ANALYSIS OF SEDIMENTARY ENVIRONMENT OF A LAKE CORE AT BARROW 6000 YEARS AGO

It deals with sedimentary environment from a lake core at Barrow 6000 years ago. The lake core is got at the southwest corner of Elson lagoon at the northmost of Barrow, Alaska, USA, 1 km apart from coast line, where the water depth is 2 m. The mean depth of the lake is 7 m, with a maximum depth of 12 m at Plover Point. The 4 AMS ¹⁴C ages are 6610°À 60 at 11 cm, 6720°À 130 at 28 cm, 6770°À 130 at 49 cm, 6990°À 90 at 63cm, respectively. The top of the core (20 cm) represents marine sedimentary environment, the middle part (20-32 cm) transition facies sediment , and the bottom (32-60 cm) continental facies sedimentary environment. The lower part of the core contains many non-marine shellfish ostracods, such as Candona, Potamocypris sp. Limuocythere sp. (31-60 cm), and low salt environmental foraminiferal fauna, such as Elphidium albiumbilicatum, Elphidium elavatum and Elphidium orbiculare (35-60 cm). In the upper part, non-marine shellfish ostracods vanish, with in eurythermal and euryhalinous foraminiferal fauna in low-salt environment. Instead the shellfish ostracods is Cytleromorpha macchesneyi, and the foraminiferal fauna includes Ammotium cassis (19-35 cm), Elpliolium excavatum alba and E. askundi (0-19 cm). The diatoms occur at the depth of 30 cm; the combination in the lower part consists of caloneis bacilhum, Cacconeis scufellum, Eanotia praeruptavar, Navioula rhynchocephala, Navicnla semen, and Pinnularia isostauron, these are all freshwater diatoms, with no fragments of marine plankton diatoms, indicating an environment of estuary delta. The diatoms in the upper part include Melosiro sulcata, Melosiva sulcatavar, crenulata, Melosira arctica, Amphoraproteus, var. laevistriata, Diploneis entomon and Diploneis bombonides; there are also several spesies of marine plankton diatom, such as Chaetoceros, Actinocylus and coscinodiscus, which are badly damaged and coere carried here by storm surge and ocean current; the diatom combination represents an offshore neritic zone environment. It is identical with the records on changes of sea level, sedimentary rate, and temperature were from Q-mode factor analysis on changes of sedimentary grain size of 25 indexes and chemical composition of 45 indexes. This research was financially supported by funding from National Natural Science Foundation of China (49971078).