Full
FAN Liyong,born in 1978,Ph.D.,is a senior engineer. E-mail: lyfan123_cq@petroChina.com.cn.
Outline
Coal accumulation is a crucial component of the global carbon cycle,facilitating the large-scale and long-term burial of atmospheric CO2 on land. It is one of the primary factors leading to a decrease in atmospheric CO2 concentration,which in turn causes a drop in global temperatures and can trigger the onset of an ice age. At the end of the Carboniferous period,a basin-wide coal accumulation event(Coal #8+9)occurred in the North China Basin,after which the globe entered the Early Permian P1 ice age. This suggests a potential causal link between the widespread coal accumulation in the NCB and the onset of the P1 ice age. To investigate this relationship,this study focuses on Coal #8+9 in the Ordos Basin. Spectral analysis was performed on its natural gamma ray logging curves to reconstruct the accumulation duration of Coal #8+9. Based on coal thickness,carbon content,and apparent density data,the carbon burial rate of the peatland was reconstructed. Using this rate and the estimated area of the Late Carboniferous peatland in the NCB,the annual carbon burial amount in the basin during that time was calculated. Subsequently,based on existing atmospheric data,the annual reduction in atmospheric CO2 concentration resulting from this carbon burial was estimated,ultimately revealing the relationship between coal accumulation in the Late Carboniferous NCB and the onset of the P1 ice age. The results indicate that Milankovitch cycles of obliquity(35.5 kyr)and precession(21.7 kyr)were identified in Coal #8+9 of the North China Basin. The depositional duration is estimated to be between 98.31 kyr and 277.66 kyr,with an average of 188.20 kyr. The carbon burial rate of the peatland ranged from 42.41 to 78.87 g/·a, with an average of 59.21 g/m2·a. According to estimates of total atmospheric mass and CO2 concentration,removing approximately 2.13 GtC from the atmosphere is required to lower the atmospheric CO2 concentration by 1 μL/L. The annual carbon burial amount in the Late Carboniferous NCB was calculated to be between 3.82×107 t and 7.01×107 t,averaging 5.33×107 t. This corresponds to an annual reduction in atmospheric CO2 concentration of 1.79×10-2~3.33×10-2 μL/L,with an average of 2.51×10-2 μL/L. The atmospheric CO2 concentration before the end-Carboniferous coal accumulation was approximately 400 μL/L,while it was about 200 μL/L before the onset of the P1 ice age. Based on the average annual carbon burial rate of the NCB,it would take only about 8000 years to reduce atmospheric CO2 by 200 μL/L,reaching the level associated with the P1 ice age inception. However,the average depositional duration of Coal #8+9 is 188.20 kyr,far exceeding the time required to reach the ice age threshold. Therefore,the massive carbon burial in the NCB could have led to a rapid decrease in atmospheric CO2 concentration just before the onset of the P1 glaciation. The decoupling of ρCO2 from continental silicate weathering,coupled with the rapid expansion of tropical rainforests and their repeated reorganization,indicates that the extensive coal accumulation in the NCB during the latest Carboniferous was the primary cause of the atmospheric CO2 decline preceding the P1 ice age.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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