Structural Significance of the Mid-level Décollement Within the Western Sichuan Fold-And-Thrust Belt (WSFTB), Insights From Sandbox Modeling

The WSFTB is located outboard of the eastern Tibetan Plateau, western China. It has received great attention due to high earthquake risks and rich resources of oil and gas. For both issues, the detailed structural configuration and deformation mechanism behind it are of great importance, but remain unclear due to the complexity created by the presence of multiple décollements. The effect of regionally distributed shallow Triassic salt décollement (SD) and the basal one (BD) has been well understood. In this paper, we focus on the third décollement situated between them. We conducted three sandbox experiments by varying this mid-level décollement (MD) from absence to presence, and from frictional to viscous, to test the effect on diversity of regional structural configuration. Our experimental results illustrated that 1) Absence of MD facilitated decoupling on SD, forming the greatest contrast between subsurface deformation front and the blind one beneath SD; 2) Frictional MD itself showed little decoupling, while its weakness reduced the bulk strength of deep structural level, lowering decoupling effect on SD and leading to approximating deformation fronts in the shallow and deep; 3) The viscous MD, along with SD relieved the resistance on their interbed layer. Consequently, the fastest deformation propagation rate and farthest deformation front (in all the experiments) occurred in the middle structural level. The modeled fold and thrust structures are comparable with the southern, central and northern WSFTB respectively, suggesting that varied MD may control the along-strike structural variations presented. The results also indicate that MD can alter the deformation partition in depth of any other multiple décollement system.

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THE REGIONAL GEOLOGY OF THE BONAPARTE GULF TIMOR SEA AREA

The APPEA Journal ◽

10.1071/aj73010 ◽

1974 ◽

Vol 14 (1) ◽

pp. 77 ◽

Cited By ~ 3

Author(s):

Robert A. Laws ◽

Gregory P. Kraus

Keyword(s):

Late Cretaceous ◽

Late Jurassic ◽

Oil And Gas ◽

Upper Jurassic ◽

Structural Configuration ◽

Structural Pattern ◽

Source Areas ◽

Timor Sea ◽

Early Palaeozoic ◽

Sea Area

The present structural configuration of the Bonaparte Gulf-Timor Sea area is essentially the result of Mesozoic and Tertiary fragmentation of a once relatively simple Permo-Triassic Basin. A northwest-southeast Palaeozoic structural grain in the southeastern portion of the area resulted from early Palaeozoic faulting, possibly tied to aborted rift development. This faulting effectively controlled sedimentation throughout the Phanerozoic. Pronounced northeast-southwest Jurassic to Tertiary structural trends dominate the central and northern area, paralleling the present edge of the continental shelf and swinging south southwest into the northern extension of the Browse Basin. Post-Palaeozoic epeirogenies which had the greatest effect on the regional structural pattern occurred in the mid-Jurassic, Early Cretaceous, within the Eocene and in the Plio-Pleistocene.The Kimberley and Sturt Blocks flanking the basin to the south and east constituted the most important source areas for clastic sedimentation throughout the Phanerozoic. Periodic contributions during the Mesozoic were derived from a postulated source to the northwest in the vicinity of the present-day Timor Trough.The maximum thickness of Phanerozoic sediments present within the Bonaparte Gulf-Timor Sea area exceeds 50,000 ft (15,000 m). Early Palaeozoic to Carboniferous evaporites, carbonates and clastics are unconformably overlain by a thick sequence of Permian deltaic sediments in the southeastern Bonaparte Gulf Basin. This is succeeded by a Triassic to Middle Jurassic transgressive-regressive clastic sequence, grading northwestward to marginal marine and marine clastics and carbonates. The Permian to mid-Jurassic sediments are unconformably overlain by Upper Jurassic sands and shales, mainly fluvial in the southeast and north, becoming more marine westward. These clastics are everywhere succeeded by a monotonous sequence of Cretaceous shales and shaly limestones followed by a generally north to northwesterly thickening wedge of Tertiary carbonates and minor elastics.Hydrocarbon shows have been noted offshore in rocks of Carboniferous, Permian, Late Jurassic, Late Cretaceous and Eocene age. Porous clastics in conjunction with thick and laterally-extensive, organically-rich shales are present within the Palaeozoic and Mesozoic sequences. These sediments, in association with fault- and diapir-related anomalies and stratigraphic plays, combine to make certain provinces of the Bonaparte Gulf-Timor Sea area prospective in the search for viable oil and gas reserves.

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Kinematics of a Hybrid Thick-thin-skinned Fold and Thrust Belt Recorded in Neogene Syntectonic Wedge-top Basins, Southern Central Andes Between 35° and 36°S, Malargüe, Argentina

Thrust Fault-Related Folding ◽

10.1306/13251340m943099 ◽

2011 ◽

Author(s):

Pablo Kraemer ◽

José Silvestro ◽

Federico Achilli ◽

Walter Brinkworth

Keyword(s):

Central Andes ◽

Thrust Belt ◽

Fold And Thrust Belt ◽

Southern Central

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Late Cretaceous Uplift in the Malargüe fold-and-thrust belt (35ºS), southern Central Andes of Argentina and Chile

Andean geology ◽

10.5027/andgeov40n1-a05 ◽

2013 ◽

Vol 40 (1) ◽

Cited By ~ 12

Author(s):

Jose Francisco Mescua ◽

Laura Beatriz Giambiagi ◽

Victor Alberto Ramos

Keyword(s):

Late Cretaceous ◽

Central Andes ◽

Thrust Belt ◽

Fold And Thrust Belt ◽

Southern Central

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The crustal structure in the transition from the on land fold-and-thrust belt to the offshore accretionary prism in the Taiwan arc-continent collision

10.5194/egusphere-egu2020-2846 ◽

2020 ◽

Author(s):

Joaquina Alvarez-Marrón ◽

Dennis Brown ◽

Juan Alcalde ◽

Ignacio Marzán ◽

Hao Kuo-Chen

Keyword(s):

Continental Margin ◽

Seismic Tomography ◽

Accretionary Prism ◽

Crustal Thickening ◽

Accretionary Wedge ◽

Thrust Belt ◽

Deformation Front ◽

Coast Line ◽

Transition Area ◽

Fold And Thrust Belt

The region of Taiwan is undergoing active, oblique arc-continent colision between the Luzon Arc on the Philippine Sea Plate and the continental margin of Eurasia. The Fold-and-Thrust Belt (FTB) in Taiwan passes southwards into a submarine accretionary wedge at the Manila subduction zone. The aim of this contribution is to examine how an on land FTB changes into a marine accretionary prism in the context of an oblique arc-continent collision. The Miocene pre-orogenic sediments of the continental margin are widespread in the FTB ca. 23&#176; latitude while the offshore wedge is built up dominantly by Pliocene to recent syn-orogenic sediments. In the transition area from the marine accretionary wedge ca. 21&#176; latitude to the on land FTB, the thrust wedge is climbing up the slope of the Eurasian continental margin. The deformation front is at sea floor depth of ca. 4 km in the south to less than 1 km as it reaches the coast line. Here we use the island surface geology, marine reflection seismic profiles, and seismic tomography models to construct contour maps of the basal thrust and the depth to the Moho across a transition area from near 23&#176; to near 21&#176; latitude. In this zone, the deformation front draws a convex curvature as the wedge widens from ca. 50 in the north and south, to more than 130 km near 22&#176; latitude. The basal thrust surface shows a scoop shape as its dip changes from southeast near the coast line to east southward. The basal thrust reaches over 7 km deep beneath the rear of the FTB before ramping into de basement and merging into the Chaochou fault at 10 km depth. Offshore, it shows a gentler dip from 7 km to c. 10 km depth before getting steeper towards the east below the Hengchung Ridge. The basal cuts laterally along-strike through the margin&#8217;s sedimentary cover to incorporate thicker Miocene pre-orogenic sediments onto its hanging wall as it passes from the offshore wedge to the on land FTB.In the offshore area, the Moho (we use a Vp proxy of 7.5 km/s extracted from the seismic tomography) shallows southeastward, from near 25 km depth below the shelf slope break to less than 17 km depth below the offshore wedge near 21.5&#176; latitude before it starts to deep east towards beneath the Taiwan coast. The Moho dips northeast from near 25 km depth below the coast near Kaohsiung, to near 40 depth below the rear of the FTB at 23.5&#176;, latitude. This complex morphology of the Moho may be related to the changes in crustal thickness and the obliquity of the collision. Because of this, crustal thickening is less pronounced beneath southern Taiwan where the thinner part of the margin is colliding with the arc.This research is part of project PGC2018-094227-B-I00 funded by the Spanish Research Agency from the Ministry of Science Innovation and Universities of Spain.

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Geological origins of seismic bright spot reflections in the Ordovician strata in the Halahatang area of the Tarim Basin, western China

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0055 ◽

2018 ◽

Vol 55 (12) ◽

pp. 1297-1311 ◽

Cited By ~ 2

Author(s):

Wei Yang ◽

Xiaoxing Gong ◽

Wenjie Li

Keyword(s):

Tarim Basin ◽

Oil And Gas ◽

High Amplitude ◽

Hydrothermal Activity ◽

Hydrocarbon Exploration ◽

Western China ◽

Bright Spot ◽

Gas Reservoirs ◽

Seismic Section ◽

Bright Spots

Anomalously high-amplitude seismic reflections are commonly observed in deeply buried Ordovician carbonate strata in the Halahatang area of the northern Tarim Basin. These bright spots have been demonstrated to be generally related to effective oil and gas reservoirs. These bright spot reflections have complex geological origins, because they are deeply buried and have been altered by multi-phase tectonic movement and karstification. Currently, there is no effective geological model for these bright spots to guide hydrocarbon exploration and development. Using core, well logs, and seismic data, the geological origins of bright spot are classified into three types, controlled by karstification, faulting, and volcanic hydrothermal activity. Bright spots differing by geological origin exhibit large differences in seismic reflection character, such as reflection amplitude, curvature, degree of distortion, and the number of vertically stacked bright spots in the seismic section. By categorizing the bright spots and the seismic character of the surrounding strata, their geological origins can after be inferred. Reservoirs formed by early karstification were later altered by epigenetic karstification. Two periods of paleodrainage further altered the early dissolution pores. In addition, faults formed by tectonic uplift also enhanced the dissolution of the flowing karst waters. Some reservoirs were subsequently altered by Permian volcanic hydrothermal fluids.

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Earthquakes and depleted gas reservoirs: which comes first?

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-2-7507-2014 ◽

2014 ◽

Vol 2 (12) ◽

pp. 7507-7519

Author(s):

M. Mucciarelli ◽

F. Donda ◽

G. Valensise

Keyword(s):

Oil And Gas ◽

Gas Reservoirs ◽

Po Plain ◽

The Public ◽

Hydrocarbon Traps ◽

Fold And Thrust Belt ◽

Depleted Gas Reservoirs ◽

The Impact ◽

Practical Implications ◽

Shed Light

Abstract. While scientists are paying increasing attention to the seismicity potentially induced by hydrocarbon exploitation, little is known about the reverse problem, i.e. the impact of active faulting and earthquakes on hydrocarbon reservoirs. The recent 2012 earthquakes in Emilia, Italy, raised concerns among the public for being possibly human-induced, but also shed light on the possible use of gas wells as a marker of the seismogenic potential of an active fold-and-thrust belt. Based on the analysis of over 400 borehole datasets from wells drilled along the Ferrara-Romagna Arc, a large oil and gas reserve in the southeastern Po Plain, we found that the 2012 earthquakes occurred within a cluster of sterile wells surrounded by productive ones. Since the geology of the productive and sterile areas is quite similar, we suggest that past earthquakes caused the loss of all natural gas from the potential reservoirs lying above their causative faults. Our findings have two important practical implications: (1) they may allow major seismogenic zones to be identified in areas of sparse seismicity, and (2) suggest that gas should be stored in exploited reservoirs rather than in sterile hydrocarbon traps or aquifers as this is likely to reduce the hazard of triggering significant earthquakes.

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