Syndepositional deformation of the Permian Capitan reef carbonate platform, Guadalupe Mountains, New Mexico, USA
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Permian shelf strata equivalent to the Capitan reef are cut by at least 13 closely spaced syndepositional dip-slip faults in Slaughter Canyon, Guadalupe Mountains, New Mexico, USA. The control of five of these faults on platform development, architecture, stratigraphy and diagenesis is revealed by an integrated stratigraphic, sedimentological and structural framework within a 500-m-wide and 200-m-high outcrop window. Here, faulting and fault-related deformation acted as a primary control on changes in thickness, facies and stratal geometry, and resulted in the local steepening, shallowing and even the reversal of dip in shelf strata. The role of primary depositional relief in controlling changes in thickness and stratal geometry was of secondary importance. The relationship between geopetal fabrics (average dip=12° towards 141°) and bedding shows that during deposition of the Yates Formation fault growth was concurrent with down-to-the-basin tilting (and rotation?) of at least 6–8°. This tilting appears to have been the main control on the down-dip expansion of shelf strata towards the basin. A further 4–6° of basinward tilt occurred after fault growth, during deposition of the Tansill Formation and later. The syndepositional faults reported here have a maximum displacement of 24 m. Most tip-out below asymmetric growth folds and have high displacement-distance gradients typical of growth faults and faults cutting unlithified strata. The average rate of fault displacement (0.021 m/ka) and the maximum rates of fault propagation (0.088–0.123 m/ka) were normally less than the platform accumulation rates (0.053–0.336 m/ka). Thus, the faults were normally blind and rarely broke the platform top so that slumps and fault-scarp degradation breccias are rare. The fault zones were substantially modified by diagenesis during platform development. They are up to 9 m wide, taper both up and downward, have irregular margins and complex fills mainly of sedimentary origin. Their margins and fill were subject to extensive modification by karstic(?)/mixing zone dissolution, gravitational collapse and dolomitising fluids. Consequently, tectonic fabrics and kinematic indicators are rare. Preserved tectonic fabrics consistently indicate a normal and reverse dip-slip sense of movement. Previously, these faults were mistaken for ‘neptunian’ dykes and fissures, so that the Seven Rivers and Yates 1–2 HFS shelf stratigraphy has been miscorrelated across them. It is apparent that the stratal relationships exposed in the Guadalupe Mountains do not simply preserve the original depositional morphology of the Capitan-equivalent shelf. The subsidence history, stratigraphy and development of the platform succession is more complex than previously thought. The study has important implications for many aspects of the Capitan system, including: (i) shelf-reef correlations, (ii) the controls on platform architecture and development, (iii) Capitan reef palaeobathymetry, (iv) diagenesis, and (v) the amplitude of sea-level changes affecting the platform's stratigraphic development.
Digital Object Identifier (DOI)
Hunt, David W., "Syndepositional deformation of the Permian Capitan reef carbonate platform, Guadalupe Mountains, New Mexico, USA" (2003). KIP Articles. 7789.