The geological framework for Hvideklint, south-east Denmark, using glaciodynamic sequence stratigraphy

Glaciodynamic sequence stratigraphy provides a practical model for grouping and classifying complex geological data to aid interpretation of past climatic and environmental development in Quaternary successions. The principles of glaciodynamic sequence stratigraphy are applied here to summarise the complex glacial geological framework of Hvideklint on the island of Møn, south-east Denmark. The framework of the superimposed deformed Hvideklint is presented in a reconstructed geological cross-section of Hvideklint. For the construction of the architecture of the glaciotectonic complex, the interpretation of structures below sea level was based on a detailed new survey of the cliff section combined with construction of successive approximation balanced cross-sections. The new description is supported by drill hole data from the Jupiter database. Where chalk is not glaciotectonically deformed, the constructed depth to the top-chalk-surface is generally located about 30 m below sea level. In Hvideklint, thrust sheets with chalk are exposed 20 m above sea level, and the balanced cross-section constructions indicate that the décollement surface for a Hvideklint glaciotectonic complex is located about 80 m below sea level. Between the décollement level and the top of the complex, two or more thrust-fault flat-levels and connecting ramps add to the complex architecture of Hvideklint.

Balanced cross-section across the Siwaliks of the Trijuga Valley, eastern Nepal

The strata of the Siwalik Group in the Trijuga valley is dissected by two thrusts, repeating the succession three times and forming a longitudinal Dun Valley. The total thickness of the Siwalik strata exceeds 5000 m in the area. A balanced cross-section has been constructed across the Siwalik Range in the Trijuga valley showing that the Main Himalayan Thrust (MHT) lies at the depth of about 5.2 km from the surface. The Main Frontal Thrust (MFT), Kamala Tawa Thrust (KTT), Marine ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­Khola Thrust (MKT) and Main Boundary Thrust (MBT) ramp-up from the MHT. Along with these faults, fault-bend anticlines associated with these thrusts have shortened the Siwalik of the area. The shortening across the area has been calculated to be approximately 33.7 km.

Role of structural inheritances in the development of the Mountain Front Flexure in the Lurestan region of the Zagros belt

<p>The Mountain Front Flexure is a major structure of the Zagros orogenic system, and is underlain by the deeply rooted and seismically active Mountain Front Fault system. These coupled structural features divide the belt from its foreland and their trace is sinuous, forming salients and recesses. The origin and tectonic significance of the Mountain Front Fault system and its sinuosity are still unclear, with most of hypotheses pointing to a strong structural control exerted by geological inheritances. In this work we combine interpretation of seismic reflection profiles, earthquake data, geomorphic analysis, and geological observations, to build a balanced cross section across the Mountain Front Flexure in the Lurestan region. Our data are suggestive of a hybrid tectonic style for the Lurestan region, characterised by a major and newly developed crustal ramp in the frontal portion of the belt (i.e the Mountain Front Fault) and by the reactivation of steeply dipping pre-existing basin-bounding faults, along with a minor amount of shortening, in the inner area. Specifically, the integration of our results with previous knowledge indicates that the Mountain Front Fault system developed in the necking domain of the Jurassic rift system, ahead of an array of inverted Jurassic extensional faults, in a structural fashion which resembles that of a crustal-scale footwall shortcut. Within this structural context, the sinusoidal shape of the Mountain Front Flexure in the Lurestan area arises from the re-use of the original segmentation of the inverted Jurassic rift system.</p>

A Balanced Geological Cross-Section along Kohalpur – Surkhet Area of Sub-Himalayan Range, Mid-Western Nepal

The Sub-Himalayans Zone comprises a tectonic wedge of syn-orogenic sediments along the outer Himalayan Belt. Sediments are integrated into the accretionary prism from the foreland Indo-Gangetic plain, undergo a tectonic cycle within it, and eventually are eroded. The structural sketch map unveils westward-plunging arcuate structures on the leading location of the Outer Belt. A balanced cross-section has been constructed across the Sub-Himalayan Hills of the Kohalpur-Surkhet region of mid-western Nepal in order to determine the structural geometry of the region and to calculate tectonic shortening. The mid-western Nepal Sub-Himalaya has an emergent splay fan geometry with no major prevailing thrust contains the Main Boundary Thrust (MBT), the Bheri Thrust, the Babai Thrust and the Main frontal Thrust (MFT) which are all imbricate of the main decollment which ramp up-section through the 5 km thick tectonic sedimentary prism. North-south shortening across the mid-western Nepal, Kohalpur-Surkhet section has been approximately 29 km, or 55% shortening.

Examining the tectono-stratigraphic architecture, structural geometry, and kinematic evolution of the Himalayan fold-thrust belt, Kumaun, northwest India

Existing structural models of the Himalayan fold-thrust belt in Kumaun, northwest India, are based on a tectono-stratigraphy that assigns different stratigraphy to the Ramgarh, Berinag, Askot, and Munsiari thrusts and treats the thrusts as separate structures. We reassess the tectono-stratigraphy of Kumaun, based on new and existing U-Pb zircon ages and whole-rock Nd isotopic values, and present a new structural model and deformation history through kinematic analysis using a balanced cross section. This study reveals that the rocks that currently crop out as the Ramgarh, Berinag, Askot, and Munsiari thrust sheets were part of the same, once laterally continuous stratigraphic unit, consisting of Lesser Himalayan Paleoproterozoic granitoids (ca. 1850 Ma) and metasedimentary rocks. These Paleoproterozoic rocks were shortened and duplexed into the Ramgarh-Munsiari thrust sheet and other Paleoproterozoic thrust sheets during Himalayan orogenesis. Our structural model contains a hinterland-dipping duplex that accommodates ∼541–575 km or 79%–80% of minimum shortening between the Main Frontal thrust and South Tibetan Detachment system. By adding in minimum shortening from the Tethyan Himalaya, we estimate a total minimum shortening of ∼674–751 km in the Himalayan fold-thrust belt. The Ramgarh-Munsiari thrust sheet and the Lesser Himalayan duplex are breached by erosion, separating the Paleoproterozoic Lesser Himalayan rocks of the Ramgarh-Munsiari thrust into the isolated, synclinal Almora, Askot, and Chiplakot klippen, where folding of the Ramgarh-Munsiari thrust sheet by the Lesser Himalayan duplex controls preservation of these klippen. The Ramgarh-Munsiari thrust carries the Paleoproterozoic Lesser Himalayan rocks ∼120 km southward from the footwall of the Main Central thrust and exposed them in the hanging wall of the Main Boundary thrust. Our kinematic model demonstrates that propagation of the thrust belt occurred from north to south with minor out-of-sequence thrusting and is consistent with a critical taper model for growth of the Himalayan thrust belt, following emplacement of midcrustal Greater Himalayan rocks. Our revised stratigraphy-based balanced cross section contains ∼120–200 km greater shortening than previously estimated through the Greater, Lesser, and Subhimalayan rocks.

Landslide Interpretation of the Northeast Flank of Kohala Volcano, Hawaii

The Hawaiian Island volcanic edifices have shed at least 15 giant submarine landslides, each classified as either a slump or debris avalanche. Controversy exists regarding the number, size, and type of landslides on the northeast flank of Kohala Volcano. This study provides a new interpretation for the Kohala flank based on contour and balanced cross-section analysis. Specifically, contours indicate that there is a landslide extending from the summit to the coast between Pololu and Waipio Valleys. The contour evidence also shows that the slide plane is planar and dips less steeply than the topographic slope. Balanced cross sections show the slide plane to be approximately 950 m deep immediately downhill from the zone of depletion, and the slide plane presumably reaches the surface at the base of the coastal cliffs on the northeast coast of Kohala mountain. The lower part of the landslide once extended from the coast to approximately 10 km offshore, but this portion now has been completely removed, apparently as a debris avalanche. Removal of this distal landslide mass created a 200 to 450 m headwall that is now topographically represented by sea cliffs. This newly identified slide/debris avalanche is informally named the “Kohala landslide.” Based on cross-cutting relations of landslide faults with Hawi series lava flows, the upper slide part of the landslide moved sometime between 270 and 60 ka. The age of the lower, debris avalanche part is even less certain and depends on whether canyons cut in the seafloor after the avalanche movement were eroded in the subaerial or submarine environment.