HR: 0800h
AN: PP41A-0577    [Abstracts]
TI: Large-Scale Neoproterozoic Slope Instability due to Lack of Bioturbation ? A Case From the Yangtze Platform (Hunan Province, Central China)
AU: * Heubeck, C E
EM: cheubeck@zedat.fu-berlin.de
AF: Institut f�r Geologische Wissenschaften, Freie Universit�t Berlin, Malteserstrasse 74-100, Berlin, 12249 Germany
AU: Vernhet, E
EM: evernhet@zedat.fu-berlin.de
AF: Institut f�r Geologische Wissenschaften, Freie Universit�t Berlin, Malteserstrasse 74-100, Berlin, 12249 Germany
AU: Zhu, M
EM: myzhu@nigpas.ac.cn
AF: Nanjing Institute of Geology and Palaeontology, 39 Beijing Donglu, Nanjing, 210008 China
AU: Zhang, J
EM: myzhu@nigpas.ac.cn
AF: Nanjing Institute of Geology and Palaeontology, 39 Beijing Donglu, Nanjing, 210008 China
AB: Neoproterozoic and basal Cambrian strata of the Yangtze platform, China, include fossiliferous, shallow-water, stratigraphically discontinuous carbonate environments and mostly fossil-free deep-water but stratigraphically continuous siliciclastic environments. Stratigraphic sections in the slope facies of the Neoproterozoic Doushantuo Formation, mostly in southern Hunan Province, relate these two environments to each other and constrain slope geometry and processes in the time interval following the end of the Neoproterozoic glaciation. In the sections, numerous discontinuities due to slides, olistostromes, and slump folds modify the original anoxic, shaly, cherty, and phosphatic sediments. Volumetrically most significant are 10 - 60m thick sections of gently-deformed, shallow-water dolomitized grain- and packstone slide blocks which are embedded in and overlie deep-water shales with discordant, planar surfaces displaying drag features. Correlation of these contrasting lithologies and of their contacts over tens of km suggests the existence of several regional sedimentary detachment horizons on the Hunan slope. Reconstructions constrain the slides to exceeding 70 km in lateral extent and approximately 50 km in runout distance. Stratigraphically upsection, large slump folds and slide masses continue in the Liuchapo Formation and approximately to the pC-C contact. The low degree of internal deformation in the large slide sheets may be partially caused by early-cemented, brittle phosphorites acting as basal glide planes. These phosphorites contain evaporite-replacement crystals and textures; they are likely correlatable with phosphorites that form three regional marker units on the shallow-water platform and suggest the existence of restricted, shallow-water environments to the shelf edge, abutted by a steep upper slope susceptible to regional collapse. The lack of bioturbation in the Neoproterozoic and the resulting high saturation of fine-grained sediment with organic matter, fluid, and gas, along with a strongly developed primary anisotropy from suspension settling and chemical precipitation may have facilitated the initiation of sediment displacement and increased the runout distance. Concurrently developing Doushantuo-age shelf grabens in nearby Hubei Province may favor active tectonics and associated seismicity as a possible trigger mechanism over sea-level changes.
DE: 9320 Asia
DE: 9619 Precambrian
DE: 4558 Sediment transport
DE: 4802 Anoxic environments
DE: 3022 Marine sediments--processes and transport
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting