Evolution of Early Palaeozoic Carbonate Platform, South Qinling Mt.

Cui Zhilin; Mei Zhichao; Meng Qingren; Qu Hongjun

Early Palaeozoic carbonate platform of South Qinling Mt. was developed on the north passive mar-gin of the Yangtze plate. Cambrian and Ordovician carbonate stratigraphy, more than 2000 metres inthickness, is outcropped between Shanyang-Fengzhen Fault and Ningshan-Baihe Fault(Fig. 1).Fiv a fu-ties associations are recogrrized, including anoxic /dysaerobic facies association(A1)，deeper ramp /slopefacies association(A 2)，Shoal facies association(A3)，lagoon and tidal}lat facies association(A 4) andmixed shelf facies association(Fig. 2)·Evolution of the carbonate platform is divided into three phases(Fig.3).Middle Cambrian-Early Ordovician rimmed shelf phase is characterised by oc currence of asouth edge builtup of shoal facies association up to 500 metres in thickness and a south slope of nodularlim es tone,micritic limestone, clay shale and breccias. Inner platform deposits are composed of cyclic la-goonal massive dolostone and laminated dolostone, recording small-scale sea-level changer. Evident fallin sea level resulted from tectonic uplift led to existence of late Early Ordovician palaeokarst and karstconglomerates, which are cupped by Middle-Late Ordovician mixed shelf facies association of the thirdphase containing a transgressive and regressive cyde.Horizontal distributinn of facies zones proves lee side of platform northward and wind side sonth-w ard. It als oimpli esprobably submergedthat there was a possible ancient land on north side of platform(Fig.4)，but it wasunder Shanyang-Fengzhen Fault afterwards.

Department of Geology Northwest University Xi'an 710069;

2 Institute of Geophysics Chinese Academy of Sciences Beijing 100083

Received Date: 1995-05-20

Publish Date: 1997-03-10

Key words:

Abstract: Early Palaeozoic carbonate platform of South Qinling Mt. was developed on the north passive mar-gin of the Yangtze plate. Cambrian and Ordovician carbonate stratigraphy, more than 2000 metres inthickness, is outcropped between Shanyang-Fengzhen Fault and Ningshan-Baihe Fault(Fig. 1).Fiv a fu-ties associations are recogrrized, including anoxic /dysaerobic facies association(A1)，deeper ramp /slopefacies association(A 2)，Shoal facies association(A3)，lagoon and tidal}lat facies association(A 4) andmixed shelf facies association(Fig. 2)·Evolution of the carbonate platform is divided into three phases(Fig.3).Middle Cambrian-Early Ordovician rimmed shelf phase is characterised by oc currence of asouth edge builtup of shoal facies association up to 500 metres in thickness and a south slope of nodularlim es tone,micritic limestone, clay shale and breccias. Inner platform deposits are composed of cyclic la-goonal massive dolostone and laminated dolostone, recording small-scale sea-level changer. Evident fallin sea level resulted from tectonic uplift led to existence of late Early Ordovician palaeokarst and karstconglomerates, which are cupped by Middle-Late Ordovician mixed shelf facies association of the thirdphase containing a transgressive and regressive cyde.Horizontal distributinn of facies zones proves lee side of platform northward and wind side sonth-w ard. It als oimpli esprobably submergedthat there was a possible ancient land on north side of platform(Fig.4)，but it wasunder Shanyang-Fengzhen Fault afterwards.

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Evolution of Early Palaeozoic Carbonate Platform, South Qinling Mt.

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