5:15 PM - 7:15 PM
[MIS14-P06] Paleoenvironmental change in the East Asia mid-Latitude during the middle to late Pleistocene: Insights from the laminated carbonate in Gobi Desert, Mongolia
Keywords:Giant Gobi Lake, carbonate sediment, carbon and oxygen isotope, Pleistocene, laminated structure
In the Valley of Lakes region of northern Gobi Desert, southern Mongolia, which currently experience an arid climate, there are some salt lakes [Boon Tsagaan Lake (average depth of 9.3 meters) and Orog Lake (average depth of 3 meters)]ranging in north-south width from several kilometers to around 20 kilometers. Geomorphological studies have suggested possible existence of an ancient giant lake called “Giant Gobi Lake” stretching over 200 kilometers width and the maximum depth exceeding 100 meters (Komatsu et al., 2001; Lehmkuhl et al., 2018). The development of this giant lake is estimated to have occurred during the last interglacial, last glacial, and the mid-Holocene, based on the OSL ages of lake sediments (Lehmkuhl et al., 2018). However, the exact timing remains unknown, and the mechanisms of its formation are also unknown. In July 2023, we conducted a survey in the Valley of Lakes area and discovered numerous laminated carbonates cemented on the desert pavement (several centimeters thick), at a site 40 km north of Orog Lake. This may be laminated carbonate in a shallow lacustrine environment of the Giant Gobi Lake, suggesting the possibility of an even larger lake development than previously assumed by prior studies. In this study, we conducted various analyses on the discovered laminated carbonate to investigate the timing of development of the giant lake and to explore the climate system that sustained it.
In this study, we first conducted a geomorphological analysis using ArcGIS to reconstruct the size and depth of the ancient lake that deposited the laminated carbonate. Next, we conducted micro-scale elemental mapping analysis (1 pixel: 20 µm) using µXRF at the Atmosphere and Ocean Research Institute of University of Tokyo. In addition, at the Kochi Core Center, we performed micro-scale milling along the structure using Geomill326 (at intervals of 0.1–0.2 mm), followed by a pretreatment to remove organic matter using hydrogen peroxide. Thereafter, we conducted oxygen and carbon isotope ratio measurements for about 400 samples using an Isoprime precisION.
Furthermore, U/Th dating for determining the age of the samples is currently being conducted at National Taiwan University.
First, our geomorphological analysis suggests that a much larger lake (300 km in width, and the maximum depth exceeding 200 meters) may have existed in the Gobi Desert in the past, exceeding the size previously estimated in prior studies (Komatsu et al., 2001; Lehmkuhl et al., 2018). The elemental mapping analysis revealed that the sample was composed of the following three parts: lower well developed laminated structures consisting of alternating dark and gray part, middle small pebble part, and upper part showing stromatolite texture. In addition, stable isotope ratio measurements showed variations in δ13C (-0.70‰ to +7.90‰) and δ18O (-8.65‰ to -1.71‰), reflecting the laminated structure. Furthermore, U/Th dating, although still preliminary, suggests that the deposition may have occurred during the middle to late Pleistocene (about 300,000 to 60,000 years ago). We will later make corrections for the concentration of foreign origins to recalculate more precise age values. And comparing these results with records such as the oxygen isotope ratios of Chinese speleothems (Cheng et al., 2016), we aim to investigate paleoenvironmental changes in the mid-latitudes of East Asia during the middle to late Pleistocene.
In this study, we first conducted a geomorphological analysis using ArcGIS to reconstruct the size and depth of the ancient lake that deposited the laminated carbonate. Next, we conducted micro-scale elemental mapping analysis (1 pixel: 20 µm) using µXRF at the Atmosphere and Ocean Research Institute of University of Tokyo. In addition, at the Kochi Core Center, we performed micro-scale milling along the structure using Geomill326 (at intervals of 0.1–0.2 mm), followed by a pretreatment to remove organic matter using hydrogen peroxide. Thereafter, we conducted oxygen and carbon isotope ratio measurements for about 400 samples using an Isoprime precisION.
Furthermore, U/Th dating for determining the age of the samples is currently being conducted at National Taiwan University.
First, our geomorphological analysis suggests that a much larger lake (300 km in width, and the maximum depth exceeding 200 meters) may have existed in the Gobi Desert in the past, exceeding the size previously estimated in prior studies (Komatsu et al., 2001; Lehmkuhl et al., 2018). The elemental mapping analysis revealed that the sample was composed of the following three parts: lower well developed laminated structures consisting of alternating dark and gray part, middle small pebble part, and upper part showing stromatolite texture. In addition, stable isotope ratio measurements showed variations in δ13C (-0.70‰ to +7.90‰) and δ18O (-8.65‰ to -1.71‰), reflecting the laminated structure. Furthermore, U/Th dating, although still preliminary, suggests that the deposition may have occurred during the middle to late Pleistocene (about 300,000 to 60,000 years ago). We will later make corrections for the concentration of foreign origins to recalculate more precise age values. And comparing these results with records such as the oxygen isotope ratios of Chinese speleothems (Cheng et al., 2016), we aim to investigate paleoenvironmental changes in the mid-latitudes of East Asia during the middle to late Pleistocene.