, and Alnus) pollen grains, although absolute pollen abundances are generally much lower.
Samples 191-1179C-12H-4, 90-94 cm (149.22 mbsf), 13H-4, 90-94 cm (158.72 mbsf), 15H-CC (181.94 mbsf), 19H-CC (219.88 mbsf), 23H-CC (256.80 mbsf), and 24H-CC (266.43 mbsf) are barren of palynomorphs.
The radiolarians present in sediments from Site 1179 lithostratigraphic Units I and II core-catcher samples range in age from late Miocene to Quaternary. Common to abundant radiolarians are present in most sediments, with the exception of Samples 191-1179B-4H-CC and 191-1179C-5H-CC, 9H-CC, and 12H-CC (Table T3). The low concentration of radiolarians in Samples 191-1179C-5H-CC, 9H-CC, and 12H-CC (Table T3) possibly resulted from an increase in diatom and silicoflagellate production. The concentration of radiolarians in Sample 191-1179B-4H-CC was decreased by the presence of volcanic ash and calcareous microfossils. Samples 191-1179C-22H-CC (~248 mbsf) through 25H-CC (~273 mbsf) are barren of radiolarians, but fish teeth are present in these samples. Radiolarians reappear in Samples 191-1179C-26R-CC (~283 mbsf) and 27R-CC (~293 mbsf) and continue down through the chert layers. Sample 191-1179D-9R-1, 58-62 cm (~358 mbsf), contains radiolarians of Early Cretaceous age.
Radiolarian preservation is good in lithostratigraphic Unit I (0 to ~221.5 mbsf). Radiolarian preservation is moderate in lithostratigraphic Unit II (~221.5 to ~246 mbsf). Many of the radiolarians in these samples have broken tests and show evidence of silica dissolution and recrystallization. Radiolarian preservation is poor in Units III and IV. In Samples 191-1179C-26R-CC (~283 mbsf) and 27R-CC (~293 mbsf), identification of species was hindered by a high degree of silica recrystallization. Sample 191-1179D-9R-1, 58-62 cm, had a moderately high degree of silica recrystallization; certain species were less affected by the recrystallization, allowing identification.
Samples 191-1179B-1H-CC (7.53 mbsf) and 2H-CC (16.74 mbsf) are assigned to the late Quaternary Botryostrobus aquilonaris Zone (Hays, 1970). The beginning of the middle Quaternary Stylatractus universus Zone (Hays, 1970) is marked by the appearance of Stylacontarium acquilonium in Sample 191-1179B-3H-CC (27.14 mbsf). Also, the faunal assemblages found in Sample 191-1179B-3H-CC and the absence of B. aquilonaris suggest that the boundary between the B. aquilonaris Zone and the S. universus Zone occurs between Cores 191-1179B-2H and 3H. The appearance of S. universus in Sample 191-1179B-4H-CC (36.06 mbsf) confirms that this sample is in the S. universus Zone.
Sediments in Samples 191-1179B-5H-CC (46.16 mbsf), 6H-CC (55.25 mbsf), and 191-1179C-2H-CC (58.28 mbsf) have been assigned to the early Quaternary Eucyrtidium matuyamai Zone (Hays, 1970; Foreman, 1975) on the basis of the presence of E. matuyamai. The faunal assemblage in Sample 191-1179B-3H-CC (67.87 mbsf) suggests that the boundary between the E. matuyamai Zone and the late Pliocene Lamprocyrtis heteroporos Zone (Hays, 1970; Foreman, 1975) occurs between Cores 191-1179C-2H and 3H. The L. heteroporos Zone continues through Sample 191-1179C-7H-CC (105.92 mbsf).
The boundary between the L. heteroporos Zone and the middle Pliocene Sphaeropoyle langii Zone (Foreman, 1975) is marked by the disappearance of S. acquilonium in Sample 191-1179C-8H-CC (115.81 mbsf). The faunal assemblage suggests that the sediments remain in the S. langii Zone through Sample 191-1179C-12H-CC (153.97 mbsf). The boundary between the S. langii Zone and the Stichocorys peregrina Zone (Riedel and Sanfilippo, 1970, 1978) is marked by the appearance of Stichocorys delmontensis and abundant S. peregrina. This boundary occurs between Samples 191-1179C-12H-CC and 13H-CC (162.95 mbsf).
Radiolarians present in Samples 191-1179C-13H-CC through 18H-CC indicate that the section is of middle to late Miocene age, based on the presence of S. delmontensis, S. peregrina, and Sphaeropoyle robusta. The early late Miocene Didymocyrtis antepenultima Zone (Riedel and Sanfilippo, 1970) begins in Sample 191-1179C-20H-CC. This zone is marked by the presence of D. antepenultima and Diartus hughesi. These species are also found in Sample 191-1179C-21H-CC.
Sample 191-1179D-9R-1, 58-62 cm (~358 mbsf), contains radiolarians of Early Cretaceous age. This is evident from the presence of Eucyrtis micropora, a species that ranges from the Valanginian to Barremian.