河南泌阳凹陷古近系核桃园组核二段沉积体系

SEDIMENTARY SYSTEMS IN THE MEMBER 2 OF HETAOYUAN FORMATION OF PALEOGENE IN BIYANG DEPRESSION OF HENAN PROVINCE

古近系核桃园组核二段沉积时期泌阳凹陷总体处于从断陷向坳陷转换的过渡阶段。本文利用测井、钻井和C、O同位素等资料 ,研究了核二段各砂组沉积时期的沉积环境、相带分布、砂体展布以及沉积演化规律。核二段沉积时期 ,泌阳凹陷发育 5种沉积体系类型 :辫状河三角洲、扇三角洲、曲流河三角洲、近岸水下扇和盐湖沉积体系。物源供给条件和古地形严格控制了泌阳凹陷各种沉积体系的发育。在陡坡带的中、西部地区发育扇三角洲沉积体系 ,而在陡坡带东部则发育近岸水下扇沉积体系 ;在东北部缓坡带发育辫状河三角洲 ,而在西北部缓坡带则发育曲流河三角洲。借用C、O同位素数据估算核二段沉积时期平均古水温为 2 8.17℃ ,最高 4 6 .8℃ ;环境指标Z值平均为 12 6 .84 ,表明核二段为盐湖咸水沉积条件。从纵向上δ13C、δ18O及Z、t演化看 ,核二段演化表现为两个旋回 :从三砂组底到二砂组底部为第一次湖水变咸和湖盆收缩 。

Biyang Depression was in the stage of transition from fault depression to down warping depression during the sedimentary time of the Member 2 of Hetaoyuan Formation of Paleogene. Sedimentary environment and its evolution, distribution of sedimentary facies and sand bodies are discussed on the base of the data of log, drilling and C, O isotope. Five sedimentary systems, i e., braided river delta, fan delta, delta, inshore subaqueous fan and saline lake, were distinguished in Member 2 of Hetaoyuan Formation, the Biyang depression. The properties and distributions of these sedimentary system are controlled by paleotopography and supplying condition of sediments. There exits fan delta sedimentary system in the west and middle of the steep slope, while inshore subaqueous fan in the east. There is braided river delta sedimentary system in the northeast of the gentle slope, while delta in the northwest. According to the calculation from the data of C, O isotope, the average paleowater temperature is 28.17 ℃, and the average paleosalinity index is 126.84, indicating its saline setting. In addition, two depositional cycles are shown according to the evolution of δ 13 C, δ 18 O, Z and t . The first cycle is from bottom of the Member 2 of Hetaoyuan Formation to the bottom of third sand group, and the second cycle from the bottom of third sand group to top of the Member 2 of Hetaoyuan Formation.