Shelf Edge to Slope to Basin-Floor Clinoforms and Turbidite Variability of the Southernmost Neuquen Basin Infill: Jurassic Los Molles Formation, Argentina

Abstract

This study describes the clinoforms and turbidite-system architecture of the southernmost Neuquen Basin margin. Excellent Jurassic clinoforms and turbidite-system architectures of the Los Molles Formation, Neuquen Basin expose continuous shelf to slope to basin-floor deposits for kilometers, with visible 2–300 meters high basin-margin clinoforms. Use of a high resolution digital elevation model (DEM) and satellite images, ground photo-panels and sedimentary measured sections allow the deposits to be correlated over 20 × 20 km, along depositional dip and strike. At the shelf edge the deposits have meter-thick structureless or cross-stratified sandstone to conglomerate beds, with abundant silicified wood that incise 30 m in places into the underlying muddy slope deposits. Slope deposits are dominated by thin laminated or structreless mud with thin (cm) sandstone beds. Isolated, up to5–10 m thick and tens to hundred meters wide, erosionally based sandstone and conglomerates with abundant mud clasts are interpreted as slope channels encased in mudstones. Toward the base of the slope, turbidite channels have a higher width-to-depth ratio, and they become laterally more extended (hundreds of meters). The basin floor deposits are interpreted as basin-floor turbidite channels and lobes based on their low relief (rarely erosional at the base) and lateral continuity for kilometers. These deposits are dominated by structureless and normally graded sandstone beds which are dm to m thick. Mapping of the individual 10–15 m basin-floor lobes shows the changes in facies from proximal to distal from dominantly structureless amalgamated and non-amalgamated sandstone beds to dominantly normal graded and laminated sandstone beds. Bed thickness increases from about 15 cm on average to 30 cm and then decreases again to 15 cm from proximal to distal. Grain size shows a more complex pattern but in general increases and then decreases form proximal to distal. On the basin floor there are also thick beds (up to 3–4 m) of pebble-conglomerate debris flow and mud flow deposits, that are more common in the older deposits (below the turbidite lobes) but also present within the lobe units. Lower to Middle Jurassic Los Molles Formation has been previously interpreted as syn-rift to post rift deposits. The architecture of the Neuqen Basin margin shows trends which are generally valid in many basins with a wide range of grain size and similar tectonic setting.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015