THE EFFECT OF RIFT SHOULDER EROSION ON STRATAL PATTERNS AT PASSIVE MARGINS - IMPLICATIONS FOR SEQUENCE STRATIGRAPHY

Numerical modelling indicates that the erosion of uplifted rift flanks at passive margins has a profound effect on offshore stratigraphic pa tterns. Flexural uplift, due to isostatic rebound in response to erosi on, extends far into the basin and causes uplift of the shelf. As a re sult, the contemporaneously deposited sedimentary wedge displays a cha racteristic offlap pattern. When the rift shoulder is largely eroded, onlap-promoting mechanisms related to cooling of the lithosphere enabl e sediments to onlap onto the basin margin. The initial offlapping and subsequent onlapping strata form one complete second-order deposition al sequence comprising a shelf-margin-, transgressive-and highstand-sy stems tract. The modelling inferences are in broad agreement with stra tal patterns and basin geometries observed on the U.S. east coast, the southeastern Brazilian and southeastern Australian passive margins an d the Transantarctic Mountains-Ross Sea Shelf system. The initial offl aps caused by erosion of rift shoulders have important implications fo r the deriviation of eustatic signals from coastal onlap patterns.