Using geophysical logs to identify Milankovitch cycles and to calculate net primary productivity(NPP) of the Late Permian coals,western Guizhou,China

论文摘要

Milankovitch periodicities of 123 kyr（eccentricity）, 35.6 kyr（obliquity）, and 21.2 kyr（precession） were identified in geophysical logs of three Late Permian coals: 17#, 18#, and 17 + 18#, from the Songhe mining area in western Guizhou Province. Based on the astronomic temporal framework, the periods of deposition of the 17#（5.6 m）, 18#（6.4 m）, and 17 + 18#（5.4 m） coals were constrained to 140.8–119.8 kyr, 160–136.2 kyr, and 135–114.9 kyr,respectively. The overall depositional period of the 18# coal of 160–136.2 kyr was further subdivided using the wavelet analysis method, into short and precise periods corresponding to the Milankovitch periodicities. It includes one eccentricity periodicity（123 kyr）, three obliquity periodicities（35.6 kyr）, and five precession periodicities（21.2 kyr）. Different thicknesses of the subdivided coal sections, equivalent to the same time span of deposition, indicate different rates of coal deposition, i.e., thicker sections imply higher rates while the thinner sections represent lower rates. The combination of the measured average carbon concentration with the density of the coals gave rise to long-term average values of carbon accumulation rates for the Late Permian coals, in the range of 42.4–50.6 g?C?m-2?a-1. This range corresponds to the long-term average carbon accumulation rates for the initial peat in the range of 60.6–72.3 g?C?m-2?a-1. Based on the known quantitative relation between net primary productivity（NPP）values and long-term average carbon accumulation rates for the Holocene tropical peatlands, the range of NPP values for the Late Permian tropical peatlands was estimated as 242.4–433.8 g?C?m-2?a-1.A comparison of existing information about peatland NPP levels of various ages and latitudes indicated that when conditions of high rain and high humidity prevail in the palaeo-peatland at given latitude, the NPP rates will vary with changes in atmospheric concentration of CO2 and O2. This relationship may lead to the use of coals as an indicator for the concentration of these gases（CO2 and O2） in the contemporaneous atmosphere encompassing the long records of coal deposition.

论文目录

• 1 Introduction
• 2 Geological settings
• 3 Geophysical data and spectral analysis
• 4 Results
• 5 Period of coal deposition and the internal time framework construction
• 6 Peatland productivity
• 7 Discussion
• 8 Conclusions
• Authors’contributions
• Competing interests
• Publisher’s Note

文章来源

类型: 期刊论文

作者: Zhi-Ming Yan,Long-Yi Shao,David Large,Hao Wang,Baruch Spiro

来源: Journal of Palaeogeography 2019年01期

年度: 2019

分类: 基础科学,工程科技Ⅰ辑

专业: 地质学,石油天然气工业,矿业工程

单位: College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing),Faculty of Engineering, University of Nottingham,Department of Earth Sciences, Natural History Museum,London

基金: supported by the National Natural Science Foundation of China(Grant No.41572090)

分类号: P618.11;P631.81

页码: 31-42

总页数: 12

文件大小: 1670K

下载量: 46