%0 Journal Article
%A Alonso Zarza, Ana María
%A Zhao, Z.
%A Song, C. H.
%A Li, J. J.
%A Zhang, J.
%A Martín Pérez, Andrea
%A Martín García, Rebeca
%A Wang, X. X.
%A Zhang, Y.
%A Zhang, M. H.
%T Mudflat/distal fan and shallow lake sedimentation (upper Vallesian–Turolian) in the Tianshui Basin, Central China: Evidence against the late Miocene eolian loess
%D 2009
%@ 0037-0738
%U https://hdl.handle.net/20.500.14352/43650
%X The Tianshui Basin in central China contains a thick sedimentary sequence (~1400 m) of continentaldeposits, Aragonian to Villafranchian (Miocene-Pliocene) in age. Intense Himalayan movements around thePaleogene/Miocene boundary triggered the uplift of mountain ranges around the Tianshui Basin, providingthe deposition site for continental sediments. The sedimentary infill of the basin consists of four stratigraphic units (I to IV). This paper focuses on Unit II. Most of the accommodation space was occupied by Unit I, so during the sedimentation of Unit II, the morphology of the basin was relatively flat, promoting thedevelopment of wide distal fan/mudflat areas and wide shallow lakes. Deposits include: red mudstones,pedogenic and groundwater calcretes, reworked calcrete deposits, sheet-floods, fluvial channels, rippledsandstones/siltstones, ooidal/peloidal packstones, palustrine limestones, bioturbated marls and intraclasticlimestones/marls. The characteristics and organization of the deposits indicate the gradual transition fromalluvial to lake environments. Within the distal fan/mudflat, the deposition of reworked calcrete clasts as oneof the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and redclays. At the lake margins, the presence of ooids and palustrine limestones suggests the possibility of ramplikemargins within different energy settings. The origin of some of the deposits of the basin's QA-I section isunder discussion, and their consideration as eolian has been recently proposed. However, we believe thispossibility is precluded by the characteristics of the deposits. Our proposal has important implications forrevising the interpretation of Miocene paleoclimatic conditions in central Asia.
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