The transgression of an erg - sedimentation and reworking/soft-sediment deformation of aeolian facies: the Cretaceous Troncoso Member, Neuquén Basin, Argentina.

STRÖMBACK, A.; HOWELL, J.A.; VEIGA, G.D.

The Neuquén Basin: a case study in sequence stratigraphy and basin dynamics

Geological Society

Lugar: London; Año: 2005; p. 163 - 183

Abstract: The Cretaceous Troncoso Inferior Member of the Huitrin Formation comprisesfluvial and aeolian facies that form a drying-upwards succession within the Neuque´n Basin.The basal fluvial sandstones were deposited as braided river deposits and lie unconformablyon top of either the deep-marine Agrio Formation or, locally, the shallow-marine ChorreadoMember (Huitrin Formation.). In places, the fluvial sandstones are interbedded withremnants of aeolian deposits recording an arid environment and ephemeral flows. In thestudy area the upper section is predominantly aeolian and was controlled by northerlywinds with both linear and transverse dune types being deposited. The depositionalsystem was rapidly flooded and dune topography (relief ranging between 2 and 35 m)was preserved on its top surface. In addition to dune topography, the Troncoso dunes alsoshow evidence of reworking and in situ soft-sediment deformation related to the flooding.The principal aim of this paper is to document the soft-sediment deformation andpreservation of topography associated with the flooding of the dune field.Within the soft sediment deformed and reworked sediments at the top of the TroncosoInferior Member spatial and temporal relationships indicate that they formed in a specificsequence. Initially, water-escape processes created convolutedly folded and dish structuresthat were concentrated in areas of slightly higher preserved dune topography. Secondly, theconvolutedly folded and dish facies were eroded and reworked by wave undercutting andmigrating three-dimensional dunes in a shallow-marine environment. This subaqueousreworking resulted in an interbedded massive and cross-stratified unit. With further deepeningof the water, the topography became stabilized and the uppermost part of the interval(0.1–0.3 m) was reworked by waves across most of the basin. In the topographic lowsbetween dunes, liquefaction-induced sediment gravity flows deposited massive–flatlaminatedfacies.The reworked and soft-sediment deformed aeolian dune topography is overlain by theevaporites of the Troncoso Superior Member. The distribution of flood-related facies andthe amount of preserved dune topography (2–35 m) indicates that the transgression musthave been rapid but of low energy.