现代泥炭地中蕴藏着巨量的碳,泥炭地生产力的高低会影响全球碳循环及全球气候变化。前人对全新世以来泥炭地生产力做了大量研究,但对前第四纪的深时阶段的泥炭地生产力则极少涉及,其主要原因是缺少精确的定年方法。以二连盆地吉尔嘎郎图凹陷早白垩世6号煤为例,利用地球物理测井信号进行频谱分析并获得煤层中米兰科维奇旋回周期参数(123 ka(偏心率):38.1 ka(斜率):22.1 ka(岁差)),将米兰科维奇旋回作为深时地层时间的度量工具,计算出6号煤层碳的聚集速率为35.1~38.9 g C/(m~2·a),进一步推算出其所代表的泥炭地的碳聚集速率为46.2~51.2 g C/(m~2·a),净初级生产力(NPP)为231~256 g C/(m~2·a)。将该计算结果与全新世同一纬度带泥炭地生产力水平比较,并结合前人研究成果综合分析影响因素,得出早白垩世泥炭地生产力水平主要受温度和大气中二氧化碳含量控制,而这两种因素又与气候相关联,则泥炭地生产力的研究可能对进一步了解古气候提供帮助。
英文摘要:
Peatlands contain a huge amount of carbon whose productivity will affect the global carbon cycle and even climate change. A number of productivity researches have been done on the Holocene peats, but few is dealing with the pre-quaternary due to a lack of precise dating method. In this paper, the geophysical logging signals were used to analyze the Milankovitch orbital cycles which were further used as a tool to date the "deep time" and to measure the carbon accumulation rates of the paleo-peatlands. The spectrum analysis has been conducted on the geophysical logging signals of a thick coal (No.6 seam) of the Early Cretaceous in the Jiergalangtu sag of the Erlian Basin, and the Milankovitch cycle parameters of 123 ka (eccentricity):38.1 ka (slope):22.1 ka (precession) have been obtained for this coal. These Milankovitch cycles were used as "measurement" to calculate the carbon accumulation rate and the net primary productivity (NPP) based on the carbon contents and coal rank of coal. The No.6 coal had a carbon accumulation rate of 35.1~38.9 g C/(m~2·a) which corresponds to the carbon accumulation rate of 46.2~51.2 g C/(m~2·a) and the net primary productivity (NPP) of 231~256 g C/(m~2·a) for the Early Cretaceous peatlands. A comprehensive comparison with the productivity levels of the Holocene peatlands (NPP) of 150~250 g C/(m~2·a) in the same latitude confirmed that the productivity level in the Early Cretaceous peatlands were controlled by paleo-temperature and concentration of carbon dioxide in the atmosphere. As the paleotemperature and concentration of carbon dioxide were closely related to the paleoclimates, these productivity values of the paleo-peatland would help us understand more about paleoclimates of "deep time".