Constance Cooper

Braided rivers, and their terminal deltas, played a critical role in clastic terrestrial deposition prior to the Devonian. After which, rooting land plants profoundly impacted fluvial systems by stabilizing channels, this facilitated a transition to abundant meandering rivers. While commonly overlooked and misidentified in modern and ancient environments, braid-deltas are found in the sedimentary record and in remote locations, today. Constance Cooper and advisor Professor Christopher Fedo have identified and studied an active ephemeral, river-dominated, braid-delta in order to provide a Holocene example of a braid-delta depositional environment.

Ivanpah Dry Lake (IDL) is located within the Southern Basin-and-Range Province in California, directly adjacent to the Nevada state line near Primm, Nevada in the Mojave Desert. The Northwest margin of IDL is fed by an ephemeral braided-fluvial system ending with a braid-delta complex that appears to be active during extreme, short-lived rainfall events. Changes in braid-delta configurations are identified using time-series images from the past decade to indicate the multiple depositional and degradational events that have occurred. Analysis will be paired with Landsat/ Copernicus images from GoogleEarth ProTM and a small unmanned aircraft system image to monitor the evolution of the braid delta. In each sequential image details of each facies boundary position, channels, braid-delta lobes, and jet deposits will be documented for semi-annual comparisons. This provides the capacity to establish both the geometry of a deposit and the rates of formation and erosion. Preliminary analysis also identified that the delta appears to prograde, utilizing multiple styles of sedimentation moving along the base of channels. This includes what appears to be “jet” deposits mentioned above, which get their name from high-velocity flow and sediment scatter through a narrow restriction. This form of deposition is important in understanding the intense energy behind depositional events. From existing reconnaissance analysis, degradation of the braid-delta lobes and jet deposits are happening across a short period of time, so erosion of these braid-delta lobes and jet deposits are happening on an inter-annual scale. To identify what is driving this relationship between deposition and degradation at IDL, observations of hourly rain and wind records allows a year-to-year potential for documenting specific events of sediment deposition and their subsequent erosional modification with implications for preservation potential. Methods are established for gathering research data to make modern facies assessments and to define an active braid-delta environment. The importance of this research is to build a stronger modern facies assessment from pre/post major storms to understand the evolution of braid-delta deposition and their preservation potential within the rock record.