Site 1136 is located at 59°S on the eastern margin of the SKP, ~35 km east of Site 1135. The relatively thin (~162 m) sediment sequence above basement is composed of ~61 m of lower-middle Eocene foraminifer-bearing nannofossil ooze unconformably overlying ~67 m of Lower and Upper Cretaceous calcareous ooze, sands, and silty clays. The minimum sedimentation rate above and below the major unconformities, is ~10 m/m.y. (Fig. F5).
Relatively good recovery in Cores 183-1136A-2R through 7R revealed an expanded lower to middle Eocene section (foraminifer Zones AP7-AP6; nannofossil Zones CP12b-CP9) containing well-preserved microfossils. This interval has not been recovered from previous drill holes on the Kerguelen Plateau or any other southern high-latitude sites because recovery was prevented by chert stringers. Recovery of this key section at Site 1136A should aid in the refinement of high-latitude middle Eocene biostratigraphic zonations.
The first sediments below the unconformity (lithostratigraphic Unit III) consist of light brown ooze, of probable early Maastrichtian to Cenomanian age, containing abundant inoceramid prisms, sponge spicules, and ostracodes in addition to common planktonic foraminifers and nannofossils. A major hiatus occurs at the boundary between this unit and the zeolitic sands and silty clays of lithostratigraphic Units IV and V. These upper bathyal to outer neritic sediments contain dilute but relatively well-preserved microfossil assemblages (including palynomorphs) of probable mid- to late Albian age, indicating a minimum age for the underlying basalts of ~105-106 Ma. Marine lower Albian has not been recovered during previous drilling on the Kerguelen Plateau. The dark green sands and clays are similar in microfossil composition to Albian sediment drilled at Site 511 (Leg 71) on the Falkland Plateau and appear to be only slightly younger in age than complementary nonmarine, palynomorph-bearing lower Albian red-brown silts and claystones from Site 750 (Leg 120) on the SKP.
The first core recovered no sediment so the first material we dated was from Sample 183-1136A-2R-CC. Preservation is good and nannofossils are abundant in this sample, and, based on the presence of Chiasmolithus solitus, Chiasmolithus sp. cf. Chiasmolithus grandis, and Neococcolithes dubius in the absence of Nannotetrina fulgens and Discoaster kuepperi, we dated this sample as early middle Eocene (upper Zone CP12b-CP13). We also noted rare Lapideacassis sp. and Coronocyclus prionion. We assigned Sample 183-1136A-3R-CC to the same zone, although several discoasters (Discoaster barbadiensis, Discoaster sublodoensis, and Discoaster praebifax) along with Coccolithus formosus and Ellipsolithus sp. document a warmer water influence. Preservation is moderate because of overgrowths on the discoasters.
Based on the presence of common D. kuepperi, abundant D. praebifax, Toweius magnicrassis, rare Discoaster lodoensis, Discoaster sp. cf. D. sublodoensis (five rayed and overgrown) and a single but perfectly preserved specimen of Discoaster cruciformis (Zones CP10-CP12a), we assigned Sample 183-1136A-4R-CC to Subzone CP12a. We also noted Sphenolithus moriformis, C. formosus, and Markalius inversus.
No specimens of D. sublodoensis are present in Sample 183-1136A-5R-CC, which belongs to Subzone CP11b. D. kuepperi is common to abundant and large T. magnicrassus (15 µm) is common.
A few Tribrachiatus orthostylus are present in Sample 183-1136A-6R-CC (which also contains D. lodoensis) and are common in 7R-CC. On that basis we assign both to combined Zones mid-CP11a-CP10, although the former might belong one zone higher if T. orthostylus is reworked. Similarly, the latter sample might belong a half zone lower because it contains no impeccable D. lodoensis. Also present in Sample 183-1136A-7R-CC are Sphenolithus radians, Toweius pertusus (Zones CP5-CP10), Discoaster binodosus (eight rayed), and abundant D. kuepperi (Zones CP10-CP12b).
A marked disconformity separates the above sequence from Sample 183-1136A-9R-CC, which contains a lower Maastrichtian nannoflora strongly diluted by a buff-colored zeolitic silty clay. Present are a few Kamptnerius magnificus, Micula decussata, Reinhardtites levis, Arkhangelskiella cymbiformis, common Biscutum magnum, and a few fragmented Watznaueria barnesae. We noted no Biscutum coronum or Nephrolithus spp., so we assigned the sample to the lower Maastrichtian B. magnum Zone.
Two lithologies were represented in Sample 183-1136A-10R-CC, including a buff zeolitic clay very poor in nannofossils and rich in detrital carbonate. A dark green lithology, however, also rich in zeolite, yielded a mid-Cretaceous assemblage better represented in the subjacent core catcher, as described below.
Samples 183-1136A-11R-CC through 14R-CC (dark clay) contained an abundant and well-preserved assemblage with few to common Axopodorhabdus albianus. In the absence of Eiffellithus turriseiffelii, Sollasites falklandensis, and Eiffellithus monechiae (= Eiffellithus cf. Eiffellithus eximius of authors), we assign them to the tropical/temperate nannofossil Zone NC9A of Bralower et al. (1992, 1993) or the Austral lower Biscutum constans Subzone of Wise and Wind (1977) and Wise (1983). This assignment assumes that S. falklandensis is absent form this site not because of ecological exclusion but rather extinction. Other members of the assemblage include common Prediscosphaera columnata/avitus (6 µm), Prediscosphaera spinosa, rare Sollasites horticus, common Eprolithus floralis, plus Nannoconus truitti, Braarudosphaera africana, Octocyclus reinhardtii, Rhagodiscus splendens, Tetrapodorhabdus decorus, Cyclagelosphaera margerelii, W. barnesae, Watznaueria biporta, Watznaueria ovata, Repagalum parvidentatum, Rotelapillus laffittei, Broinsonia sp. cf. B. dentata, Lapideacassis sp. cf. L. mariae (no spines), B. constans, and Biscutum dissimilis (in Sample 183-1136A-10R-CC).
We reproportioned the correlations of nannofossil datums given in Bralower et al. (1992, 1993, fig. 2) to the newer time scale calibration of Gradstein et al. (1995) for the Albian, and we derived a numerical age for the base of A. albianus of ~106 Ma. Similarly, Subzone NC9A, to which we assigned Cores 183-1136A-10R through 14R, ranges from 105 to 106 Ma. According to this recalibration of the Bralower et al. nannofossil datums, this would be the maximum age for the bottom of the sedimentary sequence at this site (or minimum age for the top of the igneous sequence). In their compilation of Lower Cretaceous nannofossil zones, Bown et al. (1998, fig. 5.2) also recognize nannofossil Subzones NC8C, 9A, and 9B and their definitions; however, these authors extend Subzone NC9A into the upper Albian, rather than confining it to the mid- Albian as do Bralower et al. (1993). In addition, Bown et al. (1998) place the last occurrence datum of S. falklandensis above rather than below the first occurrence datum of A. albianus. They do not, however, attempt to tie their datums to a linear time scale. Nevertheless, their correlations might provide closer agreement between the nannofossil and palynomorph correlations for the age of Sample 183-1136A-10R-CC, which is assigned according to palynomorphs to the upper rather than the mid-Albian (see "Palynology"). Until more precise calibrations are established for Albian nannofossil zones, any numerical ages assigned to zonal boundaries must still be considered only approximate.
Planktonic foraminifers of Paleogene and Late Cretaceous age are comparable to those encountered during previous drilling on the Kerguelen Plateau and are very similar to those recovered from Sites 1135 and 1138 during Leg 183 drilling. The Eocene can be characterized in terms of the Antarctic (AP) zonal scheme of Stott and Kennett (1990; modified by Huber, 1991, and Berggren, 1992). Cita et al.'s (1997) Late Cretaceous biostratigraphy for the Southern Ocean, modified during Leg 183 drilling within the framework of Huber's (1992) Late Cretaceous Austral realm zonal scheme, is used for dating Upper Cretaceous sediments. Further refinement is needed in the Cenomanian to Campanian. Major stratigraphic gaps exist for the Early Cretaceous in the south polar region because of hiatuses and poor microfossil preservation. Therefore, no detailed zonal scheme exists for high-latitude faunas. We therefore compare foraminifers in the stratigraphically lowest part of the section to Albian assemblages encountered during Leg 71 drilling (Deep Sea Drilling Project Site 511) on the Falkland Plateau (Krasheninikov and Basov, 1983; Bralower et al., 1993).
The first core contained only sand and gravel, and we obtained no paleontological core-catcher sample. We examined core-catcher samples from all subsequent cores. Planktonic foraminifers are abundant and well preserved in the Eocene nannofossil ooze of Unit II but are less common in the Upper Cretaceous as a result of dilution by abundant inoceramid prisms. Approximately 60% of the >63-mm size fraction of washed-carbonate residue of Sample 183-1136A-9R-CC consists of these 1- to 2-mm-long calcite crystals. Rare, but moderately well-preserved, foraminifers occur in the clay-rich Albian sediments.
Sample 183-1136A-2R-CC contains a well-preserved assemblage of typical high-latitude middle Eocene acarinimids, subbotinids, Globanomalina spp., and Pseudohastigerina. The age-diagnostic species include Pseudohastigerina micra, Acarinina primitiva, Acarinina matthewsae, and probable Acarinina bullbrooki, placing this sample in the zonal range AP8-AP9. Chiloguembelina spp. and a small six- to seven-chambered planispiral form comparable to Praetenuitella sp. (Huber, 1991, pl. 4, figs. 3, 4) are also common in this sample. Acarinina matthewsae is absent in Sample 183-1136A-3R-CC; we accordingly assign it to Zone AP8. Present in this sample and the subjacent Eocene cores is a very compressed form of Globanomalina, which has four chambers in the final whorl and a distinct peripheral keel. We compare this form to the Paleocene species Globanomalina pseudomenardii. We also found this species in Hole 1135A during Leg 183 drilling (see "Biostratigraphy" in the "Site 1135" chapter), but it has not been previously reported on the Kerguelen Plateau.
Acarinina bullbrooki is absent from the next sample downhole. We assigned this and the subjacent three samples (Samples 183-1136A-5R-CC to 7R-CC) to the AP7 interval that ranges from the last occurrence of A. bullbrooki to the base of the An. primitiva range. Other common elements of the fauna are Globanomalina planoconicus, Globanomalina australiformis, Subbotina velascoensis, Guembelitrioides spp., and Chiloguembelina cubensis. The first appearance datum of P. micra is found approximately within the middle of Zone AP7 (Huber, 1991). On this basis, we assign Samples 183-1136A-4R-CC to 6R-CC, containing P. micra, to the upper part of this zone, and Sample 183-1136A-7R-CC, in which P. micra is absent, to the lower part of Zone AP7. We obtained no core catcher for Core 183-1136A-8R.
The middle Eocene foraminifer-bearing ooze of Unit II unconformably overlies a short interval (~15 m) of light brown calcareous ooze dated as Late Cretaceous. The core catcher of the single core representing this interval (Sample 183-1136A-9R-CC) is dominated by inoceramid prisms but contains relatively common and well-preserved Campanian planktonic foraminifers. The assemblage includes Globigerinelloides multispinus, Heterohelix globulosa, Heterohelix planata, Archeoglobigerina australis, Schackoina multispinata, Globotruncana spp., and Globigerinelloides impensus. Globigerinelloides impensus is a late Campanian marker. The presence of this species allowed us to place the sample in the total range zone bearing that name. It occurs with a small planispiral form resembling G. impensus, which is comparable to Globigerinelloides sp. recorded by Huber (1990, pl. 1, figs. 8, 9) and Quilty (1992, pl. 1, figs. 22, 23) and present in the Campanian across the Kerguelen Plateau (see "Biostratigraphy" in the "Site 1135" chapter, "Biostratigraphy" in the "Site 1137" chapter, and "Biostratigraphy" in the "Site 1138" chapter). Inoceramid prisms are common in samples of this age.
The zeolitic sands and silty clays of Unit IV and V that lie unconformably below the Campanian nannofossil ooze contain extremely rare but relatively well-preserved planktonic foraminifers. Among the abundant detrital carbonate grain aggregates and zeolite crystals in Samples 183-1136A-11R-CC to 14R-CC, we find impoverished, low-diversity assemblages that lack characteristic Upper Cretaceous taxa, but contain small genera such as Globigerinelloides, Hedbergella, and Schackoina. We found the best preserved and abundant microfossils of this interval in Sample 183-1136A-14R-CC. In this sample, we recognized Hedbergella planispira and Hedbergella delrioensis. The occurrence of these species in the absence of bisereal Heterohelix spp. and ornate keeled forms is indicative of the Early Cretaceous (Caron et. al., 1985; Bralower et al., 1993).
Palynomorphs were found in the lowermost sediment cores. Sample 183-1136A-10R-CC definitely represents a marine environment, possibly from shallow water, close to shore. The kerogen is dominantly of marine origin, composed of amorphous organic matter and more than 90% dinoflagellate cysts.
The dinoflagellate flora are diverse, well preserved, and contain the genera Oligosphaeridium, Litosphaeridium, Trichodinium, Spiniferites, Gardodinium, and Pseudoceratium. According to Williams (1993), the species Litosphaeridium siphonophorum, identified in this sample, is a good index fossil for a mid- to late Albian age. Another taxon, Pseudoceratium exquisitum, also indicates a mid- to late Albian age. We also found a few smooth, thin-walled trilete spores, which are not age diagnostic but indicate a terrestrial influence.
Sample 183-1136A-14R-CC, from the terminal sediment core, also contains a marine flora, but the environment represents a stronger terrestrial influence than in the previous sample. The terrestrial influence is reflected by diverse spores with various wall shapes and appendices; the material also contains fungal spores and Vitrisporites sp., a saccate pteridosperm pollen. Among a rich flora of dinoflagellate cysts, we also found organic foraminiferal remains (test linings).