Well, the ol' Blog turned 100 today (with this very post). To mark such an exciting, arbitrary milestone, I reckon i'll introduce a new feature for the Dynamic Earth: Sed Structure Sunday! Each sunday, I'll post a picture of some sedimentary structure, ancient or modern, cross-stratification or form-set, for the internets to enjoy.
Today's structure comes from the Wilkins Peak Member of the Eocene Green River Fm, in SW Wyoming (click on the picture and it will get larger!):
Interference Ripple Formsets! These little bastards form where there are two dominant paleoflow directions, and reflect the complexity that many flows exhibit as they move sediment around. It also serves as a good example as to why ripples are, for the most part, the most useless of the sed structures; they are commonly subject to extremely local whims of turbulent flow. Oh well!