32 research outputs found
Formulation of reference solutions for compaction process in sedimentary basins
This paper is devoted to the development of semianalytical solutions for the deformation induced by gravitational compaction in sedimentary basins. Formulated within the framework of coupled plasticity–viscoplasticity at large strains, the modeling dedicates special emphasis to the effects of material densification associated with large irreversible porosity changes on the stiffness and hardening of the sediment material. At material level, the purely mechanical compaction taking place in the upper layers of the basin is handled in the context of finite elastoplasticity, whereas the viscoplastic component of behavior is intended to address creep-like deformation resulting from chemomechanical that prevails at deeper layers. Semianalytical solutions describing the evolution of mechanical state of the sedimentary basin along both the accretion and postaccretion periods are presented in the simplified oedometric setting. These solutions can be viewed as reference solutions for verification and benchmarks of basin simulators. The proposed approach may reveal suitable for parametric analyses because it requires only standard mathematics-based software for PDE system resolution. The numerical illustrations provide a quantitative comparison between the derived solutions and finite element predictions from an appropriate basin simulator, thus showing the ability of the approach to accurately capture essential features of basin deformation
Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain
Buntsandstein deposits generated in a slowly
subsiding basin on the western margin of the Iberian
Chain are represented by a stratigraphic succession of
fluvial deposits less than 100 m thick (conglomerates,
sandstones, and shales). Diagenetic processes in sandstones
can be grouped as eodiagenetic, mesodiagenetic,
and telodiagenetic. Eodiagenesis can be associated
with Muschelkalk, Keuper, and probably early Jurassic
times. Mesodiagenesis is probably related to
Jurassic times. Diagenetic chemical reactions suggest a
maximum burial less than 1.5 km and low temperatures
(<120ºC). Patterns of porosity reduction by
compaction and cementation suggest four diagenetic
stages: (1) Loss of primary porosity by early
mechanical compaction; (2) early cementation (Kfeldspar
and dolomite); (3) dissolution of cements; and
(4) framework collapse by re-compaction. These stages
are manifested by the presence of two types of sandstone.
Type I sandstones present high intergranular
volume (mean, 30%). Type II sandstones are characterized
by high compactional porosity loss and exhibit
low values of intergranular volume (mean, 16.9%).
Type II sandstones are associated with the dissolution
of cement and later re-compaction of type I sandstones.
An intermediate telodiagenetic phase is deduced
and related to the sharp unconformity between
Lower Cretaceous sediments and the underlying sediments.
This suggests that a mechanically unstable
framework collapsed during the Cretaceous, generating
type II sandstones. The analyzed diagenetic paths have
a wide applicability on similar marginal areas of rift
basins