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Reports: DNI853553-DNI8: Detecting Signals of Sediment Supply in the Stratigraphic Architecture of an Outcropping Pleistocene Delta Complex

Brian W. Romans, Virginia Polytechnic Institute and State University

The following narrative summarizes the second, and final, year of this ACS-funded research, which is part of the Petroleum Research Fund Doctoral New Investigator grant program. This research aims to better constrain and quantify the role of sediment supply on stratigraphic patterns. Although sediment supply has been considered a fundamental control on stratigraphy for decades, the incorporation of sediment flux in models is poorly constrained and largely qualitative. Thus, the overall goal of this project is to quantify paleo-sediment flux in a natural sedimentary system from the stratigraphic record. This project involves the integration of geological field work (outcrop characterization and sampling) with measurement and analysis of cosmogenic radionuclides from sediment samples. Cosmogenic radionuclides (CRNs) are produced in material at the Earth surface via the interaction with cosmic rays and have been used by geomorphologists for over a decade to determine landscape erosion rates from sediment at the outlet of a drainage basin. This technique has only rarely been applied to sediment samples from the stratigraphic record.

The second year of this grant built on the active first year and was very successful. The Ph.D. student (Mason) spearheading this work attended the American Geophysical Union fall meeting in San Francisco in December 2014 to present preliminary data and interpretations. Mason and the P.I (Romans) visited the field site for the final time during January 2015 (for a total of four trips). This field work yielded data in the form of photo-panoramas, observations about large-scale stratigraphic architectures, and a new suite of sediment samples to be dated by optically stimulated luminescence (OSL), which we hope will improve our current depositional age-model. In May 2015, these new OSL samples were sent to the luminescence laboratory at CENIEH (Centro Nacional de Investigacion sobre la Evolucion Humana) in Burgos, Spain, to be dated by lab manager, sedimentologist, and collaborator Dr. Gloria Lopez. The samples are currently being processed and will be analyzed imminently, with results to be reported at scientific meetings and in peer-reviewed publications over the following year. (Note: we have already submitted an extension of this grant to use the remaining funds for this purpose, which was approved by ACS in August 2015.)

The first year of the grant saw a vigorous campaign to sample for CRNs in buried sediment. Those data were produced at the Purdue PRIME Lab in fall 2014 and are now in hand. A major goal of this project is to invert sediment supply rates from stratigraphy; thus we used concentrations of CRNs from 15 samples of modern and Pleistocene sediments (Fig. 1). These catchment-wide erosion and paleo-erosion data were most recently presented at the American Association of Petroleum Geologists (AAPG) Annual Convention and Exhibition in Denver, CO in June 2015. Mason garnered valuable and encouraging feedback from both industry and academic geoscientists during his poster presentation. Figure 2, below, is taken from our AAPG poster and shows simplified stratal architectures, a 26Al/10Be age model, and calculated paleo-erosion rates as inverted from the stratigraphy of the Pleasant Canyon complex, Panamint Mountains, California. The remaining work to be done for this project includes: quantifying uncertainty in our methods, analyzing the paleo-erosion rates within the context of the interpreted stratigraphic framework, and quantifying the variability of erosion rates preserved in alluvial fan stratigraphy in lateral and vertical spatial domains. Mason and Romans expect to submit a paper summarizing these results to a refereed journal (possibly EPSL or GSA Bulletin) in the spring or summer of 2016.

We do not plan to acquire or analyze additional CRN samples, or other samples of any kind, for this project. The resolution provided by the current data set are sufficient to make interesting and impactful observations into processes of erosion at the catchment scale through time, and relationships between sediment supply and stratigraphic architecture in linked catchment-fan sedimentary systems.  

Overview of grant-related activities for 2014-2015:

á      Present research at AGU fall meeting (December 2014)

á      Field work in Panamint Valley (January 2015)

á      Sampling for OSL (January 2015)

á      Send OSL samples to CENIEH Spain for analyses (May 2015)

á      Present research at AAPG Annual Meeting and Exhibition in Denver (June 2015)

Figure 1: Study area details including measured stratigraphic section showing sedimentologic facies and stratigraphic evolution.

Figure 2: One million year record of paleo-erosion rates from the Pleasant Canyon catchment, Panamint Mountains, as preserved in Pleistocene alluvial-fan stratigraphy. A: Al/Be derived age model from Pleasant Canyon complex. B: paleo-erosion rates from the same samples as A, showing modern catchment-wide erosion and Pleistocene catchment-wide paleo-erosion rates. C: Simplified stratigraphic architecture of the Pleasant Canyon complex with schematic CRN sample locations.