Distinguish of Varves and Laminations in Cretaceous Lacustrine Sediments in Songliao Basin, North-East of China
Enxiao Yu1, Chengshan Wang1, Zhaoda Ma1, and Fushuang Zhou2
1School of Earth Science and Mineral Resources, China University of Geosciences, Beijing, China
2Dagang Oilfield Company, PetroChina, Tianjin, China
Extremely fine grained lacustrine sediments of the Early Cretaceous Nenjiang formation were studied in the excavated SK1 Core in Songliao Basin, North-East China. The section consists mainly of mudstones with nearly no obvious lamination and shales with obvious laminations. The mudstones, with no obvious laminations, are mainly composed of clay and terrestrial debris (Fig. 1). The shales with obvious laminations are mainly composed of laminations rich in terrestrial debris and laminations rich in clay, without any terrestrial debris larger than silt sands (Fig.2). Varves with four laminations, less than 0.1mm in thickness, two of which are rich in terrestrial debris and the others lack terrestrial debris are commonly observed to record seasonal climatic changes in the lacustrine sediments(Fig.3). Pyrites were often observed to be rich in the upper part of the laminations rich in terrestrial debris, and just below the clay-rich laminations without any terrestrial debris (Fig.4). Quiet, anoxic lacustrine bottom water is critical for the preservation of the laminations and the occurrence and preservation of pyrite.
AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013