--> Controls on Lateral Facies Variability in the Ferron “Notom” Delta (Turonian), Western and Southern Henry Mountains, Utah, USA

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Controls on Lateral Facies Variability in the Ferron “Notom” Delta (Turonian), Western and Southern Henry Mountains, Utah, USA

Abstract

Deltaic deposits contain vast petroleum reservoirs and source rocks, but facies models have not advanced at the same pace as the growing body of work demonstrating multiple controls on facies distribution and sequence development in modern deltas. Refinement of these models requires more studies documenting lateral sedimentological and ichnological facies changes in well-exposed ancient deltas. Presented here are depositional strike and dip transects through world-class exposures of deltaic strata in the Ferron “Notom” delta on the western and southern flanks of the Henry Mountains Syncline, southeastern Utah. One transect covers the complete 16 km-long strike profiles of two 10 m-thick delta front sandstone bodies with discrete mouth bar and channel facies marking the locations of riverine input. Most delta front facies contain a stressed suite of low abundance, low diversity, diminutive traces, but ichnosuites downdrift of river mouths are comparatively unstressed with a high abundance of deep, vertical, or U-shaped suspension feeding burrows. This distribution of ichnosuites contrasts sharply with existing models and likely reflects abundant nutrient supply in river-born waters carried southward by coastal currents, or alternatively, reduction of physio-chemical stresses during seasonal reversal of coastal currents. The 8 km-long dip profile covers several sandstone bodies below and above a major subaerial unconformity (SU). Up-dip, the SU is marked by heavily rooted coastal plain facies and incised channels atop mouth bar and delta front facies. Down-dip, the SU descends relative to the coastal plain/channel facies, becoming a cryptic surface encased within coarsening-upward delta front cycles. The SU separates a lower package of offlapping mouth bar/delta front strata with multiple discontinuities from an upper, nearly complete progradational succession capped by channel and coastal plain facies. This change in stratal stacking marks a change from a low-accommodation, falling stage delta complex to a comparatively higher accommodation progradational-aggradational delta. New insights to the controls on deltaic facies variability are gained through these unique windows into deltaic architecture via the superb exposure.