Multiple Stratigraphy Study of the Ordovicianin SW Ordos,China

The Ordovician(485.4 Ma-443.8Ma)is the longest period of the Paleozoic,which was characterized by a peak of greenhouse climate in Earth history,as well as extreme high sea level(Haq and Schutter,2008;Munnecke et al.,2010),with warm and humid conditions in early-middle period and seawater temperature up to 45℃(Trotter et al.,2008).

The Ordovician Magnetostratigraphy and Cyclostratigraphy:A Review

The study of magnetostratigraphy and cyclostratigraphy in the last two decades has provided a great deal of opportunities to improve the geologic time scale.The Cenozoic and Mesozoic geologic timescale have been well calibrated(Gradstein et al..2012;Ogg et al,2012;Cohen et al.,2018).However,for the Paleozoic era the uncertainty over boundary ages are still very large.

The Remagnetization of Marine Carbonate Rocks of the Late Ordovician in Pingliang Section,Southwest Ordos(China)

The natural remnant magnetization(NRM)of carbonate rocks in particular must be understood for the construction of a meaningful Paleozoic geomagnetic polarity time scale.This would enable evaluating geomagnetic features(e.g.reversal frequency)and would provide a paleomagnetic dating tool(Voo,1990).

鄂尔多斯西南缘陕西崛山剖面马家沟组牙形刺兼论马家沟组顶界的穿时性

鄂尔多斯盆地西南缘奥陶系出露广泛且分布连续,而有关马家沟组的时代在不同地区存在较大的差异,制约了盆地周缘地层划分和对比。陕西岐山地区崛山剖面的马家沟组上部识别出牙形刺6属10种,属于上奥陶统Belodina compressa带至Belodina confluens带。因此,崛山剖面马家沟组上部的时代为晚奥陶世早—中期。通过对各地区马家沟组的时代对比,发现马家沟组的顶界穿时,范围下至中奥陶统达瑞威尔阶中上部,上达上奥陶统凯迪阶下部。