Deep-water Sedimentary Structures of Yanchang Formation in Southern Ordos Basin and the Geological Significance

doi:10.19657/j.geoscience.1000-8527.2018.01.12

Abstract

Abstract:

The Chang7 member of Yanchang Formation in the southern margin of Ordos Basin develops typical gravity flow deposits. It is found that the gravity flow deposits develop various sedimentary structures in the field investigation on field outcrops, mainly including bottom layer structures, soft-sediment deformation structures. These deep-water sedimentary structure combinations can well reveal that deep-water gravity flow deposits are widely developed under the background of slope breaks in the study area. Slip-slump deposits, sandy debris flow deposits and turbidite deposits are the most widely developed types of deep-water gravity flow deposits in the study area. Slip-slump structures and soft-sediment deformation structures are the sedimentary response of triggering mechanism, while bottom layer structures are the sedimentary response of sandy debris flow deposits and turbidite deposits. After the comprehensive analysis of characteristics of a large number of tuff interlayers, plant debris developed in deep-water mudstone, a large number of light yellow mud gravel developed in deep-water sandstone and other sedimentary characteristics of the formation in the study area, it is inferred that the earthquake, volcanic eruption and seasonal floods are the most advantageous triggering factors of deep-water gravity flow deposits in the study area.

Key words: Ordos Basin, Yanchang Formation, gravity flow deposit, bottom layer structure, syngenetic deformational structure

CLC Number:

TE121.3

WANG Zhen, ZHANG Yuanfu, ZHANG Na, GAO Yong, JIAO Chaowei, BAI Yiming, ZHANG Bowen, WEI Kangqiang. Deep-water Sedimentary Structures of Yanchang Formation in Southern Ordos Basin and the Geological Significance[J]. Geoscience, 2018, 32(01): 121-132.

Figures/Tables 12

Fig.1 Tectonic units of Ordos Basin and the location of the study area

Fig.2 The outcrop sections of deep-water sedimentation and sedimentary structure characteristics of Yanchang Formation in the study area

Fig.3 Graphs showing the flute cast at the bottom of deep-water gravity flow sand of Yanchang Formation in the study area

Fig.4 Graphs showing the groove cast at the bottom of deep-water gravity flow sand of Yanchang Formation in the study area

Fig.5 The slide structure characteristics of deep-water gravity flow sand of Yanchang Formation in the study area

Fig.6 The slide cast at the bottom of deep-water gravity flow sand of Yanchang Formation in the Huluhe section in the study area

Fig.7 Graphs showing the load cast of deep-water gravity flow sand of Yanchang Formation in the study area

Fig.8 Graphs showing the flame structure of deep-water gravity flow sand of Yanchang Formation in the study area

Fig.9 Graphs showing the ball-and-pillow structure of deep-water gravity flow sand of Yanchang Formation in the study area

Fig.10 The other types of soft sedimentary deformation structures of Yanchang Formation in the study area

Fig.11 The indicative signs for the formation mechanism of the gravity flow deposit of Yanchang Formation in the study area

Fig.12 Sedimentary patterns of deep-water gravity of Yanchang Formation in southern Ordos Basin

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