Shipboard analyses using calcareous nannofossils and planktonic foraminifers reveal a Pleistocene to upper Pliocene sequence in the top 54 mbsf and a poorly preserved upper Miocene interval from 54 to 20 mbsf. Sediment from Hole 1197B was cored from ~60 to ~670 mbsf and yielded age-diagnostic material of variable quality. The hole penetrated an upper Miocene to possible Pliocene sequence unconformably overlying an upper middle Miocene sequence. The majority of the cores from this hole contain no age-diagnostic fauna. Table T4 lists the nannofossil and planktonic foraminifer datums used for age assignments. See "Age Model" for age vs. depth and sedimentation rate data. In addition, benthic foraminiferal assemblages and biogenic constituents were evaluated as environmental indicators. Core catcher samples were the basis for the primary analysis, and some additional samples from within selected intervals were studied to refine the biostratigraphy.
The top seven cores contain abundant late Pliocene through Pleistocene nannofossils. Sample 194-1197A-1H-2, 136 cm, contains common Emiliania huxleyi and abundant Gephyrocapsa spp. (>4 µm) among other taxa and can be assigned an age of 0.08-0.26 Ma. Sample 194-1197A-1H-CC contains only abundant Gephyrocapsa spp. (>4 µm) but no E. huxleyi or Pseudoemiliania lacunosa. This suggests an age of 0.26-0.46 Ma. The last occurrence (LO) of P. lacunosa (0.46 Ma) is placed between Samples 194-1197A-1H-CC and 2H-CC based on the presence of the species in the latter sample. The LO of Calcidiscus macintyrei (1.7 Ma) is located between Samples 194-1197A-4H-CC and 5H-CC. Discoasters were first encountered in Sample 194-1197A-7H-1, 28-30 cm, and this sample is thus older than 2.0 Ma. Sample 194-1197A-7H-1, 28-30 cm, contains Discoaster brouweri, but other species of discoasters are absent. This indicates that the sample has an age of 2.0-2.5 Ma. Below this core, the few core catcher samples available for analysis were barren of nannofossils. The only exception was Sample 194-1197A-20X-CC, which yielded rare specimens of nannofossils, including Reticulofenestra pseudoumbilicus, which suggests an age older than 3.7 Ma.
Samples 194-1197B-2R-CC through 34R-CC yielded generally rare specimens of nannofossils, and no age-diagnostic species were found. By contrast, Samples 194-1197B-35R-CC through 37R-CC yielded common nannofossils. The presence of Cyclicargolithus floridanus and the absence of Sphenolithus heteromorphus in these samples indicates an age of 11.9-13.6 Ma for this interval. Samples 194-1197B-38R-CC through 57R-CC yield generally common nannofossils, with index species S. heteromorphus consistently present. This relatively long interval can be dated by the species stratigraphic range as 13.6-18.2 Ma. Sample 194-1197B-61R-CC also contains common nannofossils. Sphenolithus belemnos and Sphenolithus disbelemnos were found, suggesting an age of 18.5-19.3 Ma (early Miocene). Samples 194-1197B-62R-CC and 63R-CC, which are above a conglomerate and basement, contain only rare or few nannofossils. Index taxa are not present in these two samples, but the flora resemble impoverished early Miocene assemblages.
Samples 194-1197A-1H-CC through 7H-CC reveal an upper Pleistocene (Zone N23) to upper Pliocene (Zones N20-N21) conformable sequence reaching a depth of 54.4 mbsf. Samples 194-1197A-8X-CC through 20X-CC are either barren, lack age-diagnostic fauna, or have 0% recovery. The exceptions are Samples 194-1197A-17X-CC and 20X-CC, which are tentatively assigned an early Pliocene to late Miocene age.
Samples 194-1197A-1H-CC through 5H-CC are Pleistocene based on the presence of Globorotalia truncatulinoides, combined with the LO datums of Globorotalia tosaensis and first occurrence of Pulleniatina finalis. Sample 194-1197A-1H-CC contains the "pin" morphotype of Globigerinoides ruber and therefore has a minimum age of 0.12 Ma based on the Pacific LO datum of this species. Sample 194-1197A-5H-CC contains Globigerinoides extremus, which places its LO datum (1.8 Ma) between Samples 194-1197A-4H-3, 12-14 cm, and 5H-CC, whereas the LO of Globigerinoides fistulosus (1.77 Ma) is placed between 194-1197A-4H-CC and 5H-CC. The LO of Globorotalia pseudomiocenica is placed between Samples 194-1197A-7H-1, 28-30 cm, and 7H-CC, whereas G. tosaensis and Globorotalia limbata are observed in Samples 194-1197A-6H-CC and 7H-CC. This interval can therefore be assigned to the late Pliocene (top of Zones N21 and N20-N21, respectively). Some age-diagnostic taxa are conspicuously absent. For example, Dentoglobigerina altispira and Sphaeroidinellopsis seminulina are expected to occur in these samples but are not observed. In addition, altered specimens of the Pleistocene index fossil G. truncatulinoides were present.
Samples 194-1197A-8X-CC through 20X-CC were either barren, lacked age-diagnostic assemblages, or had 0% recovery and as a result cannot be precisely dated. Sample 194-1197A-17X-CC contains Globorotalia plesiotumida and Globigerinoides bulloideus. It is tentatively assigned to Zones N17 through N19, whereas Sample 194-1197A-20X-CC contains Globigerinoides conglobatus, Globoquadrina dehiscens, and Globoquadrina baroemoenensis, indicating a Zone N17 age.
Sample 194-1197B-3R-CC was the first sample to contain age-diagnostic planktonic foraminifers. Samples 194-1197B-3R-CC through 13R-CC are subject to variable preservation and intermediate to low abundances. Many index fossils are absent or difficult to identify; thus, disappearances or absences have limited diagnostic utility. The interval can be placed within Zones N16 to N18 (4.8-11 Ma), reflecting a late Miocene to earliest Pliocene age range. The upper age limit (4.8 Ma) can be defined between Samples 194-1197B-6R-CC and 8R-CC by specimens of Globoquadrina (e.g., G. baroemoenensis, G. dehiscens, and G. globosa), which were consistently present, whereas the lower age limit was defined by the sporadic occurrence of G. plesiotumida, Globigerina apertura, and G. bulloideus. The age range reference for these globoquadrinids is that of Kennett and Srinivasan (1983), who stipulated the LO datum of G. baroemoenensis as extending to the top of Zone N18 (late late Miocene). Since then, this zone has been moved into the early Pliocene; thus, there is a discrepancy as to the absolute date of the LO datum for this species. This species is unique in these samples because its last appearance can be reliably determined. This matter is dealt with by means of an error box in "Age Model".
The next age-diagnostic Sample is 194-1197B-15R-1, 1-4 cm (184.6 mbsf), which contains Globorotalia siakensis and indeterminate specimens of Globorotalia (F.) robusta that reflect a middle Miocene age between Zones N12 and N13 (12.3-11.65 Ma). Additional samples proved to be barren of planktonic foraminifers. Samples 194-1197B-15R-1, 29-31 cm, 15R-CC, and 21R-CC (251.9 mbsf) contain the same age-diagnostic fauna, suggesting a range between Zones N12 and N14. The apparent hiatus between Sections 194-1197B-13R-CC and 15R-1 (spanning the middle to late Miocene boundary) is supported by a prominent downlapping unconformity on the corresponding seismic profile (see "Seismic Stratigraphy"). The hiatus is placed within Sample 194-1197B-14R-CC (175 mbsf), which is barren of fauna. Samples 194-1197B-24R-CC through to basement at ~670 mbsf contain poorly preserved, low-abundance, nondiagnostic fauna, or are barren.
Microscopic analysis of biogenic constituents (>63 µm), particularly the diverse and often abundant benthic foraminifers, provided data for paleoenvironmental interpretation of the cores from Hole 1197A (Table T5).
Samples 194-1197A-1H-CC (6.13 mbsf) through 6H-CC (53.79 mbsf), in lithologic Unit I (see "Lithostratigraphy and Sedimentology"), are dominated by planktonic foraminifers and pteropods. Upper bathyal benthic foraminiferal taxa, including Cibicidoides, nodosarids, and agglutinated taxa, are common and diverse through this interval. In addition, bioclastic debris from deep hard-bottom communities, including small bryozoan colonies and fragments, solitary corals, alcyonarian spicules, and miliolid foraminifers, is a conspicuous component of this interval.
Sample 194-1197A-7H-CC (54.59 mbsf) marks the transition between the upper interval of predominantly pelagic input and the lower interval of predominantly neritic components. Sample 194-1197A-9X-1, 31-34 cm (59.91 mbsf), is characterized by recrystallized neritic debris and planktonic foraminifers. This sample is from the vicinity is of an apparently reworked hardground (see "Lithostratigraphy and Sedimentology").
Samples 194-1197A-10X-CC (69.43 mbsf) through 20X-CC (165.4 mbsf), representing lithologic Unit II (see "Lithostratigraphy and Sedimentology"), recovered abundant neritic debris, including well-preserved specimens of larger benthic foraminifers, including Lepidocyclina, Amphistegina, Cycloclypeus, and Operculina. The foraminiferal assemblage also includes planktonic foraminifers, as well as Cibicidoides spp., Hoeglandina elegans, and other taxa characteristic of outer neritic/upper bathyal water depths.
Samples 194-1197B-2R-1, 84-86 cm (59.91 mbsf), to 22R-1, 22-24 cm (252.1 mbsf), represent lithologic Units II and III (see "Lithostratigraphy and Sedimentology") and contain abundant neritic debris. A middle neritic source of origin is again indicated by the larger benthic foraminiferal assemblage, which includes Lepidocyclina, Amphistegina, Cycloclypeus, and Operculina. Cibicidoides spp., H. elegans, and other outer neritic/upper bathyal benthic foraminifers are also common. Preservation of fossils ranges from moderate to very poor within this interval. The fossil assemblages between Units II and III differ primarily in the more diverse assemblage in Unit II as compared with the dominance of relatively uniform Lepidocyclina in the sediments of Unit III (see Table T5).
Samples 194-1197B-23R-1, 44-46 cm (261.9 mbsf), through 33R-1, 52-55 cm (358.3 mbsf), represent lithologic Subunit IVA (see "Lithostratigraphy and Sedimentology"). They contain varying proportions of planktonic foraminifers, outer neritic/upper bathyal benthic foraminifers, and silt- to medium sand-sized neritic debris that sometimes includes smaller and larger benthic foraminifers from middle to inner neritic water depths. Samples 194-1197B-34R-1, 96-98 cm (368.4 mbsf), through 57R-CC (598.4 mbsf), representing lithologic Subunit IVB, contain relatively less identifiable neritic debris and substantial amounts of terrigenous clays (see "Lithostratigraphy and Sedimentology"). Increasing lithification downsection complicated assessment.
Samples 194-1197B-58R-7, 66-67 cm (607.4 mbsf), through 62R-CC (641.5 mbsf) are coarse, larger benthic foraminifer-rich grainstones representing most of lithologic Unit V. Bryozoan fragments are also common. Lepidocyclina and Amphistegina are the dominant genera with Cycloclypeus and Operculina present. Samples 194-1197B-63R-4, 89-91 cm (651.0 mbsf), and 64R-2, 125-127 cm (658.3 mbsf), are dark-colored sandstones and conglomerates containing bivalves and Operculina foraminifers.
Hole 1197B did not reach basement but did penetrate dark-colored siliciclastic sandstone and conglomerates whose major clasts appear to be of volcanic origin (lithologic Unit V; see "Lithostratigraphy and Sedimentology"). Thus, the sediments retrieved may reflect an early stage in the flooding of volcanic terrain, as their biotic constituents indicate an origin in inner neritic water depths. The dark sandstone is overlain by Lepidocyclina-rich grainstones with clasts originally produced in middle-neritic water depths, possibly in an open-shelf setting where they were rounded and mixed. The shells also show evidence of transport and likely reworking, as many are well-rounded and blackened or glauconite-filled. Thus, the water depth of the depositional environment is uncertain. However, in two samples, 194-1197B-60R-CC (621.3 mbsf) and 61R-CC (641.5 mbsf), that were disaggregated, only taxa characteristic of middle neritic water depths were seen.
The fine bioclastic sediments of Unit IV appear to have been deposited in a distal periplatform setting in outer neritic to upper bathyal water depths, as indicated by the benthic foraminiferal assemblage. These sediments are dominated by a mixture of fine neritic and planktonic debris, with occasional pulses of slightly coarser sediments that originated in middle to inner neritic depths, as indicated by debris from larger benthic foraminifers that lived within the euphotic zone. The major biogenic constituent difference between subunits in Unit IV is that Subunit IVB received pulses of terrigenous input and the origin of the fine carbonate debris is difficult to determine, whereas Subunit IVA has very little noncarbonate and pulses of recognizable neritic debris. The sequence of sediments seen in lithologic Unit V and Subunit IVB appear to represent a transgressive episode to a distal periplatform setting, followed in Subunit IVA by a progressive increase in platform influence that becomes dominant in Unit III.
Lithologic Unit III (see "Lithostratigraphy and Sedimentology") is characterized by abundant neritic debris, including well-preserved specimens of larger benthic foraminifers. A middle neritic source of origin is indicated by the larger benthic foraminiferal assemblage, whereas the prevalence of outer neritic/upper bathyal benthic foraminifers indicates that the neritic material was transported to a proximal periplatform depositional setting at outer neritic to upper bathyal paleowater depths.
Although there are intervals of fine to medium sand-sized grainstones within Unit III, the predominance of coarser neritic debris, particularly of larger benthic foraminifers, rather abruptly increases at the base of Unit II (175 mbsf). Lepidocyclina dominate sediments of Unit III, which were deposited in the late middle Miocene. A more mixed assemblage with particularly abundant Amphistegina (Fig. F17) is characteristic of the sediments deposited within the late Miocene. However, Lepidocyclina (Fig. F18) are common to abundant in the sediments that were transported from the platform top onto this proximal periplatform setting during the late Miocene. The prevalence of these sediments supports observations from Sites 1196 and 1198 that the range of Lepidocyclina likely extended through the late Miocene, as it does on the Queensland Plateau (Betzler, 1997).
Although depth differences between the platform at Site 1196 and the sediments in lithologic Units II and III at Site 1197 indicate that the latter were deposited ~100 m below the platform top, the sporadic occurrence of Cibicidoides and other outer bathyal/upper neritic benthic foraminifers indicates that the paleowater depths were likely outer neritic depths (150-200 m). This conclusion is supported by the absence of deep euphotic red algal crusts or in-place specimens of very large, flat larger foraminifers such as Cycloclypeus spp. or Lepidocyclina (Eulepidina) sp. that can take advantage of low-light conditions in the 100- to 150-m depth range. The prolific shedding of platform sediments ceased in the late Miocene or early Pliocene as transgression or subsidence deepened the site and hemipelagic sedimentation prevailed.