Cenozoic Sediments Research Articles

Geochemical Characteristics and Origin of Crude Oils from Sunda and Asri Basins, Indonesia

The Sunda and Asri Basins are back-arc basins located SE of Sundaland at the present day. These basins contain Cenozoic sediments deposited in a Paleogene half-graben system. This rifing was followed by sagging during the Neogene associated with a north-south major fault system in the eastern part. The Sunda and Asri Basins constitute significant petroliferous basins in Indonesia which have produced more than a billion barrels of oil equivalent. Some studies conducted focus on geochemistry only in Sunda or Asri Basins, but a comprehensive geochemical study integrating data from both basins have never been conducted. This is the first paper to integrate the geochemical characteristics and the origin of crude oils from Sunda and Asri Basins. A total of eighteen crude oils were investigated to delineate their characteristics. The results provide an explanation about the origin of the organic matter and the genetic relationship between crude oils from Sunda and Asri Basins, and their probable source rocks. This study presents an in-depth geochemical characterization. The crude oils were classified as aliphatic oils, as indicated by their high saturated hydrocarbon fractions (>50 %). The API gravity values of the crude oils range from 25.3 to 39, and their sulfur content was low (0.01 %). Geochemistry analysis reveals a novel interpretation of crude oils originating from shale source rock deposited under oxic-suboxic conditions. Sunda and Asri crude oils exhibited relatively similar stable carbon compositions. The modest concentrations of biomarker 18α(H)-oleanane (OL) indicate that the source age is younger than Late Cretaceous. The crude oil in the Sunda and Asri Basins were charged from source rocks that reached early to peak maturity. The results of the current study strongly indicate the differentiation in lacustrine organofacies of crude oils from the Sunda and Asri Basins. The source rock for these crude oils were shales from the Paleogene syn-rift Banuwati Formation.

A Comparative Geophysical Study of Major Basins in the Pranhita–Godavari Rift, India and Rio Grande Rift, USA

ABSTRACT In this study, we compare and contrast two major sub-basins in the Pranhita-Godavari rift in eastern India (Chintalapudi subbasin) and the Rio Grande rift in the western United States (Albuquerque basin) using bouguer gravity data analysis and integrated profile modeling constrained with seismic, drilling, and geological data. The Chintalapudi sub-basin formed during the break-up of Gondwana around 350 Ma, while the Albuquerque basin formed much later (30–35 Ma) in the interior of North America approximately synchronous with extension in the Basin and Range province. The Chintalapudi sub-basin is narrow and deep; and associated with a −60 mGal (low) gravity anomaly that is mostly due to Gondwana fluvial sediments of late Carboniferous (~350 Ma) to early Cretaceous age (~120 Ma). The negative gravity anomaly associated with the Albuquerque basin is −55 mGals (low) and the Cenozoic sediments were deposited on Mesozoic and Palaeozoic strata with Precambrian crystalline rocks being exposed along the basin flanks. This sub-basin is wide and shallow. Major faults which bound these basins were delineated by gravity modeling that integrated all of the available constraints, and the average depth to the basement at the basin centers calculated from gravity modeling is 4–5 km. However, for Chintalapudi sub-basin, if the residual gravity anamoly is considered, it may be reduced to about 3.5 km.

Late Cenozoic sedimentary records of the uplift of the Karlik Mountain and aridification of the Hami Basin, central Asia

The Karlik Mountain, at the extreme easternmost Tianshan, marks the terminus of the modern Central Asian Orogenic Belt and serves as a natural laboratory for exploring how strain spreads from the margins of the Eurasian plate to its interior. This study investigates Cenozoic strata, including Oligocene-Miocene Taoshuyuanzi Formation and Pliocene Putaogou Formation, in the Hami Basin through detailed facies analysis, detrital zircon U-Pb geochronology, and magnetic susceptibility to reconstruct the Cenozoic mountain-building history and climate variation of the easternmost Tianshan. Provenance analysis indicates that the Cenozoic sediments were derived from the north and can thus be used to reflect the mountain-building processes of the Karlik Mountain. Facies analysis shows that the Taoshuyuanzi Formation began with fan delta deposits at the lake margin, followed by lacustrine deposits, while the Putaogou Formation is dominated by alluvial fan deposits. The synchronization with intense aridification, as revealed by sedimentary features, allows us to propose that the coarse-grained alluvial deposition in the Putaogou Formation of the Hami Basin marks the Pliocene uplift of the Karlik Mountain. The magnetic susceptibility increased dramatically in the Pliocene, with the trend correlating well with that of the lithology coarsening. The tectonic uplift of easternmost Tianshan, along with the subsequent extreme aridity associated with the global cooling and orogenic barrier, facilitated the preservation of magnetite, leading to the accumulation of alluvial deposits with increased magnetic susceptibility during the Pliocene.

The Lomonosov Ridge, central Arctic Ocean - the world's longest submarine ridge of continental origin: outline of the history of exploration, morphology, sediment deposition, and exhumation of the North American and Central ridge segments

We have accessed the North American segment of the Lomonosov Ridge in the central Arctic Ocean by a 12-month hovercraft expedition on drifting sea ice and revisit legacy seismic data to explore the geological history of the ridge. Seismic reflection images on the North American segment resemble the acoustic reflection sequence calibrated by scientific drilling at the ACEX site on the Central ridge segment, although the thickness of the Cenozoic sediment section is reduced to 70%. A base-Cenozoic unconformity is present north of about 88 o 30’ N and older sediments dip towards the Makarov Basin along the entire ridge segment. During the Eocene, sediment drifts were deposited along the flanks on top of the North American segment north of 87 o N as well as next to the ACEX drill site on the Central segment of the ridge. Two local sediment lenses deposited at the Canadian end of the Lomonosov Ridge document local ridge-uplift events at about 56 Ma and 48 Ma during the Eurekan Orogeny. Compressional velocity gradients derived from published seismic reflection/refraction measurements are consistent with 1-3 km of Cretaceous/early Cenozoic exhumation of an up to 500 km wide swath of continental crust along the polar continental margin including the Lomonosov Ridge, Svalbard and Franz Josef Land .

Late Cenozoic deformation of the northeastern Pamir and the west Kunlun Mountains: Insights from anisotropy of magnetic fabrics and sedimentary analysis

Understanding the late Cenozoic temporal and spatial development of northeastern Pamir and the west Kunlun Mountains (WKMs) is critical for our knowledge of intracontinental orogeny in Central Asia. In this study, sedimentary analyses and anisotropy of magnetic fabrics (AMF) studies were conducted in four sections along the foreland of the northeastern Pamir and the WKMs. Combined with the results of previous researches, our AMF and sedimentological results reveal a shift in paleocurrent directions from variable azimuths in the Kelizuoyi Formation to northward-directed azimuths in the upper strata in the Kekeya, Keliyang and Keyikejia sections, suggesting a gradually northward migration of the WKMs and its foreland basin. Since the early Miocene, the prevailing drainage systems in the Aertashi and Paojianggou sections have been mainly controlled by the northeastern Pamir and the drainage systems in the Kekeya, Keliyang and Keyikejia sections were controlled by the uplift of the WKMs. The constant paleocurrent and regional strain directions in the Paojianggou section support a pre-existing arcuate Pamir since the early Miocene. Under these circumstances, the evolution of late Cenozoic sediment succession and the characteristics of the AMF in the Paojianggou section were mainly controlled by crustal thickening and exhumation of the Pamir.

Neogene–Quaternary Channel Evolution and Provenance Shift of the Middle Yellow River

AbstractThe formation age of the middle Yellow River and the existence of a northward‐flowing river have been fiercely debated. The age distribution of detrital zircon varied spatiotemporally and produced contradictory provenance interpretations. The Jinshaan Gorge, the main part of the middle Yellow River and key to studying fluvial evolution and clarifying disputes, developed its topography during the late Cenozoic. In this study, we systematically review the Cenozoic tectonic evolution of the North China Craton, perform detrital zircon U–Pb dating in the Neogene−Quaternary sediments and investigate the topography along the Jinshaan Gorge, and the sedimentology and chronological framework of these sediments. We propose that the Gorge of the middle Yellow River could have developed since the Neogene, controlled by the tectono‐geomorphologic evolution of the North China Craton in a dominantly extensional environment. No evidence supports a northward‐flowing river during the Early Pleistocene or even earlier in the Jinshaan Gorge. We attribute the provenance variations of the Cenozoic sediments to detrital mixing of diverse geological units, local and distant, and especially highlight the systematic provenance shift between the Neogene and Quaternary sediments caused by bedrock downcutting and recycling aeolian sediments. The increased 1.5−0.33 Ga component of the lower Yellow River during the Early Pleistocene was likely caused by enhanced loess accumulation and should not be individually used as a proxy for the Yellow River formation. We emphasize the significance of a comprehensive study of river evolution.

From Bottom‐Water Production to Warm Water Intrusions—The Cenozoic History of Bottom‐Current Evolution Offshore the Denman‐Shackleton Region, East Antarctica

AbstractThe deep glacial trough and hinterland of the Denman Glacier (East Antarctica) makes the area around the Shackleton ice shelf sensitive to ice loss due to warmer deep water intruding onto the continental shelf in the near future. In addition, the configuration of the ocean currents offshore is an important factor in priming the local and regional vulnerability to warm water intrusions. Here, we use reflection seismic data sets from the Bruce Rise offshore the Denman‐Shackleton region to investigate the Cenozoic history of the ocean bottom current configurations offshore and their influence on the Cenozoic sedimentation patterns of the Denman‐Shackleton region. On the Bruce Rise, sediment drift building, and erosional features indicate three distinct ocean current configurations, (a) the production of dense shelf waters in times of a smaller East Antarctic Ice Sheet (EAIS), (b) periods dominated by a strong Antarctic Slope Current (ASC) and (c) periods with a weak ASC. During the early establishment of the EAIS, the Denman‐Shackleton area contributed to the production of Antarctic Bottom Water, a process which stabilizes the regional ice sheet. With a growing icesheet, the ASC strengthened representing an effective barrier between the continental shelf and the warmer water masses of the deeper ocean during most of the times of an extended EAIS. The transition in the paleoceanographic setting from a strong, erosive ASC, toward a weak ASC increases the vulnerability of the Denman‐Shackleton continental shelf to deep water intrusions as we are observing today.

Biogenic opal δ18O in marine deep-sea sediments through the Cenozoic Era and implications for ocean cooling

Benthic foraminifera δ18O increased by 5.4 ‰ through the Cenozoic Era, the past 65 million years of Earth's history. This increase is attributed to growth of global ice sheets and global ocean cooling. On the other hand, δ18O measurements of planktonic foraminifera do not exhibit significant change. These measurements initially were interpreted to suggest cool tropical and subtropical temperatures and introduced the concept of the “cool tropics paradox”, in which global bottomwater temperatures were significantly warmer but tropical surface temperatures were not during the early Cenozoic. This lack of change in δ18O of planktonic foraminifera was explained by secondary postburial alteration of the primary planktonic isotope signal.We provide an alternative record of sea surface water characteristics of Cenozoic Era by measuring δ18O of siliceous microfossils. This scarce phase of marine silica, unaltered biogenic opal-A, composed of diatoms, radiolaria and sponge spicules, was separated and purified from deep-sea Cenozoic sediments. We measured δ18O of siliceous microfossils from a set of drilled cores: DSDP 278 from the South Pacific, DSDP 513 from the South Atlantic, and ODP 1050–1053 and DSDP 391 from the subtropical North Atlantic. The purity of the biogenic opal and its mineralogical phase was assessed with SEM, SEM/EDS, XPS, and XRD.The δ18O of biogenic opal-A fluctuates around an average value of 43.0 ‰ through the Cenozoic Era, comparable to the Southern Ocean average of 43.2 ‰ of diatoms and radiolaria from the last 30,000 years which represent the last glacial and interglacial period and suggesting cold surface temperatures of 2–7 °C, both in the subtropical and polar latitudes. Taking into consideration changes in δ18O associated with bottomwater interaction with the lower crust and changes in sea level associated with waxing and waning of ice sheets, we conclude lack of or minimal change in the surface water temperature through the Cenozoic Era. This revives the original idea of the “cool tropics” paradox with a carbonate independent δ18O record and without issues associated with diagenesis of benthic and planktonic foraminifera.

Cretaceous-Cenozoic cooling history of central-northern Tibet: Insights from the fission track thermochronology of detrital apatite from sediments of the Tuotuohe Basin

Deciphering the interactions between tectonic and exhumation processes in the Tanggula Mountains (central-northern Tibetan Plateau) can provide insights into the processes of the Tibetan plateau uplift and its geomorphic evolution. In this study, we present new detrital apatite fission track (AFT) data from Cenozoic sediments of the Tuotuohe Basin (northeastern part of the Qiangtang terrane) and its periphery (including the Tanggula Mountains), with the aim to reconstruct the cooling history of the Tanggula Mountains during the Cretaceous and the Cenozoic era. Our results show that the provenance of detrital material evolved in the Tuotuohe Basin and highlight that previously deposited sediments were recycled into the Tuotuohe Basin at ∼ 27.5 Ma. The data further outline that the Tanggula Mountains and the Tuotuohe Basin experienced three major phases of tectonic uplift and exhumation: 122–106, 65–54, and 44–35 Ma. These exhumation-induced cooling phases might be related with three phases of primary tectonic activity, i.e., the collision between the Qiangtang and Lhasa terranes (central part of the Tibetan Plateau) that started during the Early Cretaceous, the collision of the Indian and Eurasian plates in the Early Cenozoic and finally, the “hard collision (the Indian and Eurasian continents)” that occurred during the Early Eocene–Oligocene.

Linking Taiwan to the Cathaysia Block during the Cenozoic: Evidence from Pb isotopes in detrital K-feldspar

The Cenozoic sedimentary rocks on the island of Taiwan hold significant implications for understanding tectonic and drainage evolutions in SE China, but the provenance of these rocks remains controversial. Here we derived Pb isotopes in detrital K-feldspars from the drainage systems in western Taiwan to evaluate the provenance of sediments and reveal the evolution of Cenozoic sedimentary. Our findings indicate that the fluvial sediments eroded from the Cenozoic sedimentary rocks were primarily derived from the eastern Cathaysia Block (91%), with minor contributions from the Yangtze River catchment. Spatially, the northern part of Taiwan contains more sediments derived from the Yangtze River catchment than the southern part. The Cathaysia Block has been crucial in supplying detritus to Taiwan since the Eocene, whereas the contribution of the Yangtze Block varies greatly at different sedimentary periods. Two major shifts in provenance occur at the boundaries between Eocene, Oligocene, and Miocene, which may be related to the changes in drainage systems and landscapes in eastern China.

Northward expansion of the West Kunlun orogenic belt during the Cenozoic and its implications for the evolution of the northwest Tibetan Plateau: Constraints from sediment dispersal patterns in the Buya Basin, China

The West Kunlun orogenic belt, which defines the northwestern margin of the Tibetan Plateau, holds important information on plateau growth. Despite its significance, views about its uplift history continues to be under debate, with two competing hypotheses involving episodic uplift or northward expansion, related to a fixed or movable plateau boundary, respectively. The Buya Basin, a small basin located between the North and South Kunlun terranes, is key to understanding the Cenozoic uplift history of the West Kunlun orogenic belt. In this study, we conducted sedimentary and detrital zircon UPb geochronological analyses on the Cenozoic sediments of the Buya Basin. According to the findings of the sedimentary investigation, the Cenozoic strata of the basin generally show gradual changes from low- to high-energy deposition interrupted by a reverse trend in the Anjuan Formation. Moreover, the detrital zircon UPb geochronological results indicate that the Buya Basin received sediments initially from the Songpan–Ganzi and South Kunlun terranes during the deposition of the Keziluoyi to Pakabulake formations and then from the South and North Kunlun terranes during the deposition of the Artux Formation. This change in sediment dispersal patterns demonstrates that the uplift of the West Kunlun orogenic belt has expanded northwards to the North Kunlun terrane, which suggests that the northwestern boundary of the Tibetan Plateau has been a northward-moving feature in the context of India–Eurasia convergence. Along with previous studies, we suggest that the northward expansion of the northwest Tibetan Plateau is accommodated by decoupling deformation along the southern Tarim Basin, with northward thrusting of the foreland fold-and-thrust belts in the upper crust and southward underthrusting in the lower plate.

Late Miocene tectonic forcing of climate transition in the northeastern Tibetan Plateau

Interactions among late Cenozoic global cooling, tectonic activity and regional climate evolution of the northeastern Tibetan Plateau remain elusive. To further understand the relative contributions of global climate change and tectonism, we conducted a comprehensive study of heavy minerals, rock magnetism, and branched glycerol dialkyl glycerol tetraethers (brGDGTs) in late Cenozoic sediments of the Laojunmiao section (ca. 12.7 Ma to 5 Ma) in the Jiuxi Basin. Our results reveal a notable increase in magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) at 8.5 Ma, aligning with an accelerated decrease in temperature captured by brGDGTs. Combined with heavy mineral analysis, we propose that the profound changes in magnetic parameters and temperature are closely linked to the intensive uplift of the northern Qilian Shan since 8.5 Ma. Furthermore, this ongoing uplift has occurred simultaneously with persistent aridification in the Jiuxi Basin and its adjacent regions. The Qilian Shan might have reached a threshold elevation and began to act as a moisture barrier to northwestward moisture since 8.5 Ma. By synthesizing hydroclimate evolution records from the northeastern Tibetan Plateau, we deduce that changing topography resulting from tectonic uplift may have exerted a significant influence on regulating the moisture distribution in this region during the mid- to late Miocene.

In-situ radiogenic heat production in the Cenozoic sediments of the North sea

Radioactive decay is a significant heat source in sedimentary basins. Spectral gamma ray logs from the North Sea well 1/2-2 were used to obtain the uranium, thorium and potassium concentrations in the Cenozoic sediments beneath the well. On average, the sediments contain 1.86 ± 0.37% potassium, 10.12 ± 2.55 ppm thorium and 2.74 ± 1.54 ppm uranium. Abnormally high, up to 8 ppm, uranium concentrations were measured in the transition zones between the Nordland and the Hordaland Group and in the Sele Formation of the Rogaland Group.The estimated heat production rate, of all in-situ radioactive isotopes, is, on average, 1.281 ± 0.35 μW/m3. About 12% (0.143 ± 0.31 μW/m3) can be contributed to potassium, 46% (0.570 ± 0.14 μW/m3) to thorium and 42% (0.567 ± 0.31 μW/m3) to uranium. The estimated radiogenic heat rates vary significantly across the main stratigraphic units. On average, radiogenic heat production is more intensive in shale-dominated material (1.33 ± 0.31 μW/m3) than in sand-rich sediments (0.84 ± 0.36 μW/m3). High heat production rates are very closely related to high uranium concentration. In the “hottest” (2.012 ± 0.27 μW/m3) unit, the Sele Formation, the uranium accounts for about 69% of the generated heat, while the thorium and the potassium contribute with 24% and less than 7%, respectively. In the ”coldest” (0.782 ± 0.35 μW/m3) unit, the Forties, the relative contribution of uranium is only about 36% and that of potassium and thorium are about 18% and 46%, respectively.The radiogenic heat rates in the Cenozoic sediments should be integrated in future evaluations of the geothermal potential in the North Sea.

An updated chronostratigraphic framework for the Cenozoic sediments of southeast margin of the Tibetan Plateau: Implications for regional tectonics

As one of the most important accommodation zones during the India-Asia collision, the southeast margin of the Tibetan Plateau (SEMTP) is characterized by many large-scale strike-slip faults, a regional low-relief relict that has been deeply incised by several continental scale rivers that originate from central Tibet, and numerous plant and vertebrate fossil biotas residing in Cenozoic sedimentary basins. Therefore, the SEMTP not only provides a meaningful constraint on the geodynamic evolution of the Tibetan Plateau, but also serves as an exemplar to understand the various interactions among surface uplift, drainage network reorganization, climate change, and biodiversity. Precise dating of Cenozoic sediments in the basins of the SEMTP is crucial for understanding these processes. Previously, the geochronologic framework of Cenozoic sediments in the SEMTP largely relied on fossils and regional stratigraphic correlations, which often involved circular reasoning and large uncertainties. In the past two decades, high-resolution magnetostratigraphy, detrital zircon geochronology, and isotopic dating of interbedded tephra layers have been carried out on SEMTP Cenozoic sedimentary basins in Yunnan and eastern Xizang provinces, SW China. Using these new data, we build a revised chronostratigraphic framework for Cenozoic sediments in SEMTP, and use this updated temporal framework to contextualize regional tectonics and climate change. The new chronostratigraphic framework shows that (1) many of the “Neogene” sedimentary basins based on plant fossils and regional lithostratigraphic correlation in the SEMTP were actually formed in the late Eocene and early Oligocene; (2) most of the Paleogene sedimentary successions in the SEMTP ended at the late Eocene-early Oligocene and were unconformably overlaid by Middle-Late Miocene sediments. Oligocene-Early Miocene sediments are often regionally absent. Sedimentary structures within the basin successions show that Paleogene basins were generally formed in compressional settings while the Late Miocene basins were mostly developed in extensional settings. The new chronostratigraphic framework, together with analyses of sedimentary basin structures, suggests that the SEMTP began to experience crustal shortening early in the India-Asia collision (∼50 Ma), producing Paleogene sedimentary basins and giving rise to the subsequent widespread surface uplift and regional erosion in the Oligocene-Middle Miocene. Tectonic inversion from compression to extension since the Middle Miocene precludes significant uplift of the SEMTP after this time, which may be related to geodynamic changes in the evolution of the Tibetan Plateau.

Large paleoearthquakes and Holocene faulting in the Southeastern Gorny Altai: implications for ongoing crustal shortening in Central Asia

ABSTRACT Shrinking of intermontane basins and expansion of their flanking ranges by reverse faulting and backthrusting in two counter-dipping systems is a typical mechanism of crustal shortening and mountain building in Central Asia. This mechanism is realized along the Kurai Fault Zone (southeastern Gorny Altai). Motions on two reverse fault systems maintained thrusting of the Kurai Range and the Kubadru Uplift on the Kurai Basin sediments and caused the growth of a foreberg before the mountain front. Forberg separates narrow Aktash Basin from the Kurai Basin. The paleoearthquakes were generated by reverse faults that delineate the foreberg. Analysis of the QuickBird satellite images, drone imagery, trenching, archaeoseismological research, radiocarbon dating, dendrochronology, and previous results show that eleven large (М W = 6.5–7.6) paleoearthquakes left traces as surface ruptures along the Kurai Fault Zone: twice before 7.5 ka BP, three events between 7.5 and 5.9 ka BP (7.0, 6.3, and 5.9–5.8 ka BP), one from 5.8 to 4.6 ka BP, four more at 4.6, 3.2, 1.5, and 1.3–1.2 ka BP, and the ultimate earthquake no older than 1450–1650 AD. The time difference between large earthquakes was from 200 to 1700 years. Surface faulting occurred mainly along the northern border of the foreberg where fault scarps are progressively younger northward and the Cenozoic sediments of the Aktash Basin thus become involved into uplift. GPR data to a depth of 12 m confirm the complex structure and slip geometry of the observed surface ruptures. The fault scarps are located < 1 km from the planned route of the gas pipeline from Russia to China, and the potential seismic hazard has to be taken into account in its design and construction.

The transition from backarc extension to Andean growth: Insights from geochronologic, sedimentologic, and structural studies of Mesozoic and Cenozoic sedimentary and volcanic rocks in south-central Chile (36°S)

Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous. It has been proposed that the preceding Jurassic-Early Cretaceous extensional regime that resulted in a low-relief volcanic arc and the backarc Neuquén basin came to an end, giving way to shortening and Andean growth from the Late Cretaceous onward. Nevertheless, there are disagreements regarding the timing and nature of this transition to Andean orogenesis. To address these issues, we conducted geochronologic (U–Pb and 40Ar/39Ar), sedimentologic, and structural studies on Mesozoic-Cenozoic sedimentary and volcanic rocks in the Río Maule area (Principal Cordillera, Chile, 36°S). From our findings and prior analyses, we propose the following tectono-stratigraphic evolution of the region. (1) Marine deposition of the Tithonian-Hauterivian Baños del Flaco Formation took place in an extensional backarc basin. (2) After a ∼ 40 Myr hiatus, fluvial deposits of the Colimapu Formation and volcanic rocks of the Plan de los Yeuques Formation accumulated during the Cenomanian-Danian. Whereas the Colimapu Formation displays evidence of syndepositional shortening, the Plan de los Yeuques Formation exhibits synextensional growth strata. Contrary to other studies, our results suggest that the Chilean part of the Principal Cordillera was largely a zone of active deposition rather than an elevated fold-thrust belt during the Late Cretaceous. We propose that sedimentation occurred within a series of relatively stable intermontane subbasins generated by shortening, followed by extension. (3) After a ∼ 20 Myr hiatus, middle Eocene to early Miocene (Lutetian-Aquitanian) accumulation of a thick succession of andesitic lavas and minor clastic sediments of the Abanico Formation occurred in an intraarc extensional basin. (4) Finally, major shortening and uplift of previously deposited Mesozoic-Cenozoic rocks took place throughout the Neogene. This phase constituted the primary contractional deformation in the Andes of south-central Chile and Argentina. In terms of the transition to early Andean deformation, we propose that structural deformation did not generate a major, regional-scale fold-thrust belt during the late Albian-Santonian. Modest extension, tectonic quiescence, or low-magnitude shortening seem to have dominated during the early to middle Cenozoic.

Mesozoic structural evolution of the Northern South China Sea margin using potential field modelling

This study conducts a comprehensive geophysical inspection of the Northern South China Sea Margin (NSCSM), a complex and pivotal area for unraveling the tectonic history of Southeast China. We employ structural interpretation of the gravity and magnetic data by applying processing techniques and 2D forward modelling to delineate and subdivide the primary subsurface structures, and also to identify the sedimentary basins. Our findings reveal that the NSCSM exhibits a succession of extensional forearc basins above a heterogeneous basement, including a Mesozoic Andean-type magmatic arc and a Western Pacific-type marginal oceanic basin. It has substantial variations in crustal densities and susceptibilities across the NSCSM, reflecting its intricate geological history. The integrated interpretation of this study highlights the substantial impact of the Indosinian and Yanshanian thrusting and orogenies. These geological processes have played a significant role in deformation partitioning, leading to the development of elongated troughs and basins intersected by numerous prominent structures trending in the NE, ENE, and EW directions. The Indosinian faults provide insights into the boundary between these structures, which formed due to the Dian-Qiong Suture and the Paleo-Pacific Plate subduction. These tectonic processes have major structural trends, particularly impacting the offshore forearc region in the NE and EW directions, characterized by deep basins overlying thin crust. Our study also identifies multiple minor trends, including horse-tails and secondary fault systems of the Yanshanian origin, which inherited from the regional tectonics. These trends suggest that post-orogenic stresses and shearing have played a role in rotational and ridge jump processes during the opening and closing phases of the South China Sea (SCS). Furthermore, an uneven relationship exists between the calculated magnetic anomaly and the thickness of Cenozoic sediments, with a significant increase in sediment depth observed in the southern NSCSM compared to both crustal thickness and its heterogeneity.

Fossil Equidae in the Linxia Basin with Biostratigraphic and Paleozoogeographic Significance

AbstractThe Linxia Basin is characterized by an abundance of Cenozoic sediments, that contain exceptionally rich fossil resources. Equids are abundant in the Linxia Basin, the fossil record of equids in this region including 16 species that represent 10 genera. In comparison to other classic late Cenozoic areas in China, the Linxia Basin stands out, because the fauna and chronological data accompanying Linxia equids render them remarkably useful for biostratigraphy. The anchitheriines in the region, such as Anchitherium and Sinohippus, represent early equids that appeared in the late stages of the middle and late Miocene, respectively. Among the equines, most species of Chinese hipparions have been identified in the Linxia Basin and some species of the genera Hipparion and Hippotherium have FAD records for China. Furthermore, Equus eisenmannae is one of the earliest known species of Equus in the Old World and is well‐represented at the Longdan locality. Some species with precise geohistorical distributions can serve as standards for high‐resolution chronological units within this framework. Located at the eastern margin of the Tibetan Plateau and subject to considerable uplift, the Linxia Basin has served as a biogeographic transition area for equids throughout the late Cenozoic.

Plume‐Modified Lithosphere Mantle Controlled the Cenozoic Sediment Thickness in the Tarim Basin

AbstractThe Cenozoic sediments are very thick in the southwest Tarim Basin and very thin in the northwest, but what controls these variations is unclear. Here, we use two‐dimensional thermo‐mechanical models to investigate how the lateral variations in rheological strength and depletion density of cratonic lithosphere mantle affect the cratonic basin deformation. Model results show that the basin basement uplift occurs above either the region with crustal thickening or high depletion in the mantle. A model with a stronger and density‐depleted northern half of cratonic lithosphere mantle in the context of compression matches the differential Cenozoic subsidence and deformation observed in the Tarim Basin well. We propose that a Permian plume led to the lateral heterogeneity of the lithosphere mantle under the Tarim craton, and the modified lithosphere mantle characteristics caused the differential Cenozoic sediment thickness in the Tarim Basin.

Cenozoic sedimentary evolution of the Tiereke section on the northern Tarim Basin: implications for the intracontinental mountain building of the Eastern Tian Shan

The Tian Shan is one of the world's largest intracontinental orogens and provides an excellent example for deciphering the intracontinental responses to the tectonics of plate boundaries. Despite its significance, the timing and driving mechanism of the Cenozoic mountain building of the Tian Shan in the context of the India–Eurasia collision remain controversial. In this study, Cenozoic stratigraphy of the Tiereke section along the western Kuqa Depression of the northern Tarim Basin on the south foreland of Eastern Tian Shan (east of 80°E) has been investigated. The results indicate that the Cenozoic deposition of the Tiereke region sequentially experienced a transgression from the Kumugeliemu Group to the Suweiyi Formation and a regression from the Suweiyi to the Kuqa Formations. Based on the contact relationships and conglomerate textures, three stages of high-energy alluvial deposition have been identified in the lower Kumugeliemu Group, upper Jidike and Kangcun–Kuqa Formations, respectively. These sedimentary events were interpreted to represent phases of Eastern Tian Shan mountain building at c. 54 Ma, c. 27 Ma and since c. 9.7 Ma according to previous magnetostratigraphic results, which were possibly related to the initial India–Eurasia collision, the collision between the India and Tarim lithospheric mantles, and the basinward propagation of deformation, respectively. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change