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doi:10.2204/iodp.proc.324.106.2010

Paleontology

Sediments at Site U1349 are composed of reddish cherts and pinkish nannofossil ooze (Cores 324-U1349A-1W through 4R; stratigraphic Unit I; see "Sedimentology") and underlying siliciclastic and volcaniclastic sediments (Cores 4R through 7R; stratigraphic Units II and III). Shipboard calcareous microfossil studies focused mainly on the Unit I sediments, and calcareous nannofossil study extended to Units II and III.

Calcareous nannofossils in the sediments at Site U1349 are rare to common in abundance and are poorly preserved throughout Unit I and barren in underlying Units II and III. Planktonic foraminifers from Unit I are very high in abundance and diversity with good preservation in the nannofossil ooze of Core 324-U1349A-2R, whereas those from other chert-rich levels are poorly preserved and/or low in abundance. The zonal marker species and other age-diagnostic species of planktonic foraminifers strongly indicate that Core 2R is correlated to the middle–late Albian transition. Further age constraints on other examined levels above and below are also possible by some age-diagnostic species, allowing the Unit I sediments to be dated to the Albian–Cenomanian. The ooze of Core 2R yields a diverse benthic foraminifer assemblage, and the estimated bathymetric range is middle bathyal.

Calcareous nannofossils

Calcareous nannofossils in the sediments at Site U1349 are rare to common in abundance and poorly preserved throughout Unit I (Cores 324-U1349A-1W through 4R). The underlying sediments (Units II and III) are barren of calcareous nannofossils.

The dominant taxon in the analyzed samples is Watznaueria barnesae, a typical Cretaceous taxon; few other species are identified (Table T2). In Sample 324-U1349A-1W-1, 9–10 cm, only the additional presence of Watznaueria britannica points to the Lower to mid-Cretaceous. The pinkish ooze below (Sample 324-U1349A-2R-1, 0–1 cm) is mainly composed of subrounded abiogenic calcite particles together with frequent to abundant and highly overgrown specimens of Reinhardites levis (upper Campanian to Maastrichtian) and occasionally abundant Diazmolithus lehmanii (entire Cretaceous) and Cretarhabdus striatus (Aptian to Cenomanian). Hence, the assignment of chronostratigraphic range is difficult based solely on calcareous nannofossils. In Sample 324-U1349A-3R-1, 5–6 cm, only the presence of Rhagodiscus robustus, in addition to W. barnesae, provides a potential range from the Barremian to upper Albian (Zone NC5–Subzone NC10a). The lowermost fossiliferous horizon is Sample 324-U1349A-4R-1, 9–10 cm, which contains some specimens of Rotelappilius sp. and Zeugrhabdotus sp. that are common constituents of the entire Cretaceous assemblage.

Foraminifers

Planktonic foraminifers

The planktonic foraminifer record from stratigraphic Unit I at Site U1349 is marked by a mid-Cretaceous assemblage (Table T3). Although foraminifer occurrence is limited by chert-rich lithologies, pinkish nannofossil ooze in Core 324-U1349A-2R shows exceptionally high abundance and diversity of a middle–late Albian assemblage with good preservation.

Sample 324-U1349A-1W-1, 5–9 cm (chert-encrusting pinkish chalk), yields moderately to poorly preserved individuals of hedbergellids and a poorly preserved rotaliporid specimen. The stratigraphic range is tentatively assigned to the upper Cenomanian (Rotalipora globotruncanoides Zone).

Planktonic foraminifers from Sample 324-U1349A-2R-1, 1–2 cm, are marked by high abundance and diversity with good preservation and correlated to the middle–upper Albian transition. The faunal elements are predominantly the ticinellids (Ticinella primula, Ticinella madecassiana, and Ticinella roberti) with abundant Hedbergella wondersi and Globigerinelloides bentonensis as well as rare hedbergellid taxa. It is noteworthy that rare individuals of the ticinellids exhibit a transitional morphological state to Biticinella breggiensis (i.e., primary apertural openings at both umbilical and spiral sides but not fully connected to each other). This level is therefore very close to the top of the Ticinella primula Zone. Foraminifer specimens with relatively good preservation were also retrieved from Sample 324-U1349A-4R-1, 9–10 cm. The assemblage is marked by the occurrence of few T. madecassiana together with forms assignable to Hedbergella rischi (sensu Bellier and Moullade, 2002). The combination of these two planktonic taxa can be interpreted as indicating the early part of the T. primula Zone.

Benthic foraminifers

As is the case of planktonic foraminifers, a high-abundance diverse benthic foraminifer assemblage is recorded from the pinkish nannofossil ooze of Sample 324-U1349A-2R-1, 1–2 cm (Table T4). This assemblage is characterized by relatively large sized individuals. The most dominant are calcareous trochospiral taxa, which are largely Osangularia and, subordinately, Gyroidinoides. Some nodosariids (Lenticulina, Saracenaria, Planularia, Psilocitharella, and fragmentary Laevidentalina) constitute a subordinate proportion of the assemblage (10% of total benthics). Identified agglutinated taxa are mainly abundant Gaudryina as well as rare Ammosphaeroidina and small-sized Spiroplectinella. The dominance of Osangularia and presence of some nodosariids most likely indicate a middle bathyal setting (Sliter and Baker, 1972; Sikora and Olsson, 1991). Other faunal elements are also conformable with a coeval middle bathyal assemblage along the Atlantic margins (Holbourn et al., 2001).