PALEOSEDIMENTARY ENVIRONMENT AND PALEOCLIMATE CONDITIONS REVEALED BY HOLOCENE SEDIMENTS FROM NEAR LAKE HOVSGOL, NORTHERN MONGOLIA

This study examines the paleoenvironmental evolution of a sequence of fluvial-lacustrine Holocene sediments in the Il Horoo Gol (river) valley area from north-west of Lake Hovsgol in northern Mongolia. No glaciers are currently preserved in the area however a valley glacier extended to the end of the Il Horoo valley during the last glacial maximum (LGM; marine isotope stage [MIS] 2 or 3) and produced very well preserved terminal moraines. Older (MIS 6?), less well-preserved terminal and recessional moraines are also present in the lowland areas. Our study area was located between these different age moraines.

Samples were collected from 5 sites – 3 trenches were excavated in post-glacial fluvial deposits associated with relatively flat fluvial terraces adjacent to Il Horoo Gol and 2 trenches were excavated in post glacial lacustrine-bog sediments preserved in a hummocky area within the older recessional moraine complex. Initial radiocarbon results indicate that the sequence is at least 9000 years old.

Previous studies of cores taken from Lake Hovsgol, Lake Baikal and other locations in Mongolia suggest that the early-mid Holocene was relatively humid with the forest-steppe boundary located further to the south and lake levels were relatively high. The mid-Holocene was characterized by drought conditions although the timing and details are disputed. More humid conditions returned during the late Holocene (Propenko et al., 2007; Kataoka et al., 2001). Initial pollen, grain size, organic content, carbonate content, and macrofossil analyses confirm these broad trends. For example, both fir and pine species were present in the early to mid Holocene but become rare in our late-Holocene sediments. In addition, marl layers are prevalent in the early-mid Holocene portion of the sequence and contain diatom species such as Fragilaria, Cymbella, Gomphenoma parylum, and Eunotia, as well as bivalves, snails, and fish vertebrae indicative of freshwater environments possibly implying a more humid climate and higher lake levels. Reconstruction of the paleo-depositional environment combined with the paleoclimate indicators will allow us to better constrain the nature and timing of complex environmental changes that have occurred in this part of Mongolia since the LGM.