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In northern Hispaniola, the Imbert Formation (Fm) has been interpreted as an orogenic "mélange" originally deposited as trench-fill sediments, an accretionary (subduction) complex formed above a SW-dipping subduction zone, or the sedimentary result of the early oblique collision of the Caribbean plate with the Bahama Platform in the middle Eocene. However, new stratigraphical, structural, geochemical and geochronological data from northern Hispaniola indicate that the Imbert Fm constitutes a coarsening-upward stratigraphic sequence that records the transition of the sedimentation from a pre-collisional forearc to a syn-collisional basin. This basin was transported on top of the Puerto Plata ophiolitic complex slab and structurally underlying accreted units of the Rio San Juan complex, as it was emplaced onto the North America continental margin units. The Imbert Fm unconformably overlies different structural levels of the Caribbean subduction-accretionary prism, including a supra-subduction zone ophiolite, and consists of three laterally discontinuous units that record the exhumation of the underlying basement. The distal turbiditic lower unit includes the latest volcanic activity of the Caribbean island arc; the more proximal turbiditic intermediate unit is moderately affected by syn-sedimentary faulting; and the upper unit is a (chaotic) olistostromic unit, composed of serpentinite-rich polymictic breccias, conglomerates and sandstones, strongly deformed by syn-sedimentary faulting, slumping and sliding processes. The Imbert Fm is followed by subsidence and turbiditic deposition of the overlying El Mamey Group. The 40Ar = 39Ar plagioclase plateau ages obtained in gabbroic rocks from the Puerto Plata ophiolitic complex indicate its exhumation at ~45-40 Ma (lower-to-middle Eocene), contemporaneously to the sedimentation of the overlying Imbert Fm. These cooling ages imply the uplift to the surface and submarine erosion of the complex to be the source of the ophiolitic fragments in the Imbert Fm, during or shortly after the emplacement of the intra-oceanic Caribbean island arc onto the continental margin. [ABSTRACT FROM AUTHOR]

Groundwater isoscapes are increasingly applied to a variety of hydrologic investigationsincluding recharge, paleoclimates and catchment processes. Generating stable waterisoscapes from a single sample taken from open-hole wells, as is typically the case, posesissues for fractured rock environments that are not present in porous media. To explore thevalue of isoscapes produced in fractured rock using open boreholes, a study was undertakenacross Central and Eastern Ontario, Canada where both sedimentary and crystalline bedrockare highly prevalent as aquifers. The study also aims to reveal the hydrologic factorsdominating the stable isotopic value of shallow groundwater in fractured rock. Toexplore this, a network of nine multi-level wells (25 intervals total) across threefield sites were sampled monthly from February 2017 to November 2018 for δ2Hand δ18O. Two rounds of tritium sampling were also conducted during that timeperiod. Multi-level wells were designed based on the results of 2-m interval constanthead tests, which enabled the identification of high transmissivity zones (2–3 perwell). To contrast these results, a larger, regional groundwater geochemistry datasetproduced by the Ontario Geologic Survey (OGS) was utilized. The OGS dataset,consisting of domestic and monitoring open-hole wells, was filtered to includeonly drilled bedrock wells in the same geologic formations as the multi-level wells(n=162). Spearman correlations between δ2H and various hydrologic parameters wereanalysed for both data sets to identify if stronger correlations existed from multi-levelwells than open-hole wells. Parameters included drift thickness, bedrock geology,surficial geology, vadose zone thickness, well depth, well transmissivity, tritiumvalue and average annual precipitation among others. For the temporal multi-leveldata, δ2H was averaged seasonally to explore whether a seasonal component ofsampling drives the strength of the correlations observed. This could be used tooptimize how isoscapes are generated in fractured rock. From the results of thecorrelation analysis, parameters that highly correlated with δ2H were used in amultiple regression analysis to identify the dominant parameters governing stableisotopes in shallow fractured rock. Results of these analyses will be presented. [ABSTRACT FROM AUTHOR]