Physical properties of the shallow sediments in late Pleistocene formations, Ursa Basin, Gulf of Mexico, and their implications for generation and preservation of shallow overpressures

Permeability‐porosity relationships of shallow mudstones in the Ursa Basin, northern deepwater Gulf of Mexico

“…Comparison of in situ permeabilities (Table 2) with previously published vertical permeabilities. Permeabilities were measured using consolidation experiments [ Binh et al , 2009; Bryant et al , 1975; Dugan , 2008], constant head technique [ Stump , 1998], transient pulse decay technique [ Yang and Aplin , 2007], and were calculated from a permeability model [ Yang and Aplin , 1998]. Gray‐shaded area shows compilation of permeability‐porosity data of argillaceous sediments by Neuzil [1994].…”

“… Yang and Aplin [1998, 2007] published permeability studies on mudstones from passive margins like the Norwegian margin, North Sea, and Caspian Sea. However, only a few Gulf of Mexico permeability studies have been published to date [ Binh et al , 2009; Bryant , 2002; Bryant et al , 1975, 1986; Dugan , 2008; Long et al , 2008; Stump , 1998] despite the large interest in regional petroleum resources. Bryant et al [1975] and Bryant [2002] published permeability results on a large number of marine sediment samples with varying clay contents from all areas of the Gulf of Mexico in both shallow and deep water as well as shallow and deep subsurface.…”

“… Dugan [2008] performed permeability measurements on 8 samples from Keathley Canyon from depths between 5 and 300 mbsf. Two studies analyzed whole cores from the same IODP sites in the Ursa Basin as analyzed in this study from depths down to almost 600 mbsf; Binh et al [2009] measured permeability on 14 whole core samples and Long et al [2008]primarily measured the compression behavior of 32 whole cores but also estimated in situ permeabilities. However, it is rare that the samples are also well characterized with respect to their composition, mineralogy, and permeability‐porosity relationship, and that they are used for in situ permeability determination and upscaling purposes Gamage et al [2011]…”

What causes large submarine landslides on low gradient (<2°) continental slopes with slow (∼0.15 m/kyr) sediment accumulation?

“…The aim of this contribution is to characterize the general behavior of a submerged 2° continental slope with low sediment accumulation. This is in contrast to previous studies whose focus was mainly on case studies [ Dugan and Flemings , , ; Binh et al , ; Hustoft et al , ; Stigall and Dugan , ]. Moreover, there is currently no study that quantifies the term “rapid” with respect to excess pore pressure generation due to rapid deposition.…”

“…Pore pressures in excess of hydrostatic have been measured by drilling at several continental margins worldwide [e.g., Kvalstad et al, 2005;Flemings et al, 2008]. Laboratory experiments and modeling have shown that consolidation of soft marine sediments during burial can generate excess pore pressures when certain preconditions, such as high sedimentation rates, are fulfilled [Binh et al, 2009;Stigall and Dugan, 2010]. Modeling has shown that rapid (∼30 m/kyr) and prolonged (several thousand years) sediment deposition from river discharges or ice streams can generate sufficiently high overpressure ratios to directly cause failure of nearly flat slopes or weaken the slope to an extent that a moderate earthquake can cause failure [Stigall and Dugan, 2010].…”