Facies differentiation in fine grained sediments using inorganic whole-rock elemental data within the Ferron Sandstone Member, Notom delta complex, south-central Utah

The whole rock inorganic geochemical composition of 210 samples from fine grained lithologies of the Ferron Sandstone Member, and over and underlying Tununk and Bluegate Shale members of the Mancos Formation have been determined. Changes in the whole rock geochemistry are used to define a six- fold chemostratigraphic correlation framework between seven measured sections over an approximately 25km dip-oriented transect of the Notom Delta Complex in South-central Utah.

The key elements used to define the chemostratigraphic framework are Al2O3, Na2O, MgO, K2O, Rb, V, TiO2 and Nb, and are shown to indicate that the geological factors controlling the geochemical variations within each chemostratigraphic unit are primarily controlled by changes in related changing feldspar abundances, changing clay mineral species and periodic volcanogenic influences.

When the chemostratigraphic correlation is placed against detailed facies descriptions and sequence stratigraphic interpretations, it is apparent that the major changes in whole rock geochemistry are related to changes in depositional facies, rather than to any chronostratigraphic surfaces. The whole rock geochemistry clearly differentiates mudstones deposited in marine conditions from those deposited in fluvial environments and highlights the presence of fluvially derived mudstones within demonstrably marine deltaic depositional environments. Their presence is attributed to episodic fluvial flooding events that result in deposition of hyperpycnites, which have been previously documented within the Ferron Sandstone Member.