The Popigai impact ejecta layer in the Monte Vaccaro section, Piobbico, Italy
Abstract
Previously the ejecta from the impact creating the ca. 100 km large Popigai crater in Siberia has been found in Late Eocene sediments in the Massignano section, near Ancona in Italy. Here the ejecta layer is associated with an iridium anomaly, shocked quartz, and abundant clinopyroxene-bearing spherules weathered to so called pancake spherules. Recently we showed that the ejecta is also associated with an enrichment of H-chondritic chromite grains (>63 μm), possibly representing unmelted fragments of the impactor (Boschi et al., 2017). Here we report the first discovery of the Popigai ejecta at another locality in Italy. We found the ejecta in the Monte Vaccaro section, 90 km northwest of Ancona, at the same biostratigraphic level as in the Massignano section. The ejecta layer contains shocked quartz, abundant pancake spherules and an iridium anomaly, just like at Massignano. We measure peak Ir concentrations of 686 ppt, a factor of three higher than the Ir anomaly in the Massignano section. The limestone across the ejecta in the Monte Vaccaro section contains fewer terrestrial spinel grains than at Massignano, making searches for extraterrestrial chromite grains also in size fractions <63 μm feasible. Grains in the size fractions 32-63 μm generally tend to be a factor 10-30 more common than >63 μm grains. The smaller the size fraction of a sedimentary extraterrestrial chromite residue that can be studied, the more statistically robust inferences can be made. The preliminary results for grains in the 32-63 μm fraction from the Monte Vaccaro section indicate a more complex scenario than that based on the >63 μm fraction of chromites recovered from the Massignano section. ReferencesBoschi, S., Schmitz, B., Heck, P.R., Cronholm, A., Defouilloy, C., Kita, N. T.,Monechi, S., Montanari, A., Rout, S. S., Terfelt, F., 2017. Late Eocene 3He and Ir anomalies associated with ordinary chondritic spinels. Geochim. Cosmochim. Acta 204, 205-218.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMEP11B1557B
- Keywords:
-
- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 2129 Interplanetary dust;
- INTERPLANETARY PHYSICS;
- 6205 Asteroids;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6240 Meteorites and tektites;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS