Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism

The IODP‐ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well‐preserved peak ring. The borehole penetrated a sequence of post‐impact carbonates and a unit of suevites and clast‐poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre‐impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long‐distance transport of weakened material during collapse of the transient cavity and final crater formation

Seismic imaging and attribute analysis of Chicxulub Crater central sector, Yucatán Platform, Gulf of Mexico

Chicxulub Crater, formed ~66Ma ago by an asteroid impact on the southern Gulf of Mexico, is the best preserved of the three large multi-ring basins in the terrestrial record. The crater structure is characterized by a semi-circular concentric ring pattern, marking the crater basin, peak ring, terrace zone and basement uplift. Analysis of a grid of 19 seismic reflection profiles using seismic attributes, marker horizons, contour surfaces and 3-D views is used to investigate the stratigraphy of the central zone. We used interactive software and routine applications to map the impact breccias, breccia-carbonate contact and post-impact carbonates. Four horizons marked by high-amplitude reflectors representing high-impedance contrasts were identified and laterally correlated in the seismic  images. Complex trace attribute analysis was applied for petrophysical characterization. Surface contour maps of base and top of stratigraphic packages were constructed, which mapped the impactites and post- and pre-impact carbonate stratigraphy. Basin floor, marked by the contact between the impact breccias and overlying carbonates is shown by laterally discontinuous high-amplitude reflectors. Discontinuous scattered reflectors interpreted as the upper breccias beneath the crater floor, have an average thickness of ~300msm. The Paleogene sedimentary units are characterized by multiple reflectors with lateral continuity, which contrast with the seismic response of underlying breccias. The basal Paleocene sediments follow the basin floor relief. Upwards in the section, the carbonate strata are characterized by horizontal reflectors, which are interrupted by a regional unconformity. Onlap/downlap packages over the unconformity record a period of sea level change

Seismic imaging and attribute analysis of Chicxulub Crater central sector, Yucatán Platform, Gulf of Mexico

Chicxulub Crater, formed ~66Ma ago by an asteroid impact on the southern Gulf of Mexico, is the best preserved of the three large multi-ring basins in the terrestrial record. The crater structure is characterized by a semi-circular concentric ring pattern, marking the crater basin, peak ring, terrace zone and basement uplift. Analysis of a grid of 19 seismic reflection profiles using seismic attributes, marker horizons, contour surfaces and 3-D views is used to investigate the stratigraphy of the central zone. We used interactive software and routine applications to map the impact breccias, breccia-carbonate contact and post-impact carbonates. Four horizons marked by high-amplitude reflectors representing high-impedance contrasts were identified and laterally correlated in the seismic images. Complex trace attribute analysis was applied for petrophysical characterization. Surface contour maps of base and top of stratigraphic packages were constructed, which mapped the impactites and post- and pre-impact carbonate stratigraphy. Basin floor, marked by the contact between the impact breccias and overlying carbonates is shown by laterally discontinuous high-amplitude reflectors. Discontinuous scattered reflectors interpreted as the upper breccias beneath the crater floor, have an average thickness of ~300msm. The Paleogene sedimentary units are characterized by multiple reflectors with lateral continuity, which contrast with the seismic response of underlying breccias. The basal Paleocene sediments follow the basin floor relief. Upwards in the section, the carbonate strata are characterized by horizontal reflectors, which are interrupted by a regional unconformity. Onlap/downlap packages over the unconformity record a period of sea level change

Planetary Sciences, Geodynamics, Impacts, Mass Extinctions, and Evolution: Developments and Interconnections

Research frontiers in geophysics are being expanded, with development of new fields resulting from technological advances such as the Earth observation satellite network, global positioning system, high pressure-temperature physics, tomographic methods, and big data computing. Planetary missions and enhanced exoplanets detection capabilities, with discovery of a wide range of exoplanets and multiple systems, have renewed attention to models of planetary system formation and planet’s characteristics, Earth’s interior, and geodynamics, highlighting the need to better understand the Earth system, processes, and spatio-temporal scales. Here we review the emerging interconnections resulting from advances in planetary sciences, geodynamics, high pressure-temperature physics, meteorite impacts, and mass extinctions

Paleomagnetic behavior of volcanic rocks from Isla Socorro, Mexico

The direction and magnitude of the geomagnetic field vary both spatially and temporally and undergo significant departures from that of a geocentric axial dipole. In order to properly characterize persistent behaviors, time-averaged field models must be based on the highest quality data. Here we present full-vector paleomagnetic data for volcanic units exposed in the southeast quadrant of the island of Socorro, Mexico. We carried out a joint expedition between the Scripps Institution of Oceanography and the Universidad Nacional Autónoma México to Isla Socorro in January of 2005 during which we collected oriented paleomagnetic samples from 21 sites, representing as many as 10 different volcanic units (the oldest of which is ∼540 ka). We subjected over 100 specimens to the most up-to-date paleointensity methods, and included the standard reliability checks. In an earlier study, Bohrson et al. (1996) proposed a series of widespread eruptive events, based on similarities of argon/argon dates. Paleointensity from specimens that conform to the strictest acceptance criteria are available from both the (unoriented) original sample collection and our fully oriented (but as yet undated) new collection. Correlation between the two collections is however problematic. The time-averaged direction from Socorro is consistent with that expected from a geocentric axial dipole, and the time-averaged intensity is 30.0±7.1 μT, equivalent to a virtual axial dipole moment (VADM) of 67.6±16.0 ZAm2

A rock- and paleomagnetic study of a Holocene lava flow in Central Mexico

Magnetic measurements of the Tres Cruces lava flow (ca. 8500 years BP, Central Mexico) show the presence of two remanence carriers, a Ti-rich titanomagnetite with a Curie temperature between 350 and 400 °C and a Ti-poor magnetite with a Curie temperature close to 580°C. Magnetic changes after heating indicate that the titanomagnetite exsolves into magnetite w and ilmenite when the sample is heated to 580 °C. Paleointensity estimates with the Thellier and Thellier method [Thellier, E., Thellier, O., 1959. Sur l'intensité du champ magnetique terrestre dans le passe historique et geologique. Ann. Geophysique., 15, 285-376] were only successful up to temperatures of 350 to 400 °C. This temperature corresponds with the Curie temperature of the titanomagnetite, which is probably pseudo-single or multi-domain. Therefore, the paleointensities should be interpreted with caution. The magnetic composition changes after 580 °C heating may explain the large w variations in previous paleointensity determinations for the Tres Cruces rocks [Gonzalez, S., Sherwood, G., Bohnel, H., Schnepp, E., 1997. Palaeosecular variation in Central Mexico over the last 30,000 years: the record from lavas. Geophys. J. Int., 130, 201-219] using the [Shaw method Shaw, J., 1974. A new method of determining the magnitude of the palaeomagnetic field: application to five historic lavas and five archaeological samples. Geophys. J. R. Astr. Soc., 39, 133-141]

Late Paleozoic or early Mesozoic magnetizations in remagnetized Paleozoic rocks, State of Oaxaca, Mexico

Characteristics of the Oaxaca Terrane of southern Mexico suggest that the record of a complete Wilson cycle is present. The local basement is composed of high-grade rocks of the Oaxaca Complex, which is considered to have North American affinities based on Grenvillian lithologies and ages. In contrast, early Paleozoic sedimentary rocks in depositional contact with the Oaxaca Complex have very close faunal affinities with the Olenid-Ceratopygid trilobite province of Argentina. Late Paleozoic faunas indicate that by this time the Oaxaca Terrane was once again associated with North America. In an attempt to gain further insight into the drift history of this area, we have undertaken a paleomagnetic study of the Paleozoic sedimentary rocks of Oaxaca.The results of our study indicate that the entire Paleozoic section was remagnetized in the same paleomagnetic field at some time following late Paleozoic sedimentation, emplacement of an igneous complex, and the earlier of two folding events. Fold and conglomerate tests show that the remagnetization occurred prior to deposition and folding of overlying early Cretaceous sediments. The Oaxaca Paleozoic rocks were therefore remagnetized sometime between late Permian and early Cretaceous. Since the exact age of remagnetization is not known, we compare our result with data from cratonic North America for the bracketed range of magnetization ages. This analysis indicates that as much as 28[deg] of net counterclockwise rotation could have occurred between Oaxaca and cratonic North America subsequent to the Oaxaca remagnetization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27031/1/0000019.pd

Paleomagnetic results from Grenvillian-aged rocks from Oaxaca, Mexico: Evidence for a displaced terrane

In order to test the possibly displaced nature of the Proterozoic (`Grenville'-aged) Oaxaca terrane, a paleomagnetic study was carried out on gneissic and meta-igneous (anorthosite) rocks with metamorphic ages reported to be between 1100 and 900 Ma. Using alternating field (AF) and thermal demagnetization techniques, we have isolated two magnetic directions: a shallow and southerly direction (D = 155[deg], I = -1[deg]) and a very steeply down direction (D = 6[deg], I = +74[deg]). It seems likely that the shallow direction is a remagnetization associated with a slight reheating and cooling due to a nearby Permian-Triassic intrusion. The steep direction is interpreted as a magnetization acquired during uplift and cooling following the Oaxacan Orogeny, and gives a paleopole at 47[deg]N, 93[deg]W with an age of ~950 Ma. This pole is at least 40[deg] from the Grenville Loop of the North American apparent polar wander path and the observed paleolatitude of 60[deg]N is much higher than that predicted for Oaxaca if it had always belonged to North America in the same relative position it has today. The high paleolatitude obtained for the Oaxaca terrane does not preclude, however, that it was part of North America during Grenvillian times, but in that case its position would have been much closer to Ontario and Quebec than it is today.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28036/1/0000475.pd