Data report: preliminary assessment of Pleistocene sediment strength in the Ursa Basin (Gulf of Mexico continental slope) from triaxial and ring shear test data

We report the preliminary results of a triaxial and ring shear study on clay-rich, fine-grained Pleistocene sediments cored in Ursa Basin, Gulf of Mexico continental slope. Specimens from Integrated Ocean Drilling Program (IODP) Expedition 308 Sites U1322 and U1324 document friction coefficients in the range of 0.13–0.31, with internal angles of friction of ~7.4°–17.2° in ring shear experiments. At intermediate (7.624 MPa) to high (15.237 MPa) overburden pressure, the majority of the samples tested show velocity weakening, whereas lower overburden pressures do not give a clear trend regarding velocity weakening or strengthening of the samples. In consolidated-undrained triaxial tests, peak shear stresses observed are between 27 and 140 kPa, with the strongest sample by far coming from a core catcher section. We suspect that this is an effect of fabric changes induced during hydraulic piston coring. One sample coming from the base of a mass transport deposit at Site U1322 is the weakest one tested. Young’s moduli calculated range from 2 to 17.4 kPa. Stress paths indicate slight overconsolidation of the samples, which is in line with the information gained from preconsolidation stresses in other studies. Permeability determined from consolidation data is in the range of 10–16 to 10–17 m2, and hydraulic conductivity is around 10–9 to 10–10 ms–1. Grain density of the tested samples is around 2.7 g/cm3, and water content ranges from 18.3% to 30.7%

Geologie und Strukturentwicklung der Blankuskopf- und Wildberggruppe im südlichen Brandnertal (Rätikon, Österreich)

Detailed geological mapping and structural analysis of the Blankuskopf- and Wildberggroup in the Rätikon area (Vorarlberg/Austria) was carried out in the framework of a Diploma-thesis at the University of Freiburg. The full stratigraphy of the Northen Calcareous Alps (NCA) can be found in the area, starting with the skythian Bundsandstein and continuing up to the upper Cretaceous Kreideschiefer, as well as lithologies from the south-Penninic Arosazone. The structural style of the mapping area is characterized by many folds and thrusts and shows two mean features: 1) From the lower to the higher tectonic unit and from NW to SE there is a change in transport direction from NW via N to NE. This change is linked to a clockwise rotation of each unit with respect to its underlying unit. 2) Within each unit there is a change in transport direction from NW in its western part to N in its eastern part. This is especially pronounced in the well-conserved unit of the Blankuskopfgroup. The structures are the result of horizontal shortening as well as dextral shearing. The latter is represented by the fl exing of fold-axes and clockwise rotation

Mass wasting at the base of the South central Chilean continental margin: the Reloca Slide

Offshore south central Chile (35° S–42° S), the morphology of the lowermost continental slope and trench floor witnesses a voluminous submarine mass-wasting event. The blocky slide body deposited in the Chile Trench at 73°46´ W 35°35´ S was targeted for study during RRS JAMES COOK Cruise JC23 and termed Reloca Slide. Its size of about 24 km3, its steep and high headscarp, the spatial distribution of slide deposits and the cohesive nature of major slide blocks make it interesting to address the issue of tsunami generation. We have obtained seismic reflection data that partly reveal the internal structure of the slide body. Gravity core samples were retrieved that will allow the slide to be dated and linked to the history of sedimentation and slope stability along this particular segment of the Chilean convergent margin. At present we assume a Holocene age for the sliding event