Sediment deformation in Miocene and post-Miocene strata, Northeastern Brazil: Evidence for paleoseismicity in a passive margin

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil

“…Lithologically, unit PB1 is typically composed of golden yellow endured sandstones and breccias either with massive bedding or a large variety of ductile and brittle deformation structures (i.e., massive sandstones with isolated sand fragments and breccias, undulatory strata, sand dykes and diapirs, sinks and bowls, pebbly pockets, plunged sediment mixtures, fitted sand masses, cone-shaped cracks, fault grading and sedimentary enclaves). These features, fully described and illustrated in Rossetti et al (2011), have been related by these authors to seismic shocks of high surface-wave magnitude (i.e., Ms>5 or 6) that took place contemporaneous to or shortly after sediment deposition. Unit PB1 also includes a large volume of non-indured and undeformed deposits.…”

“…Noteworthy is that tectonic deformation disrupted this paleosol and the underlying strata, as recorded by faults, joints and, secondarily folds, the latter being particularly abundant in exposures located in the Conde-Garapu Horst (see figures 3 and 4 of Rossetti et al 2011). The process of paleosol formation was so intense that it locally altered the entire profiles to produce highly oxidized strata.…”

“…Rossetti et al 2011) formed on the top of the Barreiras Formation. Therefore, the stratigraphic position of these deposits will be reviewed in the light of new stratigraphic and sedimentological data presented herein.…”

“…These include sharply bounded, fining upward massive or stratified conglomerates and sandstones interbedded with mudstones, as well as massive, poorly sorted sandstones commonly with dispersed granules and clasts of laterite concretions. These strata are related to fluvial environments and debris flows, though they might include nearshore marine-influenced strata in areas located nearby the modern coastline, as suggested by the presence of burrows such as Skolithos, Thalassinoides, Planolites, Diplocraterion, and Teichichnus (Rossetti et al 2011).…”

Soft Sediment Deformation Structures Triggered by the Earthquakes: Response to the High Frequent Tectonic Events during the Main Tectonic Movements

“…While the soft sediments (mud, soft siliceous sediment and carbonate ooze) with the grain size are less than 0.005 mm, the strength of finegrain sediments and clays decrease owing to seismic shear stress effect, resulting in the complex rheological phenomenon that occurs ( Figure 10C). Three axis vibration test of saturated soft soil presents when the seismic intensity is 7 or greater (amount to the earthquake magnitude is 5.6), and muds usually do not be liquefied but it happens with thixotropic flow, which is triggered by shocking [55,56]. The earthquake magnitude for thixotropic deformation is higher than liquefied deformation [57].…”