Sequence stratigraphy and facies architecture of the Cretateous Ferron Notom Delta Complex, South-central Utah, U.S.A.

摘要

The superbly exposed three-dimensional outcrop belt of the Turonian Ferron Notom Delta Complex in South-central Utah, contains chronostratigraphically significant bentonite beds, which are useful as datums and consequently allow application of the concept of shoreline trajectory to parasequence (PS) stacking patterns. Forty-three parasequences are identified in the Ferron Notom Deltaic Complex. They can be further grouped into 18 parasequence sets and 6 sequences. Parasequences generally show repeated successions of sequentially aggradational-progradational, degradational, progradational-aggradational, and retrogradational stacking patterns, which match the recently developed accommodation succession model. Wheeler analysis and shoreline trajectory analysis also recognized high-frequency (approximately 100,000 yr cycle) and high-amplitude (up to about 60 m) relative sea-level changes. Among the various controlling factors causing cyclicity, glacio-eustasy is likely to be the major control on the cyclicity of Ferron deposition, with autogenic control being secondary.;Seven architectural elements are recognized at the fluvial to marine transition of parasequence 12a: prodelta fines, prodelta hyperpycnites, frontal splays, terminal distributary channels, abandon channel fills, and accreting mouth bars. Terminal distributary channels are filled by lateral migration of mouth bars or mud plugs following channel abandonment. A single mouth bar shows a change from frictional dominated inner mouth bars characterized by gently inclined, cross-bedded clinoforms, to inertial dominated outer mouth bars characterized by steeply inclined, parallel laminated foresets. Accretionary mouth bars group into mouth bar complexes.;The Ferron Notom Delta Complex shows evidence for wave-, river-, tide-, and storm-influence. Facies "asymmetry" has been recognized in most parasequences, with homogenous, sand-prone, wave-dominated shorefaces with minor fluvial contribution in the north, compared to heterolithic multi-distributary fed, wave-influenced, river-dominated shorelines to the south. Facies changes through a relative sea-level cycle follow a very similar pattern. All highstand and falling stage, and most lowstand parasequence sets show wave-influenced asymmetric forms. Transgressive parasequence sets show consistent wave-dominated symmetric growth patterns. Besides fluvial discharge and wave energy, variations in basin morphology and persistent longshore drift played major roles in unevenly distributing wave and fluvial energy along the coast, and therefore developed either asymmetric or symmetric delta morphologies.