Data report: revised composite depth scales for Sites U1336, U1337, and U1338

Abstract

The eastern equatorial Pacific (EEP) is one of the most dynamic regions of the open ocean. To fully appreciate the history of this area in the time domain, correlative and complete sedimentary records are required from multiple drill sites. One essential step for each site is the construction of an accurate composite depth scale, whereby selected intervals of successive cores from proximal holes are spliced together to render a full stratigraphic section. Here, we generate revised composite depth scales for Integrated Ocean Drilling Program (IODP) Sites U1336, U1337, and U1338, recovered during IODP Expeditions 320 and 321. Composite sections were generated using physical properties data overlain on high-resolution scanned images of adjacent core sections from all holes cored at a site. Coring disturbance, particularly deeper in the holes, prevented composite construction to total depth at each site. At Site U1336, utilizing two holes, the composite record reaches almost 135 m core composite depth below seafloor (CCSF). At Site U1337, with four holes, a depth of close to 450 m CCSF was reached with only three gaps. Using the three holes of Site U1338, a composite section of almost 400 m CCSF was developed with only two breaks. Composite depth records are crucial for working on these sites because sediment composition varies considerably over short (<30 cm) depth intervals. The composite gamma ray attenuation density records will be particularly important to a range of studies in the region because they can be coupled to those collected at earlier drill sites in the EEP.

Methods

“…It should also allow maximum stratigraphic correlation between three holes because no whole-round samples would be taken from Hole B or Hole C, except from XCB cores at deep depths, where decimeter-scale stratigraphic correlation between holes using various techniques (e.g., GRA, magnetic susceptibility, and NGR) often becomes very difficult (e.g., Wilkens et al, 2013).…”

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

“…Revised CCSF-A depths for both biostratigraphic and magnetostratigraphic data were calculated by adding an offset depth to the CSF-A depth for each core, according to Table T5 in Wilkens et al (2013). They further refined depths within cores from all three holes at Site U1338 caused by intracore stretching or squeezing and referred to these depths as "Adjusted CCSF."…”

“…They further refined depths within cores from all three holes at Site U1338 caused by intracore stretching or squeezing and referred to these depths as "Adjusted CCSF." In Tables AT47, AT52, and AT57, Wilkens et al (2013) adjusted depths for a total of 843 samples. Of these samples, 232 show no adjustment (0 cm), 281 show an average adjustment of +16 cm, and 330 show an average adjustment of -17 cm.…”

“…Top and bottom hole, core, section, interval measurements are from Table T3 in . Top and bottom CSF-A and CCSF-A depths are from Table T5 in Wilkens et al (2013). Revised depth = midpoint CCSF-A (m)/site growth factor (Fig.…”

“…To compensate for this distortion, CCSF-A depths for Site U1338 were divided by a growth factor of 1.11, resulting in a third set of depths, the corrected composite depths (CCSF-B, in meters) (see Table T23 in the "Site U1338" chapter [Expedition 320/321 Scientists, 2010b]). Subsequently, CCSF-A depth data from Site U1338 were revised by Wilkens et al (2013), who also provide a discussion of IODP depth scale terminology.…”