Abstract:

The Gaoyuzhuang Formation of the Changcheng System in northern Hebei Depression is dominated by carbonates and can be roughly divided into shallow water platform and deep water platform-basin facies zones and further divided into five different facies tracts.Based on the correlation analysis of carbonate rock sample testing results,the authors of the paper discuss the enrichment mechanisms of their elements and components and environmental significance.The analysis shows that geochemical characters are closely related to the initial sedimentary environment in the study area:the Ca/Mg ratio is the lowest in supralittoral zone where dolomite is predominant,gradually increases from intertidal zone to slope zone,and reaches its highest value in deep water basin where calcite dolomite is predominant.The average Na content is the highest in supralittoral zone where it is be-neficial to dolomitization and preservation of Na.The contents of Mn and Fe are the highest in intertidal zone but relatively low in the platform-basin.The contents of trace elements as Al,K,V,P and Ti tend to increase from shallow to deep water sedimentary environment,thus could be used to indicate relatively changes of ancient water depth and sea level.Sr is mainly hosted in calcite.The average Sr content and 1000 Sr/Ca ratio tend to increase from shallow water platform to deep water platform-basin.The blue green microalgae rich in Sr is the main rock-forming organism for stromatolite dolomite,and the stromatolite dolomite is more highly developed in the supralittoral zone and intertidal zone than in subtidal zone.Thus the average Sr content and 1000 Sr/Ca ratio are relatively high in the supralittoral zone and intertidal zone.All of these indicate that geochemical characters of carbonates can be regarded as an effective indicator of sedimentary facies.

Key words: sedimentary environment, geochemical character, carbonate rock, Gaoyuzhuang Formation, Changcheng System, northern Hebei Depression