Crowleys Ridge in southeastern Missouri preserves Cretaceous to Eocene marginal marine sediments deposited in the northwestern portion of the Mississippi Embayment. Sandwiched between the Paleocene Porters Creek Formation and the uppermost Cretaceous Owl Creek Formation is the Paleocene Clayton Formation. Four trenches were excavated and a complete section of Clayton Formation was sampled at a large strip mine in Stoddard County, Missouri. The Clayton at this location consists of 185 cm of graded deposit, the lower part of which includes large Owl Creek rip-up clasts containing layers of microtektites, invertebrate fossils, and abundant terrestrial and marine palynomorphs. Driller's logs and electric logs covering ∼9000 km 2 were reviewed. Well data confirm the consistent thickness and lithology of the Clayton Formation in this part of the Mississippi Embayment. Based on sedimentological and palynological data from this study, the Clayton Formation in the northwestern Mississippi Embayment appears to be a megatsunami deposit resulting from post-impact effects (early Paleocene) associated with the Chicxulub impact event.

Abstract Fluvial sandstone sheets may appear uniform initially, but detailed examination tends to reveal sharp lithologic contrasts across bounding surfaces. The mid-Cretaceous Muddy Sandstone of southeast Colorado, USA contains two sandstone sheets and provides examples of such potential permeability barriers. Sediment bodies bound and respective bounding surfaces are, in order of ascending rank: bar and dune deposits (1 st - to 3 rd -order), nested channel fills (4 th -order), channel fills (5 th -order), channel belts (6 th -order), nested valley-fills (7 th -order), valley-fills (8 th -order), and sequences (9 th -order). Bar and dune through channel-belt deposits commonly have permeability barriers because the episodes of waning flow common to their deposition tend to cause draping of surfaces and filling of scours locally with finer grained deposits. Channel-fills through sequences tend to have permeability barriers related to juxtaposition of permeable and non-permeable lithofacies during successive incision-and-fill events. Fluvial sandstone sheets can have reduced permeability in paleodip orientation that operates on the scale of individual wells because of draping of down-dip-oriented bar- and dune-accretion surfaces. A dip-oriented grain, reducing permeability in the strike direction, may arise on the scale of fields, because of permeability barriers formed at nested channel through higher-order valley and sequence boundaries.