泥河湾地区晚新生代生物地层带

LATE CENOZOIC BIOSTRATIGRAPHIC ZONATION OF NIHEWAN BASIN

本文根据岩石地层、哺乳动物化石及古地磁资料的综合分析研究，将泥河湾地区晚新生代生物地层划分为５个生物地层时限带（ｂｉｏｓｔｒａｔｉｇｒａｐｈｉｃｉｎｔｅｒｖａｌ－ｚｏｎｅ）并推算出每个带的年限，它们是：（１）Ｈｉｐｐａｒｉｏｎｈｏｕｆｅｎｅｎｓｅ时限带，？～３．３０Ｍａ；（２）Ｍｉｍｏｍｙｓｏｒｉｅｎｔａｌｉｓ时限带，３．３０～２．４８Ｍａ；，（３）Ｍｉｍｏｍｙｓｙｏｕｈｅｎｉｃｕｓ时限带，２．４８～１．８７Ｍａ；（４）Ａｌｌｏｐｈａｉｏｎｙｓｃｆｐｌｉｏｃａｅｎｉｃｕｓ时限带，１．８７～０．９７Ｍａ；（５）Ｍｉｃｒｏｔｕｓ时限带，０．９７～０．３０Ｍａ（以后）．同时探讨了第四纪下限，指出Ｅｑｕｕｓ到达泥河湾地区的时间可能接近３．００Ｍａ。

Based on designation of two biostiatigraphic composite reference sections for Late Cenozoic biostratigraphic strata in the Nihewan basin, establishment of stratigraphic ranges of 37 mammalian taxa in the reference sections and correlation of the two sections with each other and with the resulted stratigraphic and magnetostratigraphic framework, five continuous biostiatigraphic interval-zones are defined.The proposed interval-zones are bounded by six important faunal events which are identified in the reference sections. Compared the magnetic-polarity stratigraphy of the reference sections with the standard magnetic polarity time scale, the five proposed interval-zones and the approximate ages of their lower and upper boundaries in the reference sections are determined as follows. (1)Hipparion Houfenense interval-zone, ? ￣ 3.30 Ma;(2)Mimomys orientalis interval-zone, 3.30 ￣ 2.48Ma, (3) Mimomys youhenicus interval-zone, 2.48 ￣ 1.87Ma; (4)Allophaiomys cf. pliocaenicus interval-zone, 1.87 ￣ 0.97 Ma, (5)Microtus interval-zone, 0.97 ￣ 0.73Ma(later). The lower boundary of the Quaternary is also briefly diseussed here.The faunal events suggest that Equus arrived at Nihewan around 3.00 Ma, which is the earliest Equus record in China.