Site 1124, drilled on the Rekohu Drift in 4000-m water depth, proved a challenge for dating because of the poor preservation of microfossils in the Oligocene and Neogene strata; despite this, the nannofossils proved the most useful for dating throughout the hole. Foraminifers provided good resolution in the uppermost Miocene-Pliocene and in the Cretaceous and Paleogene. Good radiolarian faunas are present in the upper Neogene, upper Oligocene, and Cretaceous-Paleocene and were particularly useful in resolving the Oligocene/Miocene boundary. Diatoms are poorly preserved and of little value in the Paleogene and Cretaceous but provided additional biostratigraphic resolution and evidence of sediment provenance in the upper Neogene. The biostratigraphy of Site 1124, as determined by the various microfossil groups, is summarized in Figures F15 and F16.
The following major intervals have been determined by combining results from all groups:
Pleistocene-Holocene (0-1.8 Ma), 0 to ~65 mbsf, lithostratigraphic Subunit IA;Pliocene (1.8-5.3 Ma), 65 to ~115 mbsf, lithostratigraphic Subunit IB (upper);
late Miocene (5.3-11.2 Ma), 115 to ~210 mbsf, lithostratigraphic Subunits IB (lower) and IC (upper);
late early-middle Miocene (~11.2-19 Ma), 210 to 290 mbsf, lithostratigraphic Subunit IC (lower);
hiatus (~3.4 m.y.), 290 mbsf;
earliest Miocene (~22.4-23.6 Ma), 290 to 322 mbsf, lithostratigraphic Unit II;
late Oligocene (23.6-~27 Ma), 322 to 412 mbsf, lithostratigraphic Unit III;
hiatus = Marshall Paraconformity (3-5 m.y.), 412 mbsf;
early Oligocene ([? 30] 32-34 Ma), 412 to 419 mbsf, lithostratigraphic Unit IV; hiatus (~2 m.y.), 419 mbsf;
late middle-early late Eocene (36-38 Ma), 419-428 mbsf, lithostratigraphic Unit V; hiatus (>20 m.y.), 428 mbsf;
Late Cretaceous to early late Paleocene (59-~66 Ma), 428-473 mbsf, lithostratigraphic Unit VI; and
Cretaceous/Tertiary boundary, lost between 463-467 mbsf.
The micropaleontological biostratigraphy of Site 1124 is mostly based on the onboard study of core-catcher samples. Samples from Holes 1124A and 1124B were used for the uppermost part of the section, and Samples from Hole 1124C for the majority. Additional samples were taken from within selected cores to address specific age and paleoenvironmental questions. The absolute ages assigned to biostratigraphic datums follow the references listed in Tables T2, T3, T4, T5, all in the "Explanatory Notes" chapter.
Samples obtained from Hole 1124C, together with several samples taken from Holes 1124A and 1124B, were examined for nannofossil biostratigraphy (Tables T3, T4; Fig. F17). Well-preserved nannofossils were found only in the upper sections of this site. Differential dissolution becomes stronger from Sample 181-1124C-11H-CC (112.95 mbsf) and downward. In some of the samples, only dissolution-resistant forms, such as discoasterids and large-sized coccoliths, including Cyclicargolithus floridanus and C. abisectus, were left. Thirty-four age-diagnostic datum levels were identified as summarized in Table T4. The preliminary biochronology suggests that this site recovers a continuous 410-m-long record from the upper Oligocene (~27 Ma) to the Pleistocene (Fig. F17). The lower part of Hole 1124C (410 to 473 mbsf) records parts of the Paleogene and uppermost Cretaceous with several hiatuses. There are at least four hiatuses truncating the record, leaving less than 50% of the mid-Oligocene to the lowermost Cretaceous preserved.
Signs of dissolution were observed even at the very top of the sequence. The first two commonly used datums (the reversal of dominance between Gephyrocapsa oceanica and Emiliania huxleyi and the first occurrence [FO] of E. huxleyi) for the uppermost Pleistocene cannot be identified because of dissolution effects, which have dissolved the bridge structures of gephyrocapsiids and the I-shaped elements of the distal shields of Emiliania huxleyi. The only reliable age datum we could find for the uppermost Pleistocene was the last occurrence (LO) of Pseudoemiliania lacunosa (0.24 Ma) in Sample 181-1124C-2X-1, 146 cm (21.06 mbsf).
The Pleistocene is ~60 m thick, as marked by the FO of medium-sized Gephyrocapsa (1.67 Ma) in Sample 181-1124C-5H-CC (56.09 mbsf). In the same sample, the LO of Calcidiscus macintyrei (1.60 Ma) was found. In the next downcore sample (Sample 181-1124C-7H-CC, 75.09 mbsf) observed was the LO of Discoaster brouweri (1.96 Ma). Well-preserved discoasterids were found in the next three cores, facilitating a good correlation of this interval to the standard zonation of the late Pliocene. The zonal markers of the top boundaries of the Zones NN17, NN16, and NN15 were found in Samples 181-1124C-8HCC to 10H-CC (84.35-102.72 mbsf), respectively (Fig. F15; Table T4).
From Sample 181-1124C-11H-CC (112.95 mbsf) to 30X-CC (284.3 mbsf), nannofossils are poorly to moderately preserved. The absence of marker species belonging to Ceratolithus, Amaurolithus, Discoaster, Sphenolithus, and Helicosphaera makes it impossible to make an unambiguous correlation of this interval with the standard zonal scheme. It is hard to pinpoint where the Miocene/Pliocene boundary is. The presence of Minylitha convallis, a short-ranged late Miocene dissolution-resistant species, indicates that the interval between 154.92 and 183.22 mbsf was deposited between 7.7 and 9.3 Ma. The presence of the short-ranged Catinaster calyculus (LO 9.64 Ma) and C. coalitus (FO 10.8 Ma, marker of the base of Zone NN8) in the next three samples from Sample 181-1124C-19X-CC through 21X-CC further confirms the correlation.
The boundary between the middle and late Miocene (11.2 Ma) is bracketed by the LO of Coccolithus miopelagicus (10.94 Ma) in Sample 181-1124C-22X-CC (216.96 mbsf) and the LO of Calcidiscus premacintyrei (12.65 Ma) in Sample 181-1124C-23X-CC (226.59 mbsf). Within the middle Miocene, the LO of Sphenolithus heteromorphus in Sample 181-1124C-25X-CC (245.88 mbsf) marks the top of Zone NN5 at 13.52 Ma. Below this level, the nannofossils are poorly preserved. Strong dissolution has caused many samples to be barren of nannofossils or to contain only fragments and few robust specimens. The lack of Sphenolithus and Helicosphaera in the interval between Samples 181-1124C-25X-CC (245.88 mbsf) and 33X-CC (322.68 mbsf) almost precludes any possibility of correlation. The poorly preserved discoasterids in this interval, however, show a transition from the Discoaster deflandrei complex to the D. variabilis group at ~260 mbsf (between Samples 181-1124C-26X-CC and 27X-CC; 255.4 to 264.95 mbsf). This level indicates approximately the boundary of the middle and early Miocene at ~16.4 Ma. The trace but persistent occurrence of Geminilithella rotula down to Sample 181-1124C-29X-CC (276.41 mbsf) suggests that this level still belongs to the early Miocene younger than 19.6 Ma. The sudden termination of D. druggii in Sample 181-1124C-31X-CC (303.08 mbsf) indicates that this level is near the first appearance of this marker species at the top of Zone NN2 at 23.2 Ma. The sudden appearance of a diverse group of Oligocene Sphenolithus three samples downward (Sample 181-1124C-34X-CC; 322.49 mbsf) also supports this interpretation. The interval between 276.41 and 303.08 mbsf is either a condensed lower Miocene section of the early Miocene or it contains a small hiatus with less than 3 m.y. missing. The absence of nannofossils in the core catcher of this core (Sample 181-1124C-30X-CC; 284.3 mbsf), and the general poor preservation of the flora in samples below and above, makes it difficult to evaluate which interpretation is correct. It is likely that there is a disconformity in Core 181-1124C-30X (Fig. F15).
The topmost Paleogene is recorded in Cores 181-1124C-34X to 42X, as marked by the presence of age-diagnostic late Oligocene assemblages. The common occurrence of Sphenolithus delphix (LO 23.8 Ma), S. capricornutus (LO 23.7 Ma), S. conicus (LO 21.8 Ma), and S. umbrellus (LO 23.6 Ma) (Berggren et al., 1995) in Samples 181-1124C-34X-CC to 36X-CC (322.68-351.71 mbsf) provides a suite of excellent biochronologic markers for this interval. Sample 181-1124C-34X-CC (332.49 mbsf) is older than 23.8 Ma, based upon the co-existence of Sphenolithus delphix and S. capricornutus. The same sample (Sample 181-1124C-34X-CC at 332.49 mbsf) records the LO of Reticulofenestra bisectus, indicating an age of 23.9 Ma. The FO of Sphenolithus delphix in Sample 181-1124C-36X-CC marks an age of 24.3 Ma, whereas the LO of Chiasmolithus altus at 26.1 Ma in Sample 181-1124C-35X-CC (342.34 mbsf) further strengthens the biochronologic determination of this interval. The occurrence of S. ciperoensis, together with the absence of S. distentus in Samples 181-1124C-39X-CC (380.95 mbsf) through 43X-1, 66 cm (410.36 mbsf), suggests that the bottom of this interval (i.e., 410.36 mbsf) is not the true FO of S. ciperoensis; rather, it is still younger than the datum level of the LO of S. distentus (27.5 Ma).
Four reliable markers of the earliest Oligocene all occur consecutively in the next several sections in Core 181-1124C-43X: the LO of Reticulofenestra umbilicus (31.3 Ma) and the LO of Isthmolithus recurvus (31.8-33.1 Ma; Berggren, 1995) in Sample 181-1124C-43X-2, 57 cm (411.77 mbsf), the LO of Ericsonia formosa (32.8 Ma), and the acme of Clausicoccus subdistichus (33.3 Ma) in Sample 181-1124C-43X-6, 66 cm (417.86 mbsf). However, the disappearance of I. recurvus (range ~32 to 35.5 Ma) and Dictyococcites bisectus (FO 38 Ma) in Sample 181-1124C-44X-1, 100 cm, and downcore, indicates that there is a stratigraphic break between this sample and the sample above (i.e., between Samples 181-1124C-44X-1, 7 cm, at 419.36 mbsf and 44X-1, 100 cm, at 420.3 mbsf). We interpret this to mean that there might be a hiatus of at least 4.5 m.y. duration (from 33.3 to 38 Ma).
The assemblages contained in Sample 181-1124C-44X-1, 100 cm, to 44X-6, 50 cm (420.3 to 427.3 mbsf) is of middle Eocene age, as characterized by Discoaster barbadiensis, Coccolithus eopelagicus, Cyclicargolithus floridanus, Ericsonia formosa, and Reticulofenestra umbilicus (FO 43.7 Ma). As constrained by the absence of Dictyococcites bisectus and the presence of Reticulofenestra umbilicus, this interval is bracketed between 38 and 43.7 Ma.
In the very bottom of the core-catcher of Core 181-1124C-44X (428.97 mbsf), just below the black mudstone, a moderately preserved nannofossil assemblage indicative of the middle Paleogene was found. The presence of Fasciculithus tympaniformis in this sample clearly indicates that the sample is older than at least 55.3 Ma. An additional sample taken from the very top of the next core (Sample 181-1124C-45X-1, 29 cm, 429.29 mbsf) contains abundant, well-preserved nannofossils of middle Paleocene age. The presence of Hornibrookina teuriensis suggests that this level is older than its LO at 58.3 Ma. It is evident that in, or at the base of, the dark brown mudstone in Sample 181-1124C-44X-CC exists a major hiatus that separates the middle Paleocene below (>58.3 Ma) from the middle Eocene (between 38 and 43.7 Ma) above.
The nannofossils in sediments below the unconformity are generally abundant and moderately preserved. The abundant occurrence of Fasciculithus tympaniformis, F. ulii, and F. pilateaus and the absence of any Helicolithus in the three samples of Core 181-1124C-45X (429 to 438.62 mbsf) suggest strongly that this interval is within Zone NP5 with an age older than 58.4 Ma (FO Helicolithus) and younger than 59.9 Ma (FO of F. ulii). The FO of the first Sphenolithus species, S. primus, in Sample 181-1124C-46X-CC (445.83 mbsf) marks the age of 60.6 Ma. Within this core, the FO of Chiasmolithus bidens occurs in Sample 181-1124C-46X-5, 59 cm, indicating an age of 60.7 Ma. These two datum levels collectively suggest that this core (1124C-46X, 438.62 to 445.83 mbsf) belongs to the Zone NP3. Without finding the marker species for the base of NP4, it is difficult to evaluate whether this zone is missing. In the next two lower samples, three age-diagnostic datums were found: Cruciplacolithus tenuis (the marker of the base of Zone NP2 at 64.5 Ma) in Sample 181-1124C-47X-CC (457.46 mbsf), Cruciplacolithus primus (FO 64.8 Ma), and Hornibrookina teuriensis (FO 64.9 Ma) in Sample 181-1124C-48X-CC (463.32 mbsf). The presence of these species suggests that this interval is very near to the base of the Tertiary (65 Ma).
The next two samples from Core 181-1124C-49X, the last core in the sequence, contain typical flora of the Late Cretaceous (>65 Ma) as characterized by abundant occurrence of Micula spp., Arkhangelskiella cymbiformis, Prediscosphaera cretacea, and Broinsonia enormis. However, it appears that the contact between Cretaceous and Tertiary was not recovered, and occurs between Sample 181-1124C-48X-CC and the top of Core 181-1124C-49X.
Throughout most of the Site 1124 section, the planktonic foraminiferal assemblages show evidence of variable, selective dissolution. Selective dissolution of planktonic foraminifer tests affected our ability to find all of the regionally expected taxa of potential use in the site biostratigraphy and to have confidence in the distribution of some of the observed events (Tables T5, T6, T7).
At this site, the Quaternary interval is not easy to recognize or subdivide biostratigraphically, using foraminifers. The stratigraphic range of some taxa is different from that found south of the Subtropical Convergence.
Sediments down to Sample 181-1124C-5H-5, 88-93 cm (0-53.5 mbsf), are younger than 2.6 Ma (late Pliocene-Recent, Nukumaruan [Wn], Castlecliffian [Wc], and Haweran [Wq] Stages), because they contain sporadic Globorotalia crassula (FO 2.6 Ma).
These faunas contain common Globorotalia inflata. Globorotalia puncticuloides morphotypes are particularly common in Core 181-1124A-1H to Core 181-1124C-5H, in contrast to southern Leg 181 sites, where their last appearance was consistently ~0.6-0.7 Ma. Globorotalia puncticuloides morphotypes become much rarer below Core 181-1124C-5H. No G. cavernula (FO 0.2 Ma) were found, but Globorotalia hirsuta (FO 0.45 Ma) occurs in the surface sample (Sample 181-1124B-1H-1, 0-2 cm).
A crude subdivision of this interval is provided by the sporadic occurrences lower down of the Globorotalia tosaensis-G. truncatulinoides lineage. Keeled G. truncatulinoides morphotypes (FO ~2 Ma in tropics and subtropics) occur down to Sample 181-1124C-5H-CC. Unkeeled morphotypes of G. tosaensis (3.2-1 Ma) occur in Samples 181-1124C-5H-5, 88-93 cm, and 7H-4, 98-100 cm. Based upon this, Core 181-1124C-5H is 1-2 Ma. Common Globorotalia inflata triangula (LO ~2 Ma) are present in Sample 181-1124C-7H-CC.
Samples 181-1124C-8H-3, 140-142 cm, and 8H-5, 10-12 cm (80.1 mbsf), are of late Pliocene age (2.6-3.0 Ma, Mangapanian Stage), because of the presence of dextral, unkeeled Globorotalia crassaformis (3.0-2.1 Ma) and lack of G. crassula or G. crassacarina (FO 2.6 Ma).
Samples 181-1124C-8H-CC to 9H-CC (84.4-94.1 mbsf) are mid-Pliocene in age (3.0-3.6 Ma, Waipipian Stage), based on the occurrence of abundant G. inflata (FO 3.7 Ma) and G. inflata triangula (FO 3.6 Ma), sinistral Globorotalia crassaformis (LO 3.0 Ma, Samples 181-1124C-8H-CC and 9H-CC), G. puncticuloides (FO 3.6 Ma, Sample 181-1124C-9H-4, 107-109 cm), and G. crassaconica (LO 3.0 Ma, Sample 181-1124C-9H-CC). In southern Leg 181 sites, Globorotalia inflata occurred in low numbers and as small specimens down to this level. It was not as dominant in the late Pliocene as it was in the temperate latitudes at Site 1124.
Sample 181-1124A-10H-1, 76-78 cm (94.5 mbsf), is of mid-Pliocene age (~3.6-3.7 Ma, late Opoitian Stage), based on the occurrence of Globorotalia inflata triangula (FO 3.6 Ma), common G. pliozea (last common occurrence [LCO] 3.6 Ma), common G. inflata (FO 3.7 Ma), and sparse G. puncticulata (LO 3.7 Ma).
Samples 181-1124C-10H-CC to 11H-CC (102.7-113 mbsf) are of early Pliocene age (3.7-4.7 Ma, Opoitian Stage), based on the occurrence of common Globorotalia puncticulata (FO 5.2 Ma, LO 3.7 Ma) and G. crassaconica (FO 4.7 Ma), and supported by the sporadic presence of G. pliozea (3.6-5.4 Ma, Sample 181-1124C-110H-1, 89-91 cm).
Samples 181-1124C-14H-2, 100-102 cm, to 17X-CC (134.2-168.7 mbsf) are of largely undifferentiated late Miocene age (5.6-9.9 Ma, late Tongaporutuan and early Kapitean Stages), based on the presence of sinistral Globorotalia miotumida (FO 10.5 Ma, LO 5.6 Ma) and the first downhole occurrence of the distinctive Globoquadrina dehiscens (LO 9.9 Ma) in Sample 181-1124C-20X-CC (335 mbsf). The interval can be coarsely subdivided on the presence of Sphaeroidinella paenedehiscens (FO ~8 Ma) in Sample 181-1124C-14H-CC (141.1 mbsf).
Samples 181-1124C-20X-CC to 21X-CC (197.57-207.36 mbsf) are of late middle Miocene to early late Miocene age (13.2-9.9 Ma, Lillburnian to early Tongaporutuan Stages), based on the presence of Globoquadrina dehiscens (LO 9.9 Ma) and sporadic Globorotalia miotumida and Globigerina nepenthes (FO 11.8 Ma) in Sample 181-1124C-21X-CC. Samples 1124C-22X-5, 124-128 cm, to 24X-CC are middle Miocene in age (late Clifdenian-Lillburnian Stages), based on the presence of sporadic, poorly preserved Globorotalia praemenardii (15.8-13.2 Ma), and one Globorotalia amuria (LO 13 Ma, in Sample 181-1124C-22X-5, 124-128 cm). A good population of Orbulina suturalis (FO 15.1 Ma, LO 10.5 Ma) occurs in Sample 181-1124C-22X-CC.
Samples 181-1124C-28X-CC and 29X-CC (274.6-276.4 mbsf) are of late early Miocene age (19-16.7 Ma, Altonian Stage), based on the presence of Catapsydrax dissimilis (LO 16.7 Ma), Globigerinoides cf. trilobus (FO 19 Ma) and one Globorotalia incognita (21.6-18.5 Ma) in Sample 181-1124C-29X-CC.
Samples 181-1124C-30X-CC to 42X-CC (284.3-409.7 mbsf) mostly contain low-diversity benthic foraminiferal faunas, with extremely rare planktonic forms occurring in fewer than 50% of the residues. In most instances, the only planktonic forms present are large specimens of the thick-walled Catapsydrax dissimilis (FO ~34 Ma, LO 16.7 Ma). In New Zealand sections, C. dissimilis is abundant in the uppermost Oligocene and lower Miocene (Waitakian and Otaian Stages). Sample 181-1124C-31X-CC has an assemblage with common Cassidulina cuneata, rare Gyroidina soldanii, Pullenia sp., Cassidulina sp., Cibicidoides sp., and isolated specimens of Globigerina opima nana.
Sample 181-1124C-40X-CC (390.1 mbsf) contains benthic foraminifers Cibicidoides praemundulus (LO 23.8 Ma), Cassidulina cuneata (FO 27 Ma) and planktonic Catapsydrax unicavus. This assemblage is tentatively assigned to the late Oligocene (27-23.8 Ma, Duntroonian-early Waitakian Stage).
Sample 181-1124C-43X-CC is a calcareous plankton ooze, with abundant and robust specimens of Subbotina angiporoides LO 30 Ma), Catapsydrax unicavus, Globigerina euapertura, and also contains common small Paragloborotalia gemma (LCO 32 Ma, FO 35 Ma). In the absence of a continuous set of samples in this zone, it cannot be ascertained if we deal with P. gemma LCO (~32 Ma) or P. gemma LO (~30 Ma); hence, the 32 Ma date should be used with caution. If we deal with the P. gemma LO event, the age might be near 30 Ma. The sample lacks Globigerinatheka index, which in this region is abundant in samples older than 34.3 Ma, and Subbotina linaperta, which ranges up to near the top of the Eocene. Therefore, we conclude that the age of the sample is early Oligocene (34.3-32 Ma, early Whaingaroan Stage). This suggests a time gap of 5 m.y. (late Whaingaroan Stage) across the Marshall Paraconformity at 412 mbsf, between early Oligocene (>32 Ma) and late Oligocene (<27 Ma).
Samples 181-1124C-44X-1, 67-69 cm, to 44X-6, 50-52 cm (420-427.3 mbsf), are of late middle to early late Eocene age (42-36 Ma, Bortonian to early Kaiatan Stages), based on the common presence of Pseudogloboquadrina primitiva (LO 36 Ma), Globigerinatheka index (FO 42 Ma), and Nuttallides truempyi (New Zealand LO 36 Ma). The upper part of this interval appears to have an age within the range 38.4-36 Ma, based on the occurrence of Ponticulosphaera semiinvoluta (FO 38.4 Ma) in Samples 181-1124C-44X-1, 67-69 cm, and 44X-5, 93-95 cm.
Thus, there is a considerable hiatus (and lithologic change) between Sample 181-1124C-43X-CC and the top of Core 181-1124C-44X, with a minimum time gap of ~2 m.y., within the late Eocene (all Runangan and late Kaiatan Stages).
Samples from 181-1124C-44X-CC to 47X-CC (429.1-457.6 mbsf) are early Paleocene (65-60 Ma, early Teurian Stage). Sample 181-1124C-44X-CC (429.1 mbsf) contains two different lithologies: a dark brown mudstone and a pink-colored marl. The dark brown mudstone is barren of foraminifers and is probably of middle Eocene age, as it grades up into foraminifer-bearing, calcareous brown shales assigned to the interval above. The light-colored sample is rich in large benthic foraminifers, including Gavelinella beccariiformis and Nuttallides "truempyi," which assigns the sample a Paleocene age, older than 55 Ma. There are no planktonic foraminifers in this sample, possibly the result of dissolution of carbonate in the water masses, before burial on the seafloor.
Sample 181-1124C-45X-CC (438.7 mbsf) contains a diverse and rich planktonic assemblage, including Morozovella conicotruncata, M. angulata, M. praecursoria, M. aff. trinidadensis, Subbotina spp., and the benthic forms Aragonia ouezzanensis, Gavelinella beccariiformis, Pullenia coryelli, Gyroidinoides globosus, and Alabamina creta. The assemblage correlates to the lower part of the standard planktonic foraminifer Zone P3 (60-61 Ma), Sealandian, early late Paleocene.
Samples 181-1124C-46X-CC through 47X-CC (445.8-457.5 mbsf) contain a totally different assemblage, largely composed of superabundant small globigerinids, typical of the early Paleocene (early Danian). In Sample 181-1124C-46X-CC occur abundant Globanomalina compressa, common Globoconusa daubjergensis, Subbotina simplissima, and S. triloculinoides. No S. pseudobulloides were observed. Rare benthic forms include Nuttallinella florealis and Spiroplectammina spectabilis. The assemblages may be assigned to the upper part of standard planktonic foraminifer Zone P1 (61.2-63.0 Ma).
In Sample 181-1124C-47X-CC, the assemblage contains even smaller planktonic specimens than in the core-catcher immediately above, with rare Globanomalina compressa, Globigerina fringa, G. simplissima, Globoconusa daubjergensis, Guembelitria cretacea, and the same benthic forms as immediately above. The assemblage is assigned to the top of Subzone P1b or lower Subzone P1c (~63 Ma).
The pink and indurated limestone in Sample 181-1124C-48X-CC yields only isolated and tiny (63-µm fraction) planktonic forms. A tiny form with five chambers in the last whorl, slightly trochoid spire, and open umbilicus was found. We assign it to Globigerina eugubina, indicative of Subzone P1a (near 64.9 Ma).
The Cretaceous/Tertiary (K/T) boundary was not recovered. It occurs between Sample 181-1124C-48X-CC and the top of Core 181-1124C-49X.
Samples 181-1124C-49X-3, 135-150 cm, and 49X-CC (471.7-473.1 mbsf) are Late Cretaceous in age (71-65 Ma, Maastrichtian and Haumurian).
The two samples from this interval contain very few planktonic foraminifers. The only three specimens recovered are of Rugoglobigerina rugosa and Hedbergella holmdelensis, assigned a general Maastrichtian age. This agrees with the rich and diverse benthic assemblage, containing Globorotalites michelinianus, Neoflabellina aff. semicirculata, Quadrimorphina sp., Allomorphina sp., Gyroidinoides sp., Nuttallinella florealis, Bolivina incrassata, Loxostomum gemmum, Valvulinera sp., Gavelinella beccariiformis, Dorothia oxycona, Saccamina placenta, Hormosina ovula, Gaudryina healyi, Psammosphaera sp., Karrerulina conversa, Spiroplectammina spectabilis, S. dentata, Rhabdammina sp., ?Trochamminoides sp., and unidentified agglutinated species.
A possible reason for the sudden appearance of calcareous planktonic forms immediately above the (not recovered) K/T boundary might be a drop in the level of the CCD, below the Late Cretaceous paleodepth of ~2-3 km of this site.
A summary of foraminiferal ages in terms of the New Zealand stage classification, and local chronological calibration of these stages, can be found in Table T2, in the "Explanatory Notes" chapter.
Diatoms and silicoflagellates are present in sufficient numbers and good preservation in two core intervals at this site to base a stratigraphic assignment on them (Table T8): (1) upper Neogene (upper Miocene to Holocene) as at Site 1123 further east on the northern slope of the Chatham Rise; and (2) upper Oligocene to lowermost Miocene, from Core 181-1124C-31X to 41X.
In the Upper Cretaceous to lower Oligocene sediments below Core 181-1124C-42X, erosion and low sedimentation rates have resulted in dissolution of diatoms.
At this site even fewer stratigraphic marker species were encountered than at Site 1123, and most of the datums applied are last occurrences of these species (Fig. F15). Useful marker species for the late Neogene and early Miocene to late Oligocene can be found in Table T9.
Of these datums, the stratigraphic first occurrence of Nitzschia fossilis may originally have been slightly deeper than in Sample 181-1124C-14X-CC, but because of the poor preservation in the sediments below, its first occurrence can only be documented from this sample upsection. The poor preservation of diatoms in Cores 181-1124C-9X and 10X suggests that a hiatus may be present between Samples 181-1124C-8X-CC and 9X-CC.
Silicoflagellates are present but rare. Their abundance is not sufficient to recognize silicoflagellate zones. The few species found support the ages determined by the diatoms. Sample 181-1124C-3X-CC contains Dictyocha lingii and Mesocena quadrangula and, therefore, must be placed in the Pleistocene Mesocena quadrangula Zone. In Sample 181-1124C-16X-CC, the presence of Paradictyocha apiculata places this sample into the Miocene Corbisema triacantha Zone.
Reworking of Eocene and Oligocene diatom valves and silicoflagellate skeletons is present in the lower Miocene-upper Oligocene diatomaceous sediments. In the upper Neogene section, there are Eocene and Oligocene forms plus reworked Miocene and Pliocene specimens.
Radiolarian biostratigraphy at Site 1124 is based on the examination of 52 core-catcher samples and four core samples (Table T10). Radiolarian faunas are abundant and well preserved in the upper part of the section (Samples 181-1124A-1H-CC to 181-1124C-8H-CC, 4.7-84.35 mbsf), whereas the interval between Samples 181-1124C-9H-CC and 16H-CC (94.14-159.3 mbsf) contains rare, sporadic radiolarians. The lower part of lithostratigraphic Unit I (Samples 181-1124C-17X-CC to 30X-CC, 168.7-284.3 mbsf) is barren, which suggests extensive dissolution in this interval. The upper part of the lithostratigraphic Unit II (Samples 181-1124C-31X-CC to 42X-CC, 303.08-410 mbsf) contains moderately well-preserved early Miocene to late Oligocene radiolarians.
The last occurrence of Axoprunum angelinum occurs in Sample 181-1124C-3H-CC (37.1 mbsf), indicating an age younger than 0.78 Ma, based on its recorded datum in Sample 181-1123A-4H-CC (at the base of Brunhes normal epoch). Sample 181-1124C-5H-CC (56 mbsf) contains the FO datum of Theocorythium trachelium (FO 1.6-1.7 Ma in equatorial Pacific), which indicates an earliest Pleistocene age.
In Sample 181-1124C-7H-CC (75 mbsf), the first occurrence of Cycladophora davisiana davisiana (FO 2.91-3.08 Ma) indicates the sample is of late Pliocene age. The interval between Samples 181-1124C-8H-CC and 11H-CC (84.35-113 mbsf) is estimated to be of a late Miocene to Pliocene age, based on the occurrence of Sphaeropyle langii (FO 6.0-6.2 Ma). Samples between 181-1124C-12H-CC and 16H-CC (121.7-159.3 mbsf) contain Stichocorys peregrina, Eucyrtidium calvertense, and Stylacontarium bispiculum. They indicate a Miocene age.
Sample 181-1124C-32X-CC (313 mbsf) yields a radiolarian fauna including Cyrtocapsella cf. tetrapera (FO 23.62 Ma), Lychnocanoma matakohe, and rare Phormocyrtis alexandrae, which is assigned to the lower part of the Cyrtocapsella tetrapera (RN1) Zone of Sanfilippo and Nigrini (1998), based on the fauna from the next lowest sample (181-1124C-33X-CC). The estimated age is earliest Miocene.
In the interval between Samples 181-1124C-33X-CC and 35X-CC (322.68-342.34 mbsf), radiolarian faunas are highly diversified. They are characterized by the presence of few to abundant Lychnocanoma elongata, Stichocorys negripontensis, Lychnocanoma conica, Anthocyrtidium marieae, ?Lophocyrtis inaequalis, Lophocyrtis galenum, Theocorys purii, and Phormocyrtis alexandrae. The faunas are assigned to the Lychnocanoma elongata (RP22) Zone of Sanfilippo and Nigrini (1998), giving a latest Oligocene age (23.62-24.6 Ma). The faunas are very similar to those from calcareous siltstone of the Puriri Formation, Northland, in New Zealand (O'Connor, 1997a, 1997b).
Sample 181-1124C-39X-CC (381 mbsf) contains Heliodiscus tunicatus and Eucyrtidium sp. The former species ranges from the Cryptocarpium ornatum Zone to the Theocyrtis tuberosa Zone (O'Connor, 1997a, 1997b) and is of early Oligocene age.
Sample 181-1124C-42X-CC (409.69 mbsf) yielded a radiolarian fauna including Lychnocanoma amphitrite, Lychnocanoma babylonis, and Lophocyrtis sp., which indicate an Oligocene age.
The interval between Samples 181-1124C-47X-CC and 48X-3, 44-45 cm, yielded only a rare Amphisphaera aotea, which is assigned to the Amphisphaera aotea (RP1) Zone of Hollis et al. (1997). The estimated age is earliest Paleocene (64.5-65 Ma) for the interval.
The foraminiferal faunas throughout the Neogene and upper Oligocene of Site 1124 show signs of strong to very strong dissolution, consistent with having accumulated below the foraminiferal lysocline. Dissolution appears to be strongest through the upper Oligocene and Miocene and slightly less in the Pliocene and Quaternary. Throughout this entire interval, the foraminiferal assemblages that remain are particularly sparse and required washing large core-catcher samples to obtain ~100 planktonic specimens in the Pliocene and Pleistocene or to obtain any planktonic specimens in many of the Miocene and Oligocene samples.
The hallmarks of dissolution are the reduced abundance of, first, planktonic and, to a lesser extent, benthic foraminifer specimens. Accompanying this is the large number of fragmented planktonic specimens and chambers and the decreasing planktonic percentage of the total foraminiferal assemblage. In terms of the planktonic composition of the fauna, there is a selective and progressive loss of the more solution-prone taxa (e.g., Globigerina, Globigerinoides, Praeorbulina, Orbulina, small Globorotalia) and of the smaller specimens. In many instances the small remaining assemblage is of low diversity, consisting of only one or two more solution-resistant taxa (e.g., Catapsydrax, Globoquadrina, Globorotalia inflata, Sphaeroidinella). The last, less-calcified chamber of many specimens is often dissolved away.
The benthic faunas also often appear to have a reduced diversity, having lost many of the smaller and more solution-prone taxa. The faunas often consist of 10-20 larger, thicker-walled taxa (e.g., Oridorsalis, Globocassidulina, Dentalina, Melonis, Gyroidina, Pullenia, and Martinotiella).
A preliminary study of pairs of dark-colored (cool hemipelagic) and light-colored (warm pelagic) lithologies within the Pleistocene indicates that in the dark-colored intervals planktonic foraminifer percentages are lower (30%-70%) than in the lighter intervals (70%-95%) and that planktonic foraminiferal abundance in the darker intervals is ~30% of that in the light. Similarly, the number of planktonic test fragments, expressed as a ratio of the number of whole tests, is about twice as much in the darker intervals than the lighter.
In the Miocene and upper Oligocene, the darker horizons have planktonic percentages of 0%-20% compared with ~20%-50% in the lighter intervals. Many darker horizons have no planktonic forms present. Planktonic foraminiferal abundance is greatly reduced in both intervals compared with the Pleistocene, and the fragment-to-whole test ratio is greatly increased. These observations suggest that dissolution was stronger during the cooler periods than the warmer ones, and, possibly, planktonic productivity was higher during the warmer intervals. Dissolution is prevalent, however, throughout both cool and warm intervals.
The late Oligocene to Holocene benthic foraminiferal assemblages are relatively constant and typical of mid-bathyal to abyssal depths, above the CCD. More detailed quantitative work is required to see if these solution-impacted assemblages show changes that reflect water mass or other environmental shifts.
The evidence suggests that throughout most of the Neogene, Site 1124 was swept by corrosive bottom waters. This is most marked in the Miocene, where many assemblages have fewer than 10% planktonic foraminifers, compared with a normal oceanic assemblage above the lysocline, which would have >99% planktonic forms.
The early Oligocene foraminiferal assemblage in Sample 181-1124C-43X-CC, which has oceanic overhead conditions at upper abyssal depths, has normal planktonic foraminiferal assemblages in both abundance (~99% foraminifers) and composition. There is some evidence, however, for dissolution, seen in the presence of common planktonic test fragments in the finer sand fractions.
The late middle to early late Eocene foraminiferal assemblages in Core 181-1124C-44X contain a normal upper abyssal or lower bathyal, benthic fauna (e.g., common occurrence of species of Oridorsalis, Nuttallides truempyi, Gyroidina, Dentalina), with 90%-99% planktonic forms showing no obvious signs of dissolution.
This interval contains benthic foraminiferal assemblages typical of deep bathyal to abyssal paleo-water depth. Planktonic percentages are variable, between 0% and 100%. The extreme variation in planktonic concentration is an enigma: there are no planktonic forms, but diversified benthic foraminifers are abundant in Samples 181-1124C-49X-CC (Late Cretaceous) and 45X-CC (?late Paleocene), and planktonic oozes in the samples in between, of early Paleocene age. One explanation for no planktonic assemblages might be a relatively shallow CCD, with extreme dissolution of pelagic calcareous tests, and sufficiently oxic bottom water to yield high-diversity benthic assemblages, none of which show signs of mass-flow sorting or abrasion. Another possibility is a severely restricted and oxygen deficient mid-water mass, in a relatively restricted oceanic basin. Temporal expansion of this mid-water mass to the surface would prevent planktonic blooms; its expansion to the bottom of the basin might yield dark brown clays, as seen in the middle Eocene interval of Core 181-1124C-44X. An argument against a surface water-mass restriction is the fact that radiolarian and nannofossil assemblages persist.
Backtracking considerations for the area of this site, slightly landward of oceanic basement, with ~1 km of sediment fill, might place the paleo-water depth around 2000-3000 m in the Late Cretaceous through Paleocene. The diverse benthic assemblage with frequent and robust Gavelinella beccariiformis, Nuttallides, Nuttallinella, Pullenia corylli, Aragonia (Paleocene), Gyroidinoides and Globorotalites (both Cretaceous), various deep-water agglutinated foraminifers, common ataxophramiids, and Quadrimorphina, are compatible with a deep-water setting.
Fluctuations in the abundance and preservation of diatoms in the sediment indicate two periods of increased primary productivity: the latest Miocene to Holocene and the late Oligocene to earliest Miocene.
The late Neogene diatom assemblages are composed of temperate to subtropical species, with an admixture of displaced subantarctic diatoms, which document the input of material picked up by the Lower Circumpacific Deep Water further south.
In the upper Oligocene to lower Miocene sediments, the assemblages are also characterized by temperate to subtropical species. During this period of sedimentation, an input of Antarctic-subantarctic species is not evident.