Geological Events Research Articles

Genetic and Ecological Divergence of Cinnamon Hummingbird Amazilia rutila (Aves: Trochilidae) Continental Populations Separated by Geographical and Environmental Barriers

Background and Research Aims: Historical geological events and climatic changes have played important roles in shaping population differentiation and distribution within species. Amazilia rutila (Trochilidae) is a widespread hummingbird species in the tropical dry forest along the Pacific slope and the Yucatán Peninsula in Mexico. Methods: We used mitochondrial DNA sequence, ecological niche modelling and niche divergence tests to determine the effects of major geographic barriers and environmental variability on genetic and niche divergence of A. rutila continental populations. Results: Our results revealed three genetic groups without haplotype sharing corresponding to the distribution of individuals/populations from the Pacific slope W of the Isthmus of Tehuantepec (PAC), in Oaxaca and Chiapas E of the Isthmus of Tehuantepec (CHIS_OAX) and those from the Yucatán Peninsula and Guatemala (YUC). Values of neutrality tests suggest past demographic expansion without effective population size changes over time, and the time since the demographic expansion ranged between 39.4 and 84.45 ka BP. Each genetic group differed in their position in environmental space, with low-to-very limited overlap in the fundamental climatic niche dimensions of all groups analyzed, particularly between YUC and PAC. Analysis of climate differentiation and ecological niche comparisons showed that the environmental space occupied by these mtDNA groups is similar but not identical. Conclusion: We conclude that the genetic differentiation of A. rutila is consistent with a model of population isolation by geographical barriers and environmental differences. Inferences about the consequences of past demographic expansion and isolation underlying intraspecific evolutionary relationships await further study. Implications for Conservation: Our findings highlight the importance of preserving evolutionary significant units of this widespread hummingbird species. Conservation actions must consider intrinsic requirements of evolutionarily distinct populations and the environmental drivers that shape their distributions, maximizing preservation of intraspecific genetic variability and monitoring changes in genetic diversity.

Phylogeography of Falagoniamexicana Sharp, 1883 (Coleoptera, Staphylinidae, Aleocharinae).

Falagoniamexicana is an aleocharine distributed from northern Mexico to Guatemala and El Salvador. It is associated with Attamexicana ants and lives within their piles of waste or external debris. The phylogeography and historical demography of 18 populations from Mexico, Guatemala, and El Salvador were studied. The data set encompasses a 472 bp fragment of the COI. Results suggest that F.mexicana was originated during Middle Pliocene (ca. 0.5 Mya), starting its diversification at the Upper Pleistocene and Holocene. Populations were recovered forming at least four main lineages, with a significant phylogeographic structure. Evidence of contemporary restricted gene flow was found among populations. The historical demography suggests that the geographic structure is due to recent physical barriers (e.g., Isthmus of Tehuantepec) rather than ancient geological events. Also, recent geological and volcanic events in the east of the Trans-Mexican Volcanic Belt and the Sierra Madre Oriental might be responsible for the restricted gene flow among populations. Skyline-plot analyses suggested that a demographic expansion event took place at the end of the Late Quaternary glacial-interglacial cycles.

Characterization and interpretation of seismic signals generated by 7th February 2021, Dhauliganga disaster (India)

On 7th February 2021, a rockslide triggered debris flow hit the Rishiganga-Dhauliganga valley in the Chamoli district of Uttarakhand (India). Over 200 casualties and an estimated loss of 202 million USD to the infrastructural establishments were reported due to this disaster. The study area is highly seismically active; therefore, a dense seismic activity monitoring network is available in this region. Recent studies have suggested that geological hazard events have distinct seismic signatures that can be used to identify the event type, detect onset times and duration and interpret the hazard chain evolution. Studying these event-specific seismic signals can be a step forward in designing a landslide detection system for the region. While most previous studies focused on a single event, detailed research on the complete hazard chain is limited. Therefore, in this research, a combination of some signal processing techniques such as band-pass filter, Ensemble Empirical Mode Decomposition (EEMD), Short-time Fourier Transform (STFT), and Power Spectrum Density (PSD) was applied to process and analyze the seismic signal data. The signal data of nine seismic stations located within a 300 km radius of the event location were considered for the study. A detailed signal processing was carried out to obtain a signal with a high Signal-to-Noise Ratio (SNR). The observations were combined with satellite imagery to interpret the event dynamics and understand the complete hazard chain. This study provides a better insight into hazard event characterization and interpretation methodology used for post-hazard assessment and emergency response.

Phylogenomics reconciles molecular data with the rich fossil record on the origin of living turtles

Although a consensus exists that all living turtles fall within either Pleurodira or Cryptodira clades, estimating when these lineages split is still under debate. Most molecular studies date the split in the Triassic Period, whereas a Jurassic age is unanimous among morphological studies. Each hypothesis implies different paleobiogeographical scenarios to explain early turtle evolution. Here we explored the rich turtle fossil record with the Fossilized Birth-Death (FBD) and the traditional node dating (ND) methods using complete mitochondrial genomes (147 taxa) and a set of nuclear orthologs with over 10 million bp (25 taxa) to date the major splits in Testudines. Our results support an Early Jurassic split (191–182 Ma) for the crown Testudines with great consistency across different dating methods and datasets, with a narrow confidence interval. This result is independently supported by the oldest fossils of Testudines that postdate the Middle Jurassic (174 Ma), which were not used for calibration in this study. This age coincides with the Pangaea fragmentation and the formation of saltwater barriers such as the Atlantic Ocean and the Turgai Strait, supporting that diversification in Testudines was triggered by vicariance. Our ages of the splits in Pleurodira coincide with the geologic events of the Late Jurassic and Early Cretaceous. Conversely, the early Cryptodira radiation remained in Laurasia, and its diversification ensued as all its major lineages expanded their distribution into every continent during the Cenozoic. We provide the first detailed hypothesis of the evolution of Cryptodira in the Southern Hemisphere, in which our time estimates are correlated with each contact between landmasses derived from Gondwana and Laurasia. Although most South American Cryptodira arrived through the Great American Biotic Interchange, our results indicate that the Chelonoidis ancestor probably arrived from Africa through the chain islands of the South Atlantic during the Paleogene. Together, the presence of ancient turtle diversity and the vital role that turtles occupy in marine and terrestrial ecosystems underline South America as a chief area for conservation.

Geological characteristics of the Cua Dai beach zone by geophysical data and the relation to the regional accretion - erosion phenomenon

This study presents some research results on the relationship between the geological environment of the surface layer and the level of modern tectonic activity in the sea waters of the Hoi An - Cua Dai area based on the interpretation of high-resolution shallow seismic data combined with the surface sediments’ grain-size analysis and other available data sources. The results show that the surface geological environment in the coastal waters North of the Thu Bon river fault is influenced by modern tectonic activities, believed to be a part of causing geological catastrophic events.

Earth’s crust and physical fields of the oceans

Some problems of the formation and development of oceanic regions with various variants of endogenic regimes (with the exception of island arcs, which, in the author’s opinion, belong to late Alpine geosynclines) are considered. Calculated geological events and anomalies of physical fields within them are determined by heat-mass-transfer schemes in the tectonosphere. The reliability and accuracy of the latter is related to the quantity and quality of information about the content of the regimes. In the oceans, such data is scarce. The article attempts to attract additional information about the formation of the Earth’s crust of a typical oceanic basin. It was presented in the form of oceanization (destruction and basification) of the continental crust with a slightly increased basicity. The process included the uplift and denudation of the upper block up to 10 km thick, the intrusion of mafic and ultrabasic rocks from the mantle in a concentration increasing with depth into the lower approximately 20—30 km of the crust. Seismic wave velocity and density in the crustal basement were almost equal to the properties of the warmed mantle rocks. The final stage of magmatism was presented in a large part of the region during the period of recent activation by the removal of partially molten matter from the shallow asthenosphere up to the surface. Similar models have also been constructed for other endogenous regimes. In all cases, significant scatter in the ages of the process stages and the order of formation of asthenolite sources rising from different depths of the upper mantle were unavoidable. The resulting thermal models were averaged effects for the considered variants of heat and mass transfer. The control of the reality of these constructions was carried out according to the correspondence of known events of geological history, allowing a quantitative description, and anomalies of physical fields. In this work, the second part is considered. The calculated velocity sections of the upper mantle regions, the heat flow distribution, and the values of mantle gravity anomalies were compared with the experimental data. In all cases, the agreement reached is satisfactory. The discrepancies can be explained by errors in observations and calculations

Integrated approach using petrophysical, gravity, and magnetic data to evaluate the geothermal resources at the Rahat Volcanic Field, Saudi Arabia

It is necessary to develop and explore geothermal resources to achieve sustainable development and clean renewable energy around the Globe. Geothermal energy is crucial to the future energy supply to meet the environmentally friendly energy demand of the World. The Rahat Volcanic Field (Kingdom of Saudi Arabia) is the oldest and lengthiest Cenozoic Volcanic Field in the World. It is a dominantly a mature mafic Volcanic Field that holds three major geological events; the historic eruption (1256 C.E.), the five fingers (∼4500–1500 BP), and the seismic swarm (1999 C.E.). These incidents were studied by utilizing geological information and geophysical data sets. Geophysical and geostatistical research includes gravity and magnetic survey data, including different log curves and major elements, obtained from water samples as well as of volcanic rocks obtained by X-ray fluorescence (XRF). To gain an understanding of the subsurface thermal structure, these datasets were analyzed. The primary goal of this study is to identify the prominent potential geothermal resources with the help of an available data set. Findings suggest that beneath the historic eruption site along with the fissure eruption, on the western side, there is a geothermal anomaly with a surface footprint of about 35 km2. Analyzing gravity and magnetic data as well as density and magnetic susceptibility variations in rock samples led to the mapping of this anomaly. It has been inferred through integrated study that statistical analysis of major elements will be helpful to validate the results of the outcome.

Mineralization Regularities of the Bainiuchang Ag Polymetallic Deposit in Yunnan Province, China

The Bainiuchang Ag polymetallic deposit is located at the junction between the Cathaysia, Yangtze, China and Indosinian blocks. It has experienced many geological events, and records excellent conditions for multiple mineralization. In this paper, elemental correlation analysis, cluster analysis, factor analysis, a semivariogram of Zn/Pb values, mineralization distribution and trend surface analysis have been carried out based on the prospecting database and ore body model. Our results show that Ag–Pb–Zn were mineralized at moderate temperatures. Tin was mineralized at high temperatures, and Sn and Zn/Pb values are well correlated. The Zn/Pb values can be used for tracing the ore-forming fluid. The semivariogram revealed that the Zn/Pb values are moderately spatially dependent, with good mineralization continuity in the 100° and 10° directions. The spatial pattern of the elemental grade correlates with mineralization enrichment. The trend surface analysis shows that the Ag, Pb, Zn, and Cu mineralization is weak in the south and strong in the north of the deposit, and the Sn grades and Zn/Pb values are high in the south and low in the north. High-temperature Sn, medium-temperature Cu, and medium-temperature Ag–Pb–Zn mineralization have occurred in a south-to-north trend. Therefore, the source of the ore-forming fluid was in the southern part of the mining area. During the migration of the ore-forming fluid from south to north, different minerals were precipitated due to changes in the physicochemical environment. The spatial patterns of mineralization may provide a basis for studying the formation of the ore deposit, and can guide ore exploration and mining in the mine area and similar ore deposits elsewhere.

Emplacement history of volcaniclastic turbidites around the central Azores volcanic islands: Frequencies of slope landslides and eruptions

Volcanic islands export clastic material to their surrounding oceans by explosive eruptions, lava emissions, biogenic production on their shelves, and failure of their slopes, amongst other processes. This raises the question of whether geological events (in particular, eruptions and landslides) can be detected offshore and dated, and whether any relationships (for example, with climate changes) can be revealed using sediment cores. The volcanically active central Azorean islands (Faial, Pico, São Jorge, and Terceira), with their neighboring submarine basins, are potentially good candidates for such an analysis. Here, chronostratigraphies of four gravity cores collected amongst the islands are constructed based on twelve radiocarbon dates and two dates derived by geochemically correlating primary volcaniclastic turbidites with ignimbrites on Faial and Terceira Islands. Age-depth models are built from the hemipelagic intervals to estimate individual turbidite dates. Volumes of turbidites are modeled by multiplying basin areas with bed thickness, allowing for various turbidite thinning rates and directions. The volumes of landslide-generated turbidites are only comparable with the largest volumes of their adjacent upper-slope submarine landslide valleys; therefore, such turbidites in the cores likely derive from these largest landslides. Emplacement intervals between turbidites originating from both landslides and pyroclastic density currents are found to be mostly a few thousand years. Frequencies of landslide-generated turbidites and hemipelagic sedimentation rates were both highest in the past 8 k.y. compared to preceding periods up to 50 k.y. High hemipelagic sedimentation rates are interpreted to be related to sea-level rise, allowing more shelf bioproduction and release of particles by coastal erosion. The coincident increased frequencies of submarine landslides may also be associated with the increased sediment supply from the islands, resulting in a more rapid build-up of unstable sediments on submarine slopes. Notably, the emplacement frequencies of turbidites of pyroclastic density current origins do not suggest the decreased eruption frequency toward the Holocene that has been found elsewhere.

The Miocene Climatic Optimum at the interface of epicontinental sea and large continent: A case study from the Middle Miocene of the Eastern Paratethys

The Miocene Climate Optimum (MCO) and the subsequent Miocene Climate Transition (MCT) are important biotic, environmental and geologic events. Here we address whether this holds true for the epicontinental Eastern Paratethys Sea (today's Black – Caspian Sea region). Two Tarkhanian – lower Chokrakian sequences of Middle Miocene age in the Kerch Peninsula were investigated using foraminifera, calcareous nannofossils, molluscs, fish otoliths, spores and pollen, oxygen and carbon stable isotopes and strontium isotope stratigraphy (SIS). Our results show that the marine environment during the Tarkhanian to early Chokrakian in the study area was characterized by open shelf conditions (near upper part of lower sublittoral zone), variable water column stratification and bottom water oxygen levels. Biostratigraphy and new SIS data suggest an age of >15.5 (∼16.0?) – 14.75 Ma for the Tarkhanian, which implies a considerably longer duration (> 0.75 Ma vs. 0.1 Ma) than was previously suggested. The maximum transgression seen in the middle Tarkhanian could be dated to ∼15.5–15.1 Ma and correlates with the highstand of sequence Bur 5/Lan 1 (15.2 Ma) and terminal phase of the MCO. The vegetation indicates a gradual change from subtropical humid (early Tarkhanian) to arid (early Chokrakian) conditions, which reflect the MCT. The climate change in the Eastern Paratethys occurred slightly earlier than in the Central Paratethys, possibly related to the existence of the large flat Eurasian continent.

Historical Landscape Evolution Shaped the Phylogeography and Population History of the Cyprinid Fishes of Acrossocheilus (Cypriniformes: Cyprinidae) According to Mitochondrial DNA in Zhejiang Province, China

Geological events and landscape features, as well as changes in the climate during the Pliocene period, have shaped the distribution of genetic diversity and demographic history of freshwater fish in mainland China. In this study, we investigated the phylogeny and population genetic structure of Acrossocheilus species (A. fasciatus, A. kreyenbergii and A. wenchowensis) in the Zhejiang region by the mitochondrial cytochrome b (cyt-b) and control (D-loop) region s. Mitochondrial phylogenetic analysis revealed three major lineages (lineages A, B and C), which may represent A. fasciatus, A. wenchowensis and A. kreyenbergii, respectively. Our results revealed that A. fasciatus and A. wenchowensis diverged from A. kreyenbergii in the Zhejiang region. The uplift of the Wuyi Mountains and the Xianxia Mountains served as an important geographic barrier in the diversification of the three Acrossocheilus species. The most recent common ancestors (TMRCAs) of the three lineages and lineages A + B were dated to 1.859 and 1.614 myr, respectively. Our results indicate that the effective population sizes of A. fasciatus and A. wenchowensis remained constant from the past to the present, as supported by ABC analysis. For conservation and protection, a strategy is required because of their genetic uniqueness, and we suggest that the two regions divided by the Xianxia Mountains be regarded as different management units (Mus), conforming to the major zoological regions of the Zhejiang region.

Neogene–Quaternary tectonic, eustatic and climatic events shaped the evolution of a South American treefrog

AbstractAimUnderstanding how past geological and climatic events could have generated intraspecific genetic variation at different temporal and spatial scales in the Neotropics requires a model encompassing distinct ecoregions. Because Anura species have their evolutionary history affected by climate and environmental changing, it is a suitable model to investigate the signatures of Neotropical historical events in species populations. Here we used a treefrog species to test hypotheses associated with tectonic, eustatic and climatic events along with isolation‐by‐environment and isolation‐by‐distance spatial patterns in genetic diversity.TaxonScinax squalirostris (Lutz, 1925), Anura: Hylidae.LocationAtlantic Forest, Cerrado, Chaco, Uruguayan Savanna and Pampas ecoregions in South America.MethodsWe sequenced nuclear and mitochondrial data from 219 individuals of S. squalirostris sampled at 26 locations in South America. We performed statistical phylogeographic analyses and reconstruction of spatiotemporal dispersal dynamics. Ecological niche modelling was conducted to predict spatial changes in environmental suitability from the Last Glacial Maximum to the Holocene and present day.ResultsWe recovered a significant phylogeographic break roughly dated back to the Miocene (~7.6 Ma), coinciding with the retraction of marine incursions in the Paraná basin. Most dispersal events occurred in cooler periods of the Pliocene–Pleistocene transition. The spatial pattern in genetic diversity was not correlated with geographical distance or environmental variables.Main ConclusionsScinax squalirostris had a quasi‐stable distribution through time. Neogene–Quaternary tectonic, eustatic and climatic events drove the demographic history and dispersal dynamics of species, with a phylogeographical break dated to the Miocene coinciding with retractions of marine incursions in the Paraná basin. Lineage dispersal spread from the southern Atlantic Forest and retrieved gene flow signals congruent with the cold periods of the Pliocene and Pleistocene.

MFEE: a multi-word lexical feature enhancement framework for Chinese geological hazard event extraction.

Event Extraction (EE) is an essential and challenging task in information extraction. Most existing event extraction methods do not specifically target the Chinese geological hazards domain. This is due to the unique characteristics of the Chinese language and the lack of Chinese geological hazard datasets. To address these challenges, we propose a novel multi-word lexical feature enhancement framework (MFEE). It effectively implements Chinese event extraction in the geological hazard domain by introducing lexical information and the designed lexical feature weighting decision method. In addition, we construct a large-scale Chinese geological hazard dataset (CGHaz). Experimental results on this dataset and the ACE 2005 dataset demonstrate the approach's effectiveness. The datasets can be found at https://github.com/JieGong1130/MFEE-dataset. The code can be found at https://github.com/JieGong1130/MFEE-master.

Cadmium isotope evidence deciphers enhanced marine productivity during the middle Mesoproterozoic (the Xiamaling formation, North China)

The interval between 1800 and 800 Ma has long been regarded as “boring billion” which lacks major geologic events in marine sediments. Recent studies, however, showed that multiple ocean-atmospheric oxygenations, together with the evolution of eukaryotes occurred in this period. In North China, the ca. 1400 Ma Xiamaling Formation has been reported as a well-preserved sedimentary succession that faithfully records the primary information of multi-geochemical signatures. Iron speciation, trace element, and organic geochemical analyses, together with biomarker and δ15N measurements recognized an ocean with nitrogen limitation, dynamic oceanic chemocline, and the presence of significant populations of both red and green algae from the Xiamaling Formation black shales. However, the precise paleo-productivity of the Xiamaling Formation still remains poorly understood. This study reports analytical results of Cadmium (Cd) isotopes (δ114Cd) from the Xiamaling Formation, which is subdivided into Units 1–5 in a descending order in the Xiahuayuan borehole section of the North China Craton. The newly obtained δ114Cd values, together with other previously published geochemical data are employed to evaluate nutrient utilization by phytoplankton and primary productivity in the 1.4 Ga ocean of North China. The δ114Cd values show a positive excursion from the lower Unit 3 to upper part of Unit 1 in the studied section. Unit 3 yields the lightest δ114Cd value. Integrating the previously published major and trace elements, organic carbon isotopes, total organic carbon (TOC) concentrations, nitrogen isotopes, iron speciation, and biomarkers, we suggest that the non-euxinic condition and lowest nutrient utilization rate may account for the light isotope compositions in Unit 3. Increase in δ114Cd from Unit 3 to lower Unit 2 is interpreted to be triggered by the elevated nutrient utilization rate and paleo-productivity. The pronounced increase in δ114Cd from the lower Unit 2 to upper Unit 2 may be due to the redox change from non-euxinic to euxinic conditions, coupled with an increasing nutrient utilization rate. Although nutrient utilization rate increased from Unit 3 to Unit 2, the consumption of nutrients in the ocean was still likely incomplete, which therefore slowed down the evolution of phytoplanktons in the 1.4 Ga ocean in the North China Craton.

Regional synthesis of the Ordovician geology and stratigraphy of China

Abstract China presently comprises several independent tectonic palaeoplates or terranes and parts of other blocks, which have been assembled over geological time. In the Ordovician, these blocks included South China, North China, Tarim, Qaidam, Junggar, Qiangtang-Qamdo, Lhasa and partially Himalaya, Sibumasu and Indochina, as well as the Altay-Xing'an and Songpan-Garze fold belts, which were discrete but near-adjacent. Twelve stratigraphic megaregions bounded by tectonic sutures or major fault zones can be recognized. Some of them are further differentiated into several regions according to the lithological and biotic facies or distinct stratigraphic sequences. Here, the palaeontologic features and biostratigraphic framework of these stratigraphic megaregions and regions are summarized. The unified biostratigraphic framework presented herein is supported by 33 graptolite biozones and 27 conodont biozones, together with supplementary biozones, communities or associations of brachiopods, trilobites, cephalopods, chitinozoans, acritarchs and radiolarians. With constraints of integrative chronostratigraphy, biostratigraphy, chemostratigraphy, cyclostratigraphy and magnetostratigraphy, along with some geochronologic data, our understanding of the temporal and spatial distribution of the Ordovician lithostratigraphic units on these major blocks has been significantly advanced. Vast amounts of new data accumulated in recent decades also constrain the major Ordovician geological and biotic events evident in China, such as marine anoxia, faunal turnovers and tectonic orogenies.

Silurian to Cretaceous geological evolution of southern Mexico and its connection to the assembly and break-up of Western Equatorial Pangaea: geochronological constraints from the northern Sierra de Juárez Complex

Abstract The Sierra de Juárez Complex (SJC) of southern Mexico contains an extensive geological record from Precambrian to Cenozoic, involving Rodinia, NW Gondwana, western equatorial Pangaea, and eastern peninsular Mexico. It is thus critical for palinspastic reconstructions and lithotectonic correlations, mainly between the Mexican and NW South America terranes. In this contribution, we investigate the tectonic evolution of the northern SJC from Silurian to the Lower Cretaceous on the basis of fieldwork, petrography, and zircon U–Pb geochronology by laser ablation–inductively coupled plasma mass spectrometry. Our results allow us to constrain five main geological events: (1) Middle Paleozoic sedimentation along NW Gondwana during transtensional tectonics; (2) volcanosedimentary activity between 292 and 281 Ma in NW Gondwana during Rheic Ocean closure; (3) early-middle Permian metamorphism related to flat-slab subduction postdating Pangaea assembly; (4) Lower–Middle Jurassic anatexis and magmatism coeval with regional shearing at c. 175 Ma influenced by transtensional tectonics along eastern peninsular Mexico during Pangaea tenure; and (5) intermediate to acid magmatism between c. 136 and 129 Ma, correlated with the Zongolica continental arc in southern Mexico, followed by deep-crustal shearing related to either the formation of the extensional Chivillas basin or the Upper Cretaceous–Cenozoic contractional episode documented in the Cuicateco Terrane.

U–Pb geochronology: its development and importance in Canada

This article presents a history of the development of U–Pb geochronology with emphasis on the role of Canadian researchers and some of its applications to Canadian geology. Modern U–Pb dating is the result of work by many individuals over the past 60 years, but the most important was Tom Krogh, who established methods that allowed determination of precise ages (<0.1% errors) on zircon using isotope dilution thermal ionization mass spectrometry. This was followed by the introduction of new analytical approaches by others, notably secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry that allow intracrystal domains to be dated. U–Pb geochronology is now an indispensable tool for understanding the Earth. In collaboration with field mapping, it has vastly improved our understanding of the geological history of Canada as well as important geological events such as mass extinctions, secular changes in geological processes, and the birth of the solar system.

Redox conditions and ecological resilience during Oceanic Anoxic Event 2 in the Western Interior Seaway

Oceanic Anoxic Events (OAEs) are important geological events that may be analogues to future climate-driven deoxygenation of our oceans. Much of the global ocean experienced anoxic conditions during the Cenomanian–Turonian OAE (OAE2; ∼94 Ma), whereas the Western Interior Seaway (WIS) experienced oxygenation at this time. Here, organic geochemical and palynological data generated from Cenomanian–Turonian age sediments from five sites in the WIS are used to investigate changing redox and ecological conditions across differing palaeoenvironments and palaeolatitudes. Heterogeneity across the sites is apparent, but important relationships and trends among oceanographic variables are recognised: 1) Increasing total organic carbon (TOC) and CaCO3 percentages indicate the onset of a sea-level maximum towards the end of OAE2; 2) C28 sterane is shown to be a useful marker for prasinophyte abundance, and concurrent increases in this marker and overall sterane abundance indicate prasinophyte-driven increase in algal productivity in a stratified water column; and 3) sterane ratios can be a more reliable geochemical proxy than redox proxies for assessing the Benthic Oxic Zone. Our redox data do not always follow established trends for the WIS overall, particularly for proximal settings. We therefore surmise that local effects, such as nutrient-driven expansion of the oxygen minimum zone and/or sedimentation-driven anoxia just below the sediment-water interface, have overprinted regional trends.

Mitochondrial, morphological and environmental data partially support current subspecies designation inAmazilia yucatanensishummingbirds

AbstractHistorical geological events and Pleistocene climatic fluctuations have played important roles in shaping distribution and population differentiation across taxa. The buff-bellied hummingbird (Amazilia yucatanensis) is widely distributed along the Gulf of Mexico slope and the Yucatan Peninsula. Here, we obtained measurements and sequenced two mitochondrial DNA fragments from currently recognized subspecies: Amazilia yucatanensis yucatanensis (YUC), Amazilia yucatanensis cerviniventris (CER) and Amazilia yucatanensis chalconota (CHA). Additionally, we tested for their genetic and morphological differentiation, demographic expansion, palaeoclimatic distribution and niche overlap. Our results reveal genetic differentiation between two groups of populations: (1) from the Yucatan Peninsula to Veracruz (YUC+CER); and (2) from Veracruz to Tamaulipas (CHA). Neutrality tests and Bayesian skyline plots suggest past demographic expansion without changes in the effective population size over time. The potential distribution was fragmented at the Trans-Mexican Volcanic Belt and expanded northwards during the Last Glacial Maximum and Mid-Holocene to current conditions. Niche overlap was higher between YUC and CER. The environmental space occupied by subspecies was more similar to each other than expected by chance but significantly non-equivalent. Our results provide new insight on the distribution of this widespread hummingbird species and suggest that fragmentation during glaciations and differences in habitat have played a role in the recent diversification.

Groundwater‐Controlled Deposition of Equatorial Layered Deposits in Central Arabia Terra, Mars

AbstractEquatorial Layered Deposits (ELDs) reveal aspects of past depositional environments useful for timing climatic and geological events on Mars. However, their formation has several contending hypotheses which reflect a diverse range of possible environments. To better constrain their formation mechanism, we analyzed the stratigraphic and mineralogical characteristics and mapped the distribution of ELDs within three close craters, Sera, Jiji, and an unnamed crater in central Arabia Terra. Analyses of craters' geology allowed us to reconstruct the paleo‐environments where ELDs have been deposited. Thinning and thickening sequence trends show shared and repeated variations in the depositional environment, reflecting sediment accumulation strongly controlled by a regional groundwater reservoir. Layered deposits are characterized by monohydrated and polyhydrated sulfate signatures implying an interaction between water and rock in acidic conditions. Our study contributes to the understanding of regional geological processes in Arabia Terra revealing long‐term aqueous activity.