45910-AC8
Modern Andean Foreland Basin Lakes: Keys to Deciphering Ancient Foreland Basin Lacustrine Stratigraphy
Introduction
Our research team has made substantial progress over the past year in collecting sedimentologic and stratigraphic data on modern lakes and wetlands of the Andean foreland basin deposystem and connecting these deposystems to sedimentation and transport processes in upstream watersheds. Our major goal is to produce descriptive facies and stratigraphic models for lake and wetland deposits across a range of tectonic and climatic settings in the Argentina and Brazilian portions of the Andean foreland basin deposystem. Our target study areas include the Bermejo megafan system of the Argentine foreland basin (foredeep to backbuldge basins), the wedgetop basins of the arid Puna highland region of Argentina (L. Pozuelos) and the humid lowland wedgetop basins of N. Argentina (L. La Brea), the Pantanal backbulge, and the large Laguna Mar Chiquita of the central Argentinian broken foreland.
Research Team
To date our research team has involved the participation of the following individuals:
Prof. Andrew Cohen and Ph.D. student Michael McGlue-U. Arizona
Prof. Mario Assine and MSc student Hiran Zani-State U. Sao Paulo, BR
Dr. Alicia Kirschbaum and undergraduate student Julieta Omarini-U. Salta, AR
Dr. Geoffrey Ellis and Dr. Peter Swarzenski-USGS
Methods and Progress
The focus of our field work has been to initially collect a representative suite of surface sediment samples from a series of target lakes, wetlands and their upstream watersheds, followed by selected coring (using a combination of Livingstone piston corers, hammer corers, push corers and vibracorers) to obtain a vertical/temporal record of facies variability in the target lakes. For each lake we are following up the field work with lab studies, including sedimentologic characterization of the surface samples (granulometry, petrography TOC/TIC and Rock Eval), and initial core description, sedimentology and geochronology (210Pb and 14C) of the cores.
We are augmenting our fieldwork and analytical work on field samples with a distributional and morphometric analysis of lakes across the entire Andean foreland using satellite imagery and GIS. This will serve to both provide an understanding of the controls on distribution and shape of lakes and their upstream megafan deposystems throughout the foreland and will also place our selected study lakes in a broader context.
During our first year of this grant we conducted two field campaigns, totaling 7 person-months, visiting and sampling the following lakes and watersheds in Argentina and Brazil:
1. Rio Bermejo, AR actualistic provenance study. We collected 110 bedload sand samples (2 kg each) from hinterland tributaries, megafan streams and the trunk river; samples from the Bermejo watershed proper, spanning the wedgetop, foredeep, forebulge, and backbulge depozones. Samples are currently being prepared for provenance analysis, petrography and heavy mineralogy to be carried out beginning late 2008.
2. Bermejo Watershed Surface Water Stable Isotope Database. We have collected more than 140 surface water samples over two field seasons (Oct 2007, July 08) for oxygen isotope work, spanning the entire watershed (85 to 4000 masl from the high elevation Puna region to the Paraguay River. These samples are currently in the queue for analysis at the UA Stable Isotope Laboratory.
3. Non Marine Sedimentation and Paleoenvironments in the Arid Puna/Pozuelos Basin. We have collected about 75 surface sediment samples, 5 sediment cores (up to 5 m in length), and 12 fluvial sand (bedload) samples from this region. For these sites we have collected water chemistry data, organic geochemistry and sedimentological samples. Analyses have been completed on the cores and samples, and geochronology work is in progress on the cores. We expect to present these results at the AAPG National Meeting in 2009.
4. Pantanal Backbulge Wetlands. We have collected ~200 surface sediment samples from Lagoas Mandiore, Vermelha and Guiava; 6 sediment cores (up to 2 m in length) from Mandiore; 4 sediment cores (up to 2 m in length) from Vermelha; Analytical work at the UA/UMN on these samples will begin in early 2009. We will submit samples from these areas for Rock Eval studies to the USGS (Ellis) in late 2008 and are planning follow up fieldwork tentatively scheduled for June 2009.
5. Lacustrine Facies Models. We have collected ~100 surface sediment samples from Mar Chiquita and La Brea, 5 short sediment cores (La Brea – 1; Laguna Tita Moreno – 1; Laguna Grande-1; Palmar de Indarte – 1; Laguna Doctuer – 1; Laguna Vandano – 1); and 7 water samples. Water chemistry analysis and Rock Eval organic geochemistry work are currently in progress for Mar Chiquita. Samples for granulometry analysis are currently being prepared at the UA for Mar Chiquita, while the sedimentology of the La Brea samples is underway at the University of Salta.
