ABSTRACT The Laptev Sea Rift in the East Siberian continental margin plays an important role in the geodynamic models for the opening of the Eurasia Basin. The active Gakkel Ridge, which also represents the boundary between the North America and Eurasia plates, abruptly meets the continental margin of the Laptev Sea. On the continental shelf in the prolongation of the Gakkel Ridge, a rift developed since the Late Cretaceous/Early Cenozoic with the formation of five roughly north-south trending depocenters. To better understand the evolution of this rift, a basin modeling study was carried out with PetroMod® software. The modeled sections used in this study were developed on the basis of depth-converted reflection seismic sections. The sections cover the Anisin Basin in the north and the southeastern margin of the Ust´ Lena Rift in the south. The numerical simulations are supported by tectonic and sedimentological field data that were collected in outcrops during the CASE 13 expedition to the New Siberian Islands in 2011. For the Anisin Basin different scenarios were modeled with rift onsets between 110 Ma and 66 Ma. The results show that the present-day temperature field in the area of the Anisin Basin and at the southeastern margin of the Ust´ Lena Rift is characterized by horizontal, seafloor-parallel isotherms. Geohistory curves extracted from the 2D simulations indicate a twofold rift evolution with a stronger initial subsidence in the Late Cretaceous to Early Paleogene and a moderate subsidence in Late Paleogene and Neogene times. Based on the modeling results, an early rift onset around 110 Ma seems to be more realistic than a later one around 66 Ma.

Abstract The Cenozoic tectonic evolution of the Gangdese arc, formed by juvenile crustal growth during the Mesozoic, remains ambiguous. Here, we conducted a petrological, geochronological and geochemical study of Oligocene (32–24 Ma) granitoids with protolith ages of 57–49 and 27 Ma from the eastern Gangdese arc. Geochemically, these rocks are divided into three groups. Group I has high CaO and Sr, and low REE contents, representing plagioclase-rich cumulates. Group II contains relatively high K 2 O, Pb and REE, and low Na 2 O contents, and is crystallized from evolved magmas. Group III has relatively high Al 2 O 3 and Sr, and low MgO, Y, Yb, Cr and Ni concentrations, and is thickened lower-crust-derived adakitic rocks. The inherited zircon magmatic cores of these rocks have distinctly different ε Hf ( t ) values (−9.88 to +8.50), whereas the magmatic rims have a narrow range of ε Hf ( t ) values (−3.29 to +5.22). The Hf isotopic homogenization indicates intensive mixing of melts derived from the old and juvenile crustal materials. We concluded that the Cenozoic magmatic or sedimentary rocks were buried into the thickened lower crust and melted to generate the Oligocene granitoids, and that the Gangdese arc experienced lasting Paleogene crustal thickening and reworking.

ABSTRACT Five genetic categories of sedimentary basins have been active within the Indus-Yarlung suture zone and in the neighboring High Himalaya since early Cenozoic time. These include: (1) the Xigaze forearc basin (Aptian–early Eocene), (2) the north Himalayan foreland basin (Paleocene–Eocene), (3) the Kailas extensional basin (Oligocene–Miocene), (4) the Liuqu wedge-top basin (early Miocene), and (5) a set of at least six rift and supradetachment basins that formed by arc-parallel extension (late Miocene–Pleistocene). The older basins (categories 1 and 2) were filled with predominantly deep-marine turbiditic deposits, which shoaled through time to subaerial (but very low) elevations. The other basins (categories 3–5) were filled with alluvial-fan, fluvial, and lacustrine sediments, and these formed at progressively higher elevations, culminating in category 5 basins at essentially modern (or slightly higher than modern) elevations (~4000–5000 m). Development of diverse basin types was a response to changing orientations and relative magnitudes of principal stresses in the upper crust of the suture zone and the northern Himalayan thrust belt. Through the Cenozoic, the orientation of maximum compressive principal stress (σ 1 ) changed from approximately horizontal and north-south (Paleocene–Eocene) to approximately vertical with least compressive principal stress (σ 3 ) oriented north-south (Oligocene–Miocene), to horizontal and north-south (early Miocene), to nearly vertical with σ 3 oriented approximately east-west (late Miocene–present). Tectonic stresses associated with the degree of coupling between the converging plates were also potentially important, especially during the Oligocene–Miocene, when the subducting Indian slab was rolling backward relative to the upper Eurasian plate, and during middle to late Miocene time, when the Indian slab was subducting nearly flat beneath the High Himalaya and southern Tibet. Preservation of these extensive sedimentary basins in an orogenic system that is generally being eroded rapidly and deeply stems from original basin-forming mechanisms that produced very large-scale basins (the forearc and early foreland basins) and subsequent evolution of the Himalayan thrust belt in a manner that has isolated High Himalayan basins behind an orographic barrier that protects them from erosion. Recent incision by trans-Himalayan and orogen-parallel suture-zone rivers, however, threatens future preservation of these High Himalayan basins (particularly categories 4 and 5).

In NW Argentina (~26°S), adjacent to the Puna Plateau of the central Andes, exhumation and deformation propagated from west to east across the Puna Plateau and Eastern Cordillera during early–late Cenozoic time. Presently existing data do not indicate a clear eastward younging trend in exhumation in the Precordillera and northern Sierras Pampeanas at the southeastern flank of the Puna Plateau at ~28°S. In this study, we mapped an ~80-km-wide transect at a latitude of ~28°S in the Sierra de Las Planchadas and the Fiambalá Basin. Apatite fission-track (AFT) ages from six samples from thrust fault hanging walls are between 20 and 14 Ma, and apatite helium (U-Th)/He ages from five samples range from 21 Ma west of the Sierra de Las Planchadas to 2 Ma in the Fiambalá Basin. Several samples record mixed apatite (U-Th)/He ages and pre-Cenozoic AFT ages, indicating partial resetting through the 120–60 °C temperature window and suggesting a depth of exhumation between ~6 and 3 km. Thermal modeling of AFT and (U-Th)/He ages indicates cooling from ca. 22 Ma until 2 Ma and a younging trend to the east. These ages are consistent with previously published AFT ages in the Fiambalá region and AHe ages in the Eastern Cordillera to the northeast and suggest Miocene exhumation and deformation in the Precordillera at 28°S and the Eastern Cordillera at 26°S. From a kinematic standpoint, the region of the Precordillera at 28°S may be considered a continuation to the south of the Eastern Cordillera at 26°S, implying a single continuous SW-NE–striking deformation front along this portion of the central Andes. Detrital zircon U-Pb ages from Upper Miocene strata in the Fiambalá Basin suggest that Permian–Miocene rocks in the Sierra de Las Planchadas are the primary source of the Miocene basin fill. This is consistent with previously published eastward-directed paleocurrent data and other provenance proxies and indicates that uplift of the Sierra de Las Planchadas began no later than ca. 9 Ma.

We analyzed the plant macro- and mesofossil records deposited in the Paleocene oil shales of the Boltysh crater (Ukraine) in terms of leaf morphology and its implication for reconstruction of the vegetation and paleoecology of the region. During the early Cenozoic, the Boltysh astrobleme formed a geothermal crater lake that accumulated sediments, preserving a record from the Paleocene to the early middle Eocene. These sediments contain fossil leaf fragments of ferns and angiosperms that grew close to the lake. The occurrence of the Mesozoic fern Weichselia reticulata is of importance. This discovery suggests the survival of this Jurassic to Cretaceous fern into the early Paleogene in the refugial geothermal ecosystem of the Boltysh crater area. Our finding is the youngest record of this fern, although it was a widespread and common element of secondary vegetation during the Cretaceous. The local survival of this fern may have been fostered by the unique combination of edaphic environmental factors of the Boltysh hydrothermal area. Other plant fossils include fragments of leaves that represent ferns likely belonging to lineages that diversified in the shadow of angiosperms, as well as remains of the flowering plants Pseudosalix , Sorbus , Comptonia , and ? Myrica leaf morphotypes.

Abstract As the traditional exploration plays in the main productive basins of North Africa and the Middle East become more ‘mature’, attention is increasingly focusing on more challenging, older and deeper plays in the main producing basins and on high-risk, but more conventional, plays in under-explored frontier areas. This shift brings with it a range of technical and commercial challenges that must be addressed, if exploration in the region is to remain an attractive proposition. Exploration in North Africa and the Middle East has traditionally focused on the prolific Mesozoic- and Cenozoic-sourced petroleum systems of the Nile Delta, the Sirte Basin, the Pelagian Shelf, and the Arabian Plate and on the Palaeozoic-sourced petroleum systems of the Berkine, Ghadames, Illizi, Ahnet and Murzuq basins, the Central Arabian Basin, the Qatar Arch and the Rub Al Khali Basin. Together these form one of the most prolific petroleum provinces in the world and, as a consequence, there has been little commercial incentive to invest in exploring more challenging and riskier plays in these areas. However, as the need to find new reserves becomes imperative, attempts are increasingly being made to test new play concepts and to extend already proven plays into new areas. Key recent developments in this regard include the recognition of the hydrocarbon potential of the Neoproterozoic to Early Cambrian (‘Infracambrian’) sedimentary section lying below the traditionally explored Palaeozoic succession in many basins in North Africa. In some areas, particularly the Berkine Basin in Algeria, the Nile Delta in Egypt and the Rub Al Khali Basin in Saudi Arabia, attention is also increasingly being focused on developing deeper gas plays, both in new areas and beneath existing producing fields. The technical challenges associated with these deeper gas plays are immense and include difficult seismic imaging of deep prospects, low porosity and permeability, high temperature and pressure and a critical need to identify ‘sweet spots’ where either locally preserved primary reservoir characteristics or secondary enhancement of reservoir quality through palaeo-weathering and/or fracturing allow commercial rates of gas production to be achieved. Despite these challenges, it is clear that the future for exploration in many of the more mature basins of North Africa and the Middle East will increasingly lie in evaluating such older and more deeply-buried plays.