Fresh-water and salt-water distribution in passive margin sediments; insights from Integrated Ocean Drilling Program Expedition 313 on the New Jersey margin

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doi: 10.1130/GES00855.1
Author(s): Lofi, Johanna; Inwood, Jennifer; Proust, Jean-Noël; Monteverde, Donald H.; Loggia, Didier; Basile, Christophe; Otsuka, Hironori; Hayashi, Takeshi; Stadler, Susanne; Mottl, Michael J.; Fehr, Annick; Pezard, Philippe A.
Author Affiliation(s): Primary:
Université Montpellier, Geosciences Montpellier, Montpellier, France
University of Leicester, United Kingdom
Université de Rennes 1, France
Rutgers, the State University of New Jersey, United States
Université Joseph Fourier, France
University of Tokyo, Japan
Akita University, Japan
Federal Institute for Geosciences and Natural Resources, Germany
University of Hawaii, United States
RWTH Aachen University, Germany
Volume Title: Geosphere (Boulder, CO)
Source: Geosphere (Boulder, CO), 9(4), p.1009-1024. Publisher: Geological Society of America, Boulder, CO, United States. ISSN: 1553-040X
Note: In English. 69 refs.; illus., incl. sects., 3 tables, sketch map
Summary: On the New Jersey shelf (offshore North America), the presence of pore water fresher than seawater is known from a series of boreholes completed during the 1970s and 1980s. To account for this fresh water, a first hypothesis involves possible present-day active dynamic connections with onshore aquifers, while a second involves meteoritic and/or sub-ice-sheet waters during periods of lowered sea level. Expedition 313 drilled three boreholes on the middle shelf, offering a unique opportunity for the internal structure of the siliciclastic system to be accessed, at scales ranging from the depositional matrix to the continental margin. This enables the stratigraphic architecture to be correlated with the spatial distribution and salinity of saturating fluids. Expedition 313 revealed both very low salinities (<3 g/L) at depths exceeding 400 m below the seafloor and evidence for a multilayered reservoir organization, with fresh- and/ or brackish-water intervals alternating vertically with salty intervals. In this study we present a revised distribution of the salinity beneath the middle shelf. Our observations suggest that the processes controlling salinity are strongly influenced by lithology, porosity, and permeability. Saltier pore waters generally occur in coarse-grained intervals and fresher pore waters occur in fine-grained intervals. The transition from fresher to saltier intervals is often marked by cemented horizons that probably act as permeability barriers. In the lowermost parts of two holes, the salinity varies independently of lithology, suggesting different mechanisms and/or sources of salinity. We present an interpretation of the sedimentary facies distribution, derived from core, logs, and seismic profile analyses, that is used to discuss the margin-scale two-dimensional reservoir geometry and permeability distribution. These proposed geometries are of primary importance when considering the possible pathways and emplacement mechanisms for the fresh and salty water below the New Jersey shelf.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 21 Hydrogeology and Hydrology; Aquifers; Atlantic Ocean; Boreholes; Chloride ion; Chlorine; Concentration; Continental margin; Continental shelf; Cores; Expedition 313; Fresh water; Geophysical methods; Geophysical profiles; Geophysical surveys; Ground water; Halogens; IODP Site M0027; IODP Site M0028; IODP Site M0029; Integrated Ocean Drilling Program; Marine sediments; New Jersey; North Atlantic; Permeability; Pore water; Porosity; Salinity; Salt water; Sediments; Seismic methods; Seismic profiles; Surveys; United States; Vertical seismic profiles; Well logs
Coordinates: N393803 N393803 W0733718 W0733718
N393357 N393357 W0732950 W0732950
N393110 N393110 W0732448 W0732448
Record ID: 2013059401
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