对腾格里沙漠东南缘格状沙丘主、副梁和新月形沙丘表面气流的野外观测发现分离流、附着未偏向流和附着偏向流等3种背风坡次生气流。前者以弱的反向流为特征,多发生在横向气流条件下,坡度较陡的背风坡上;后二者具有相对高的风速,多发生在坡度缓和的背风坡上,其方向在横向气流条件下保持原来的方向,在斜向气流作用下发生偏转,且其强度为原始风入射角的余弦函数。根据3种次生气流强度、方向等特征,阐述了其相应的风成沉积过程和可能产生的层理类型,并对利用风成交错层理恢复古气流环境中的有关问题作了初步探讨。
Data from different types of dunes suggest that the near surface air-flow over dune lee side varied with dune morphology and primary wind direction relative to dune crest-line. It is found that three types of secondary air-flow exist according to their directions and magnitudes, they are: return flow, attached and not deflected flow, and attached and deflected flow. Return flow, characterized by lower velocity, occurred on stepper lee slops in transverse flow conditions; attached flow with higher wind velocity occurred on gentle lee slops. The attached flow could be deflected in the oblique primary wind environment but not deflected in transverse flow conditions, and its magnitude is the cosine function of primary wind direction relative to dunes . According to the nature of three types of secondary flow, the authors expound the corresponding sedimentary processes and possible stratification types, and also discuss the aeolian cross-strata as an indicator of paleowind environment.
[1] Hunter R E. Basic types of stratification in small aeolian sand dunes[J]. Sedimentology, 1977 24: 361-388.
[2] Kocurek G, Dott Jr R H. Distinction and uses of stratification types in the interpretation of eolian sand[J]. J. Setiment. Petro
[3] Phy K, Tsoar H. Aeolian sand and Sand Dunes[M]. London: Unwin Hyman,1990. 392.
[4] Lancaster N. Geomorphology of Desert Dunes[M]. London: Routaledge, 1995.345.
[5] Hoyt J H. Air and sand movement in the lee of eolian sand dunes[J].Sedimentology 1966,7:137-144.
[6] Franck a, Kocurek G.Lee side airflow model of aeolian sand dunes[J]. Sedimentology 1996,451-458.
[7] Hunter R A. Kinematic model for the structure of lee-side deposition[J]. Sedimentarology,1985,32:409-422.
[8] Anderson R S. The pattern of grainfall deposition in the lee of eolian dunes[J]. Sedimentology, 1988, 35:175-185.
[9] McDonald R R, Anderson R S. Experimental verification of aeolian saltation and lee side deposition models[J]. Sedimentology, 1995, 42:39-56.
[10] Howard A D. Effect of slope on the threshold of motion and its application to orientation of wind ripples[J]. Geol. Soc. Am. Bull, 1977, 88:853-856.
[11] Havholm K, Kocurek G. A preliminary study of the dynamics of the modern draa, Algodonis, southeastern California,USA[J]. Sedimentology,1988, 35: 649-669.
[12] Lancaster N. The dynamics of star dunes: an example from the Gran Desieerto, Mexico[J]. Sedimentology, 1989,36:273-289.
[13] Jackson P S and Hunt J C R. Turbulent winds flow over a low hill[J].Q.J.R.Metro.Soc.1975, 101: 939-955.
[14] Tsoar H. Dynamic processes acting on a longitudinal (seif) dune[J]. Sedimentology,1983, 30: 567-578 .
[15] Sweet M L , Kocurek G. An empirical model of aeolian dune lee-face airflow[J]. Sedimentary Geology, 1990,37:1023-1038.
[16] Rubin D, Hunter R.Reconstractig bedforms from compound cross-bedding. In:Brookfield M E,Ahlbrandt T S. Eolian Sediment and Processes. Amsterdam: Elsever, 1983.407-427.
[17] Tsoer H,Yaalon D H. deflection of sand movement a long-itudinal (seif)dune:Use of fluorescent dye as a tracer [J]. Sedimentology, 1983,36:25-39.
[18] Handisty J, Whitehouse R J S. Evidence for a new sand tran-sport process from experiments on Saharan dunes[J]. Nature, 1988, 332:532-534 .
[19] Fryberger S G. Dune forms and wind regime. In: McKee E D. A Study of Global Sand Seas. Washington: Prof. Pap. US Geol. Surv. 1052,1979.137-169.
