falling stage systems tract (FSST)
In regressive sequence systems tract forms when the rate of sea level drop or the rate of subsidence, is higher than the rate of sedimentation. This increases sediment influx seaward because the sediments are being deposited further away from shore along margins on the platform. Sediments accumulate further and further below margins of the platform and the sediment availability is reduced to this location. The sea level drops also shifts the type of transport further out onto the slope and decreases the surface area onto which the sediment may be deposited. At the same time "a smaller area of the shallow sea floor is in contact with the carbonate factory" resulting in retrograding shelves. Slope failure occurs frequently during the falling systems tract, and as a result debris-flows, grain-flows, and deposits of primarily thickened wedges and fans develop. Additionally, the winnowing and erosion of platform corals, sediments and shallow water sediments, exposed during falling systems tracts are deposited seaward along the slope.(Handford and Loucks 1993)
Click on the figure which represents a cross-section of a regressive sequence of a normal carbonate cycle. The regressive sequence is denoted by the sequence of sediments ranging from 0 to -150.0 on the bar scale adjacent to the picture.
Tuesday, February 24, 2015