Parsing autogenic and allogenic processes in aeolian stratigraphy

I am beyond excited to present highly collaborative work that begins to parse records of autogenic processes and allogenic forcings preserved within set-scale aeolian architecture in two companion articles: (1) numerical experiments (preprint) and (2) the scour-fill dominated Jurassic Page Sandstone, Arizona (preprint).

synStrat
Set-scale aeolian architecture from a numerical model of dynamic dune topography driven by steady allogenic boundary conditions. Color represents time of deposition.

In the first companion article, a reduced complexity model of aeolian dune strata-formation is developed and applied to explore the roles of autogenic processes on the preservation of allogenic sourced from three sets of external environmental forcing. In each scenario, rapid dune growth is found to completely cannibalize early dune deposits, thus shredding any records of early allogenic or autogenic signals. However, later dune deposits are found to contain commingled autogenic and allogenic signals. This theoretical work frames five working hypotheses surrounding the nature of aeolian dune deposits for future workers to explore and discuss! The source code (Matlab) will reproduce all figures in this article is available here. A Python version is planned.

cardenasJSR2018
Page Sandstone. Early dune deposits (smaller sets in B,D) are preferentially preserved in antecedent lows in paleotopography.

In the companion article, collaborator Benjamin Cardenas leads interpretation of set-scale aeolian architecture within multiple exposures of the Page Sandstone (Jurassic) near Page Arizona, USA. This work interprets the set-scale architecture of the Page Sandstone to record multiple transgressions of the Carmel Sea. Drying, and associated decreases in base-level between transgressions liberates significant quantities of sand.  After drying, dune growth and scour are interpreted to cannibalize early dune deposits, except for those created in antecedent lows in paleotopography. Ongoing dune motion in the dry sand sea creates scour and fill architecture which is thought to characterize autogenic dune behavior. Eventually, the Carmel Sea completely transgresses the sand accumulation, and shuts down the aeolian system at the end of the Page (pun intended).

JohnFest 2018!

In celebration of Dr. John Anderson‘s upcoming retirement at Rice University, I have the privilege of giving a short research talk during an all-day research symposium, appropriately entitled JohnFest!. JohnFest! is composed of a series of talks given by John’s past and present students and post-docs. For this special occasion, I am excited to be presenting my postdoctoral work, which John has supported and mentored over the past year and a half, a reduced complexity model of Texas’ coastal barrier system.

A PDF document of the presentation is available to download here

johnAnderson_waders

Industry-Rice Earth Science Symposium 2018: Texas’ coastal barrier response to sea-level rise

iress2018Just in time for the Industry-Rice Earth Science Symposium 2018, the newest iteration of the reduced complexity coastal barrier model was summarized as a poster presentation. Be sure to click on the image to the right to download a high resolution jpeg image of the poster!

Exploring the morphodynamic response of Texas’ coastal barriers to sea-level rise

agu2017For AGU Fall Meeting 2017 in New Orleans, I gave a talk on the application of a simple morphodynamic model to forward model the response of coastal barriers (islands and peninsulas) to spatially variable sea-level rise over centuries. Within the model, coastal barrier geomorphology is simplified to a suite of characteristic scales and surface processes are simplified to parameterized expressions that characterize geomorphic responses to relative sea level rise. The abstract for this presentation is in an earlier post (Getting ready for AGU 2017), and a PDF of the presentation is available here (opens in a new window)!

Getting ready for AGU 2017!

Exploring the morphodynamic response of coastal barriers to sea-level rise along the Texas Gulf Coast

Swanson, T.1, Lorenzo-Trueba, J.2, Anarde, K.1, Odezulu, C.1, Anderson, J.1, Nittrouer, J1.

1 Rice University
2 Montclair State University

The Texas portion of the Gulf Coast spans nearly 600 kilometers and is chiefly composed of barrier islands and peninsulas that shelter numerous landward communities from damaging storm surge and waves. Presently, this coastal barrier system is evolving at an unprecedented rate, as sediment that comprises these protective barriers is being depleted while sea-level rise is accelerating, reducing the resilience of coastal communities. To help explain the morphodynamic response of Texas’ coastal barrier system to anticipated accelerated sea-level rise, a reduced complexity morphodynamic model is constructed from a combination of extant models of barrier morphodynamics, alongshore sediment transport, and time-variable ravinement depth. The model is initialized using a simplified geometric depiction of the barrier system morphology obtained from regional bathymetric and topographic surveys, and sediment composition from best-available subsurface geodatabases. Simulation timesteps capture the morphodynamic response of coastal barriers to accelerated sea-level rise by tracking the motion of key geomorphic boundaries within the barrier system: ravinement depth, shoreline, and bay line. The motion of these boundaries is calculated via parameterized expressions of alongshore, cross-shore, and barrier over-wash sediment transport that represent the time-integrated effect of short-term coastal processes, such as day-to-day waves and storms, and longer-term processes such as sea-level rise, dynamic barrier morphology, and barrier sediment composition. Model results are comparable with historical records and geological interpretations of regional coastal change sampled over a broad range of time and spatial scales.

Time and location: Tuesday, 12 December 2017 14:10 – 14:25 New Orleans Ernest N. Morial Convention Center – 353-355

Please check out the innovative work presented by Ben Cardenas, which uses a surface model for aeolian dune topography, with newly developed routines that allow for aeolian dune climb, and preservation of dune stratification:

Coupling Aeolian Stratigraphic Architecture to Paleo-Boundary Conditions: The Scour-Fill Dominated Jurassic Page Sandstone

Cardenas, B.1, Kocurek, G.1, Mohrig, D.1, Swanson, T2.

1 The University of Texas at Austin
2 Rice University

The stratigraphic architecture of aeolian sandstones is thought to encode signals originating from both autogenic dune behavior and allogenic boundary conditions within which the dune field evolves. Mapping of outcrop-scale bounding surfaces and sets of cross-strata between these surfaces for the Jurassic Page Sandstone near Page, AZ, USA, demonstrates that dune autogenic behavior manifested in variable dune scour depth, whereas the dominant boundary conditions were antecedent topography and water-table elevation. At the study area, the Page Sandstone is ~ 60 m thick and is separated from the underlying Navajo Sandstone by the J-2 regional unconformity, which shows meters of relief. Filling J-2 depressions are thin, climbing sets of cross-strata. In contrast, the overlying Page consists of packages of one to a few, meter-scale sets of cross-strata between the outcrop-scale bounding surfaces. These surfaces, marked by polygonal fractures and local overlying sabkha deposits, are regional in scale and correlated to high stands of the adjacent Carmel sea. Over the km-scale outcrop, the surfaces show erosional relief and packages of cross-strata are locally truncated. Notably absent within these cross-strata packages are early dune-field accumulations, interdune deposits, and apparent dune-climbing. These strata are interpreted to represent a scour-fill architecture created by migrating large dunes within a mature dry aeolian sand sea, in which early phases of dune-field construction have been cannibalized and dune fill of the deepest scours is recorded. At low angles of climb, set thickness is dominated by the component of scour-depth variation over the component resulting from the angle of climb. After filling of J-2 depressions, the Page consists of scour-fill accumulations formed during low stands. Carmel transgressions limited sediment availability, causing deflation to the water table and development of the regional bounding surfaces. Each subsequent fall of the water table with Carmel regressions renewed sediment availability, including local breaching of the resistant surfaces and cannibalization of Page accumulations. The Page record exists because of preservation associated with Carmel transgressions and subsidence, without which the Page would be represented by an erosional surface.

Time and location: Wednesday, 13 December 2017 13:40 – 18:00 New Orleans Ernest N. Morial Convention Center – Poster Hall D-F

Rice Coastal Sedimentology celebrates World Oceans Day

oceansDay2017

Members of the Coastal Sedimentology Group (myself included!) preformed physical demonstrations of processes responsible for sea level rise and how higher sea levels threaten coastal communities for World Oceans Day at the Houston Museum of Natural Science. A big thanks to Dr. Lauren Simkins, Lindsay Portho, and Tian Dong for making our time at the museum a success! Thanks to Dr. Simkins for developing an informative pamphlet which can be downloaded via this link. More information surrounding this event is available on the Rice University webspage and through a “News Fix” video made possible by CW 39.

oceansDay2017b

My role in this collaborative effort was to design and construct a two dimensional wave tank with a highly exaggerated profile of coastal relief, dynamic sea level control and a paddle wave maker to demonstrate how rising sea level allows storm waves and even fair weather waves to over-top protective barrier islands and threaten coastal communities. The wave tank was constructed using many opensource hardware and software tools. Please send me a quick note if you would like plans or help constructing your own wave tank; otherwise check this blog again, as I intend to do a write-up on how to build, wire, and program the wave tank. It was a lot of fun to construct! A big thanks to the Shell Center for Sustainability for funds to purchase components to build the tank.