Abstract
Seven isotopic and eight trace element (TE) profiles across shell growth lines are presented, based on over 1000 stable isotope and electron microprobe analyses on six brachiopod shells (Gigantoproductus), to quantify seasonal temperature change in the early Carboniferous Moscow Basin. Evidence for good shell preservation is the retention of original prismatic shell microstructure and the general lack of cathodoluminescence in shell interiors. Only shell edges show luminescent calcite. Other evidence for good preservation of the six shells includes undetectable Fe and Mn contents in mid-shell areas compared with high Fe and Mn contents at shell edges, different trends of 813C and 8180 between shell edges and mid-shell areas, and distinct growth lines in the prismatic secondary layers. Forty-one 8180 cycles are found in six profiles, with amplitudes ranging from 0.2%c to 2.7%c. The majority of cycles vary in amplitude from-0.4%0 to-1.2%0, with a mean of-0.8%o, representing annual temperature change of 2'C to 6'C in the early Carboniferous tropical zone. This seasonality is compatible with the-3'C modern tropic annual temperature range, and contrasts significantly with the conclusion based on growth rings of fossil woods that there was no significant seasonal variations in the tropics during the early Carboniferous. For carbon isotopes, temperature-depended metabolic activity appears to be the main factor controlling 81 3C variations- The numbers of cycles recorded in 180 profiles, 13C profiles, Mg profiles, and growth lines are 41, 41, 40, and 37 respectively. The similarity in cyclicity of these four different measures argues that they are all controlled by seasonal-dependent factors, such as temperature and metabolic rate. Except for number of cycles, there are no significant controlled by temperature, TE contents may be controlled by metabolic rates and perhaps the reproductive cycle.
Wang, Huayu (1998). Oxygen isotope records of carboniferous seasonality on the Russian platform. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1998 -THESIS -W264.