Pattern and origin of the present-day tectonic stress in the Australian sedimentary basins

Two basic factors are identified that contribute to overpressure in different sedimentary basins of the world, including the South Caspian Basin (SCB): tectonic stress and subsurface temperature. Two overpressure zones are identified in the SCB: 1. An upper zone (depth interval 600–1200 m), conditioned by disequilibrium rock compaction (undercompaction) and 2. A lower zone (zone of decompaction) conditioned by hydrocarbon generation (depth below 5 km). The lower overpressure zone is the most intense and depends on the thickness of the shale sequence, the content and type of organic matter, and the temperature conditions of kerogen transformation to hydrocarbons. In this zone the greatest risk is associated with gas generation at depths greater than 9 km, due to both more intense thermal breakdown of kerogen and the cracking of liquid hydrocarbons generated earlier. Overpressure is a major cause of diapirism and mud volcanism in SCB.

Download Full-text

Tectonic stress controls saucer-shaped sill geometry and emplacement mechanism

Geology ◽

10.1130/g47604.1 ◽

2020 ◽

Vol 48 (9) ◽

pp. 898-902

Author(s):

R.J. Walker ◽

S.P.A. Gill

Keyword(s):

Host Rock ◽

Shear Failure ◽

Sedimentary Basins ◽

Tectonic Stress ◽

Tensile Failure ◽

Magma Source ◽

Primary Control ◽

Base Length ◽

Source Pressure ◽

Emplacement Mechanism

Abstract Saucer-shaped sills are common in sedimentary basins worldwide. The saucer shape relates to asymmetric sill-tip stress distributions during intrusion caused by bending of the overburden. Most saucer-shaped sill models are constructed using a magma-analogue excess source pressure (Po) to drive host-rock failure, but without tectonic stress. Here we present axisymmetric finite-element simulations of radially propagating sills for a range of tectonic stress (σr) conditions, from horizontal tension (σr < 0) to horizontal compression (0 < σr). Response to σr falls into four regimes, based on sill geometry and failure mode of the host rock. The regimes are considered in terms of the ratio of tectonic stress versus magma source pressure R = σr/Po: (I) initially seeded sills transition to a dike during horizontal extension (R < 0); (II) with R increasing from 0 towards 1 (compressive σr), sill base length increases and sill incline decreases; (III) where 1 < R < 2, sill base length relatively decreases and sill incline increases; and (IV) where R > 2, sills grow as inclined sheets. Sills in regimes I–III grow dominantly by tensile failure of the host rock, whereas sills in regime IV grow by shear failure of the host rock. Varying σr achieves a range of sill geometries that match natural sill profiles. Tectonic stress therefore represents a primary control on saucer-shaped sill geometry and emplacement mechanism.

Download Full-text

Burial and Heat Flux Modelling along a Southern Vøring Basin Transect: Implications for the Petroleum Systems and Thermal Regimes in the Deep Mid-Norwegian Sea

Geosciences ◽

10.3390/geosciences11050190 ◽

2021 ◽

Vol 11 (5) ◽

pp. 190

Author(s):

Tiago Abreu Cunha ◽

Henrik Rasmussen ◽

Heinrich Villinger ◽

Akinniyi Akintoye Akinwumiju

Keyword(s):

Heat Flux ◽

Surface Heat Flux ◽

Sedimentary Basins ◽

Tectonic Stress ◽

Surface Heat ◽

Distal Margin ◽

Thermal Gradients ◽

Burial History ◽

Mantle Dynamics ◽

Vøring Basin

A key aspect on the evolution of rifted terranes and the prospectivity of the overlying sedimentary basins is heat. Temperature determines the deformation regime of crustal and mantle rocks and, thus, the style of rifting and geometry of rift basins. The generation of hydrocarbons from organic-rich rocks and reservoir conditions depend primarily on temperature. In this study, we model the thermal–burial history of the southern Vøring Basin (Mid-Norway Margin) along a regional transect (2-D), integrating basin- and lithospheric-scale processes. A model that accounts for the main extensional pulses that shaped the Mid-Norway Margin is in good general agreement with the present–past geothermal gradients inferred from borehole temperature and maturity data and the surface heat flux measurements in the proximal and intermediate margin. This supports a near steady-state, post-rift margin setting, following the break-up in the early Eocene. Significant discrepancies are, however, observed in the distal margin, where the borehole temperatures suggest (much) higher thermal gradients than model predicted and implied by the average surface heat flux. We speculate that the higher thermal gradients may result from deep-seated (mantle dynamics) thermal anomalies and/or recurrent hydrothermalism during periods of greater tectonic stress (regional compression and glacial loading rebound) and test the implications for the maturity of the Vøring Basin. The modelling results show, for example, that, depending on the thermal model assumptions, the depth and age of the optimal mid-Late Cretaceous source-rock horizons may vary by more than 2 km and 10 Ma, respectively.

Download Full-text

Geomechanical characterization of sedimentary basins using tectonic stress and strain

Geosciences Journal ◽

10.1007/s12303-020-0006-8 ◽

2020 ◽

Vol 24 (6) ◽

pp. 669-678

Author(s):

Uy D. Vo ◽

Chandong Chang

Keyword(s):

Sedimentary Basins ◽

Tectonic Stress ◽

Stress And Strain ◽

Geomechanical Characterization

Download Full-text

Control of obliquity directions on structural development, from rifting to inversion: Examples from the Tethyan domain

10.5194/egusphere-egu21-16343 ◽

2021 ◽

Author(s):

Oscar Fernández ◽

Adrià Ramos ◽

Jesús García-Senz ◽

Antonio Pedrera

Keyword(s):

Regional Scale ◽

Sedimentary Basins ◽

Eastern Alps ◽

Tectonic Stress ◽

Rift System ◽

Structural Development ◽

Thrust Belts ◽

Tectonic Transport ◽

Stress Orientations ◽

Tectonic Extension

Oblique rift systems form when the axis of rifting is not orthogonal to the direction of tectonic extension, normally due to pre-existing zones of weakness that influence the location and orientation of new faults. Irrespective of the regional-scale obliquity, most individual extensional faults will tend to nucleate according to the orientation of the tectonic stress orientations, and therefore normal to the direction of maximum extension. Transfer faults in oblique systems will tend to form parallel to the direction of extension and, in contrast to orthogonal rifting, will play a major role in the architecture and development of the rift and its sedimentary basins.An intriguing feature in oblique rift systems is the formation of reverse structures evocative of wrench tectonics during the syn-rifting stage. This stems from the orientation of geological structures relative to the direction of tectonic extension. Even slight changes in tectonic transport direction or stress orientations during the development of the rift system can lead to events of transpression or transtension along transfer structures. Because of the relevance of transfer structures in oblique systems, transpression can result in the appearance of discontinuities in the sedimentary record that are often interpreted as, somewhat incongruent, inversion events.Oblique structures also play a crucial role during the full inversion of the rift system during convergence, particularly so because tectonic shortening will strike at an angle to the orientation of faults. Irrespective of the evolution of oblique rifting and inversion, the initial fault pattern is also normally preserved in fully inverted systems involved in fold-and-thrust systems. In many of cases, when the original rift obliquity is not well understood, the characteristic rhomboidal pattern is interpreted to relate to wrench tectonics. &#160;In this presentation we will review evidence from Iberia, Northwestern Africa and the Eastern Alps to discuss the role that obliquity plays in rift development and its inheritance in fold-and-thrust belts with different degrees of inversion.

Download Full-text

A slow earthquake in the Santa Maria basin, California

Bulletin of the Seismological Society of America ◽

10.1785/bssa0820052087 ◽

1992 ◽

Vol 82 (5) ◽

pp. 2087-2096

Author(s):

Hiroo Kanamori ◽

Egill Hauksson

Keyword(s):

Sedimentary Basins ◽

Tectonic Stress ◽

Oil Field ◽

Period Range ◽

Santa Maria Basin ◽

Motion Data ◽

Radiated Energy ◽

Field Evidence ◽

Regional Tectonic ◽

Santa Maria

Abstract An ML = 3.5 earthquake near Santa Maria, California, was recorded by the Southern California Seismic Network and a TERRAscope station at Santa Barbara (SBC) on 31 January 1991. The waveform of this event is dominated by 2- to 5-sec waves, and is different from that of ordinary events with similar size. Inquiries into operations in several oil fields in the area revealed that hydro-fracturing at a pressure of about 80 bars was being done at a depth of 100 to 300 m in the Orcutt oil field in the Santa Maria basin from about 9 to 11 a.m. on 31 January and the earthquake occurred in the afternoon. Field evidence of 30-cm displacement to a depth of 300 m was reported. The field evidence as well as the first-motion data indicates that the event had a thrust mechanism with the P axis in the NNE - SSW direction, which is in agreement with the regional stress field. From the analysis of the SBC record and the field evidence, we conclude that the source must be shallower than 1 km and the ratio of the radiated energy to the seismic moment is about 6.2 × 10−7, one to two orders of magnitude smaller than that of ordinary earthquakes. The occurrence of this earthquake demonstrates that release of regional tectonic stress in shallow sediments can yield significant seismic radiation at periods of a few seconds, the period range of engineering importance for large structures, and has important implications for excitation of long-period ground motions from large earthquakes in sedimentary basins.

Download Full-text