in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
Sedimentary Facies of the Upper Jurassic Suining and Penglaizhen
Formations in the Central Sichuan Basin, SW China
Xiaoping Xie 1* , Yongdong Wang 2 , Bihong Fu 3
1. School of Geography and Tourism, Qufu Normal University, Qufu 273165, China
2. Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China (E-mail: xp.xie@163.net)
The Sichuan basin extends for 1000 km E-W and
500 km N-S, and is mainly filled with Mesozoic
continental redbeds. The upper Jurassic strata are of
terrestrial origin and extensively distributed in the
Sichuan Basin, which are subdivided into the Suining
and the Penglaizhen Formations, ascendingly (Xia et al.,
1982). The Suining Formation deposits are mainly of
brownish-red mud and brownish-red siltstones, where-
as the Penglaizhen Formation consists of sandstones
and mudstones. Both of these two formations are con-
formably contacted (Fig.1). The Penglaizhen Forma-
tion disconformably underlies the Lower Cretaceous
Cangxi Formation (Fig.2), and is assigned to the Late
Jurassic on the basis of abundant ostracods such as
Darwinula oblonga and Darwinula leguminella
(Bureau of Geology and Mineral Resources of Sichuan
Province, 1982, 1991).
Fig.1 The boundary between tSuining and Penglaizhen
formations cropped out near Suining City, Sichuan Province
Fig.2 The boundary between the Upper Jurassic
Penglaizhen Formation and the Lower Cretaceous Cangxi
Formation in Santai County, Sichuan Province
The sedimentary facies features and sedimentary
structures are synthetically analyzed in order to clarify
the sedimentary environment and evolution of the
central Shichuan Basin during the Later Jurassic
episode. Our study results show that the basin is widely
covered with a set of lacustrine grayish to reddish,
purple-red mudstone or shale interbedded with feld-
spathic fine-grained sandstone, and these deposited
beds are nearly horizontal occurrence. The sedimentary
particles are relatively fine-grained both in the Suining
and Penglaizhen Formations, showing that the
tectogenesis is relatively stable during the Late Jurassic
Epoch (Wu et al., 2003; Wang et al., 2001). However,
in the Late Jurassic of Penglaizhen stage, the basin is
characterized by widely-spread varigrained and vari-
colored thick sandstone, mudstone and fine
conglomerate of river or alluvial fan subfacies, and
there are usually sediments and coarse sedimentary
particles of relatively large thickness in the Upper
Jurassic, reflecting rapid uplift of the mountains around
the basin. According to the study of sedimentary
structure, sediment particles and colors, the central
Sichuan Basin should have undergone a warm climate
during the Suining stage and hot climate from the
beginning of the Penglaizhen stage.
The sedimentary environment of the Suining
Formation in early Late Jurassic epoch in this area is
mainly considered as permanent lake, marsh and
floodplain, however, the sedimentary environment of
the Penglaizhen Formation in late Late Jurassic epoch
is mainly considered as a floodplain, seasonal lake and
intermittent lake (Fig.3).
Fig.3 Sketch map of paleogeography of the Late Jurassic in
the Sichuan Basin, China
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