Showing papers on "Varve published in 1982"

Green River laminites: Does the playa-lake model really invalidate the stratified-lake model?

Abstract: Proponents of the playa-lake model have proposed deposition of most of the Green River Formation microlaminated carbonates (including oil shales) in lakes that were not perennially stratified (meromictic). However, there is a variety of evidence favoring a meromictic depositional environment: (1) close similarity of much of the lamination to varves in modern meromictic lakes, (2) evidence that hydrologic events favoring development of meromixis (chemical stratification) occurred prior to deposition of major accumulations of oil shale, (3) mutually exclusive distribution of fossil nekton (especially fish) and normal lacustrine benthos (including mollusks), and (4) analogy with a Quaternary playa that became a meromictic lake following increased inflow. The playa-lake model is untenable for the typical fish-bearing, kerogen-rich microlaminated sediments. These laminites were probably deposited in a large ectogenic meromictic lake—a chemically stratified lake that formed when increased fresh-water inflow “drowned” a saline playa complex.

Recent increase in mercury sedimentation in a forest lake attributable to peatland drainage

Abstract: In order to gain information about the natural background levels and about the recent history of mercury in Finnish waters, mercury profiles were determined in two lakes in which annually laminated sediment is deposited, and which differ from each other with respect to the history of land use in their drainage areas. Annual sediment laminations or varves allow a precise dating of the studied sequence, and their existence indicates undisturbed recording of the history of the environment.