Relationship Between Eustatic Sea Level Changes and Basement Subsidence

Abstract

Geohistory reconstructions based on well data provide a direct and quantitative method of estimating basement subsidence. Geohistories, in addition to responding to rates of sediment accumulation and to local and regional subsidence mechanisms, also reflect eustatic sea level changes. We have determined quantitatively that component of subsidence that is common to a worldwide set of wells. After compensating for the response of the crust to sedimentation, we find some correlations between the global rate of subsidence and low-frequency changes in the height of eustatic sea level as determined from the stratigraphic interpretation of seismic data. These results suggest that basement subsidence data, which are independent of the techniques used previously, may be used to re ognize variations in eustatic sea level. However, we are unable to determine the size of the eustatic sea level excursions because of difficulties in determining and separating variations in lithospheric rigidity, thermal subsidence, and sediment supply independent of tectonic subsidence and sea level variation. We compare subsidence curves in an empirical fashion with published eustatic sea level curves, thus avoiding the application of geologic models involving crustal properties we cannot quantify. Geohistory analysis is also a powerful means of studying subsidence on a regional scale and so of deducing the regional tectonic history. We illustrate this point by subsidence maps through time for the North Sea.