Regional Stratigraphic Correlation Research Articles

Occurrence of Mafic Rocks within Ediacaran Strata in the Aksu Region, NW Tarim Craton, and its Geological Implications

AbstractThe Tarim Craton is an ancient Precambrian continental block, and detailed knowledge of its thermo‐tectonic history is crucial for understanding the early history of continental evolution. Abundant layered mafic rocks, which have commonly been regarded as basalts, occur within the Ediacaran Sugetbrak Formation (Fm.) in the Aksu region of the northwestern Tarim Craton. Clear intrusive features have now been discovered, including mafic rocks truncating Ediacaran sedimentary layers, exhibiting an intrusion‐baked margin where they interact with both the overlying and bottom wall rocks, and displaying a fine‐grained transition zone from their interior to their margins. The new findings demonstrate that these mafic rocks within the Aksu Ediacaran strata were not erupted basalts but instead are intrusive diabase dykes. Therefore, these mafic rocks cannot be used to constrain the timing of the Sugetbrak Fm. in the Aksu area, nor as marker layers for regional stratigraphic correlation. Furthermore, the Ediacaran thermo‐tectonic evolution in this region, deduced from the assumption that the mafic rocks are lavas, needs to be revised.

The Paleogene Forebulge Carbonate Banks, Zagros Foreland Basin, Northern Iraq: their Paleogeography, Basin Evolution, and Economic Implications

The Paleogene sequence of Zagros foreland basin NE Iraq during the Late Paleocene- Middle Eocene is punctuated by linear and disconnected chains of carbonate bank-ramp associations. These carbonate units had developed over the NW-SE trending Paleogene basin forebuldge. Discussion of origin, facies type, and stratigraphic architecture of these banks and associated facies was fully covered by the first part of this research project. In this part the chronostratigraphic synthases of the sequence, the paleogeography, and basin evolution is examined as an integral part of the investigation of the evolution of the Paleogene Zagros foreland basin. Research methods include regional stratigraphic correlation, and biostratigraphic data compilation to infer the chronostratigraphic sequence of the events. The paleogeographic facies mapping and basin history are reviewed accordingly. Research data are collected from 15 master surface sections. In addition to the re-examination and re-interpretation of 40 previously studied surface and subsurface well logs, which are compiled for basin-wide study and regional paleogeographic mapping. The analysis of the compiled biostratigraphic data shows that the inferred age of the associated stratigraphic units is as follows: Sinjar Formation. (E. Thanetian – L. Ypresian), Khurmala Formation (Ypresian - E. Lutetian), Kolosh Formation (Daian -Thanetian), and Aaliji Formation (Danian - Ypresian). Based on this chronostratigraphic synthesis, the basin forebulge history during the Paleogene period is divided into 5 stages: the Pre-bank, Early Bank Development, Bank-ramp Development, Back-bank Lagoon, and Lagoonal dolomitization stage. The paleogeography and paleofacies maps of each stage is discussed in terms of the basin forebulge evolution. An alternative hydrocarbon play of the forebulge-controlled Paleogene sequence is discussed, with a case study from the Sufaiyah oil field of northwest Iraq.

Newly discovered diamictite and cap carbonate couplet in the southern Alxa Block, northwestern China: Implications for stratigraphic correlation and Marinoan glaciation

Neoproterozoic glaciogenic diamictite and cap carbonate couplets have played a pivotal role in understanding glacial-interglacial cycles and establishing regional stratigraphic correlation. The Alxa Block in northwestern China preserves a sequence of Neoproterozoic diamictites along its southern margin, but the age and origin of the succession remain debatable due to the lack of discovery of cap carbonate. We report newly discovered cap carbonates that overlie the diamictites of the Shaohuotonggou Formation in the Longshoushan region in the southern Alxa Block. Based on detailed geological investigations, we identified massive diamictites, stratified diamictites, and cap carbonates in the lower part of the formation. The presence of ice-rafted dropstones, bullet-shaped and facetted clasts, glacial striations, and relatively low chemical index of alteration values of sedimentary matrix support a glaciogenic origin of the diamictites. The 2- to 2.6-m-thick cap carbonates are mainly composed of thinly laminated microcrystalline dolomites and show sheet cracks, cemented breccias, and tepee-like structures at the basal part of the unit. These features and their consistently negative δ13C values (−5.2‰ to −2.2‰) are characteristic of Marinoan-age cap carbonates (ca. 635 Ma). The quasi-continuous deposition of the massive diamictites, stratified diamictites, and cap carbonates suggests that the formation of this couplet was closely related to the Marinoan glaciation and subsequent deglaciation. We propose a three-stage depositional model for the glaciogenic succession and recommend that the diamictite and cap carbonate couplet in the Alxa Block provides a credible mark of the Cryogenian−Ediacaran boundary for further stratigraphic correlation and investigation.

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.

High‐Resolution Paleomagnetic Secular Variation Since ∼13 ka From a Loess Section in Northwest China and a Regional Geomagnetic Directional Model for East Asia

AbstractPaleomagnetic secular variation (PSV) records provide important information for the dynamic processes of the Earth's geomagnetic field, and also can be used for regional stratigraphic correlation. We conducted a paleomagnetic study on a high sedimentation rate Holocene loess section (the Minle section) with precise 14C age constraints in Northwest China. Rock magnetic results indicate that single domain and pseudo‐single‐domain magnetites are the main magnetic carriers of the natural remanent magnetization. Combining the alternating field demagnetization and thermal demagnetization results, we obtained a high‐resolution PSV record with both absolute declination and inclination since ∼13 ka. Combining with previously published sedimentary records in East Asia, we developed an East Asian PSV reference curve over the past 14 ka (EASed14k) by relocating all the data to a common location (30ºN, 108ºE) and averaging them through Fisher statistics. We further generated a regional geomagnetic directional model spanning the past 14 ka for East Asia (SCHA.EAS14k), using the in situ PSV records and applying the revised spherical cap harmonic analysis in space and cubic B‐spline in time. The predicted directional curves from this model at the common location are consistent with the EASed14k curves, which represent the first‐order variation of the geomagnetic field in this area. The established reference curve and regional model for East Asia in this study will be used for regional and global comparison of the geomagnetic field.

Depositional facies of Cambrian Series 2 – Miaolingian transition in the El Sahuaral Hill, central Sonora, Mexico: Paleoenvironments and regional stratigraphic correlation

Studies on lower Paleozoic sedimentary facies are scarce in northwestern Mexico, and the information is mainly restricted to Ordovician sequences in central Sonora. Series 2 – Miaolingian detrital-carbonate deposits of the El Sahuaral Hill located in central Sonora, northwestern Mexico, were analyzed for siliciclastic and carbonate microfacies, and biofacies based on the presence of trilobites. This research fills a gap in the knowledge of Cambrian strata in Mexico and is based on 25 thin sections, where the microfacies analysis resulted in recognition of one siliciclastic (M1), eight carbonate microfacies (M2-M9), and three biofacies (B1–B3). Based on the information obtained, the silicilastic microfacies (M1) for the Proveedora Formation indicates a shallow marine environment in intertidal to subtidal conditions related to the Skolithos ichnofacies. The carbonate microfacies M2, M3, M4, and M5 for the Buelna Formation denote a carbonate platform that varies between a lagoonal environment of open circulation and a restricted platform. Microfacies M6 and M7 for the Cerro Prieto Formation were deposited in carbonate sand shoals and banks within a moderate-energy environment in restricted platform, and open marine to platform-margin sand shoal within a high-energy environment. On the other hand, the faunal associations in the El Gavilán Formation allow to recognize three main biofacies: B1 is characterized by the presence of Euagnostus and abundant of agnostid trilobites; B2 is characterized by the presence of various genera of trilobites of the family Oryctocephalidae; and B3 represents trilobites of the genera Elrathina and Bathyuriscus. In accordance with the above, for the El Gavilán Formation, it is established that it was deposited on an external platform, transiting to a deeper environment towards the slope area. Microfacies M8 and M9 of the El Tren Formation indicate a transition from an open marine platform to a restricted circulation lagoonal environment, possibly at the outer margin of the carbonate platform, exposed to surface waters and mixed with meteoric water.The El Sahuaral Hill strata record environmental and eustatic changes, where abrupt facies change occurred from inner to outer platform during the Cambrian Series 2 – Miaolingian. The above correlate with other deposits in North America (Nevada, California, and British Columbia) which record relatively drastic eustatic changes at the platform edge. Furthermore, the lithological and faunal characteristics of the El Gavilán Formation in the El Sahuaral Hill suggest an affinity with the deposits of Sonora, Clayton Ridge in Nevada and the Burgess Shale Lentil, which is a member of the Stephen Formation in British Columbia, where the paleogeographic identity with the North American craton is confirmed within an outer platform environment.

Stratigraphic framework and sedimentary evolution during the Cryogenian-Ediacaran transition in northeastern Sichuan Basin, South China

The northeastern Sichuan area in the northern Yangtze margin has unique Ediacaran geological records, especially the Doushantuo Formation (DST), and become a hot research area in recent years. However, the Cryogenian-Ediacaran (C-E) boundary has not been precisely identified, which restricts the in-depth study of geological information during this crucial transitional period and is unfavorable for a systematic and complete understanding of the Yangtze Block and even the global paleogeographic pattern. This study conducted stratigraphy, sedimentology, and chronostratigraphy to establish the stratigraphic framework and sedimentary evolution of the C-E transition strata in northeastern Sichuan. The results showed that the Ediacaran sediments, without the cap dolomite, unconformably overlaid the Cryogenian sediments in the studied area. The Member II of the DST, characterized by 50–160 m of red-green sandstone (approximately equivalent to the original Chengkou “Guanyinya Formation”), directly overlaid the Cryogenian sediments and displayed a 623 ± 2.3 Ma maximum depositional age from the detrital zircon U–Pb dating. Regional stratigraphic correlations indicate that the C-E transition strata in northeastern Sichuan had a consistent lithological association and sedimentary sequence characteristics but differed from the Three Gorges. Typically, the upper Nantuo massive glacial diamictites transition to the icebergs rafted lonestone-bearing mudstones at the top, then change upward to DST barrier coast sandstones. The proposed DST of the northeastern Sichuan Basin was divided into three lithostratigraphic members without the regional Member I cap dolomite: (i) Member II purple-red, gray-green sandstone strata, (ii) Member III black mudstone strata, and (iii) Member IV P–Mn bearing strata. During the C-E transition, the study area experienced (i) the global deglaciation stage in the terminal Marinoan glaciation and (ii) the filling-leveling up stage with clastic rocks in the early Ediacaran. Overall, the early Ediacaran of northeastern Sichuan succeeded the paleogeographic features of the late Cryogenian.

Age dating of Paleocene Meirenfeng Formation and its significance for the hydrocarbon source rocks in the East China Sea basin

The Meirenfeng Formation, a critical Paleogene stratigraphic unit within the Yangtze Sag in the East China Sea Basin, has long suffered from uncertain age estimation due to limited paleontological evidence, which has consequently hindered regional stratigraphic correlation. This study employed zircon U–Pb age dating through the LA-ICP-MS method to two tuff samples extracted from the CJ-2 well. The obtained ages are approximately 61.0 ± 1 Ma and 62.25±1 Ma, respectively, which confirms the sedimentary age of the Meirenfeng Formation as Paleocene Danian-Selandian. This age directly correlates it to the Paleocene Yueguifeng Formation in the Lishui-Jiaojiang Sag, a confirmed source of hydrocarbons. In addition, geochemical investigations conducted on the shale samples from the Meirenfeng Formation indicate a medium to good abundance of organic matter and a kerogen type of III. The regional seismic profile further reveals that the Meirenfeng Formation in the Yangtze Sag extends continuously to the Zhedong Depression, boasting a maximum residual thickness of up to 2000m. This suggests a similar Paleocene period of extensive stretching and rifting in the Zhedong Depression. This research offers the first robust age estimation for the Meirenfeng Formation in the Yangtze Sag, providing an essential geological foundation for accurate tectonic history reconstruction, Paleocene stratigraphic subdivision, regional correlation, and hydrocarbon prospectivity assessment within the East China Sea Basin.

A machine-learning based approach to predict facies associations and improve local and regional stratigraphic correlations

The geological record has challenged stratigraphers through time. Many depositional, tectonic and paleobiological events require stratigraphic positioning to determine temporal relationships among such events. This task is complicated and challenging, especially in sedimentary succession with scarcity or lack of paleontological content bearing biostratigraphic value and radiometric ages. Therefore, subjective personal criteria adopted during correlations and field mapping activities make stratigraphic correlations more complex and confusing. New methodological approaches are necessary to test human expertise in recognizing stratigraphic units with environmental significance and to contribute to stratigraphic correlations based on quantitative data. We used cores obtained by coal drilling campaigns during the 1970s and 1980s on the southern border of the Paraná Basin, southern Brazil, to generate a quantitative database. Data obtained from gamma spectrometry in the cores of Carboniferous to Permian age measured total count (cps), potassium (K), uranium (U) and thorium (Th). We used machine learning (ML) to predict facies associations and to confront the quantitative database with the three facies associations mapped through time based on qualitative geological mapping criteria. The k-nearest neighbors (KNN) algorithm reached maximum accuracy values of 86.0%% and f1-score of 90.0%, 73.0% and 91.0% for facies associations 1, 2 and 3, respectively, using exponential moving average and normalized data. This KNN-based method using gamma spectrometric data opened new possibilities to perform local and regional stratigraphic correlations using quantified data. New tests must be performed to improve this promising correlation method in other regional settings and related basins.

New data on Silurian (Llandovery) sinacanthids from Wuhan, South China and their biostratigraphic and paleobiogeographic implications

Sinacanthids are a group of Silurian spine-based mysterious taxa, probably representing a lineage of stem chondrichthyans. New sinacanthid fossils attributed to Sinacanthus wuchangensis, S. triangulatus, Sinacanthus sp., Neosinacanthus planispinatus, Tarimacanthus bachuensis, Eosinacanthus shanmenensis, and fin spine morphology 1, 2 and 3 are identified from the upper member of the Qingshui Formation and the Fentou Formation (Telychian, Llandovery) of Wuhan, South China. These sinacanthid fin spines are similar to those from the Rongxi Formation in northwestern Hunan and the Ymogantau Formation in the northwestern Tarim. This study provides further evidence for the presence of diverse sinacanthid faunas from the South China plate. As the part of the Zhangjiajie Vertebrate Fauna of China, they have great significance in the paleogeographic division of vertebrates and the regional stratigraphic division and correlation. The Silurian sinacanthids from China were mainly grouped into three assemblages, i.e., the Wentang/Tataertag assemblage (early Telychian), the Fentou/Ymogantau assemblage (middle Telychian), and the Maoshan assemblage (middle to late Telychian). In addition, the sinacanthids from the South China plate, Tarim plate, and Qiongzhong block belong to the Zhangjiajie Vertebrate Fauna and there was certain extent of migration of sinacanthids among these areas during the Telychian, Silurian.

A new isochron for stratigraphic correlation in the Permian Delaware Basin and beyond

Altered volcanic ash, preserved as bentonite clay within sedimentary depositional units, can facilitate regional stratigraphic correlation. While many bentonite ash beds have been documented in core extracted over decades of hydrocarbon exploration in the Delaware Basin, a particular ∼1 cm-thick bentonite has been identified at a distinct stratigraphic position, at a sedimentary facies transition from thin-bedded calciclastic turbidites to thick-bedded siliciclastic turbidites, in the compositionally-mixed upper Wolfcamp formation. A comparison of geochemical analyses of the ash from two cores and petrophysical correlations across eight wells was conducted to test the regional correlation of the ash. Despite diagenetic alteration since seafloor deposition ∼280 Ma, nearly identical geochemical trends between incompatible elemental subsets, including light and heavy rare earth elements, large ion lithophiles, and high field strength elements, suggest that these two ash deposits originated from the same volcanic center. Detailed sedimentologic analyses and lithostratigraphic correlations across three cores spaced tens of km apart confirm that the ash bed is bound by correlative quiescent deepwater strata. Based on the chemical composition, probable timing of deposition, and proximity, we speculate that the Las Delicias Arc produced this ash, and it was transported by wind and deposited as a hemipelagite into the Delaware Basin deep marine environment. This discovery implies the existence of the ash marker in other cores within Late Paleozoic western equatorial Pangea, e.g. in compositionally-mixed deep marine deposits of the Midland Basin and outcropping deposits around the Greater Permian Basin and beyond, which would facilitate regional chronostratigraphic correlation for a critical time in Earth's history.

Middle-late Eocene to Early Miocene micropaleontology of the ANH–TIERRALTA–2–X–P well: Biostratigraphic implications for southwestern deposits of the Sinú-San Jacinto belt (Colombian Caribbean)

The Eocene and Oligocene deposits of the southwestern region of the Sinú-San Jacinto Belt (SSJB) in NW South America were formed in marine environments influenced by fluvial discharges from the northern Andes of Colombia. However, these deposits are not well-exposed on the surface, which has limited the study of micropaleontological assemblages that could improve our understanding of the chronostratigraphic and paleoenvironmental characteristics of these rocks. In this study, we analyzed two cores of one of the thickest Cenozoic stratigraphic sections in the Caribbean region, from the ANH-TIERRALTA-2-X-P stratigraphic well, using palynomorphs and calcareous nannofossils. Our analysis allowed us to determine the age of deposition and understand the biostratigraphic patterns of marine and terrestrial microfossils in these nearshore deposits. We found that the first cored interval, from 2122 m to 2026.9 m, corresponds to marine rocks accumulated between the middle and late Eocene. The second interval, from 1130 m to 731.6 m, showed patterns of terrestrial and marine microfossils, which indicate the middle-late Eocene to the Early Miocene age. Palynological and calcareous nannofossil biostratigraphy were consistent in the middle to upper Eocene and Lower Miocene deposits, but discrepancies were observed in the Oligocene deposits. We attributed this to reworking or broader biostratigraphic ranges of certain palynological markers used in the biozones. Determining the age of the middle to upper Eocene and upper Eocene to lower Oligocene deposits was challenging due to the limited number of well-calibrated biostratigraphic markers. As a result, accurate correlation with the late Eocene – early Oligocene stratigraphic record from other parts of the SSJB is hindered, demonstrating that regional stratigraphic correlations based on biostratigraphy alone are problematic.

Improvement of the description of ostracods of the family TRACHYLEBERIDINAE

Introduction. The definition of criteria for separating closely related species of representatives of the genus Cythereis is currently incomplete. Ostracods of this genus have wide intraspecific variability and high adaptability to changing living conditions. These factors make it difficult to use these ostracod species for regional stratigraphic correlation. In addition to the selection of criteria for species separation, there is a problem of the imperfection of the terminological apparatus for describing ostracods, which complicates the description of species and omits potentially important information for the separation of related species. Analysis of previous publications. Numerous works are devoted to the issue of the development of the terminological apparatus for describing ostracods, however, qualitative methods of description are inherent only to certain large taxa, where a separate method of description has been developed for each taxon. Ostracods of the genus Cythereis are widespread in the Cretaceous Tethys. Their wide variability is considered by various authors often without taking into account intraspecific variability and adaptation, which leads to the selection of subspecies or ignoring variability. Materials and methods. Numerous ostracods of the species Cythereis hirsuta Damotte&Grosdidier from the Late Cenomanian and Cythereis ornatissima (Reuss) from the Turonian of Ukraine were used in the work. Ostracods were selected from different deposits according to the conditions of origin. Results and discussion. The paper describes in detail the morphology of ostracods of the genus Cythereis with qualitative characteristics of morphological elements. The ontogenetic changes of the two species and the change in morphology depending on the conditions of existence are also described. The change in the morphology of juvenile forms depending on the conditions of existence is described separately. Conclusions. Based on the study and description of numerous paleontological materials, a number of refinements were proposed to the descriptive characteristics of the morphological elements of ostracod valves of members of the family TRACHYLEBERIDINAE Sylvester-Bradley, 1948 and the genus Cythereis in particular. The proposed clarifications regarding the morphology of the mesosculpture made it possible to describe in detail the ontogenetic changes of the studied species and their differences in adult stages depending on the facial conditions of existence. It should be noted that a detailed scheme for describing the morphology of mesosculpture is proposed for the first time in the literature. The paleontological description of numerous materials from the Middle Cretaceous of Ukraine allowed to establish the morphological elements that are of primary importance for the separation of related species within the genus. The analysis of these elements suggests that some of the similar species from the outcrops of Europe and Asia are actually other species. The question of their phylogenetic ties can be solved under the condition of studying ontogenesis and expanding the geography of research. Based on this, the validity of the names of the studied species from the territory of Ukraine is also contradictory to the actual comparison with the holotype collection.

Strike-slip influenced stratigraphic and structural development of the Foula Sandstone Group, Shetland: implications for offshore Devonian basin development on the northern UK continental shelf

The island of Foula, located 25 km SW of Shetland, preserves a gently folded, 1.6 km thick sequence of Middle Devonian sandstones spectacularly exposed in kilometre-long cliff sections >350 m high. These rocks unconformably overlie likely Precambrian-age amphibolite facies basement rocks that are intruded by sheeted granites. The onshore succession is similar in age to the nearby Lower Clair Group offshore to the west. New mapping, incorporating the use of drone imagery in the inaccessible cliff sections, uses down-plunge projections to show that growth folding and faulting on Foula were contemporaneous with sedimentation during basin filling. The large-scale structural geometry is consistent with the regional constrictional strain due to the sinistral transtension associated with movements along the Walls Boundary–Great Glen fault zone system during the Mid-Devonian. Detrital zircon provenance studies indicate that the Devonian sequences of Foula (and nearby Melby in western Shetland) show similarities with the Clair Group and Orkney successions. We suggest that NE–SW transtensional fold development contemporaneous with regional subsidence in the Devonian basins of Scotland may be more widespread than previously realized. Large, kilometre-scale folds previously interpreted to be related to Permo-Carboniferous inversion may therefore have initiated earlier in the basin evolution sequence than previously realized. Supplementary material: Appendices A, Methodologies; B, Regional stratigraphic correlation table; C, Heavy mineral data; D, Detrital zircon data; and E, 3D virtual outcrop models are available at https://doi.org/10.6084/m9.figshare.c.6442552

Depositional Sequences of the Itararé Group in the Region of Mafra (SC) and their Regional Correlation

The Itararé Group, Permocarboniferous of the Paraná Basin, has its deposition associated with the Late Paleozoic Ice Age (LPIA), which encompassed multiple glacial advance-retreat cycles. Recognizing the nature of the processes that form these rocks is essential to understand the diversity of glacial and non-glacial depositional systems that were active during the LPIA. Previous authors have carried out sedimentological and stratigraphic studies in outcrops of the Itararé Group in the Santa Catarina and Paraná states, however, the integration between these areas and the delimitation of glacial cycles is still little known. Seeking to increase the knowledge on the stratigraphy of the Itararé Group, this work aims to investigate its facies in five shallow boreholes in the Mafra region, northern Santa Catarina state. In this region, 300 meters of cores sampled almost the entire stratigraphic succession of the Itararé Group. We further integrate our results with published data from Alfredo Wagner, Vidal Ramos, Presidente Getúlio, Doutor Pedrinho and São João do Triunfo in order to build a regional stratigraphic framework. A total of 33 sedimentary facies were recognized and organized in five genetic associations, corresponding to subaqueous outwash fans, rain-out and mud settling, thin-bedded turbidites, mass- transport deposits, and thick-bedded turbidites. The regional stratigraphic correlation allowed the recognition of 5 glacial cycles, corresponding to depositional sequences of deglaciation. They show signs of glacial influence that diminish toward the top, where deltaic deposits developed as climatic conditions improved. Diamictites are present in all areas and distributed preferentially in the lower and middle sequences. They consist of mass- transport deposits with origin attributed to gravitational instability due to sediment accumulation in melting and glacial retreat phases.

Early Cretaceous palynofloras from the Bongor basin, Chad, and their palaeoenvironmental and palaeoclimatic significances

A systematic palynological investigation of borehole core and cutting materials enable the correlation of twenty-three wells in the Lower Cretaceous Bongor Basin, Chad. These borehole samples are dated as Early Cretaceous and three ascending palynological zones are recognized, the upper Hauterivian to lower Barremian Dicheiropollis Total Range Zone (I), the upper Barremian Sergipea–Zhonghuapollis Assemblage Zone (II), and the Aptian Afropollis–Pilosisporites–Ephedripites–Cicatricosisporites Assemblage Zone (III). A new species of gymnosperm pollen, Sergipea multipapillata sp. nov., is described from the palynoflora of the Bongor Basin. Regional stratigraphic correlation based on palynofloras of Lower Cretaceous is given between the Bongor Basin and its neighbouring area. In the Early Cretaceous the Bongor Area was an inland sedimentary basin, the changes in the palynoflora indicate changing patterns of vegetation, the palaeoclimate is reconstructed as mainly hot and arid, with seasonal precipitation and transient warm and humid breaks.

Sedimentology and New Paleogeographic Data of the Lower Eocene Chouabine Formation in the Gafsa Basin (Tunisia), Southern Tethyan Margin

Abstract Facies and paleo-environment reconstruction applied to the lower Eocene Chouabine deposits occurring in the Gafsa area in Tunisia provided important information on sediment cyclicity and paleogeographic conditions. From west to east, four sections were surveyed: Tamerza (25 m), Oued Thelja (48 m), Jebel Ong (25 m), and Jebel Chamsi (45 m). Furthermore, the facies stacking pattern allowed for the reconstruction of depositional environments in relation to sea level changes. The Chouabine Formation is formed by the succession of three sequences composed of marls, phosphorites, and carbonates. There are five main facies organized into two transgressive cycles. The gradual transition of facies from intertidal to circatidal environments unraveled the sedimentation on a homoclinal ramp, episodically swept by upwelling currents. The Chouabine Formation is made of deepening–upwards cycles. Each cycle ranges from 2 to 5 m in thickness. The proximal-distal transition of depositional environments was gradually increasing from intertidal to offshore environments. Lateral variation of thickness and facies is generated by the reactivation of inherited NW-SE extensive and/or transtensive faults, acting since the late Cretaceous during the intermediate closing phase of the Neotethys. Synsedimentary tectonics has created trap structures favouring confinement conditions in the center of the basin, permitting the accumulation and preservation of large thicknesses of phosphate deposits. Based on new litho- and biostratigraphic data, this study presents for the first time a clear and detailed regional stratigraphic correlation and paleogeographic maps.

Middle Jurassic intracontinental evolution of East Asia: Insights from the Tianshifu-Dongyingfang basin of the Liaodong Peninsula, NE China

AbstractThe Middle Jurassic intracontinental shortening event in East Asia, known as episode A of the Yanshanian Movement in the eastern North China Craton and the first phase of the Daebo Orogeny in the Korean Peninsula, respectively, has been thoroughly studied during the past two decades. However, the timing of its beginning, duration, and deformational processes are still highly controversial because few studies have probed the correlations between episode A of the Yanshanian Movement and the first phase of the Daebo Orogeny. The Tianshifu-Dongyingfang basin, located in the northern Liaodong Peninsula, is filled with complete Jurassic sequences that can be compared with those in the eastern North China Craton to the west of the Tan-Lu fault zone and the Korean Peninsula. Regional stratigraphic correlations suggest that the Tianshifu-Dongyingfang basin contains not only the syntectonic conglomerates, but also the lower and upper unconformities A1 and A2 of episode A of the Yanshanian Movement, which separated the syntectonic conglomerates from the underlying Early–Middle Jurassic coal measures and the overlying Late Jurassic red beds, respectively. Detailed field survey and structural analysis show that the development of syntectonic conglomerates and unconformities A1 and A2 were controlled by the imbricate thrust fault system in the basement, which resulted from the WNW–ESE compression inversed from the fault-slip data. The youngest detrital zircon U-Pb ages obtained near unconformities A1 and A2 show that the WNW–ESE compression of episode A of the Yanshanian Movement in the Liaodong Peninsula initiated at ca. 171 Ma and ended at least by 163 Ma. Our new structural and geochronological data, combined with data from the neighboring areas, suggest that episode A of the Yanshanian Movement and the first phase of the Daebo Orogeny belong to a single intracontinental shortening event, the compressional deformation of which was derived from the westward, lowangle subduction of the Paleo-Pacific plate and transmitted to the Korean and Liaodong Peninsulas at ca. 172–170 Ma and to the eastern North China Craton to the west of the Tan-Lu fault zone at 170–165 Ma.

Sedimentology and New Paleo-geographic Data of the Upper Cretaceous-Lower Paleocene Haria Formation in the Gafsa Basin (Tunisia) Southern Tethyan Margin

Abstract Facies associations and environmental evolution of the late Cretaceous–lower Paleocene shallow platform of the Haria Formation (upper Maastrichtian–Danian–Selandian) have been studied from the Gafsa basin, located in southern Tunisia. Four main lithostratigraphic units have been identified. Unit 0, deposited on a restricted platform, is organized into aggradational and shallowing-upward sequences. Unit 1 is composed of shallowingand deepening-upward sequences that are deposited in externally restricted platform environments. Unit 2 is a peritidal shallowing-upward sequences deposited in shallow restricted environments ranging from the intertidal to supratidal environments. Unit 3,is composed of shallowing-upward sequences corresponding to the “muddy” type in the lower part, deposited in the proximal part of the shallow restricted external platform, and the “grainy” type in the upper part, representing wave-dominated bioclastic shoals and channel deposits. The proximal-distal transition of depositional environments gradually ranges from lagoon to offshore environments. Lateral variation of thickness and facies is generated by the reactivation of NW-SE extensive and/or transtensive faults, acting since the late Cretaceous during the intermediate closing phase of the Neotethys. These tectonic features were also expressed by changes in facies. The Haria Formation’s mixed carbonate-marls successions are classified into seven major facies associations, with carbonates considered a new facies represented by channel deposits and lumachellic limestones. This study establishes for the first time a clear and detailed regional stratigraphic correlation and paleogeographic maps based on the new litho- and biostratigraphic data.

Integrated study of the Doushantuo Formation in northwestern Hunan Province: Implications for Ediacaran chemostratigraphy and biostratigraphy in South China

The Ediacaran Doushantuo Formation in South China documents profound biological and environmental changes after the Neoproterozoic global glaciations. However, since the geological records of these changes are scattered in various lithofacies, the establishment of the co-evolutionary pattern of life and environment largely relies on regional stratigraphic correlation. A negative δ13C excursion in the upper Doushantuo Formation in the shelf-margin facies has been correlated with different δ13C chemostratigraphic features in the Doushantuo Formation in the shelf-lagoon facies: either with EN3 (widely regarded as equivalent to the Shuram excursion in Oman) or with EN2, which occur respectively in the upper and middle Doushantuo Formation in the Yangtze Gorges area of South China. Here we report new litho-, chemo-, and biostratigraphic data of the Douoshantuo Formation at the Caojunba section in shelf-margin facies, where the lithostratigraphic sequence and carbon isotopic profile resemble those at other shelf-margin sections, e.g., the Yangjiaping and Zhongling sections. Diverse microfossils including nine genera and eighteen species of acanthomorphic acritarchs are found from the upper Doushantuo Formation at Caojunba, which represent to date the first report of the upper Doushantuo acritarch assemblage from the shelf-margin facies in South China. The newly recovered microfossil assemblage includes Hocosphaeridium anozos, H. scaberfacium, Tanarium conoideum, and clustered leiospheres, and these taxa support the stratigraphic correlation of upper Doushantuo Formation between shelf-margin and shelf-lagoon facies. This correlation indicates that the interval with negative δ13C values in the upper Doushantuo Formation of shelf-margin facies is likely equivalent to EN3. This correlation also suggests that the δ13C profiles of the EN3/Shuram excursion interval in different facies in South China have various expressions (e.g., stratigraphic range, magnitude), making its regional and continental correlations more challenging. On the other hand, the discovery of acritarch assemblage characteristic of the upper Doushantuo Formation in the Yangtze Gorges area from shelf-margin facies confirms their potential as an independent stratigraphic tool in the subdivision and correlation of Ediacaran strata.