Michael M. McGlue and Geoffrey S. Ellis
U.S. Geological Survey
Laguna Mar Chiquita (~31°S, 63°W; Argentina) provides an outstanding opportunity to examine the relationships between depositional processes and organic matter accumulation in a modern thick-skinned foreland basin lake. Because of its tectonic origins and the prevailing mesic climate of the Argentine Pampas, the hydrologically-closed, saline Laguna Mar Chiquita serves as a potential present-day analog to underfilled lake phases of the petroliferous Eocene Green River Formation of the western United States. Depositional environments in Laguna Mar Chiquita were determined through: (1) bathymetric surveying; (2) particle size, mineralogical, and organic geochemical analyses of a grid of modern lake-bottom sediment samples (n=61); and (3) assessment of published limnological datasets. Trends in sediment composition and grain size suggest the presence of open-lake, sublacustrine delta, and lake-margin depositional environments. The muds of the open-lake environment are relatively rich in organic matter (average weight % of total organic carbon = 2.9) and characterized by Type II kerogen (average hydrogen index = 220 mg hydrocarbon/g total organic carbon). The lateral variability of organic facies is minimal. Lake-wide, the quality of organic facies is constrained primarily by siliciclastic dilution and early diagenesis, which are a function of depositional environment and water-column oxidation in the shallow (low accommodation) basin, respectively. Over short time intervals (10[sup]2[/sup] - 10[sup]4[/sup] years), modern analog data suggest that climatically-driven water-level fluctuations influence source-rock potential in thick-skinned foreland basin lakes. Over time intervals >10[sup]5[/sup] years, contraction and lateral migration of the basin flexural profile control stratal-stacking patterns and the potential for hydrocarbon play development.
AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013