SKP Site 1135, 59°42´S latitude, was the southernmost site drilled during Leg 183. A 526-m succession of Quaternary to Upper Cretaceous sediments was recovered.
Underlying a thin cover of Pliocene diatom ooze (lithologic Unit I) is a 238-m-thick expanded section of middle Eocene to uppermost Paleocene nannofossil ooze with well-preserved calcareous microfossils (lithologic Subunits IIA and IIB). This interval is not well represented in cores recovered during previous coring on the Kerguelen Plateau or elsewhere in the Southern Ocean at these high latitudes (~60°S). Despite chert stringers in the section, recovery was relatively good, resulting in a section that should provide an opportunity to improve high-latitude Paleogene biostratigraphic correlations. Below an incomplete K/T boundary in Core 183-1135A-28R recovery was generally poor through a Maastrichtian to Santonian chalk section in which microfossil preservation is variable and decreases at depth (lithologic Subunits IIIA to IIIC). Maastrichtian-Campanian foraminifers, however, are extremely well preserved. The seafloor depth at this location was 1567 m; thus, the site lay well above the carbonate compensation depth during the Paleogene and Cretaceous. Although drilling at Site 1135 did not succeed in reaching the basement objectives, it provided the most expanded Upper Cretaceous carbonate section continuously cored on the Kerguelen Plateau.
Sedimentation rates were high in the Paleogene ooze (up to 15 m/m.y.) and Cretaceous chalks (8 m/m.y.; see Fig. F7). The Paleocene section, however, is abbreviated by hiatuses, and the overall sedimentation rate was only 1.7 m/m.y. The K/T boundary, although lithologically distinct, also appears to have been abbreviated in that the basal high-latitude Danian nannofossil Zones NA1 and NA2 are missing.
Only a small core-catcher sample was recovered in the first core, which contained a semiconsolidated piece of diatom ooze with a few etched nannofossils (Coccolithus pelagicus). The diatom Thalassiosira insigna is abundant, and we assigned the sample to the mid-Pliocene T. insignis/Thalassiosira vulnificus Zone. We described no other diatoms from this hole, although some are present in the Paleogene.
Samples 183-1135A-2R-CC to 4R-CC contain a middle Eocene assemblage consisting of Reticulofenestra umbilica, Chiasmolithus solitus, Chiasmolithus expansus, Neococcolithes dubius, sporadic Chiasmolithus grandis, plus Zygrablithus bijugatus, and we assigned the samples to Subzone CP14a. A few overgrown six- and eight-rayed discoasters are present in Sample 183-1135A-3R-CC and may represent somewhat warmer conditions than in the subjacent core.
No core-catcher sample was recovered in Core 183-1135A-5R, and R. umbilica is extremely rare in Sample 183-1135A-6R-CC, which we tentatively assign to the next older zone. We assigned Samples 183-1135A-7R-CC to 16R-CC to the combined Zone CP12-CP12b (upper part) based on the absence of R. umbilica and Discoaster kuepperi. The index taxon used to separate those two zones, Nannotetrina fulgens, is either absent or extremely rare at this site in that we did not observe it in any core-catcher sample. We first noted Discoaster praebifax and Discoaster saipanensis in Sample 183-1135A-12R-CC and Nannotetrina cristata in 13R. No sediment was recovered in Core 183-1135A-14R. Discoaster sublodoensis was recovered within the "few" category in Sample 183-1135A-15R-CC and increases somewhat in abundance downhole.
We assigned Sample 183-1135A-17R-CC to the lower part of Subzone CP12b and Subzone CP12a based on the presence of D. kuepperi and D. sublodoensis. Discoaster lodoensis is abundant and large (up to 22 µm). Also present are rare to few D. praebifax and Discoaster barbadiensis and abundant D. lodoensis and Coccolithus formosus. Core 183-1135A-18R recovered no sediment.
Discoaster sublodoensis and D. praebifax are absent in Samples 183-1135A-19R-CC and 20R-CC, but D. lodoensis and Sphenolithus radians are common; we assigned the sample to the early Eocene Zone CP11b. Also present are common to abundant Toweius magnicrassus and a small assortment of discoasters.
Tribrachiatus orthostylus is common to abundant in Samples 183-1135A-21R-CC to 23R-CC, which we assigned to the combined lower CP11 to CP10 Zones of Okada and Bukry (1980) or Zone NP12 of Martini (1971). We did not observe Coccolithus crassus, which is used to separate CP11 from CP10. Other taxa noted within this interval were Sphenolithus moriformis, nine-rayed Discoaster nonaradiatus, and Discoaster binodosus, rare to abundant D. lodoensus (up to 27 µm), abundant D. kuepperi, common Girgisia gammation, few Markalius inversus, and, in Section 183-1135A-23R-CC, abundant S. radians. No sediment was recovered in Core 183-1135A-24R.
Sample 183-1135A-25R-CC lies very close to the Eocene/Paleocene boundary and contains Discoaster multiradiatus, small fasciculiths, Prinsius bisulcus, Thoracosphaera operculata operculi, N. dubius, and possible Discoaster diastypus. Sample 183-1135A-17R-CC, on the other hand, is clearly latest Paleocene in age, as it contains D. multiradiatus, large fasciculiths, common Coccolithus robustus, small (6-µm) Heliolithus spp., Toweius eminens, Chiasmolithus consuetus, and possible Discoaster mohleri. We assigned it to Zone CP8.
Thoracosphaera operculata and other thoracosphaerids are abundant, fasciculiths are rare and small (5-6 µm), and Prinsius martinii is very abundant in Sample 183-1135A-27R-CC, which we tentatively assign to the high-latitude nannofossil Zone NA6. Kamptnerius magnificus is a rare Cretaceous contaminant in this sample.
We examined several samples within Core 183-1135A-28R to locate the K/T boundary. The boundary appeared to be marked by a disconformity in Section 183-1135A-28R-2 between 124 and 125 cm, where a bioturbated white and greenish chalk is overlain by white chalk. Below the boundary, nonbioturbated white chalk clasts(?) contain a characteristic uppermost Cretaceous assemblage, whereas the green glauconitic matrix sediment between these clasts yielded a few Danian taxa, such as Hornibrookina sp., Cruciplacolithus primus (7 µm) and Chiasmolithus danicus, and abundant M. inversus. This interval appears to be an erosional or mass-wasting event (see "Lithostratigraphy").
White chalk immediately above this contact yielded highly abundant Prinsius dimorphosus, abundant T. operculata, and common C. primus/Cruciplacolithus tenuis, an assemblage we assigned to the lower Paleocene Zone NA3 as Zones NA1 and NA2 are missing here. This is not a complete K/T boundary, and there has apparently been nondeposition or more likely erosion and/or mass-wasting along this contact.
Preservation in Sample 183-1135A-28R-CC is noticeably diminished compared to the Danian in that most of the specimens are fragmented and unidentifiable. We assign this sample and the next four down to 32R-CC to the late Maastrichtian Cribrosphaerella daniae Subzone of the Nephrolithus frequens ssp. miniporus Zone, following the high-latitude zonation of Watkins et al. (1996). The assemblage includes rare N. frequens ssp. miniporus in Sample 183-1135A-29R-CC. Within this and Sample 183-1135A-30R-CC we noted abundant Prediscosphaera cretacea, Prediscosphaera bukryi, Gartnerago obliquum, K. magnificus, Arkhangelskiella cymbiformis, Repagalum parvidentatum, Lucianorhabdus cayeuxii, Acuturris scotus, Eiffellithus turriseiffelii, G. obliquum, Cribrosphaerella ehrenbergii, L. cayeuxii, and Micula decussata; common Cretarhabdus conicus, C. daniae rims, and Ahmuellerella octoradiata; and few Lithraphidites carniolensis, Biscutum constans (small, ~4 µm), and Prediscosphaera stoveri. The abundance of N. frequens varies from rare in Sample 183-1135A-30R-CC to abundant in 32R-CC.
We assigned Sample 183-1135A-33R-CC, containing abundant Biscutum magnum and Glaukolithus bicrescenticus, to the respective early Maastrichtian zone and subzone that bear those names. Reinhardtites levis is also abundant, and we noted Rhagodiscus angustus, Calculites obscurus, Monomarginatus quaternarius, P. stoveri, and Biscutum dissimilis in the assemblage. We noted Biscutum notaculum and rare Placozygus sigmoides in the subjacent Sample 183-1135A-34R-CC, which belongs to the same subzone and zone.
Specimens of Neocrepidolithus watkinsii are few in Samples 183-1135A-35R-CC and 36R-CC, which we assigned to the latest Campanian zone of that name. Nephrolithus corystus are few in the former sample, but well preserved, and the overall preservation of this assemblage is moderate. Some specimens show signs of overgrowth. For the most part, Nephrolithus is poorly preserved in Sample 183-1135A-36R-CC; however, only the rims are preserved.
We tentatively assigned Samples 183-1135A-37R-CC and 38R-CC to the N. watkinsii Zone, although we saw no Nephrolithus in either core, despite the fact that preservation improved to moderate/good in the latter core catcher. We observed the first Watznaueria barnesae (few in number) downhole in Sample 183-1135A-38R-CC; rare Lapideacassis and Helicolithus trabeculatus are present in 39R-CC.
Biscutum coronum is rare in Sample 183-1135A-39R-CC, which we assigned to the zone of that name. We did not distinguish the Psyktosphaera firthii from the subjacent R. parvidentatum Subzone because we saw no Nephrolithus species in this part of the section. Monomarginatus spp. are also absent, but rare B. dissimilis is present.
Samples 183-1135A-40R-CC to 42R-CC belong to the Aspidolithus parcus ssp. expansus Subzone of the B. coronum Zone based on the presence of the nominate taxon, including the subspecies Aspidolithus parcus ssp. constrictus in Sample 40R-CC. Neocrepidolithus watkinsii is large (major axis = 13.5 µm) with well-developed spines, but a single specimen of B. dissimilis is very small (~ 4.5 µm), with only seven elements. Both B. magnum and B. coronum are few in Sample 183-1135A-41R-CC, in which preservation is improved over the superjacent sample. We noted Reinhardtites elegans (= Reinhardtites anthophorus of many authors [small openings observed in phase contrast light on either side of the central column]) in Sample 183-1135A-42R-CC along with abundant Tranolithus phacelosus.
Eiffellithus eximius is rare to few but consistently present in Samples 183-1135A-43R-CC to 46R-CC, which we assign to the late Campanian zone of that name and the R. levis Subzone. Prediscosphaera sp. cf. P. grandis (11.5 µm) and H. trabeculatus are rare in Sample 43R-CC. Biscutum coronum is common to abundant in this and the subjacent core catcher, but B. magnum is rare. Holococcoliths are abundant in contrast to intervals of similar age at Site 750, which indicates that Site 1135 was well above the lysocline during the Cretaceous. Sample 183-1135A-45R-CC, however, is silicified and essentially barren of extractable nannofossils.
Sample 183-1135A-47R-CC contains Seribiscutum primitivum, B. coronum, B. dissimilis, and R. anthophorus but no R. levis; we assigned it to the early Campanian Chiastozygus garrisonii Zone. A hiatus may separate it from the superjacent sample. No core-catcher samples were received from Cores 183-1135A-48R and 49R as recovery in this portion of the hole (Cores 183-1135A-45R to 51R) was less than 10%.
Nevertheless, we detected the mid- to upper Coniacian Zeugrhabdotus kerguelensis Subzone of the Placozygus fibuliformis Zone in Sample 183-1135A-50R-CC, where Z. kerguelensis is rare but distinctive and accompanied by Thiersteinia ecclesiastica. Quadrum gartneri is common. Thiersteinia ecclesiastica is also present in Sample 183-1135A-51R-CC, where it is accompanied by common to abundant Eprolithus floralis, abundant S. primitivum, common W. barnesae, and few H. trabeculatus, E. eximius, and A. octoradiata. We assigned this sample and Sample 183-1135A-52R-CC to the Z. kerguelensis Subzone.
Sample 183-1135A-54R-CC contained few E. floralis, E. eximius (with bar angles at 15° off the major and minor axes), K. magnificus, G. obliquum, and possible Reinhardtites anthoporus. We consider it no older than middle Turonian in age. Sample 183-1135A-55R-CC yielded few nannofossils, and we made no age assignment.
The Neogene record of Site 1135 is represented by some biosiliceous ooze recovered with ice-rafted sand and gravel in core-catcher Sample 183-1135A-1R-CC. The diatom-rich ooze contains a low-diversity Neogene planktonic foraminifer assemblage dominated by left-coiling Neogloboquadrina pachyderma (Zone AN7).
Well-preserved middle Eocene faunas (Zone AP10) containing common Chiloguembelina cubensis, Globigerinatheka index, Subbotina linaperta, and Acarinina collatea characterize core-catcher Samples 183-1135A-2R-CC to 8R-CC. The planktonic foraminifer fauna in this interval is relatively low in diversity and dominated by long-ranging, slow-evolving acarininids and subbotinids. Assemblages lack many of the distinctive morozovellids, hantkeninids, turborotalids, and globigerinathekids found in Eocene-age sediments at low latitudes. Biostratigraphic correlation of these sediments is therefore limited. Acarininid abundance and diversity increases temporarily in Sample 183-1135A-8R-CC. Morozovella spinulosa, a keeled species in this sample, is usually limited to the lower latitudes and appeared briefly at this site, perhaps indicating warmer surface waters.
The downhole first appearance datum (FAD) of G. index occurs in Core 183-1135A-9R. This datum marks the boundary between Zones AP10 and AP9 and allowed us to assign Sample 183-1135A-9R-CC to the early middle Eocene Zone AP9. The planktonic foraminiferal fauna that characterizes the two subjacent samples (183-1135A-11R-CC and 12R-CC) is low in diversity and dominated by long-ranging, slow-evolving species of Acarinina and Subbotina. Owing to the presence of Pseudohastigerina micra, the increasing scarcity and small size of C. cubensis, and the absence of Globanomalina spp., we assign these samples to the early middle Eocene zonal range AP8-AP9.
In addition to common acarininids and subbotinids, Samples 183-1135A-13R-CC to 20R-CC contain Globanomalina australiformis, which serves as a useful upper Paleocene to lower Eocene guide fossil. The FAD of P. micra probably occurs near the middle of Zone AP7, although, as recorded by Huber (1991) in Hole 738B during Leg 119, this species occurs only sporadically on the Kerguelen Plateau during its range and the timing of this event is not certain. Accordingly, based on the presence of this species in Samples 183-1135A-13R-CC to 17R-CC and on the absence of Acarinina bullbrooki, we assign this interval to the upper part of Zone AP7. Samples 183-1135A-19R-CC to 23R-CC contain Acarinina primitiva but lack P. micra. We therefore tentatively placed the samples from this interval in the lower part of the same zone, Eocene Zone AP7. In addition, these samples contain Pseudohastigerina wilcoxensis and an extremely compressed form possesing a distinct keel. We compare the morphology of this form to Globanomalina pseudomenardii but are aware that this species is normally restricted to the upper Paleocene.
Upper Paleocene-lower Eocene assemblages dominated by large acarininids, Subbotina eocaena, Globanomalina spp., and, less frequently, Chiloguembelina morsei, occur in Samples 183-1135A-25R-CC to 27R-CC. The exact position of the Paleocene/Eocene boundary in the high latitudes, as defined by planktonic foraminifers, is uncertain (see Stott and Kennett, 1990, and Huber, 1991, for discussion). We tentatively place this boundary between Samples 183-1135A-23R-CC and 25R-CC, based on the absence of Acarinina wilcoxensis in Core 183-1135A-26R-CC. Further sampling and close observation of the ranges of key species are required define and locate this boundary more precisely. At present, because of low core recovery in this interval and studies limited to the examination of core-catcher samples, we do not know if this boundary is present in Site 1135 cores.
The downhole FAD of G. australiformis occurs between Samples 183-1135A-26R-CC and 27R-CC. Based on the absence of this species, we assign the latter sample to late Paleocene Zone AP4. This is the last core-catcher sample stratigraphically above the K/T boundary containing foraminifers of Paleocene age. It is likely that several early Paleocene biozones are present within Core 183-1135A-28R, although absence of the basal high-latitude nannofossil Zones NA1 to NA3 suggests that the basal Paleocene is abbreviated above the K/T boundary.
Sample 183-1135A-28R-CC contains a well-preserved and diverse assemblage of Cretaceous (upper Maastrichtian) planktonic foraminifers typical of the high latitudes. The fauna is characterized by Abathomphalus mayaroensis, Hedbergella sliteri, Heterohelix globulosa, Heterohelix planata, and Pseudotextularia elegans, placing this sample in the uppermost Maastrichtian Pt. elegans Zone of Huber (1992). An assemblage composed of Globigerinelloides subcarinatus, Globigerinelloides multispina, H. globulosa, H. planata, H. sliteri, Globotruncanella petaloidea, rare A. mayaroensis, and Archeoglobigerina cretacea occurs in Samples 183-1135A-29R-CC to 30R-CC. In the absence of Pt. elegans, we assign these samples to the G. subcarinatus Subzone.
Globigerinelloides subcarinatus is absent from core catchers below Sample 183-1135A-30R-CC. We assign samples that lack this species but contain Archeoglobigerina australis, Rugoglobotruncana circumnodifer, and rare A. mayaroensis (Samples 183-1135A-30R-CC to 34R-CC) to the early Maastrichtian G. petaloidea Subzone. Despite good preservation of planktonic foraminifers in the upper Maastrichtian of Subunit IIIA, we note that A. mayaroensis and Abathomphalus intermedius, the nominate taxa for early and late Maastrictian biozones (Huber, 1991) are only found in occasional samples. This appears to have been the case in upper Maastrichtian sediments recovered at other high-latitude drill sites (Huber, 1991; Sliter, 1977; Quilty, 1992) as well as sites drilled during Leg 183, and it calls into question the biostratigraphic utility of these species at this latitude.
Diverse and well-to moderately well-preserved lower Maastrichtian assemblages occur in Samples 183-1135A-35R-CC to 41R-CC. Abundant H. globulosa, Ag. australis, Globotruncanella havanensis, Rugoglobotruncana circumnodifer, Globotruncana bulloides, occasional Shackoina multispinata, and a single specimen of A. intermedius in Sample 183-1135A-35R-CC allow us to place it in the G. havanensis Zone, which is recognized by Huber (1992) and Cita et al. (1997). Keeled forms, including A. intermedius, are absent from the next two samples downhole. Preservation deteriorates dramatically in the subjacent sample, Sample 183-1135A-38R-CC. Only small, dissolution-resistant species that are of limited biostratigraphic use remain. Globigerinelloides impensus, however, a distinctive and robust upper Campanian marker, appears to be absent, and on this basis we also assign this the sample to the early Maastrichtian G. havanensis Zone.
Preservation improves slightly in Sample 183-1135A-39R-CC. Because of the presence of G. impensus, we assign this and the two subjacent samples to the late Campanian zone bearing the same name. We also noted the presence in Samples 183-1135A-39R-CC to 44R-CC of a planispiral form conspecific with the Globigerinelloides sp. recorded by Huber (1990, pl. 1, figs. 8, 9) and Quilty (1992, pl. 1, figs. 22, 23) from other Kerguelen sites. This form resembles G. impensus but is described as differing from it by having a smoother wall, less compressed test, and slightly different stratigraphic range. We found it commonly occurring with G. impensus. Inoceramid prisms are a common component of the >63-µm washed carbonate residues in these samples. Interestingly, samples from the G. impensus Zone at Site 1138 are also rich in inoceramid prisms.
Preservation of microfossils deteriorates in the more highly lithified green-gray calcareous chalks of Subunit IIIC. Age-diagnostic planktonic foraminifers are difficult to identify in some of the core-catcher samples from this interval. Moderately well-preserved assemblages are present in Samples 183-1135A-42R-CC to 47R-CC. Based on the presence of A. cretacea and the absence of G. impensus and Ag. australis, we assigned these samples to the long-ranging early Campanian A. cretacea Zone. Recovery was low because of drilling problems near the bottom of the hole, and there was no sediment in the core-catcher samples of Cores 183-1135A-48R and 49R. Preservation and recovery improved slightly in the three subjacent cores (Samples 183-1135A-50R-CC to 52R-CC). In these rather poorly preserved samples, we recognized A. cretacea, S. multispinata, Globotruncana spp., Whiteinella baltica, and probable Marginotruncana, suggesting a Coniacian age. The terminal three cores, Cores 183-1135A-53R-CC to 55R-CC, contain more highly lithified chalks from which we were unable to extract individual foraminifers.