| Summary: | N/A The Baumkirchen sequence, exposed in a clay pit near Innsbruck, Western Austria, is comprised of lacustrine sediments dating to before the last glacial maximum, and is well known in Alpine Quaternary stratigraphy as the stratotype of the transition from the Middle to Upper Würmian. The sequence provides a unique opportunity to investigate the climate and environment of the central Inn Valley and the Eastern Alps during the last glacial cycle. While the site has been known for over 100 years and investigated in detail during the 1970s, advances in analytical methods have led to a renewed research effort. Around 300 m of drill cores were recovered in a recent drilling campaign and investigated with several state-of-the-art methods. This work reports the results of this investigation. The length of the known sequence has been extended to at least 250 m (the base was not reached). The sequence is generally made up of mineralogically diverse laminated clayey silt comprised of clay to fine silt background sediments punctuated by frequent mm-scale event layers. These event layers are most often hyperpycnites (deposited from underflows driven by fluvial inflow) but also include turbidites deposited by slope failure derived flows. Around 1% of the sequence is unlaminated including several short sections associated with evidence of slumping. A short section containing gravel horizons amongst unlaminated and laminated silts with matrix supported clasts (sand to pebble sized) of diverse and exotic origin is interpreted as ice-rafted debris. On the basis of the chronology, and subtle but systematic differences in the sedimentology, elemental composition, and mineralogy of the sediments, two lake phases were identified. The older, spanning MIS 4 and possibly the beginning of MIS 3 (ca. 71-83 until ca. 54-61 ka), contains numerous coarse event layers originating from the Inn or Sill rivers indicating a relatively close inflow into a small lake. The younger, spanning mid to late MIS 3 (ca. 41-46 ka until 33.3-33.6 ka), contains event layers originating from a local source to the south and few from the Inn or Sill, indicating a more distant Inn/Sill inflow and a larger lake, probably extending tens of km up the Inn Valley. The mechanism of damming is poorly constrained, especially for lake phase 1, but a large alluvial fan at the confluence of the Inn and Ziller valleys is most likely for lake phase 2. The 9-19 ka long hiatus between the lake phases is interpreted as a period of fluvial incision. The section of ice-rafted debris dating to the MIS 4/3 boundary (lake phase 1) is interpreted as the first direct evidence of a MIS 4 ice advance in the Eastern Alps and indicates a minor advance that only just extended into the major Alpine valleys (in contrast to the advance into the foreland in the Western Alps). Pollen analysis revealed very poorly developed vegetation indicative of extremely cold and dry conditions during MIS 4. However, the vegetation was better developed during mid to late MIS 3 where two interstadials and corresponding stadials were identified. The interstadials were characterised by well-developed open vegetation with stands of trees but no forests, indicative of mild and more humid conditions. The upper interstadial is confidently correlated to Greenland interstadial 7, the first such firm correlation of an Alpine pollen record interstadial to a Greenland interstadial. Samuel J. Barrett Abweichender Titel der CD-ROM: electronic supplementary data Dissertation University of Innsbruck 2017
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