Subaqueous mass-transport processes, including gravity-induced slides, slumps and debris flows, are one of the mechanisms for transport of sediment into the deep sea.

Systematic study of morphologies, textures and depositional structures in mass-transport deposits (MTDs), as well as associated sedimentary lithofacies, can also help to reveal aspects of tectonic evolution and sedimentary history of basins. 

Dr. LI Wenjie and Prof. CHEN Jitao from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) and their American cooperators investigated the multi-bedded carbonate MTDs from mid- and late-Darriwilian to early-Sandbian from the aspects of sedimentology and stratigraphy in the Wuhai area, Inner Mongolia, China.

The study was published in Sedimentology.

Internal structures and depositional processes of carbonate MTDs are relatively poorly understood compared with siliciclastic facies due to their comparative paucity in the rock record.

Moreover, it is challenging to decipher the evolution and internal features of MTDs using remotely-sensed data and drill cores of modern deposits. Accordingly, outcrop-scale study on carbonate MTDs is one important work of sedimentologists.

In this study, the researchers measured and described the Kelimoli and Wulalike formations of several sections at centimeter scale. They described the MTDs layers in detail, measured hundreds of proxies of paleoslope orientation indicators, and made line drawings in the field and laboratory to illustrate the soft-sediment deformation structures (SSDS).

According to the data and field observation, they concluded the deformational succession of carbonate slump structures, and several unique sedimentary models of carbonate mass flow.

Tectonic events related to passive to foreland basin transitions, and associated platform foundering and steepening of the slope were proposed to be the trigger mechanism of the deposition of these MTDs.  

These findings improved the understanding of transport mechanisms of carbonate MTDs and provided a template for predicting deformational trends of other ancient carbonate slope mass movements. The stratigraphic and facies model may be applicable to the tectonic history of sedimentary basin analysis and unconventional hydrocarbon resource (such as shale gas) exploration of the western margin of North China.

This research was supported by the Strategic Priority Research Program (B) of Chinese Academy of Sciences and National Science Foundation of the United States. 

Fig.1  Imbricated beds and folds of the Kelimoli Formation at the Xilaifeng section (Image by NIGPAS)

Fig. 2 Breccia-filled channels of the Wulalike Formation at the Yixiantian section (Image by NIGPAS)

Fig. 3 Facies model of coarse-grained calciclastic submarine channels formed in steep siliciclastic slope settings (Image by NIGPAS)