Thrust Uplift Research Articles

Landslides and growing folds: A lesson from the Kura fold-and-thrust belt (Azerbaijan, Georgia)

Active fold-and-thrust belts create new landslide-prone slopes during tectonic deformation propagation. However, studies on landslide distribution in newly formed fold-and-thrust belts are limited. In this study, we present a new inventory of landslides in the Kura fold-and-thrust belt, a tectonically active, but relatively low-altitude southern margin of the Greater Caucasus. The area has been tectonically framed in the last ~2–3 Ma and is represented by folds and thrusts deforming Miocene to Quaternary sediments. Through satellite imagery analysis, we mapped nearly 1600 landslides, with a quarter currently active. While landslides cover <1 % of the area, they tend to cluster at higher elevations and in regions with relatively high local relief. Landslides predominantly occur in tectonically uplifted areas, affecting the highest and steepest parts of growing anticlines and the steep slopes of incising valleys intersecting active thrust faults. Based on observed landslide distribution in folds at different stages of development, we propose a conceptual model for the temporal evolution of landslide patterns in weak sediment-based fold-and-thrust belts: 1) In the initial stages, slow-moving slope deformations affect incipient thrust fronts. With the flanks of the growing anticline lacking sufficient steepness, landslides tend to concentrate in deep valleys intersecting the uplifting hanging walls. 2) With ongoing thrust uplift, growing and steepening anticlines become more prone to planar sliding when dip slopes exceed friction angle, and valley development creates additional dip slopes, resulting in widespread landslides. 3) In the final stage, erosional decay reduces topographic relief, leading to badland formation with gully erosion and decreased landslide occurrence.

Facies and depositional model of alluvial fan dominated by episodic flood events in arid conditions: An example from the Quaternary Poplar Fan, north‐western China

AbstractAlluvial fans are usually constructed through episodic flood events. Despite the significance of these ephemeral floods on the morphodynamics of alluvial fans, depositional responses to the variations in flood conditions are still poorly documented. This greatly limits the ability to interpret ancient sedimentary successions of fans and the associated flood hydrodynamics. The Quaternary Poplar Fan from endorheic Heshituoluogai Basin provides an optimal case for addressing this issue. Based on the variations in facies associations and flood conditions, three depositional stages – namely; lobe building stage, channel building stage and the abandonment stage – are identified. During the lobe building stage the Poplar Fan is predominately constructed through incised channel flood, sheetflood and unconfined streamflood, with coeval development of distal surficial ephemeral ponds. The channel building stage is characterized by the development of gravelly braided rivers. However, only scour pool fill deposits are preferentially preserved in the Poplar Fan. During the abandonment stage, erosional lags and aeolian sands randomly occur throughout the fan, while gully deposits can only be found in the distal fan. The distinctive facies architecture of the Poplar Fan is likely to be the result of periodicity of climate fluctuations between wetter and drier conditions during the Late Pleistocene to Holocene. The ephemeral floods formed under wetter conditions usually show high discharge and sediment concentrations which facilitate the lobe building processes. During the drier periods, only gravelly braided rivers can be developed through ephemeral floods as the intensity and frequency in precipitation, discharge and sediment concentrations of the flood flows significantly decrease. The abandonment stage of the fan may occur between recurring flood episodes or during the driest periods. Furthermore, the long‐term (105 to 106 year) geomorphic evolution of the Poplar Fan shows the influence of tectonic activities. The ongoing thrust uplift tectonic activities have caused destruction of the fan but can also facilitate the fan‐head trench/incision of the fan, which in turn facilitate the progradation of the fan. This study proposes a new depositional model for alluvial fans constructed through episodic flood events, which shows the character of both sheet‐flood dominated and stream‐flow dominated end members of alluvial fans. These findings supplement the understanding of the variability of the alluvial fans and provide means to characterize rock record of alluvial fans and their associated flood and climate conditions.

Geochemical characteristics and Thermal Evolution of Paleogene Source Rocks in Lunpola Basin, Tibet Plateau

Lunpola Basin is the first exploration area with industrial oil flow in the hinterland of Tibetan Plateau and the target horizon is the Paleogene Niubao formation and Dingqinghu formation. Based on drilling data from multiple wells, the organic matter abundance, type and maturity of Paleogene source rocks in Lunpola Basin were measured and analyzed using organic geochemistry method. The 67 samples data from middle Niubao formation show that the average of TOC (wt.) is 3.50, S1+S2 is 30.55 mg/g; and the Tmax is 427 ∼ 442 °C, δ13CPDB is -25.6‰ ∼ -29.3‰ and Ro is 1.37%∼1.84%. The 53 samples data from upper Niubao formation show that the average of TOC (wt.) is 4.16%, S1+S2 is 30.16 mg/g. and the Tmax is 421 ∼ 440 °C, δ13CPDB is -26.9‰ ∼ -28.7‰ and Ro is 0.61%∼1.35%. The 70 samples data from lower Dingqinghu formation show that the average of TOC (wt.) is 4.16%, S1+S2 is 30.16 mg/g and Ro is 0.58%, and the Tmax is 421 ∼ 440 °C, δ13CPDB is -26.9‰ ∼ -28.7‰. These three sets of source rocks have high organic abundance and kerogen type of I- II1. Based on the previous studies of W-1 well in JiangjiaCo depression, XL-3 well in JiangriaCo depression and Z-1 well PaCo depression, a 2D model of north-south tectonic and thermal evolution in Lunpola basin is simulated by Schlumberger's PetroMod method. The results show that the XL-5 well of Niubao formation in Diezong area of Lunpola basin began to generate oil at 41.3Ma and reached the peak of hydrocarbon generation at 36.4Ma; and upper Niubao formation began to generate oil at 38.4Ma and hydrocarbon generation peaked at 31.9Ma. The lower Dingqinghu formation began to generate oil at 24.2Ma. At the end of upper Dingqinghu formation, the basin began the uplift and denudation stage at 23Ma, but the middle and upper Niubao formation and the Lower Dingqinghu formation are still active for hydrocarbon generation. The simulation also shows that the primary deposits in main source rocks are thin in the thrust uplift belt of southern basin and have not entered the stage of oil generation, and that the main oil source area is the Paleogene depression in central basin.

Insights on the seismotectonics of the western part of northern Calabria (southern Italy) by integrated geological and geophysical data: Coexistence of shallow extensional and deep strike-slip kinematics

We assess the seismotectonics of the western part of the border area between the Southern Apennines and Calabrian Arc, centered on the Mercure extensional basin, by integrating recent seismicity with a reconstruction of the structural frame from surface to deep crust. The analysis of low-magnitude (ML≤3.5) events occurred in the area during 2013–2017, when evaluated in the context of the structural model, has revealed an unexpected complexity of seismotectonics processes. Hypocentral distribution and kinematics allow separating these events into three groups. Focal mechanisms of the shallower (<9km) set of events show extensional kinematics. These results are consistent with the last kinematic event recorded on outcropping faults, and with the typical depth and kinematics of normal faulting earthquakes in the axial part of southern Italy. By contrast, intermediate (~9–17km) and deep (~17–23km) events have fault plane solutions characterized by strike- to reverse-oblique slip, but they differ from each other in the orientation of the principal axes. The intermediate events have P axes with a NE-SW trend, which is at odds with the NW-SE trend recorded by strike-slip earthquakes affecting the Apulia foreland plate in the eastern part of southern Italy. The intermediate events are interpreted to reflect reactivation of faults in the Apulia unit involved in thrust uplift, and appears aligned along an ~WNW-ESE trending deep crustal, possibly lithospheric boundary. Instead, deep events beneath the basin, which have P-axis with a NW-SE trend, hint to the activity of a deep overthrust of the Tyrrhenian back-arc basin crust over the continental crust of the Apulia margin, or alternatively, to a tear fault in the underthrust Apulia plate. Results of this work suggest that extensional faulting, as believed so far, does not solely characterizes the seismotectonics of the axial part of the Southern Apennines.

Sandstone Petrology and Geochemistry of the Kolhan Basin, Eastern India: Implications for Basin Tectonics

The 2.2-2.1 Ga pear shaped Kolhan basin show the development of a time transgressive group in a passive rift setting caused due to the fragmentation of the Columbia supercontinent. The Kolhans while showing a variability in the thickening/thinning of the quartzo-feldspathic, quartzolithic, and quartzose sandstones, do also show a similarity in compositional and dispersal characteristics to both underlying and overlying strata, phenomenon termed here congruence. A combined petrologic and geochemical analysis of sandstone suites (congruence suite) can be used to track changes in the sediment supply from adjacent areas if (1) a long-term record of the basin fill is available (2) the source signal is preserved by “proximal” depositional conditions and (3) diagenetic alteration of sediments is limited. Provenance-derived variations in sandstone compositions are therefore a key in unraveling regional tectonic histories. The basin axis controlled the progradation direction which was likely driven by climatically induced sediment influx, a eustatic fall, or both. In the case of the incongruent shift, increased sediment supply permitted the rivers to cross the basinal deep. Temporal association of the Kolhans with tectonic structures in the belt indicates that syntectonic thrust uplift, not isostatic uplift or climate, caused the influx of quartz. The Kolhans display increasing textural and mineralogical maturity from base to top of its lithological succession. Continued regression and peneplanation heralded the deposition of supermature sandstone in the uppermost horizons of the Kolhans.

Integrating Sandstone Petrology and Nonmarine Sequence Stratigraphy: Application to the Late Cretaceous Fluvial Systems of Southwestern Utah, U.S.A.

ABSTRACT Petrographic and dispersal data are essential to correct interpretation of mechanisms that create continental sequence-stratigraphic architecture. A case study from southern Utah demonstrates that Upper Cretaceous (upper Santonian-Campanian) alluvial successions in the southernmost part of the Cordilleran foreland basin were deposited by fluvial systems of contrasting drainage directions and provenance, and suggests that different mechanisms governed their sequence architecture. Most of the rivers flowed northeast, subparallel to the basin foredeep. Less common fluvial systems flowed to the east-southeast. The fluvial sandstones fall naturally into four petrofacies: (1) quartzofeldspatholithic (mean Qt61F19L20); (2) feldspatholithic (Qt29F19L52); (3) quartzolithic (Qt75F6L20); and (4) quartzose (Qt99F1L1). Petrofacies 1 and 2 were derived from mixed supracrustal and basement sources to the southwest and south, respectively, whereas petrofacies 3 and 4 were derived from uplifted thrust sheets of the Sevier orogenic belt to the southwest and west, respectively. Only the east-southeast-flowing rivers transported the quartzose petrofacies. The fluvial strata, which include the uppermost Straight Cliffs, Wahweap, and Kaiparowits formations, form two large-scale stratigraphic successions typically interpreted as continental stratigraphic sequences hundreds of meters thick. Each succession begins with an amalgamated braided-fluvial deposit, grades to mudstone-rich strata with low sandstone-body connectivity, and culminates in highly connected sandstone bodies with multistory stacking. The basal amalgamated deposits of each succession are architecturally similar, but their compositional and dispersal characteristics are different. Quartzofeldspatholithic, quartzolithic, and quartzose sandstones above the lower base-level shift are variable, but generally similar in compositional and dispersal characteristics to both underlying and overlying strata, a phenomenon termed here congruence. In contrast, quartzose amalgamated fluvial sandstone above the upper base-level shift differs sharply in composition and dispersal direction from underlying and overlying lithic-rich strata. The foredeep axis controlled the progradation direction of the congruent shift, which was likely driven by climatically induced sediment influx, a eustatic fall, or both. In the case of the incongruent shift, increased sediment supply permitted the rivers to cross the foredeep. Temporal association of the upper amalgamated deposit with active structures in the thrust belt and foreland basin indicates that syntectonic thrust uplift, not isostatic uplift or climate, caused the influx of quartz.

Three evolutionary stages of the collision orogenic deformation in the Middle Yangtze Region

A discussion of collision orogenic deformation has been made for the Middle Yangtze Region. Based on its deformation assemblage orders, three developing stages are classified successively as compression thrust uplift, strike-slip escape rheology and tension extension inversion. The collision orogenesis of the studied region has been divided into three developing periods of initial, chief and late orogeny. Based on the data from Wugong Mts., Jiuling Mts. and Xuefeng Mts., for each stage, its variation of stress and strain axes, the conversion of joint fractures and their relative tectonic evolution are described, models are plotted and corresponding explanations are made for the rock chronology dating value in the same tectonic period.

Evolution of Qinling Mianlue Belt: Evidence from Sedimentology and Tectonics of the Northern Yangtze, China

Evolution of Qinling Mianlue Belt: Evidence from Sedimentology and Tectonics of the Northern Yangtze, China

Application of a critical wedge taper model to the Tertiary transpressional fold-thrust belt on Spitsbergen, Svalbard

The Tertiary opening of the North Atlantic Ocean involved major and long-lived overall dextral transpression between the Svalbard and Greenland plates. On Spitsbergen, this tectonic event is manifest as a 100–200-km-wide contractional fold-thrust belt in the form of an east-pinching prism. This belt can be subdivided into (1) a western, basement-involved hinterland province that reveals more complex deformation, including thrust, transcurrent, and normal faulting, and (2) an eastern thin-skinned fold-thrust belt with structures oriented subparallel (north-northwest–south-southeast) to the transform plate boundary. The time-space distribution and interaction of different structural styles of Tertiary deformation evident on Spitsbergen support a model with linked, long-term and short-term (episodic) dynamic growth of a composite contractional and transcurrent fold-thrust wedge. The growth of a narrow, high-taper (critical-supercritical) contractional wedge occurred during northward-directed crustal shortening (stage 1) in an oblique, dextral transcurrent setting. Crustal thickening in the form of thrust uplift and basin inversion and strike-slip duplexing during the main contractional event (stages 2 and 3) created an unstable, supercritical wedge of basement and cover rocks in the hinterland. At the same time, a broader and more homogeneous frontal part of the wedge developed eastward by in-sequence imbrication in order to reduce the taper angle. Local erosion and lateral wedge extrusion (stages 3 and 4) modified the oversteepened hinterland wedge to a critical taper angle. Continued tectonic activity in the hinterland caused renewed internal imbrication of the frontal wedge, where deformation was accommodated by tear faulting and out-of-sequence thrusting (stage 4). Adjustment toward a stable taper geometry included local extension (stage 5) and erosion and sedimentation. In a transpressional fold-thrust belt, as on Spitsbergen, out-of-plane (orogen oblique to parallel) transport in the hinterland may cause local and lateral supercritical and subcritical wedge tapers. Hinterland geometries could trigger adjustments in a frontal thrust wedge in a decoupled situation, and/or orogen oblique or parallel motions in a coupled situation. Changing kinematics may thus be expected along strike in such an orogen.

An Apatite Fission Track Transect across the Rockies at Jasper, Alberta: Preliminary Results of a Thrust Uplift Study

An Apatite Fission Track Transect across the Rockies at Jasper, Alberta: Preliminary Results of a Thrust Uplift Study

Evidence from aeromagnetics on the configuration of Matachewan dykes and the tectonic evolution of the Kapuskasing Structural Zone, Ontario, Canada

By digital image processing of federal–provincial aeromagnetic survey data for the south-central Superior Province, we have obtained an improved picture of the distribution of dykes in the huge Matachewan mafic dyke swarm (2454 Ma). We deduce from it a picture of post-emplacement deformation in the vicinity of the uplifted granulite gneisses of the Kapuskasing Structural Zone (KSZ). Matachewan dykes are emplaced in three subswarms. The two easterly subswarms are clearly truncated by the KSZ's eastern boundary faults. The western subswarm shows an open Z-bend as it crosses the KSZ, but it does not reveal any major fault offset. On the plausible assumption (supported by paleomagnetic data) that the subswarms were originally intruded radially, the horizontal strain suffered by the KSZ since emplacement of the dykes is mainly a northeast–southwest-trending band of dextral transcurrent deformation, which in the northeast is discontinuous and concentrated in a fault (horizontal offset 60–80 km) and in the southwest widens through a series of horsetail splays into an ~80 km wide zone of distributed strain. The KSZ is believed to have formed by a major, crustal-scale, thrust uplift along the KSZ's southeastern margin. Some thrusting is recorded by the dyke pattern, but this can account for only part of the ~20 km of differential uplift seen in the KSZ. Most likely, the mainly transcurrent deformation recorded by the dykes is a secondary event, and the primary period of thrust uplift predated dyke injection.

Mountain Flank Thrusting in Rocky Mountain Foreland, Wyoming and Colorado

The principal mountain ranges of the Wyoming and Colorado foreland were raised asymmetrically by Laramide uplift which began in latest Cretaceous time as dominantly vertical movement along arcuate trends. Uplift continued into the Paleocene, and the steeper flanks of some ranges developed into large overturned folds by local compressive forces marginal to the main uplifts. Along segments of maximum uplift, overturned folds were broken and thrust far over the basin synclines in latest Paleocene or earliest Eocene time. Throughout the long period of uplift the adjacent basins were downwarped continuously and received sediment from the rising mountains. The process of uplift by folding and thrusting better explains observed structure of mountain flanks than the older ideas of block uplift along high-angle faults or thrust uplift by regional compression. Fold-thrust structures are best known along the major Wyoming thrust zones bordering, on the south, the Wind River and Granite Mountains and the Washakie and Owl Creek Mountains. Other examples of faulted overturned folds occur in Colorado along the Golden thrust of the Front Range and Willow Creek thrust in western Colorado. In all these areas thrusts are well documented by subsurface control which includes both deep wells and seismic data.