Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications

• Published in: Marine Geophysical Research
• Main Authors: Mitchell, Neil C., Dubois, Nathalie
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Bottom Ekman layer; Coriolis effect; Equatorial sediment focusing; Pacific plate model; True polar wander; New Zealand; Pacific; Antarc*; Antarctica
• Online Access: https://research.manchester.ac.uk/en/publications/96f75c28-4f48-4424-b825-3542ab7814a3; https://doi.org/10.1007/s11001-013-9196-2; https://pure.manchester.ac.uk/ws/files/21606550/POST-PEER-REVIEW-NON-PUBLISHERS.PDF; http://www.wkap.nl/journalhome.htm/0025-3235

If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that 230Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260-267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed 230Th carried by bottom currents towards the equator ("focusing"). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25-20.1 Ma but is well developed for the interval 8.55-14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P2O5 (proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10-25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05-14.25 Ma, the latitudes of the seismic anomalies ...