Few terrestrial localities preserve more than a trace lithic record prior to ca. 3.8 Ga greatly limiting our understanding of the first 700 Ma of Earth history, a period inferred to have included a spike in the bolide flux to the inner solar system at ca. 3.85-3.95 Ga (the Late Heavy Bombardment, LHB). An accessible record of this era may be found in Hadean detrital zircons from the Jack Hills, Western Australia, in the form of μm-scale epitaxial overgrowths. By comparing crystallization temperatures of pre-3.8 Ga zircon overgrowths to the archive of zircon temperature spectra, it should, in principle, be possible to identify a distinctive impact signature. We have developed Ti-U-Th-Pb ion microprobe depth profiling to obtain age and temperature information within these zircon overgrowths and undertaken a feasibility study of its possible use in identifying impact events. Of eight grains profiled in this fashion, four have overgrowths of LHB-era age. Age vs. temperature profiles reveal a period between ca. 3.85-3.95 Ga (i.e., LHB era) characterized by significantly higher temperatures (approximately 840-875°C) than do older or younger zircons or zircon domains (approximately 630-750°C). However, temperatures approaching 900°C can result in Pb isotopic exchange rendering interpretation of these profiles nonunique. Coupled age-temperature depth profiling shows promise in this role, and the preliminary data we report could represent the first terrestrial evidence for impactrelated heating during the LHB.early Earth | impact crater | lunar cataclysm | secondary ion mass spectrometry T he LHB is the period from ca. 3.85-3.95 Ga during which an intense flux of asteroidal and/or cometary bodies is hypothesized to have impacted the Moon (1). A variety of theories have been proposed to explain the LHB (2-5) culminating with the "Nice model" (5-7). This model posits that a fundamental shift in orbital resonance among the Jovian planets at ca. 3.9 Ga destabilized the disk of planetesimals in the outer solar system resulting in the scattering of numerous bodies into the inner solar system. Tera et al. (1) introduced the concept of a late lunar cataclysm to explain isotopic fractionations in rocks returned from the heavily cratered lunar highlands. Specifically, U-Pb, and Rb-Sr isochrons yielded recrystallization ages between 3.85-3.95 Ga. The parent/daughter behavior in these two geochronologic systems are quite different but result in similar system disturbances (i.e., U and Sr are highly refractory whereas Pb and Rb are variably volatile). Thus, a profound thermal event, such as from an impact at the appropriate scale of a "cataclysm," could have caused resetting of both chronometers, albeit for different reasons. Much of the evidence in support of the LHB hypothesis comes from 40 Ar∕ 39 Ar age spectra of lunar highland crust samples (3,8,9), interpreted to yield apparent "plateau" ages between 3.8-4.0 Ga due to the resetting of the K-Ar system via collisional heating (see review in 10).

Short running title: Lateral 3-D depositional architecture of small-scale cycles Abstract.Quantifying the geometries of evaporite deposits at the <1 km scale is critical in our understanding of similar ancient depositional systems, but is challenging given the tendency of evaporite minerals to dissolve at surface conditions. A high-resolution stratigraphic study in Brightling Mine, UK, provides insight into the threedimensional architecture and lateral continuity of anhydrite and carbonates within the basal Purbeck Formation. We conducted a field mapping study, combined with X-ray diffraction, petrographic microscopy, and δ 13 C and δ 18 O isotope analysis of samples.The stratigraphic interval contains five facies. The rhythmic sequences, in stratigraphic order are: (1) brown-grey microbial laminite, (2) black, fissile shale, and (3) dark brown-grey laminar marl, capped by blue-grey porphyritic nodular anhydrite.The interpreted environment of deposition is a shallow marine sabkha subject to

Most regional studies of reservoir and seals focus on large-scale sequences and their architecture. However, understanding flow and geochemical processes happening in the subsurface requires a multiscale approach from the pore-size to the field-size. Here we focus on an intermediate, 'inter-well' scale loosely defined as 100-1000 meter scale. This inter-well scale is crucial as it represents the minimum distance between an injector and a producing well. Hence, constraints on the heterogeneities in the reservoir or within a sealing lithology can guide the production geologist during EOR or CCS operations. In this paper, we present a review of existing outcrop analogues for the subsurface of Qatar that were considered for our study. Out of the different possibilities, we selected outcrops from Wadi Naqab (Ras-Al-Khaima, UAE) as an analogue for the subsurface reservoirs in Qatar, and we focused on mine outcrops in the U.K. as potential analogues to derive the 3D geometry of evaporite-carbonate sequences analoguous to the Hith Formation. The Jurassic limestones at Wadi Naqab appear layer cake at the scale of observation, but we demonstrate here that even though beds rarely pinch out, the facies within bed changes markedly at a scale of Ͻ200 meters. For subsurface applications, this could be significant if the change in facies correlates with a change in petrophysical properties. The anhydrite layers at Brightling Mine are mostly composed of nodular, sabkha-type layers, inter-bedded with shallow-water algal limestones and shales. These lithologies are continuous at a 500 meters scale, but scouring impacts on the thickness of the deposits. Again, this could have important mechanical implications during CCS operations, because the interface of different lithologies and their thicknesses control fracture propagation within reservoirs and seals. We conclude that more geometrical heterogeneities exist in both reservoir and seals than previously thought, and that inter-well scale data are needed to inform subsurface reservoir models. We also caution that one of the limitations of using outcrop analogues is that porosity and permeabilities are not preserved during uplift, and thus petrophysical properties within numerial reservoir modelling need to be populated using subsurface data.

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