Sedimentary Basin Analysis Of The Cretaceous Ancient Desert In The Ordos Basin

The ancient desert is a desert system formed in the geological history period.The study of its evolution has important significance for the formation and evolution of modern desert,and also has economic value for guiding mineral exploration.In China,the study of paleo desert system is still at the stage of recognition and simple description,the research on its system is very low now.As the most recent typical "greenhouse earth" period—— Cretaceous,the desert area in it is much larger than now,and there are large-scale regional deserts,which are more than twice the area of the Sahara.It is important to study the evolution of the ancient desert in the Cretaceous period for understanding the pattern of the present desert and the evolution trend under the future greenhouse effect.In this paper,the empirical relationship formula of modern sand dune morphological parameters combined with the measured part of the ancient sand dune morphological parameters is used to quantitatively restore the height of some sand dunes,so as to semi quantitatively construct the desert framework.This method can be used as a new way to analyze the original appearance of sedimentary sand dunes,but the application of this kind of relationship needs to be cautious and multi angle verification,so that the data has statistical significance.The Cretaceous Luohe formation in Ordos Basin is characterized by a typical paleo desert sand sea environment in the inland craton basin.The whole facies belt is a continuous accumulation of thick aeolian lithofacies,and the aeolian dune type has a complete desert evolution sequence.In the ancient desert of Ordos Basin,the shape of sand dunes from the edge to the center has obvious evolution rules from small to large and super large.The sand dunes in the center of the desert represent the sedimentary peak with a height of 100 meters and a stable extension of more than 1000 meters.The marginal facies of ancient desert is small isolated sand dune,the height of sand dune is generally 4-8M,and the deposition of wet hills,short River and debris flow facies is mainly.In the central direction,the sand dunes become larger obviously,the height of the sand dunes is generally 10-30 m,some of which can exceed 300 m,forming a huge sand mountain.The phase state is dominated by single type and compound type sand dunes,among which there are only about 10% dry hills and almost no wet hills.