许家窑组及许家窑文化层年代问题的磁性地层学证据

许家窑文化遗址的发现将传统上被认为是早更新世前后的泥河湾层的年代范围推至晚更新世 ,由此建立的许家窑组被确认为我国北方晚更新世湖相沉积的标准地层。近几年对包含许家窑文化层在内的泥河湾层用高分辨率磁性地层学方法研究结果表明 ,在文化层以下 3m处发现了厚度达 6 m以上且分布连续的反向极性带 (未见底 ) ,综合分析认为 ,该反向极性带为松山反向极性带。这一发现否定了在文化层以下 4— 5 m处存在布莱克反向极性偏移的报道。根据松山反向极性时的结束时间为距今 78万年及泥河湾层的沉积速率推算 ,许家窑泥河湾层的年代范围应为早更新世晚期至中更新世 ,而许家窑文化层应为中更新世早期。由此可见 ,泥河湾层的年代范围及分组方案尚需用多种手段进一步研究才能定论

MAGNETOSTRATIGRAPHIC EVIDENCE FOR THE AGE OF THE XUJIAYAO PALEOLITHIC LAYER AND THE XUJIAYAO FORMATION

The Nihewan layer has been regarded as Early Pleistocene sediments since it was named in 1920s. After the Xujiayao paleolithic site was dicovered,the age of the Nihewan layer was extended to the Later Pleistocene and the Nihewan layer in Xujiayao was named Xujiayao Formation which is regarded as the Later Pleistocene type lacustrine sediments. The magnetostratigraphy results of high resolution made recently show that the Matuyama reversed polarity zone is 3 m below the paleolithic layer. It means the age of the Nihewan layer at Xujiayao and the paleolithic layer within it can not be the Later Pleistocene in age. It should be the same as the traditional Nihewan layer ranging in age from Early Pleistocene to Early Middle Pleistocene.