Late Guadalupian carbonate rocks and other deposits of the northwest shelf of the Delaware basin exhibit a wide variety of primary and secondary features indicative of sedimentary environments ranging from extensive evaporite-bearing coastal sabkhas in the north and west to longshore bars and marginal reefs in the south and east. Detailed examination of outcrops of the Seven Rivers, Yates, and Tansill Formations in the hilly area west and southwest of Carlsbad, New Mexico, reveals that the known cyclicity of these deposits stems from more than 250 oscillations of relative sea level, spread over a period roughly estimated to have exceeded 5 m.y. Many or most of these oscillations appear to have been of a few meters only, but, because of the low relief of the shelf and the roximity of its surface to sea level, they were accompanied by shifts of up to scores of kilometers in the various depositional environments. These shifts were most marked in gently shelving littoral zones, which, at different times, appear to have ranged from the shelf margin to as much as 50 to 60 km farther west and northwest. They are least marked where contemporary relief was greatest, as at the shelf margin and on longshore bars which appear to have separated inner and outer parts of the shelf during much of upper Artesia deposition. Relative sea-level oscillations of glacio-eustatic origin offer a possible cause of major rhythmicity such as that at formation level, but the absence of smaller scale cycles in some other approximately contemporaneous shelf deposits elsewhere in the w rld argues in favor of a local or regional cause, such as varying rates of epeirogenic subsidence.