Abstract
Abstract Soft-sediment deformation (SSD) structures are widespread in the sedimentary record, and numerous triggering mechanisms can induce its development, including glaciation, earthquakes, overloading, ground-water fluctuations, and wave movement. The Late Cretaceous Uberaba Formation preserves SSD structures as small- and large-scale load casts and associated flame structures, pseudonodules, and convolute laminations observed in the contact of three well-defined intervals among fine- to coarse-grained lithic and conglomeratic sandstone with fine-grained arkose and mudstone beds. Based on the morphology of the SSD structures, sedimentary facies of the Uberaba Formation, and similarities with previous observations in the geological record and laboratory models, these features are assigned to liquefaction-fluidization processes as the major deformational mechanism triggered by seismic and aseismic agents. We propose that a deformation occurred just after the sedimentation triggered by seismic shock waves and overloading, induced by the sudden deposition of coarse-grained sandy debris on fine-grained sediments. Some of these structures can be classified as seismites, providing evidence of intraplate seismicity within the inner part of the South American Platform during the Late Cretaceous. This seismic activity is likely related to the uplift of the Alto Paranaiba High along reactivations of regional structures inherited from Proterozoic crustal discontinuities and coeval explosive magmatism of the Minas-Goias Alkaline Province.
Highlights
Soft-sediment deformation structures are conspicuous features found in both ancient and modern, shallowly buried, loose, and water saturated sediments (Allen 1982, Owen 1987)
The northeastern border of the basin was affected by the uplift of the Alto Paranaíba High and plutono-volcanic magmatism of the Minas-Goiás Alkaline Province
At least three distinct surfaces along the contact between lithic sandstone and conglomerate with fine-grained arkose and mudstone contain widespread soft-sediment deformations interbedded with undeformed strata
Summary
Soft-sediment deformation structures are conspicuous features found in both ancient and modern, shallowly buried, loose, and water saturated sediments (Allen 1982, Owen 1987). A wide range of natural triggers, including bioturbation, flooding, overloading, sudden oscillations of groundwater, slumping, storm waves, or seismic shaking (Lowe 1975, Allen 1986, Owen 1987, Shiki et al 2000, van Loon 2009, Owen et al 2011) can lead to the development of these structures In the latter case, when liquefaction and/or fluidization are related to seismic activity, they can be designated as seismites (Seilacher 1969, 1984, 1991, Gibert et al 2011, Moura-Lima et al 2011, Rossetti et al 2011). We explore the geological evolution of alkaline provinces and structural uplifts that affected the Bauru Basin, aiming to associate tectonic and/or regional magmatic events with the intraplate tectonic activity
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