Different scales of salt-sediment interaction around passive diapirs

<p>Passive diapirism entails ongoing, near-surface syndepositional growth of a salt stock or wall. As such, the diapirs and intervening minibasins influence the development and geometries of associated sedimentary strata. In this short overview, we distinguish between two scales and aspects of salt-sediment interaction that reflect a depositional continuum from the topographic highs of diapir roofs to the lows of depocenters. At the larger, multi-km scale, minibasin tectonostratigraphic successions form bowls, troughs, wedges, or layers that respond to differential evacuation of the deep salt layer. These successions have internal concordant, onlapping, or truncated geometries, and they stack into different patterns based on the evolution of active salt tectonic processes. At the smaller scale, passive diapirs create local sea-floor scarps due to drape folding of the diapir roof over the edge of the rising diapir. Depending primarily on the thickness of the roof, this results in tabular or tapered composite halokinetic sequences within 1 km or less of the diapir edge. It is important to keep these geometries and processes separate as they have distinct implications for sediment transport and deposition as well as the definition and detailed geometries of hydrocarbon traps in three-way truncations against diapirs and welds.</p>

The lower Miocene flint conglomerate, Jylland, Denmark: a result of the Savian tectonic phase

The early Miocene was an important period for the development of the eastern North Sea. Tectonism in North-West Europe resulted in uplift of the Scandinavian mountains, reactivation of salt structures, inversion of old graben structures and deposition of the most coarse-grained deposits in the Danish pre-Quaternary succession. Some of these deposits were later cemented into conglomerates. The deposits are common in the fluvial parts of the Billund Formation (Aquitanian) and the basal transgressive lag of the late Aquitanian – Burdigalian Klintinghoved Formation capping the Billund Formation. Questions remained as to the age of these deposits and what they infer about tectonic events in the region. This study reviews the geology of the flint-dominated conglomerates and presents the first dates for a sample of these unique deposits. We observe grain sizes up to 5 cm diameter. Palynological analyses place the sample as early Miocene. Some samples from the area have suggested a local source near active salt structures, associated with the uplift of the pre-Neogene sedimentary successions. We suggest that the common occurrences of flint clasts in the lower Miocene succession reveal significant erosion of Upper Cretaceous and Danian chalk, likely associated with the uplift of the Scandinavian lowlands during the Savian tectonic phase, early Miocene.

Dissolution collapse of a growing diapir from radial, concentric, and salt-withdrawal faults overprinting in the Salinas de Oro salt diapir, northern Spain

A geomorphic investigation of the Salinas de Oro salt diapir in the Pyrenees reveals that the ring fracture pattern related to the karstic collapse of the diapir crest may vary significantly depending on the rates of dissolution and salt flow, and the rheology of the overburden. The salt diapir has well-developed concentric faults related to salt dissolution subsidence throughout the Quaternary. Roof strata accommodate subsidence by a combination of downward sagging and brittle collapse leading to the development of a ring monocline that is broken by 5 to 20 m throw conjugated normal faults and a 40 m throw, 9.5-km-long and 200-m-wide keystone graben. The salt diapir top has >100-m-long sinkholes that coalesce to form hollows >70 m deep. Up to 3-km-long radial grabens with a 70 to 90 m vertical throw overprint concentric-ring faulting and displace Quaternary deposits demonstrating active salt flow and diapir rise. Radial faults are linked with salt-withdrawal faults of the Andia Fault Zone (AFZ). Salt flow from the AFZ into the Salinas de Oro salt diapir causes brittle gravitational extension of limestone strata leading to a sequence of grabens and Quaternary faults >10 km long and several hundred meters deep.