Based on comprehensive analysis of field work, petrological and geochemical characteristics, this paper studies the characteristics and origin of giant patch dolomite of the Lower-Middle Ordovician HangGuletag Formation in Wuligezitag area, NE Tarim Basin, China. It can be seen in the field that the grayish yellow giant patch dolomite partially develops in the black thin-bedded micritic limestone, with an irregular boundary not controlled by sedimentation. The giant patches are several meters in size (the largest >10 m) which is larger than and quite different from the several-centimeter (decimeter) burrow-related dolomite or leopard fur dolomite. Microscopically, it consists of micro-finely and planare(s) dolomite crystals with a size near 100 μm. Besides, it is also characterized by its unique geochemical features: 1) δ¹³C_PDB (−1.34‰-−0.62‰) accords with the range of Early Ordovician seawater while δ¹⁸O_PDB (−8.01‰ -−4.79‰) is higher; 2) ⁸⁷Sr/⁸⁶Sr  (0.711000-0.711535, AVG=0.710863) is much higher than that of limestone and contemporaneous seawater; 3) average high Fe and Mn content (2001.32 and 601.73 μg/g, respectively) and low Sr and Ba (33.14 and 8.27 μg/g, respectively) content versus that of limestone; 4) dolomite has slightly negative Eu anomaly and similar REE composition and distribution patterns compared with limestone; 5) low order degree value (AVG=0.6). This study reveals that the dolomitization was related to fault and occurred in low-temperature and shallow-burial environment in Early-Middle Ordovician. Dolomitizing fluid was generated from the concentrated formation fluid in lower-middle member of HangGuletag Formation and underlying Tursaktag Group. Most Mg²⁺ came from the stabilization of quasi-stable carbonate minerals, and the transformation of clay minerals of (calcareous) mud in the limestone strata not only provided a little Mg²⁺ but caused the rise of ⁸⁷Sr/⁸⁶Sr. Dolomitizing fluid was likely to be richened in Xingdi-related normal fault and fractures which also acted as the main fluid pathways, and it finally caused the partial dolomitization of nearby limestone strata.

The responses of the global mean climate and the ENSO to a substantial weakening of the Atlantic Meridional Overturning Circulation (AMOC) are studied using water-hosing experiment in a coupled ocean-atmosphere general circulation model. With 1 Sv freshwater input in the North Atlantic, the AMOC slows down rapidly and weakens by almost 90%, reducing the northward oceanic heat transport, leading to a sea surface temperature (SST) dipole in the Atlantic. Through atmospheric teleconnections and local air-sea interaction, warm SST anomalies are found over the tropical Pacific. However, neither zonal SST gradient nor zonal wind stress changes significantly. The depth and slope of thermocline in tropical Pacific do not change too much, either. Accordingly, the variability of ENSO activity is essentially unchanged. These results indicate that in this model, fresh water perturbation may influence global mean climate, but has little impact on ENSO.