The Mapepe Formation of the Fig Tree Group in the southern part of the Barberton Greenstone Belt (BGB) includes three major petrologic suites:(1) volcaniclastic rocks, (2) terrigenous rocks, and (3) chemical or precipitative deposits. These comprise three lithofacies associations reflecting the main elements of the Mapepe deposystem: (a) a basinal association, composed of fine tuff, mud, and, locally, banded ferruginous chert, jasper, and iron formation, that accumulated under quiet subaqueous conditions; (b) a fan-delta association composed of sandstone and conglomerate deposited adjacent to uplifts; and (c) a shallow-water association, including chert, jasper, bedded barite, and terrigenous and volcaniclastic units. Terrigenous sediments in the Mapepe Formation were eroded from underlying Onverwacht Group and penecontemporaneous felsic volcanic rocks. The composition of the detritus changes up section. The lowest conglomerates lack clasts of felsic volcanic rock and vary in composition from outcrop to outcrop, reflecting derivation from local, immediately underlying greenstone sources. Higher units are regionally more uniform in composition and contain clasts representing both deeper levels of erosion and felsic volcanic sources. The absence of sediment eroded from metamorphic rocks or plutonic rocks and the uniformly low detrital quartz content of Mapepe sandstones suggest that tonalitic plutons were not widely exposed in Mapepe time.The earliest Mapepe deposystem consisted of a single large basin in southeastern parts of the BGB that accumulated iron formation and ferruginous sediments. During middle Mapepe time, this basin was divided by the nascent Onverwacht anticline. Middle and late Mapepe sedimentation occurred within paired foreland basins lying along the northwestern and southeastern margins of the BGB and separated by a structural and topographic high marking the Onverwacht anticline, which may have developed as a shared forebulge. These basins were flanked to the northwest and southeast, respectively, by uplifts, probably fold-and-thrust belts. In the southeastern basin, the lower sequence of shale, iron-formation, and jasper, deposited under quiet, deep-water conditions, is overlain by shale interbedded with coarse clastic detritus derived from uplifts to the southeast. In the northwestern basin, the lowest Mapepe strata include a basal 5-to 10-m-thick shallow-water sequence of felsic tuff, chert, jasper, and barite succeeded by 100-200 m of fine deep-water felsic tuff. The overlying 200-300 m consists of basinal

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The Puye Formation in north‐central New Mexico is a very coarse‐grained fanglomerate which was deposited on the eastern flank of the Jemez caldera. Pyroclastic deposits occur within the Puye in the form of airfall pumice beds and the remnant of at least one pyroclastic‐surge deposit. This pyroclastic‐surge deposit shows the effects of fluidization and soft‐sediment deformation in the form of: (1) intrusive sedimentary plumes; (2) upwardly injected gravelly pipes; (3) ‘pocket structures’ similar to those of Postma (1983), and; (4) oversteepened and deformed cross‐stratification. Fluidization and soft‐sediment deformation resulted from a combination of the mechanical instability and high, possibly pressurized, fluid content of the deposit. This metastable condition was a consequence of the nature of the flow which deposited the sediment: a rapidly depositing, high‐velocity sediment gravity flow. The fluids in pyroclastic surges may be either gas or liquid. However, because of the coarse grain‐size of the fluidized sediment, it is suggested that liquids were responsible for the features described in this paper. Evidence also suggests that locally fluidization, liquefaction, and soft‐sediment deformation took place penecontemporaneously with deposition.

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