Syn‐depositional thin‐ and thick‐skinned extensional tectonics in the mid‐Cretaceous Lasarte sub‐basin,western Pyrenees

In the mid‐Cretaceous Lasarte sub‐basin (LSB) [northeastern Basque‐Cantabrian Basin (BCB)] contemporaneous and syn‐depositional thin‐ and thick‐skinned extensional tectonics occur due to the presence of a ductile detachment layer that decoupled the extension. Despite the interest in extension modes of rift basins bearing intra‐stratal detachment layers, complex cases remain poorly understood. In the LSB, field results based on mapping, stratigraphic, sedimentological and structural data show the relationship between growth strata and tectonic structures. Syn‐depositional extensional listric faults and associated folds and faults have been identified in the supra‐detachment thin‐skinned system. But stratigraphic data also indicate the activation of sub‐detachment thick‐skinned extensional faults coeval with the development of the thin‐skinned system. The tectono‐sedimentary evolution of the LSB, since the Late Aptian until the earliest Late Albian, has been interpreted based on thin‐ and thick‐skinned extensional growth structures, which are fossilized by post‐extensional strata. The development of the thin‐skinned system is attributed to the presence of a ductile detachment layer (Upper Triassic Keuper facies) which decoupled the extension from deeper sub‐detachment basement‐involved faulting under a regional extensional/transtensional regime.     

Source‐to‐sink relationships along the South‐Central Chilean margin: evidence from detrital apatite fission‐track analysis

Detrital fission‐track studies on sedimentary basins surrounding eroding mountain belts provide a powerful tool to reconstruct exhumation histories of the source area. However, examples from active arc‐trench systems are sparse. In this study, we report detrital apatite fission‐track (AFT) data from Holocene and Pleistocene turbiditic trench and modern river sediments at the Chilean margin (36°S‐47°S). Sediment petrography and detrital AFT data point to different major sediment sources, underlining the need for multidisciplinary studies: whereas sediment petrography indicates the erosion of large volumes of volcanic detritus, no such volcanic signal is seen in the detrital age pattern. Areally subordinate plutonic units are identified as the main, often unique sources. This result has important implications for studies of fossil systems, where the feeder areas are eroded, and where the youngest age population is often interpreted to indicate active volcanism. For the southernmost part of the study area in the Patagonian Andes, where the source area is mainly composed of granitoids, the sediment is derived from only small portions along the main divide, pointing to focused glacial erosion there. Our detrital AFT data show no exhumational signal that could be related to the subduction of the actively spreading Chile Ridge at c. 47°S and to the opening of a slab window beneath the South American Plate.     

Genealogy of the Singaporean black‐and‐white house

The distinctive black‐and‐white houses from Singapore's colonial era that survive in enclaves as fine dwellings for the present‐day elite have been recognized and documented as a type. In this paper we tell the story of their cultural formation, which is one of remarkable hybridity. Various influences were brought to bear and resolved into the black‐and‐white house‐type, which was not invented ‘all at once’ in Singapore, but developed over the course of more than two centuries. We begin the story in India, when British settlers learnt from local Bengali practices to make serviceable dwellings for a climate that they found difficult. The overhanging roofs that shaded walls and the tall internal volumes were formalized with reference to European expectations of geometry and finish, and the bungalow was born. In British Malaya the bungalow was further hybridized with the house on stilts that was well known to the indigenous tradition. This produced the spatial configuration that is to be found also in the Singapore houses, with their extensive verandas on an upper floor level. Their distinctive colouring comes from a different tradition: the black‐and‐white Tudoresque style that was very popular in Britain and sometimes called ‘Old English’. This was used by the British colonizers so that they could feel more at home in surroundings that were in a far‐off foreign cultural environment.     

Large‐scale connectivity of fluvio‐deltaic stratigraphy: Inferences from simulated accommodation‐to‐supply cycles and automated extraction of chronosomes

Multiscale simulation of fluvio‐deltaic stratigraphy was used to quantify the elements of the geometry and architectural arrangement of sub‐seismic‐scale fluvial‐to‐shelf sedimentary segments. We conducted numerical experiments of fluvio‐deltaic system evolution by simulating the accommodation‐to‐sediment‐supply (A/S) cycles of varying wavelength and amplitude with the objective to produce synthetic 3‐D stratigraphic records. Post‐processing routines were developed in order to investigate delta lobe architecture in relation to channel‐network evolution throughout A/S cycles, estimate net sediment accumulation rates in 3‐D space, and extract chronostratigraphically constrained lithosomes (or chronosomes) to quantify large‐scale connectivity, that is, the spatial distribution of high net‐to‐gross lithologies. Chronosomes formed under the conditions of channel‐belt aggradation are separated by laterally continuous abandonment surfaces associated with major avulsions and delta‐lobe switches. Chronosomes corresponding to periods in which sea level drops below the inherited shelf break, that is, the youngest portions of the late falling stage systems tract (FSST), form in the virtual absence of major avulsions, owing to the incision in their upstream parts, and thus display purely degradational architecture. Detailed investigation of chronosomes within the late FSST showed that their spatial continuity may be disrupted by higher‐frequency A/S cycles to produce “stranded” sand‐rich bodies encased in shales. Chronosomes formed during early and late falling stage (FSST) demonstrate the highest large‐scale connectivity in their proximal and distal areas, respectively. Lower‐amplitude base level changes, representative of greenhouse periods during which the shelf break is not exposed, increase the magnitude of delta‐lobe switching and favour the development of system‐wide abandonment surfaces, whose expression in real‐world stratigraphy is likely to reflect the intertwined effects of high‐frequency allogenic forcing and differential subsidence.     

Forest‐Cover Change from Labor‐ and Capital‐Intensive Commercial Logging in the Southern Chocó Rainforests*

This article examines two key aspects of land‐cover change in the south of the Chocó region. First, it assesses and compares the local impact on forest condition of labor‐intensive and capital‐intensive commercial logging. Second, it assesses the regional significance and permanency of these changes. Studies of land‐cover change associated with commercial logging have focused almost exclusively on capital‐intensive extraction and have assumed that after logging, degraded forests are transformed into agricultural cover. This study shows that both capital‐ and labor‐intensive logging result in similar land‐cover changes (i.e., forest degradation) if the timber sought is the same. However, labor‐intensive loggers also seek timber species not sought by capital‐intensive loggers, and this impact is statistically different from the impact of the extraction of the first group of species. Results also show that only a small fraction (20–30 percent) of the area logged is later converted to agricultural cover types. The persistence of logged forests means that up to 20 percent of the remaining forest cover could correspond to forests with significant and lasting levels of degradation. Furthermore, the different production requirements for each group of species also mean that there is a spatial differentiation in the impact of logging in the region. Logged forests are arranged into two consecutive corridors on each side of access routes (e.g., rivers). The first corridor corresponds to a narrow (approximately 1‐km) band of high‐intensity degradation. The second, broader (approximately 2‐km) forest band, with lower levels of degradation, extends inland along first‐tier corridors. A key factor determining the permanency of this land‐cover pattern is the strong control local communities have over the land in the region. This limits the spread of patterns observed in other frontier areas, especially the conversion of logged forests into agricultural cover.     

Late Pliocene–early Pleistocene deep‐sea basin sedimentation at high‐latitudes: mega‐scale submarine slides of the north‐western Barents Sea margin prior to the shelf‐edge glaciations

At high‐latitude continental margins, large‐scale submarine sliding has been an important process for deep‐sea sediment transfer during glacial and interglacial periods. Little is, however, known about the importance of this process prior to the arrival of the ice sheet on the continental shelf. Based on new two‐dimensional seismic data from the NW Barents Sea continental margin, this study documents the presence of thick and regionally extensive submarine slides formed between 2.7 and 2.1 Ma, before shelf‐edge glaciation. The largest submarine slide, located in the northern part of the Storfjorden Trough Mouth Fan (TMF), left a scar and is characterized by an at least 870‐m‐thick interval of chaotic to reflection‐free seismic facies interpreted as debrites. The full extent of this slide debrite 1 is yet unknown but it has a mapped areal distribution of at least 10.7 × 10³ km² and it involved >4.1 × 10³ km³ of sediments. It remobilized a larger sediment volume than one of the largest exposed submarine slides in the world – the Storegga Slide in the Norwegian Sea. In the southern part of the Storfjorden TMF and along the Kveithola TMF, the seismic data reveal at least four large‐scale slide debrites, characterized by seismic facies similar to the slide debrite 1. Each of them is ca. 295‐m thick, covers an area of at least 7.04 × 10³ km² and involved 1.1 × 10³ km³ of sediments. These five submarine slide debrites represent approximately one quarter of the total volume of sediments deposited during the time 2.7–1.5 Ma along the NW Barents Sea. The preconditioning factors for submarine sliding in this area probably included deposition at high sedimentation rate, some of which may have occurred in periods of low eustatic sea‐level. Intervals of weak contouritic sediments might also have contributed to the instability of part of the slope succession as these deposits are known from other parts of the Norwegian margin and elsewhere to have the potential to act as weak layers. Triggering was probably caused by seismicity associated with the nearby and active Knipovich spreading ridge and/or the old tectonic lineaments within the Spitsbergen Shear Zone. This seismicity is inferred to be the main influence of the large‐scale sliding in this area as this and previous studies have documented that sliding have occurred independently of climatic variations, i.e. both before and during the period of ice sheets repeatedly covering the continental shelf.     

Sea‐level and ocean‐current control on carbonate‐platform growth,Maldives, Indian Ocean

Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region.     

Late Ediacaran syn‐rift/post‐rift transition and related fault‐driven hydrothermal systems in the Anti‐Atlas Mountains,Morocco

The syn‐rift/post‐rift transition of the late Ediacaran‐mid Cambrian Atlas rift is characterized by the interplay of several processes, such as a widespread episode of fracturing and tilting, associated with encasement of fault‐controlled vein metallic ore deposits of economic importance, and carbonate production and phosphogenesis (Taguedit Bed, Tabia Member) bordering rift‐flank uplifts. A correlatable unconformity marks the end of these processes and the beginning of a thermal subsidence‐dominated regime with development of a more stable, carbonate, peritidal‐dominated platform (Tifnout Member). Late Ediacaran microbial carbonate production and phosphogenesis extended in discontinuous belts around the periphery of uplifted rift shoulders and flanks. Karst development is interpreted to have formed along synsedimentary faults and fractures during abrupt tectonic uplift associated with emplacement of polymetallic hydrothermal dikes (rich in Cu, Fe and subsidiary Pb, Zn). Isotopic analysis indicates that speleothem precipitation in karstic palaeocaves displays significantly lighter δ¹³C and δ¹⁸O values as compared to the host dolomite, implying calcite precipitation by terrestrial fluids rich in decomposing organic matter and/or microbial activity in the cave system.     

Structural controls on the stratigraphic architecture of net‐transgressive shallow‐marine strata in a salt‐influenced rift basin: Middle‐to‐Upper Jurassic Egersund Basin,Norwegian North Sea

In this study, we integrate 3D seismic reflection, wireline log, biostratigraphic and core data from the Egersund Basin, Norwegian North Sea to determine the impact of syn‐depositional salt movement and associated growth faulting on the sedimentology and stratigraphic architecture of the Middle‐to‐Upper Jurassic, net‐transgressive, syn‐rift succession. Borehole data indicate that Middle‐to‐Upper Jurassic strata consist of low‐energy, wave‐dominated offshore and shoreface deposits and coal‐bearing coastal‐plain deposits. These deposits are arranged in four parasequences that are aggradationally to retrogradationally stacked to form a net‐transgressive succession that is up to 150‐m thick, at least 20 km in depositional strike (SW‐NE) extent, and >70 km in depositional dip (NW‐SE) extent. In this rift‐margin location, changes in thickness but not facies are noted across active salt structures. Abrupt facies changes, from shoreface sandstones to offshore mudstones, only occur across large displacement, basement‐involved normal faults. Comparisons to other tectonically active salt‐influenced basins suggest that facies changes across syn‐depositional salt structures are observed only where expansion indices are >2. Subsidence between salt walls resulted in local preservation of coastal‐plain deposits that cap shoreface parasequences, which were locally removed by transgressive erosion in adjacent areas of lower subsidence. The depositional dip that characterizes the Egersund Basin is unusual and likely resulted from its marginal location within the evolving North Sea rift and an extra‐basinal sediment supply from the Norwegian mainland.     

Oligocene‐Miocene Great Lakes in the India‐Asia Collision Zone

The Himalayan‐Tibetan Plateau is Earth's highest topographic feature, and formed largely during Cenozoic time as India collided with and subducted beneath southern Asia. The >1300 km long, late Oligocene‐early Miocene Kailas basin formed within the collisional suture zone more than 35 Ma after the onset of collision, and provides a detailed picture of surface environments, processes and possible geodynamic mechanisms operating within the suture zone during the ongoing convergence of India and Asia. We present new geochronological, sedimentological, organic geochemical and palaeontological data from a previously undocumented 400 km long portion of the Kailas basin. The new data demonstrate that this part of the basin was partly occupied by large, deep, probably meromictic lakes surrounded by coal‐forming swamps. Lacustrine facies include coarse‐ and fine‐grained turbidites, profundal black shales and marginal Gilbert‐type deltas. Organic geochemical temperature proxies suggest that palaeolake water was warmer than 25 °C, and cyprinid fish fossils indicate an ecology capable of supporting large fish. Our findings demonstrate a brief period of low elevation in the suture zone during Oligocene‐Miocene time (26–21 Ma) and call for a geodynamic mechanism capable of producing a long (>1000 km) and narrow basin along the southern edge of the upper, Asian plate, long after the onset of intercontinental collision. Kailas basin deposits presently are exposed at elevations >6000 m, requiring dramatic elevation gain in the region after Kailas deposition, without strongly shortening the upper crust. Episodic Indian slab rollback, followed by break‐off and subsequent renewal of flat‐slab subduction, can account for features of the Kailas basin.