Ysabel Calderón

Amber from western Amazonia reveals Neotropical diversity during the middle Miocene

Tertiary insects and arachnids have been virtually unknown from the vast western Amazonian basin. We report here the discovery of amber from this region containing a diverse fossil arthropod fauna (13 hexapod families and 3 arachnid species) and abundant microfossil inclusions (pollen, spores, algae, and cyanophyceae). This unique fossil assemblage, recovered from middle Miocene deposits of northeastern Peru, greatly increases the known diversity of Cenozoic tropical–equatorial arthropods and microorganisms and provides insights into the biogeography and evolutionary history of modern Neotropical biota. It also strengthens evidence for the presence of more modern, high-diversity tropical rainforest ecosystems during the middle Miocene in western Amazonia.

Seismic evidence of gas hydrates, multiple BSRs and fluid flow offshore Tumbes Basin, Peru

Identification of a previously undocumented hydrate system in the Tumbes Basin, localized off the north Peruvian margin at latitude of 3°20′—4°10′S, allows us to better understand gas hydrates of convergent margins, and complement the 36 hydrate sites already identified around the Pacific Ocean. Using a combined 2D–3D seismic dataset, we present a detailed analysis of seismic amplitude anomalies related to the presence of gas hydrates and/or free gas in sediments. Our observations identify the occurrence of a widespread bottom simulating reflector (BSR), under which we observed, at several sites, the succession of one or two BSR-type reflections of variable amplitude, and vertical acoustic discontinuities associated with fluid flow and gas chimneys. We conclude that the uppermost BSR marks the current base of the hydrate stability field, for a gas composition comprised between 96% methane and 4% of ethane, propane and pure methane. Three hypotheses are developed to explain the nature of the multiple BSRs. They may refer to the base of hydrates of different gas composition, a remnant of an older BSR in the process of dispersion/dissociation or a diagenetically induced permeability barrier formed when the active BSR existed stably at that level for an extended period. The multiple BSRs have been interpreted as three events of steady state in the pressure and temperature conditions. They might be produced by climatic episodes since the last glaciation associated with tectonic activity, essentially tectonic subsidence, one of the main parameters that control the evolution of the Tumbes Basin.

Petroleum Systems Restoration of the Huallaga—Marañon Andean Retroforeland Basin, Peru

Abstract The Huallaga–Maranon retroforeland basin system of northern Peru is deformed by both thick- and thin-skinned tectonics. The thrust system is complex and resulted from the reactivation of a west-verging Permian fold and thrust belt capped by an important salt detachment. This chapter presents 2-D petroleum modeling from an updated balanced cross section and sequential restoration through the Huallaga–Maranon wedge-top basin. The sequential restoration has been calibrated by thermochronological dating and thickness variations in Cenozoic synorogenic sediments. It shows two important stages of the deformation (Middle Eocene and Late Early Miocene). Late Triassic/Early Jurassic Pucara Group and Late Cretaceous (Raya and Chonta formations) classic source rocks are present in the Huallaga–Maranon foreland basin, but the revision of the stratigraphy replaced in its updated structural context allowed us to highlight a new Late Permian source rock (Shinai Formation). 2-D modeling of kerogens maturity evolution and hydrocarbon (HC) accumulations in the sequential restoration shows that first Andean structures (Middle Eocene and Late Early Miocene) could preserve HC accumulations in the Chazuta thrust sheet footwall. In the eastern Maranon basin, more recent structures (Late Miocene–Pliocene) such as Santa Lucia could also have been charged. Deep subthrust structures stay unexplored in the Peruvian fold and thrust belts. The Huallaga–Maranon foreland system is probably the best example of subtrap attractiveness in Peru.