A library made of dust
The rolling hills and riverbanks around Tashkent hold one of the world's most important terrestrial climate archives. These are not ordinary hills, but massive accumulations of loess—wind-blown silt—that have built up over hundreds of thousands of years. In some places near Tashkent, these deposits reach thicknesses of 70 to 90 meters. The dust itself is composed of fine mineral particles, mostly quartz between 0.01 and 0.05 mm in size, blown from the vast deserts of Central Asia.
Visible in exposed sections, like those along the Chirchik River, is a distinct pattern of alternating layers. Light-yellowish bands of pure loess alternate with darker, browner bands of what are called paleosols—ancient, buried soils. This sequence records major global climate shifts, from frigid ice ages to warm interglacial periods. The entire stack of layers is a detailed timeline; it allows scientists to see the history of the region's environment.
Reading the climate code
Each layer in the Tashkent loess-paleosol sequences records a different climatic era. The thick, light-colored loess layers correspond to cold, dry glacial periods. During these times, vegetation was sparse, and strong winds picked up immense quantities of dust from barren landscapes, depositing it across the region. Analysis shows these layers are dominated by coarser dust particles, indicating more intense wind energy.
The dark layers are the paleosols. These formed during warmer, wetter interglacial periods, similar to our current climate. With more moisture, vegetation flourished, and its decomposition created organic soil. These soil-forming processes also led to the formation of new magnetic minerals, causing the paleosols to have a higher magnetic susceptibility than the loess layers. Scientists use this property, along with particle size analysis and dating techniques like optically stimulated luminescence (OSL), to correlate these layers with global climate records, such as marine isotope stages. For example, a well-developed paleosol can be confidently correlated to a warm period like Marine Isotope Stage 5, the last interglacial period. Some sections near Tashkent, like the Kadyrya section, contain layers that date back to the Matuyama reversed polarity epoch, over 780,000 years ago.