Organic geochemistry of peat deposits from the postglacial Lake Erie Basin lakes, Ohio: Paleoecological and paleoclimatic implications.

摘要

Cores of organic-rich sediments were collected from three types of wetlands, i.e., Springville Marsh (an inland marsh), Sheldon's Marsh (a coastal marsh on Lake Erie) and the remnant of the Black Swamp (an inland swamp) in the postglacial Lake Erie Basin in northwestern Ohio. Detailed organic geochemical analyses were conducted in combination with geological, paleoecological and palynological analyses in an effort to understand the vegetational and climatic evolution in the study area and to test the applicability of organic geochemistry in paleoecological and paleoclimatic reconstruction.; HPLC analyses of chlorophylls and carotenoids revealed that the chlorophyll-a derived compounds are the dominant pigments in the sediments. Changes in carotenoid distribution were found to be correlated with the abundance of diatoms and chrysophytes in Springville Marsh core SV-1. Steryl esters of pheophorbide-a were common in the sediments from the three wetland cores. In particular, the peat and muck deposits that accumulated under the lake environment contain a relatively high concentration of these esters while aerial/subaerial exposure does not favor their formation. GC and GC-MS analyses of various groups of lipids (alcohols, hydrocarbons, ketones and aldehydes, fatty acids and hydroxy acids) revealed a dominance of long-chain aliphatic components, suggesting the important input of higher plant wax in sediments. Variations in the concentration of sterols, n-alkanols and some geochemical parameters (e.g., the ratios of C{dollar}sb{lcub}16{rcub}{dollar}/C{dollar}sb{lcub}28{rcub}{dollar} n-alkan-1-ols and 24-methylcholest-5-en-3{dollar}beta{dollar}-ol/C{dollar}sb{lcub}28{rcub}{dollar} n-alkan-1-ol) appeared to correlate with paleoecological changes revealed in both Springville Marsh core SV-1 and Sheldon' s Marsh core SM91-1. PyGC and PyGCMS analyses of wetland plant species and extracted sediments proved to be useful in distinguishing gymnosperms from angiosperms and in distinguishing aquatic vascular plants from others. Variations in the distribution of the pyrolysis products of the extracted sediments from Springville Marsh core SV-1 and Sheldon's Marsh core SM91-1 reflected changes in the types of vegetation in the wetlands during their evolution.; In conclusion, this study confirmed that organic geochemical analyses can be useful in reconstructing paleoecological evolution and in differentiating various types of wetlands. The palynological study suggests that the regional climate around 13,000 B.P. was cool and wet, and the Lake Erie Basin has experienced a warming climatic trend that has been noted elsewhere in Ohio.