Pub Date : 2019-07-30DOI: 10.1344/GEOLOGICAACTA2019.17.8
H. Barcelona, G. Peri, D. Winocur, A. Favetto
The present research explores the Bañitos-Gollete geothermal field located in the Frontal Andes Cordillera over the Pampean flat-slab. We carried out an audiomagnetotelluric survey in order to define the underground geoelectrical structure and to understand the link between the geothermal fluid flow path and the main geological structures. 2-D audiomagnetotelluric models suggest that the deep-rooted N-S fault system controls the geothermal flow path. We propose a conductive heat-driven system, taking into consideration the geologic setting and the supposed low geothermal gradient of this tectonic environment. The mature Na-Cl waters from Gollete and an estimated reservoir temperature of ~140ºC are consistent with this conceptual model. Further investigations are required to assess the geothermal potential of the study area, and the present work likely represents only the first but necessary step in the exploration process.
{"title":"Audiomagnetotelluric survey at the Bañitos-Gollete geothermal area, main Andes Cordillera of San Juan, Argentina.","authors":"H. Barcelona, G. Peri, D. Winocur, A. Favetto","doi":"10.1344/GEOLOGICAACTA2019.17.8","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2019.17.8","url":null,"abstract":"The present research explores the Bañitos-Gollete geothermal field located in the Frontal Andes Cordillera over the Pampean flat-slab. We carried out an audiomagnetotelluric survey in order to define the underground geoelectrical structure and to understand the link between the geothermal fluid flow path and the main geological structures. 2-D audiomagnetotelluric models suggest that the deep-rooted N-S fault system controls the geothermal flow path. We propose a conductive heat-driven system, taking into consideration the geologic setting and the supposed low geothermal gradient of this tectonic environment. The mature Na-Cl waters from Gollete and an estimated reservoir temperature of ~140ºC are consistent with this conceptual model. Further investigations are required to assess the geothermal potential of the study area, and the present work likely represents only the first but necessary step in the exploration process.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43482922","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-23DOI: 10.1344/geologicaacta2019.17.7
P. Fialho, A. Balbino, M. Antunes
The Langhian Vc unit of Brielas section (Caparica road, Almada), in the marine Miocene of the Lower Tagus Basin (West Portugal), is rich in batoid species. In this study, batoids are represented by 149 isolated fossil teeth and a single fossil dental plate collected from a bulk sample of washed and sorted sediment. A total of 12 species belonging to the orders Rhinopristiformes, Rajiformes, Torpediniformes and Myliobatiformes were identified. All genera and some species are known to have extant representatives. Aetobatus cappettai Antunes and Balbino, 2006, is described now from Langhian material which suggests it is older than previously supposed. The biogeographic ranges, environmental constraints and behaviour of the species described in this study point out to an infralittoral environment characterized by the dominance of warm water conditions, where episodic upwelling contributed to the occurrence of different types of batoids coexisting in the same habitat.
{"title":"Langhian rays (Chondrichthyes, Batomorphii) from Brielas, Lower Tagus Basin, Portugal.","authors":"P. Fialho, A. Balbino, M. Antunes","doi":"10.1344/geologicaacta2019.17.7","DOIUrl":"https://doi.org/10.1344/geologicaacta2019.17.7","url":null,"abstract":"The Langhian Vc unit of Brielas section (Caparica road, Almada), in the marine Miocene of the Lower Tagus Basin (West Portugal), is rich in batoid species. In this study, batoids are represented by 149 isolated fossil teeth and a single fossil dental plate collected from a bulk sample of washed and sorted sediment. A total of 12 species belonging to the orders Rhinopristiformes, Rajiformes, Torpediniformes and Myliobatiformes were identified. All genera and some species are known to have extant representatives. Aetobatus cappettai Antunes and Balbino, 2006, is described now from Langhian material which suggests it is older than previously supposed. The biogeographic ranges, environmental constraints and behaviour of the species described in this study point out to an infralittoral environment characterized by the dominance of warm water conditions, where episodic upwelling contributed to the occurrence of different types of batoids coexisting in the same habitat.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":"1 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42184610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-18DOI: 10.1344/GEOLOGICAACTA2019.17.6
A. Khalifa, Z. Çakır, L. Owen, S. Kaya
The left-lateral strike-slip Adiyaman fault is located in eastern Turkey within the plate boundary deformation zone between Arabia and Anatolia. The Adiyaman fault is a major splay from the East Anatolian Fault (EAF), one of the most important tectonic structures in the Eastern Mediterranean region. These faults are consequence of the collision between the Arabian and Anatolian plates and the resulting westward tectonic escape of Anatolia. Although the EAF has been intensively studied since its discovery in the late 1960s, little is known about the Adiyaman fault and its tectonic activity. In this study, we extract geomorphic indices including mountain-front sinuosity (Smf), valley floor width-to-height ratio (Vf), stream length-gradient (SL), catchment Asymmetry Factor (AF) and hypsometric integrals and curves (HI and HC) to evaluate the relative tectonic activity of the Adiyaman fault. These three geomorphic indices (AF, HI, and HC) are averaged to define an index for Relative Tectonic Activity (RTA) that allows the Adiyaman fault to be divided into categories of low, moderate and high RTA. The results confirm that the Adiyaman fault is an active fault with high to moderate Quaternary tectonic activity. However, this fault is of minor importance on accommodating plate boundary deformation, as evidenced by the recent crustal motions determined by GPS studies. Nevertheless, it is worthwhile to note that the Adiyaman fault still poses a significant seismic hazard for the region despite its relatively moderate tectonic activity.
{"title":"Evaluation of the Relative Tectonic Activity of the Adıyaman fault within the Arabian-Anatolian.","authors":"A. Khalifa, Z. Çakır, L. Owen, S. Kaya","doi":"10.1344/GEOLOGICAACTA2019.17.6","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2019.17.6","url":null,"abstract":"The left-lateral strike-slip Adiyaman fault is located in eastern Turkey within the plate boundary deformation zone between Arabia and Anatolia. The Adiyaman fault is a major splay from the East Anatolian Fault (EAF), one of the most important tectonic structures in the Eastern Mediterranean region. These faults are consequence of the collision between the Arabian and Anatolian plates and the resulting westward tectonic escape of Anatolia. Although the EAF has been intensively studied since its discovery in the late 1960s, little is known about the Adiyaman fault and its tectonic activity. In this study, we extract geomorphic indices including mountain-front sinuosity (Smf), valley floor width-to-height ratio (Vf), stream length-gradient (SL), catchment Asymmetry Factor (AF) and hypsometric integrals and curves (HI and HC) to evaluate the relative tectonic activity of the Adiyaman fault. These three geomorphic indices (AF, HI, and HC) are averaged to define an index for Relative Tectonic Activity (RTA) that allows the Adiyaman fault to be divided into categories of low, moderate and high RTA. The results confirm that the Adiyaman fault is an active fault with high to moderate Quaternary tectonic activity. However, this fault is of minor importance on accommodating plate boundary deformation, as evidenced by the recent crustal motions determined by GPS studies. Nevertheless, it is worthwhile to note that the Adiyaman fault still poses a significant seismic hazard for the region despite its relatively moderate tectonic activity.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48074453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-05DOI: 10.1344/GEOLOGICAACTA2019.17.5
R. Galdos, Angels Canals i Sabaté, E. López, Joaquín Moreno
The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguia diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent.
{"title":"Tourmaline records hydrothermal events related to Zn-Pb mineralization around the Murguía diapi.","authors":"R. Galdos, Angels Canals i Sabaté, E. López, Joaquín Moreno","doi":"10.1344/GEOLOGICAACTA2019.17.5","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2019.17.5","url":null,"abstract":"The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguia diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46211934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-05-27DOI: 10.1344/GEOLOGICAACTA2019.17.4
Pedro J. M. Costa, D. Silva, L. Figueirinhas, J. Lario
Quartz grains collected from Arauco and Mataquito (central Chile) after the 2010 Maule tsunami presented an overwhelming dominance of dissolution textures. The analysis of superficial imprints proved that some grains were mechanically impacted before deposition. However, the percentage of grains with fresh surfaces and percussion marks was significantly lower than average values from other tsunami deposits elsewhere in the world. In this work, we discuss the reasons for such results in the context of the geomorphological setting of the areas analyzed and its influence on the microtextural signatures observed. The data presented in this study evidences a geographic dependence in the type of microtextures in the areas analyzed. For example, in Arauco the abundance of dissolution textures decreases rapidly towards the center of the embayment and increases towards the rocky headlands of its westernmost sector. By contrast, an increase of mechanical marks (e.g. fresh surfaces) is observed in the central region of the Arauco’s embayment. Similarly, in Mataquito, dissolution features are more abundant in the headlands or small capes, while there is a higher presence of mechanical marks in sandy embayments. The results of this study demonstrate the importance of the geomorphological context as a controlling factor in the intensity of mechanical imprints on the surface of quartz grains transported by tsunamis and deposited in the inner shelf and coastal areas. Therefore, our results suggest that without a detailed geomorphological contextualization microtextural discrimination can lead to misleading interpretations. Hence, there is a need for more microtextural analysis on tsunami deposits in order to assess the variability in the geographic distribution and intensity of microtextures imprinted on the surface of quartz grains deposited during a tsunami event.
{"title":"The importance of coastal geomorphological setting as a controlling factor on microtextural...","authors":"Pedro J. M. Costa, D. Silva, L. Figueirinhas, J. Lario","doi":"10.1344/GEOLOGICAACTA2019.17.4","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2019.17.4","url":null,"abstract":"Quartz grains collected from Arauco and Mataquito (central Chile) after the 2010 Maule tsunami presented an overwhelming dominance of dissolution textures. The analysis of superficial imprints proved that some grains were mechanically impacted before deposition. However, the percentage of grains with fresh surfaces and percussion marks was significantly lower than average values from other tsunami deposits elsewhere in the world. In this work, we discuss the reasons for such results in the context of the geomorphological setting of the areas analyzed and its influence on the microtextural signatures observed. The data presented in this study evidences a geographic dependence in the type of microtextures in the areas analyzed. For example, in Arauco the abundance of dissolution textures decreases rapidly towards the center of the embayment and increases towards the rocky headlands of its westernmost sector. By contrast, an increase of mechanical marks (e.g. fresh surfaces) is observed in the central region of the Arauco’s embayment. Similarly, in Mataquito, dissolution features are more abundant in the headlands or small capes, while there is a higher presence of mechanical marks in sandy embayments. The results of this study demonstrate the importance of the geomorphological context as a controlling factor in the intensity of mechanical imprints on the surface of quartz grains transported by tsunamis and deposited in the inner shelf and coastal areas. Therefore, our results suggest that without a detailed geomorphological contextualization microtextural discrimination can lead to misleading interpretations. Hence, there is a need for more microtextural analysis on tsunami deposits in order to assess the variability in the geographic distribution and intensity of microtextures imprinted on the surface of quartz grains deposited during a tsunami event.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42369328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-31DOI: 10.1344/GEOLOGICAACTA2019.17.1
S. Timón-Sánchez, F. López-Moro, R. Romer, D. Rhede, A. Fernández-Fernández, C. Moro-Benito
The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO 2 ) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE 2 O 3 ). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE 2 O 3 contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes.
{"title":"Late-Variscan multistage hydrothermal processes unveiled by chemical ages coupled with compositiona.","authors":"S. Timón-Sánchez, F. López-Moro, R. Romer, D. Rhede, A. Fernández-Fernández, C. Moro-Benito","doi":"10.1344/GEOLOGICAACTA2019.17.1","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2019.17.1","url":null,"abstract":"The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO 2 ) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE 2 O 3 ). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE 2 O 3 contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48748359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-21DOI: 10.1344/GEOLOGICAACTA2019.17.2
S. Khan, M. Shah
Excellent dolomite exposures are observed in the eastern Salt Range (Pakistan), where the Cambrian Jutana Formation consists of two distinct units (i.e. oolitic – pisolitic unit and massive dolomite unit). Field observations revealed that the lower, oolitic-pisolitic unit mostly comprises medium to thick bedded, interlayered brown yellowish dolostone containing ooids/pisoids and faunal assemblages, and grey whitish sandstone with distinct depositional sedimentary features (i.e. trough-, herringbone- and hhummocky crossbedding). The upper massive dolostone unit consists of thick bedded to massive dolostone. These two units are separated by shale. Petrographic studies identified three dolomite types, which include: fine crystalline dolomite (Dol. I), medium-coarse crystalline dolomite (Dol. II) and fracture associated, coarse crystalline dolomite (Dol. III). Stable isotope studies indicate less depleted δ 18 O values for Dol. I (-6.44 to -3.76‰V-PDB), slightly depleted δ18O values for Dol. II (-7.73 to -5.24‰V-PDB) and more depleted δ 18 O values for Dol. III (-7.29 to -7.20‰V-PDB). The δ 13 C values of the three dolomite phases are well within the range of Cambrian sea-water signatures. Furthermore, δ 26 Mg-δ 25 Mg signatures (Dol. I; δ 26 Mg=-1.19 to -1.67, δ 25 Mg=-0.61 to -0.86 and Dol. II; δ 26 Mg=-1.34 to -1.59, δ 25 Mg=-0.70 to -0.83) indicate three phases of dolomitization in different diagenetic settings. First, an initial stage of dolomitization during the early Cambrian resulted from altered marine, Mg-rich fluids associated with the mixing zone mechanism. Second, a late stage of dolomitization was associated with burial during late Permian. A third dolomitization phase was related to post-Eocene times.
{"title":"Multiphase dolomitization in the Jutana Formation (Cambrian), Salt Range (Pakistan): evidences from field observations, microscopic studies and isotopic analysis","authors":"S. Khan, M. Shah","doi":"10.1344/GEOLOGICAACTA2019.17.2","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2019.17.2","url":null,"abstract":"Excellent dolomite exposures are observed in the eastern Salt Range (Pakistan), where the Cambrian Jutana Formation consists of two distinct units (i.e. oolitic – pisolitic unit and massive dolomite unit). Field observations revealed that the lower, oolitic-pisolitic unit mostly comprises medium to thick bedded, interlayered brown yellowish dolostone containing ooids/pisoids and faunal assemblages, and grey whitish sandstone with distinct depositional sedimentary features (i.e. trough-, herringbone- and hhummocky crossbedding). The upper massive dolostone unit consists of thick bedded to massive dolostone. These two units are separated by shale. Petrographic studies identified three dolomite types, which include: fine crystalline dolomite (Dol. I), medium-coarse crystalline dolomite (Dol. II) and fracture associated, coarse crystalline dolomite (Dol. III). Stable isotope studies indicate less depleted δ 18 O values for Dol. I (-6.44 to -3.76‰V-PDB), slightly depleted δ18O values for Dol. II (-7.73 to -5.24‰V-PDB) and more depleted δ 18 O values for Dol. III (-7.29 to -7.20‰V-PDB). The δ 13 C values of the three dolomite phases are well within the range of Cambrian sea-water signatures. Furthermore, δ 26 Mg-δ 25 Mg signatures (Dol. I; δ 26 Mg=-1.19 to -1.67, δ 25 Mg=-0.61 to -0.86 and Dol. II; δ 26 Mg=-1.34 to -1.59, δ 25 Mg=-0.70 to -0.83) indicate three phases of dolomitization in different diagenetic settings. First, an initial stage of dolomitization during the early Cambrian resulted from altered marine, Mg-rich fluids associated with the mixing zone mechanism. Second, a late stage of dolomitization was associated with burial during late Permian. A third dolomitization phase was related to post-Eocene times.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":"17 1","pages":"1-18"},"PeriodicalIF":1.5,"publicationDate":"2019-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44558610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1344/geologicaacta2019.17.3
{"title":"Comments on Percrocuta carnifex (Percrocutidae) based on new fossil material from Nagri Fm Pakistan.","authors":"","doi":"10.1344/geologicaacta2019.17.3","DOIUrl":"https://doi.org/10.1344/geologicaacta2019.17.3","url":null,"abstract":"","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":"1 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66404896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-20DOI: 10.1344/GEOLOGICAACTA2018.16.4.10
M. Ortuño, M. Viaplana-Muzas
The activity of normal faults in the Central-Western Pyrenees is mainly detected by the disruption of paleic landforms surviving to Plio-Quaternary incision: the remnants of a Low-Relief Topography (LRT) that probably originated asynchronically during the Oligocene and Miocene. We propose a new method for mapping the LRT remnants that combines automatic analysis of digital topography and cross-checking with regional databases of Quaternary landforms. We focus on an area where the location of the main-drainage divide seems to be influenced by the activity of the Bedous-Pic de Midi du Bigorre set of faults and by the North Maladeta Fault. Neotectonic markers defined by the remnants of LRT envelops are tectonically displaced up to ~700m by the previously identified faults, but also along new faults observed in between them. A western prolongation of the North Maladeta Fault has been identified for the first time, implying a 75km total trace length, almost twice thepreviously published value. A restoration of the fault block motion was performed assuming a regional uplift across the range, enhanced in the northern part of the Axial Zone. This uplift leads to an outer arch extension along the Maladeta-Bedous Fault System. The resulting paleo-topography shows a broad southern paleo-flank (up to ~120km long) with a gentle regional gradient (~1o) and a much shorter and steeper northern paleo-flank (~4o gradient, up to 30km-long). This configuration suggests that the LRT remnants now located North of the main divide were connected to the Ebro Basin. The results are supported by previous studies on age and source provenance of major alluvial systems mantling the northern and southern flanks of the chain.
中-西比利牛斯山脉正断层的活动主要是通过保存到上新世-第四纪切口的苍白地貌的破坏来检测的：低起伏地形（LRT）的残余，可能在渐新世和中新世异步起源。我们提出了一种绘制LRT遗迹的新方法，该方法结合了数字地形的自动分析和与第四纪地形区域数据库的交叉检查。我们关注的区域主要排水分水岭的位置似乎受到Bedous Pic de Midi du Bigorre断层和North Maladeta断层活动的影响。LRT包络残余物定义的新构造标志物被先前确定的断层构造位移高达~700m，但也沿着它们之间观察到的新断层位移。首次确定了北马拉德塔断层的西部延伸，这意味着总迹线长度为75km，几乎是之前公布值的两倍。假设整个范围内存在区域隆起，轴向带北部增强，则对断块运动进行了恢复。这种隆起导致了沿着Maladeta Bedous断层系统的外拱形延伸。由此形成的古地形显示了一个宽阔的南部古侧翼（长达约120km），具有平缓的区域梯度（约1o）和一个更短、更陡的北部古侧翼（约4o梯度，长达30km）。这种配置表明，现在位于主分水岭以北的LRT遗迹与Ebro盆地相连。这一结果得到了先前对覆盖该链南北两侧的主要冲积系统的年龄和来源的研究的支持。
{"title":"Active fault control in the distribution of Elevated Low Relief Topography in the Central-Western Pyrenees","authors":"M. Ortuño, M. Viaplana-Muzas","doi":"10.1344/GEOLOGICAACTA2018.16.4.10","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2018.16.4.10","url":null,"abstract":"The activity of normal faults in the Central-Western Pyrenees is mainly detected by the disruption of paleic landforms surviving to Plio-Quaternary incision: the remnants of a Low-Relief Topography (LRT) that probably originated asynchronically during the Oligocene and Miocene. We propose a new method for mapping the LRT remnants that combines automatic analysis of digital topography and cross-checking with regional databases of Quaternary landforms. We focus on an area where the location of the main-drainage divide seems to be influenced by the activity of the Bedous-Pic de Midi du Bigorre set of faults and by the North Maladeta Fault. Neotectonic markers defined by the remnants of LRT envelops are tectonically displaced up to ~700m by the previously identified faults, but also along new faults observed in between them. A western prolongation of the North Maladeta Fault has been identified for the first time, implying a 75km total trace length, almost twice thepreviously published value. A restoration of the fault block motion was performed assuming a regional uplift across the range, enhanced in the northern part of the Axial Zone. This uplift leads to an outer arch extension along the Maladeta-Bedous Fault System. The resulting paleo-topography shows a broad southern paleo-flank (up to ~120km long) with a gentle regional gradient (~1o) and a much shorter and steeper northern paleo-flank (~4o gradient, up to 30km-long). This configuration suggests that the LRT remnants now located North of the main divide were connected to the Ebro Basin. The results are supported by previous studies on age and source provenance of major alluvial systems mantling the northern and southern flanks of the chain.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":"16 1","pages":"499-518"},"PeriodicalIF":1.5,"publicationDate":"2018-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47130696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-20DOI: 10.1344/GEOLOGICAACTA2018.16.4.5
F. Sàbat, B. Gelabert, A. Perea
Despite forming part of the Balearic group of islands, Minorca differs stratigraphically and structurally from Majorca and Ibiza: i) Paleozoic rocks are abundant in Minorca but are very scarce in Majorca and are absent in Ibiza. Eocene-Oligocene sediments are virtually absent in Minorca but crop out extensively in Majorca, ii) Contractional structures in Minorca differ in direction (aligned SW-NE in Majorca and Ibiza and N-S in Minorca) and in age from those in Majorca and Ibiza. In addition, Paleozoic deposits of Minorca do not correlate with those of Sardinia, where in addition the Triassic sediments are not very abundant. Contractional deformation in Sardinia is in part older (late Eocene-early Miocene) than in Minorca (early Miocene?). Given its Neogene clockwise rotation, Minorca cannot be considered a small block dragged by the early Miocene counter clockwise rotation of the Corsica-Sardinia block. Furthermore, the Paleozoic and Mesozoic stratigraphy of Minorca (siliciclasticlate Paleozoic rocks, Triassic Germanic facies and Jurassic carbonates) has affinities with that of the southern part of the Catalan Coastal Ranges. Thus, of all the Balearic islands, Minorca seems to have traveled the farthest during the Valencia Trough rifting with the result that it resembles an exotic island forming part of the Balearic foreland.
{"title":"Minorca, an exotic Balearic island (western Mediterranean)","authors":"F. Sàbat, B. Gelabert, A. Perea","doi":"10.1344/GEOLOGICAACTA2018.16.4.5","DOIUrl":"https://doi.org/10.1344/GEOLOGICAACTA2018.16.4.5","url":null,"abstract":"Despite forming part of the Balearic group of islands, Minorca differs stratigraphically and structurally from Majorca and Ibiza: i) Paleozoic rocks are abundant in Minorca but are very scarce in Majorca and are absent in Ibiza. Eocene-Oligocene sediments are virtually absent in Minorca but crop out extensively in Majorca, ii) Contractional structures in Minorca differ in direction (aligned SW-NE in Majorca and Ibiza and N-S in Minorca) and in age from those in Majorca and Ibiza. In addition, Paleozoic deposits of Minorca do not correlate with those of Sardinia, where in addition the Triassic sediments are not very abundant. Contractional deformation in Sardinia is in part older (late Eocene-early Miocene) than in Minorca (early Miocene?). Given its Neogene clockwise rotation, Minorca cannot be considered a small block dragged by the early Miocene counter clockwise rotation of the Corsica-Sardinia block. Furthermore, the Paleozoic and Mesozoic stratigraphy of Minorca (siliciclasticlate Paleozoic rocks, Triassic Germanic facies and Jurassic carbonates) has affinities with that of the southern part of the Catalan Coastal Ranges. Thus, of all the Balearic islands, Minorca seems to have traveled the farthest during the Valencia Trough rifting with the result that it resembles an exotic island forming part of the Balearic foreland.","PeriodicalId":55107,"journal":{"name":"Geologica Acta","volume":"16 1","pages":"411-426"},"PeriodicalIF":1.5,"publicationDate":"2018-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42485177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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