苏北盆地阜宁群时期的古气候和水介质的物理化学条件分析

PALAEOCLIMATIC CONDITIONS AND PHYSICOCHEMICAL PROPERTIES OF WATER BODIES IN THE NORTH JIANGSU BASIN DURING THE FUNING GROUP DEPOSITION(PALAEOGENE)

摘要:

苏北盆地是一个大型的中、新生代沉积盆地,多旋回性地壳运动使盆地内部进一步分异,发育了一系列的北东、北东东向的南陡北缓的断陷性箕状凹陷。在盆地各凹陷中,普遍发育一套阜宁群沉积,并自下而上划分为四个岩性段,其主要岩性、电性特征和标志层详见表1。长期以来,人们传统地将阜宁群视为纯陆相沉积,但通过近些年来对古生物、岩矿及地球化学等方面所作的工作,确认阜宁群沉积在陆相沉积环境总的背景下,其中阜二、四段曾遭受海侵,形成海陆过渡相沉积。

Abstract:

Some speculations upon the palaeoclimatic conditions in the North Jiangsu Basin during the Funing Group deposition(Palaeogene)have been made in the light of the palaeomagnetic, palaeontological and sedimentological methods,and the detailed analyses have also been made on physicochemical properties of the water bodies in the basin at that time with the aid of the indicators of palaeosalinity, palaeotemperature, palaeodepth, pH and Eh values and the degree of oxidation and reduction.
The North Jiangsu Basin lay in the low-to middle-latitude zones(11-23°N), and the palaeoclimates should be tropical or subtropical during the Funing Group deposition. The water bodies in Members 1 and 3 were para-acidic fresh-brackish watet with shallower water depths, suggesting a oxidation-weak reduetion environment, whereas those in Members 2 and 4 were para-alkaline brackish water with deeper water depths, suggesting a reduction-strong reduction environment. The temperatures of the water bodies ranged in general between 23 and 30℃during the Funing Group deposition. It is clear that the results outlined above are of some interest in the study of the Palaeogene sedimentary environments in eastern China and in the search for oil and gas.