5th Swiss Geoscience Meeting, Geneva 2007
Use of subsidence curves in a geodynamic frame
Wilhem Caroline*, Hochard Cyril* & Stampfli Gérard M.*
*Institut de Géologie et de Paléontologie, Anthropole, Université de Lausanne, CH1015 Lausanne (Caroline.Wilhem@unil.ch)
The usefulness of subsidence curves as a constraint on geodynamic modelling
does not need to be proved. However, the application of subsidence curves in
the development of geodynamic scenarios is a field that has still to be explored.
Ziegler and Cloetingh (2004) summarized the state of knowledge on the
dynamic processes that control the evolution of extensional basins. Lithospheric
stretching induces tectonic subsidence (isostatic adjustment) and thermal uplift
(astenospheric upwelling) during the syn-rift stage followed by thermal
reequilibration during the post-rift stage. Rifted basins may develop in different
tectonic settings such as a stable continent, a back-arc, a syn-orogenic or a
post-orogenic environment. The geodynamic context in which tectonic events
take place is deduced by the compilation of various types of geological data
(stratigraphy, geochemistry, faunal provincialism, geochronology…).
Subsidence curves shed light on the evolution in space and time of stratigraphic
series. Coupling the latter with more conventional methods allows better
constraining of the timing and modalities of the geodynamic events that affected
a given area. Therefore, the subsidence curves are an excellent tool to interpret
the stratigraphic data in terms of tectonic events.
Hochard (2006) created a Geodynamic Information Database (GIDB) developed
in ArcGis 9.2. This geodatabase integrate geological data necessary to
elaborate the paleo-geodynamic reconstructions. On this base, a new module of
subsidence analysis has been added. This module is made of three main
components that describe the data and the stages necessary for the
subsidence analysis. These components are inter-connected geographic tables
characterised by their own parameters. The first one named “Subsidence
Curves” contains all the subsidence curves compiled from the literature. The
second one named “Subsidence Compilations” allows assembling several
curves (different ages and close from each other) in one synthetic curve
representing a same tectonostratigraphic unit (terrane) or a part of it. The third
one named “Subsidence Events” enumerates all the possible dynamic
interpretation for the different trends of subsidence curves. The incorporation of
this module in the GIDB allows bringing a geodynamic interpretation to the
subsidence analysis. The scheme presented below (Fig. 1) describes the part of
the GIBD concerning the subsidence analysis.
The investigated area belongs to the Central Asian Orogenic Belt (CAOB)
situated between the Siberian craton and the assemblage constituted by the
North China and the Tarim blocks. This belt is a large accretionary complex
formed between 1000 Ma and 250 Ma (closure of the Paleoasian Ocean) by the
collage of different kinds of tectonostratigraphic terranes: island arc, seamounts
and microcontinents (Windley et al., 2007). The plurality and the diversity of the
tectonostratigraphic terranes and paleo-basins witness the tectonic complexity
of the area. Therefore, the subsidence analysis is a very useful tool to constrain
5th Swiss Geoscience Meeting, Geneva 2007
the timing of the geodynamic events. Practically, the idea that different terranes
may share common dynamic events during some stages and undergo different
ones during some other stages of their existence is reflected in the trend of the
subsidence curves. The comparison and correlation of the subsidence
signatures within the same tectonostratigraphic unit and between different units
allow at first the characterisation of the answers to a single phenomenon, and
then the possible identification of this phenomenon over large areas. The
preliminary investigation that allows choosing the key area for this work was
done by establishing a terrane map of this region and a set of well-constrained
geodynamic reconstructions (Stampfli et al., in prep.).
Figure 1. Geodatabase scheme of the subsidence analysis.
REFERENCES
Hochard, C. & Stampfli, G.M. 2006: Paleogeodynamic reconstructions concepts
and examples; using GIS and database. poster at the EGU General Assembly,
Vienna.
Windley, B.F., Alexeiev, D., Xiao, W., Kroener, A. & Badarch, G. 2007: Tectonic
models for accretion of the Central Asian orogenic belt. Journal of the
Geological Society of London, 164, 31-47.
Ziegler, P.A. & Cloetingh, S. 2004: Dynamic processes controlling evolution of
rifted basins. Earth-Science Reviews, 64, 1-50.