Type division and controlling factor analysis of 3rd-order sequences in marine carbonate rocks

Type division and controlling factor analysis of 3rd-order sequence are of practical significance to tectonic analysis, sedimentary environment identification, and other geological researches. Based on the comprehensive analysis of carbon and oxygen isotope trends, paleobathymetry and spectral-frequency of representative well logs, 3rd-order sequences can be divided into 3 types: (a) global sea level (GSL) sequence mainly controlled by GSL change; (b) tectonic sequence mainly controlled by regional tectonic activity; and (c) composite sequence jointly controlled by GSL change and regional tectonic activity. This study aims to identify the controlling factors of 3rd-order sequences and to illustrate a new method for classification of 3rd-order sequences of the middle Permian strata in the Sichuan Basin, China. The middle Permian strata in the Sichuan Basin consist of 3 basin-contrastive 3rd-order sequences, i.e., PSQ1, PSQ2 and PSQ3. Of these, PSQ1 is a GSL sequence while PSQ2 and PSQ3 are composite sequences. The results suggest that the depositional environment was stable during the deposition of PSQ1, but was activated by tectonic activity during the deposition of the middle Permian Maokou Formation

Nitrogen deposition has minor effect on soil extracellular enzyme activities in six Chinese forests

Soil extracellular enzymes play a key role in mediating a range of forest ecosystem functions (i.e., carbon and nutrients cycling and biological productivity), particularly in the face of atmospheric N deposition that has been increasing at an unprecedented rate globally. However, most studies have focused only on surface soils in a single ecosystem. In this study, we aimed to determine whether the effect of simulated N deposition on the activities and ratios of soil enzymes changes with soil depth across six forest ecosystems in eastern China. We collected soil samples from three blocks x four soil depths (0-10 cm, 10-20 cm, 20-40 cm and 40-60 cm) x three N treatment levels (control, 50 and 100 kg N ha(-1) year(-1)) at each of the six forest ecosystems. We measured the activities of seven soil enzymes involved in C-, N- and P-cycling. We found that 4-5 years of N addition had no significant effect on the activities and ratios of these enzymes inmost cases. The interactions among N addition, site and soil depth on soil enzyme activities were not significant, except that acid phosphatase activity showed site-specific responses to N addition. Our findings suggest that the activities of soil enzymes involved in C-and N-cycling generally do not track simulated N deposition in the six forest ecosystems. Further work on plant, soil and microbial characteristics is needed to better understand the mechanisms of soil enzyme activities in response to N deposition in forest ecosystems. (C) 2017 Elsevier B.V. All rights reserved