This study highlights a new by-product source for cobalt by recycling Paleoproterozoic Mn deposits.We present a geochemical modeling approach utilizing Principal Component Analysis(PCA)for available geochemical data o...This study highlights a new by-product source for cobalt by recycling Paleoproterozoic Mn deposits.We present a geochemical modeling approach utilizing Principal Component Analysis(PCA)for available geochemical data of Paleoproterozoic manganese deposits found in Africa and Brazil,which exhibit anomalous cobalt contents(up to 1200 ppm)along with other metals such as copper,nickel,and vanadium.The PCA results for the correlation coefficient matrix of the Enrichment Factor(_(EF))values of major and trace elements from samples of eight Mn deposits found in Africa and Brazil(Kisenge-Kamata,Moanda,Nsuta in Africa,and Azul,Buritirama,Lagoa do Riacho,Morro da Mina,and Serra do Navio in Brazil)yielded a cumulative variance of 53.3%for PC1(34%)and PC2(19.3%).In PC1,the highest positive loadings correspond to the variables Mn_(EF),Ni_(EF),and Co_(EF),while the highest negative loadings correspond to the variables Si_(EF),Fe_(EF),K_(EF),Ti_(EF),Cr_(EF),and Zr_(EF).PC2 exhibits the highest positive loadings for the variables Ca_(_(EF)),Mg_(EF),and P_(EF),while the highest negative loadings are for Cu_(EF)and V_(EF).The biplot diagram representation showed that clusters of vectors Mn_(EF),Ni_(EF),Co_(EF),V_(EF),and Cu_(EF)influence samples of Mn-carbonate rock,Mn-carbonate-silicate rock,Mn-silicate rock,and Mn-carbonate-siliciclastic rock,all with high Co_(EF)values(up to 414).The cluster of vectors Ca_(_(EF)),Mg_(EF),and P_(EF)significantly influence carbonate rock and dolomite marble,which have low Co_(EF)values(close to 0).The cluster of vectors Si_(EF),Fe_(EF),K_(EF),Ti_(EF),Cr_(EF),and Zr_(EF)strongly influences siliciclastic rock,which exhibits low Co_(EF)values.On the other hand,the cluster of vectors Cu_(EF)and V_(EF)influences oxidized Mn ore,which exhibits Co_(EF)values of up to 108.The results reveal a dichotomy regarding the origin of cobalt and other metal enrichments in these deposits linked to the Mn redox cycle.This process involves the formation of Mn-oxyhydroxides with the adsorption of Co and other metals under oxic conditions,followed by the burial of these Mn oxides in an anoxic diagenetic environment,where microbial sulfate reduction leads to the nucleation of Mn-carbonates and the formation of metal-rich sulfides(Fe,Co,Ni,V).Additionally,detrital input and sulfide phases(e.g.,framboidal pyrite)for the formation of Mn-rich siliciclastic rocks associated with Mn-carbonate rocks are evidenced by proxies Si_(EF),Fe_(EF),K_(EF),Ti_(EF),Cr_(EF),and Zr_(EF).This new exploration approach,supported by geochemical modeling through PCA,enhances our understanding of the genesis of these Paleoproterozoic manganese deposits and highlights a new route for cobalt exploration.In the increasing global demand for cobalt,particularly in applications involving electric vehicle batteries and energy storage,exploring these deposits emerges as an alternative source to produce these critical metals.展开更多
We herein describe an associated partial postcranial skeleton of a theropod dinosaur discovered in the Lower Cretaceous Xinminpu Group of the Yujingzi Basin, in the Jiuquan area of Gausu Province, northwestern China. ...We herein describe an associated partial postcranial skeleton of a theropod dinosaur discovered in the Lower Cretaceous Xinminpu Group of the Yujingzi Basin, in the Jiuquan area of Gausu Province, northwestern China. Features of its humerus, such as strongly expanded proximal and distal ends, a well developed medial tuberosity, distal condyles expressed on the humeral cranial surface, and a hypertrophied entepicondyle, definitively establish the therizinosauroid affinities of the specimen. It differs from other therizinosauroids in having a shallow, poorly demarcated glenoid fossa with a prominent rounded and striated tumescence on the dorsomedial surface of its scapular portion, and a pubis with a strongly concave cranial margin. It represents a new taxon, Suzhousaurus megatherioides gen. et sp. nov. Cladistic analysis recovers Suzhousaurus as the sister taxon of Nothronychus mckinleyi from the mid-Cretaceous of western North America; together, they are basal members of the Therizinosauroidea, more derived than the Early Cretaceous Falcarius and Beipiaosaurus but less derived than Alxasaurus and the Therizinosauridae. Along with ＂Nanshiungosaurus＂ bohlini from possibly coeval beds in the Mazongshan area of northern-most Gansu, Suzhousaurus represents one of the largest-known Early Cretaceous therizinosauroids, demonstrating that this clade attained considerable body size early in its evolutionary history.展开更多
The X-ray fluorescence and ICP methods were used to analyze 60 outcrop samples of black shale, of which 15 were collected from Belait, 15 from the Setap Shale, 15 from Temburong, and 15 from the Trusmadi for- mations....The X-ray fluorescence and ICP methods were used to analyze 60 outcrop samples of black shale, of which 15 were collected from Belait, 15 from the Setap Shale, 15 from Temburong, and 15 from the Trusmadi for- mations. The average compositions of the shales from the study area are 64.62%, 63.95%, 62.32%, 63.84% SiO2, 1.84%, 2.14%, 2.04%, 1.99% MgO, 2.55%, 3.12%, 2.89%, 2.72% K2O, 0.32%, 0.30%, 0.32%, 0.53% CaO, 5.86%, 6.06%, 7.14%, 6.60% Fe2O3, 207×10-6, 180×10-6, 213×10-6, 200×10-6 Rb, and 56×10-6, 49×10-6, 50×10-6, 32×10-6 Sr for the Setap Shale, Temburong, Belait and Trusmadi samples, respectively. The high Rb/Sr ratios of 3.8, 3.7, 4.2, and 6.1 are attributed to the lowest contents of Sr due to reducing conditions prevailing. The high Rb/K ratio sug- gests either brackish marine or rapid deposition that prevented equilibrium between Rb and K in the shales and ma- rine waters.展开更多
Stability level of tunnels that exist in an underground mine has a great influence on the safety,production and economic performance of mines.Ensuring of stability for soft-rock tunnels is an important task for deep c...Stability level of tunnels that exist in an underground mine has a great influence on the safety,production and economic performance of mines.Ensuring of stability for soft-rock tunnels is an important task for deep coal mines located in high in situ stress conditions.Using the available information on stratigraphy,geological structures,in situ stress measurements and geo-mechanical properties of intact rock and discontinuity interfaces,a three-dimensional numerical model was built by using 3DEC software to simulate the stress conditions around a tunnel located under high in situ stress conditions in a coal rock mass in China.Analyses were conducted for several tunnel shapes and rock support patterns.Results obtained for the distribution of failure zones,and stress and displacement felds around the tunnel were compared to select the best tunnel shape and support pattern to achieve the optimum stability conditions.展开更多
Studies on outcrop-scale structures have been conducted at the Garba complex. This study aims to add the high-resolution of the South Sumatra region to reconstruct the structural geology and implications of tectonics ...Studies on outcrop-scale structures have been conducted at the Garba complex. This study aims to add the high-resolution of the South Sumatra region to reconstruct the structural geology and implications of tectonics for the region. The study area is commonly referred to as crystalline basement highs forming the southwestern boundary of the Paleogene South Sumatra basin. The structures commonly show the NW-SE, NNW-SSE, and ENE-WSW trends. The methodology used includes field mapping, analysis of Digital Elevation Model (DEM), petrography, and X-ray fluorescence (XRF). The major fractures include wrench slip, reverse, and normal faults, while the observable microstructures comprise pull-apart calcite veins, shear joints, boudins, parasitic folds, and the augens. The earlier structuring episode was probably related to crustal extension, perhaps associated with the Paleogene rifting that occurred along the western margin of Sundaland. In the Late Neogene, tectonic compression took place in the entire region, allowing inversion of the Pre-Tertiary sequence. As compression waned in the Pleistocene, extension commenced, and a number of the ENE-WSW tensional block faulting developed and intersected the older NNW-SSE alignments. It is important to note that the latest tectonic event in conjunction with deep erosional denudation had likely exhumed the terrain and eventually shaped the present-day fractured and rough landforms in the study area.展开更多
This study provides a comprehensive analysis of the recent volcanic seismic swarm in the southern Red Sea,specifically west of the Farasan Islands,southwest of Saudi Arabia.For a period of 7 days from July 29 to Augus...This study provides a comprehensive analysis of the recent volcanic seismic swarm in the southern Red Sea,specifically west of the Farasan Islands,southwest of Saudi Arabia.For a period of 7 days from July 29 to August 4,2025,the Saudi National Seismic Network(SNSN)recorded over 300 minor earthquakes,with local magnitudes(ML)ranging from 1.65 to 4.7 within latitude 16.6147 and longitude 41.2075(55 to 60 km west of the Farasan Islands).The swarm occurred in a vertical spreading at varying depths ranging from 4.5 to 30 km and included two earthquakes with local magnitudes of ML 4.33 and 4.7 at depths of 10 km and 13 km,respectively.The examination of the source mechanisms for the two largest earthquakes(ML=4.3,4.7)has revealed a normal mechanism that corresponds with the main direction of the Red Sea rift(northwest-southeast).Furthermore,the frequency contents of the majority of the swarm were measured at lower frequencies(below 1 Hz).According to the SNSN database,the recent swarm occurred in an area that had previously seen swarm activity and is located within a distance of 150 km from previous similar swarms that took place in 2007 and 2011 in the southern Red Sea.These similar swarms led to the formation of a new island on the northern edge of the Zubair Islands,which was called Al Jadid Island in 2011.The similarity between these swarms encompasses their number,depth range,vertical distribution,and eruption period to some extent.The results obtained indicated that the recent swarm is associated with volcanic activity,specifically a new magmatic intrusion that occurred beneath the middle of the southern Red Sea region.Thus,the possibility of the beginning of the formation of a new volcanic island in that location is raised.A hypothetical volcanic eruption scenario was developed,predicting heavy and light ash trajectories,potential threats to the Farasan Islands,southern Saudi Arabia,and other neighboring countries as a whole.展开更多
The paleogeographic reconstruction of fragmented and dispersed continents often poses a challenge due to the lack of information regarding the nature of that extend beneath passive margin basins.To define the width of...The paleogeographic reconstruction of fragmented and dispersed continents often poses a challenge due to the lack of information regarding the nature of that extend beneath passive margin basins.To define the width of the continental crust beneath passive margin basins and its implications for paleogeographic reconstruction of conjugate continental margins,this study investigates the architecture of the stretched continental crust of the southern South Atlantic conjugate margin.The investigated region encompasses South Africa,Namibia,southern Brazil,and Uruguay,which were formed during the Mesozoic rifting of SW Gondwana.Employing a multi-tool approach combining seismic interpretation,gravity,magnetometry,and U-Pb isotopic data,the research aims to quantify the extension of stretched continental crust and its implications for plate reconstructions.The study reveals that the restored stretched crust spans at least 150 km,emphasizing the significance of considering connections between both margins for realistic paleogeographic reconstructions.Furthermore,the distinct U-Pb zircon age distribution patterns between SW Africa and SE South America reinforce the lack of direct connections despite their Gondwanan origin.The missing link estimated in this study is around 150 km,comparable in size to major mountain ranges such as the Andean or Urals.This work sheds light on critical aspects of Earth’s dynamic crustal evolution and emphasizes the need for comprehensive reconstructions considering stretched and eroded crust in the South Atlantic conjugate margin.展开更多
The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come fr...The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come from the Cretaceous paleosols of the Marília Formation(Bauru Basin,SE Brazil),in which the T.barretti ichnofabric and rhizoliths represent the biotic record.Beetle larvae are considered to be the most likely T.barretti tracemakers in these paleosols.The intensity and recurrence of bioturbation suggest that the windows of opportunity for beetle population growth were very short and controlled by the progressive substrate desiccation after flood cessation.The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events that provided the resource inputs necessary for their living during rainy seasons.The results also show that in fluvial systems with high discharge variations,the boundaries between a“pre-desiccation suite”and a“desiccation suite”in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels.Therefore,the frequency of flooding events,the lowered water table,and the rapidity of substrate desiccation constrained colonization by other burrowers and may be considered as firstorder factors controlling the generation of a monotypic T.barretti ichnofabric.Thus,the monotypic Taenidium ichnofabric in the Scoyenia ichnofacies context is an ichnomarker of brief windows for colonization in highly seasonal environments.展开更多
基金the Department of Geology at the Federal University of Ceará(DEGEO-UFC)and Prof.Dr.Felipe Holanda dos Santos for their support and guidance during the research process.FHS would like to thank the Society of Economic Geologists(SEG)for the Student Research Grant.WAS is funded by CNPq,under grant number(407255/2022-2).
文摘This study highlights a new by-product source for cobalt by recycling Paleoproterozoic Mn deposits.We present a geochemical modeling approach utilizing Principal Component Analysis(PCA)for available geochemical data of Paleoproterozoic manganese deposits found in Africa and Brazil,which exhibit anomalous cobalt contents(up to 1200 ppm)along with other metals such as copper,nickel,and vanadium.The PCA results for the correlation coefficient matrix of the Enrichment Factor(_(EF))values of major and trace elements from samples of eight Mn deposits found in Africa and Brazil(Kisenge-Kamata,Moanda,Nsuta in Africa,and Azul,Buritirama,Lagoa do Riacho,Morro da Mina,and Serra do Navio in Brazil)yielded a cumulative variance of 53.3%for PC1(34%)and PC2(19.3%).In PC1,the highest positive loadings correspond to the variables Mn_(EF),Ni_(EF),and Co_(EF),while the highest negative loadings correspond to the variables Si_(EF),Fe_(EF),K_(EF),Ti_(EF),Cr_(EF),and Zr_(EF).PC2 exhibits the highest positive loadings for the variables Ca_(_(EF)),Mg_(EF),and P_(EF),while the highest negative loadings are for Cu_(EF)and V_(EF).The biplot diagram representation showed that clusters of vectors Mn_(EF),Ni_(EF),Co_(EF),V_(EF),and Cu_(EF)influence samples of Mn-carbonate rock,Mn-carbonate-silicate rock,Mn-silicate rock,and Mn-carbonate-siliciclastic rock,all with high Co_(EF)values(up to 414).The cluster of vectors Ca_(_(EF)),Mg_(EF),and P_(EF)significantly influence carbonate rock and dolomite marble,which have low Co_(EF)values(close to 0).The cluster of vectors Si_(EF),Fe_(EF),K_(EF),Ti_(EF),Cr_(EF),and Zr_(EF)strongly influences siliciclastic rock,which exhibits low Co_(EF)values.On the other hand,the cluster of vectors Cu_(EF)and V_(EF)influences oxidized Mn ore,which exhibits Co_(EF)values of up to 108.The results reveal a dichotomy regarding the origin of cobalt and other metal enrichments in these deposits linked to the Mn redox cycle.This process involves the formation of Mn-oxyhydroxides with the adsorption of Co and other metals under oxic conditions,followed by the burial of these Mn oxides in an anoxic diagenetic environment,where microbial sulfate reduction leads to the nucleation of Mn-carbonates and the formation of metal-rich sulfides(Fe,Co,Ni,V).Additionally,detrital input and sulfide phases(e.g.,framboidal pyrite)for the formation of Mn-rich siliciclastic rocks associated with Mn-carbonate rocks are evidenced by proxies Si_(EF),Fe_(EF),K_(EF),Ti_(EF),Cr_(EF),and Zr_(EF).This new exploration approach,supported by geochemical modeling through PCA,enhances our understanding of the genesis of these Paleoproterozoic manganese deposits and highlights a new route for cobalt exploration.In the increasing global demand for cobalt,particularly in applications involving electric vehicle batteries and energy storage,exploring these deposits emerges as an alternative source to produce these critical metals.
基金We are grateful to Ji Qiang, Tang Zhilu, and Peter Dodson for their generous help. We also thank Zhang Yuqing for the preparation of FRDC-GSJB-99 Equal thanks go to every member of the field team. Early drafts of this paper benefited from discussions with Lindsay Zanno and Bucky Gates. Funding was provided by the Ministry of Science and Technology of China （973 Project： 2006CB701405） to Ji Qiang, the National Natural Science Foundation of China （40672007） the Hundred Talents Project of Ministry of Land and Resources of China to You Hailu, and Bureau of Geology and Mineral Resources of Gansu Province to Li Daqing.
文摘We herein describe an associated partial postcranial skeleton of a theropod dinosaur discovered in the Lower Cretaceous Xinminpu Group of the Yujingzi Basin, in the Jiuquan area of Gausu Province, northwestern China. Features of its humerus, such as strongly expanded proximal and distal ends, a well developed medial tuberosity, distal condyles expressed on the humeral cranial surface, and a hypertrophied entepicondyle, definitively establish the therizinosauroid affinities of the specimen. It differs from other therizinosauroids in having a shallow, poorly demarcated glenoid fossa with a prominent rounded and striated tumescence on the dorsomedial surface of its scapular portion, and a pubis with a strongly concave cranial margin. It represents a new taxon, Suzhousaurus megatherioides gen. et sp. nov. Cladistic analysis recovers Suzhousaurus as the sister taxon of Nothronychus mckinleyi from the mid-Cretaceous of western North America; together, they are basal members of the Therizinosauroidea, more derived than the Early Cretaceous Falcarius and Beipiaosaurus but less derived than Alxasaurus and the Therizinosauridae. Along with ＂Nanshiungosaurus＂ bohlini from possibly coeval beds in the Mazongshan area of northern-most Gansu, Suzhousaurus represents one of the largest-known Early Cretaceous therizinosauroids, demonstrating that this clade attained considerable body size early in its evolutionary history.
文摘The X-ray fluorescence and ICP methods were used to analyze 60 outcrop samples of black shale, of which 15 were collected from Belait, 15 from the Setap Shale, 15 from Temburong, and 15 from the Trusmadi for- mations. The average compositions of the shales from the study area are 64.62%, 63.95%, 62.32%, 63.84% SiO2, 1.84%, 2.14%, 2.04%, 1.99% MgO, 2.55%, 3.12%, 2.89%, 2.72% K2O, 0.32%, 0.30%, 0.32%, 0.53% CaO, 5.86%, 6.06%, 7.14%, 6.60% Fe2O3, 207×10-6, 180×10-6, 213×10-6, 200×10-6 Rb, and 56×10-6, 49×10-6, 50×10-6, 32×10-6 Sr for the Setap Shale, Temburong, Belait and Trusmadi samples, respectively. The high Rb/Sr ratios of 3.8, 3.7, 4.2, and 6.1 are attributed to the lowest contents of Sr due to reducing conditions prevailing. The high Rb/K ratio sug- gests either brackish marine or rapid deposition that prevented equilibrium between Rb and K in the shales and ma- rine waters.
文摘Stability level of tunnels that exist in an underground mine has a great influence on the safety,production and economic performance of mines.Ensuring of stability for soft-rock tunnels is an important task for deep coal mines located in high in situ stress conditions.Using the available information on stratigraphy,geological structures,in situ stress measurements and geo-mechanical properties of intact rock and discontinuity interfaces,a three-dimensional numerical model was built by using 3DEC software to simulate the stress conditions around a tunnel located under high in situ stress conditions in a coal rock mass in China.Analyses were conducted for several tunnel shapes and rock support patterns.Results obtained for the distribution of failure zones,and stress and displacement felds around the tunnel were compared to select the best tunnel shape and support pattern to achieve the optimum stability conditions.
文摘Studies on outcrop-scale structures have been conducted at the Garba complex. This study aims to add the high-resolution of the South Sumatra region to reconstruct the structural geology and implications of tectonics for the region. The study area is commonly referred to as crystalline basement highs forming the southwestern boundary of the Paleogene South Sumatra basin. The structures commonly show the NW-SE, NNW-SSE, and ENE-WSW trends. The methodology used includes field mapping, analysis of Digital Elevation Model (DEM), petrography, and X-ray fluorescence (XRF). The major fractures include wrench slip, reverse, and normal faults, while the observable microstructures comprise pull-apart calcite veins, shear joints, boudins, parasitic folds, and the augens. The earlier structuring episode was probably related to crustal extension, perhaps associated with the Paleogene rifting that occurred along the western margin of Sundaland. In the Late Neogene, tectonic compression took place in the entire region, allowing inversion of the Pre-Tertiary sequence. As compression waned in the Pleistocene, extension commenced, and a number of the ENE-WSW tensional block faulting developed and intersected the older NNW-SSE alignments. It is important to note that the latest tectonic event in conjunction with deep erosional denudation had likely exhumed the terrain and eventually shaped the present-day fractured and rough landforms in the study area.
文摘This study provides a comprehensive analysis of the recent volcanic seismic swarm in the southern Red Sea,specifically west of the Farasan Islands,southwest of Saudi Arabia.For a period of 7 days from July 29 to August 4,2025,the Saudi National Seismic Network(SNSN)recorded over 300 minor earthquakes,with local magnitudes(ML)ranging from 1.65 to 4.7 within latitude 16.6147 and longitude 41.2075(55 to 60 km west of the Farasan Islands).The swarm occurred in a vertical spreading at varying depths ranging from 4.5 to 30 km and included two earthquakes with local magnitudes of ML 4.33 and 4.7 at depths of 10 km and 13 km,respectively.The examination of the source mechanisms for the two largest earthquakes(ML=4.3,4.7)has revealed a normal mechanism that corresponds with the main direction of the Red Sea rift(northwest-southeast).Furthermore,the frequency contents of the majority of the swarm were measured at lower frequencies(below 1 Hz).According to the SNSN database,the recent swarm occurred in an area that had previously seen swarm activity and is located within a distance of 150 km from previous similar swarms that took place in 2007 and 2011 in the southern Red Sea.These similar swarms led to the formation of a new island on the northern edge of the Zubair Islands,which was called Al Jadid Island in 2011.The similarity between these swarms encompasses their number,depth range,vertical distribution,and eruption period to some extent.The results obtained indicated that the recent swarm is associated with volcanic activity,specifically a new magmatic intrusion that occurred beneath the middle of the southern Red Sea region.Thus,the possibility of the beginning of the formation of a new volcanic island in that location is raised.A hypothetical volcanic eruption scenario was developed,predicting heavy and light ash trajectories,potential threats to the Farasan Islands,southern Saudi Arabia,and other neighboring countries as a whole.
基金supported by the UNISINOS-PETROBRAS and UNISINOS-CNODC Cooperation Agreements.
文摘The paleogeographic reconstruction of fragmented and dispersed continents often poses a challenge due to the lack of information regarding the nature of that extend beneath passive margin basins.To define the width of the continental crust beneath passive margin basins and its implications for paleogeographic reconstruction of conjugate continental margins,this study investigates the architecture of the stretched continental crust of the southern South Atlantic conjugate margin.The investigated region encompasses South Africa,Namibia,southern Brazil,and Uruguay,which were formed during the Mesozoic rifting of SW Gondwana.Employing a multi-tool approach combining seismic interpretation,gravity,magnetometry,and U-Pb isotopic data,the research aims to quantify the extension of stretched continental crust and its implications for plate reconstructions.The study reveals that the restored stretched crust spans at least 150 km,emphasizing the significance of considering connections between both margins for realistic paleogeographic reconstructions.Furthermore,the distinct U-Pb zircon age distribution patterns between SW Africa and SE South America reinforce the lack of direct connections despite their Gondwanan origin.The missing link estimated in this study is around 150 km,comparable in size to major mountain ranges such as the Andean or Urals.This work sheds light on critical aspects of Earth’s dynamic crustal evolution and emphasizes the need for comprehensive reconstructions considering stretched and eroded crust in the South Atlantic conjugate margin.
基金the Sao Paulo Research Foundation(FAPESP)for supporting and funding this work(grant 2015/17632-5)The Brazilian National Council for Scientific and Technological Development(CNPq)is also thanked for the Ph.D.grant provided to DLN(140807/2017-9)+3 种基金the post-doctoral fellowship grant to DS(159548/2018-7)the research grants to AB(310734/2020-7)RGN(310377/2019-6)FSBL(307951/2018-9,303977/2021-3).
文摘The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come from the Cretaceous paleosols of the Marília Formation(Bauru Basin,SE Brazil),in which the T.barretti ichnofabric and rhizoliths represent the biotic record.Beetle larvae are considered to be the most likely T.barretti tracemakers in these paleosols.The intensity and recurrence of bioturbation suggest that the windows of opportunity for beetle population growth were very short and controlled by the progressive substrate desiccation after flood cessation.The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events that provided the resource inputs necessary for their living during rainy seasons.The results also show that in fluvial systems with high discharge variations,the boundaries between a“pre-desiccation suite”and a“desiccation suite”in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels.Therefore,the frequency of flooding events,the lowered water table,and the rapidity of substrate desiccation constrained colonization by other burrowers and may be considered as firstorder factors controlling the generation of a monotypic T.barretti ichnofabric.Thus,the monotypic Taenidium ichnofabric in the Scoyenia ichnofacies context is an ichnomarker of brief windows for colonization in highly seasonal environments.
