Sequence architecture and sedimentary characteristics of a Middle Jurassic incised valley, western Sichuan depression, China

Jun-Long Liu,Fu-Xiang Huang,Wei Yin,Hai-Yue Yu,Tian-Yun Wang,You-Liang Ji,Wen-Shu Li

doi:10.1007/s12182-017-0211-0

Abstract

The Middle Jurassic Shaximiao Formation encompasses tens of meters of thick lowstand meandering valley (LMV) strata in the western Sichuan foreland basin. Ancient LMVs newly discovered in this area were further studied based on sequence stratigraphy and seismic sedimentology. The aim of the present study was to investigate the sedimentary characteristics, sequence architecture, and the controls on LMV deposition in this tectonically active basin using field survey data, seismic sections, seismic amplitude imaging, core description, and comprehensive application of drilling data. The results show the following: (1) Three regional sequence boundaries and two flooding surfaces were recognized, and the Shaximiao Formation was divided into two-third-order sequences and four systems tracts. (2) Three sedimentary facies associations were identified: incised valley-fill, tributary channel, and overbank facies. Incised valleys are 5–17 km wide, 20–60 m deep and traceable for 120 km along their axes. (3) In the downstream segment, the role of tectonism gradually diminishes, and periodic base-level changes control the form and evolution of the incised valleys. Three types of LMVs—A1, A2, and A3—developed with changes in base level (lake level); of these types, the base level of the A3 LMV was likely the lowest.

Highlights

Incised valleys have been widely discussed in terms of traditional depositional models (Vail et al 1977; Posamentier and Vail 1988; Van Wagoner et al 1988; Zaitlin et al 1994; Willis 1997; Veiga et al 2002; Catuneanu 2006; Catuneanu et al 2009); detailed analysis of Edited by Jie HaoThe Jurassic Shaximiao (J2s) Formation was deposited during a stable tectonic period in the western Sichuan foreland basin
The results show the following: (1) Three regional sequence boundaries and two flooding surfaces were recognized, and the Shaximiao Formation was divided into two-third-order sequences and four systems tracts
Based on Catuneanu’s depositional sequence scheme (Catuneanu 2006), three regional sequence boundaries (SB) and two flooding surfaces (FS) were recognized, and the Shaximiao Formation was divided into two-third-order sequences (SQ1 and Sequence 2 (SQ2)) with four systems tracts and several parasequences (Table 1, Fig. 5)

Summary

Introduction

Incised valleys have been widely discussed in terms of traditional depositional models (Vail et al 1977; Posamentier and Vail 1988; Van Wagoner et al 1988; Zaitlin et al 1994; Willis 1997; Veiga et al 2002; Catuneanu 2006; Catuneanu et al 2009); detailed analysis of Edited by Jie HaoThe Jurassic Shaximiao (J2s) Formation was deposited during a stable tectonic period in the western Sichuan foreland basin. Through integrating previous interpretations with applications of sequence stratigraphy and seismic sedimentology, researchers identified lowstand meandering valleys (LMVs) in this area (Zhu 2009; Li 2011; Qian et al 2012). Previous studies have described the distribution patterns of the sedimentary environments and depositional facies of the Shaximiao Formation in this area; these. (1) Horizontal 3D seismic slices reveal the abnormality of infilled incised valleys, which were approximately 10 km in width during the early depositional periods of both members of the formation; this finding may contradict the interpretation that the Shaximiao Formation was deposited by classical meandering rivers. Further investigations are needed to identify the sequence architecture and sedimentary characteristics of these LMVs

Objectives

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Discussion

Conclusion