Data report: dissolved minor element compositions, sediment major and minor element concentrations, and reactive iron and manganese data from the Lesser Antilles volcanic arc region, IODP Expedition 340 Sites U1394, U1395, U1396, U1399, and U1400

Abstract

We measured dithionite-extractable iron and manganese along with a variety of bulk sedimentary solid and dissolved phases to constrain diagenetic reactions occurring within the sediment package of Grenada Basin, which is within the Lesser Antilles volcanic arc region. Core material was obtained during Integrated Ocean Drilling Program Expedition 340. For this report we focus primarily on five sites; three sites are located in the northern portion of the study area off the island of Montserrat (Sites U1394-U1396), and two sites are located farther south off the island of Martinique (Sites U1399 and U1400). Sediments throughout this region include tephra-rich volcanic sands, hemipelagic mud sequences, and carbonate-rich sequences, with widely variable proportions over short (centimeter scale) depth intervals. Regardless of the main sediment type, organic carbon contents are low with average values of 0.19 ± 0.1 wt% at Site U1394, 0.13 ± 0.08 wt% at Site U1395, 0.13 ± 0.06 wt% at Site U1396, 0.28 ± 0.08 wt% at Site U1399, and 0.23 ± 0.15 wt% at Site U1400. Carbonate contents are more variable, ranging between 0 and ~80 wt%, in cores from Sites U1394-U1396 and between 1 and 40 wt% at both Sites U1399 and U1400. These variations in carbonate content likely reflect variable dilution with volcanogenic sediment. Pore fluids reflect a range of diagenetic conditions from oxidizing (sulfate rich) to sulfate-reducing conditions. Reactive major elements (Ca and Mg) as well as a number of minor elements show a range of diagenetic behaviors from reactions likely related to carbonate dissolution or precipitation to exchange reactions between pore fluids and the volcanic-rich sedimentary substrate and clay formation. However, significant site-to-site variability is seen in the diagenetic behavior of these elements. Solid-phase reactive Fe ranges from 0.18 to 0.75 wt% at the northern sites and 0.4 to 1.5 wt% at the southern sites, whereas reactive Mn ranges from 0 to 0.1 wt% in the north and 0 to 0.3 wt% in the south. Sites U1399 and U1400 are located west of the island of Martinique in Grenada Basin in 2900 and 2745 m water depth, respectively (Fig. F1). The lithology of these two sites is similar and is composed of hemipelagic mud, interbedded tephra layers, volcaniclastic turbidites, and deformed sediments (see the "Expedition 340 summary" chapter [Expedition 340 Scientists, 2013a]); Le Friant et al., 2015). Site U1400 is located west of Martinique but closer in proximity to the island than Site U1399 (Fig. F1). Introduction Analytical methods Pore fluid extractionsPore fluids were obtained from all sediment cores presented in this report (Table T1). Sampling occurred every 10 m unless the sediment was unsuitable for pore fluid extraction (i.e., because of sands, debris, or other mission-specific rationales). Sampling procedures are described in detail in the "Methods" chapter (Expedition 340 Scientists, 2013b); however, we present a brief description for completeness. A 10 to 15 cm section of whole-round core was remo...

Diagenesis in tephra-rich sediments from the Lesser Antilles Volcanic Arc: Pore fluid constraints

“…This fraction likely represents a mixture of the regional volcanogenic signature, the more distal atmospheric dust signature, as well as any diagenetic overprinting (clay formation) by more radiogenic seawater Sr isotope values.Indeed for the other sites the bulk sediment 87 Sr / 86 Sr values are generally between the carbonate and non-carbonate values (SupplementalTable 3) although we do note here the somewhat surprisingly high Sr concentrations at Site U1395 even though the 87 Sr / 86 Sr values bracket the range of values noted here(Murray et al, 2016). The Sr isotope values of the pore waters at Site U1396 have the lowest 87 Sr / 86 Sr values of any of the cores and we infer that this site is the most impacted by reaction with volcanogenic material.…”

“…Most of the data and methods described in this manuscript are available from the IODP data repository or through the various post-cruise data reports (Le Friant et al, 2013;Murray et al, 2016). Nevertheless, for completeness we briefly review the methodology here.…”

“…All pore fluid data for this manuscript were presented within data reports associated with the expedition with the exception of the 87 Sr / 86 Sr (Expedition 340 Scientists, 2013;Le Friant et al, 2013;Murray et al, 2016). The reader is directed to those communications for full data sets and analytical details; however, Sr and Sr isotope data for the pore fluids are present in Supplemental Table 1 and for the sediment solid phases in Supplemental Tables 2 and 3.…”

“…Table 3) following the general approach outlined above for the pore fluids. These samples were digested as described in Muratli et al (2010 and and the ancillary data for these digests are available in Murray et al (2016).…”

“…Dashed lines denote bottom water concentrations. Alkalinity, NH 4 , Ca, Mg, and SO 4 2data are fromLe Friant et al (2013) and minor ion data is fromMurray et al (2016).…”