Early modification stage (preresurge) sediment mobilization in the Lockne concentric, marine-target crater, Sweden
Article first published online: 12 FEB 2013
© The Meteoritical Society, 2013.
Meteoritics & Planetary Science
Volume 48, Issue 3, pages 321–338, March 2013
How to Cite
Sturkell, E., Ormö, J. and Lepinette, A. (2013), Early modification stage (preresurge) sediment mobilization in the Lockne concentric, marine-target crater, Sweden. Meteoritics & Planetary Science, 48: 321–338. doi: 10.1111/maps.12058
- Issue published online: 18 MAR 2013
- Article first published online: 12 FEB 2013
- Manuscript Accepted: 23 NOV 2012
- Manuscript Received: 31 JUL 2012
- Swedish Research Council. Grant Number: 90449201
- Swedish Deep Drilling Program
- International Continental Scientific Drilling Program. Grant Number: AYA2008-03467
- Spanish Ministry of Science and Innovation
Lockne is a concentric impact structure due to a layered target where weak sediments and seawater covered a crystalline basement. A matrix-supported, sedimentary breccia is interlayered between the crystalline breccia lens and the resurge deposits in the crater infill. As the breccia is significantly different from the direct impact breccia and the resurge deposit, we propose a separate unit name, Tramsta Breccia, based on the type locality (i.e., the LOC02 drilling at Tramsta). We use granulometry and a novel matrix line-log method to characterize the sedimentology of the Tramsta Breccia. The obliquity of impact combined with the layered target caused an asymmetric, concentric transient crater, which upon its collapse controlled the deposition of the breccia. On the wide-brimmed downrange side of the crater where the sedimentary target succession was removed during crater excavation, wide, overturned basement crater ejecta flaps prevented any slumping of exterior sediments. Instead, the sediments most likely originated from the uprange side where the brim was narrow and the basement crater rim was poorly developed, sediment-rich, and relatively unstable. Here, the water cavity wall remained in closer proximity to the basement crater and, aided by the pressure of the collapsing water wall, unconsolidated black mud would flow back into the crater. The absence of interlayered resurge deposits in the Tramsta Breccia and the evidence for reworking at the contact between the overlying resurge deposits and the Tramsta Breccia indicate that the slumping was a rapid process (<75 s) terminating well before the resurge entered the crater.