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Abstract:
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A secondary basin corresponds with a second order depositional cycle, is limited by two erosional surfaces which are also the boundaries of a seismic sequence. In other words, a secondary basin is a component of an overall sedimentary basin.
A secondary basin is formed at the same time with a tectonic phase where the three most important
factors are faulting, subsidence and uplifting. Basin-forming faults are usually normal faults and are called "syn-depositional fault".
The reconstruction of a sedimentary basin, is rather complicated, but it is very necessary for basin
analysis, facial analysis and compilation of lithofacies-paleogeographic maps, as the dimensions
and thickness of the present secondary basin are not the same as of the primitive basin. To get a true picture of the primitive basin one must carry out the following steps:
- Drawing the recontructed geologic sections
- Reconstructing the sediment thickness
- $$h_1 = h_2\roof t 3 {K.\frac {P_1}{P_2}}$$
where $h_1$ is the primitive thickness
$h_2$ is the present thickness
K is the shrinkage coefficient (depending on the rock type) -
- $P_1$ is the primitive common porosity -
$P_2$ is the present common porosity
- Reconstructing the integrated geologic-sedimentary sections: -
+ Width of the basin $$L_1=C.[L_2-\sum_{t=1}^n L_{1i}+\sum_{t=1}^mL_{2i}+\sum_{t=1}^fL_{3i}]$$ where $C$ is a correction coefficient: $C=l.25$ (digenetic stage), 1.55 (catagenetic stage) and 1.9 (metagenetic stage).
+ Thickness of the basin: $H_1 = ch_2$
- Reconstructing the boundaries of the basin
- Reconstructing the isopach map
- Compiling the lithofacies-paleogeographic map. |