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Soft‐sediment deformation structures from the Alcântara Formation (late Albian to Cenomanian), São Luís Basin, northern Brazil, consist of (1) contorted structures, which include convolute folds, ball‐and‐pillow structures, concave‐up paths with consolidation lamination, recumbently folded cross‐stratification and irregular convolute stratification that grades into massive beds; (2) intruded structures, which include pillars, dykes, cusps and subsidence lobes; and (3) brittle structures, represented by fractures and faults displaying planes with a delicate, ragged morphology and sharp peaks. These structures result from a complex combination of processes, mostly including reverse density gradients, fluidization and liquefaction. Reverse density gradients, promoted by differential liquefaction associated with different degrees of sediment compaction, led to the genesis of convolute folds. More intense deformation promoted the development of ball‐and‐pillow structures, subsidence lobes and sand rolls, which are attributed to denser, and thus more compacted (less liquefied), portions that sank down into less dense, more liquefied sediments. Irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation. The subsidence of beds was accompanied by lateral current drag and fluid escape from water‐saturated sands. In addition, the fractures and faults record brittle deformation penecontemporaneous with sediment deposition. All these mechanisms were triggered by a seismic agent, as suggested by a combination of criteria, including (1) the position of the study area at the edge of a major strike‐slip fault zone that was reactivated several times from the Albian to the Holocene; (2) a relative increase in the degree of deformation in sites located closer to the fault zone; (3) continuity of the deformed beds over large distances (several kilometres); (4) restriction of soft‐sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata; (5) recurrence through time; and (6) similarities to many other earthquake‐induced deformational structures.

ABSTRACT. As the number of phylogeographic studies on Amazonian birds increases, spatially and temporally different scenarios are gradually replacing previous interpretations of Amazonian historical biogeography. At the same time, recent studies have improved significantly our understanding of Amazonian geological history during the late Tertiary and Quaternary, two periods regarded as critical for the recent diversification of the Amazonian avifauna. The notion that geologically older and more stable areas of Amazonia (such as the Brazilian and Guianan shields) functioned as "species-pumps", whereas geologically more dynamic areas (such as the western Amazonian lowlands) mostly "captured" part of the diversity generated nearby, was supported by a recent phylogeographic study focusing on a species complex of the genus Xiphorhynchus (Dendrocolaptidae). Here, I review 14 recent additional molecular datasets to assess whether this historical scenario can be extended to other lineages of Amazonian birds as well. The reviewed datasets indicated, among other things, a clear dichotomy in the diversification histories of species associated with seasonally flooded versus upland forests, and those with high versus low dispersal capabilities. Many "core" lineages of upland species found nowadays in western Amazonia are clearly associated with more basal lineages from the Brazilian shield, Guianan shield, and the Andes, indicating a more recent history in this geologically dynamic region. On the other hand, lineages associated with seasonally flooded forests seem to have an ancient history in western Amazonia, apparently expanding over the geologically more stable areas only recently. Most sister taxa of the reviewed lineages exhibited levels of pairwise sequence divergence consistent with splitting events dating back to a time frame stretching from the late Miocene to the early Pleistocene (late Tertiary and early Quaternary periods), a period when significant physiographic and landscape changes took place in Amazonia. When interpreted together, all reviewed studies provide evidence that geology and landscape evolution are tightly linked with the timing and mode of differentiation of Amazonian birds.

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