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The mid-Cretaceous (Late Albian-Early Cenomanian) sedimentary succession between Wyoming and Texas, which is generally attributed to transgression during the early part of the third-order Greenhorn cycle, reveals three thin sequences of unusually large, regional extent, deposited during three higher order marine cycles. These three sequences are preserved in outcrop sections and wells in central and southeastern Colorado, northeastern New Mexico and northwestern Oklahoma. We conducted an integrated study utilizing sedimentology, micropaleontology, palynology and organic geochemistry in order to understand the environmental details of the marine-terrestrial transitions during a continental flooding event and how they fit into the larger picture of the first-order Zuni Sequence. Each of the three sequences (referred to as sequences 3.1, 3.2 and 4) records biofacies shifts of over 200 km within vertical sections of less than 20 in that mark ephemeral Tethyan flooding into southeastern Colorado. In each sequence, basal fluvial-paralic sandstone with non-marine fossil assemblages and isotopic and palynofacies signals passes vertically into marine-influenced shale and sandstone. Marine fossils, mainly as moderately diverse agglutinate foraminiferal biotas, nearshore dinoflagellate cysts and acritarchs, and Skolithos ichnofauna, become progressively poorer up-dip until only brackish-tolerant ichnofauna, sparse agglutinate foraminifers and non-marine palynomorphs remain. Two of the three thin sequences record previously unrecognized transgressions that appear to have lasted no more than a million years each, accompanied by …