Minor Elements Utility in Paleo-lake Evolvement and Signification of Lower Tertiary Fning Formation，Gaoyou Sag, Subei Basin

According to the study vertical variations of trace elements: Boron(B) and Strontium(Sr) contents testing in clay rock of tertiary Funing Formation(from bottom to up :E1f1、 E1f2、 E1f3、 E1f4), Gaoyou sag, Subei Basin of China., the water of palaeolake in Gaoyou sag of Subei Basin changed from freshwater(E1f1、E1f3) gradually to salt water(E1f2、E1f4). The calcareous cement is formed in early diagenesis. It also means that Gaoyou palaeolake was twice opened to the sea from the first section of Fning Formation to the fourth (E1f1-E1f4). During the second and fourth of Funing Formation (E1f2、E1f4）, the Gaoyou palaeolake was the deepest and the area was largest. Comprehensive analysis of trace elements indicates that palaeo-salinity and depth fluctuated during different sedimentary periods. The sedimentary periods of Funing Formation can be divided into 9 intermediate cycles with relative lake level change. The paleolake level was relative rising quickly in the second and fourth of Funing Formation (E1f4) and relative descending quickly in the first Funing Formation (E1f1). Key words: palaeolake； trace elements； lower tertiary Fning Formation； Gaoyou sag