341 Sediments, Clastic (Posters)

Wednesday, 28 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

A MODERN ANALOG FOR RIVER-DELTA SYSTEM STRONGLY AFFECTED BY MONSOON PRECIPITATION IN SEMI-ARID AREA FROM DAIHAI LAKE, NORTH CHINA: IMPLICATIONS FOR MORPHODYNAMICS OF FROUDE SUPERCRITICAL FLOW

Paper number: 341-27
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

This paper focuses on the effects of strongly seasonal and yearly variable precipitation patterns in a semi-arid area. Specifically, it explores the effects on a modern river-delta system, Daihai Lake, north China, what concerns their dynamics, and the resultant sedimentary facies and architectural properties.

Daihai Lake is a hydrological closed basin with a maximum length of 18 km and a maximum width of 10km encompassing an area of 150km2.It is located in Inner Mongolia, northern China which a semi-arid zone with an average yearly precipitation in 350mm. Furthermore, most of the annual precipitation falls in a few downpours that last from only hours to days, transform rivers into particularly flashy systems that transmit nearly 100% of their water and sediment discharge during high-intensity floods. These rivers of the drainage built 13 deltas (lobes) along the margin of the lake. In this study, Bantanzi river-delta system, one of these surrounding systems was choose to dissect. To achieve the original purpose, detailed geological information were collected from flied, which include 29 trenches with a depth of 1.5-2.0m, river cut bank section with 1.2km in length and 1.8m in height, and 5 profiles of ground-penetrating radar (GPR) with a total length of 4km.

As a result of high-intensity floods, deposits of this river-delta system are dominated by flashflood deposits. They consist of more than 80-100% of Froude transcritical and supercritical sedimentary structures at a high deposition rate, such as backset cross strata, scour and fill structures, gradational planar laminations, convex-up low-angle bedforms, convolute beddings, and even small scale cyclic steps bedforms, as a result of the high flow velocities and sharp-peaked flood hydrograph. These Froude transcritical and supercritical structures occur consequent and distinct along the cut-bank section from proximal to distal which benefits to analyze the morphodynamics of upper flow regime. Low-angle downstream accretion and aggradational packages instead of well-developed macroforms or bar forms are the recognizable architectural characteristics. These depositional units are commonly capped by mud drapes which commonly show desiccation cracks.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-287985

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