page_title: Back-stripping
section_title: General Theory
hierarchical_section_title: Back-stripping / General Theory
caption_attribution_description: English: Procedure to correct the depth of a sedimentary unit for eustasy and water depth (which equals to calculate the total subsidence relative to a stationary datum) and subsequently to perform a "backstripping", e.g. to take out the effect of sediment loading from the total subsidence and to calculate the amount of tectonic subsidence (i.e. subsidence due to a tectonic driving force) relative to a stationary datum. This procedure is valid in a water-filled basin, where the sediments and the crust are in isostatic equilibrium with the underlying mantle (according to Airy isostasy model)
context_page_description: Back-stripping is a geophysical analysis technique used on sedimentary rock sequences - the technique is used to quantitatively estimate the depth that the basement would be in the absence of sediment and water loading. This depth provides a measure of the unknown tectonic driving forces that are responsible for basin formation. By comparing backstripped curves to theoretical curves for basin subsidence and uplift it is possible to deduce information on the basin forming mechanisms.
  The technique developed by Watts & Ryan in 1976 allows for the recovery of the basement subsidence and uplift history in the absence of sediment and water loading and, therefore isolate the contribution from the tectonic forces responsible for the formation of a rift basin. It is a method by which successive layers of basin fill sediment are "stripped off" the total stratigraphy during analysis of that basin's history. In a typical scenario, a sedimentary basin deepens away from a marginal flexure, and the accompanying isochronous strata typically thicken basinward.
context_section_description: As a result of their porosity, sedimentary strata are compacted by overlaying sedimentary layers after deposition.  Consequently, the thickness of each layer in a sedimentary sequence was larger at the time of its deposition than it is when measured in the field.  In order to consider the influence of sediment compaction on the thickness and density of the stratigraphic column, the porosity must be known.  Empirical studies show that the porosity of rocks decreases exponentially with depth.  In general we can describe this with the relationship:
  
  where  is the porosity of the rock at depth ,  is the porosity at the surface and  is a rock specific compaction constant.
caption: Schematic diagram of the back-stripping technique relating to equation (2).  The loaded column relates to equation (3), and the unloaded column to equations (4) and (5)
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