Planktonic foraminifer biostratigraphy at Site 925: middle Miocene–Pleistocene

Abstract

Ocean Drilling Program Site 925 is situated on Ceara Rise in the western tropical Atlantic at 4û12 ′ N, 43û30 ′ W and in 3041 m water depth. The section contains well-preserved planktonic microfossils through the late Miocene, with only moderate dissolution of carbonate in the middle Miocene. No unconformities are apparent.Datums used to establish the biozonation, and to further reÞne the age model, were constrained shipboard to within 1.5 m. In general, one sample per core has been re-examined to identify all species present. Globorotalia menardii, Globorotalia tumida, Globorotalia truncatulinoides, Pulleniatina obliquiloculata, and Neogloboquadrina dutertrei vary considerably in abundance, and each is occasionally absent in the Pleistocene, which suggests signiÞcant oceanographic change through this interval. The published ages assigned to planktonic foraminifer datums are compared to those suggested by the astrochronologic time scale. Several signiÞcant discrepancies (>0.25 m.y.) are found. Some are due to taxonomic problems (e.g., Þrst occurrence [FO] of Pulleniatina Þnalis, FO and last occurrence [LO] of Hirsutella cibaoensis, LO Neogloboquadrina acostaensis ), but many may identify real diachrons (e.g., LO Hirsutella margaritae and FO Truncorotalia crassaformis ). Discrepancies that involve zonal boundary markers (FO Globoturborotalita nepenthes and LO Fohsella fohsi ) should be further studied, as revisions to the Neogene zonation may be in order.Global rates of planktonic foraminiferal taxonomic evolution are compared to values measured at Site 925. SigniÞcant discrepancies are found, which suggests that the closing of the Central American Seaway decoupled patterns of evolution in the tropical Atlantic and PaciÞc.An assessment of planktonic foraminiferal dissolution at all Þve sites in the Ceara Rise depth transect reveals three apparent ÒtransgressionsÓ of corrosive bottom water to shallower depths on the rise between 10 and 12 Ma, at 7 Ma, and at 1 Ma.

Integrated stratigraphy and astronomical calibration of the Serravallian/Tortonian boundary section at Monte Gibliscemi (Sicily, Italy)

“…In contrast to delayed low-latitude arrival of N. acostaensis at Ceara Rise, P. mayeri shows a delayed extinction of more than 0.7 million years with respect to the Mediterranean (LO at 10.49 Ma at Ceara Rise, Chaisson and Pearson, 1997;LO at 11.205 Ma in the Mediterranean, this paper). As a result, the N14=N15 and N15=N16 zonal boundaries are strongly diachronous between the low-latitude and the mid-to high-latitude North Atlantic.…”

“…The earliest neogloboquadrinids are known from the late-Middle Miocene in the North Atlantic region Huddlestun, 1984;Zachariasse and Aubry, 1994). These earliest representatives are immigrants which must have come from regions north of Iceland since the earliest spreading of this group in the tropical region is in the early-Late Miocene (Zachariasse and Aubry, 1994;Chaisson and Pearson, 1997).…”

“…The first occurrence of N. acostaensis at these tropical localities, however, resulted from migration (e.g., Zachariasse, 1992). The invasion of N. acostaensis at the tropical Ceara Rise has recently been dated at 9.82 Ma using astronomical tuning (Chaisson and Pearson, 1997). This age indeed shows that the FO of N. acostaensis in the tropical region is significantly younger than in the Mediterranean.…”

Surface temperatures of the Mid-Pliocene North Atlantic Ocean: implications for future climate

“…Semi-quantitative analysis of the foraminiferal faunas at Site 925 (Chaisson & Pearson 1997) reveals an assemblage remarkably similar to the present-day faunas in the region, suggesting warm tropical SSTs at this site not unlike modern conditions.…”

Methods

“…The age estimates presented are adjusted to the timescale of Expedition 320/321. Planktonic foraminifer taxonomic concepts selectively follow those of Bolli and Saunders (1985), Spezzaferri and Premoli Silva (1991), Chaisson and Leckie (1993), Leckie et al (1993), Spezzaferri (1994), Chaisson and Pearson (1997), Pearson and Chaisson (1997), Olsson et al (1999), and Pearson et al (2006).…”