Gérôme Calvès

Tectonics of the Deccan Large Igneous Province: an introduction

SOUMYAJIT MUKHERJEE1*, ACHYUTA AYAN MISRA2, GÉRÔME CALVÈS3 & MICHAL NEMČOK4,5 Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai 400 076, Maharashtra, India Exploration, Reliance Industries Ltd, Mumbai 400 701, Maharashtra, India Université Toulouse 3, Paul Sabatier, Géosciences Environnement Toulouse, 14 avenue Edouard Belin, 31400, Toulouse, France EGI at University of Utah, 423 Wakara Way, Suite 300, Salt Lake City, UT 84108, USA EGI Laboratory at SAV, Dúbravskácesta 9, 840 05 Bratislava, Slovakia

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.

Geochemical Evidence for Large‐Scale Drainage Reorganization in Northwest Africa During the Cretaceous

West African drainage reorganization during Cretaceous opening of the Atlantic Ocean is deciphered here from geochemical provenance studies of Central Atlantic sediments. Changes in the geochemical signature of marine sediments are reflected in major and trace element concentrations and strontiumneodymium radiogenic isotopic compositions of Cretaceous sedimentary rocks from eight Deep Sea Drilling Project (DSDP) sites and one exploration well. Homogeneous major and trace element compositions over time indicate sources with average upper (continental) crust signatures. However, detailed information on the ages of these sources is revealed by neodymium isotopes (expressed as ENd). The ENd(0) values from the DSDP sites show a three-step decrease during the Late Cretaceous: (1) the Albian-Middle Cenomanian ENd(0) values are heterogeneous (–5.5 to 214.9) reflecting the existence of at least three subdrainage basins with distinct sedimentary sources (Hercynian/Paleozoic, Precambrian, and mixed Precambrian/Paleozoic); (2) during the Late Cenomanian-Turonian interval, ENd(0) values become homogeneous in the deepwater basin (–10.3 to 212.4), showing a negative shift of 2 epsilon units interpreted as an increasing contribution of Precambrian inputs; (3) this negative shift continues in the Campanian-Maastrichtian (ENd(0) 5 215), indicating that Precambrian sources became dominant. These provenance changes are hypothesized to be related to the opening of the South and Equatorial Atlantic Ocean, coincident with tectonic uplift of the continental margin triggered by Africa-Europe convergence. Finally, the difference between ENd(0)values of Cretaceous sediments from the Senegal continental shelf and from the deepwater basins suggests that ocean currents prevented detrital material from the Mauritanides reaching deepwater areas.

Tectonics of the Deccan Large Igneous Province

Understanding the Deccan Trap Large Igneous Province in western India is important for deciphering the India–Seychelles rifting mechanism. This book presents 13 studies that address the development of this province from diverse perspectives including field structural geology, geochemistry, analytical modelling, geomorphology and geophysics (e.g., palaeomagnetism, gravity and magnetic anomalies, and seismic imaging). Together, these papers indicate that the tectonics of Deccan is much more complicated than previously thought. Key findings include: the Deccan province can be divided into several blocks; the existence of a rift-induced palaeo-slope; constraints on the eruption period; rift–drift transition mechanisms determined for magma-rich systems; the tectonic role of the Deccan or Réunion plumes; sub-surface structures reported from boreholes; the delineation of the crust–mantle structure; the documentation of sub-surface tectonic boundaries; post-Deccan-Trap basin inversion; deformed dykes around Mumbai, and also from the eastern part of the Deccan Traps, documented in the field.