Most interpretations of the stratigraphic record are founded on the premise that the depositional environments that produced it either have not changed appreciably through time, or else have changed very slowly. Paradoxically, some of the most important transitions in the sedimentary archive are those interpreted to reflect relatively rapid, comprehensive paleoenvironmental change. Recognition of the anomalous nature of such transitions is vital to accurately understanding their significance but is not systematically incorporated in current stratigraphic models. The new term “xenoconformity” is therefore proposed, and defined as a stratigraphic surface or gradational interval that records a fundamental, abrupt, and persistent change in sedimentary facies across basinal to global scales. Xenoconformities may mark major paleoenvironmental tipping points and signal transformations in how paleoenvironmental signals were transferred into the stratigraphic record.