Salt tectonics on passive margins: examples from Santos, Campos and Kwanza basins

Abstract

Salt flows downslope, irrespective of overburden. In salt basins on passive margins, the salt will tilt and flow towards the ocean immediately after continental rifting has ended due to thermal subsidence. Using real examples, as well as physical and numerical models, tilting is shown to be relatively rapid, enhanced by isostatic rebound updip and loading downdip where salt pools and inflates behind an outer high. In the Santos, Campos and Kwanza basins, this outer high is represented by an embryonic mid-Atlantic ridge, amplified in height by the differential weight of the inflating salt. Widespread extension and translation of overburden, utilizing both seaward- and landward-dipping normal faults, characterizes the early evolution of the inboard region. Inflation and contraction occur outboard, the effects of which tend to expand in a landward direction over time. Rapid accumulation of salt implies wholesale dewatering of pre-salt sediments, the water possibly permeating the salt once it has reached a burial depth of c. 3 km. The process of thermal subsidence, salt drainage and isostatic amplification is an efficient mechanism for moving sediment on passive margins tens of kilometres seaward during a relatively short period and helps explain why great thicknesses of salt can accumulate there in the first place.

Enigmatic structures within salt walls of the Santos Basin—Part 1: Geometry and kinematics from 3D seismic reflection and well data

“…4), and key periods of salt-related deformation are indicated. The timing of proximal extension is based on Guerra and Underhill (2012) and Quirk et al (2012); the timing of distal extension is based on observations presented here and in Jackson et al (2014). Two slightly different periods of regional shortening are indicated based on observation presented here and those presented by by Guerra and Underhill (2012).…”

“…Grainstones and oolitic shoals accumulated along the proximal northwestern basin margin; farther basinward to the southeast, beyond the palaeo-shelf edge, a very fine-grained, marldominated succession was deposited (Modica and Brush, 2004). At this time thermal and isostatic subsidence was focused toward the centre of the embryonic oceanic spreading centre and, during the latest Albian, this subsidence tilted the basin southeastward, creating a thin-skinned array of predominantly seaward-dipping normal faults that broke the Albian carbonate platform into extensional rafts Rouby et al, 1993;Cobbold et al, 1995;Mohriak et al, 1995;Guerra and Underhill, 2012;Quirk et al, 2012).…”

“…A key feature of this debate is the Albian Gap Cobbold et al, 1995;Mohriak et al, 1995;Ge et al, 1997;Modica and Brush, 2004;Gemmer et al, 2005;Davison et al, 2012;Guerra and Underhill, 2012;Quirk et al, 2012). Some researchers think the Albian Gap formed mostly by Late Cretaceous gravity-driven extension of the suprasalt cover, in which case the structures in our study area may be part of the Late Cretaceous shortening system that accommodates this extension (e.g., Mohriak et al, 1995;Modica and Brush, 2004;Quirk et al, 2012). Others interpret that the Albian Gap formed due to salt expulsion driven by progradation of basin-margin clastic wedges across a pre-existing salt wall (Ge et al, 1997;Gemmer et al, 2005;Kr ezsek et al, 2007).…”

Petroleum Geology and Hydrocarbon Potential of the Adriatic Basin, Offshore Croatia

“…A geological interpretation of the profile is shown in the box beneath the section and includes petroleum system elements. Jackson and Cramez, 1989), offshore Brazil (Quirk et al, 2012) and offshore Angola (Duval et al, 1992;Jackson 1992a, 1992b;Jackson et al, 1994), and has been supported by modelling studies (Vendeville et al, 1987). Halokinesis and dissolution-driven pod formation has been described for tectonically-confined Triassic basins in the UK North Sea Central Graben (for example Hodgson et al, 1992;Smith et al, 1993;Stewart, 2007;Goldsmith et al, 2003).…”

Heterogeneity of folding in Zechstein (Upper Permian) salt deposits in the Kłodawa Salt Structure, central Poland

“…This in di cates that flow and fold ing of salt beds, in fact, be gins long be fore the ini ti a tion of salt pil low or diapir ini ti ation and that prob a bly only a min ute in cli na tion of beds trig gers salt flow. Also re cently, grav ity-driven slid ing, flow and fold ing of stratiform beds have been well-doc u mented by seis mic data in salt basins lo cated on con ti nen tal slopes (Davison et al, 2012;Fiduk and Ro wan, 2012;Fort and Brun, 2012;Adam and Krezsek, 2012;Quirk et al, 2012;Strozyk et al, 2012). These data show that in clined salt beds flow down wards in re sponse to grav ity and sed i ment load ing and that the grav ity-driven slid ing and flow leads to de for ma tion of the evaporite se quence as well as an in crease in its total thick ness down the slope, prior to diapirism.…”