Deformation features in Paleogene sands in the Hoegaarden area (Belgium)

During excavation works for the construction of the TGV track along the motorway Brussels-Liège (E40) near the interchange Tienen-Hoegaarden-Jodoigne a number of interesting, but only temporary outcrops were created. These outcrops offered not only the occasion to learn more about the stratigraphy, paleogeography and paleobotany of the Paleogene, but also revealed some particular deformation features. The Outgaarden Section, SE of the interchange, showed chaotically deformed sands at the base of the Upper Paleocene Tienen Formation. The highly viscous deformation features originated in a high-energy depositional environment. Dewatering, mass movements and strong currents caused the syndepositional, probably gravitationally-induced sediment deformation. The Goudberg Section, NW of the interchange, exposed the Overlaar Petrified Forest, of which part of the silicified tree-stumps were recovered to constitute the main feature of the planned GEOPARK HOEGAARDEN. In this section tectonically-induced faulting could be demonstrated. The fault shows a clear normal displacement. A sinistral strike-slip displacement is moreover supposed. Faulting occurred prior to the deposition of the Pleistocene loam cover but definitively postdates the deposition of the Ypresian clays. It is proposed that this faulting event in the Tertiary sediments may be caused by a reactivation of underlying master faults in the Lower Paleozoic basement of the Brabant Massif.

The Lower Siwalik - Basement unconformity in the Sub-Himalaya of eastern Nepal and its significance

South of the Main Boundary Thrust (MBT), in the Sub-Himalaya of central and eastern Nepal, pre­ Siwalik rocks in the form of fault bound slices are known to occur. Recently the present authors have mapped these rocks in the Udayapur district of south eastern Nepal. In the area about 1 km wide pre­ Siwalik rocks extend for over 50 km along a NE-SW direction. In the eastern area around Ttntale village (near the Tawa Khola-Baijanatb Khola confluence), the stromatolitic dolomites of Tintale Formation of the pre-Siwalik Group is overlain by the Lower Siwalik with a prominent unconformity marked by a 4.5 m thick basal conglomerate. Likewise, in the western area along the Manba Khola, the Siwalik Group overlies the pink sandstones and shales of the Manba Formation of the pre-Siwalik Group with an unconformity, again with a conglomerate horizon at the base. It is perhaps the only occurrence where the base of the Siwalik Group is recorded in Nepal. In this part of the Himalaya, the Siwalik sediments directly overlie the Precambrian-Lower Paleozoic (?) basement rocks with an unconformity. The basement rocks along with its Siwalik cover was brought to the surface by thrusting within the Sub-Himalaya.