Third order depositional sequences in continental rifts: a systems tract model for half-grabens, applied to the Lower Cretaceous of Sergipe-Alagoas Basin

Abstract

Flexural-margin derived syn-rift deposits were analyzed using a Sequence Stratigraphy approach. Depositional sequences were classified as third order sequences with their origin associated with tectonic cycles within a half-graben framework. Changes in displacement rate along individual border faults segments as well as variations in sedimentary supply and creation of accommodation space were responsible for the stratal pattern of these sequences. A system tract model was built using detailed core analyses, electrical logs and isotopic data. The stratigraphic signature of these third order sequences is composed by two regressive systems tracts interposed by a transgressive one. The initial regressive tract is deposited during the active phase of the tectonic cycle and the others are related to the quiescent phase, when the high frequency climatic cycles become more evident.