Abstract The Chicxulub impact ∼66 Ma ago formed a large basin on the Yucatán platform, filled by sediments that provide a record of carbonate deposition, sea level and climate changes in the Gulf of Mexico. We study the post-impact sequence drilled in the Yaxcopoil-1 borehole in the crater terrace zone. The post-impact section is 792 m thick, overlying the impactites and Cretaceous carbonates. Section analyzed is between 400 and 792 m, formed by twelve units of limestones, dolomites, argillaceous/silicified limestones and calcarenites. Carbonates show cross-lamination, flow-currents, parallel lamination, cyclic graded bedding and styolitic structures. Study is based on core analyses, logging, petrography, digital scanned images, magnetic properties and X-ray diffraction and X-ray fluorescence geochemistry. The basal units U1–U4 represent low-energy deep bathyal environments and fine-grained facies varying from mudstone to wackestone. Sediment deposits, reworked and transported from the platform and crater rim, show textural and grain size changes from grainstone to packstone. Geochemical and magnetic susceptibility logs record effects of hydrothermal alteration, with secondary mineral assemblages. The SiO 2 and CaO contents display wide ranges, negatively correlated. Fe 2 O 3 , TiO 2 , Al 2 O 3 and K 2 O oxides show similar patterns downhole. The Sr and MgO show a positive correlation, except for the basal sediments. Paleocene units U1–U3 show increasing density, increasing seismic velocity and upward decreasing porosity. Upper units U5–U12 are characterized by laminated black shales and marls with microfacies varying from wackestone to packstone, with planktic and benthic foraminifera and bioclasts. Unit U9 shows low density and seismic velocity and increased porosity. Depositional environments vary from low-energy deep bathyal inside the basin to shallow neritic outside the crater rim. Sediments of the internal carbonate ramp to external neritic environments record sea level changes and platform subsidence/uplift.

Abstract In this contribution, we use all three components of the gravity vector observations to compute a regional geoid and demonstrate the advantages of using the horizontal components alongside the vertical component. We apply the one-step integration method within the remove-compute-restore framework; where the long-wavelength part of the geoid is recovered from Earth’s gravitational models while the harmonicity of the computational space is ensured by removing the topographic effects. We create a system of linear equations using a discretized form of the one-step integration method and use the Tikhonov technique to deal with the numerical instability due to its implicit downward continuation and to determine the geoid at higher resolution, e.g., 1 ′ × 1′. We propose a novel method to estimate the Tikhonov regularization parameter using the discrepancy principal and a stable solution of the geoid at lower resolution, e.g., 3′ × 3′. The results reported are based on real airborne gravity vector observations collected over Colorado, USA. The scattered observations at flight level are directly inverted to the disturbing potential at grid points on the reference ellipsoid, where geoid heights are then computed using Bruns formula. We evaluate the external accuracy of the geoid by comparing it with GNSS/levelling data and estimate the location-based internal uncertainties (error) of the geoid heights through formal error propagation. As part of this contribution, the airborne gravity vector data used in this study are also available for research purposes upon request to the corresponding author.

Most methods for processing seismological data require a suitable velocity model characteristic for the given region being defined. This is also the case of the Reykjanes Peninsula in SW Iceland, where the REYKJANET seismic network was built to monitor local seismicity in the rift zone. At present, four previously published 1D velocity models (SIL, BRA, TRY and VOG) can potentially be used, prompting us to determine which one is the best. In order to address this issue, we arranged a contest in which all four 1D models and one additional 3D model (T3D) were entered. Uniform methodology for classifying the models was applied and included an analysis of: (i) post-1ocalization travel-time residuals, (ii) residuals of the P-wave first-motion incidence angle and (iii) model-predicted and measured Rayleigh-wave dispersion. We discovered that no single model was unequivocally the most optimal, as the differences between them proved rather minor. A common shortcoming of all the models is the bias of the P-wave first motion incidence angle residuals, which may be a general problem for methods working with P-wave amplitudes (e.g., moment tensor solutions). The VOG model was selected with a weak preference. Finally, we propose a simple method for modifying any of the 1D models by adding a station-dependent surface layer with a vertical velocity gradient. This way, a pseudo-3D model is generated which is fully competitive with a true 3D model while retaining the simplicity of 1D ray tracing. The efficiency of this correction was demonstrated using the VOG model. The corrected VOG model provides post-1ocalization residuals comparable with the true 3D model T3D, has zero bias in predicting the P-wave first-motion incidence angles, and agrees acceptably in predicting the Rayleigh-wave phase-velocity known from other sources. While calculations with a 3D model can be clumsy, the proposed pseudo-3D model is defined by few parameters and is very easy to use. Its applicability is limited to earthquake sources deeper than the deepest lower limit of the topmost layer below the stations.