The magnitude and cause of short-term eustatic Cretaceous sea-level change: A synthesis

No consensus currently exists regarding the magnitude of Cretaceous short-term (less than 3 Ma in duration) eustatic sea-level change. The lack of a consensus limits the ability to predict sedimentary facies and architecture and to assess the potential drivers of eustasy during a period of Earth history considered as significantly warmer than today. Consequently, this review documents, weighs, synthesises, and summarises records of short-term relative sea-level change and evaluates the observed trends in magnitude within the context of potential climatic drivers and their eustatic expression. Although Cretaceous sea-level change is addressed in many publications, estimates of absolute values are relatively limited, often cover short time intervals, and use different methods. Based upon integrated geological and statistical analyses, four broad episodes of magnitude change have been identified. Three of these episodes reflect trends of increasing magnitudes of sea-level change from the Berriasian to early Hauterivian, late Hauterivian to Aptian, and Santonian to Maastrichtian. The fourth episode reflects a decreasing magnitude trend from the Albian to Coniacian. In addition, the maximum magnitude of sea-level change, at an approximate stage level, has been identified and categorised as slight (less than 10 m), modest (10 to 40 m), or significant (41 to 65 m). Significant magnitudes are inferred for the Valanginian, Aptian, Albian, and Maastrichtian; exclusively slight magnitudes are restricted to the Berriasian. Such an assessment casts doubt on the repeated and stratigraphically widespread episodes of very large magnitudes (more than 75 m) advocated by some workers, and instead defines distinct periods and magnitudes of sea-level change that should be globally reflected in sedimentary facies patterns. For example, intervals of sea-level fall of significant magnitude are commonly associated with the increased delivery of sediment into basinal settings, including the marked progradation of shallow-marine sediments, whilst up-systems tract there can be enhanced development of karst and erosional features. Because climatically driven eustasy is the likely cause of short-term sea-level change, an assessment of the characteristic maximum magnitude limits of the principal climatic drivers (thermo-, aquifer-, and glacio-eustasy) has been made. Such a comparison argues for glacio-eustasy as the driver of significant short-term sea-level change. In addition, climate proxy data demonstrates that the Valanginian, Aptian, Albian, and Maastrichtian are intervals of cooling within the Cretaceous, thereby supporting the link between significant magnitudes and glacio-eustasy.