Southern Mexico Research Articles

Soil development and ancient Maya land use in the tropical karst landscape: Case of Busiljá, Chiapas, México

AbstractThe soil mantle of the tropical karstic landscapes of Southern Mexico was shaped by specific processes of pedogenesis and long‐term human impacts of ancient Maya agriculture. To understand the interaction between natural and human‐induced soil‐forming processes in the calcareous mountains of Chiapas state, we studied soil toposequences around the Classic Maya site of Budsilhá and related them to the archaeological evidence of settlement and land‐use distribution. Soil chemical analysis, micromorphological observations, and clay mineral identification were carried out in key soil profiles at the main geoforms. Limestone hills are occupied by shallow Rendolls which are usually perceived as incipient soils. However, high content of silicate clay composed of kaolinite and vermiculite and ferruginous clayey soil material observed at macro‐ and microscale backed the hypothesis that these soils were formed from the residues of thick Terra Rossa after their erosion. Swampy lowlands are occupied by thick clayey gleyic soils with clay mineral assemblages similar to those in the upland Rendolls. We suppose that the mineral matrix of the lowland soils is largely derived from the pedosediments of eroded upland Terra Rossa, which lost original ferruginous pigmentation and aggregation due to redoximorphic processes. Some wetland soils contain neoformed gypsum that is atypical for humid tropics; sulfide‐sulfate transformation under fluctuating redox conditions could promote gypsum synthesis. Ancient Maya land use was closely related to soil‐geomorphic conditions: settlements with homegardens occupied calcareous hills, whereas the primary agricultural domain was developed on lowland soils after their drainage by artificial canals.

First record of the water mite species Arrenurus (Arrenurus) munovus Cook, 1980 from Belize, including the description of the female (Arrenuridae, Hydrachnidia, Acari)

We provide the description of the so far unknown female of Arrenurus munovus Cook 1980 as well as additional morphological data for the male. This is the first record of the species since its description from Southern Mexico and is extending the known distribution about 370 km east to the south-eastern of the peninsula de Yucatan. This is the first record of an Arrenurus species from Belize, as well as the first species level data on the Belizean freshwater mite fauna.

New records of two marsupials (Didelphimorphia, Didelphidae) and conservation notes from southern Mexico

In Mexico opossums are difficult to find, and much of their natural history, ecology, and behavior are unknown. Through photographic and visual records, we obtained data on the presence of two species of marsupials in southern Mexico. We report new municipal records of Derby’s woolly opossum, Caluromys derbianus in Veracruz, and new municipal records of the Gray four-eyed opossumPhilander opossum for Oaxaca, Veracruz, and Chiapas. Local mammal records are crucial for understanding the biology and ecology of species, as well as identifying its threats.

New state records for the riffle beetle Tolriolus ungulatus (Hinton, 1934) (Coleoptera: Elmidae) from southern Mexico

New state records for the riffle beetle Tolriolus ungulatus (Hinton, 1934) (Coleoptera: Elmidae) from southern Mexico

Predicting the potential distribution and coexistence of Chagas disease vectors in the Americas.

Predicting the potential distribution and coexistence of suitable geographic areas for Chagas disease vectors in the Americas is a crucial task for understanding the eco-epidemiological dynamics of this disease. The potential distribution and coexistence of 3 species-Rhodnius prolixus (Hemiptera: Reduviidae), Cavernicola pilosa (Hemiptera: Reduviidae), and Rhodnius pictipes (Hemiptera: Reduviidae) were modeled. Presence records were obtained and environmental variables were selected based on correlation analysis, Jackknife analysis and knowledge of the biology and natural history of the species. The MaxEnt algorithm included in the kuenm package of R software was used for modeling the potential distribution, and various scenarios of the BAM diagram (Biotic, Abiotic, and Movement variables) were evaluated. The variables contributing to the final models were different for each species. Rhodnius pictipes showed a potential distribution in South America, particularly in Brazil, Bolivia, Peru, Colombia, Venezuela, Guyana, and Suriname. Areas with environmentally suitable conditions for R. prolixus were located in southern Brazil, Peru, Colombia, southern Mexico, Guatemala, El Salvador, and Honduras, whereas for C. pilosa they were in southeastern Brazil, southeastern Central America, Peru, Ecuador, Colombia, Venezuela, Guyana, Suriname, and French Guiana. Co-occurrence analysis revealed distinct patterns in the neotropical region, with some areas indicating the potential distribution of 1 or more species. In Brazil, occurrence and co-occurrence areas were concentrated in the northwest and southeast regions. Overall, this study provides valuable information on the potential distribution and coexistence of vectors, which can inform targeted vector control strategies and contribute to global efforts in combating Chagas disease.

Geographic and Climatic Variation in Resin Components and Quality of Pinus oocarpa in Southern Mexico Provenances.

In Mexico, there is a deficit in the production of pine resin, because it relies on natural forests only. Therefore, it is necessary to select provenances and phenotypes of potential species such as P. oocarpa. The objective was to determine the difference between provenances and the variation in resin components and quality, as well as the effect of geographic and climatic factors. Resin from five provenances was collected from southern Mexico. The percentage of rosin, turpentine and water was obtained, as well as the acidity and saponification index. P. oocarpa resin had 80.94% rosin, 7.7% turpentine and 11.49% water. The saponification and acidity index was 125.47 and 117.49 mg KOH.g-1, respectively. All variables showed differences (p ≤ 0.0001) between provenances. The provenance contributed between 6.44 and 11.71% to the total variance, the error contributed between 88.29 and 93.56%. Geographic and climatic variables only had an effect on the percentage of turpentine; the correlation was negative with altitude and longitude, but positive with temperature and precipitation. The results allow defining seed collection sites for resin plantations and orienting the selection for a P. oocarpa improvement program.

Gender, Immunological Response, and COVID-19: An Assessment of Vaccine Strategies in a Pandemic Region of Oaxaca, México

COVID-19 is no longer a public health emergency of international concern, but long COVID’s effects are yet to be fully understood. Hence, globally, SARS-CoV-2 is still a profound threat to public health and of perilous nature as a zoonotic disease. Timely vaccination provided to individuals worldwide during the pandemic phase was under a certain degree of control; however, few studies have reported the effectiveness of vaccines administered in Mexico, and its surveillance is paramount. Furthermore, an unknown proportion of Mexican individuals have not yet received any vaccine, and the circulation of the Omicron, Pirola, and FLiRT variants is ongoing. A cross-sectional serology survey study design was employed, involving 150 individuals from Southern Mexico (Oaxaca) whose humoral immune responses after vaccination were tested by an ELISA; the receptor-binding domain of the SARS-CoV-2 spike protein served as a recombinant antigen in the ELISA. One hundred thirty-nine out of 150 individuals (92.6%; 95%-CI = 87–95%) examined were positive for the ELISA, but in 11 individuals, the vaccines did not induce any immune response. Interestingly, the immune responses (antibody prevalence and levels) of females (58%) were higher (T= −2.21; p-value = 0.02) than those of males (41%). However, in this sample population of Southern Mexico, age, vaccine type, comorbidity, and body mass index did not have any effect (p > 0.05) after COVID-19 vaccination. Taking all results together, here, we present factors that affected immune responses of individuals during the first vaccination campaign in Oaxaca, Mexico; however, vaccine surveillance during the post-pandemic phase needs further investigation.

New paleofloristic and geochronological U–Pb zircon data in late Paleozoic deposits of the Matzitzi formation in southern Mexico

The fossil flora of the Matzitzi Formation, is a fluvial unit of late Paleozoic age exposed in southern Mexico, has been studied since the last century; however, the discovery of new plant elements during the last decade imposes a reevaluation of two aspects that have always been the subject of debate: the depositional age of the unit and the taxonomy of its paleoflora. The objective of the present work is to report new paleofloral records from two areas of the Matzitzi Formation as well as their chronological implications. The study sites are named Carretera and Coatepec. Nineteen genera and 11 species have been identified in beds from the Carretera site, whereas 23 genera and 16 species in beds from the Coatepec site. The analysis of floral assemblages of both sites shows that they share 49% of taxa. Ovopteris, Lesleya, Lobatopteris, and Trigonocarpus are unique to the Carretera site, while Coatepec is characterized by the presence of cf. Bjuvia, Schizoneura, and Velascophyllum. When analyzing the greatest ranges of the paleoflora awareness for the Carretera site indicates that deposition of these beds took place in a time interval that may span between Pennsylvanian and lower Permian. On the other side, the floral assemblage recovered from the Coatepec site indicates that the hosting beds were deposited in upper Permian time. U–Pb detrital zircon geochronology indicates that the maximum depositional age of the fossiliferous beds at the Carretera and Coatepec sites are of 276 ± 15 Ma and 254 ± 11 Ma, respectively. The integration of the paleontological and geochronological data obtained in this work suggests that the analyzed floral assemblage recovered from the Carretera site is of Kungurian age, whereas the one from the Coatepec site is of Lopingian age. Alternatively, we explore the possibility that deposits that are presently grouped within the Matzitzi Formation could be the vestiges of different fluvial cycles associated with different tectonic settings. Finally, the work on this unit has not finished, since there are still localities where its flora and age are still unknown.

Rates of change and phylogenetic signal in Mixtec tone

Abstract Despite the abundance of tonal languages around the world, the diachrony of tone is still poorly understood, especially when compared to segmental sound change. This lacuna has contributed to the untested assumption that tones are inherently unstable and change unpredictably. This paper addresses the questions of whether tones change faster than segments and whether tones show less phylogenetic signal than segments in the Mixtec languages of southern Mexico. To this end, I created a database of tonal and segmental sound changes across a sample of 42 Mixtec languages. I calculated phylogenetic signal with the metric D and estimated rates of change with a hidden Markov model across a posterior sample of phylogenetic trees. The results show that the majority of tone changes show phylogenetic signal and that they generally do not change at a faster rate than segments.

Detection of IgG antibodies against the receptor binding domain of the spike protein and nucleocapsid of SARS-CoV-2 at university students from Southern Mexico: a cross-sectional study

BackgroundNatural infection and vaccination against SARS-CoV-2 is associated with the development of immunity against the structural proteins of the virus. Specifically, the two most immunogenic are the S (spike) and N (nucleocapsid) proteins. Seroprevalence studies performed in university students provide information to estimate the number of infected patients (symptomatic or asymptomatic) and generate knowledge about the viral spread, vaccine efficacy, and epidemiological control. Which, the aim of this study was to evaluate IgG antibodies against the S and N proteins of SARS-CoV-2 at university students from Southern Mexico.MethodsA total of 1418 serum samples were collected from eighteen work centers of the Autonomous University of Guerrero. Antibodies were detected by Indirect ELISA using as antigen peptides derived from the S and N proteins.ResultsWe reported a total seroprevalence of 39.9% anti-S/N (positive to both antigens), 14.1% anti-S and 0.5% anti-N. The highest seroprevalence was reported in the work centers from Costa Grande, Acapulco and Centro. Seroprevalence was associated with age, COVID-19, contact with infected patients, and vaccination.ConclusionUniversity students could play an essential role in disseminating SARS-CoV-2. We reported a seroprevalence of 54.5% against the S and N proteins, which could be due to the high population rate and cultural resistance to safety measures against COVID-19 in the different regions of the state.

Nascent transcription reveals regulatory changes in extremophile fishes inhabiting hydrogen sulfide-rich environments.

Regulating transcription allows organisms to respond to their environment, both within a single generation (plasticity) and across generations (adaptation). We examined transcriptional differences in gill tissues of fishes in the Poecilia mexicana species complex (family Poeciliidae), which have colonized toxic springs rich in hydrogen sulfide (H2S) in southern Mexico. There are gene expression differences between sulfidic and non-sulfidic populations, yet regulatory mechanisms mediating this gene expression variation remain poorly studied. We combined capped-small RNA sequencing (csRNA-seq), which captures actively transcribed (i.e. nascent) transcripts, and messenger RNA sequencing (mRNA-seq) to examine how variation in transcription, enhancer activity, and associated transcription factor binding sites may facilitate adaptation to extreme environments. csRNA-seq revealed thousands of differentially initiated transcripts between sulfidic and non-sulfidic populations, many of which are involved in H2S detoxification and response. Analyses of transcription factor binding sites in promoter and putative enhancer csRNA-seq peaks identified a suite of transcription factors likely involved in regulating H2S-specific shifts in gene expression, including several key transcription factors known to respond to hypoxia. Our findings uncover a complex interplay of regulatory processes that reflect the divergence of extremophile populations of P. mexicana from their non-sulfidic ancestors and suggest shared responses among evolutionarily independent lineages.

Infants who are rarely spoken to nevertheless understand many words

Theories of language development-informed largely by studies of Western, middleclass infants-have highlighted the language that caregivers direct to children as a key driver of language learning. However, some have argued that language development unfolds similarly across environmental contexts, including those in which childdirected language is scarce. This raises the possibility that children are able to learn from other sources of language in their environments, particularly the language directed to others in their environment. We explore this hypothesis with infants in an indigenous Tseltal-speaking community in Southern Mexico who are rarely spoken to, yet have the opportunity to overhear a great deal of other-directed language by virtue of being carried on their mothers' backs. Adapting a previously established gaze-tracking method for detecting early word knowledge to our field setting, we find that Tseltal infants exhibit implicit knowledge of common nouns (Exp. 1), analogous to their US peers who are frequently spoken to. Moreover, they exhibit comprehension of Tseltal honorific terms that are exclusively used to greet adults in the community (Exp. 2), representing language that could only have been learned through overhearing. In so doing, Tseltal infants demonstrate an ability to discriminate words with similar meanings and perceptually similar referents at an earlier age than has been shown among Western children. Together, these results suggest that for some infants, learning from overhearing may be an important path toward developing language.

Behavioral and biological parameters of six populations of Triatoma pallidipennis (Heteroptera: Reduviidae) from areas with high and low prevalence rates of Trypanosoma cruzi human infection

In Mexico, more than 30 species of triatomines, vectors of Trypanosoma cruzi, the etiological agent of Chagas disease, have been collected. Among them, Triatoma pallidipennis stands out for its wide geographical distribution, high infection rates and domiciliation. Local populations of triatomines have shown notable biological and behavioral differences, influencing their vectorial capacity. Six behaviors of epidemiological importance, namely, egg-to-adult development time, median number of blood meals to molt to the next instar, instar mortality rates, aggressiveness (delay in initiating a meal), feeding time and defecation delay, were evaluated in this study for six populations of T. pallidipennis. Those populations from central, western and southern Mexico were arranged by pairs with a combination of high (HP) and medium (MP) of Trypanosoma cruzi human infection and most (MFC) and low (CLF) collection frequencies: HP/MFC, HP/CLF, and MP/MFC. The development time was longer in HP/CLF populations (> 220 days). The median number of blood meals to molt was similar (7–9) among five of the six populations. Mortality rates were greater (> 40 %) in HP/CLF and one MP/MFC populations. All studied populations were aggressive but exhibited slight differences among them. The feeding times were similar (≥ 10 min) for all studied populations within instars, increasing as instars progressed. An irregular pattern was observed in defecation behaviors, with marked differences even between the two populations from the same pair. High percentages of young (57.3–87.9 %), and old (62.4–89.8 %) nymphs, of female (61.1–97.3 %) and male (65.7–93.1 %) of all the studied populations defecated quickly (while eating, immediately after finishing feeding or < 1 min postfeeding). Our results indicate that the HP/MFC populations are potentially highly effective vectors for transmitting T. cruzi infections, while HP/CLF populations are potentially less effective vectors T. cruzi infections.

RESPUESTA AGRONÓMICA DEL FRIJOL (Phaseolus vulgaris L.) A LA APLICACIÓN DE BIOFERTILIZANTES PROVENIENTES DE RESIDUOS PECUARIOS EN CHIAPAS, MÉXICO

&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt; Beans (&lt;em&gt;Phaseolus vulgaris&lt;/em&gt; L.) are an integral part of the basic diet in Mexico and are one of the most important crops. Mexico is the seventh producer worldwide and one of the main consumers of it. Within Mexico, the state of Chiapas is the sixth-largest producer with 68,515 t per year, with a yield of 0.59 t ha&lt;sup&gt;-1&lt;/sup&gt;. However, the excessive use of chemical fertilizer has degraded soil quality and increased production costs. &lt;strong&gt;Objective:&lt;/strong&gt; To study the agronomic response of the bean crop treated with biofertilizers originated from livestock excreta through anaerobic digestion (effluents). &lt;strong&gt;Methodology:&lt;/strong&gt; Variables plant growth variables seed germination, flowering, photosynthesis, and the presence of pathogens were compared. The treatment evaluated were soils treated with bovine manure (treatment 1) and swine manure (treatment 2) after anaerobic digestion, urea (treatment 3) as chemical fertilizer, and control without fertilizers (treatment 4). &lt;strong&gt;Results:&lt;/strong&gt; In general, the use of biofertilizers improved the yield per plant, as well as accelerated the development of the plants compared to the control, which was attractive for the producers. In addition, the use of biofertilizers in the soil decreased the presence of pathogens and increased the microbial population, which can be beneficial in soil recovery. &lt;strong&gt;Implications:&lt;/strong&gt; The cost of biofertilizer production was 13.5 USD for m&lt;sup&gt;3&lt;/sup&gt;, which was cheaper than chemical fertilizers. However, a detailed analysis of the application costs of biofertilizers is recommended. &lt;strong&gt;Conclusion:&lt;/strong&gt; The practice of using livestock effluents (biofertilizer) is proposed as a complement to agroecological practices to improve agricultural production and recover soil fertility in southern Mexico. &lt;/p&gt;

Relaxed minds for healthier food choice at school: A field experiment in southern Mexico

Stress leads to unhealthy food choices since the school-age stage. Yet, there is limited evidence particularly in low- and middle-income countries regarding the impact of stress-reduction strategies on school-age children's food choices. Such aspects were crucial during the recent COVID-19 pandemic, which exacerbated psychological distress and unhealthier food choices among children. Two years after the pandemic began, we conducted a field experiment in southern Mexico to assess the impact of stress-reduction strategies on the food choices of over 1400 children aged 9–12. Half of the school-classes in the sample were randomly assigned to a stress reduction strategy namely meditation, which comprised six audios with basic relaxation techniques and intuitive messages to guide food choices. Additionally, all participants received information signalling that an amaranth snack was nutritious (i.e., the healthy snack), which was paired with a chocolate bar (i.e., the unhealthy snack) as part of a snack choice experiment. Students that practiced meditation were slightly more likely to choose the healthy snack than those in the control group, but the effect was not statistically significant. Upon collecting their snack, students had the chance to exchange their original choice for the other snack. Students that meditated were more likely to exchange their originally chosen “unhealthy snack” towards the healthy snack than students in the control group. The meditation program effectively reduced chronic stress among treated children. The effect was larger among students attending schools in lower-income areas. Our study sheds some light on the challenges to translate an improved psychological well-being into healthier food choices at school.

The Trans-Crustal Evolution of Miocene Magmatism Parental to Epithermal Mineralization in the Sierra Madre del Sur, Southern Mexico

Abstract Arc-related volcanism results from the interplay of magmatic processes occurring in trans-crustal systems that consolidate over time in a given location. Trans-crustal systems comprise extensive networks of magma reservoirs and conduits at different depths, wherein melts cyclically differentiate and segregate before reaching the surface. The study of these systems provides valuable insights into crustal-scale phenomena, such as the evolution of the continental crust and the formation of metallogenic regions. In this study, we address the trans-crustal magmatic evolution of lower Miocene magmatism parental to several intermediate-sulfidation epithermal deposits in the eastern Sierra Madre del Sur igneous province, southern Mexico. Using a multi-methodological approach, we document changes over ca. 1.1 Myr in the magmatic system that fed andesitic-to-felsic volcanism in this region. We employ whole-rock REE ratios and λ parameters—which are used to quantify the shape of a REE pattern—to track the involvement of pressure-sensitive minerals in the deep-crustal magmatic evolution. The andesitic rocks consist of lava flows, porphyries, and dikes that collectively show REE patterns suggestive of control by fractionated or residual (i.e. in crustal melting) amphibole and/or clinopyroxene. In contrast, the felsic rocks consist of rhyolitic–dacitic ignimbrites, domes, and dikes that show contrasting REE patterns suggestive of control by plagioclase, clinopyroxene, amphibole, and/or garnet. The distinct pressure-sensitive mineral assemblages in the andesitic and felsic rocks indicate that the locus of deep-crustal magma evolution varied within the middle–lower crust. These magmas were episodically injected into ephemeral shallow crustal reservoirs (shortly?) before being erupted, inducing a progressive thermomechanical maturation of the middle–upper crust. Meanwhile, low degrees of crustal assimilation occurred as recorded by Mesozoic inherited zircon ages and Sr–Nd–Pb radiogenic isotopes. An extensive middle–lower crustal magma evolution has been linked to the formation of porphyry Cu deposits (i.e. ‘fertile’ magmatism). Given that intermediate-sulfidation epithermal deposits may be genetically linked with porphyry Cu deposits, the documented processes could have contributed to the formation of epithermal deposits in the region. However, magmatic fertility proxies resemble those from infertile magmas worldwide. Since these proxies have been exclusively applied to porphyry-type deposits, our results highlight the importance of developing new geochemical exploration tools applicable to a wider range of ore deposits.

An inclusion of Melastomataceae leaf from the Miocene amber of Simojovel de Allende, Chiapas, México

Melastomataceae Jussis a family well represented in tropical biomes and is characterized by a distinctive venation pattern in its leaves. The worldwide fossil record consists mainly of leaves that date back to the Palaeocene. However, this family is poorly represented in the fossil record in Mexico. Here, we show a new finding of a Melastomataceae leaf preserved as inclusion in amber outcrops in Chiapas that preserves evidence of the complex Miocene ecosystem through well-preserved fossil organisms. The morphological characteristics described were based on shape and venation patterns and compared with extant or fossil organisms with similar patterns, allowing us to assign individuals to one of the genera and species hypotheses, or name them as a new species. The fossil leaf has ovate to elliptical lamina, nanophyll size, long petiole, and basal acrodromous venation, with one pair of secondaries emerging from the petiole and merging at the leaf apex and opposite percurrent epimedial tertiary veins. This combination of characteristics are typical of Miconia Ruiz & Pavón and have not been observed together in any leaf recordings for this family, proposing a new fossil species. This discovery confirms the presence of Melastomataceae in Southern Mexico during the Miocene, which was once part of the tropical rainforest of the Simojovel Formation of Chiapas, Mexico.

Epibiotic ciliate communities on the crayfish Procambarus (Austrocambarus) sp. cultivated in a rustic aquaculture in southern Mexico

Rustic aquaculture systems represent a sustainable production alternative in the world, providing appropriate conditions for the establishment of epibiotic ciliates on crayfish. However, the impact of epibiotic ciliates on the aquaculture production has been insufficiently studied hitherto. The objective of this work was to identify the epibiotic ciliates on the surface of the crayfish Procambarus (Austrocambarus) sp. and analyze whether there is any correlation between seasonality and environmental conditions in an artificial pond in Chiapas, Mexico. The crayfish were collected during dry and rainy seasons to investigate their ciliate epibionts. Some physical and chemical parameters of the sampled water were measured and correlation matrix analyses were applied to detect possible relationships between the presence of ciliates and environmental parameters. Thirteen species belonging to the subclasses Peritrichia and Suctoria were identified. Significant differences were found for some environmental parameters and species recorded in both seasons. The present data could help to better understand the relationship bewteen the epibiotic ciliate community on crayfish and some environmental parameters in aquaculture systems.

Bee and butterfly records indicate diversity losses in western and southern North America, but extensive knowledge gaps remain.

Pollinator losses threaten ecosystems and food security, diminishing gene flow and reproductive output for ecological communities and impacting ecosystem services broadly. For four focal families of bees and butterflies, we constructed over 1400 ensemble species distribution models over two time periods for North America. Models indicated disproportionally increased richness in eastern North America over time, with decreases in richness over time in the western US and southern Mexico. To further pinpoint geographic areas of vulnerability, we mapped records of potential pollinator species of conservation concern and found high concentrations of detections in the Great Lakes region, US East Coast, and southern Canada. Finally, we estimated asymptotic diversity indices for genera known to include species that visit flowers and may carry pollen for ecoregions across two time periods. Patterns of generic diversity through time mirrored those of species-level analyses, again indicating a decline in pollinators in the western U.S. Increases in generic diversity were observed in cooler and wetter ecoregions. Overall, changes in pollinator diversity appear to reflect changes in climate, though other factors such as land use change may also explain regional shifts. While statistical methods were employed to account for unequal sampling effort across regions and time, improved monitoring efforts with rigorous sampling designs would provide a deeper understanding of pollinator communities and their responses to ongoing environmental change.

The influence of topography and transport history on the composition of clastic deposits from the Jurassic Tlaxiaco basin, southern Mexico: limitations on the use of mineral and chemical indices as proxies for paleoclimate

ABSTRACT The mineral and chemical composition of clastic deposits is commonly used as a proxy for reconstructing the climatic history of the Earth. A mineralogical and chemical study of clastic deposits from the Jurassic Tlaxiaco basin of southern Mexico illustrates that the entire sedimentary system in which detritus is generated, subaerially transported, and deposited exerts a major control on the composition of sedimentary rocks, placing some constraints on the use of mineral and chemical indices as paleoclimatic proxies. Since clastic deposits of the Tlaxiaco basin were formed under similar humid climatic conditions, but in sedimentary systems with different topography and transport histories, they represent a natural laboratory for testing the control that these parameters exert on the composition of clastic rocks. Our petrographic and chemical results show that, in sedimentary systems associated with low relief and in which detritus had the possibility of being temporarily stored in floodplains and meandering bars, parent rocks and the derivative detritus interacted with weathering fluids over a long time, producing clastic deposits with composition that is representative of the weathering conditions and climate of the region. On the other hand, in environments associated with steep and tectonically active relief, the rates of sediment transport and burial exceed the rate at which weathering can generate detritus, producing sedimentary deposits with composition that largely underestimates potential weathering and provide unreliable information on climate. Mineral and chemical indices should be considered as reliable paleoclimate proxies only when sedimentological data indicate that the sedimentary system allowed sediment interaction with weathering fluids over a long time.