Aspects of Calcareous Nannofossil Biostratigraphy and Abundance in the Pliocene and Late Miocene of Site 905

Abstract

Continental rise Site 905 yielded upper Miocene and Pliocene uniform hemipelagic mud (a contourite) from approximately 215 to 540 meters below seafloor. The nannofossil biostratigraphy of this interval was reexamined using closely spaced samples from core interiors. Additionally, total nannofossil abundances and dominant species and species group abundances were determined to evaluate the potential of this section for extracting sequence stratigraphic information. The data indicate that the putative hiatuses at the end of the late Pliocene (Zones NN17 and NN18) and in the early Pliocene (Zones NN13 and NN14) probably are condensed intervals, but the base of the late Miocene is almost certainly marked by an unconformity. Judging from carbonate content and sedimentation rate both, nannofossil abundance may be governed by carbonate dissolution or by siliciclastic dilution. Consequently, condensed sections cannot be identified by the abundance of pelagic component in the sediment alone, as is possible in equivalent age Gulf of Mexico sediments. Where nannofossil preservation is adequate in consecutive samples, as in the early Pliocene and latest late Miocene, total nannofossil abundance fluctuates regularly and with a periodicity of less than 10 5 yr, which suggests that dilution of the pelagic component occurred with a frequency probably related to astronomical forcing.

A magnetostratigraphic calibration of Middle Miocene through Pliocene dinoflagellate cyst and acritarch events in the Iceland Sea (Ocean Drilling Program Hole 907A)

“…Our observations for Hole 907A are consistent with those of the Salisbury Embayment, eastern U.S.A. where this species disappeared at c. 10.5 Ma (lower Tortonian; de Verteuil and Norris, 1996), and recorded a similar age within the middle of zone DN8 (mid-Tortonian; Gartner and Shyu, 1996) for its HO in the continental slope off New Jersey. For eastern North Atlantic IODP Site U1318, Louwye et al (2007b) recorded this species rarely but persistently throughout the investigated Lower and Middle Miocene sequence which extends to 12.1 Ma (upper Serravallian).…”

“…commun., 2007). De Verteuil and Norris (1996) used the HO of H. obscura to define the top of their DN9 zone in the upper Tortonian (c. 7.5 Ma) of the Salisbury Embayment, eastern U.S.A. A similar position at the top of zone DN9 was reported for the HO from the continental margin of New Jersey Gartner and Shyu, 1996). In eastern North Atlantic DSDP Site 555, the HO was reported within the lower part of nannofossil zone NN11 (upper Tortonian, Edwards, 1984;Backman, 1984), whereas H. obscura ranges to the nannofossil zone boundary NN5/6 in DSDP Hole 548A (Brown and Downie, 1985;Müller, 1985), although here the HO is probably lost within an apparent hiatus separating the upper Middle Miocene from middle Upper Miocene (Snyder et al, 1985).…”

“…In eastern North Atlantic DSDP Site 555, its HO has been observed in the upper Serravallian or lower Tortonian (Edwards, 1984;Backman, 1984). Its HO has also been recorded from the Salisbury Embayment, eastern U.S.A. within the lower part of zone DN8 (c. 10.4 Ma, lower Tortonian; de Verteuil and Norris, 1996), and it has a well defined HO within zone DN6 (mid-Serravallian) of ODP Hole 905A on the New Jersey continental rise Gartner and Shyu, 1996). A single record in ODP Hole 903A on the New Jersey continental shelf within zone DN9 (upper Tortonian, is suspected of being reworked based on its unusually high stratigraphic position.…”

“…For the Salisbury Embayment, eastern U.S.A., de Verteuil and Norris (1996) reported its HO at the top of their zone DN9 dated to c. 7.5 Ma (upper Tortonian). An HO at the top of zone DN8 has been reported from the continental slope off New Jersey (upper Tortonian, Gartner and Shyu, 1996), whereas it is still present in the Lower Pleistocene of western North Atlantic DSDP Site 603C (M.J.H., unpubl. data; Canninga et al, 1987).…”

“…It has been reported sporadically from offshore New Jersey, western North Atlantic, with an LO established from one sample in the Upper Oligocene of ODP Hole 906A and an LO in the Middle Miocene dinocyst zone DN5 of ODP Hole 905A (c. 13 Ma, de Verteuil, 1996;Gartner and Shyu, 1996). In western North Atlantic DSDP Hole 603C, this species occurs at the base of the hole at 5.82 Ma (upper Messinian) (M.J.H, unpubl.…”