Previous   |    Next

doi:10.2204/iodp.proc.329.103.2011

Paleontology and biostratigraphy

The sediment at Site U1365 is primarily brown zeolitic metalliferous pelagic clay, chert, and porcellanite (Fig. F35; see also “Igneous lithostratigraphy, petrology, alteration, and structural geology”). Twelve core catcher samples representative of the entire ~75 m sedimentary section were taken for examination of biogenic components (Table T5). Samples were processed by washing over a 63 µm sieve and then analyzing under a stereo-microscope in the shipboard Paleontology Laboratory (see “Paleontology and biostratigraphy” in the “Methods” chapter [Expedition 329 Scientists, 2011]). The brown pelagic clay is rich in ichthyoliths (mainly fish teeth; Fig. F36) and, in lesser amounts, radiolarians.

Fish teeth

The number of complete fish teeth preserved in the >63 µm sediment fraction of Samples 329-U1365A-1H-CC through 5H-CC, 14H-CC, and 24H-CC; 329-U1365B-2H-CC; and 329-U1365C-3H-CC and 5H-CC was counted to estimate total abundance throughout the section. Fish tooth abundance varied from 0 to >300 teeth per sample. Fish teeth were grouped into six categories based on overall morphology: triangular outline with angulated sides, conical (long and short), platelike, V-shaped, star-shaped, and sawlike. The distribution of ichthyoliths at Site U1365 is tabulated in Table T5 and illustrated in Figure F37. The highest abundance of fish teeth was observed in Sample 329-U1365A-2H-CC (13.3 mbsf). Our results are comparable with those of nearby Sites 595 and 596, at which the highest concentration of triangular fish teeth was observed at ~12 mbsf (Winfrey et al., 1987). This depth is estimated to be of Oligocene or Eocene age at Site 596.

A 2 cm long tooth fragment (Fig. F38) was found serendipitously in chert gravel recovered in Section 329-U1365A-20H-1 (59.7 mbsf). The tooth fragment was extraordinarily well preserved and has been assigned provisionally to the Cretaceous shark genus Squalicorax.

Radiolarians

Radiolarians were found in most core catcher samples studied. The abundance ranged from absent to common (>50 per 10 g of sediment), and preservation ranged from good (majority of specimens complete with minor recrystallization, dissolution, or breakage) to poor (strong dissolution, recrystallization, or breakage; many specimens unidentifiable). The highest concentration and best preservation of radiolarians was observed in Samples 329-U1365A-5H-CC and 14H-CC. For these two samples, representative taxa were identified by C. Hollis (GNS Science, New Zealand) postexpedition. The common occurrence of species Actinomma sp., Archaeodictyomitra cf. lamellicostata, Allevium gallowayi, Dictyomitra multicostata, and Neosciadiocapsa cf. diabloensis suggests an age of mid-Maastrichtian for Sample 329-U1365A-5H-CC. In Core 329-U1365A-14H, the common occurrence of Amphisphaera priva, Cryptamphorella macropora, and Xitus spicularis suggests an age of mid-Campanian (Fig. F35). Additional postexpedition studies will necessary to refine these preliminary age determinations. Radiolarian taxonomic concepts follow Sanfilippo and Riedel (1985). Age assignments are based on Hollis and Kimura (2001). Figure F39 shows examples of radiolarian species found at Site U1365.

Foraminifers

Foraminifers are extremely rare at Site U1365. Planktonic taxa were found only in very low numbers in Sample 329-U1365A-1H-CC (5.88 mbsf); they were moderately dissolved. Benthic foraminifers were represented by simple agglutinated forms only. Their abundance ranges from absent in most samples to rare in Samples 329-U1365A-3H-CC and 329-U1365C-3H-CC (Table T5).

Top of page   |    Previous   |    Next