Geologica Acta

The Chicxulub Crater Drilling Program - Borehole Core Characterization, Scanning and Logging

2024-11-11T10:42:05+00:00

Continuous core recovery, core scanning and physical property logging for characterization and petrophysics analyses in the Chicxulub drilling projects are reviewed. We focus on the Yaxcopoil-1 borehole, one of the Chicxulub boreholes drilled in the terrace zone that sampled the post-impact carbonates, impact breccias and target Cretaceous carbonates. Yaxcopoil-1 was continuously cored from 404 m to 1511 m, with core recovery of 98.5 %. The laboratory studies on drill cores include digital core scan images of cores and slabs, physical properties, mineralogy and geochemistry. The crater formed by an asteroid impact on the Yucatan platform at ~66 Ma ago, marking the Cretaceous/Paleogene boundary. It has a 200 km rim diameter and is not exposed at the surface, covered by ~1 km of carbonate sediments; thus its studies require geophysical surveys and drilling. Core analyses and 3-D and 2-D scans provide data on the stratigraphy, composition, textures, deformation and hydrothermal alteration. Impact breccias are heterogeneous materials, with clasts of melt, carbonates and basement in carbonate-rich and melt-rich matrix. The lower breccias were emplaced by high-temperature basal surges, which were followed by collapse of the impact plume and lateral curtains. The upper breccias are reworked air-fall deposits of the post-collapse stage. The crater formed a depositional basin, filled by sediments that preserve records of sea level and sediment transport across the platform. The Paleogene sequence is formed by limestones, dolomites, calcarenites and limestone conglomerates. The target sequence is formed by limestones, calcarenites, dolomite breccias and anhydrites. The studies show the usefulness of continuous coring and core analyses to constraint the crater formation, impact deformation, ejecta and impact dynamics.

An Integrated Remote Sensing, Petrographic, and Mineralogical Techniques for Mapping of Marble Deposits in the Vicinity of the Ophiolite Sequence in North Pakistan

2024-12-10T16:47:27+00:00

Marble, a high-pressure and high-temperature metamorphic rock primarily composed of calcium carbonate (CaCO3) and calcium magnesium carbonate (CaMgCO3), has been utilized extensively by ancient civilizations for various architectural purposes globally. The expansion of marble production during the 19th century facilitated its widespread use, with major quarries emerging in various regions, notably China, India, Italy, and Turkey. Despite its historical significance and economic importance, mapping and identifying marble deposits in remote and inaccessible areas remain challenging.

This study presents an integrated approach utilizing advanced remote sensing techniques for mapping carbonate lithologies in the Northwest Mohmand District, Khyber Pakhtunkhwa, Pakistan. By employing advanced spaceborne thermal emission and reflection radiometry (ASTER) imaging coupled with iterative adaptive reweighted regression (IARR), principal component analysis (PCA), minimum noise fraction (MNF), and spectral angle mapper (SAM) classification techniques, we processed and analysed the ASTER images using the Environment for Visualizing Images (ENVI) software. Subsequently, geographic information systems (GIS), ArcMap, and ArcScene software were used for spatial analysis and model generation.

Validation of the results was conducted through extensive fieldwork, X-ray diffraction (XRD), and petrographic analysis. The XRD and petrographic data corroborated the findings derived from the classified ASTER imagery, confirming the presence of significant concentrations of dolomite and calcite, which are indicative of carbonate deposits. The integration of these techniques underscores the efficacy of remote sensing as a viable tool for identifying and mapping mineralized zones in remote locations.

The findings of this study have significant implications for Pakistan's marble industry, particularly in Khyber Pakhtunkhwa, Punjab, and Baluchistan, where an estimated 300 million tons of marble reserves exist. Leveraging remote sensing techniques, this research contributes to the delineation of valuable marble resources and facilitates recommendations for targeted exploration activities in the Mohmand area and beyond.

Latest Barremian - early Aptian chronostratigraphy and sedimentary evolution of the northwestern Maestrat Basin

2024-07-12T10:10:16+00:00

Some aspects on the age and correlation of the upper Barremian-lower Aptian stratigraphic units of the NW Maestrat Basin were uncertain prior to this study, due to the differing lithostratigraphy of the marginal Oliete subbasin compared to the more depocentral Galve and Morella subbasins. New magnetostratigraphic, ammonite and sedimentological data presented in this study refine the age and sequence stratigraphy of the upper Barremian-lower Aptian succession, enabling a direct and precise correlation across these subbasins. Three third-order TR sequences are identified. The lower boundary of Sequence 1 corresponds to a transgressive surface found on top of the continental red beds of the lower Morella Fm. These beds are equivalent in age to the continental succession of the upper Blesa Fm. (Fm. (Oliete subbasin). The boundary between the M1 and M0r magnetozones (latest Barremian) is found above this surface, in the lower part of the Alacón Fm. Sequence 1 includes the lower part of the Alacón Fm., which passes basinwards to the upper Morella and Xert formations. Sequence 2 corresponds to the upper part of the Alacón Fm and basinwards to the Cap de Vinyet and Barra de Morella members of the Forcall Fm. The boundary between the M0r and C34n magnetozones (earliest Aptian) is found towards the lowermost part of Sequence 2. Sequence 3 includes the Josa Fm and its offshore equivalents, the Morella la Vella Mb. and the Villarroya de los Pinares Fm. Additionally, the overall facies distribution in successive depositional stages is reconstructed, describing the lateral transition from marginal protected to open marine areas. The improved chronostratigraphic framework presented here will enable more accurate correlations with other subbasins of the Maestrat Basin, and the reconstructed sedimentary evolution may be useful for the interpretation of other Lower Cretaceous successions of the Tethys.

Paleogene kinematics of the central Catalan Coastal Ranges: temporal constraints from magneto-chronology and provenance analysis in synorogenic deposits in the SE margin of the Ebro Basin (NE Spain)

2024-11-06T15:52:11+00:00

The precise determination of the tectonic deformation timing such as thrust emplacement has always been a challenge for understanding the evolution of fold-and-thrust belts. In the Catalan Coastal Ranges, this issue has traditionally been addressed through the mapping and the analysis of the syn-tectonic successions preserved in the SE margin of the Ebro Basin. However, the age of the Paleogene contractional structures located towards the hinterland and responsible of the inversion and uplift of the inherited Mesozoic structure remained uncertain due to the lack of preserved syn-kinematic strata in these areas. With the aim of better understand the contractional evolution of the area during the Paleogene, this work presents a tectono-stratigraphic analysis approach that combines structural reconstructions, provenance analysis and magnetostratigraphic dating in well-exposed synorogenic sediments in the central SE margin of the Ebro Basin. The results of the study allow to establish the precise age of the main contractional structures present in the central Catalan Coastal Ranges. The combined analysis has revealed that: i) the inversion of the Montmell-Vallès Faults System started in the Bartonian and continued up to the late Priabonian, and ii) the emplacement of the Gaià-El Camp Thrust and the formation of the Cabra-Carme Anticline took place from early to late Priabonian and was the responsible of the sudden increased of the sedimentation rates. A later decrease of the sedimentation rates during late Priabonian (chron C15n) has been interpreted as the prelude of the end of the Paleogene compressional phase in the area.