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doi:10.2204/iodp.proc.342.103.2014

Biostratigraphy

Coring in Hole U1402B recovered a 15 m thick sequence of Holocene–Pleistocene dark gray silty clay. Calcareous nannofossils are few, moderately well preserved, and age diagnostic. Planktonic foraminifers are rare and well preserved but largely comprise long-ranging taxa. Benthic foraminifers are rare and well preserved and indicate an upper bathyal depth. Radiolarians are very rare.

Calcareous nannofossils

Calcareous nannofossil biostratigraphy is based on analysis of both core catcher samples from Hole U1402B (Samples 342-U1402B-1H-CC and 2H-CC). Nannofossils are few, exhibit low diversity, and are diluted by abundant clay and silt particles. The samples contain common Emiliania huxleyi and can be assigned to upper nannofossil Zone NN21, within the E. huxleyi acme interval (<0.7 Ma). Rare Cretaceous and Eocene reworked specimens are present.

Radiolarians

Radiolarians are very rare in the examined cores. One sample (342-U1402B-1H-CC) was barren and the other sample (2H-CC) contained only two specimens, one specimen of Actinomma leptodernum Jorgensen and one specimen of Lithelius minor group Jorgensen. A. leptodernum is an extant species that appears to be restricted to the late Quaternary (radiolarian Zone RN17; <0.18 Ma) (Bjørklund, 1976; Nigrini and Moore, 1979). L. minor group ranges from Late Cretaceous to recent (Hollis, 1997).

Planktonic foraminifers

Planktonic foraminifer biostratigraphy is based on analysis of both core catcher samples in Hole U1402B. The samples contain many sedimentary grains (quartz and sulfide) and micaceous particles, but planktonic foraminifers are rare. The preservation of planktonic foraminifers is generally good to excellent.

In Sample 342-U1402B-1H-CC, the faunal assemblage includes Globigerinoides ruber (pink), G. ruber (white), Globorotalia (Globoconella) inflata, Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globigerina bulloides, and Globigerina quinqueloba. Some warm-water specimens of Globigerinoides sacculifer and Globigerinoides pyramidalis are also present. G. ruber (pink) is commonly found in tropical Pleistocene assemblages.

In Sample 342-U1402B-2H-CC, planktonic foraminifers are rare, but preservation is good. Specimens of G. bulloides, N. pachyderma, N. incompta, G. quinqueloba, and Orbulina universa were recovered. The assemblage appears to be similar in age (Pleistocene) to Sample 1H-CC.

Benthic foraminifers

Benthic foraminifers were examined semiquantitatively in core catchers 342-U1402B-1H-CC and 2H-CC. Benthic foraminifers in this hole are rare relative to total sediment particles. Preservation of foraminifer tests was generally very good except for some possibly reworked specimens showing moderate to poor preservation. The occurrence of benthic foraminifers at this site is shown in Table T2.

In Sample 342-U1402B-1H-CC (6.97 mbsf), both Islandiella australis and Cassidulina minuta are dominant, and Melonis affinis, Nonionellina labradorica, and Nonionellina turgica are subordinate. The presence of Praeglobobulimina ovata might indicate a slightly suboxic environment. In addition to these well-preserved specimens, a few poorly preserved nonionid specimens are present. Overall, the assemblage indicates an upper bathyal paleodepth.

Sample 342-U1402B-2H-CC (14.24 mbsf) predominantly yields I. australis. A few C. minuta, rare N. labradorica, and Quinqueloculina sp. are also present. The very low diversity and occurrence of some Stainforthia specimens might indicate a suboxic environment. Preservation of foraminiferal tests is generally very good, with the exception of a few possibly reworked nonionid specimens. The assemblage also indicates an upper bathyal paleodepth.

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