江西信江盆地晚白垩世风成沙丘的发现及其古风向

长期以来,江西信江盆地晚白垩世圭峰群塘边组(K2t)均定为水成沉积,本文的研究结果则认为属风成沉积.沉积结构、构造和石英沙颗粒表面特征研究结果表明,该组的主体岩性为紫红色中-细粒净砂岩,基本不含泥质和云母等悬移质,大型高角度平板状交错层理发育,层系厚度巨大,风成沙丘前积层特征明显,石英沙磨圆度好,在电子显微镜下普遍可见风成沙特有的碟形撞击坑、新月形撞击坑和毛玻璃化表面特征,属于风成沙丘沉积.古流向恢复表明,信江盆地以西风为主,东北风为次,同时见有少量东南风与西北风.根据当时的古地理格局及地表风带模式判断,研究区位于当时的北半球西风带和东北信风带之中,同时可能存在东南向和西北向的古季风.

Late Cretaceous eolian dunes and wind directions in Xinjiang basin, Jiangxi Province, China.

The Tangbian Formation (K2t), middle part of the Late Cretaceous Guifeng Group in Xinjiang Basin, Jiangxi Province, has long been thought to be aqueous. However, based on our study, it is attributed to eolian. Many evidences, including purple red, well sorted and rounded, medium to fine-grained pure sandstone with little suspension load such as clay, silt and mica, well developed thick, large scale and high dip tabular planer cross-bedding characterized by eolian dune foresets and typical eolian grain surface textures such as dish-shaped impact scars, crescent-shaped impact scars and frosted surface under electronic microscope, indicate that the Tangbian Formation was deposited in eolian dune environment. The paleo-current reconstruction has proved that the dominative prevailing is westerly and second prevailing is northeasterly with a little amount of southeasterly and northwesterly. Based on the paleogeography and earth surface wind belt model, the studied area was located in the Cretaceous between north hemisphere westerlies and northeast trades and possibly influenced by southeast and northwest monsoons.