ABSTRACT The provenance of middle Permian to Maastrichtian sandstones from the subsurface of the Marañon and Ucayali Basins was determined through U-Pb dating of 113 detrital zircon samples from 21 hydrocarbon exploration wells. An additional 52 samples representing many of the subsurface lithostratigraphic units drilled in the Marañon and Ucayali Basins were collected from 42 outcrop localities in the Huallaga Basin and one outcrop locality in the Pachitea sub-Basin for U-Pb dating. The exposed units were analyzed to determine whether the outcrop sandstones had the same provenance as their subsurface counterparts. Analytical results show that profound temporal changes in long-term detrital zircon provenance were observed in all the basins; spatial changes in detrital zircon populations between and within the Marañon and Ucayali Basins appear to be less significant. Western pre-Andean “Peruvian” source areas were major contributors of detrital zircons to sandstones in all the basins, especially during the middle Permian to Late Jurassic. Zircons with ages that are contemporaneous with the deposition of these sandstones were contributed by active continental arcs or locally via erosion and recycling of Permo-Triassic plutons. Abundant Neoproterozoic–Cambrian zircons were likely derived locally from the Pampean arc and Puncoviscana Formation (now buried in Peru) that formed in western Amazonia prior to emplacement of the Marañon Complex. Conversely, the primary sources for Archean to middle Paleoproterozoic detrital zircons were through local erosion and recycling of Paleozoic and Mesozoic sandstones and from recycling of Solimões Basin sandstones. Direct provenance from more distant central and eastern Amazonian cratonic source areas is possible but is considered unlikely. Regional Late Middle Jurassic to Early Cretaceous uplift of the ancestral Solimões Basin, the eastern Marañon and Ucayali Basins, and western Amazonia caused a major shift in regional detrital zircon provenance, from local and western “Peruvian” sources to proximal western Amazonian cratonic sources. The development of new fluvial drainage areas in western Amazonia rapidly replaced less important long-distance detrital zircon sources from central and eastern Amazonia. Sources of local and west-derived “Peruvian” detrital zircons diminished by the Late Cretaceous (Cenomanian) as the Pampean arc and Puncoviscana Formation were buried from north to south; contemporaneous zircons were largely trapped within a deep back-arc basin west of the Marañon Complex. Detrital zircons from local “Peruvian” source areas continued to be important for Upper Cretaceous sandstones in the Huallaga and southwestern Ucayali Basins but were replaced by proximal western Amazonian cratonic-sourced zircons by the end of the Cretaceous. Similar detrital zircon-age populations observed in middle Permian to Lower Cretaceous sandstones suggest that subsurface correlations may be imprecise in certain areas. Local recycling and redeposition of zircons from older sandstones is regarded as a more important mechanism for the formation of key hydrocarbon reservoir sandstones than was previously known.

Abstract Basaltic volcanism occurs at all the active volcanic systems of São Miguel. For the last 30 ka, the eruption of basaltic magma has been particularly significant in the areas between the three polygenetic volcanoes – Sete Cidades, Fogo and Furnas – and two basaltic fields have developed: the Picos Fissural Volcanic System (PFVS) and the Congro Fissural Volcanic System (CFVS). About 5 ka ago volcanic activity at CFVS ended abruptly and since then almost all basaltic activity has been concentrated at the PFVS, where about 30 eruptions have taken place. Despite the absence of eruptive activity, the Congro system represents one of the most active seismic areas in the archipelago. It shows episodes of volcanic deformation that are indicative of magma ascent, which halted beneath the volcanic system. Two historical eruptions are associated with the PFVS. The 1563 eruption at Pico do Sapateiro was of basaltic composition, whereas that of the 1652 eruption was, for almost two centuries, also considered to be basaltic. This event had, however, a Vulcanian style and involved the production of large amounts of fine ash and the growth of three trachyte domes with associated coulées. It was accurately described in contemporary historical accounts.

Abstract In recent years much progress has been made in researching a wide variety of extreme events on São Miguel. In addition there are a number of volcano-related risks that impact upon the people of São Miguel. Some of these may occur both before and during volcanic emergencies (e.g. earthquakes), whilst others render São Miguel dangerous even when its volcanoes are not erupting (e.g. flooding, landslides, tsunamis and health impacts, especially the effects of CO 2 seepage into dwellings). In this chapter we first define what vulnerability means to the people of São Miguel, and relate this to the cultural and economic characteristics of the island. The following aspects of vulnerability are discussed: (a) physical (i.e. housing, settlement and the characteristics of evacuation routes and plans); (b) demographic and economic; and (c) social and cultural and perceptual (i.e. whether people have an accurate cognition of risk). Particular areas of concern relate to housing: the identification of isolated dwellings that would be difficult to evacuate; the vulnerability/resilience of evacuation routes following recent infrastructure improvements; characteristics of the island’s transient population; management of livestock under emergency conditions; local leadership roles; and educational outreach.