DISTINCT TIDAL SIGNATURES IN THE FERRON “NOTOM DELTA”: IMPLICATIONS FOR TIDAL PROCESSES IN THE SOUTHWESTERN CRETACEOUS INTERIOR SEAWAY

The importance of tidal processes in the southwestern portion of the Interior Seaway during Late Cretaceous has been a long debate, and many previous workers argue microtidal conditions. The main focus of the current study is, thus, to further investigate the significance of tidal processes in this portion of the Seaway based on detailed analysis of tidal deposits preserved in the Turonian Ferron “Notom Delta” in southern Utah, USA.

Tidal signatures are identified in both the delta-front successions and the incised-valley deposits setting near the top of the fluvial-deltaic complex. Diagnostic features indicating tidal process include: (1) the common occurrence of lenticular, wavy, flaser bedding; (2) the wide spread of reactivation surfaces and double-mud drapes in the dune-scale cross strata; (3) inclined heterolithic strata (IHS) and sigmoidal bedding with tidal rhythmites in tidal point bar deposits; (4) cyclic vertical variation in facies and bed thickness and the common occurrence of sand-mud couples; and (5) bidirectional dipping cross strata in the tidal channel deposits. Plotting lamina number versus thickness also shows distinct neap-spring cycles.

Paleoenvironment reconstruction based on detailed facies analysis in locations where the subtidal to supratidal sequences are well preserved suggests a tidal range of 3-5 m, in mesotidal to macrotidal conditions. This is also supported by the wide occurrence of tidal flat and salt-marsh deposits and the overall lack of barrier island and inlet facies. This study, coupled with several observations in the Cenomanian-Coniacian Ferron “Last Chance Delta”, shows that mesotidal or even macrotidal conditions probably are rather common in this portion of the seaway during Late Cretaceous.