Decreasing uplift rates and Pleistocene marine terraces settlement in the central lesser Antilles fore-arc (La Desirade Island, 16 degrees N)

International audienceThis study investigates the Lesser Antilles fore-arc at the latitude of Guadeloupe Archipelago and evidences that La Désirade Island, the eastermost island of the forearc, displays a staircase coastal sequence including four uplifted marine terraces and an upper reefal platform with mean shoreline angle elevations ranging from 10 to 210 m above sea level (asl). The platform paleobathymetry is constraint by a detailed analysis of the sediments. We propose a revised morphostratigraphy for this coastal sequence including 5 paleo-shorelines based on six U/Th dating from aragonitic corals from the three lowest terraces combined with paleobathymetric analysis of the fossil corals present in the upper platform. Terrace and upper platform carving of construction periods occurred during Marine Isotopic Stages MIS 5e, MIS 9, and during the intervals MIS 15–17, MIS 19–25 and MIS 31–49 (upper coral reef platform). Our results evidence a bulk decreasing uplift rate since early Calabrian to Present-Day, clearly documented since 310 ka (MIS 9) (from 0.14 to 0.19 to ca 0 mm/y). Our data are consistent with first the transient influence of the subducting oceanic Tiburon ridge during Calabrian, then with other parametres of the subduction zone since late Calabrian to Present-Day (dip of the slab, basal erosion of the upper plate, inherited structures …)

Sedimentology, palaeoenvironments and biostratigraphy of the Pliocene-Pleistocene carbonate platform of Grande-Terre (Guadeloupe, Lesser Antilles forearc)

International audiencePliocene and Pleistocene deposits from Grande-Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation both controlled by rapid sea-level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 ('Calcaires inférieurs à rhodolithes') deposited during the late Zanclean to early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal-rich deposits, which dominate the western part of Grande-Terre, change to planktonic foraminifer-rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 ('Formation volcano-sédimentaire', 'Calcaires supérieurs à rhodolithes' and 'Calcaires à Agaricia') was deposited during the late Piacenzian to early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal-dominated ramp that changes upward into a homoclinal, coral-dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea-level fall. Finally, Sequence S4 ('Calcaires à Acropora') probably formed during the Calabrian, developing as a coral-dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in late Calabrian times

Characterizing the Neogene tectono-sedimentary evolution of the Northern Lesser Antilles forearc: a land-sea study

International audienceIn the frame of the ANR program GAARanti, aiming to track regional emersion surfaces and potential timing of land emersion or drowning, we conducted new field studies in islands belonging to the Anguilla Bank (Saint Barthélémy, Saint Martin, Tintamarre and Anguilla), the northernmost bank located in the forearc of the Lesser Antilles subduction zone and south of the Anegada passage. Our new micropaleontological, sedimentological and paleoenvironmental investigations allow a highly accurate calibration of the Neogene successions using large benthic foraminifers, planktonic foraminifers and calcareous nannofossils. We determine three main regional unconformities cropping out on the islands of the Anguilla bank.Interpretations of seismic lines acquired during the AntiTheSis (2016) and GARANTI (2017) cruises allow to reconstruct the tectono-sedimentary evolution of the offshore forearc basins, between South Saba Bank and Sombrero Basin. We use our well constrained onshore dataset and petroleum industry wells drilled in the Saba Bank to propose a constrained sismostratigraphy of offshore basins and onshore-offshore correlations.At regional scale, we identify three main unconformities dated: (1) Late Eocene, (2) Mid Miocene (ca 15 Ma) and (3) Zanclean (4 Ma).The Late Eocene unconformity is related to compressional tectonics and led to the emergence of most of our study area. Then subsidence occurred and topographic depressions were infilled by Oligocene to Early Miocene deposits, partly controlled by extensional fault activity along NW-SE and ENE-WSW faults systems bounding the Kalinago Basin and Anguilla Bank, respectively. The Mid Miocene unconformity is related to tectonics with increasing importance from south to north, thus probably related to the onset of the opening of Anegada Passage. This unconformity is related to emergence and erosion on the Anguilla and Saba Banks. The northern Antilles then subsided and most of basins reveal passive infilling during Middle Miocene to Pliocene. The Zanclean unconformity is related to localized uplifts that led to the final emergence of Anguilla, Tintamarre and St Martin carbonate platforms

Oligocene to Pliocene paleogeography of the northern Lesser Antilles arc.

International audienceIn the frame of the GAARAnti ANR-17-CE31-0009 project, we aim at establishing the paleogeography of the arc/forearc areas of the Northern Lesser Antilles over the last 35 Ma to bring constraints for the mammal fauna dispersion paleo-biogeographic models from south America to Greater Antilles. Available paleogeographic maps are ancient (Stephan et al., 1990; Iturralde-Vinent & McPhee, 1999) and contradictive. During that time, the forearc of the Lesser Antilles subduction zone strain pattern accommodated (i) strain partitioning related to subduction obliquity and (ii) progressive trench bending by several episodes of differential vertical and horizontal motions which may have built and/or destroyed continental areas allowing south american terrestrial mammals to reach the Greater Antilles or isolating some south American mammals on newly formed islands. We conducted new studies, onshore on the Anguilla Bank islands and offshore in Kallinago Trough and Wallichi Plateau to reconstruct the evolving paleogeography of this area. We used: 1) new micropaleontological, sedimentological and paleoenvironmental results acquired onshore and from dredged samples during the GARANTI Cruise in may 2017; 2) a database of seismic profiles from various sources: CPEM 1980; ANTITHESIS 2016 and GARANTI 2017 cruises.Onshore, we revised the stratigraphy of the Neogene series. Offshore, we established a seismic stratigraphy and correlated the seismic units and erosional unconformities with the onshore lithostratigraphic successions. We then built paleogeographic maps for different time spans: late Eocene-early Oligocene, late Oligocene-Aquitanian, Burdigalian, early Langhian, mid-late Miocene and Zanclean. During late Eocene-early Oligocene most the area was emergent except in the Kallinago Trough. Significant subsidence periods occurred during Burdigalian and mid-late Miocene and most of the terrestrial areas were drowned. During early Langhian and Zanclean numerous small islands occurred

Investigating Northern Lesser Antilles strain evolution during Eocene

International audienceUpper 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

Geodynamic of the Lesser Antilles Back arc Domain; contributions of the GARANTI cruise, in the Grenada Basin

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Paleogeographic reconstructions of the northern Lesser Antilles during the Neo-gene (24-2 Ma)

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