Hole 1196A is composed of 662.6 m of Miocene limestone and dolomite underlain by upper Oligocene siliciclastics. Calcareous nannofossils found near the middle of the carbonate platform sequence indicate an age of 13.6-18.2 Ma. Nannofossils were also found in claystone directly below the carbonate platform sequence beginning at Core 194-1196A-70R), providing an estimated age of 24.2-24.6 Ma. The latter sample was also examined for planktonic foraminifers, but only rare, non-age diagnostic taxa were found. Core catcher samples of lithified reef facies were not processed for nannofossils or planktonic foraminifers, as representative samples proved to be barren of these microfossils. A thin section of Sample 194-1196A-1R-1, 1-4 cm, contained age-diagnostic planktonic foraminifers of the Globorotalia tosaensis-truncatulinoides lineage and provided a maximum age of 3.2 Ma.
Microscopic analysis of biogenic constituents including benthic foraminifers provided data for biostratigraphic analysis and paleoenvironmental interpretation. Distinctive benthic foraminifers in Samples 194-1196A-25R-1, 78 cm, through 35R-1, 38 cm, and 194-1196B-33Z-1, 79-81 cm, through 51Z-1, 0-5 cm, indicate an age of 13.3-15.2 Ma. Core catcher samples were the primary basis for analysis, supplemented by thin sections and direct core observations. Table T5 summarizes those observations.
Although the first two core catcher samples were processed for nannofossils examination, no specimens were found. The remaining core catcher samples are lithified reef facies and were not processed for nannofossils. However, Sample 194-1196A-34R-1, 40-44 cm, from a thin siltstone bed near the middle of the carbonate platform (see "Lithostratigraphy and Sedimentology") contains the following taxa: Coccolithus pelagicus, Reticulofenestra haqii, Reticulofenestra producta, Sphenolithus abies, and Sphenolithus heteromorphus. The presence of the last species constrains the age of the sample to 13.6-18.2 Ma. Another sample from the last core immediately below the carbonate platform (Sample 194-1196A-70R-1, 133 cm) contains common well-preserved nannofossils including Zyghrablithus bijugatus, Reticulofenestra bisecta, and Cyclicargolithus floridanus. This assemblage, coupled with the absence of Sphenolithus ciperoensis, suggests an age of 24.2-24.6 Ma.
Samples 194-1196B-20Z-CC, 32Z-CC, 45Z-CC, and 47Z-CC are barren of calcareous nannofossils. Sample 194-1196B-40Z-1, 2 cm, contains rare nannofossils including S. heteromorphus, which constrains the age to 13.6-18.2 Ma. Samples 194-1196B-40Z-1, 18 cm, and 49Z-CC also contain rare nannofossils, which reflect impoverished assemblages of middle to early Miocene age.
Benthic foraminifers characteristic of shallow carbonate platform environments are abundant throughout most of the sequence sampled in Hole 1196A (Table T5). Rhodoliths and red algal fragments are the major constituents of the limestones and dolomites, found in Samples 194-1196A-1R-1, 112-114 cm (1.12 mbsf), through 65R-5, 30-33 cm (621 mbsf).
In lithologic Unit I (see "Lithostratigraphy and Sedimentology"), benthic foraminifers belonging to the common tropical genus Amphistegina are abundant in most rhodolith-dominated facies. In this facies, benthic foraminifers are sufficiently well preserved to be identified in hand specimen or by surficial examination using a stereomicroscope (e.g., Samples 194-1196A-1R-1, 112-114 cm [1.12 mbsf], through 10R-1, 132-134 cm [87.12 mbsf]; Table T5). Thin sections are required to determine the taxa of larger benthic foraminifers that accompany Amphistegina. For example, Sample 194-1196A-1R-1, 1-4 cm, confirmed not only the presence of very robust, often broken and rounded Amphistegina but also exceptionally robust Operculina complanata and a small piece of a specimen of Lepidocyclina sp.
In Samples 194-1196A-9R-2, 73-75 cm (78.25 mbsf), through 16R-1, 74-76 (144.24 mbsf), and 18R-3, 118-121 (166.85 mbsf), through 19R-3, 60-62 cm (175.8 mbsf), the larger benthic foraminifers were primarily seen as molds of varying morphologies (Table T5).
The benthic foraminiferal assemblage in Samples 194-1196A-20R-1, 111-113 cm (183.01 mbsf), through 35R-1, 38-40 cm (326.68 mbsf) (lithologic Subunit IIA; see "Lithostratigraphy and Sedimentology") is characterized by abundant porcellaneous foraminifers of the order Miliolina. Of key importance is the occurrence of Flosculinella botangensis (Fig. F32), which is believed to be restricted to Zones N9-N10 (13.3-15.2 Ma) in northern Australia (Chaponiere, 1984). These alveolinids occur with large soritid foraminifers including an unknown species with characteristics of the genus Cyclorbiculina (Fig. F33), as well as very abundant members of the family Miliolidae. In Samples 194-1196A-39R-1, 0-2 cm (364.7 mbsf), through 42R-1, 14-16 cm (393.64 mbsf), which are part of lithologic Subunit IIIA (see "Lithostratigraphy and Sedimentology"), small rhodoliths occur in a grainstone that contains abundant Lepidocyclina and Amphistegina.
Samples 194-1196A-44R-1, 107-109 cm (413.75 mbsf), through 65R-5, 30-33 cm (620.95 mbsf), which make up lithologic Unit III and the top of Unit IV (see "Lithostratigraphy and Sedimentology"), are heavily dolomitized, and generally larger foraminifers are only preserved as molds. In Samples 194-1196A-44R-1, 107-109 cm (413.75 mbsf), though 51R-4, 56-58 cm (484.93 mbsf), Sample 194-1196A-53R-4, 122-124 cm (504.92 mbsf), and Samples 194-1196A-62R-1, 42-47 cm (586.22 mbsf), through 63R-2, 46-48 cm (597.45 mbsf), abundant molds indicate that large, flat benthic foraminifers were an important constituent of the original sediment. In Samples 194-1196A-57R-3, 30-32 cm (540.93 mbsf), through 61R-2, 46-48 cm (578.13 mbsf), molds indicative of robust larger benthic foraminifers are abundant. In Samples 194-1196A-64R-3, 145-150 cm (609.5 mbsf), and 65R-5, 30-33 cm (620.95 mbsf), the molds are smaller and indicative of abundant Amphistegina in the original sediment. Samples 194-1196A-52R-6, 46-48 cm (497.60 mbsf), and 54R-1, 127-129 cm (510.17 mbsf), through 56R-2, 47-49 cm (529.75 mbsf), appear to have a fine grainstone fabric with red algal and soritid debris, which may originally have been similar to Subunit IIA.
Lithologic Unit IV includes various facies of siliciclastic-rich dolo-stone (see "Lithostratigraphy and Sedimentology"). Two samples from this unit, Samples 194-1196A-66R-4, 106-108 cm (629.78 mbsf), and 67R-2, 90-93 cm (635.98 mbsf), contain fragments of bryozoans and red algae with abundant larger foraminifers, particularly Operculina complanata. Lithologic Unit V was dominantly siliciclastic and phosphatic; marine nannofossils were recovered from Sample 194-1196A-70R-1, 133 cm.
Benthic foraminifers characteristic of shallow carbonate platform environments are abundant throughout the sequence sampled in Hole 1196B (Table T5), which was wholly within lithologic Units I and II (see "Lithostratigraphy and Sedimentology"). Rhodoliths, red algal crusts, and fragments are the major constituent of algal-dominated facies found in Samples 194-1196B-1R-3, 37-40 cm (3.29 mbsf), through 32Z-1, 27-29 cm (180.47 mbsf). As in Hole 1196A, benthic foraminifers belonging to the common tropical genus Amphistegina are major constituents of the grainstone and packstone matrices of the rhodolith-dominated facies that are sufficiently well preserved to identify the foraminifers in hand specimen or by surficial examination using a stereomicroscope. Thin sections are required to determine the range of taxa of larger benthic foraminifers.
The benthic foraminiferal assemblage in Samples 194-1196B-33Z-1, 79-81 cm (185.69 mbsf), through 51Z-1, 0-5 cm (260.6 mbsf) (lithologic Subunit IIA; see "Lithostratigraphy and Sedimentology"), contains abundant porcellaneous foraminifers of the order Miliolina. F. botangensis (Fig. F32) is again abundant in samples from this subunit. In addition, Astrotrillina howchini, which has commonly been found in association with F. botangensis by Chaproniere (1981, 1984), was also recorded in Sample 194-1196B-49Z-1, 30-37 cm (251.5 mbsf).
Biostratigraphic evidence provided in Table T5 indicates a late Oligocene to possible late Miocene age range for the sequence sampled at Site 1196. The occurrence in lithologic Subunit IIA of the alveolinid, F. botangensis, whose age range is Zones N9-N10 (N12?), combined with data provided by nannofossils for Sample 194-1196A-34R-1, 40-44 cm (317.0 mbsf), and 194-1196B-40Z-1, 2 cm (217.8 mbsf), indicates a middle Miocene age between 13.3 and 15.2 Ma for that subunit.
Interpreting paleowater depths and depositional environments is somewhat problematic, given the poor core recovery (~13%; see "Operations"). Rhodoliths and red algae, which are the dominant constituents of most of the rocks in this sequence, can dominate carbonate facies from intertidal to depths of 150 m (Tsuji, 1993).
Likewise, the larger benthic foraminifers can occur over this range. Amphistegina, Operculina, Cycloclypeus, and Lepidocyclina are genera whose assemblages and test morphologies tend to reflect ambient light levels and water motion. Robust morphologies are most common in shallow, high light, high energy environments, often <10 m and generally <30 m water depth. For example, the robust, frequently broken Amphistegina specimens seen in the thin section from Sample 194-1196A-1R-1, 1-4 cm, may indicate beach sand, particularly when considered along with the cementation history that suggests subaerial exposure (see "Lithostratigraphy and Sedimentology"). Flatter morphologies are typical of deeper, quieter, lower-light conditions below 60 m. Very flat morphologies and the predominance of very large Cycloclypeus spp. are typically found at depths between 100 and 150 m. No biofacies indicative of these extremes were seen in the sequence.
Shape trends in the larger foraminiferal tests and molds, combined with information on the presence and types of coralline algae, coral, and other lithologic details (see "Lithostratigraphy and Sedimentology") were used to interpret paleowater depths as shown in Table T5 and are summarized below. Thin section analyses will undoubtedly refine or revise these interpretations.
Unit V is partly siliciclastic and of unknown water depths. Unit IV is mixed siliciclastics and bioclastic carbonates. In modern reef and open-shelf environments, Operculina are most commonly found at middle neritic depths (30-100 m) (Hohenegger, 1999). However, they can live in shallower environments where limited siliciclastic input diminishes water transparency (e.g., Hallock, 1984). The abundance of relatively robust Operculina in the middle of this interval, which contains not only significant siliciclastics but also exposure surfaces, likely indicates an inner-neritic water-depth range of <30 m.
Highly dolomitized intervals of Unit III are difficult to interpret because red algal crusts and fragments are often the only identifiable constituent. A possible exposure surface at the base of Subunit IIID, overlain by dolomites with Amphistegina-type molds then flat Lepidocyclina- and Operculina-type molds, may indicate a deepening upward from inner to middle neritic depths (Table T5). This interval is followed by more robust molds, indicating shallowing into Subunit IIIC. Several possible exposure surfaces have been observed within Subunit IIIC (see "Lithostratigraphy and Sedimentology"). The upward return to fabrics with flat Lepidocyclina- and Operculina-type molds suggests another deepening to middle neritic depths in the upper part of Subunit IIIB and in Subunit IIIA. The larger foraminiferal molds again become more robust in Subunit IIB, indicating shallowing to possible exposure surfaces near the base of Subunit IIA.
The soritid and miliolid foraminifers abundant in Subunit IIA commonly occur in association with seagrass. Thus, the abundance of these foraminifers, combined with frequent occurrences of trace fossils that probably derive from seagrass blades and roots, indicate that much of Subunit IIA was deposited in water depths of <10 m, certainly no deeper than 30 m. The grainstone fabric of these sediments, as noted in sample thin sections 194-1196A-33R-1, 19-23 cm, and 33R-1, 121-125 cm, indicate sufficient water motion to remove mud-sized particles despite the sediment baffling potential of the seagrass. This fabric indicates a shallow, open-platform setting, perhaps similar to Seranilla Bank on the Nicaraguan Rise in the western Caribbean (Triffleman et al., 1992), rather than a sheltered lagoonal setting.
Interestingly, the 143-m-thick Subunit IIA provides the strongest evidence for a prolonged episode of very shallow water. It is also the best age-constrained interval at 13-15 Ma, which is also approximately the time of the highest sea level stand during the middle Miocene (Haq et al., 1987). Open-platform sedimentation rates can be estimated in the range of 20-50 cm/k.y. (e.g., Hallock, 1981). Thus, 143 m of sediment could represent ~0.3-0.7 m.y. of accumulation. It may be more problematic explaining the availability of 143 m of accommodation space through this interval, as sea level rise was likely <100 m within the third-order cycle 2.4 (Haq et al., 1987), and subsidence rates are estimated to be an order of magnitude lower (see the Leg 194 Scientific Prospectus).
Possible exposure surfaces are interpreted at the top of Subunit IIA and in Subunit ID (see "Lithostratigraphy and Sedimentology"). Subunit IC appears to represent a reef interval characterized by coral/algal boundstones. The grainstones of Subunit IB are quite similar to those in Subunit ID and could possibly represent carbonate sands shed from a reef. The history of the late middle Miocene sea level fall may be contained within the Subunits ID-IB interval. Subunit IA likely represents a deepening upward to middle neritic depths in an open-platform setting. This was followed by a final shallowing trend to possible beach sands at the top, just below a hiatal surface, which is discussed in more detail in ""Lithostratigraphy and Sedimentology".
The age of Unit I is uncertain. The occurrence of Lepidocyclina spp. near the top of lithologic Unit I (i.e., a fragment in Sample 194-1196A-1R-1, 1-4 cm [0.01 mbsf] and a whole specimen in Core 194-1196A-6R-1, 76 cm [48.26 mbsf]) suggests a middle Miocene age (Zone N12) for the shallow-water carbonates at the platform top (Chaproniere 1981, 1984; Chaproniere and Betzler, 1993). However, recent studies from the Queensland Plateau indicate that the range of Lepidocyclina extends into the late Miocene (Betzler, 1997). Very recent data from Papua New Guinea also indicate that Lepidocyclina may extend into the late Miocene to at least Zone N16 (8.4 Ma) (Allan et al., 2000). Results from offshelf sites from Leg 194 could provide clarification of the upper age range of Lepidocyclina in this region.
Hole 1199A consists of 410.1 m of Miocene limestones and dolomites, as indicated by the assemblages of larger benthic foraminifers. Core catcher samples of lithified reef facies were not processed for nannofossils or planktonic foraminifers, as representative samples proved to be barren of these microfossils. Distinctive benthic foraminifers in several samples between Sample 194-1199A-20R-1, 93 cm (170.3 mbsf), and 30R-1, 39 cm (265.9 mbsf), indicate an age of 13.3-15.2 Ma for this interval. Core catcher samples were the primary basis for analysis, supplemented by direct core observations. Table T6 summarizes these observations.
Benthic foraminifers characteristic of shallow carbonate platform environments are abundant throughout most of the sequence in Hole 1199A (Table T6). Red algae (as rhodoliths) and larger benthic foraminifers are the major constituents of both limestones and dolomites that are found in Samples 194-1199A-1R-4, 21-23 cm (4.52 mbsf), through 45R-1, 16-18 cm (410.1 mbsf) (see "Lithostratigraphy and Sedimentology").
In lithologic Subunit IA (see "Lithostratigraphy and Sedimentology"), benthic foraminifers belonging to the common tropical genus Amphistegina are abundant as at Site 1196. Large individual specimens of Lepidocyclina were seen in Samples 194-1199A-6R-3, 50 cm (39.2 mbsf), and 7R-2, 20 cm (46.7 mbsf), confirming a Miocene age. The assemblages of larger benthic foraminifers in Unit I indicate euphotic depths of <100 m.
The benthic foraminiferal assemblages between Samples 194-1199A-20R-1, 93-95 cm (170.3 mbsf), and 30R-1, 39-41 cm (265.9 mbsf) Subunit IIA; see "Lithostratigraphy and Sedimentology"), are more variable than comparable intervals at Site 1196. Nevertheless, porcellaneous foraminifers of the order Miliolina are again important sediment constituents in this interval. The sporadic occurrence of F. botangensis (Table T6) is of key significance, as it is believed to be restricted to Zones N9-N10 (13.3-15.2 Ma) in northern Australia (Chaproniere, 1984). Soritids are much less prominent in this interval than at the comparable depths at Site 1196 (see Table T5).
Samples 194-1199A-35R-1, 130-132 cm (315 mbsf), through 45R-1, 16-18 cm (410.1 mbsf), which are part of lithologic Subunit IIB (see "Lithostratigraphy and Sedimentology"), represent a larger benthic foraminiferal and red algal-dominated grainstone to floatstone facies that was not seen at Site 1196. The assemblage of larger benthic foraminifers, characterized by the overwhelming dominance of Lepidocyclina in Subunit IIB, differs from that in Subunit IA, which is more diverse and tends to be dominated by Amphistegina.
Biostratigraphic evidence provided by the larger benthic foraminifers indicates a Miocene age for the sequence sampled at Site 1199. The occurrence in lithologic Subunit IIA of the alveolinid F. botangensis, whose range is Zones N9-N10 (Chaproniere, 1981, 1984), indicates a middle Miocene age for this subunit. As at Site 1196, the occurrence of Lepidocyclina in Unit I suggests a middle to late Miocene age (i.e., Chaproniere, 1981, 1984; Chaproniere and Betzler, 1993; Betzler, 1997).
The red algae and larger benthic foraminifers found in Unit I can dominate carbonate facies from intertidal to depths of 150 m (Hallock, 1984; Tsuji, 1993). Shape trends in the larger foraminiferal tests and molds, combined with information on the presence and types of coralline algae, coral, and other lithologic details (see "Lithostratigraphy and Sedimentology"), suggest paleowater depths as <100 m (Table T6).
Paleodepth estimates for lithologic Subunit IIA are not as straightforward as at comparable platform depths at Site 1196. At Site 1199, soritids were much less common, and no organic trace fossils were observed that would indicate a seagrass environment. Sediments at Site 1199 were subject to poor recovery and were relatively more variable. Combined with the 22-m elevation difference in the unit top between sites (182 mbsf at Site 1196 and 160 mbsf at Site 1199) (see "Lithostratigraphy and Sedimentology"), this facies variability on the scale of kilometers suggests some relief on the platform top. Paleowater depths are conservatively interpreted as shallower than 30 m throughout this interval.
Lithologic Subunit IIB is dominated by larger foraminifer-rich grainstone and floatstone with varying proportions of red algae. The abundance, robustness, and sorting of the Lepidocyclina indicate a range of paleowater depths between intertidal and <100 m.