In short, the shoreline does not experience a fall in sea level in a type 2 sequence.Ī type 2 sequence developed on a shelf margin, adapted from Van Wagoner et al. Similarly, rivers do not incise at the shore, and a surface of forced regression does not form seaward of the upper shoreface. Because of this, progradational parasequence stacking continues, although it may be accelerated owing to lower rates of accommodation. In a type 2 sequence, the rate of eustatic fall is not greater than the rate of subsidence at the shoreline, and as a result, the shoreline continues to experience a relative rise in sea level. Note that no falling-stage systems tract is indicated, in part because Van Wagoner did not recognize this as a separate systems tract (he included it in the HST), and in part because they are thin and often destroyed by subsequent erosion at the subaerial unconformity. All of the discussions so far in this online guide have been about type 1 sequences.Ī type 1 sequence developed on a shelf margin, adapted from Van Wagoner et al. In short, the shoreline experiences a fall in sea level in a type 1 sequence. As a result, rivers typically will incise, and a surface of forced regression will form on a wave-dominated shelf. In a type 1 sequence, there is a relative fall in sea level at the shoreline because the eustatic fall in sea level is faster than the rate of subsidence at the shoreline. Type 1 and 2 sequences differ in what happens at the shoreline during a eustatic fall in sea level. ![]() ![]() This is unfortunate, because understanding the differences between these also helps understanding the relationship between parasequences and sequences. In the older sequence stratigraphic literature (especially in the 1980s and 1990s), there was considerable discussion of type 1 and type 2 sequences, concepts that have largely since been abandoned or ignored.
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