Depocenter Migration Research Articles

Inheritance recharge of subsurface brine constrains on formation of K-bearing sand-gravel brine in the alluvial fan zone of mountain-basin system on the Qinghai-Tibet Plateau

There is a widely accepted consensus that evaporite and brine resources were formed in terminal salt lakes, however, newly discovered sand-gravel brine (SGB) occurred in the piedmont alluvial fan zone on the northern Qinghai-Tibet Plateau (QTP). Currently, there is a key scientific issue on where does the solute of SGB in the alluvial fan zone come from? The existing understanding is that the solute of high Na+, Cl− originates from halite dissolution of meteoric water, but lack of isotopic geochemical link between brine and evaporite. The Mahai Basin (MHB) on the northern QTP is a natural experimental site for the study of the above unsolved problems, due to harboring similar brine reservoir, small geographical area, thin evaporite layers and various waters in this basin. This study presents detailed analysis of H-O-Cl-Li isotopic compositions and hydrogeochemical parameters for intercrystalline brine, SGB and halite from sediment cores in the MHB. The results reveal several key findings: (1) the SGB in the piedmont alluvial fan zone of Altyn Tagh and Saishiteng Mountains presents similar geochemical characteristics of high Na+, Cl− and relatively high K+ contents (1.12–3.65 g/L in MHB), which established new occurrence model of brine resource in the ‘Fan-Lake’ system. (2) The δD (−56.90 ‰∼−17.60 ‰) and δ18O (−5.70 ‰∼6.00 ‰) values of SGB in the MHB are higher, the isotopic disparity exists in these two mountain-fan-lake systems, but they are meteoric origin and accord with their respective hydrologic circulation process. (3) The CNa/CCl ratio (∼0.8), δ37Cl (−0.26 ‰∼+0.25 ‰) and δ7Li values (+33.84 ‰∼+43.82 ‰) of SGB are comparable with those of intercrystalline brine in the MHB, indicating that inheritance recharge of salt lake brine for the formation of SGB in this basin. (4) The metallogenic model of SGB in the MHB is multifactorial control (tectonic movement, northward migration of depocenter, piedmont faulting activities and strata subsidence), which develops the topographic difference between brine reservoir of salt lake and alluvial fan zone resulting into subsurface brines recharge for the alluvial-pluvial fan reservoir.

Tectono‐sedimentary evolution of high‐displacement crustal‐scale normal faults and basement highs on rifted margins: Klakk Fault Complex and Frøya High, Mid‐Norwegian Margin

AbstractCrustal‐scale high‐displacement (>10 km) normal faults are not captured in existing tectono‐sedimentary models of rift basins. We used 2D and 3D seismic reflection and well data to perform a structural and source‐to‐sink analysis of the southern part of the Klakk Fault Complex and the western part of the Vingleia Fault Complex, Mid‐Norwegian rifted margin. The north–south trending Klakk Fault Complex has a zig‐zag to sinuous plan‐view geometry, forming a series of structural recesses and salients along strike. In cross‐section, the fault complex has a listric to convex‐up or low‐angle planar geometry with displacements above 20 km. This fault complex exhumed basement highs, the Frøya High and Sklinna Ridge, in its footwall and created a series of supradetachment basins, for example, the Rås Basin, in its hanging wall. In contrast, the northeast‐southwest trending Vingleia Fault Complex has a zig‐zag geometry in plan view and planar to listric geometry in cross‐section and displacement of up to 5 km. This fault has the Frøya High in its footwall and the southern Halten Terrace in its hanging wall. Restoration of selected structural cross‐sections shows a prominent fault‐parallel ridge, up to 15 km east of the Klakk Fault Complex interpreted as a palaeodrainage divide. This divide separates steep drainages developed along the west‐dipping footwall scarp to the Klakk Fault Complex, from broader, gentler east‐dipping drainages up to ca. 10 km long developed on a back‐tilted dip slopes along the eastern side of the Frøya High and Sklinna Ridge. Progressive headward erosion of active flank catchments was enhanced around topographically elevated structural salients to the point of capturing previous dip‐slope‐directed drainages during the earliest Cretaceous. A network of submarine canyons develop down‐dip of the drainage catchments along the Klakk Fault Complex scarp, whose geometries and length are controlled by their location with respect to the structural salients or recesses, and the presence of fault terraces. The middle Jurassic‐earliest Cretaceous synrift deposits form two seismic sequences that are filled with five distinctive seismic facies that record the evolution from a linked normal fault during rift climax to a high‐displacement stage. During the high displacement stage, exhumed local continental core complexes formed structural salients, separated along strike by structural recesses at the heads of supradetachment basins. Key elements of the high‐displacement fault stage include (i) the development of structural salients at sites of rift climax displacement maxima, (ii) development of supradetachment basins in rift climax displacement minima and (iii) migration of major depocentres away from the centre of rift climax fault segments. We synthesise these observations into a generic tectono‐sedimentary model for high‐displacement faults.

Jurassic sedimentary migration characteristics and their geodynamic implications in the Dunhuang Basin and adjacent regions, Northwestern China

The Dunhuang Basin, situated in western China along the Altyn Tagh Fault (ATF) zone, intersects the Tethys and Paleo‐Asian Ocean tectonic domains. Influenced by both the ATF system and the far‐field effects of the Qiangtang‐Lhasa‐Eurasia collision during the Mesozoic, the mechanism of the Jurassic sedimentary migration of the basin in response to tectonic movements is unclear so far. The paper uses a comprehensive approach, including field geological surveys, lithologic and lithofacies discern, stratigraphic relationships analysis and 2D seismic profile interpretation, to examine the distribution of Jurassic residual strata in the basin. The comprehensive results of our study suggest that the Dunhuang Basin exists as an isolated block with unique tectonic and sedimentary evolution characteristics. In the Early Jurassic, the Dunhuang Basin underwent initial rifting, leading to the formation of small segmented intermontane sags. This phase was marked by the coarse particle sedimentary system of alluvial fans and braided rivers, represented the near source rapid deposition in the initial formation period of the basin. Stratigraphic distribution was primarily influenced by pre‐Jurassic basement topography and was not significantly constrained by faulting during this period. The formation of these isolated discontinuous small intermontane sags indicates the segmented activities of the ATF in the Early Jurassic period. In the Middle Jurassic period, influenced by the ATF dextral strike‐slip faulting, sedimentation extended eastward and the depocenter migrated clockwise compared with the distribution of the Middle Jurassic strata within the Dunhuang Basin. This period witnessed the development of coal measure strata at the basin's margins and lacustrine fine‐grained clastic deposition in the centre. The segmented fracture of the ATF gradually initiated a unified dextral strike‐slip tectonic movement. In the Late Jurassic period, sedimentary strata were locally present in the Wanyao Sag but absent in other sags. The depocenter migrated counterclockwise compared with the distribution of Middle Jurassic strata within the Dunhuang Basin, due to regional uplift accompanied by the ATF sinistral strike‐slip faulting caused by the collision between the Lhasa Block and the Eurasia Plate. The depocenter migration of the Dunhuang Basin constrained within the ATF system from the Early to Middle and Late Jurassic can be attributed to the transition of the ATF strike‐slip faulting in context of the stress relaxation and compression between the collision of the Qiangtang and Lhasa blocks to the Eurasia Plate, respectively.

Variations of sedimentary environment under cyclical aridification and impacts on eodiagenesis of tight sandstones from the late Middle Jurassic Shaximiao Formation in Central Sichuan Basin

Understanding eodiagenesis is essential to decoding the diagenetic pathways of tight sandstones that act as excellent unconventional oil & gas reservoirs. Great paleoclimate change is capable of influencing eodiagenetic processes of tight sandstones through variations of sedimentary environment. However, it is less noted how climate gradients between the greenhouse and the hothouse conditions impact the eodiagenesis of tight sandstones. We examined eodiagenetic processes that has been operated in the Shaximiao Formation sandstones using petrographic observation, scanning electron microscopy, geochemistry, and XRD analysis to reveal impacts of the transitional climate changes on the differential eodiagenesis and implications for the diagenesis-porosity evolution. Based on sequence stratigraphy, the Shaximiao Formation is divided into four sub-members SXM1, SXM2, SXM3, and SXM4, respectively. Dark sandstones and mudstones mainly occurred in the SXM1 and the SXM2. Grey-green clastic rocks are dominant in the SXM3, whereas red mudstones frequently appear in the SXM4. Paleoclimate indices denote that a cyclical aridification from the warm-humid to hot-semiarid conditions took place from the SXM1 to the SXM4. It could have been caused by the megamonsoon effect and the paleogeographic shift along with the breakup of the Pangaea supercontinent. Combined with the migration of depocenters, the paleoclimate change resulted in transformation of sediment provenances from mafic igneous rocks to quartzose sedimentary rock along with the decreasing textural maturity. Therefore, sedimentary environments varied from the high-saline to low-saline and from low-oxygen to high-oxygen conditions respectively, which had a crucial impact on eodiagenetic cements which were formed in the Shaximiao Formation. Chlorite and laumontite cement precipitation was promoted by high-saline alkaline fluids. Chlorite proportions show an arched trend from the SXM1 to the SXM4, compatible with those of primary and secondary porosities. In contrast, laumontite proportions exhibit a decreasing variation from the SXM1 to the SXM4. High percentages of early cements are favorable to improving resistance to the compaction and preservation of primary pores. However, high chlorite (>5%) and laumontite (>10%) proportions are destructive for the reservoir quality. Large quantities of laumontite cements occupy primary pores and impede diagenetic fluids flowing and are not favorable to the dissolution. By contrast, an excess of chlorite cements can be dissolved to produce secondary pores during the organic acid release. Thus, the SXM2 is potential as a reservoir for oil & gas. Therefore, those eodiagenetic cements can control the late diagenetic evolution and the reservoir quality. Observations made here have implications for understanding tight sandstone reservoirs elsewhere in the world.

Fault propagation in pull‐apart basins and its implication on depocenter migration: A discontinuum‐based numerical study

Understanding of fault propagation in pull‐apart basins is important due to its control on the depocenter migration, which is a common characteristic of pull‐apart basins; nevertheless, the evolution law of faults in the pull‐apart basin is not very clear. Most studies based on physical simulations have rarely paid attention to the relationship between fault propagation and migration of the depocenter. In this study, we simulate the fault propagation in the underlapping, neutral and overlapping releasing bend via the discrete element simulation method and discuss the corresponding migration of the depocenter. In this paper, more parameters (maximum shear force, distribution of tensile contact force, measuring stress) were used together to find out the evolution law of faults in line with natural basins. The results reveal the process of fault propagation, which has not been proposed in the previous simulating and case studies: the fault propagates from the ends of the master faults to the centre of the releasing bend and then proceeds externally. Consequently, the depocenter of the basin, which has undergone migration, experiences a transition from the dual depocenter state at the ends of the master faults to being a single depocenter at the centre of releasing bend and finally further expands in an outward direction. The characteristics of fault development and depocenter migration for the Khanguet Sidi Neji‐Gafsa (KSG) Basin, the Vienna basin and the Gulf of California are in accord with the results observed in the simulation. This study provides a new understanding of the fault propagation in pull‐apart basins and can assist in the interpretation of the evolutionary stages that pull‐apart basins undergo.

Architectural rift geometry of the Rio do Peixe Basin (Brazil): Implications for its tectonic evolution and Precambrian heritage

Preexisting shear zones in the basement may influence the formation of normal faults in rift environments. However, the specific role and interaction between these preexisting shear zones and younger rift faults in controlling the growth of normal faults remain an area of limited understanding. The Rio do Peixe Basin (RPB), located in Brazil, was the subject of a comprehensive study using integrated airborne magnetic analysis, 2D and 3D seismic interpretation, and 3D gravity modeling. This study investigated tectonic evolution and Precambrian heritage by examining the role of basement structures in controlling the internal geometry of the RPB. The integration of geophysical data supported by field data showed that the underlying basement structures significantly influence the geometry of the basin sedimentary fill. E–W-striking structures controlled the opening of the RPB and the development of the depocenters of the basin. NE–SW-striking structures influenced the segmentation of the depocenters and, consequently, the internal geometry of the basin. Furthermore, the study revealed the migration of depocenters toward the NE associated with developing the NE–SW-striking segment of the Portalegre Fault attributed to the basin-opening process. By investigating the underlying crustal architecture, this comprehensive geophysical study sheds light on the architectural rift geometry of the RPB. The findings underscore the influence of basement structures on the internal basin architecture and provide valuable insights into its tectonic evolution and Precambrian heritage.

Article Review/ The Tectonic Evolution of Erbil Area (Ne Iraq) as a Part of the Northeastern Margin of the Arabian-Nubian Plate Throughout Albian-Early Eocene

The Albian-Early Eocene tectonic evolution of the Zagros Foreland Basin of the High Folded Zone in the Iraqi Kurdistan region has been studied based on the recent foreland basin system concept. This study showed that during the cretaceous (Albian – Cenomanian) there was a geodynamic shift from a passive margin to a foreland basin system phase, not to an active margin phase as mentioned in the previous studies. The advance of the continental margin of the Arabian-Nubian Plate (ANP) toward the subduction zone imposed a tectonic load leading to the form of a flexural wave. The consequences of the last tectonic event were reflected by the continuous deposition of the Balambo Formation. in a foredeep depozone. This happened concomitantly with a flexural emergence of the continental shelf further to the west forming a forebulge depozone represented by the deposition of reefal facies of the Qamchuqa Formation. These geodynamic changes are considered here to represent the Megasequence boundary between the Tectonic Megasequence (TMS) of AP8 and AP9. The last sequence of the passive margin was the Qamchuqa Formation Which is called the Pre-Orogenic Carbonate Platform and was separated from the Bekhme Formation by regional unconformity (Megasequence boundary). The latter is represented by the Lower Sequence of the foreland basin system, which is called the Syn-Orogenic Carbonate Platform (SCP). During the Middle Campanian, the Zagros foreland basin started with the underfilled stage, and it was entirely clear by the end of the Cretaceous comprising a broad threefold subdivision of depositional realms that translated into three stratigraphic units known as trinity underfilled units of foreland basin system. The lower carbonate unit, the pelagic and hemipelagic unit, and the upper flysch clastic unit are represented by Bekhme, Shiranish, and Tanjero Formations respectively. All of these units were superimposed during basin depocenter migration and became younger toward the southwest in front of progressing the orogenic wedge toward the Arabian Craton. During the late Maastrichtian to Paleocene – Early Eocene, the Zagros foreland basin underwent a transition from underfill to fill the stage. Deep exhumation of the orogenic wedge and ophiolite assemblage had supplied the clastic sediment of the Kolosh Formation into the basin covering the foredeep and most of the forebulge and backbulge depozones.

Evolution of the Manabí forearc basin in Ecuador: From the collision of Caribbean oceanic plateau to the build up of the Andes and Coastal Cordilleras

We investigate the evolution of the onshore Manabí forearc basin in Ecuador, which has developed on accreted oceanic terranes. We use 2D seismic profiles to identify 10 seismic units, separated by 9 unconformities. These units were dated by correlation with Ricaurte-1 well and regional stratigraphy. Unit S1 represents the first depocenter developed on the oceanic plateau before accretion. The emplacement of NE-dipping oceanic plateau slices evidencing the accretionary process dated to ∼75 Ma (Unconformity U1), was followed by folds and east-dipping thrusts at the Andes foothills that were eroded by unconformity U2 (56–41.3 Ma hiatus). The large distribution of unit S3 (late Eocene-Oligocene) over the topography inherited from the collision, points to the configuration of the post-collision forearc basin. The geometry of slope front fill and the thickening of unit S4 at the foot of the Andes reveals the building of Andean reliefs during the early Miocene. Unit S5 (17.8–15.9 Ma) is fan-shaped and abuts against the Jama fault, evidencing local extensional. After unconformity U5 (∼16 Ma), differential subsidence causes the installation of a westward-prograding sedimentary platform during the middle to late Miocene (S6 to S8). Since the Pliocene, the uplift of the Coastal Cordillera is related to localized shortening across the Jama and Canandé faults. Enhanced tectonic erosion at the tip of the margin,likely related to the Carnegie ridge subduction, could have led to underplating of offscraped material beneath the Coastal Cordillera, contributing to the uplift and enlargement of the Coastal Cordillera. The Pleistocene eastward tilt of the Santo Domingo fan (unit S10) relates to the Coastal Cordillera uplift. The fan is then deformed along the Andean thrust. This study provides a remarkable example of a forearc basin-fill developed on accreted oceanic terranes and controlled by erosional and underplating subduction processes, reactivation of inherited crustal structures, and the rise of peripheral reliefs.

Controlling factors of the gypsum-salt strata differences within two adjacent Eocene sags in the eastern Jiyang Depression, NE China and its hydrocarbon significance

Gypsum-salt rocks play a significant role in the process of hydrocarbon migration and accumulation. The fourth member of the Shahejie Formation (Es4) in Dongying Sag and the adjacent Bonan Subsag, bordered by the Chenjiazhuang Uplift, contains extensive gypsum-salt layers. However, there are notable differences in terms of the endowed horizons. Therefore, it is crucial to decrypt the factors that control the development of gypsum-salt rocks, such as paleoclimate, tectonic activity, and geomorphological differences. Comprehensive insights demonstrate that an arid-dominated climate is the primary factor for the development of gypsum-salt rocks, while the tectonic transformation and migration of depocenter also control the differential development of gypsum-salt rocks in these two areas mentioned above. Under the geological background of arid evaporation as a whole, in the lower section of the Es4 (Es4L) sedimentary period, the depocenter was situated south of Dongying Sag but far away from Bonan Subsag, resulting in the deposition of lakeshore to the shallow water of Bonan Subsag and the deep lake deposition of Dongying Sag. Therefore, the gypsum-salt deposits are lacking in the Es4L of Bonan Subsag while being well developed in the Es4L of Dongying Sag. However, in the upper section of the Es4 (Es4U) sedimentary period, due to the migration of the regional depocenter and tectonic transformation, a large-scale and relatively stable deep lake was also developed in Bonan Subsag. Consequently, gypsum-salt rocks developed in both Bonan Subsag and Dongying Sag. This study provides valuable insights for further hydrocarbon exploration in the deep strata of Dongying Sag and Bonan Subsag.

Tectonic and climatic controls on carbonate sedimentation in active orogen proximal lakes, Cenozoic Qaidam Basin, northern Tibetan Plateau

AbstractPalustrine‐lacustrine carbonates of the well‐dated Xichagou section (ca. 43 to ca. 13 Ma) next to the active Altyn Tagh Fault (ATF) are investigated in terms of abundance, lithofacies, strontium, carbon and oxygen isotopes, to differentiate tectonic and climatic controls on the evolution of intermontane lakes in the Tibetan Plateau. Volumetrically dominant siliciclastic strata document five depositional stages: mid‐Eocene alluvial fan (onshore), late Eocene fan delta (nearshore), Oligocene semi‐deep lake (offshore), early Miocene braided fluvial delta (nearshore) and mid‐Miocene fluvial plain (onshore). Carbonates are most abundant in the middle three lacustrine stages and contain various lithofacies, including calcretes, microbialites, grainstones and marlstones. Oxygen isotopes show two positive excursions (−1.17‰ and −2.59‰) at the first nearshore and late offshore stages, indicating two relatively saline stages linked to the Eocene and late Oligocene global warming climates. Carbon isotopes show a positive excursion (from −4.0‰ to +2.9‰) at the middle semi‐deep lake stage and meanwhile strontium isotopes of carbonates show a large negative excursion (from 0.7120‰ to 0.7113‰), both in response to the early Oligocene global humid and cooling climate and resultant lake expansion at the Qaidam Basin. Except for this lake expansion event, the first‐order lake transgressing, shallowing and regressing evolution at the Xichagou section were not consistent with Cenozoic global climatic change trends. Instead, the two‐stage strike‐slip faulting of the ATF probably induced the northeastward and eastward migration of basin depocenter and resulted in the lake transgression‐regression at the Xichagou section. The widespread presence and relatively minor variation in oxygen isotopes (from −7.5‰ to −7.0‰) of early Miocene microbialites in the northern Tibetan Plateau suggest a warm climate and a low relief before ca. 15 Ma.

Deciphering source-to-sink history from a solute perspective: A Sr isotope approach in the Qaidam Basin, NE Tibet

Sediment source-to-sink history is pivotal to investigating the evolution of ancient sedimentary basin. Previous study focuses mostly on reconstruction of various components of siliciclastic sedimentary systems from initial source areas through the dispersal system to deposition areas, but less on the dissolved load that displays distinct transport and deposition dynamics. Here we take the Qaidam Basin (NE Tibet) as a case to provide a solute perspective for deciphering the source-to-sink history of an intracontinental basin. The modern observations exhibit a remarkable contrast of the solute Sr isotopic regime with the northern sources (the Qilian Shan) with high 87Sr/86Sr ratios and the southern sources with low 87Sr/86Sr ratios. The paleowater solute 87Sr/86Sr ratios in the northern basin fluctuate between 0.711 and 0.715 since ∼ 54 Ma. Most of the interval remains a higher 87Sr/86Sr ratio of ∼ 0.713, indicating that the solute Sr was supplied solely by the Qilian Shan. But two periods of low 87Sr/86Sr ratio (0.711–0.712) at ∼ 44.5 - ∼32 Ma and after ∼ 16 Ma suggest that there may be two paleo-megalakes connecting the northern and southern sources, and the solute with low 87Sr/86Sr ratio from the southern sources can thus approach the northern basin via lake water mixing. The two low 87Sr/86Sr paleo-megalakes developed at the northwest of the basin at ∼ 44.5 - ∼32 Ma and at southeast of the basin after ∼ 16 Ma, suggesting a southeastward migration of the basin depocenter that was mainly caused by tectonic uplift with a subordinate impact of climate-induced lake expansion. Our results show a more complex and dynamic solute transport routing history in a large basin than that indicated by coarse clastic provenance studies, and suggest that such a solute Sr approach can be useful to trace sediment routing linked to denudation of high-grade metamorphic rocks and hydrological connections under drainage reorganization.

Cenozoic evolution of the Yangjiang-Yitong’ansha fault zone in the northern South China Sea: Evidence from 3D seismic data

The Yanjiang-Yitong’ansha Fault Zone (YYFZ) traverses the Pearl River Mouth Basin (PRMB) and plays an essential role in basin formation and hydrocarbon accumulation in the PRMB. Because of the lack of seismic data, its distribution, evolution, and effect on the basin evolution in the Cenozoic are poorly known. Based on a detailed interpretation of 3D multi-channel seismic data and previous research results, the YYFZ was identified and characterized. It comprises a series of NW-trending strike-slip faults that exhibit horsetail and en echelon structures in the map view and flower-like or Y-shaped structures in the profile view. By comprehensively analyzing the Paleogene migration of depocenters, activity characteristics of the YYFZ-related faults, and the relationships between faults and sedimentary sequences along the YYFZ, we propose the sinistral motion of the YYFZ initiated at about 35 Ma. The YYFZ served as a transfer zone during the intense rifting in the PRMB from 65 to 35 Ma. Then due to the combined effect of the Indian-Eurasian collision to the west, the Pacific subduction to the east, and the proto-SCS slab-pull to the south, it became a sinistral transtensional fault from 35 Ma to 16.5 Ma. Our results highlight the significant role of the NW-trending fault systems in the basin formation and the regional tectonic evolution of the PRMB.

Tectono-sedimentary evolution of the Paleogene Qikou Sag, Bohai Bay Basin, NE China

The Qikou Sag is a petroliferous tectonic unit within the Bohai Bay Basin, northeast China. The depositional system evolved temporally, spatially, and episodically in five rifting stages (stages 1–5) during the Paleogene and Neogene, with sedimentation responding to regional subsidence. This study focuses on the tectono-sedimentary evolution through stages 2–4, while the main oil-bearing sedimentary rocks were deposited in the Bohai Bay Basin. The depositional system exhibited retrogradation and then progradation during the rifting stage 2 (43–36.7 Ma), retrogradation in stage 3 (36.7–32.8 Ma), and upward coarsening and progradation in stage 4 (32.8–24.6 Ma). This vertical superposition corresponded to three episodic stages of rising and falling lake levels during the Paleogene, which were equivalent to a transgressive with regressive (stage 2), transgressive (stage 3), and then regressive (stage 4) cycle. The sediment fills coincided with the tectonism and the regional subsidence history of the Qikou Sag, which is composed of uplift areas and sub-sags. In this respect, the boundary fault activity around the sub-sags decreased from stages 2–4, leading to the migration of sub-sag depocenters from near faults to the center of sub-sags, which suggests that faults released control over the sedimentation. Secondly, tectonism and the total subsidence rate decreased from SQ1 to SQ7 (stages 2–3) and then accelerated at the end of stage 4 (SQ10 to SQ11). The tectonic subsidence rates decreased quicker than the total subsidence rate; this demonstrates that major rift faulting was the dominant geological process in the early Paleogene, whereas overall subsidence was dominant in the late Paleogene.

Late Eocene signals of oncoming Icehouse conditions and changing ocean circulation, Antarctica

The end of the Eocene greenhouse world was the most dramatic phase in the long-term Cenozoic cooling trend. Here we use 75,000 km of multi/single channel seismic reflection data from offshore Prydz Bay, Antarctica, to provide new insight on the Paleogene stratigraphic transition from greenhouse to icehouse conditions and reorganizing the ocean circulation changes that were invigorated by the cooling and glaciation. We identify a new prominent Paleogene transitional phase (Greenhouse to Icehouse) preserved in the deep-water sedimentary record by correlating from shelf to the continental slope. The occurrence of mega-Mass Transport Deposits (MTDs) on the slope during an early stage in the transition suggests significant instability and collapse of the upper part of the continental margin. A second stage of the transition is represented by the growth of a well-defined set of continental slope clinoforms. We estimate the formation age of the MTDs and clinoforms to be around Eocene-Oligocene Transition. The formation of the clinoforms in the transitional phase indicates sea level has risen, and large volumes sediment delivered to the margin by marine-terminating glaciers on the shelf. Finally, a subsequent marked migration of the margin depocenter toward the west and northwest, attests the onset of drift sedimentation and full glacial conditions, suggesting a more vigorous ocean circulation as the Earth entered the icehouse conditions after the Eocene-Oligocene boundary.

Structure and formation mechanism of the Pearl River Mouth Basin: Insights from multi-phase strike-slip motions in the Yangjiang Sag, SE China

• The Pearl River Mouth Basin experienced two stages of strike-slip motions along the ENE and WNW directions. • The partial reactivation of the intrabasement faults controlled the evolution of intrabasin faults. • The formation of the basin resulted from the joint effect of oblique Pacific-Eurasian subduction and the Indo-Eurasian collision. The Pearl River Mouth Basin (PRMB) experienced multi-phase rifting and complex tectono-sedimentary evolution during the Cenozoic, and is a topic of many studies regarding the basin-forming mechanism. In the present study, detailed seismic interpretation and tectonic analysis based on the 3D seismic reflection data of the Yangjiang Sag in the northwestern PRMB were carried out, to provide clues to its tectonic evolutionary history. The qualitative-quantitative analysis of fault strikes and migration of depocenter in the Yangjiang Sag indicated the dextral transtensional setting during the Paleocene to Miocene. Meanwhile, the horsetail and en echelon structures on plane view and negative flower structures in cross-section are exhibited, indicating the successive occurrence of strike-slip motions in ENE and WNW directions respectively after initial rifting combined with the structural analysis of Huizhou Sag and Baiyun Sag. In addition, thrust fault systems trending in WNW and ENE were identified in the basement. Their partial and selective reactivation in strike-slip character during the Cenozoic restricted the faults developed in the basin with differential properties. Geometrically, rhombic-shaped sags with cross-basin fault zones were formed, implying the formation of pull-apart structures along with multi-phase strike-slip motions. The pull-apart mechanism could be accounted due to the joint effect of the oblique Pacific-Eurasian subduction and the Indo-Eurasian collision during the Cenozoic.

Down under and under Cover—The Tectonic and Thermal History of the Cooper and Central Eromanga Basins (Central Eastern Australia)

The Cooper subregion within the central Eromanga Basin is the Swiss army knife among Australia’s sedimentary basins. In addition to important oil and gas resources, it hosts abundant coal bed methane, important groundwater resources, features suitable conditions for enhanced geothermal systems, and is a potential site for carbon capture and storage. However, after seven decades of exploration, various uncertainties remain concerning its tectonic and thermal evolution. In this study, the public-domain 3D model of the Cooper and Eromanga stacked sedimentary basins was modified by integrating the latest structural and stratigraphic data, then used to perform numerical basin modelling and subsidence history analysis for a better comprehension of their complex geologic history. Calibrated 1D/3D numerical models provide the grounds for heat flow, temperature, thermal maturity, and sediment thickness maps. According to calibrated vitrinite reflectance profiles, a major hydrothermal/magmatic event at about 100 Ma with associated basal heat flow up to 150 mW/m2 caused source rock maturation and petroleum generation and probably overprinted most of the previous hydrothermal events in the study area. This event correlates with sedimentation rates up to 200 m/Ma and was apparently accompanied by extensive crustal shear. Structural style and depocentre migration analysis suggest that the Carboniferous–Triassic Cooper Basin initially has been a lazy-s shaped triplex pull-apart basin controlled by the Cooper Basin Master Fault before being inverted into a piggy-back basin and then blanketed by the Jurassic–Cretaceous Eromanga Basin. The interpreted Central Eromanga Shear Zone governed the tectonic evolution from the Triassic until today. It repeatedly induced NNW-SSE directed deformation along the western edge of the Thomson Orogen and is characterized by present-day seismicity and distinct neotectonic features. We hypothesize that throughout the basin evolution, alternating tectonic stress caused frequent thermal weakening of the crust and facilitated the establishment of the Cooper Hot Spot, which recently increased again its activity below the Nappamerri Trough.

Middle Triassic sedimentary evolution in the Upper Yangtze region with implications for the collision between the South and North China Blocks

Middle Triassic marine carbonate successions deposited on the northwestern Yangtze passive continental margin preserve information about the initial collision between the South China Block (SCB) and the North China Block (NCB). We extracted data from 51 boreholes and 23 outcrops of the Middle Triassic Leikoupo Formation to interpret the spatio-temporal stratigraphic framework, depositional transition, and contractional deformation in the Upper Yangtze region. The sedimentological analysis indicates that the Leikoupo Formation may be divided into nine successions, which were overall deposited in restricted-evaporative marine platform and lagoon environments during the Anisian. From the thickness distributions of each sequence, the Upper Yangtze region is shown to have experienced northwest-southeast horizontal compression and vertical uplift, which drove northwestward migration of the coeval depocenters and marine regression. We propose that the marine deposits of the Leikoupo Formation and the contemporary paleo-uplifts can be considered products of the forebulge and backbulge depozones of a peripheral foreland basin. The Early Triassic passive continental margin in the Upper Yangtze region had thus transformed into a peripheral foreland basin in response to the collision between the SCB and NCB by the Anisian. The northwestward retreat of seawater with synchronous growth of the forebulge further supports the oblique suturing between the two rotating blocks. In response to continuous basin-ward thrusting of the Micangshan-Daba Shan and Longmen Shan belts, new transpressional flexural subsidence developed, leading to the formation of terrestrial deposits in the Late Triassic basin.

Basement-decoupled hyperextension rifting: The tectono-stratigraphic record of the salt-rich Pyrenean necking zone (Arzacq Basin, SW France)

AbstractHalf grabens and supra-detachment basins correspond to end-member basin types of magma-poor rift settings, each of them showing a characteristic stratigraphic architecture. The occurrence of a basement-cover décollement has been shown to drastically change the stratigraphic architecture of half graben basins, however, the effect of such basement-cover décollement remains to be documented in supra-detachment basins formed during hyper-extension. We investigate the tectono-stratigraphic record of the Arzacq Basin (SW France) recording the formation of a salt-rich Cretaceous hyperextended rift system. Combining 2-D and 3-D seismic reflection calibrated from well data, we show that this basin is an asymmetric syn-rift extensional syncline growing above a pre-kinematic salt layer. By mapping the sub-salt basement, we show that the formation of this syncline is controlled by the South-Arzacq Fault (SAF), soling in the sub-salt basement. Based on crosscutting relationships and the observed southward migration of syn-rift depocenters, this N110°-striking, 20°-dipping structure accommodates >10 km of thick-skinned extension. The overlying supra-salt cover coherently glided, following the basement geometry. The 3-D segmentation of the SAF and the sub-salt stratigraphic architecture of the Arzacq Basin suggest a roughly dip-slip kinematic. A post-kinematic kilometer-scale uplift is documented on the southern side of the Arzacq Basin. It may result from the increasing lithospheric thinning and thermal support at the end of asymmetric hyperextension. As salt commonly occurs in extensional settings, we believe that our description of the tectono-stratigraphic record of a basement-decoupled supra-detachment basin has global applicability to unleash the tectono-stratigraphic evolution of worldwide hyper-extended rifted margins.

Constraining the effects of dynamic topography on the development of Late Cretaceous Cordilleran foreland basin, western United States

AbstractDynamic topography refers to the vertical deflection (i.e., uplift and subsidence) of the Earth's surface generated in response to mantle flow. Although dynamic subsidence has been increasingly invoked to explain the subsidence and migration of depocenters in the Late Cretaceous North American Cordilleran foreland basin (CFB), it remains a challenging task to discriminate the effects of dynamic mantle processes from other subsidence mechanisms, and the spatial and temporal scales of dynamic topography is not well known. To unravel the relationship between sedimentary systems, accommodation, and subsidence mechanisms of the CFB through time and space, a high-resolution chronostratigraphic framework was developed for the Upper Cretaceous strata based on a dense data set integrating >600 well logs from multiple basins/regions in Wyoming, Utah, Colorado, and New Mexico, USA. The newly developed stratigraphic framework divides the Upper Cretaceous strata into four chronostratigraphic packages separated by chronostratigraphic surfaces that can be correlated regionally and constrained by ammonite biozones. Regional isopach patterns and shoreline trends constructed for successive time intervals suggest that dynamic subsidence influenced accommodation creation in the CFB starting from ca. 85 Ma, and this wave of subsidence increasingly affected the CFB by ca. 80 Ma as subsidence migrated from the southwest to northeast. During 100–75 Ma, the depocenter migrated from central Utah (dominantly flexural subsidence) to north-central Colorado (dominantly dynamic subsidence). Subsidence within the CFB during 75–66 Ma was controlled by the combined effects of flexural subsidence induced by local Laramide uplifts and dynamic subsidence. Results from this study provide new constraints on the spatio-temporal footprint and migration of large-scale (>400 km × 400 km) dynamic topography at an average rate ranging from ~120 to 60 km/m.y. in the CFB through the Late Cretaceous. The wavelength and location of dynamic topography (subsidence and uplift) generated in response to the subduction of the conjugate Shatsky Rise highly varied through both space and time, probably depending on the evolution of the oceanic plateau (e.g., changes in its location, subduction angle and depth, and buoyancy). Careful, high-resolution reconstruction of regional stratigraphic frameworks using three-dimensional data sets is critical to constrain the influence of dynamic topography. The highly transitory effects of dynamic topography need to be incorporated into future foreland basin models to better reconstruct and predict the formation of foreland basins that may have formed under the combined influence of upper crustal flexural loading and dynamic subcrustal loading associated with large-scale mantle flows.

Crustal exhumation and depocenter migration from the Alpine orogenic margin towards the Pannonian extensional back-arc basin controlled by inheritance

The formation and deformation history of back-arc basins play a critical role in understanding the tectonics of plate interactions. Furthermore, opening of extensional back-arc basins during the overall convergence between Africa and Europe is a fundamental process in the overall tectonic evolution of the Mediterranean and adjacent areas. In this frame, Miocene tectonic evolution of the western Pannonian Basin of Central Europe and its connection to inherited Cretaceous structures of the Eastern Alpine nappes are presented. Revision of published and addition of new structural and thermochronological data, as well as seismic profiles from the western Pannonian Basin is complemented by high-resolution thermo-mechanical numerical modeling in order to propose a new physically consistent tectono-sedimentary model for the basin evolution. The onset of extension is dated as ~25–23 Ma, and higher rates are inferred between 19 and 15 Ma at the south-western part of the area (Pohorje, Kozjak Domes, Murska Sobota Ridge, and Mura-Zala Basin). Rift initiation involved the exhumation of the middle part of the Austroalpine nappe pile along low-angle detachment faults and mylonite zones. The Miocene low-angle shear zones could reactivate major Cretaceous thrust boundaries, the exhumation channel of ultra-high-pressure rocks of the Pohorje Dome, or Late Cretaceous extensional structures. Miocene extension was associated with granodiorite and dacite intrusions between 18.64 and 15 Ma. The Pohorje pluton intruded at variable depth from ~4 to 16–18 km and experienced ductile stretching, westward tilting, and asymmetric exhumation of its eastern side. Terrestrial early Miocene (Ottnangian to Karpatian, 19–17.25 Ma) syn-rift depositional environment in supradetachment basins evolved to near-shore and bathyal one by the middle Miocene (Badenian, 15.97–12.8 Ma). Deformation subsequently migrated eastwards to the western part of the Transdanubian Range (Keszthely Hills) and to newly formed grabens. In this formerly emerged terrestrial area active faulting started at 15–14.5 Ma and continued through the late Miocene almost continuously up to ~8 Ma but basically terminated in the Mura-Zala Basin by ~15 Ma (early Badenian). These observations suggest a ~200 km shift of active faulting, basin formation, and related syn-tectonic sedimentation from the SW (Pohorje and Mura-Zala Basin) toward the Pannonian Basin center. Building on the above described observational and modeling data makes the Pannonian Basin an ideal natural laboratory for understanding the coupling between deep Earth and surface processes.