Paired AMS ¹⁴C Dates on Planktic Foraminifera from a Gulf of Mexico Sediment Core: An Assessment of Stratigraphic Continuity

Abstract

ABSTRACT.A series of recent papers has called for multiple radiocarbon dates on planktic foraminifera to assess stratigraphic continuity in deep-sea sediment cores. This recommendation comes from observations of anomalous 14 C dates in planktic foraminifera from the same stratigraphic level. Potential reasons include bioturbation, downslope transport, secondary calcification, carbonate dissolution, and differential preservation. In this study, paired 14 C dates on dissolution-susceptible Globigerinoides ruber and dissolution-resistant Neogloboquadrina dutertrei are used to evaluate a Gulf of Mexico sediment core. Fourteen of 15 pairs (between 8815 and 12,995 uncorrected 14 C yr BP) yield concordant uncorrected 14 C ages (mean difference -2 ± 75 yr), attesting to continuous deposition at high accumulation rates (>35 cm/kyr). For 1 pair, N. dutertrei is nearly 1000 yr younger, which is difficult to explain by any combination of dissolution and bioturbation or downslope transport, given the excellent carbonate preservation and persistent laminations. The concordant ages underscore the utility of paired 14 C dates in planktic foraminifera as a means of assessing stratigraphic continuity in deep-sea sediment sequences.

Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater–brine interface

“…Multiple studies of the sediments underlying Orca Basin have converged on a 7900 to 8500 yr timescale for the establishment of anoxic, hypersaline conditions in the basin (Addy and Behrens, 1980;Leventer et al, 1983;Meckler et al, 2008). For this study, we compared our radiocarbon values with the most recent foram record reported by Meckler et al (2008) because it includes a foraminiferal radiocarbon date in close proximity to the black-gray sediment transition depth and because radiocarbon analysis of individual foraminiferal species has confirmed stratigraphic continuity in this location (Flower et al, 2011). Adjusting these reported radiocarbon ages by the more recent, smaller reservoir age from the nearby Flower Garden Banks (Wagner et al, 2009) results in an 8700 ± 100 yr calendar age for Orca Basin brine.…”

High frequency environmental changes and deposition processes in a 2 kyr-long sedimentological record from the Cap-Breton canyon (Bay of Biscay)

“…Regarding the latter, the mixing of sediments across a gradient of increasing abundance of a given foraminiferal species will introduce relatively abundant, younger foraminifera to older levels depleted in foraminifera down core (see example in Broecker et al, 1984 or Manighetti et al, 1995), contributing to bias the age of lower level to younger values. Conversely, dissolution or secondary calcification processes on fossilized shells, which furthermore do not occur equitably on all species (see Flower et al, 2011), could potentially deviate ages towards older values (Heier-Nielsen et al, 1995). These phenomena act on limited time scales, that is, few hundred years considering well-preserved faunas not affected by preferential dissolution (Broecker and Clark, 2011).…”

“…After carefully considering the potential biases, we thus decided to construct an age model based on the radionuclide results and the AMS 14 C dates of mollusc shells only (Figure 3C, Table 1), these latter being considered in the literature to be most reliable even if the question is highly complex (e.g. Flower et al, 2011; Heier-Nielsen et al, 1995).…”