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Nature is never at steady state. Natural history is generated by ever-interacting forces that produce always surprising phenomena. Negating change is negating Nature’s essence, and the historical record, at both geological and human time scales, shows that steady state remains utopia. However, although unrealistic because constantly endangered, we...
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Context 1
... Nature in this way, however, may recall the myth about the Earth being held up by an elephant, held up by a tortoise, held up by a snake (Fig. 4; Tylor, 1865 ch.XII). The risk is that, in the exciting up-and-down course of such a complex "matrioska" modeling procedure, we lose track of the level we are in. Consequently, we may confuse hypotheses − or even hypotheses based on other hypotheses − with observations, ending up to considered them as data (e.g. slab breakoff on a ...
Context 2
... Nature in this way, however, may recall the myth about the Earth being held up by an elephant, held up by a tortoise, held up by a snake (Fig. 4; Tylor, 1865 ch.XII). The risk is that, in the exciting up-and-down course of such a complex "matrioska" modeling procedure, we lose track of the level we are in. Consequently, we may confuse hypotheses -or even hypotheses based on other hypotheses -with observations, ending up to considered them as data (e.g. slab breakoff on a ...
Citations
... As any tool, they apply well to some circumstances and badly to others. Because they are derived from one setting and extrapolated to another, and because different settings are not the same by definition, models are bound to be partly misleading even in the luckiest case (Garzanti and Sternai 2020). Their uncritical use is therefore discouraged. ...
The Zambezi River rises at the center of southern Africa, flows across the low-relief Kalahari Plateau, meets Karoo basalt, plunges into Victoria Falls, follows along Karoo rifts, and pierces through Precambrian basement to eventually deliver its load onto the Mozambican passive margin. Reflecting its polyphase evolution, the river is subdivided into segments with different geological and geomorphological character, a subdivision finally fixed by man’s construction of large reservoirs and faithfully testified by sharp changes in sediment composition. Pure quartzose sand recycled from Kalahari desert dunes in the uppermost tract is next progressively enriched in basaltic rock fragments and clinopyroxene. Sediment load is renewed first downstream of Lake Kariba and next downstream of Lake Cahora Bassa, documenting a stepwise decrease in quartz and durable heavy minerals. Composition becomes quartzo-feldspathic in the lower tract, where most sediment is supplied by high-grade basements rejuvenated by the southward propagation of the East African rift. Feldspar abundance in Lower Zambezi sand has no equivalent among big rivers on Earth and far exceeds that in sediments of the northern delta, shelf, and slope, revealing that provenance signals from the upper reaches have ceased to be transmitted across the routing system after closure of the big dams. This high-resolution petrologic study of Zambezi sand allows us to critically reconsider several dogmas, such as the supposed increase of mineralogical “maturity” during long-distance fluvial transport, and forges a key to unlock the rich information stored in sedimentary archives, with the ultimate goal to accurately reconstruct the evolution of this mighty river flowing across changing African landscapes since the late Mesozoic.
