Catastrophic flooding of an aeolian dune field: Jurassic Entrada and Todilto Formations, Ghost Ranch, New Mexico, USA

Abstract

Surveyed outcrops of the Middle Jurassic Entrada Sandstone at Ghost Ranch, New Mexico, show the unusual occurrence of preserved aeolian dune palaeotopography buried beneath subaqueous strata. The preserved dune remnants have relief up to 35 m, trend NNW, and show internal scalloped cross‐strata dipping to the WSW, with small sets occurring as both topsets and bottomsets. Outcrop data are best satisfied in computer models by 50 m high, sinuous bedforms that migrated to the WSW, while the sinuosity migrated alongcrest to the NNW. Superimposed small dunes occurred upon the stoss slope, and at the basal lee of the main bedform where they migrated alongslope to the NNW. Remnant dune palaeotopography is buried by onlapping, subaqueous, largely structureless sandstones believed to be derived by mass wasting of the upper portions of the dunes and deposited as sediment‐gravity flows that infilled between the dunes. Preservation of dune palaeotopography beneath mass‐flow deposits, with no evidence for gradually rising water, argues that flooding of the Entrada dune field was geologically instantaneous. The thickness and lithology of the overlying Todilto Formation conform to slight remnant palaeotopography on the Entrada surface. The Todilto is a laminated limestone and thinnest over remnant dune crestal areas, but thickens and increases in gypsum content downslope until it abruptly yields to a gypsum mound positioned over a remnant interdune hollow. The Todilto laminations are interpreted as seasonal varves deposited below wave base in a density‐stratified water body. The flooding event that gave rise to the controversial Todilto water body occurred during Entrada time, with Todilto deposition occurring within an already substantial water body.

Dune Casts Preserved by Partial Burial: The First Identification of Ghost Dune Pits on Mars

“…Even in the case where the dune field were completely submerged beneath water, deposition in the interdune might still take place. Pelagic sedimentation of fines settling out of the water column would be expected to drape the dunes, similar to the carbonate-draped dunes in the abovementioned example on Earth (Benan & Kocurek, 2000). Sediments draped on the dunes might be thicker in interdune areas from gravitational slumping, but overall, the deposit thickness would be of similar order and the observed pits would not form without substantial erosion of both the interdune and draping deposit.…”

“…Terrestrial instances of flooded and preserved dunes have been dominantly caused by basalt flows (Gaylord et al, 2016;Jerram et al, 2000;Waichel et al, 2008), making basalt a natural candidate for the smooth deposits on Mars. Flooding by water has also occurred on Earth, preserving the dunes in at least one case with postflooding marine limestone deposition (Benan & Kocurek, 2000). Examples of modern dunes partially submerged in lacustrine settings can be observed in Moses Lake, Washington (Bandfield et al, 2002;Petrone, 1970), and Lake Chad (Durand, 1982).…”

Ancient Stratigraphy Preserving a Wet‐to‐Dry, Fluvio‐Lacustrine to Aeolian Transition Near Barth Crater, Arabia Terra, Mars

“…Overbank flooding of the fluvial channel would have delivered water and fine sediment to the dune field, wetting sands and allowing for interdune deposition and damp aeolian accumulation (Kocurek & Havholm, 1993). Aeolian sandstones only rarely preserve whole dune forms (e.g., Benan & Kocurek, 2000;Jerram et al, 2000), but occasional flooding related to the channel systems could provide an intermittent mechanism to preserve whole dune morphologies between interdune Langford, 1989). Repeated flooding could have caused the observed layering, with each new flood wetting and trapping dune sands and depositing easily eroded fines in the interdune regions.…”

Sedimentary architecture of an ancient linear megadune (Barremian, Neuquén Basin): Insights into the long‐term development and evolution of aeolian linear bedforms

“…These are commonly referred to as ‘lateral migration’ and ‘vertical accretion’ types, given their interpreted association with bedform dynamics (Rubin & Hunter, ; Clemmensen, ; Scherer, ). Examples from the former category are broadly characterized by unimodal spread of cross‐stratification dip‐azimuths, oblique to the dip‐azimuths of the internal bounding surfaces (Clemmensen, ; Ahmed Benan & Kocurek, ; Scherer, ; Rodríguez‐López et al ., ; Besly et al ., ), and are consistent with lateral migration‐dominated models proposed by Rubin & Hunter (). Other ancient examples fall within the latter category and are characterized by a bimodal (not bipolar) distribution of cross‐stratification dip‐azimuths (Glennie, ; Steele, ; Clemmensen, ; Bose et al ., ) and are consistent with longitudinal behaviour dominated models (well explained in Rubin & Hunter, ).…”