Microstratigraphy and palaeoenvironmental implications of a Late Quaternary high‐altitude lacustrine record in the subtropical Andes
Lucía GuerraMateo A. MartiniHendrik VogelEduardo L. PiovanoIrka HajdasRicardo A. AstiniAntoine de HallerAndrea MoscarielloJean‐Luc LoizeauDaniel Arizteguí
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Abstract High‐mountain lake records in semiarid foreland settings, such as the central Andes of North‐western Argentina, are highly restricted and often deprived of well‐preserved microstratigraphic information to analyze palaeoenvironmental changes and their causes, particularly for periods prior to the Last Glacial Maximum. Laguna La Salada Grande (23°S/65°W, 4063 metres above sea‐level) is a closed shallow lake located at Cordillera Oriental, North‐western Argentina with a unique depositional record, including geomorphic and stratigraphic evidence of palaeoenvironmental changes since the Late Pleistocene. In order to understand the depositional dynamics of this mountain lacustrine system at different timescales, limnogeological multiproxy analyses together with a radiocarbon and 210 Pb‐based chronology were applied on massive and laminated sediments from La Salada Grande. Laminated deposits were further analyzed using novel sub‐centimetric mineralogical, textural and geochemical automated methods (including a combination of micro‐X‐ray fluorescence and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN ® ). Thick laminated microfacies at the beginning of the sequence record a deep and organic matter productive palaeolake prior to ca 34 ka (1 ka = 1000 years before 1950), that changed into a highly fluctuating shallower‐palaeolake with frequent detrital influxes after ca 34 ka. Microstratigraphy of the coarser‐grained detrital laminae between 31 ka and 25 ka reveals irregular and probably sub‐centennial high‐energy discharge events, pointing to convective atmospheric activity as the main trigger. After ca 21 ka the lake evolved to deeper water‐level conditions resulting in fine‐grained deposits with limited delivery of coarse‐grained sediments, followed by an abrupt lake level drop and incision. The multi‐millennial palaeoenvironmental reconstruction of La Salada Grande, and its correlation with other palaeoclimate records, shows a close link between the lacustrine depositional processes and palaeoclimate changes associated with the South American summer monsoon dynamics. This multifocal research in such an understudied environment provides key knowledge about lacustrine functioning and discharge events−climate interactions of mountain lakes of semi‐arid climates.Keywords:
Chronology
Previous British Museum datelists were published as follows: BM-I: Radiocarbon, 1 (1959), 81–6BM-V: Radiocarbon, 10 (1968), 1–7 BM-II: Radiocarbon, 2 (1960), 26–30BM-VI: Radiocarbon, 11, 2 (1969), 278–94 BM-III: Radiocarbon, 3 (1961), 39–45BM-VII: Radiocarbon, 13, 2 (1971), 157–88 BM-IV: Radiocarbon, 5 (1963), 104–8BM-VIII: Radiocarbon, 18, 1 (1976), 16–42 BM-IX: Radiocarbon, 19, 2 (1977), 143–60BM-XVII: Radiocarbon, 26, 1 (1984), 59–74 BM-X: Radiocarbon, 21, 1 (1979), 41–7BM-XVIII: Radiocarbon, 27, 3 (1985), 508–24 BM-XI: Radiocarbon, 21, 3 (1979), 339–52BM-XIX: Radiocarbon, 29, 1 (1987), 61–77 BM-XII: Radiocarbon23, 1 (1981), 14–23BM-XX: Radiocarbon, 29, 2 (1987), 177–96 BM-XIII: Radiocarbon, 24, 2 (1982), 151–70BM-XXI: Radiocarbon, 31, 1 (1989), 15–32 BM-XIV: Radiocarbon, 24, 3 (1982), 229–61BM-XXII: Radiocarbon, 33, 1 (1991), 51–68 BM-XV: Radiocarbon, 24, 3 (1982), 262–90BM-XXIII: Radiocarbon, 36, 1 (1994), 95–111 BM-XVI: Radiocarbon, 25, 1 (1983), 39–58BM-XXIV: Archaeometry, 40, 2 (1998), 413–37
Accelerator mass spectrometry
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Foreland basins are important areas of exploration for petroleum in China.According to the basin construction and evolution,the foreland basins in central and western China can be divided into four types of assemblages including the presenile,the reconstructed,the regenerated and the superimposed.This paper discusses the geological conditions of accumulation,such as the assemblages of source rock,reservoir and seal,in different foreland basins based on the examples of northwestern Junggar foreland basin(the presenile),western Sichuan foreland basin(the reconstructed),northern Chaidamu foreland thrust(the regenerated) and southern Junggar foreland basin(the superimposed).The thermal evolutions of main source rocks are stated in the four types of foreland basins.The foreland development in the late period of Himalayan movement has an obvious control on the thermal evolution of source rocks in the Chaidamu foreland thrust(the regenerated) and southern Junggar foreland basin(the superimposed).
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Progress in radiocarbon dating and calibration accuracy should lead to the development of a calibrated radiocarbon chronology of Near Eastern archaeology, particulary for historical times. The lack of such an independent and impartial chronology is a major constraint, not only in archaeological studies, but also for interdisciplinary research involving the history of man, landscape and climate in the Near East and adjacent regions.
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Chronology
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Abstract Stratigraphic Evolution of Foreland Basins - A strong case can be made that foreland basins are where the casual links between sedimentation and tectonic events were first recognized, as evidenced by the interpretations of geologists working in classic foreland areas. This Special Publication was derived from a Research Symposium entitled ?Stratigraphic Sequences in Foreland Basins ?held at the AAPG-SEPM joint annual meeting on June, 1992, in Calgary, Alberta, Canada. This volume provides a well-balanced perspective of current research on foreland basin stratigraphy and also serves as another element in the evolving framework that comprises our understanding of foreland basins. Given that so many of earth?s resources are found in foreland basins and that foreland basin strata often provide the only preserved record of the tectonic events that led to basin development, the impetus for continued studies of foreland basin strata should remain for many generations of geologists to come.
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