Transient and relict landforms in a lithologically heterogeneous post-orogenic landscape in the intertropical belt (Alto Paranaíba region, Brazil)

Marques, Karina Patrícia Prazeres; Santos, Marcilene dos; Peifer, Daniel; Silva, Clauzionor Lima da; Vidal‐Torrado, Pablo

doi:10.1016/j.geomorph.2021.107892

Cited by 10 publications

(4 citation statements)

References 90 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our results suggest that exhumation of resistant rocks in the Amazon can lead to widespread drainage reorganization and river captures, like other post-orogenic landscapes with complex lithology and little tectonic activity (Gallen, 2018;Marques et al, 2021). Exhumation of resistant rocks may slowly take place over time as the Amazon River as well as its tributaries slowly excavate their substrate at erosion rates of 5-40 m/Ma (Allard et al, 2018;Balan et al, 2005;Théveniaut & Freyssinet, 1999;Wittmann et al, 2011).…”

Section: Implications For Landscape Evolution In the Amazon Region An...mentioning

confidence: 79%

Ongoing landscape transience in the eastern Amazon Craton consistent with lithologic control of base level

Fadul

Oliveira

Val

2022

Earth Surf Processes Landf

View full text Add to dashboard Cite

Geomorphic features such as drainage captures, knickpoints, paleochannels, and wind-gaps have long been observed in the Amazon region and typically thought to result from climate change and intraplate tectonics. The influence of rock type as a trigger of these landscape transients is largely overlooked. In the eastern Guiana Shield of the Amazon Craton, shield rivers flow over to the sedimentary rocks of the Amazon Basin across a sharp lithologic transition before their confluence with the Amazon River. This transition is marked by an expressive main escarpment (ME) formed over resistant sandstones of the basal units of the Amazon Sedimentary Basin. Here, systematic patterns of divide migration and river captures provide a natural laboratory to study the influence of rock type in landscape transience in a cratonic setting. Through quantitative geomorphologic analysis of the topography, drainage divides, and rivers, we investigate if this sharp lithologic transition contributed to the observed patterns of drainage rearrangement. The results revealed that rivers of larger drainage areas flowing across shorter lengths over the resistant rocks of the ME systematically capture neighbouring basins. We argue that, as tributaries draining the shield respond to downcutting and/or base-level fall of the Amazon River, bedrock incision and knickpoint propagation are differentially slowed down by the resistant rocks according to their incision capacity, generating a series of transients such as drainage capture and divide migration. The widespread and systematic geomorphic features suggest this mechanism could be an important autogenic control of drainage network rearrangement in the Amazon region and other postorogenic landscapes as well. The protracted exhumation of resistant rocks in cratons and intraplate settings may keep landscapes in perpetual disequilibrium depending on their lithological complexity and offer an exceptional natural laboratory to study landscape dynamics associated with rock type.

show abstract

Section: Implications For Landscape Evolution In the Amazon Region An...mentioning

confidence: 79%

Ongoing landscape transience in the eastern Amazon Craton consistent with lithologic control of base level

Fadul

Oliveira

Val

2022

Earth Surf Processes Landf

View full text Add to dashboard Cite

show abstract

“…It is formed at the expense of pyroclastic and epiclastic rocks from the Mata da Corda group (upper Cretaceous) (CPRM, 2014). Despite being an important tropical Brazilian area of occurrence of thick lateritic profiles including duricrusts (Marques et al, 2021), no weathering geochronological data are available yet. The climate of the study area is Aw (Köppen-Geiger's classification), characterized by warm and dry winters and moist and warm summers.…”

Section: Sampling Sitementioning

confidence: 99%

Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U–Th) ∕ He geochronological analysis

Marques¹,

Allard²,

Gautheron

et al. 2023

Eur. J. Mineral.

Self Cite

View full text Add to dashboard Cite

Abstract. Interpreting the ages of supergene mineralogical phases in laterite is complex because they consist of polycrystalline mixtures of different phases at the microscopic scale that could be crystalized at different epochs. Among the geochronometers, the (U-Th)/He method on hematite and goethite is more often used, but ages can be difficult to interpret due to phases mixing. To resolve this issue, this study proposes a methodology for performing detailed mineralogical analysis of hematite and goethite single grains prior to their dating using the (U-Th)/He method. Strictly non-destructive mineralogy of single grains is not achievable by classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing). Therefore, we performed X-ray diffraction patterns of single grains using high-flux X-ray beams from both a rotating anode (XRD_rotat) laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on XRD_rotat only. For this purpose, two samples from the pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba region, Minas Gerais State, Brazil) were chosen because they presented a usual heterogeneity. Rietveld refinements of the XRD patterns obtained from both XRD_rotat and XRD_synch yielded similar results for the weight percentage ratio of the main phases and mean coherent domain sizes and less similar results for Al substitution rates, thus validating the XRD_rotat approach. No beam damage was observed when increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by XRD_rotat with a short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex grains also provided meaningful ages: they revealed two evolution phases of the ferruginous duricrust, which occurred at or before the Oligocene for the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the previous model for the development of pisolites. The mineralogy of single grains selected for dating is helpful for discussing the crystallization ages, and the high-flux XRD approach may be applied to other supergene mineral parageneses used for absolute dating.

show abstract

“…It is developed at the expense of pyroclastic and epiclastic rocks from the Mata da Corda Group (upper Cretaceous) (CPRM, 2014). Despite being an important tropical Brazilian area of occurrence of thick lateritic profiles including duricrusts (Marques et al, 2021), no weathering geochronological data are available yet. The climate of the study area is Aw (Köppen-Geiger's classification), characterized by warm and dry winters, and moist and warm summers.…”

Section: Sampling Sitementioning

confidence: 99%

Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U-Th)/He geochronological analysis

Marques¹,

Allard²,

Gautheron

et al. 2022

Preprint

View full text Add to dashboard Cite

Abstract. Interpreting the ages of supergene mineralogical phases in laterite is complex because they consist of polycrystalline mixtures of different phases at the microscopic scale that could be crystalized at different epochs. Among the geochronometers, the (U-Th)/He method on hematite and goethite is more used, but ages can be difficult to interpret due to phases mixing. To resolve this issue, this study proposes a methodology for performing detailed mineralogical analysis of hematite and goethite single grains prior to their dating using the (U-Th)/He method. Strictly non-destructive mineralogy of single grains is not achievable by classical tools, such as conventional powder XRD (requiring at least some mg of powder) or SEM (that can contaminate the grain by coating or fixing). Therefore, we have performed X-ray diffraction patterns of single grains using high-flux X-ray beams from both a rotating anode (XRD_rotat) laboratory diffractometer and a synchrotron beamline (XRD_synch) facility, and compared the results in order to design a method based on XRD_rotat only. For this purpose, two samples from the pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba region, Minas Gerais State, Brazil) were chosen because they presented a usual heterogeneity. Rietveld refinements of the XRD patterns obtained from both XRD_rotat and XRD_synch yielded similar results for weight percentage ratio of the main phases, Mean Coherent Domain sizes, and less for Al-substitution rates, thus validating the XRD_rotat approach. No beam-damage was observed when increasing X-ray exposure time, neither on XRD patterns nor (U-Th)/He ages. Hence, inframillimetric, undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by XRD_rotat with a short exposure, and the same grains can subsequently be dated by the (U-Th)/He geochronology. The (U-Th)/He dating of pisolitic core and cortex grains also provided meaningful ages: they revealed two evolution phases of the ferruginous duricrust, which occurred at or before the Oligocene for pisolitic core and middle Miocene for pisolitic cortex, agreeing with the previous model for the development of pisoliths. The mineralogy of single grains selected for dating is helpful for discussing the crystallization ages, and the high-flux XRD approach may be applied to other supergene mineral parageneses used for absolute dating of weathering profiles.

show abstract

Transient and relict landforms in a lithologically heterogeneous post-orogenic landscape in the intertropical belt (Alto Paranaíba region, Brazil)

Cited by 10 publications

References 90 publications

Ongoing landscape transience in the eastern Amazon Craton consistent with lithologic control of base level

Ongoing landscape transience in the eastern Amazon Craton consistent with lithologic control of base level

Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U–Th) ∕ He geochronological analysis

Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U-Th)/He geochronological analysis

Contact Info

Product

Resources

About