High-frequency and low-amplitude relative sea-level changes in the Turonian Ferron Notom Delta, Henry Mountains region Utah, USA: implications for sequence stratigraphy and hydrocarbon exploration

Abstract

The Turonian Notom Delta is one of the Ferron fluvial-deltaic wedges deposited in the foreland basins of the Cretaceous Seaway of North America. The wedge is exposed three dimensionally in the Henry Mountains region Utah, USA. High-resolution sequence stratigraphic analysis along a 35 km dip-oriented outcrop belt shows that the wedge consists of six depositional sequences. Ammonite and Inoceramid biostratigraphy and 40Ar/39Ar age dating of various bentonites show that the wedge was deposited from 91.25 Ma to 90.63 Ma, an interval of merely 0.62 Ma. Assuming each sequence is formed over a similar time span, each sequence, thus, represents about 105 yr, suggesting high-frequency depositional sequences. Amplitude of relative sea-level changes, built on shoreline trajectory, is 2–61 m, with an average of only 20 m. Fluvial incision during high-frequency and low-amplitude relative sea-level fall is mainly around the highstand prism. Incision diminishes rapidly up dip and down dip, and the resultant incised valleys are narrow and shallow. Such sea-level fluctuations also result in small, stratigraphically complex shoreline sandstones that need special attention during hydrocarbon exploration.