ACS PRF | ACS
All e-Annual Reports
39240-AC8
Eustatic vs. Climatic Forcing in a Continental-Scale Fluvial System: Revisiting the Lower Mississippi River for Ground-Truthing of the Sequence-Stratigraphic Paradigm
American Chemical Society – Petroleum Research Fund (#39240-AC8)
ANNUAL REPORT (09/01/2006 – 08/31/2007)
After a delay mainly due to Hurricane Katrina in 2005, there was significant progress in 2006-2007. Firstly, Dr. Zhixiong Shen, who is specialized in luminescence dating, joined the project in April of 2007 as a postdoctoral researcher. Dr. Shen will continue the chronology construction for the Prairie Complex using the optical dating method.
Secondly, 14 samples were dated by quartz OSL in 2006 and 9 samples are being dated by quartz OSL in 2007, in addition to the samples dated using feldspar IRSL by Mateo (2005). There are several objectives for the ongoing quartz OSL dating. The primary objective is to construct self-consistent chronologies for all the allostratigraphic sedimentary units in the Prairie Complex. Another objective is that we expect to obtain a consistent OSL chronology using OSL signals originated from quartz (Shen et al., 2007) and feldspar (Mateo, 2005) to support the assumption that the OSL were sufficiently bleached prior to sediment deposition. Preliminary quartz OSL ages are in agreement with the feldspar IRSL ages within error ranges. A final objective is that we want to use the latest technical advancements in quartz OSL dating (Murray and Wintle, 2006) to improve the accuracy and precision of the Prairie Complex optical chronology.
Thirdly, the assumption that the latent luminescence of the Prairie Complex sediments is sufficiently reset prior to deposition is further tested. Optical ages of the Holocene overbank and backswamp sediments are in good agreement with independently obtained 14C ages, suggesting sufficient luminescence resetting. If we assume the Prairie Complex sediments were deposited in a similar environment to the Holocene analogue, it is reasonable to believe that the Prairie Complex sediments are well bleached prior to deposition, echoing the results of the quartz and feldspar OSL age comparison.
Fourthly, a new technique using quartz OSL to date the Prairie Complex sediments is under development by Dr. Zhixiong Shen. This new technique is expected to significantly shorten the measurement time in OSL dating, especially for old samples like the Prairie Complex sediments. This technique will make high resolution optical dating of the Prairie Complex sediments possible. The primary results of the new technique were presented by Shen et al. (2007) in the latest UK Luminescence and ESR conference in Sheffield.
The ongoing quartz OSL dating of the Prairie Complex sediments covers most of the Prairie Complex allostratigraphic units (Saucier, 1994; Mateo, 2005), focusing on the sediments from the Baton Rouge meander belts, the Lafayette meander belts, the Halloway Prairie and the Avoyelles Prairie. More optical dating work is planned for the other parts of the Prairie Complex.
Future work will also try to compare optical ages from different grain size groups to further test the assumption that the luminescence signal of the sediments is fully reset prior to deposition.
At the moment, we are planning to build an OSL sample preparation laboratory at Tulane University. The set up of the laboratory can make the optical dating faster than at present. The laboratory can also provide students a chance to get a first touch in the optical luminescence dating method.
Mateo, Z.R.P., 2005. Fluvial response to climate and sea-level change: Prairie Complex, Lower Mississippi Valley. Unpublished MS. thesis. University of Illinois in Chicago.
Murray, A.S. and Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57-73.
Saucier, R. T., 1994, Geomorphology and Quaternary geologic history of the Lower Mississippi Valley. US Corps of Engineers, Mississippi River Commission, Vicksburg, MS, Vol. 1. 362pp.
Shen, Z.X., Mauz, B., Törnqvist, T.E. and Packman, S., 2007. Determining De of fine-grained silt quartz from very old sediments using the standardised growth curve. Presentation in the 2007 UK Luminescence and ESR Meeting, Sheffield.
