| Generally sediment cores hold a large number of sedimentary environments and ecological environment evolution process information, including biogenic silica (BSi) in sediments, the abundance of BSi in the sediments can reflect the siliceous biological productivity in the change of time and space. The author and collaborators won the ZK2 core,41.4 meters in depth, near the Big Liaohe of the southwest Liaohe Plain (coordinates:40°45'18.33",122°07'11.23") in May,2012. The core samples were disposed by various physical and chemical indicators. Using the AMS14C and OSL dating means, on the basis of a huge amount of dating data, combined with the results of granularity of sediment samples, the density of in situ, biogenic silica, carbon (including total carbon, organic carbon and inorganic carbon), foraminifera, and pollens, we aim to reveal the sedimentary environment of Liaohe Estuary on ten thousand years'scale and the evolution of the ecological environment, and emphatically discuss the change rate of the biogenic silica and carbon burial flux in kinds of sedimentary facies.Combining comprehensive test indicators, we divided the sedimentary environment of the ZK2 into four sedimentary stages with a bottom-up approach: fluvial facies (U1), limnetic facies (U2), marine deposit (U3), upper delta plain facies (U4). In combination with the age data of the layers, the deposition rates in all stages of deposition are worked out.U1 is located in the depths of 23.9?41.4 m, corresponded to the fluvial facies sedimentary stage and the age is about 25.5?33 ka BP. The lithology is given priority to beige, brown clayey silt and fine sand, with the average particle size of (2.93±0.06)? and median grain size is (2.52±0.04) ?. In this sediment section, there contain very little sporopollens, almost invisible foraminifera and ostracods. Biogenic silica (BSiO2) concentration is (0.92±0.05)%, accumulation rate is (4.95±0.43) mg SiO2 cm-2 y-1. The accumulation rate is relatively high but low amount of biogenic silica accumulation. The particulate total carbon (PC) content is (0.18±0.01)%. Particulate organic carbon (POC) content is 0.11%. Particulate inorganic carbon (PIC) content is (0.08±0.01)%.U2 is located in the depths of 13.1?23.9m, corresponded to the limnetic facies stage and the age is about 8.5?25.5 ka BP. The lithology is mainly given priority to gray silt, silty clay and clayey silt with the rarely horizontal bedding, occasional carbon spot and a small amount of shell fragments. The average particle size is (5.96±0.07) ?, median grain size is (5.69±0.08)?, and sediment particle size is smaller. In this sediment section, the foraminifer community which appears in the sequences discontinuously presents lower differentiation degrees and lower abundances with a small amount of continental ostracods. Biogenic silica (BSiO2) concentration is (1.96±0.10)%, and accumulation rate is(2.04±0.11)mg SiO2 cm-2 y-1. The accumulation rate is low with higher amount of biogenic silica accumulation. The particulate total carbon (PC) content is (0.65±0.05)%, particulate organic carbon (POC) content is (0.43±0.04)%, and the particulate inorganic carbon (PIC) content is (0.21±0.03)%.U3 is located in the depths of 2.5?13.1m, corresponded to the marine deposit stage and the age is about 1.5?8.5 ka BP. The lithology is mainly given priority to gray clayey silt with a large amount of powder sand lens in the central part. The average particle size is (4.88±0.09) ?, median grain size is (4.53±0.10)?, and sediment particle size has a slight increase. The foraminifera content is more, the average abundance is 2865, and advantage combination is Protelphidium tuberculatum and A.beccarii var.. Biogenic silica (BSiO2) concentration is (1.55±0.10)%, and accumulation rate is (0.96±0.48) mg SiO2 cm-2 y-1. The accumulation rate increases but the total amount of biogenic silica decreases. The particulate total carbon (PC) content is (0.42±0.03)%, particulate organic carbon (POC) content is (0.31±0.03)%, and the particulate inorganic carbon (PIC) content is (0.11±0.01)%.U4 is located in the depths of 0?2.5m, corresponded to the upper delta plain facies stage and the age is about 1.5 ka BP?until now. The lithology is mainly given priority to yellow, brown clayey silt. The average particle size is (6.00±0.08) ?, median grain size is (5.71±0.11) ?, and sediment particle size decreases. The foraminifera content is low and specie is single which is Ammoia beccarii var. and Psedononionella variabilis Zheng as absolutely dominating specie with dominance index greater than 98%. The sedimentary environment belongs to stranded reductive environment rich in organic matter. biogenic silica (BSiO2) concentration is (2.85±0.23)%, and accumulation rate is (8.68±0.37) mg SiO2 cm-2 y-1. The accumulation rate is big and the total amount of biogenic silica is relatively bigger. The particulate total carbon (PC) content is (0.73±0.06)%, particulate organic carbon (POC) content is (0.61±0.06)%, and the particulate inorganic carbon (PIC) content is (0.12±0.02)%.Research shows that:the ZK2's each sedimentary stage in a bottom-up approach has a low - high - low - high change trend on the average particle size and the median particle size of the overall trend is similar to the average particle size. The ? value of U1 stage is low in which high sand content and weak hydrodynamic present. But in other three stages,? fluctuates at a higher level. Their corresponding sand contents are relatively lower and hydrodynamic powers become bigger.ZK2's biogenic silica content and accumulation rate in different sedimentary stages have different changes, including that the highest biogenic silica content is 18.5 times bigger than the lowest value; the highest accumulation rate is 51.4 times bigger than the lowest. These changes show that the primary productivity of the study area has the extremely significant differences in nearly 33 ka. biogenic silica content in this region compared with other regions indicates that biogenic silica accumulation amount in the gulf and estuary is lower than ones in deep sea and ocean.The PC and POC content in the U1 stage have the highest average content, U2's begin to decline. U3's rebound and U4's turn to decline again, showing a high-low-high-low cycle change trend. The fluctuation of biogenic silica content and fluctuation of particle total carbon (PC) and particulate organic carbon (POC) content keep synchronized. In particular, lacustrine and paludal sedimentary stage formed during 17-25 cal ka BP glacial epoch appears larger fluctuations of the particles inorganic carbon (PIC) concentration, speculated that with the dry and cold climate supersaturated CaCO3 sediments separate out. The biogenic silica concentration record of drilling sediments has about 300 a hysteresis responding to the 18O isotope of Greenland ice core. |
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