לוח שנה משולב

We studied both modern soils and buried paleosols in order to understand the relationship of temperature (T°C(47)) estimated from clumped isotope compositions (∆47) of soil carbonates to actual surface and burial temperatures. On average, T°C(47) exceeds mean annual temperature by 10-15°C due to summertime bias in soil carbonate formation, and to summertime ground heating by incident solar radiation. Secondary controls on T°C(47) are soil depth and shading. Site mean annual air temperature across a broad range (0-30°C) of site temperatures is highly correlated (r2 = 0.9) with T°C(47) from soils after accounting for variations in T°C(47) with soil depth and ground heating. The highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from T°C(47) in paleosol carbonate
T°C(47) in soil and lake carbonates decreases systematically with elevation gain in the Himalaya, allowing us to to reconstruct paleoelevation from clumped isotope analysis of ancient carbonates. T°C(47) obtained from lacustrine carbonates from SW Tibet show that paleoelevations during late Miocene were similar to today.
We also measured T°C(47) from long sequences of deeply buried (≤5 km) paleosol carbonate in the Himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition. We found that paleosol carbonate faithfully records plausible soil T°C(47) down to 2.5-4 km burial depth, or ~90-125°C. Deeper than this and above this temperature, T°C(47) in paleosol carbonate is reset to temperatures >40C.