A RIFT-TO-DRIFT SUBSIDENCE-ACCOMMODATION-TIME- SERIES (SATS) MODEL

A subsidence-accommodation-time-series (SATS) diagram was developed for a theoretical stratigraphic section passing up through the axial rift during a rift-to-drift transition. The SATS model has one curve for tectonically created accommodation, a second for sediment accumulation, and a third for sediment loading (during the drift phase). The model was developed to illustrate how tectonics, structure, sedimentation, and stratigraphy interact with each other through positive and negative feedbacks to produce a stratigraphic section The SATS is a predictive model of a theoretical rift-to-drift ideal history plotting changing processes through time. The actual shape of the SATS curves will vary depending on climate (rate of weathering and sediment deposition) and actual subsidence rates, but the model is an ideal to test real world sections.

During the rift stage of thermal uplift and mechanical (listric graben) collapse the subareal (terrestrial) accommodation curve rises rapidly above base line, followed by a lagging accumulation curve as sediment fills the graben, burying the horsts. The area between the curves measures relative accommodation space.

In the to-drift phase thermal uplift transitions to thermal subsidence accompanied by sediment-load subsidence. The transition begins with a drainage reversal that initiates passive margin sediment accumulation. The combined thermal/loading subsidence curves measure total sediment accumulation, while the area between these combined curves and base level measures water depth. Both subsidence and loading curves exponentially decline (flatten with time) allowing accommodation space to fill. Initially water depth is deep as water invades the axial graben and rapidly subsiding rift margin, but during thermal/loading decay sediment accumulation catches up with accommodation allowing passive margin shelf and shoreface environments where relative sea level changes influence accommodation.

The SATS rift-to-drift model was initially developed for an undergraduate course that synthesizes stratigraphic, structural and tectonic principles to understand terrane evolution. It is used as an ideal against which actual ancient and modern sequences are modeled, compared, and tested, both in the classroom and in the field.