Neoproterozoic Rift Basins Research Articles

Biomarker signatures and depositional environment of ore-bearing black shale in the Luishia Cu–Co deposit, Democratic Republic of Congo: Implications for regional copper mineralization

The Central African Copperbelt is a globally important sediment-hosted stratiform copper cluster, with regional Cu–Co deposits controlled by Neoproterozoic rift basin. Ore formation in the Copperbelt involves multiple stages of mineralization during diagenesis, basin inversion, and collisional orogeny. Understanding the depositional environment of ore-hosting rocks is crucial for revealing the geological settings and pre-orogenic ore genesis. This paper presents a biomarker study focusing on the ore-bearing black shale in the Luishia Cu–Co deposit, Democratic Republic of Congo. The research investigates thermal maturity, source, and depositional environment of organic matter through rock organic carbon and pyrolysis analysis, chloroform bitumen “A” group component analysis, as well as saturated hydrocarbon gas chromatography-mass spectrometry (GC-MS) analysis. The results indicate significant thermal maturation of organic matter in Luishia black shale. Bacteria are identified as the primary source of organic matter followed by red algae and green algae. The sedimentary environment is characterized by a restricted rift basin under shallow marine conditions with a stratified water column. The processes of bacterial sulphate reduction (BSR) and thermochemical sulphate reduction (TSR) significantly influence the mineralization during diagenesis and basin inversion, respectively. Enhanced thermal maturity promotes methane generation which plays a role in reducing anhydrite and subsequently precipitating ore minerals. The findings have important implications for regional exploration strategies.

The origin and tectonic evolution of the late Neoproterozoic rift basin in the Tarim Craton, NW China

The Cryogenian-early Paleozoic succession in the Tarim Craton is generally regarded as a continuous rift sequence that followed the prolonged superplume-related breakup of Rodinia. However, the rift architecture and origin of the late Neoproterozoic basin are poorly known, but these are important for the understanding of the tectonic evolution of the basin and for the evaluation of the hydrocarbon potential. This paper aims to elucidate the rift architecture, distribution, origin and evolution of the late Neoproterozoic Tarim Basin by integrating outcrop investigations with well and seismic data. The late Neoproterozoic magma-rich active rifting primarily occurred in the northeastern part of the basin, whereas other areas experienced slightly younger magma-poor passive rifting. The Ediacaran succession overlaps in the northern basement uplift to show a pre-Ediacaran unconformity occurs in the northern Tarim Craton, while a sub-Cambrian unconformity traverses the entire Tarim Craton and presents a distinct truncation in the southern basement uplift. A tiered architecture exists in which narrow, deep Cryogenian grabens are overlain by a broad Ediacaran depression. Two NE-striking rift systems developed in the northeastern and southwestern Tarim. It can be inferred from the compiled data that the late Neoproterozoic rift basin evolution in the Tarim Craton can be divided into four stages: early Cryogenian rifting, late Cryogenian fault-graben, Ediacaran intracratonic depression, and end-Ediacaran regional uplifting. These results suggest that documented Neoproterozoic retreating subduction-related slab failure/detachment processes led to both active and passive rifting, which contributed to the diverse continental rift architecture and evolution of the late Neoproterozoic Tarim Basin.

Timanian Fold-and-Thrust Belt and Caledonian Overprint in the Selis Ridge Imaged by New 3D Seismic Attributes and Spectral Decomposition

The present study is a detailed structural analysis of 3D seismic data in the Selis Ridge in the western Loppa High in the Norwegian Barents Sea, to which new seismic attributes and spectral decomposition were applied. The analysis reveals that pre-Devonian basement rocks are crosscut by a 40–50 kilometers wide, several kilometers thick, E–W- to WNW–ESE-striking fold-and-thrust belt, including a steep, kilometer-thick, top-SSW shear zone. The folds display dome- and trough-shaped geometries, the thrusts appear to have been reactivated dominantly as top-west structures, and the main shear zone warps over the top of the Selis Ridge. The fold-and-thrust belt is interpreted as part of the latest Neoproterozoic (ca. 650–550 Ma) Timanian Orogeny, which potentially reworked preexisting Neoproterozoic rift basins and highs, and was reworked during E–W Caledonian contraction in the Ordovician–Silurian. The results are analogous to recent findings in the northern Norwegian Barents Sea and Svalbard. The presented interpretation provides the basis for discussing Neoproterozoic–Paleozoic plate tectonics reconstructions, the influence of Precambrian–early Paleozoic structures on post-Caledonian fault complexes, the location of the Timanian and Caledonian suture zones, Neoproterozoic rifting, and the origin of the Seiland Igneous Province.

Seismic reflection analysis of the deeply buried Neoproterozoic rift basin beneath Sichuan Basin, southern China

Seismic reflection analysis of the deeply buried Neoproterozoic rift basin beneath Sichuan Basin, southern China

Syn‐rift mass flow generated ‘tectonofacies’ and ‘tectonosequences’ of the Kingston Peak Formation, Death Valley, California, and their bearing on supposed Neoproterozoic panglacial climates

AbstractThe Kingston Peak Formation of the Pahrump Group in the Death Valley region of the Basin and Range Province, USA, is the thick (over 3 km) mixed siliciclastic–carbonate fill of a long‐lived structurally‐complex Neoproterozoic rift basin and is recognized by some as a key ‘climatostratigraphic’ succession recording panglacial Snowball Earth events. A facies analysis of the Kingston Peak Formation shows it to be largely composed of ‘tectonofacies’ which are subaqueous mass flow deposits recording cannibalization of older Pahrump carbonate strata exposed by local faulting. Facies include siltstone, sandstone and conglomerate turbidites, carbonate megabreccias (olistoliths) and related breccias, and interbedded debrites. Secondary facies are thin carbonates and pillowed basalts. Four distinct associations of tectonofacies (‘base‐of‐scarp’; FA1, ‘mid‐slope’; FA2, ‘base‐of‐slope’; FA3, and a ‘carbonate margin’ association; FA4) reflect the initiation and progradation of deep water clastic wedges at the foot of fault scarps. ‘Tectonosequences’ record episodes of fault reactivation resulting in substantial increases in accommodation space and water depths, the collapse of fault scarps and consequent downslope mass flow events. Carbonates of FA4 record the cessation of tectonic activity and resulting sediment starvation ending the growth of clastic wedges. Tectonosequences are nested within regionally‐extensive tectono‐stratigraphic units of earlier workers that are hundreds to thousands of metres in thickness, recording the long‐term evolution of the rifted Laurentian continental margin during the protracted breakup of Rodinia. Debrite facies of the Kingston Peak Formation are classically described as ice‐contact glacial deposits recording globally‐correlative panglacials but they result from partial to complete subaqueous mixing of fault‐generated coarse‐grained debris and fine‐grained distal sediment on a slope conditioned by tectonic activity. The sedimentology (tectonofacies) and stratigraphy (tectonosequences) of the Kingston Peak Formation reflect a fundamental control on local sedimentation in the basin by faulting and likely earthquake activity, not by any global glacial climate.

Internal versus external locations of the South China Craton within Rodinia during the Cryogenian: Provenance history of the Nanhua Basin

AbstractContrasting models for internal versus external locations of the South China Craton (SCC) in the supercontinent Rodinia and associated mantle plume or ocean subduction dominated tectonic processes can be resolved by detrital zircon U-Pb dating and Lu-Hf isotopic analyses on the Cryogenian Nanhua Supergroup in the central SCC. Our results show that samples from the lower Liantuo, Tiesi’ao, and Datangpo formations of the Nanhua Supergroup show three age peaks at 2.50 Ga, 2.05 Ga, and 0.85 Ga, and those of the upper Nantuo Formation yield four peaks at 2.50 Ga, 2.05 Ga, 0.85 Ga, and 0.65 Ga. The Archean and Paleoproterozoic (1.80–2.10 Ga) zircons have εHf(t) values of −16.3 to +4.7 and −23.0 to +4.2, and may be sourced from the Kongling and Douling complexes and Paleoproterozoic intrusions in the northern Yangtze Block, respectively. Early Neoproterozoic (0.70–0.96 Ga) zircon grains show variable εHf(t) values of −20.0 to +15.0. In combination with the absence of Mesoproterozoic detrital zircons in the Nanhua Supergroup, huge volumes of Neoproterozoic granitic intrusions in the northern Yangtze Block are the potential sources for the 0.70–0.96 Ga detrital zircons. Only the siltstone of the Nantuo Formation has late Neoproterozoic (0.63–0.69 Ga) detrital zircons with high and positive εHf(t) values (+7.9 to +9.4). Several granitoid intrusions (0.63–0.68 Ga) in the Wudang and Ankang uplift of the South Qinling belt in the northern Yangtze Block provide the late Neoproterozoic detrital zircons of the Nantuo Formation. These provenance analyses of the Nanhua Supergroup indicate an interior source from the SCC, rather than an exterior source from the Laurentia and Australia cratons. The Neoproterozoic rift basins and magmatic rocks in the SCC were produced by secular episodic subductions and back-arc extensions, rather than a Neoproterozoic super-mantle plume. The SCC occupied a peripheral position adjacent to northern India in Rodinia during the Neoproterozoic. These conclusions will promote our understanding of genetic mechanism and distribution prediction of the several Cryogenian–Cambrian black-shale layers and excellent source rocks in the SCC.

Single-crystal hematite (U–Th)/He dates and fluid inclusions document widespread Cryogenian sand injection in crystalline basement

The Tavakaiv Quartzite (informal) in Colorado, USA, is one of the world's largest basement-hosted clastic injectite systems and provides a glimpse into the tectonic and near-surface environment of ancient North America. The age, origin, and significance of Tavakaiv injectites has been debated for over a century, owing to inherent difficulties with assigning absolute age constraints to unfossiliferous sandstone intrusions. Here, we apply an innovative combination of single-crystal hematite (U–Th)/He thermochronometry and fluid inclusion microthermometry to hematite mineralization associated with the injectites to document the age and ambient fluid conditions of Tavakaiv injectite formation. Our approach confirms individual hematite crystals comprising commonly analyzed polycrystalline aggregates are the He diffusion domains and that hematite (U–Th)/He closure temperature increases with crystal size. We apply apatite and zircon fission-track thermochronometry to the Tavakaiv Quartzite and host rock to account for the consequences of Phanerozoic orogenic episodes on the hematite (U–Th)/He dates and explain the observed trends between hematite He date and crystal size. Our results indicate that hematite formed 676 ± 26 million years ago (arithmetic mean date ±1σ), constraining the timing of the Tavakaiv injection event. Fluid inclusion studies reveal that this mineralizing fluid was at least 200 °C and saline (>20 wt% CaCl2 equiv.). Comparison of new and previously published detrital zircon U–Pb age populations from quartzite samples yield a sediment source common to Tavakaiv bodies across a broader region and illuminate the greater areal extent of the Cryogenian injection event. We interpret that formation of basement-penetrating fracture arrays was associated with crustal extension within Rodinia at this time. This was accompanied by sand remobilization that promoted widespread sand injection within horsts bounding Neoproterozoic rift basins. The resulting sand injectites served as permeable pathways for contemporaneous circulation of saline groundwater, driven by fluid gradients in extensional and/or transtensional basins.

Neoproterozoic stratigraphic framework of the Tarim Craton in NW China: Implications for rift evolution

The Tarim Craton is overlain by thick Neoproterozoic sedimentary successions in rift tectonic setting. This study examines the latest outcrop, seismic, and drilling core data with the objective of investigating the regional stratigraphy to deeply recognize the evolution of rifting in the craton. Cryogenian to Lower Ediacaran successions are mainly composed of clastic rocks with thicknesses of 2000–3000 m, and the Upper Ediacaran successions are composed of carbonate rocks with thicknesses of 500–800 m. The rift basins and stratigraphic zones are divided into northern and southern parts by a central paleo-uplift. The northern rift basin extends through the northern Tarim Craton in an E–W direction with two depocenters (Aksu and Kuruktag). The southern rift basin is oriented NE–SW. There are three or four phases of tillites in the northern zone, while there are two in the southern zone. Given the north–south difference of the stratigraphic framework, the northern rift basin initiated at ca. 740 Ma and the southern rift basin initiated at ca. 780 Ma. During the Cryogenian and Ediacaran, the northern and southern rift basins were separated by the central paleo-uplift, finally connecting with each other in the early Cambrian. Tectonic deformation in the Late Ediacaran led to the formation of a parallel unconformity in the rift basins and an angular unconformity in the central paleo-uplift. The Neoproterozoic rift basins continued to affect the distribution of Lower Cambrian hydrocarbon source rocks. The north–south distribution and evolution of the rift basins in the Tarim Craton have implications for reconstructions of the Rodinia supercontinent.

Evolution of the Neoproterozoic rift basins and its implication for oil and gas exploration in the Tarim Basin

According to the aeromagnetic, seismic, and geological data, the surface structure, sedimentation, and distribution characteristics as well as the deep dynamic mechanism of the north-south differentiated Neoproterozoic rift basins were well investigated to reveal the tectonic evolution and its control on the distribution of the Early Cambrian sedimentary basin and source rocks in the Tarim Basin. The rift basin in the southern Tarim was a product of superplume activities during the early breakup period of the Rodinia supercontinent. It initiated in the Early Cryogenian (about 780 Ma) and appeared as NE-direction aulacogens extending into the Tarim Basin. The rift basin in the northern Tarim was a back-arc rift basin derived from the subduction of Pan-Rodinian oceanic plate, which initiated in the Late Cryogenian (about 740 Ma) and occurred as a nearly EW-direction narrow band across the Tarim Basin. The northern Tarim back-arc rift basin had similar formation and evolution process to the Late Mesozoic-Cenozoic back-arc rift basins in East Asia, both showing an oceanward migration; however, the Tarim rift basin finally evolved from the fault-depression basins into passive continental margin. The Neoproterozoic rift basins controlled not only the distribution of source rocks in the syn-rift period but also the development of Early Cambrian sedimentary basin. Nearly EW-distributed syn-rift (Cryogenian to Ediacaran) and post-rift (Lower Cambrian Yurtusi period) source rocks were likely to develop between the present Tabei uplift and central uplift belt.

Sedimentary evolution of Neoproterozoic rift basin in northern Tarim

Based on the outcrop, drilling and seismic data, the sedimentary successions, evolution and hydrocarbon exploration potential of the Neoproterozoic rift basin in the northern Tarim were firstly analyzed. Due to assembly and breakup of the Rodinia supercontinent, the Tabei paleocontinent and the Tarim paleocontinent were developed in the Tarim craton with an EW-trending back-arc rift basin between them during Neoproterozoic time; very thick marine clastic rocks, carbonate rocks and volcanic rocks (including tillite) were deposited in the Kuruktag and Aksu area of the northern Tarim, which experienced deep sea, bathyal sea and littoral sea environments with transitional delta and ice-sea. During the Early Cryogenian and the Late Ediacaran, the northern rift basin evolved from the deep sea to the littoral-neritic sea, while the lithology changed from clastic rocks to carbonate rocks. According to the field and production data, the formation and preservation of the source rocks and reservoirs indicate a good exploration potential of the Neoproterozoic rift basin.

Neoproterozoic rift basins and their control on the development of hydrocarbon source rocks in the Tarim Basin, NW China

The Proterozoic is demonstrated to be an important period for global petroleum systems. Few exploration breakthroughs, however, have been obtained on the system in the Tarim Basin, NW China. Outcrop, drilling, and seismic data are integrated in this paper to focus on the Neoproterozoic rift basins and related hydrocarbon source rocks in the Tarim Basin. The basin consists of Cryogenian to Ediacaran rifts showing a distribution of N-S differentiation. Compared to the Cryogenian basins, those of the Ediacaran are characterized by deposits in small thickness and wide distribution. Thus, the rifts have a typical dual structure, namely the Cryogenian rifting and Ediacaran depression phases that reveal distinct structural and sedimentary characteristics. The Cryogenian rifting basins are dominated by a series of grabens or half grabens, which have a wedge-shaped rapid filling structure. The basins evolved into Ediacaran depression when the rifting and magmatic activities diminished, and extensive overlapping sedimentation occurred. The distributions of the source rocks are controlled by the Neoproterozoic rifts as follows. The present outcrops lie mostly at the margins of the Cryogenian rifting basins where the rapid deposition dominates and the argillaceous rocks have low total organic carbon (TOC) contents; however, the source rocks with high TOC contents should develop in the center of the basins. The Ediacaran source rocks formed in deep water environment of the stable depressions evolving from the previous rifting basins, and are thus more widespread in the Tarim Basin. The confirmation of the Cryogenian to Ediacaran source rocks would open up a new field for the deep hydrocarbon exploration in the Tarim Basin.

Tectonostratigraphy and provenance analysis to define the edge and evolution of the eastern Wuyi-Yunkai orogen, South China

AbstractWe report three Palaeozoic sedimentary successions in northeastern South China that display markedly different tectonostratigraphic characteristics: the Jiangshan section exhibits an angular unconformity between the Upper Ordovician and Carboniferous stratra; the Shuangming section exhibits a disconformity between the lower Silurian and Upper Devonian strata; and the Xinqiao section exhibits a disconformity between the upper Silurian and Upper Devonian strata. The Shuangming and Xinqiao sections are interpreted to represent the remnant Nanhua foreland basin, whereas the Jiangshan section is in the fold-and-thrust zone of the Wuyi-Yunkai orogen. The Lizhu-Changshan thrust fault in between is interpreted to be the frontal thrust and the boundary of the orogen. Detrital provenance analysis of the Ordovician–Devonian sandstones from the Shuangming and Xinqiao sections shows that the Ordovician–Silurian, mid- to late-orogenic sandstones contain dominantly 860–780 Ma zircon populations and subordinate 2.5 Ga, 1.89–1.78 Ga, 980–950 Ma, 630–540 Ma and 430 Ma populations, indicating nearby sources including the early Neoproterozoic Sibao orogen, inverted Neoproterozoic rift basins and related plutons, recycled Ediacaran–Cambrian strata and, increasing with time, exposed Cathaysia basement and minor syn- to late-orogenic plutonic intrusions. The Devonian post-orogenic sandstones exhibit a dominant 440 Ma population with minor 2.5 Ga, 1.89–1.78 Ga, 860–780 Ma and 630–540 Ma populations, suggesting a dominant contribution from now widely exposed, mid- to late-orogenic plutonic intrusions (with or without contributions from rare volcanism of similar ages) in a residual topographic high SE of the Lizhu-Changshan fault. This residual topographic high of the Wuyi-Yunkai orogen had completely perished by early Carboniferous time, c. 60Myr after the end of the orogenic event.

Opening time and filling pattern of the Neoproterozoic Kangdian Rift Basin, western Yangtze Continent, South China

The Neoproterozoic Kangdian Rift Basin is a continental rift basin in the western Yangtze Continent. Determining its time of opening and subsequent filling pattern is an important aspect of understanding the formation and evolution of the Yangtze Continent, South China. The Luliang Formation is the early filling in the eastern part of this rift basin, and its deposition age and filling sequence are significant for studies of the regional stratigraphic correlation, opening time, and filling pattern of this basin. Having been correlated to the upper part of the Mesoproterozoic Kunyang Group or to the Neoproterozoic Chengjiang Formation, the age and regional stratigraphic correlation of the Luliang Formation have long been uncertain. This is due to a lack of reliable absolute age constraints. To address this issue, the first zircon SHRIMP U-Pb geochronology has been established for this formation, yielding two high-precision isotopic ages of 818.6±9.2 and 805±14 Ma for the tuff layers at the bottoms of the lower and upper members of the Luliang Formation, respectively. Given the error factor, the bottom age of the lower member of the Luliang Formation can be interpreted as ca. 820 Ma, corresponding to the bottom age of the lower part of the Banxi Group, which is the early filling of the Neoproterozoic Xianggui Rift Basin, a representative basin of the Neoproterozoic rift basins in the Yangtze Continent, South China. The bottom age of the upper member of the Luliang Formation can be interpreted as ca. 800±5 Ma, corresponding to the bottom age of the Chengjiang Formation in the western part of the Neoproterozoic Kangdian Rift Basin and also corresponding to the bottom age of the upper part of the Banxi Group in the Neoproterozoic Xianggui Rift Basin. These ages indicate that the Neoproterozoic Kangdian Rift Basin shares the same opening time and filling sequences as those of the other Neoproterozoic rift basins in South China. Basin analysis shows that the Neoproterozoic Kangdian Rift Basin is a typical half-graben basin, with its main boundary fault in the west and basin center in the east. This basin consisted of mini unidirectional half-graben basins in its juvenile stage and simplified to become a large united half-graben basin in its mature stage, i.e., a supradetachment basin.

Zircon SHRIMP U-Pb geochronology of the Neoproterozoic Chengjiang Formation in central Yunnan Province (SW China) and its geological significance

The Chengjiang Formation is the earliest continental clastic deposit after the Jinning Orogeny in central Yunnan Province, and therefore its accurate depositional age is significant for understanding the formation and evolution of the Neoproterozoic rift basins in southern China. However, hampered by accuracy of the dating technique, the existing age data for the Chengjiang Formation are not very reliable. A large number of magmatic zircons were obtained from the tuff interbed in the lower part of the Chengjiang Formation in Jinyang area and the bottom part of the Chengjiang Formation in Dongchuan area, central Yunnan Province, and high-precision SHRIMP U-Pb dating was carried out on these zircons. The results show that the weighted mean 206Pb/238U ages are 797.8±8.2 and 803.1±8.7 Ma respectively. In combination with related geological evidence, it has been demonstrated that the bottom boundary age of the Chengjiang Formation should be 800±5 Ma, whereas the top boundary age could be ca 725 Ma. By synthetically analyzing the latest age data for the relevant strata, it has been confirmed that the Chengjiang Formation should be correlated with the Suxiong Formation and the Kaijianqiao Formation in western Sichuan Province, the Liantuo Formation in the middle and lower Yangtze, the Hongchicun Formation and the Shangshu Formation in northern Zhejiang Province, the Puling Formation in southern Anhui Province, the Luokedong Formation and the Majianqiao Formation in northwestern Jiangxi Province, the Wuqiangxi Formation in northwestern Hunan Province, the Fanzhao Formation and the Qingshuijiang Formation in southeastern Guizhou Province, and the Sanmenjie Formation and the Gongdong Formation in northern Guangxi Province. Sedimentary cycle analysis shows that the sedimentary filling sequence of the Neoproterozoic rift basins in southern China can be divided into four cycles. Among them, Cycle II began at ca. 800 Ma, accompanied by intensive tectonic-thermal events. The zircon U-Pb ages from the bottom of the Chengjiang Formation reported in this paper indicate that the Neoproterozoic Kangdian rift subbasin probably started to develop at ca. 800 Ma and therefore missed Cycle I of the Neoproterozoic sedimentary filling sequence in southern China.

The Okcheon Supergroup in the Lake Chungju area, Korea: Neoproterozoic volcanic and glaciogenic sedimentary successions in a rift basin

The Okcheon Belt in southern Korea is an NE-SW trending fold-and-thrust belt consisting of two sedimentary basins of different origins: namely, the Chungcheong Basin and the Taebaeksan Basin. The Chungcheong Basin was a Neoproterozoic rift basin belonging to the South China Craton, while the Taebaeksan Basin was a Paleozoic shallow marine to non-marine sedimentary basin fringing the Sino-Korean Craton. These two basins merged to form the Okcheon Belt in the early Triassic by the collision of Sino-Korean and South China cratons and their boundary is currently demarcated by the South Korean Tectonic Line. The Okcheon Supergroup is herein refined to include the Neoproterozoic volcanic and glaciogenic sedimentary successions deposited in the Chungcheong Basin and is divided into the two groups: the Chungju Group consists of the Gyemyeongsan Formation, Hyangsanni Dolomite, and Daehyangsan Quartzite and the Suanbo Group is proposed to include the Munjuri, Hwanggangni, Myeongori, and Gounni formations in ascending order. The Myeongori Formation is emended to comprise the Geumgang Limestone and the Seochangni members. This lithostratigraphic scheme is correlatable with that of the Nanhua Basin in South China, suggesting that the Chungcheong Basin was an eastward extension of the Nanhua Basin during the Neoproterozoic. The geological structure of the Okcheon Supergroup in the Lake Chungju area is characterized by a number of isoclinal to tight, frequently overturned, anticlines and synclines. No major thrust faults were recognized within the study area, except the constraining bend of the South Korean Tectonic Line. Three deformational phases are empirically differentiated: D1 deformation most strongly affected the rocks of the Okcheon Supergroup; D2 deformation was produced by the collision between the Sino-Korean and South China cratons; and D3 deformation is represented by normal to strike-slip faults. D1, D2 and D3 deformational phases are referred to the Okcheon (mid-Paleozoic), Songnim (Triassic) and/or Daebo (Jurassic) orogenies, and post-Jurassic events, respectively. The Chungcheong Basin was initiated as a part of an intracratonic rift basin (Nanhua Basin) within the South China Craton in association with early Neoproterozoic break-up event of the supercontinent Rodinia. The bimodal volcanic succession of the Gyemyeongsan Formation corresponds to the initial rift episode of the Chungcheong Basin, and was succeeded by shallow marine Hyangsanni Dolomite and Daehyangsan Quartzite. The second phase of rifting at ∼750 Ma accumulated a thick bimodal volcanic succession of the Munjuri Formation which is overlain by the diamictites of the Hwanggangni Formation representing the Cryogenian global glacial event, snowball Earth. The immediately-succeeding cap carbonate, Geumgang Limestone Member of the Myeongori Formation, recorded the deglaciation event. The Seochangni Member of the Myeongori Formation is characterized by dark gray slate/phyllite facies indicating a poorly-oxygenated basin during the Ediacaran. No stratigraphic unit overlying the Gounni Formation, the youngest Neoproterozoic formation of the Okcheon Supergroup, occurs in the Lake Chungju area, and thus little is known on the Paleozoic tectonic evolution of the Chungcheong Basin. It is inferred that the medium-pressure type regional metamorphism and the predominance of ductile deformation of the Okcheon Supergroup can be attributed to the mid-Paleozoic Okcheon Orogeny which would have been in line with the Wuyun Orogeny of South China. The South China and Sino-Korean cratons should have been drifted away from the Gondwana sometime during the mid-Paleozoic and collided to form the East Asian continent at ∼250 Ma.

Neoproterozoic rifting in the southern Georgina Basin, central Australia: Implications for reconstructing Australia in Rodinia

[1] A system of northwest striking Neoproterozoic rift basins underlies Paleozoic strata in the southern Georgina Basin of central Australia. Normal faults bounding these rift basins were selectively reactivated during the mid-Paleozoic Alice Springs Orogeny and are now expressed as high-angle reverse faults that invert the preexisting rift basins. Exhumed and eroded rift basin remnants are present in the hanging wall of the Oomoolmilla, Lucy Creek, Tarlton, and Toomba reverse faults, and rift basins may be preserved in the subsurface beneath the Toko Syncline and Burke River Structural Belt. Rift basin fill indicates two periods of extension: a major rift-forming episode between approximately 700 and 650 Ma (coeval with Sturtian glacial deposits) and a second episode of extension at approximately 600 Ma (coeval with Marinoan glacial deposits). This northwest striking rift system in central Australia supports results from other regions, indicating that the Neoproterozoic continental margin of Australia consisted of northwest striking rift segments offset by northeast striking transform faults. Such a configuration is geometrically incompatible with a Laurentian continental margin consisting of northeast striking rift segments and conflicts with reconstructions such as SWEAT and AUSWUS that match Australia with western Laurentia in the Rodinia supercontinent.

Concurrent growth of uplifts with dissimilar orientations in the southern Green River Basin, Wyoming: Implications for Paleocene-Eocene patterns of foreland shortening

The diverse orientations of Precambrian-involved and fault-bounded uplifts in the Rocky Mountain foreland region seem difficult to reconcile with the inferred Paleocene–Eocene shortening direction and plate convergence. Some have hypothesized that the shortening direction rotated as much as 90° over time, whereas others have hypothesized a relatively stable strain field involving concurrent oblique slip on faults with varied strikes. The stratigraphic thicknesses of the synorogenic Paleocene–Eocene Fort Union, Wasatch, and Green River Formations in the southern Green River Basin of Wyoming are used here to define the pattern of basin subsidence and to interpret the timing of movement on two contractional structures with contrasting orientations. Isopach maps and cross sections of three sequential time-stratigraphic intervals show thinning around the north–south-oriented Rock Springs uplift and regional southward thickening of these three stratigraphic intervals. The southward thickening evidently resulted from flexural subsidence in response to loading from the adjacent east–west-oriented Uinta uplift. Stratigraphic thinning in the vicinity of the Rock Springs uplift demonstrates that growth of the underlying blind thrust system produced an area of comparatively low accommodation space within the subsiding Green River Basin. The concurrent growth of the Rock Springs and Uinta uplifts does not support a rotation of shortening direction from east–west to north–south. The margin of a Neoproterozoic rift basin may have controlled the orientation of the thrust faults bounding the north flank of the Uinta uplift, and Late Cretaceous-through-Eocene contraction caused oblique slip on these faults during structural inversion. A north–south-striking blind reverse fault underlies the west flank of the Rock Springs uplift, but Phanerozoic strata cover the Precambrian core of the uplift, so the structure within the Archean basement rocks is unknown. Despite contrasting strikes and different structural histories, the Uinta and Rock Springs uplifts responded concurrently to northeast–southwest- to east-northeast–west-southwest-directed shortening.

Differential zircon fertility of source terranes and natural bias in the detrital zircon record: Implications for sedimentary provenance analysis

Granitic intrusions emplaced within Laurentia during the Grenville Orogeny (1.15–1.05 Ga) are exceptionally Zr-rich, primarily a function of high modal zircon, relative to Paleozoic granitoids emplaced within eastern Laurentia during phases of Appalachian orogenesis. Erosion of Grenville source rocks would generate disproportionately large volumes of detrital zircon compared to less zircon-fertile source regions. The latter sources are difficult to detect by standard in situ U–Pb dating methods of detrital zircon (SHRIMP or LA-ICP-MS U–Pb analysis of centers of > 100 μm grains), or could be overlooked during sampling. Grenvillian zircon fertility biased the Neoproterozoic to Recent sedimentary record as a result of two factors: (1) zircon durability and insolubility led to recycling during repeated orogenesis; (2) inertness of zircon below the onset of anatexis means dominantly metamorphosed sedimentary terranes failed to generate significant new zircon corresponding in age to the time of accretion of those terranes to Laurentia. Zircon growth under anatectic conditions generates new zircon, commonly as overgrowths on preexisting zircon, which may be too narrow to easily analyze by laser or ion beam techniques. Accretion of metasedimentary terranes therefore could be rendered all but undetectable via standard U–Pb detrital zircon dating. Grenville age modes dominate detrital zircon age distributions for Laurentian Neoproterozoic rift basins, Appalachian Paleozoic synorogenic clastic sequences, Appalachian metasedimentary terranes, and modern rivers draining these terranes. This is an artifact of the Grenville zircon signal that echoed throughout all Paleozoic orogenies on the eastern Laurentian margin. The natural Grenville bias in the detrital zircon record is further amplified by standard sampling biases (such that large (e.g. 100–300 μm) crystals are preferentially chosen) and analytical biases (e.g. cores are much more frequently analyzed).

The Lackawanna synclinorium, Pennsylvania: A salt-collapse structure, partially modified by thin-skinned folding

The Lackawanna synclinorium is a 110-km-long structural trough in the Appalachian foreland of northeastern Pennsylvania. In map view, its hinge displays a concave-to-the-foreland (i.e., concave toward the west) curve. Historically, the entire synclinorium was thought to be an Alleghanian thin-skinned contractional structure that formed similarly to the fold trains of the central Appalachian Valley and Ridge province. Interpretation of seismic reflection data across the structure, however, suggests that the synclinorium formed primarily by the removal of salt. The trend of the central and northern synclinorium reflects the location of Upper Silurian Salina salt. In the southern synclinorium, the salt-collapse structure translated northwestward over a thrust ramp joining detachments in the Cambrian Waynesboro Formation and the Salina Group. Interpretation of seismic reflection data also suggests that the basement-cover contact deepens westward and that basement-penetrating reverse faults and a Neoproterozoic rift basin are present beneath the synclinorium. We speculate that (1) partial barriers due to sedimentation and/or reef formation, and (2) localized subsidence over a Neoproterozoic rift zone may have formed a Late Silurian restricted basin that allowed thick accumulations of Salina salt. Regional-scale salt/shale flow and/or foreland-directed (i.e., westward) fluid migration during the Alleghanian orogeny might have removed as much as 700 m of salt. The removal of this salt caused the overlying strata to collapse downward and form the synclinorium. Only in the southern synclinorium was the collapse structure modified significantly by decollement tectonics. Thus, the map-view curvature of the structure reflects greater tectonic shortening and westward translation (toward the foreland) in the southern synclinorium compared to the northern synclinorium.

History of Neoproterozoic rift basins in South China: implications for Rodinia break-up

Abstract We present here a first-order analysis of the Neoproterozoic continental rift basins in South China, focusing on the north-south trending Kangdian basin in the western part, and the Yangtze-side of the northeasterly-trending Nanhua basin. The Yangtze-side of the Nanhua basin is subdivided into the Hunan-Guangxi, the Jiangnan Ridge, and the northern Zhejiang sub-basins. The Neoproterozoic successions in these basins consist of four major sequence-sets, representing four phases of rifting. The first phase occurred at ca. 820 Ma after the 830–820 Ma bimodal magmatism and rapid crustal unroofing, and is represented by the Shiqiaopu Formation in the Hunan-Guangxi sub-basin and the Luojiamen Formation in the northern Zhejiang sub-basin. The second phase at ca. 800 Ma is represented by the Hongchicun Formation in the northern Zhejiang sub-basin. The third, a major rift phase, occurred at ca. 780–750 Ma, represented by the Sanmenjie Formation in the Hunan-Guangxi sub-basin, the Luokedong and Jingtan formations in the Jiangnan Ridge sub-basin, and the Shangshu Formation in the northern Zhejiang sub-basin. The final phase recorded the rift–drift transition during the Nantuo glaciation, estimated at ca. 750–690 Ma, with no volcanism. This was followed by a sag phase to the remainder of the Neoproterozoic, which saw the entire Yangtze Block covered with either platform carbonate deposits or basinal carbonaceous and cherty deposits. The basin history in South China prior to ca. 600 Ma can be well correlated with that in the Adelaide rift system in southeastern Australia, suggesting that South China could have been adjacent to eastern Australia in the supercontinent Rodinia, but broke away from Australia by the end of the continental rifting at ca. 750–690 Ma.