Data report: a revised biomagnetostratigraphic age model for Site U1338, IODP Expedition 320/321

Abstract

The development of late middle Miocene through recent sedimentation rates was determined for Integrated Ocean Drilling Program Site U1338 in the eastern equatorial Pacific using available geomagnetic chron boundaries and biostratigraphic biohorizons provided by calcareous nannofossils and diatoms. These data were set in a revised depth splice of the three holes at Site U1338 and provide a lower resolution image of the sedimentation rate history in the region of Site U1338 through relatively long linear interpolations between 11 chosen age-depth control points encompassing 18 My. The resulting sedimentation rates depict the movement of Site U1338 from just south of the Equator with modest sedimentation rates starting at 11 m/My to tripling of these rates near 13 Ma, when the site moved onto the Equator and into the equatorial high-productivity belt. High sedimentation rates continued into the earliest Pliocene (5 Ma) except for a 50% decrease during the so-called "carbonate crash" centered around 9.6 Ma ± 0.4 My. The site's movement north, away from the equatorial high-productivity belt, began between 5.0 and 4.2 Ma, when the site was located ~75-90 nmi north of the Equator, and resulted in a series of successively decreasing sedimentation rates to the present rate of 11 m/My, identical to the rate when sedimentation began at Site U1338 at nearly 18 Ma, when the site was located ~100 nmi south of the Equator.

Eccentricity pacing of eastern equatorial Pacific carbonate dissolution cycles during the Miocene Climatic Optimum

“…However, we were unable to reconstruct these changes prior to 16 Ma, since the onset and early phase of the MCO are not identifiable at Site U1338. This interval at Site U1338 is within the slowly sedimented, basal sedimentary succession, which was poorly recovered [ Backman et al ., ]. Taking into account uncertainties in paleobathymetric reconstructions, which could reach ~250 m according to Pälike et al .…”

Biostratigraphy and evolution of MioceneDiscoasterspp. from IODP Site U1338 in the equatorial Pacific Ocean

“…We have, therefore, chosen to present the abundance data v. depth rather than age, as age estimates inevitably will change when an improved age model based on astronomical tuning of various sediment properties becomes established. However, when summarizing relative abundances of the major Discoaster groups, we have placed these data on a low-resolution age model for Site U1338 (Backman et al 2016), using a combination of seven biomagnetostratigraphic indicators from 5.04 Ma/68.63 m to 17.74 Ma/406.43 m.…”

“…Above, the abundance patterns of discoasters are plotted v. depth. When summarizing the key trends among these patterns, we consider it useful to plot the data v. age using a low-resolution age model of Site U1338 (Backman et al 2016). Discoasters reveal distinct traits over the late early Miocene through late Miocene interval at Site U1338 (Figs 11 and 12).…”

Hydrologic Changes Drove the Late Miocene Expansion of C4 Grasslands on the Northern Indian Subcontinent

“…We recalculated the age models for ODP 717 and 718 to reflect updated biostratigraphic and geochronologic constraints (Figures S1 and S2; supporting information S1.1). The original biohorizons for Sites 717 and 718 (Gartner, 1990;Shipboard_Scientific_Party, 1988a, 1988b were updated with revised calcareous nannnofossil and planktonic foraminifera biohorizon ages (Backman, et al, 2012;Wade et al, 2011) and updated ages for the Top common Cyclicargolithus floridanus and Base Discoaster exilis horizons (Backman et al, 2016;Ciummelli et al, 2017;McNeill et al, 2017;Pälike et al, 2010). The most important changes are the updated age for the Base Nicklithus amplificus horizon (shifted from 5.9 to 6.…”