Search

International audience; The Grenada Basin separates the active Lesser Antilles Arc from the Aves Ridge, described as a Cretaceous‐Paleocene remnant of the ‘Great Arc of the Caribbean'. Although various tectonic models have been proposed for the opening of the Grenada Basin, the data on which they rely are insufficient to reach definitive conclusions. This paper presents a large set of deep‐penetrating multichannel seismic reflection data and dredge samples acquired during the GARANTI cruise in 2017. By combining them with published data including seismic reflection data, wide‐angle seismic data, well data and dredges, we refine the understanding of the basement structure, depositional history, tectonic deformation and vertical motions of the Grenada Basin and its margins as follows: 1) rifting occurred during the late Paleocene‐early Eocene in a NW‐SE direction and led to seafloor spreading during the middle Eocene; 2) this newly formed oceanic crust now extends across the eastern Grenada Basin between the latitude of Grenada and Martinique; 3) asymmetrical pre‐Miocene depocenters support the hypothesis that the southern Grenada Basin originally extended beneath the present‐day southern Lesser Antilles Arc and probably partly into the present‐day forearc before the late Oligocene‐Miocene rise of the Lesser Antilles Arc; 4) the Aves Ridge has subsided along with the Grenada Basin since at least the middle Eocene, with a general subsidence slowdown or even an uplift during the late Oligocene, and a sharp acceleration on its southeastern flank during the late Miocene. Until this acceleration of subsidence, several bathymetric highs remained shallow enough to develop carbonate platforms.

The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was one of the major global deep-time hyperthermal events of the past. Studies of shallow-marine PETM records are crucial to understand the continental hydrological response to current global warming. This study presents the first detailed documentation of the PETM in the Xigaze forearc basin located along the northern active continental margin of the eastern Tethys Ocean, and illustrates the associated environmental and hydrological changes. Based on carbon-isotope stratigraphy, foraminiferal biostratigraphy, and zircon U Pb chronostratigraphy, the PETM event was identified within a siliciclastic unit in the largely calcareous Jialazi Formation. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the siliciclastic unit, but are replaced by Shallow Benthic Zone 6 assemblages above the siliciclastic unit. High-resolution microfacies analysis indicates that the pre-PETM deposits consist of carbonate-ramp sediments followed by a sudden change to syn-PETM siliciclastic rocks, followed in turn by renewed post-PETM carbonate-ramp deposition. The siliciclastic supply increased notably during the PETM, as indicated by the thickness of both sandstone and shale intervals, resulting in a temporary demise of the carbonate ramp. Provenance analysis does not indicate any major change in the source areas of terrigenous detritus through the early Paleogene. Increasing siliciclastic supply is thus chiefly ascribed to the intensification of seasonal precipitation and consequently increased hydrological circulation in the Gangdese arc during the PETM event.

The Campo section in the Spanish Pyrenees is classical for shallow-water Paleocene-Eocene Thermal Maximum (PETM) studies. Despite extensive work in the last decades, the stratigraphic location of the onset of the negative carbon isotope excursion (CIE), and hence the Paleocene/Eocene (P/E) boundary, remains a matter of considerable debate in the Campo section. Here we present new biostratigraphic, sedimentological and carbon-isotopic data across the late Paleocene to Eocene strata to constrain the precise stratigraphic position of the P/E boundary and investigate environmental changes across the PETM. Foraminiferal assemblages of biozone SBZ4 found below the Claret Formation are replaced by SBZ6 assemblages above. Detailed microfacies analysis indicated that the pre-PETM upper Navarri Formation represents transgressive inner-ramp deposits, overlain unconformably by mixed carbonate-siliciclastic deposits of the syn-PETM Claret Formation, overlain unconformably in turn by renewed carbonate-ramp deposition in the post-PETM lower Serraduy Formation. The temporary demise of the carbonate ramp during the PETM is ascribed to increased siliciclastic supply associated with a significant change in regional hydrology driven by an increase in magnitude and frequency of extreme rainfall and runoff events.

International audience; Saint Barthélemy is the only island of the northern Lesser Antilles where it is possible to investigate in the detail the chronostratigraphy of the mixed carbonate-volcaniclastic deposits of the Paleogene Caribbean volcanic arc. Based on field mapping and new biostratigraphical and sedimentological data, we study the limestone units interbedded in the Paleogene volcaniclastic deposits. We find that four main carbonate units occur instead of previously believed six ones. Based on the ages given by the foraminifera assemblages, and taking into account the recently published 40Ar/39Ar ages of magmatic rocks, the Lower Limestone unit dates Lutetian, the Intermediate Limestone unit late (?) Bartonian-late Priabonian, the Upper Limestone late Priabonian and the Top Limestone unit early Miocene. The Paleogene carbonate beds were deposited on gently dipping submarine volcaniclastic deposits issued from emergent volcanoes, in muddy, unrimmed inner to mid-ramp setting dominated by bottom communities. A major subaerial unconformity is evidenced during the Oligocene, most probably corresponding to uplift affecting Saint Barthélemy. Our work offers a revised lithostratigraphic succession of Saint Barthélemy as a first key-point for further studies of the Paleogene Caribbean arc deposits which were dismembered following the entrance of the Bahamas Bank in the Lesser Antilles subduction zone.

Recent studies have indicated that an Andean-type orogen (Lhasaplano) developed on the Lhasa block in the Cretaceous during northward subduction of Neo-Tethyan oceanic lithosphere. When and how uplift of the Lhasaplano began, however, has remained controversial. This article integrates stratigraphic, sedimentological, tectonic, and provenance data from the latest marine to nonmarine strata in the Linzhou Basin to pinpoint the early topographic growth in southern Tibet. The Takena Formation mainly consists of lagoonal carbonates and mudstones yielding foraminiferal assemblages of Early Aptian age (ca. 123–119.5 Ma). The conformably overlying lower member of the Shexing Formation, mainly deposited in fluvial environments, was fed by volcanic and sedimentary rock fragments from the north Lhasa terrane. Clasts of the Gangdese arc to the south firstly appeared in the middle member and became dominant in the upper member of the Shexing Formation. By contrast, coarse grained, braided river facies occur in the uppermost part of the Shexing Formation, where detritus was mostly recycled from Paleozoic strata of north Lhasa, with minor volcaniclastic contribution from the Gangdese arc. Basin analysis indicates accelerating subsidence and sedimentation rates during deposition of Takena to middle Shexing strata (ca. 125–108 Ma), followed by steady subsidence during deposition of upper Shexing strata (ca. 108–96 Ma). Given this regional tectonic and sedimentary evidence, such an evolution is interpreted to reflect tectonic extension followed by thermal subsidence. Basin inversion and regional compression initiated during deposition of the uppermost Shexing strata (ca. 96 Ma), as indicated by active thrust faults and widespread accumulation of syntectonic conglomerates in the western part of the Lhasa block. This event marked the beginning of the Andean-type orogeny in southern Tibet. Such a paleotectonic evolution, from extension to tectonic inversion, is also documented in the Andes mountain range. It may be typical of the early stage growth of Andean-type active continental margins.

The development history of an oligo-mesophotic, early Miocene, isolated carbonate system (>160 m in thickness), forming the uppermost part of the Oligo-Miocene Yadana buildup (northern Andaman Sea), has been evidenced from the integration of sedimentological core studies from 4 wells (cumulated core length: 343 m), well correlations, seismic interpretation and analysis of the ecological requirements of the main skeletal components. Three types of carbonate factory operated on the top of the platform, depending on water-depth, turbidity and nutrient level: (1) a scleractinian factory developing under mesophotic conditions during periods of high particulate organic matter supplies, (2) an echinodermal factory occupying dysphotic to aphotic area of the platform coevally with the scleractinian factory, (3) a large benthic foraminiferal-coralline algal factories prevailing under oligo-mesophotic and oligo-mesotrophic conditions. The limited lateral changes in facies between wells, together with the seismic expression of the Yadana buildup, suggest deposition on a flat-topped shelf. Carbonate production and accumulation on the Yadana platform was mainly controlled by light penetration, nutrient content and hydrodynamic conditions. Scleractinian-rich facies resulted from transport of coral pieces derived from mesophotic environments (mounds?) and deposited in deeper, low light , mud-rich environments in which lived abundant communities of suspension feeders such as ophiuroids. Changes in monsoonal intensity, terrestrial runoff from the Irrawaddy River, upwelling currents and internal waves activity during the early Miocene are likely responsible for significant variations in water turbidity and nutrient concentration in the Andaman Sea, thus promoting the development of an oligo-mesophotic, incipiently drowned platform.

This study focused on uppermost Cretaceous sedimentary rocks deposited in the Himalayan region and around the core of peninsular India just before the eruption of the Deccan Traps. Detailed stratigraphic and sedimentological analysis of Late Cretaceous successions in the Himalayan Range together with literature data from the Kirthar fold-and-thrust belt and central to southeastern India document a marked shallowing-upward depositional trend that took place in the Campanian–Maastrichtian before the Deccan magmatic outburst around the Cretaceous-Tertiary boundary. Topographic uplift of the Indian peninsula began in Campanian time and is held responsible for thick sediment accumulation associated with shorter periods of nondeposition in peripheral areas (Himalayan Range, Kirthar fold belt, and Krishna-Godavari Basin) than in the central part of the Deccan Province. Surface uplift preceding Deccan volcanism took place at warm-humid equatorial latitudes, which may have led to an acceleration of silicate weathering, lowered atmospheric pCO2, and climate cooling starting in the Campanian–Maastrichtian. The radial centrifugal fluvial drainage in India that is still observed today was established at that time.

International audience

International audience; Upper plates in subduction zones are prone to record slab dynamics as their strain pattern, uplift-subsidence records and volcanic arc activity accommodates variations of slab parameters in terms of dip, density and rheology. The ANR GAARAnti aims at tracking the timing of land emersions and submersions along the Lesser Antilles subduction zone, which is key to understand the long-term mechanical behavior of this subduction zone. In particular the strain history of the northern Lesser Antilles realm, that makes the junction with the Greater Antilles, needs to be better constrain in order to elaborate paleogeographic models. In this study we combined onshore (structural and geological mapping, PMag sampling, absolute dating and biostratigraphy) and offshore investigations (seismic profiling from the 2017 GARANTI Cruise), we evidence an unprecedently described episode of Mid-Eocene shortening, south of the Anegada Trough. Moreover, we present new paleomagnetic data from the island of St. Barthélemy, indicating a Post Oligocene ~25 counterclockwise rotation that we interpret as an accommodation of trench curvature. After a restoration of the Cayman Trough to the Mid Eocene, the regional compressive structures are interpreted to be the eastward propagation of the compressional domain that accommodated the N-S shortening triggered by the collision of the Bahamas Bank. A crustal-scale cross section drawn from the forearc to the backarc across the thrusts allows us to discuss the origin of crustal thickening, magmatism and tectonics, in the study area.

In order to establish the relationship between the smooth, microperforate praehedbergellid forms of the genus Blefuscuiana with the younger, macroperforate and muricate forms typical of Hedbergella, two similar taxa but with the different characters of the two genera, are studied here: Blefuscuiana praetrocoidea (Kretchmar & Gorbachik) and its descendant Hedbergella trocoidea (Gandolfi), the type species of Hedbergella, and which typifies the Hedbergellidae.B. praetrocoidea was only found in the Early Aptian in the North Tethys. H. trocoidea ranges from the Late Aptian to Early Albian (?M. Albian) and is a cosmopolitan species. It evolves into Ticinella roberti (Gandolfi), a Late Aptian–Albian species with fused portici. The evolution of the Praehedbergellidae into the Hedbergellidae appears to be related to a relative sea-level rise in the Late Aptian and Albian (and the opening of the Proto-Atlantic) which provided a number of deep-water niches which the Hedbergellidae occupied.

Upper Jurassic-lowermost Cretaceous carbonate build-ups are imaged on seismic data in the Black Sea. They form important, untested, hydrocarbon reservoirs that are the focus of active exploration. Outcrop analogues to these build-ups around the Black Sea contain a series of subaerial exposure surfaces. The hiatuses associated with a number of these subaerial exposure surfaces have been dated in a well exposed Callovian or Upper Oxfordian to Barremian shallow-water inner platform carbonate succession (the Berdiga Formation) in the Eastern Pontides using strontium isotope stratigraphy and foraminiferal biostratigraphy. They span the latest Kimmeridgian to Tithonian or Berriasian, and the Hauterivian to Barremian. Less well constrained, but broadly contemporaneous stratigraphic gaps in multiple successions around the Black Sea provide additional insights and point to a regional driving mechanism. The timing of hiatus formation does not correspond to periods of eustatic lowstand. It does coincide, however, with Late Tithonian to Berriasian and Hauterivian to Early Aptian episodes of rifting in the Greater Caucasus Basin, located farther to the north. Thus, it is possible that subaerial exposure was caused by rift flank uplift during periods of regional extension. Uplift due to slab break off is discounted as a control because it post-dates (rather than pre-dates) locally developed Kimmeridgian magmatism. Rift-flank uplift is likely to have also affected carbonate build-ups on the intervening rift shoulders of the eastern Black Sea, the Shatskiy Ridge and the Mid Black Sea High. At outcrop, subaerial exposure is often associated with karstification and secondary porosity development. Similar processes may have occurred in the offshore helping to enhance the reservoir quality of these exploration targets.

The offshore branch of the East African Rift System (EARS) has developed during late Cenozoic time along the eastern Africa continental margin. While Neogene–Pleistocene extensional tectonic deformation has been evidenced along the northern segment of the Davie Ridge, the spatial extent of deformation further south remains poorly documented. Based on recent and various oceanographic data sets (bathymetric surveys, dredge samples and seismic profiles), our study highlights active normal faulting, modern east–west extensional tectonic deformation and Late Cenozoic alkaline volcanism at the Sakalaves Seamounts (18°S, Davie Ridge) that seem tightly linked to the offshore EARS development. In parallel, rift‐related tectonic subsidence appears responsible for the drowning of the Sakalaves Miocene shallow‐water carbonate platform. Our findings bring new insights regarding the development of the EARS offshore branch and support recent kinematic models proposing the existence of a plate boundary across the Mozambique Channel.

Open Geosciences 2(4), 514-523 (2010). doi:10.2478/v10085-010-0023-6, Published by De Gruyter Open, Warsaw

A knowledge of Himalayan erosion history is critical to understanding crustal deformation processes, and the proposed link between the orogen's erosion and changes in both global climate and ocean geochemistry. The most commonly quoted age of India–Asia collision is ~ 50 Ma, yet the record of Paleogene Himalayan erosion is scant — either absent or of low age resolution. We apply biostratigraphic, petrographic, geochemical, isotopic and seismic techniques to Paleogene rocks of the Bengal Basin, Bangladesh, of previously disputed age and provenance. Our data show that the first major input of sands into the basin, in the > 1 km thick deltaic Barail Formation, occurred at 38 Ma. Our biostratigraphic and isotopic mineral ages date the Barail Formation as spanning late Eocene to early Miocene and the provenance data are consistent with its derivation from the Himalaya, but inconsistent with Indian cratonic or Burman margin sources. Detrital mineral lag times show that exhumation of the orogen was rapid by 38 Ma. The identification of sediments shed from the rapidly exhuming southern flanks of the eastern–central Himalaya at 38 Ma, provides a well dated accessible sediment record 17 Myr older than the previously described 21 Ma sediments, in the foreland basin in Nepal. Discovery of Himalayan detritus in the Bengal Basin from 38 Ma: 1) resolves the puzzling discrepancy between the lack of erosional evidence for Paleogene crustal thickening that is recorded in the hinterland; 2) invalidates those previously proposed evidences of diachronous collision which were based on the tenet that Himalayan-derived sediments were deposited earlier in the west than the east; 3) enables models of Himalayan exhumation (e.g. by mid crustal channel flow) to be revised to reflect vigorous erosion and rapid exhumation by 38 Ma, and 4) provides evidence that rapid erosion in the Himalaya was coincident with the marked rise in marine 87Sr/86Sr values since ~ 40 Ma. Whether 38 Ma represents the actual initial onset of vigorous erosion from the southern flanks of the east-central Himalaya, or whether older material was deposited elsewhere, remains an open question.