5:15 PM - 6:45 PM
[MIS12-P02] Mineral composition of lacustrine varve in Sangiin Dalai Lake, northwestern Mongolia, and its relationship with the Holocene climate change
Keywords:Lacustrine varve, Monohydrocalcite, Northwest Mongolia, Holocene
Mongolia is located in a permafrost zone in the north and an arid desert zone in the south, and is an important region for understanding the response of permafrost and desert environments to global climate change. In this study, we attempt to elucidate paleoenvironmental changes in the region in response to Holocene climate change by examining changes in the mineral composition of lake sediments from Sangiin Dalai Lake, located in northwestern Mongolia.
The samples used in this study were surface sediment core collected in July 2016 (16SD02; about 82 cm long) and boring cores collected in March 2019 (19SD01~05; total length about 20 m) in Sangiin Dalai Lake (N49°15'42"; E98°55'23"; elevation 1885 m; depth 25 m). High-resolution elemental compositions were measured using an XRF core scanner (Itrax) at the Marine Core Research Institute (MaCRI), Kochi University, and construct a composite sediment core. An age model was constructed based on soil 14C ages. The results of the age model indicate that the deepest part of the composite core (12.4 m depth) is dated to about 38 kyr ago, 5.1 m depth to the Bølling-Allerød warm interval, and 3.2 m depth to the early Holocene.
The Holocene sediments consists of alternations of grayish calcareous mud with finely laminated layers and brownish mud with weakly laminated layers. The lithologic changes correspond to variations in the Ca/Ti ratio, reflecting multi-centennial to millennial-scale variations. The average thickness of the laminae in the grayish calcareous mud layer is about 0.32 mm, which is consistent with the sedimentation rate calculated from the age of the composite core (about 35 cm/ky, 0.35 mm/yr), suggesting that the laminae is varve. The mineral composition analysis using XRD revealed that the brownish mud layer contains monohydrocalcite (MHC) and calcite, while the grayish calcareous mud layer contains dolomite and pyrite.
MHC is a carbonate mineral that is stable at low temperatures and has been found in colder period (Fukushi et al., 2011; Eva et al., 2023). Thus, the occurrence of MHC in the upper Holocene interval of the sediment in Sangiin Dalai Lake may reflect a low water temperature environment. In addition, the brownish mud with weakly laminated layer is interpreted to have formed in a cold and wet environment, while the grayish calcareous mud with well-developed varve layer is interpreted to have formed in a warm and dry environment. We will further conduct several analyses and interpret the cause of the multi-centennial to millennial-scale changes of the paleoenvironment in this area.
The samples used in this study were surface sediment core collected in July 2016 (16SD02; about 82 cm long) and boring cores collected in March 2019 (19SD01~05; total length about 20 m) in Sangiin Dalai Lake (N49°15'42"; E98°55'23"; elevation 1885 m; depth 25 m). High-resolution elemental compositions were measured using an XRF core scanner (Itrax) at the Marine Core Research Institute (MaCRI), Kochi University, and construct a composite sediment core. An age model was constructed based on soil 14C ages. The results of the age model indicate that the deepest part of the composite core (12.4 m depth) is dated to about 38 kyr ago, 5.1 m depth to the Bølling-Allerød warm interval, and 3.2 m depth to the early Holocene.
The Holocene sediments consists of alternations of grayish calcareous mud with finely laminated layers and brownish mud with weakly laminated layers. The lithologic changes correspond to variations in the Ca/Ti ratio, reflecting multi-centennial to millennial-scale variations. The average thickness of the laminae in the grayish calcareous mud layer is about 0.32 mm, which is consistent with the sedimentation rate calculated from the age of the composite core (about 35 cm/ky, 0.35 mm/yr), suggesting that the laminae is varve. The mineral composition analysis using XRD revealed that the brownish mud layer contains monohydrocalcite (MHC) and calcite, while the grayish calcareous mud layer contains dolomite and pyrite.
MHC is a carbonate mineral that is stable at low temperatures and has been found in colder period (Fukushi et al., 2011; Eva et al., 2023). Thus, the occurrence of MHC in the upper Holocene interval of the sediment in Sangiin Dalai Lake may reflect a low water temperature environment. In addition, the brownish mud with weakly laminated layer is interpreted to have formed in a cold and wet environment, while the grayish calcareous mud with well-developed varve layer is interpreted to have formed in a warm and dry environment. We will further conduct several analyses and interpret the cause of the multi-centennial to millennial-scale changes of the paleoenvironment in this area.