Methods For Restoring and Describing Ancient Clinoform Surfaces

Abstract

AbstractClinoform geometries demarcate a relative change from shallow to deeper waters and are therefore routinely used as paleogeography and paleobathymetry indicators. Distinct segments of the clinoform surface are defined based on their discrete breaks in slope, and these points define parameters which are used to describe and compare clinoform geometries from different basins and ages. In most cases, the breaks in slope are readily interpreted, but placement of the various breaks in slope remains mostly subjective and not strictly uniform. For clinoform geometries with gentle transitions and less accentuated breaks in slope, e.g., mud-prone systems, distinct breaks in slope can vary over many kilometers depending on selection criteria and detection method. The older and more complex history of the investigated strata, the harder it becomes to correctly place the different breaks in slope.This study proposes a common reference frame using an upper regional datum, in which the geometries of ancient clinoform surfaces can be restored. Restoration is performed with standard decompaction techniques, but we compare isostatic compensation using Airy isostasy with different scenarios of flexural support for the sediment load. Regression is used to fit a surface function to georeferenced points along the restored clinoform surface, and derivatives of this surface function are used to objectively and accurately describe and measure parameters such as relief, length, and gradient, in addition to numerically defining the bottomset, foreset, and topset segments of the clinoform surface. This enables comparison with modern counterparts unaltered by postdepositional subsidence and compaction, and the proposed procedure can be applied to 2D profiles from seismic, outcrop, or closely spaced well logs. It can also help in the analyses of 3D surfaces and the trajectory of discrete breaks in slope on successive clinoform surfaces. Accurate reconstructions and objective parameterization directly affect interpretation of shelf–slope sediment partitioning and depositional environment.