Determination of the Optimal Sampling Interval for Cyclostratigraphic Analysis by Using Sampling Theorem and Accumulation Rates
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摘要: 旋回地层学方法近年来被成功应用于年代确定及重大地质事件天文影响因素的判别.采样是旋回分析中最重要的一步, 目前大多使用地球物理、地球化学替代性指标, 采样频率过高, 会大大增加测量和计算的工作量, 同时也会增加随机干扰或其他非气候因素的干扰; 采样频率过低, 可能识别不出其中所包含的米兰柯维奇旋回成分.为确定一个最佳的采样间隔, 通过对80~100 Ma理论日照量曲线及两个实测剖面3种采样间隔(密集采样间隔与约等于一个岁差周期沉积厚度四分之一和一半的采样间隔)数据分别进行谱估计并比较谱估计结果.发现在满足采样定理的前提下, 以一个岁差周期沉积厚度的约一半作为采样间隔, 既可以分析出全部的米兰柯维奇旋回信号, 又具有最少的工作量, 是旋回分析的最佳采样间隔.实际采样中需根据平均沉积速率来确定这个最佳采样间隔.Abstract: In recent years, cyclostratigraphy has been successfully applied to dating strata and recongnizing the possible astronomical forcing on major geological events. Sampling is one of the most important routines in cyclostratigraphic analysis to get the suitable geophysical or geochemical paleoclimate proxies. However, the workload will be significantly increased and random noises or other non-climatic noises will be introduced if the sampling frequency is too high; on the contrary, a lower sampling frequency may make it difficult to recognize Milankovitch signals in successions. In order to identify an optimal sampling interval, we used theoretic daily insolation data of time intervals of 80-100 Ma and two geological datasets to estimate each power spectra at three sampling intervals (high resolution, one quarter and half of one precession cycle), and then compared corresponding spectra analysis results. As a result, under the condition of satisfying the sampling theorem, sampling interval which equals to half of a precession cycle is the optimal sampling interval for cyclostratigraphic analysis. All Milankovitch signals can be identified and at the same time the workload is the least by using this optimal sampling interval. This interval should be determined according to the mean accumulation rate of the target successions during field sampling.
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Key words:
- Milankovitch theory /
- cyclostratigraphy /
- sedimentology /
- accumulation rate /
- sampling interval
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图 1 80~100 Ma日照量曲线频谱
a.采样间隔=1 ka；b.采样间隔=11 ka
Fig. 1. Spectra of 80-100 Ma daily insolation curve
图 2 M206井自然伽马测井曲线频谱
虚线：采样间隔=0.125 m；点画线：采样间隔=0.5 m；实线：采样间隔=0.875 m
Fig. 2. Spectra of well M206 nature gamma-ray logging
图 3 ODP208-1262岩心铁的XRF数据曲线频谱
虚线：采样间隔=0.02 m；点画线：采样间隔=0.06 m；实线：采样间隔=0.1 m
Fig. 3. Spectra of iron XRF data of ODP leg 208 site 1262 core
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