Research Article| August 01, 1999 Large, coherent, submarine landslide associated with Pan-African foreland flexure Paul F. Hoffman; Paul F. Hoffman 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Search for other works by this author on: GSW Google Scholar Ebbe H. Hartz Ebbe H. Hartz 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Paul F. Hoffman 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Ebbe H. Hartz 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1999) 27 (8): 687–690. https://doi.org/10.1130/0091-7613(1999)027<0687:LCSLAW>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul F. Hoffman, Ebbe H. Hartz; Large, coherent, submarine landslide associated with Pan-African foreland flexure. Geology 1999;; 27 (8): 687–690. doi: https://doi.org/10.1130/0091-7613(1999)027<0687:LCSLAW>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Ombonde detachment is a primary low-angle normal fault that developed in an undeformed Neoproterozoic carbonate shelf succession as it entered a west-dipping Pan-African subduction zone. The fault is mappable from the top of the shelf succession to the granitic basement surface at a paleodepth of 1.5 km, and the hanging wall has not been significantly deformed. The primary fault geometry is well constrained by stratigraphic cutoff relationships, irrespective of secondary rotations. The dip direction of the fault was ∼270°, and its horizontal separation was 15–18 km. The fault plane is composed of two ramps separated by a long flat segment at a paleodepth of 0.55 km. The ramps are inclined 8°–14° relative to the carbonate strata, which underwent little or no compaction, and the mean cutoff angle overall is 1.3°. Given constraints on the contemporaneous tectonic setting, the primary fault dips must equal the stratigraphic cutoff angles augmented by a taper angle for lithospheric flexure of not more than 4°. Primary mean dips of <5° are mechanically implausible for a shallow tectonic fault related to extension of nonthickened crust because of the high normal- to shear-stress ratio. However, large gravity slides have moved on detachments dipping 1°–5° on modern continental margins. A gravitational origin is therefore favored, although no toe thrust is observed on account of younger cover. Stratigraphic and sedimentologic observations indicate a relative sea-level drop of >200 m, which would have significantly reduced the water load and thereby the normal stress on a subhorizontal plane, possibly leading to excess pore-fluid pressures. This scenario is consistent with the virtual absence of macroscopic shear deformation adjacent to the fault plane. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.