四川龙门山区泥盆纪海水来自何方

WHERE DID SEA WATER OF THE LONGMEN MOUNTAIN AREA COME FROM DURING THE DEVONIAN?

摘要:

四川龙门山区的泥盆系以其发育完整、出露良好、厚度巨大、化石丰富、地层连续、层序清楚等特点驰名中外,尤其是北川桂溪—甘溪—沙窝子剖面的研究程度不断提高,已成为世界泥盆系分统分阶研究中不可多得的系统剖面。但长期以来对龙门山区泥盆纪时的古地理特点和海侵方向等关键问题,始终没有得到明确的、肯定的和统一的认识。本文就目前作者的认识,提出一些看法以供大家讨论。

Abstract:

The well-developed Devonian strata in the Longmen Mountain area, Sichuan is characterized by continuous sequences, good exposures, huge thickness and abundant well-preserved fossils. However, there is still debate about transgression direction and palaeogeography during the Devonian. The data at hand show that during the Devonian, it is impossible for the sea water of the study area to come from Guangxi and Yunnan in the south or from the Qinling Mountain area in the northwest. Furthermore, there was no remnant sea in this region during the period. On this account, the following two inferences are drawn by the author:(1) The Longmen Mountain area was structurally a terrane during the Devonian, and the Devonian strata exposed in this region at present are not autochthonous deposits; (2) The area lay on the continental margin during the Devonian, instead of to the south of Liujing, Guangxi. It is possible for sea water to get to the Longmen Mountain area at first, and then to Liujing, Guangxi. Only after rotating at an angle of 90 degrees, can the whole land mass be in the present-day position.