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Mineralogical and geochemical (major, trace and rare earth elements) studies were carried out on the clay samples of the Terani Formation, South India to investigate the paleoweathering, source rocks characteristics and tectonic setting. The chemical index of alteration (CIA), plagioclase index of alteration (PIA) values and A-CN-K diagram indicate that clays were generated from source rocks of the upper continental crust affected by intense chemical weathering. The chondrite-normalized REE patterns show considerable LREE enrichment, HREE depletion with significant negative Eu anomalies. The REE patterns, elemental ratios like Al2O3/TiO2 Cr/Ni, Eu/Eu*, (La/Lu)cn, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th, discriminant function diagram, various bivariate and ternary plots indicate the contribution of sediments from felsic and intermediate source rocks. The discriminant-function-based tectonic setting diagrams reveal passive margin setting for the source area of the Terani Formation.

The Cauvery Basin at the southeastern tip of the Indian plate was an Albian to Danian marine embayment. The Dalmiapuram Formation is composed of bioclastic wackestone and coral boundstone. Benthic foraminifera and calcareous algae are relatively common in the Dalmiapuram Formation. The fossils support an age range of upper Albian to Cenomanian, which complements previously reported nannofossils that suggest an early Albian to Turonian age. The low diversity assemblage of foraminifera and calcareous algae and other organisms in the Dalmiapuram Formation is characteristic of a near-shore carbonate shelf or ramp. The low diversity and abundance of planktic species with coral and coral-algal buildups suggests more offshore conditions, probably within storm wave-base. The δ13C and δ18O values vary greatly. The absence of correlation between Mn and Sr indicates that these limestones retain their primary isotopic signatures. Gray shale/limestone unit has positive carbon isotope excursion (CIE) of ~ 0.8 to 1.0‰ that correlate with OAE 1c event. Similarly, significant positive CIE noticed in the lower part of the coral algal limestone is attributed to OAE 1d event. This suggests that oceanic conditions that created deep-water low oxygen conditions affected the shallow-water photic zone.

In the present study, 135 cm and 125 cm sediment cores were collected from Yedayanthittu estuary at a water depth of 1 m to infer the provenance and paleoweathering conditions of the source rocks. The core samples were carbon-dated and analyzed for calcium carbonate, organic matter, and major oxides to decipher the sea level changes, source area weathering, and provenance. The calcium carbonate is chiefly derived from terrestrial and coastal input into the mangrove ecosystem, and the rapid increase of calcium carbonate percentage at certain levels of the cores is due to enrichment of shell fragment. The organic matter content of the sediments is mostly derived from terrestrial input and mangrove debris. Geochronological studies indicate that the sediments deposited during early Holocene period with an average sedimentation rate of 0.015 cm/y−1. The 14C dates and Holocene sea level curve suggest the gradual and slow sea level rise along the study area. The chemical index of alteration (CIA), plagioclage index of alteration (PIA), and A-CN-K diagram reveal that the source rocks were subjected from low to moderate intensity of chemical weathering. The index of chemical variability (ICV) values indicates that the sediments are immature to moderately mature in nature. Major oxide concentrations of core sediments indicate that they were derived mainly from recycled felsic source rocks.

The 420-m thick stratigraphic section of the Mural Formation that is exposed in the Cerro Pimas area of northern Sonora, Mexico, is composed of limestone lithofacies ranging from bioclastic wackestone to boundstone, whose biota is characterized by low diversity. Prominent age-diagnostic fossils are benthic foraminifera and long-ranging calcareous algae that indicate the Aptian/Albian boundary is close to the base of the Los Coyotes Member. The carbonates of this formation have negative to positive δ13C values (−4.63 to +2.6‰) and highly depleted δ18O values that range from −12.74 to −8.34‰. The absence of correlation between δ13C and δ18O values supports a primary marine origin for the δ13C values of these limestones. The carbon-isotopic curve of the Cerro Pimas stratigraphic section has well-defined δ13C segments (C8 – C15) that compare with published curves of similar age. In the lower part of the early Albian Los Coyotes Member, the presence of OAE 1b is indicated by an increase followed by a decrease in δ13C values, suggesting correlation with the Kilian Event. The middle part of the Los Coyotes Member has a significant negative carbon-isotope excursion correlated with the globally recognizable early Albian Paquier event. Moreover, another significant negative carbon-isotope shift is observed in the upper part of the Los Coyotes Member, which can be correlated with the Leenhardt Event. The occurrence of the Kilian, Paquier and Leenhardt Events (OAE 1b cluster) in the Cerro Pimas stratigraphy confirms the global nature of these early Albian disturbances of the carbon cycle.

Mineralogic and geochemical studies were performed in the Tecolutla and Coatzacoalcos beach sediments, located at the SW Gulf of Mexico. The main concern of this article is to infer the weathering, provenance, and degree in which trace metal pollution affects the beach sediment composition. The chemical index of weathering (CIX) for the Tecolutla and Coatzacoalcos beach sediments indicate a moderate intensity of weathering in the source area. The SiO2/Al2O3 ratio values (>6) in the Tecolutla and Coatzacoalcos sediments suggested a high compositional maturity and recycling. A difference in the Al2O3/TiO2 ratios between the Tecolutla and Coatzacoalcos beach sediments points out that the sediments were derived from intermediate and felsic igneous rocks, respectively. A negative correlation for Al2O3 against TiO2 and P2O5, and trace elements Y, Nb, V, Sc, and Cr for the beach sediments suggests an association of these elements with detrital minerals rather than aluminosilicates. The provenance discrimination based on major element concentrations indicates an intermediate and a felsic provenance for the Tecolutla and Coatzacoalcos sediments. The major and trace element geochemistry of beach sediments are associated with a passive margin setting. The Enrichment factor (EF) and Geo accumulation index (Igeo) values show that the Tecolutla sediments are moderately enriched by Cu (EF ∼ 10–17) and Cr (1

Microtextures on quartz grains from the Huatabampo (HB) and Altata (AA) beaches, Gulf of California, were analyzed by a scanning electron microscopy (SEM) to infer the depositional history and provenance. In total, 41 microtextures were identified and grouped as mechanical, mechanical/chemical, and chemical mode of origins. Among them, twenty-three microtextures represent mechanical, eight represent mechanical/chemical, and ten represent chemical origin. The microtextures of chemical origin were further classified as dissolutional and precipitational origins. Oriented etch pits, solution pits, solution crevasses, and scaling are classified as of dissolutional origin. Silica globules, silica flower, silica pellicles, crystalline overgrowth, trapped diatoms, and halite crystals are grouped as chemical precipitational origin. The V-shaped marks, straight and curved scratches revealed the combination of fluvial and high energy subaqueous beach environments. The low frequencies of upturned plates, abrasion fatigue, meandering ridges, crescentic percussion marks, bulbous edges and elongated depressions suggest the low abundance of sediments derived by aeolian transport. The microtextures of chemical origin in few grains indicated the diagenetic processes in a silica saturated intertidal zone. The quartz grains from HB and AA beaches reveal varying sizes of conchoidal fractures indicate that they were derived mainly from crystalline source rocks. The association of straight and arcuate steps along with conchoidal fractures further support that the studied quartz grains were liberated from crystalline rocks. The dominance of angular to sub-angular grains indicates short transport and rapid deposition. In addition, straight and arcuate steps are delicate features which might have been destroyed during long transportation. Thus, the presence of straight and arcuate steps features together with angular to sub-angular grains support a nearby source.

Upper Aptian-lower Albian seawater composition changes and redox conditions in limestones of the Agua Salada and Lampazos formations in Mexico were investigated by data of major oxides, trace elements, rare-earth elements, and stable isotopes. Most limestones of the Agua Salada Formation (Group 1) show REE + Y patterns consistent with precipitation from seawater whereas limestones from the upper part of the Agua Salada and Lampazos formations (Group 2) have non-seawater-like REE + Y patterns. The relationship among REE and major and trace elements indicates that contamination by detrital input is the main source of REEs, followed by Fe-oxyhydroxides. The variations in Ce anomalies were influenced by paleo-redox conditions. The carbon isotope values, low Mn/Sr ratio and absence of correlation between δ13C vs δ18O values suggest that δ13C retained its original marine signatures during diagenesis. The δ13C curve has several significant negative isotopic excursions in upper Aptian-lower Albian strata. The variations in δ13C values and their negative excursions, fossil evidence, positions of δ13C segments, and correlation of this curve with global reference curves permits documentation of OAE 1 b and the associated sub-events such as Jacob, Kilian, Paquier and Leenhardt sub-events.

Clay mineralogy and geochemical studies were carried out on sandstone and shale samples collected from the Sierra San Jose section of the Morita Formation to infer the paleoclimate and paleoweathering conditions that prevailed in the source region during the deposition of these sediments. The clay mineral assemblages (fraction

Geochemical (major oxides, trace and rare earth elements) studies were carried out on the siliciclastic rocks of the Antimonio and Rio Asuncion formations to interpret the paleoweathering conditions and provenance. The weathering indices like the Chemical Index of Alteration (CIA) and Plagioclase Index of Alterations (PIA) indicate a low to moderate intensity of chemical weathering. The chondrite normalized REE patterns of the Antimonio and Rio Asuncion formations have LREE enriched, flat HREE patterns with a negative Eu anomaly. However, a few samples from these formations show a positive or an absence of the Eu anomaly, suggesting that the sediments were dominantly derived from felsic source rocks with a minor contribution from mafic source rocks. The vertical distribution of trace elements and their ratios indicate that sequence I of the Antimonio Formation presents a signature for felsic source rocks, however, in sequence II the sediment source changed, i.e. mafic rocks were recorded (SAAF06 and SAAF07). Sequences III to VI indicate a felsic source rock. The basal and upper parts of sequence VII (samples SARAF02 and SARAF10) of the Rio Asuncion Formation indicate mafic source rocks, whereas the remaining samples were largely contributed by felsic source rocks. The lower values of ferromagnesian trace elements and their ratios in sequences VIII and IX reveal a felsic source for the upper part of the Rio Asuncion Formation. The Antimonio and Rio Asuncion formations received sediments from two different sources: Permo-Triassic granitoids of northwestern Sonora and Precambrian granitoids from Caborca and North American blocks that contributed felsic rocks. Whereas mafic elements were derived from Precambrian amphibolites and Cambrian basalts located north and south of the study area.

A multidisciplinary approach of the Aptian-Albian Mural Limestone including petrography, geochemistry and stable isotope data is undertaken for the 660-m thick Rancho Bufalo section of northeastern Sonora to characterize source of rare earth elements and to infer paleo-redox conditions. The lithofacies of limestones range from mudstone to boundstone. The unaltered signatures of the δ13C values are confirmed by using Mn and Sr concentrations and their ratios along with the absence of correlation between δ13C and δ18O values. The limestones have large variations in ΣREE and Al2O3 contents (8.0 − 95.8 ppm; 0.45% − 7.10 ppm; respectively). Most limestones show non-seawater-like REE + Y patterns with positive Eu anomalies and negative Ce anomalies. The limestones have positive Ba anomalies in six intervals and most of them were resulted due to weathering and depositional processes and not due to sea level variations. The redox proxies of U, V/Cr and V/(V + Ni) indicate that the bottom water conditions fluctuated from oxic to anoxic. The high-resolution carbon isotope curve reveals four OAE 1 b sub-events: Jacob, Kilian, Paquier, and Leenhardt. The carbon isotope curve of the Rancho Bufalo section is comparable to that of the Cerro Pimas and Peregrina Canyon sections of Mexico.

Textural, heavy minerals and geochemical (major, trace and rare earth elements) studies were undertaken on the sands from Puerto Penasco, Desemboque and Bahia Kino beaches to determine the provenance and tectonic settings. Puerto Penasco and Bahia Kino sands are coarse grained to fine grained, while Desemboque sands are fine grained. Geochemically, these sands are classified as arkose. The sands are depleted in most of the trace elements relative to upper continental crust (UCC), except for few trace elements (Sr, Rb and Ba), which are slightly enriched. High ΣREE content are observed in the Desemboque sands (94.43 ± 6.9) than in the Puerto Penasco and Bahia Kino sands (51.58 ± 17.06; 72.38 ± 9.27; respectively). The chemical index of alteration (CIA) values of Puerto Penasco, Desemboque and Bahia Kino sands (PP: 42 to 50; DE: 48 to 50; BK: 44 to 50: respectively) indicate the low intensity of chemical weathering in the source rocks. The tectonic discriminant-function-based multidimensional diagram shows arc and rift settings for Puerto Penasco sands whereas rift setting for both Desemboque and Bahia Kino sands. The heavy mineral assemblage, immobile trace elements, REE patterns, elemental ratios such Eu/Eu*, (La/Lu)cn, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th, various bivariate and ternary plots indicate the contribution of sediments from felsic composition. This interpretation is supported by the comparison of REE patterns of the Puerto Penasco, Desemboque and Bahia Kino sands with the potential source rocks exposed nearby the study areas.

Measurement of the major and trace elements were carried out on the Lower Cretaceous limestones interbedded in the volcano-sedimentary Alisitos Formation, northwestern Mexico to understand the source of rare earth elements (REEs) and paleo-redox conditions. The five limestone beds (from the base up, Unit 5 to Unit 9) of the Alisitos Formation show large variations in SiO2 content (0.9–27.9%). A low concentration of CaO is observed in Unit 6 and Unit 8, and high content of CaO is observed in Unit 5, Unit 7 and Unit 9. The limestones are depleted in many trace elements with respect to Post-Archaean Australian Shale (PAAS), whereas Sr shows slight enrichment when compared to PAAS. The concentrations of ΣREE are higher in Unit 6 and Unit 8 (37.4 ± 7.5; 46.6 ± 19.4; respectively) than Unit5, Unit7, and Unit 9 (9.1 ± 3.2; 11.3 ± 9.4; 4.2 ± 2.5; respectively). The limestones of the Alisitos Formation show a non-seawater-like REE + Y pattern with positive Eu anomalies relative to PAAS (0.95–2.47). Variations in ΣREE, Al2O3, Zr, Sc, REE + Y patterns, and Y/Ho ratios are influenced mainly by the amount of terrigenous materials. The variations in the Eu/Eu*, La/Sc and La/Co suggest that the terrigenous materials included in the lower four limestone beds (from Unit 5, Unit 6, Unit 7 and Unit 8) were likely contributed by intermediate to felsic rocks whereas terrigenous materials from Unit 9 were derived from mafic to intermediate source rocks. The slightly negative to slightly positive Ce anomalies in the studied limestones resulted from variations in the bottom water oxygenation. This was also corroborated by V/Cr and Ni/Co ratios suggesting that the depositional environments experienced large fluctuations in oxygenation conditions ranging from oxic to anoxic conditions during the deposition of limestones of the Alisitos Formation.

Major, trace, and rare earth element (REE) studies have been conducted on the Proterozoic clastic rocks of the Kerur Formation of the Kaladgi-Badami Basin, South India, to determine their paleoweathering conditions and provenance characteristics. Geochemically, these sedimentary rocks are classified as quartz arenite, arkose, litharenite, and sublitharenite. The chemical index of alteration values and the A-CN-K diagram suggest that the clastics rocks in this study underwent moderate to intensive weathering. Chondrite-normalized REE patterns with light REE enrichment, flat heavy REE, and a negative Eu anomaly also attribute felsic source-rock to sedimentary rocks of the Kerur Formation. In addition, Eu/Eu* (~0.77), (La/Lu)cn (~7.65), La/Sc (~5.39), Th/Sc (~3.49 ), La/Co (~6.79), and Cr/Th (~0.31) ratios support a felsic source for these rock types. Comparing REE patterns and Eu anomalies of the source rocks reveals that the Kerur Formation clastic rocks received a major contribution of sediments from the Dharwar Craton.

The Morita Formation is a Lower Cretaceous unit of the Bisbee Group that crops out in northern Sonora and southeastern Arizona where it was deposited within the Altar-Cucurpe, and Huachuca sub-basins of the Bisbee basin, respectively. In northern Sonora it either overlies strata of the Upper Jurassic Cucurpe Formation, the Glance Conglomerate, or strata of the Lower Cretaceous Cerro de Oro/Rancho La Colgada formations, and it grades upward into the Mural Limestone. In this contribution we characterize the stratigraphy, petrography and detrital zircon geochronology of the Morita Formation along a ca. 60 km-long northwest-southeast transect that includes the complete columns of the Mule Mountains in southeastern Arizona and the sierras San Jose, Anibacachi and Rancho Bufalo area in northeastern Sonora. Thickness of these sections varies from a minimum of 555 m in Sierra Anibacachi to a maximum of 855 m in Rancho Bufalo. In most sections, the lower half of the Morita consists of reddish siltstone and mudstone with pedogenic calcareous nodules with interbeds of mostly single-storey sandstone bodies, which changes to isolated multi-storey sandstone bodies in its upper half. In contrast, the lower part of the Rancho Bufalo column consists of reddish mudstone/siltstone with isolated, fining-upward, clast-supported, fine-pebble conglomerate beds that grades into reddish to purple, brown and green mudstone/siltstone with isolated, single-storey to multi-storey sandstone beds of its upper part. Lithofacies association in the Morita Formation suggest it is of fluvial origin but ichnofossils and local herringbone- and flaser-cross bedding in its upper part indicate intermitent marginal marine sedimentation preceding the transgression that deposited the overlying Mural shelf. Sandstone composition of the Mule and San Jose mountains is dominantly feldspatho-quartzose indicating dominant provenance from basement uplift and transitional continental areas, while composition at Sierra Anibacachi and Rancho Bufalo ranges from feldspatho litho-quartzose to litho-quartzose, indicating provenance from recycled orogen. Detrital zircon grains dated from samples of all the studied sections share very similar populations of Proterozoic to Mesozoic ages, but the Mesoproteozoic and Triassic grains compose ca. 64% of the total grains. Detrital zircon grains of Lower Cretaceous age that are only present in samples from the bottom of the Mule and San Jose Mountains help to constrain a maximum depositional age of 125.5 ± 0.8 Ma for inception of sedimentation of the Morita Formation in this region. According to this age and to observed stratigraphic relationships, we interpret that the lower contact of the Morita Formation is a disconformity with the underlying Glance Conglomerate, or with the Cerro de Oro Formation in northeastern Sonora. Similarly, according to regional stratigraphic relationships and age data known from the Cucurpe-Tuape region, in north-central Sonora, the age of this unit may be constrained to the Aptian stage, in Sonora, from ca. 125 to 115 Ma. Regional isopach curves confirm merging of the sub-basins in northeastern Sonora, continuous sedimentation of the Morita Formation, and presence of the Cananea high separating them.

The clastic rocks of the Kerur Formation Group were analyzed for major, trace and rare earth elements to infer the tectonic settings and provenance signatures. The lithology of the Kerur Formation includes basal arenite (BA), lower conglomerate (LC), quartz arenite (QA) and upper conglomerate (UC). The CIA and PIA values and A–CN–K diagram indicate a moderate to intense chemical weathering for the clastic rocks of the Kerur Formation. The bivariate plot and multidimensional diagram based on major-trace elements suggesting the clastic rocks were derived mainly from the passive margin setting. A silicic source for clastic rocks of the Kerur Formation is indicated by higher ratios of SiO2/Al2O3, ΣLREE/ΣHREE, elemental ratios, bivariate and ternary plots. REE patterns and Eu anomalies support that TTG (Tonalite-Trondhjemite gneiss), granodiorite, granitic rocks of the Dharwar Craton and the basement rock (schist) of the Kaladgi-Badami Basin could be the source rocks for the Kerur Formation. REE modeling suggests that the average composition of the Kerur Formation represents a mixture of sediments derived from a provenance consisting of 40% TTG, 30% granite, 20% granodiorite and 10% schist.

En el presente trabajo se hace una interpretación de las condiciones de meteorización y del marco tectónico del área fuente de las rocas siliciclásticas de la Formación Morita (Cretácico Inferior) a partir de datos de geoquímica de óxidos mayores obtenidos en muestras colectadas de sus columnas de la Sierra Anibacachi y el área de Rancho Búfalo, en noreste de Sonora. La Formación Morita es una sucesión siliciclástica de origen fluvial que alcanza un espesor de 560 m en la Sierra Anibacachi y 855 m en el área de Rancho Búfalo. Geoquímicamente estas rocas se clasifican como sub-litarenita, litarenita, subarcosa y arenas-Fe. Los valores de CIA y PIA junto con el diagrama A-CN-K de las areniscas de la sección Sierra Anibacachi indican una meteorización química de baja a intensa del área de origen, mientras que los valores de CIA para limolitas y lutitas muestran una intensidad moderada en el área de origen. De igual manera, los valores de CIA, PIA y el diagrama A-CN-K sugieren que las areniscas de la sección Rancho Búfalo derivaron de un área de origen con meteorización baja a intensa, mientras que las limolitas provienen de una región con meteorización baja a moderada. Las rocas siliciclásticas de las secciones Sierra Anibacachi y Rancho Búfalo muestran grandes variaciones en valores de ICV, indicando que composicionalmente varían de inmaduras a maduras. El diagrama discriminatorio tectónico basado en función multidimensional muestra campos de colisión, arco y rift para las areniscas de la sección Sierra Anibacachi, y colisión y rift para las limolitas, mientras que para las lutitas indicó colisión. Sin embargo, la mayoría de las areniscas y limolitas de la sección Rancho Búfalo se representan en los gráficos en el campo de arco, pero algunas areniscas se ubican en el campo de colisión. Las rocas silicilásticas de las secciones Sierra Anibacachi y Rancho Búfalo muestran gran variación en los ambientes tectónicos de las rocas de origen, sin embargo, los resultados obtenidos de los diagramas de función discriminante son consistentes con la evolución tectónica regional del área de estudio.

Petrography, carbon and oxygen isotopic study was carried out to interpret isotopic variations on the predominant carbonate sequence of the Dalmiapuram Formation of the Cauvery Basin, South India. The common petrographic types identified in the Dalmiapuram Formation range from wackestone to boundstone. The gray shale and limestone members show large variations in δ13C and δ18O values (Gray shale member: +1.44 to +2.40 ‰ VPDB, −3.05 to −5.92 ‰ VPDB, respectively; Limestone member: −6.07 to +2.93 ‰ VPDB; −7.08 to −0.39 ‰ VPDB; respectively). In the present study, the carbon and oxygen values are not correlated, which supports the fact that these limestones retain their primary isotopic signatures. In carbon isotope curve, one negative shift is identified in the gray shale member and a positive isotopic excursion is detected in the coral algal limestone (CAL). The observed positive isotopic excursion in the lower part of the CAL correlates with OAE1d and suggests the global nature of the late Albian OAE1d in the Cauvery Basin.

La petrografía, composiciones isotópicas (carbono y oxígeno) y geoquímicas (elementos mayores, traza y de tierras raras en calizas de la Formación Alisitos en el área Los Torotes, Baja California fueron estudiadas con el fin de documentar las variaciones elementales entre el Miembro C (MC) y el Miembro E (ME) con la finalidad de entender las condiciones diagenéticas y depositacionales. Los principales tipos petrográficos identificados fueron mudstone, wackestone y packstone. Las calizas de la Formación Alisitos muestran notables variaciones en δ13C y δ18O (+4.13 a +5.26‰; -14.17 a -6.84‰; respectivamente). Las calizas del Miembro C (MC) muestran contenidos más altos de elementos tierra raras totales (ΣREE por su siglas en inglés) (23 ± 17, n=10) que las del Miembro E (ME) (11 ± 5.5, n=9) en la Formación Alisitos. Las variaciones observadas en los contenidos de tierras raras totales en esas calizas son debido a la cantidad de material detrítico presente en ellas. Las calizas de ME registran patrones REE+Y similares a las aguas marinas, mientras MC registra firmas distintas a las aguas marinas, es decir, tienen un significante enriquecimiento de tierra raras medias. La mayoría de las muestras analizadas de la Formación Alisitos señalan anomalías negativas de Ce (Ce/Ce*: 0.67 ‒ 0.99, n=17). Las calizas estudiadas muestran tanto anomalía positiva como negativa de Eu (Eu/ Eu*: 0.58 ‒ 2.91, n=19). Las anomalías positivas de Eu identificadas en muchas muestras podrían deberse a la influencia de fluidos hidrotermales o a la co-precipitación de sulfuro de Fe hidrotermal. Las calizas de ME exhiben patrones de REE similares a las aguas marinas lo que sugiere que las mayoría de REE presentes en estas calizas son derivadas de aguas marinas. Sin embargo, las calizas de MC fueron contaminadas por materiales detríticos los cuales ocultan efectivamente las firmas similares a las aguas marinas. El material detrítico presente en las calizas de MC se derivó probablemente de rocas fuentes máficas a félsicas.

A petrographic, carbon, oxygen and strontium study of the carbonate succession of the shallow marine Kallankurichchi and Niniyur formations of the Cauvery Basin, Tamil Nadu, India was conducted to understand the isotopic variations in seawater during Maastrichtian-Danian. The limestones from both the Kallankurichchi and Niniyur formations show large variations in Mn and Sr concentrations and high Mn/Sr ratios indicate alterations of primary isotopic signatures during shallow burial diagenesis. The limestones of both the Kallankurichchi and Niniyur formations show negative δ13C (−4.73 to −0.49‰ VPDB; −5.63 to −1.87‰ VPDB; respectively) and −18O values (−8.89 to −3.66‰ VPDB; −8.56 to −5.41‰ VPDB; respectively). The carbon and oxygen isotope composition, δ13C vs. δ18O plot and Mn/Sr ratio suggest that the measured δ13C and δ18O values have been significantly altered during diagenesis. The limestones from both the Kallankurichchi and Niniyur formations show large variations in 87Sr/86Sr values (0.709310 to 0.711962; 0.708280 to 0.708398, respectively) which are higher than 87Sr/86Sr ratios of the contemporary Lower Maastrichtian (87Sr/86Sr: 0.707760) and Danian (0.707819 to 0.707833) seawaters. The elevated 87Sr/86Sr ratios in the limestones of the Kallankurichchi Formation suggest that these limestones were significantly modified by pore fluids during meteoric diagenesis. The observed large fluctuations in 87Sr/86Sr ratios in the Niniyur Formation resulted from variations in riverine input. One sample from the Niniyur Formation exhibits an unaltered 87Sr/86Sr ratio (0.707828) which is interpreted to indicate an age of 65.02 Ma.

This study focuses on the Jurassic (Huayacocotla and Pimienta Formations) and Upper Cretaceous (Mendez Formation) shales from the Molango Region, Hidalgo, Mexico. In this article, we discuss the mineralogy, major, and trace element geochemistry of the Mesozoic shales of Mexico. The goal of this study is to constrain the provenance of the shales, which belong to two different periods of the Mesozoic Era and to understand the weathering conditions and tectonic environments of the source region.

Petrography and stable isotopes (carbon and oxygen) geochemistry of limestones from the El Abra Formation, Actopan, were studied to identify their digenetic environments. The major petrographic types identified are mudstone, wackestone, grainstone, and boundstone. Most of the studied samples show positive δ 13 C values, except two samples (2 and 28), which are slightly negative values (-0.27‰ and -0.02‰). The organic remains identified in foraminiferal wackestone type can be responsible for the negative δ 13 C values. The δ 18 O values range from -12.41‰ to -4.02‰ and indicate meteoric diagenesis.

Major, trace and rare earth element (REE) geochemistry of carbonate rocks of the Neoproterozoic Shahabad Formation, southern India were studied in order to investigate the depositional environment and source for the REEs. The PAAS (Post Archaean Australian Shale) normalized REE + Y pattern of Shahabad limestones have consistent seawater-like pattern i.e., i) LREE depletion (average (Nd/Yb)SN = 0.64 ± 0.08), ii) negative Ce anomaly, iii) positive Gd anomaly (average GdSN/Gd* = 1.05 ± 0.16), iv) superchondritic Y/Ho ratio (average Y/Ho = 38.13 ± 21.35). The depletion of LREE and enrichment of HREE are clearly indicated by the (La/Yb)SN, (Dy/Yb)SN and (Nd/Yb)SN ratios, which suggest the retention of seawater characteristics in these limestones. The negative Ce anomaly reflects the incorporation of REE directly from seawater or from the pore water under oxic condition, and also reveals the mixing of two-component systems with terrigenous clay (detrital) in the marine sediments. The terrigenous input in these limestones is confirmed by positive correlation of ΣREE with Al2O3, negative correlation of ΣREE with CaO and differences in Y/Ho ratios. V, Cr, and Sc, are positively correlated with Ti, and strong positive correlation of ΣREE with Fe2O3, Ni, Cr, Sc, and Y also indicate the presence of terrigenous materials in the Shahabad limestones.

The elemental content ( major, trace and rare earth elements) of 35 Aptian–Albian limestone samples from the Mural Formation has been determined to provide information on depositional conditions and provenance. The limestones of the Mural Formation show large variations in terrigenous and carbonate contents (1.2 to 42.3% and 57.7 to 98.8% respectively). Small variations are observed in CaO concentrations in the Tuape Shale, Cerro La Puerta and Mesa Quemada members whereas large variations are found in the Cerro La Ceja, Los Coyotes and Cerro La Espina members. The majority of the limestones show high values of Th, Sc and Zr. Large variations in ΣREE content are observed among different members of the Mural Formation. Most limestones from the Mural Formation record non-seawater-like REE+Y signatures. The limestones show large variations in Ce anomalies which may be due to mixing of sediment components (biogenic and authigenic phases) and detrital materials including Fe-colloids from fluvial input. Most of the limestones show positive Eu anomalies, but some samples show negative Eu anomalies (Eu/Eu ∗ : 0.42 to 2.62). The large variations in terrigenous percentage, high Al 2 O 3 and ΣREE contents, high La N /Yb N ratios, low Y/Ho ratios and non-seawater-like REE patterns suggest that the observed variations in ΣREE contents are mainly controlled by the amount of detrital sediments in the limestones of the Mural Formation. The limestones of the Mural Formation were deposited under both coastal and open shelf environments, and they exhibit non-seawater-like REE + Y patterns. The presence of terrigenous materials in these carbonates as contaminants effectively masks the seawater signature due to their high concentration of the REE. Thus, trying to decipher the palaeoceanographic conditions represented by ancient carbonate rocks should be done cautiously since limestones deposited under open marine environments may also be contaminated by some amount of terrigenous particles. The presence of small quantities of terrigenous materials in the limestones can also reveal source rock information. The La/Sc, La/Co, Th/Sc, Th/Cr, Th/Co and Cr/Th ratios suggest that the terrigenous materials present in the limestones were mainly derived from a nearby exposed basement of intermediate to felsic igneous rocks.

To understand the paleo-redox conditions that occurred during the Albian-Danian, we have analyzed major and trace elements from limestone samples collected from three sections of the Cauvery Basin. In the Vadugarpettai quarry section, coral algal limestone (CAL) and bedded limestone show small variations in CaO content (54.4–55.5%; 51.3–54.1%, respectively) than marl and gray shale (GS) (31.9–49.7%; 26.9–40.3%, respectively). In the Vellipirangiyam quarry section, oyster Gryphaea limestone (OGL) shows larger variations in CaO content (42.5–53.9%) than Inoceramus limestone and fossiliferous limestone (52.00–52.50%; 52.70–52.80, respectively). The concentrations of immobile trace elements (Zr and Th) varied significantly between different litho-units of the sedimentary rocks of Albian-Danian age. In addition, Al2O3 shows a positive relationship with immobile trace elements such as Zr and Th, suggesting a terrigenous origin for these elements. Enrichment of U and V contents is higher in the GS and particular intervals of CAL and marl bedded limestone (MBL) of the Vadugarpettai quarry section, lower and upper parts of the OGL of the Vellipirangiyam quarry section, and lower and middle parts of the limestone sequence of the Periakurichchi quarry section. The GS and lower part of MBL (Vadugarpettai quarry section); lower and upper parts of the OGL (Vellipirangiyam quarry section); and lower, middle, and upper parts of the Periakurichchi quarry section also show enrichment of Mo. Furthermore, high values of U/Th were noticed in the CAL and MBL of the Vadugarpettai quarry section, OGL of the Vellipirangiyam quarry section and certain intervals of the Periakurichchi quarry section. Such variations in U, V, and Mo contents and the U/Th ratio in the studied sections suggest that the Cauvery Basin experienced oxic to suboxic-anoxic conditions during Albian-Danian.

The Late Cretaceous sandstones, siltstones, claystones, and shales of the Ariyalur Group of the Cauvery Basin were analyzed for their major, trace, and rare earth elemental geochemistry. They show relatively higher percentage of K 2 O than Na 2 O, and affinity with the K-feldspar. The sandstones and siltstones are depleted in most trace elements relative to upper continental crust (UCC), except for a few elements (Ni, Cr, and Ba), which are slightly enriched. The claystone and shale samples of the Ariyalur Group are enriched in Co, Ni, Cr, and Ba as compared to UCC. The average Chemical Index of Alteration (CIA) values and the A–CN–K diagram for sandstones, siltstones, claystones, and shales suggest that these were derived from weakly to moderately weathered source rocks. Intense chemical weathering in the source area during the deposition of sandstones and shales of the upper Kallamedu Formation is indicated by higher CIA and Plagioclase Index of Alteration (PIA) values. A silicic source for rocks of the Sillakkudi, Kallankurichchi, Ottakkovil, and lower Kallamedu formations is indicated by higher ratios of SiO 2 /Al 2 O 3 , ΣLREE/ΣHREE, La/Sc, Th/Sc, Th/Co, La N /Yb N , and La/Co; lower ratios of Cr/Th and Cr/Zr; and low values of TiO 2 , Sc, Cr, and Ni as well as Eu anomalies. Immobile trace element ratios, Eu anomalies, and rare earth element (REE) patterns strongly support that tonalitic gneiss, granodiorite, and granitic rocks of the Dharwar Craton could be the source rocks for most of the Ariyalur Group. REE modeling suggests that the average composition of the Sillakkudi, Kallankurichchi, Ottakkovil, and lower Kallamedu formations represents a mixture of sediments derived from a provenance consisting of 60% tonalitic gneiss, 25% granodiorite, and 15% granite. The upper Kallamedu Formation, however, shows a distinct variation in REE pattern together with high values of Cr and Ni and high Cr/Th ratios, and suggests some variation in the source rocks. The mixing calculations reveal that the average upper Kallamedu rocks can be represented by a mixture of 40% tonalitic gneiss, 30% basalt, 25% granodiorite, and 5% granitic rocks. Hence, the observed geochemical variations in the upper Kallamedu Formation could have been influenced by the Deccan Trap volcanism.

Quartz grains from the Kallamedu (late Maastrichtian) and lower Niniyur (Danian) Formations, Cauvery Basin, Southeast India were examined under a scanning electron microscope, and twenty three distinct microtextures were observed. These microtextures have been grouped into three modes of origin, viz. mechanical (thirteen features), mechanical and/or chemical (five features) and chemical (five features) origins. Quartz grains from the Kallamedu and lower Niniyur Formations show conchoidal fractures, straight steps and arcuate steps which are the characteristic microtextures of quartz grains derived from crystalline source rocks. Quartz grains from the upper Kallamedu and lower Niniyur Formations show angular to subangular outline, whereas those from the lower Kallamedu Formation show subangular to rounded outline. The dominance of angular to subangular grains and the presence of straight and arcuate steps suggest that these clastic sediments were undergone short transportation and rapid deposition. The presence of rounded grains in the lower part of the Kallamedu Formation suggests that significant amounts of quartz grains are of recycled origin. Vs, straight scratches and curved scratches, the characteristic features of marine environment, are common on the quartz grains from the lower Niniyur Formation, which is consistent with the previous interpretation. However, quartz grains from the lower Kallamedu Formation exhibit very low frequency of these features, whereas they are moderately present in the upper Kallamedu Formation, suggestive of a change in depositional conditions with time. The lower Kallamedu Formation exhibits planar and trough cross-beddings, which suggests the fluvial depositional environment. The unfossiliferous upper Kallamedu Formation contains appreciable amount of illite and mixed-layer (illite/smectite) clay minerals, which suggests that the saline conditions prevailed during its deposition. Microtextures on the quartz grains coupled with dominant clay mineral types suggest the deltaic depositional environments for the upper Kallamedu Formation.

Concentrations of major, trace, and rare-earth elements (REE) were measured in shallow marine limestone samples of the upper Miocene Kudankulam Formation, southern India, in order to investigate the geochemical variations among various litho-units. The CaCO3 content is higher in algal limestone (AL; 92 ± 1, n = 3) and clastic limestone (CL; 90 ± 2, n = 3) than sandy shell limestone (SSL; 81 ± 1, n = 3). All trace elements exhibit lower concentrations than post-Archean Australian Shale (PAAS) values, except one SSL sample. Large variations in ΣREE content are observed among CL, SSL, and AL (~14-142, ~68-124, and ~38-98, respectively). Almost all limestone samples analyzed from the Kudankulam Formation show a small negative cerium anomaly (Ce/Ce* ~0.8-0.9), except one AL sample, which lacks this cerium anomaly (Ce/Ce* ~1.04). Variations in Ce anomalies and ΣREE contents in Kudankulam limestone samples are mainly controlled by the amount of terrigenous sediments and diagenetic behavior. Shale-normalized REE ...

Clay mineral analyses were carried out on late Maastrichtian–early Palaeocene (Cretaceous–Tertiary) sedimentary rocks in the Ariyalur area of the Cauvery Basin (southeastern India). These investigations were aimed at determining the sedimentary provenance and palaeoclimate of the area in the latest Cretaceous and earliest Tertiary. The late Cretaceous deposits show significant palaeogeographic variation in clay mineral contents across the study area. Mixed-layer illite-smectites dominate the clay mineral content of the uppermost Maastrichtian of all areas, with elevated smectite, illite, palygorskite, sepiolite, kaolinite and chlorite occurring at intervals through the succession. This combination and widespread variation in the clay mineral suite suggests a lithologically highly variable source terrain and lack of sediment mixing during transport. Mixed-layer clays occur with both kaolinite and palygorskite, interpreted in terms of a seasonal (warm and wet, warm and dry) source area. The uppermost Maastrichtian of the Niniyur section displays an upward increase in illite content, suggesting that the adjacent continental area became strongly influenced by physical weathering just prior to the K/T boundary. The return of mixed-layer clays, smectite, illite and kaolinite during the early Tertiary suggests that chemical weathering in a seasonal climate once again controlled the formation of clay minerals. These results imply that the volcanism associated with the Deccan Traps had no sudden effect on the Cretaceous or Tertiary sedimentation and clay mineralogy of this area.

A carbon, oxygen and strontium isotopic study on the predominantly carbonate succession of the shallow marine Mural Formation in the Cerro Pimas locality of northern Sonora (Mexico) was undertaken to understand isotopic variations in seawater during Aptian- Albian time. Petrographic study has been carried out on these limestones to support the isotopic study. The limestones show low content of TOC, both negative and positive δ13C values (-4.1 to +2.2‰ VPDB) and d18O values varying from -13.4 to -8.9‰ VPDB. The carbon isotope composition, δ13C vs δ18O plot and Mn/Sr ratio suggest that the δ13C measured values are primary in nature and remain unaltered during diagenesis. The carbon isotope curve shows a positive δ13C excursion followed by a negative event in the lower part of the Los Coyotes Member (Lower Albian) of the Mural Formation and confirm the global nature of the episode OAE 1b in the Cerro Pimas section. The 87Sr/86Sr ratios for limestones of the Mural Formation (0.707221 to 0.707340) are similar to the ratios for Late Aptian and Early Albian seawater (0.70726 to 0.70740). In addition, 87Sr/86Sr age of the Cerro La Ceja member (113.4 Ma; Late Aptian age) is comparable to that of published zircon radiometric age. The numerical age of Los Coyotes (112.0 Ma and 111.1 Ma) and Cerro La Espina (110.9 Ma and 110.7 Ma) members indicate also Early Albian age. The whole-rock Sr isotope ages in this study are consistent with the previously published radiometric and biostratigraphic ages.

"Beach sand samples collected from two localities of the Gulf of California (Puerto Peñasco and Bahia Kino, Sonora) were analyzed in order to identify their provenance and depositional history on the basis of the different microtextures on the quartz grains. The quartz grains were examined under a scanning electron microscope which brought out thirty two distinct microtextures that can be grouped into three modes of origin, i.e., mechanical (eighteen features), mechanical and/or chemical (five features) and chemical (seven features) origin. Among nine microtextures of chemical origin, two features are of dissolutional origin, whereas five features are characteristic of precipitational origin. Most of the microtextures are common in both areas (Puerto Peñasco and Bahia Kino) but frequency of occurrence slightly varies. Quartz grains from Puerto Peñasco and Bahia Kino show conchoidal fractures, straight steps and arcuate steps, which are characteristic features of quartz grains derived from crystalline source rocks. The presence of angular to subangular outline together with straight and arcuate steps indicates that these sediments have undergone short transportation and rapid deposition. V-shaped patterns, straight scratches and curved scratches, which are characteristic features of marine environments, are common on the quartz grains of the analysed samples. Many quartz grains show subrounded outline with bulbous edges that are considered to be the product of fluvial transport. In addition, many quartz grains show subrounded to rounded outline, upturned plates and meandering ridges, which indicate that aeolian mechanisms controlled the transport of these grains. Some quartz grains show chemical precipitational features such as silica globules, silica flower, silica pellicle and trapped diatoms, which suggest that these quartz grains were derived from the silica saturated environments of intertidal zones. The present study reveals the following inferences: 1) the beach sediments in Puerto Peñasco area were transported to the area by fluvial and aeolian processes and subsequently deposited in the marine environment, and 2) the beach sediments in the Bahia Kino area were dominantly transported by fluvial processes, whereas subordinate quantity were contributed by aeolian processes and subsequently deposited in the marine environment."

"Major, trace and rare earth elements (REE) study was carried out on the Lower Cretaceous Dalmiapuram Formation in southeastern India in order to understand the geochemical variations among various litho-units. Coral algal limestone (CAL) shows high content of CaO (53 ± 0.5, n=4) than the bedded limestone (BL) (42 ± 2, n=4) and gray shales (GS) (19 ± 6, n=3). The limestones are depleted in most of the trace elements when compared with the Post-Archean Australian Shale (PAAS). Likewise, gray shales are also depleted in many trace elements (Co, V, Rb, Ba, Zr, Y, Nb, Hf and Th), whereas few elements (Ni, Cr, Sr, Pb and U) show similar concentrations with respect to PAAS. The observed large variations in ¿REE contents among CAL (18 ± 8, n=4), BL (59 ± 17, n=4) and GS (157 ± 49, n=3) are mainly due to the amount of terrigenous matter present in them. The Eu and Ce anomalies were calculated from the PAAS-normalized values. The limestones (CAL and BL) and gray shales show small variations in Eu anomalies (Eu/Eu*: 1.23 ± 0.10, n=4, 1.16 ± 0.10, n=4 and 1.17 ± 0.10, n=3, respectively). The observed positive Eu anomalies in the limestones and gray shales may be due to the presence of plagioclase feldspar. The CAL shows a negative Ce anomaly (Ce/Ce*: 0.90 ± 0.06, n=4) whereas BL shows a positive Ce anomaly (Ce/Ce*: 1.05 ± 0.14, n=4; except KI15) and gray shales show no Ce anomalies (Ce/Ce*: 0.98 ± 0.02, n=3). Variations in Ce anomalies in these limestones may be due to the mixing between sediment components and a seawater end member. The characteristics of non-seawater-like REE patterns, elevated REE concentrations, high LaN/YbN ratios and low Y/Ho ratios, suggest that the observed variations in ¿REE contents are mainly controlled by the amount of detrital sediments in the limestones of the Dalmiapuram Formation. The REE patterns and La/Sc, La/Co, Th/Co, Th/Cr, Cr/Th, and Th/Sc ratios suggest that the terrigenous materials present in the Dalmiapuram Formation were mainly derived from intermediate to felsic rocks. The limestones (CAL and BL) show positive values of Mn* and low V/(V+Ni) ratios (¿0.50) suggesting that these limestones have been deposited under oxic condition whereas gray shales show negative Mn* values and high V/(V+Ni) ratios (¿ 0.50) which support that these shales were deposited under reducing conditions."

The Albian-Danian limestones of Cauvery Basin show a wide range of d13C and d18O values (–13.2 to +1.1% and –9.0 to –2.5%, respectively). The cement samples show negative carbon and oxygen isotope values (–18.9 to –3.9% and –9.0 to –4.3%, respectively). The petrographic study reveals the presence of algae, molluscs, bryozoans, foraminifers and ostracods as major framework constituents. The limestones have microspar and equant sparry calcite cements. The pore spaces and vugs are filled with sparry calcite cement. The bivariate plot of d13C and d18O suggests that most of the samples fall in the freshwater limestone and meteoric field, while few samples fall in the marine limestone and soil calcite fields. The presence of sparry calcite cement, together with negative carbon and oxygen isotope values, indicates that these limestones have undergone meteoric diagenesis.

La sucesión sedimentaria del Grupo Cabullona que aflora en la región de Naco en el noroeste de Sonora, fue acumulada en la parte norte de la cuenca del mismo nombre durante el Cretácico Tardío. Esta sucesión que alcanzan un espesor de 2.5 km y su edad se constriñe entre 73 y 72 Ma, se divide en varias formaciones que incluyen la Formación Corral de En medio y la Arenisca Camas. En este trabajo se reporta un estudio geoquímico de las areniscas de la Formación Corral de Enmedio y de la Arenisca Camas con el fin de interpretar su paleometeorización, procedencia y marco tectónico. El rango en los contenidos de ΣREE va de 96 a 144 ppm para las areniscas de la Formación Corral de Enmedio y de 74 a 169 ppm para las de la Arenisca Camas. Los diagramas de REE normalizados con condrita para las areniscas de ambas formaciones tienen patrones de enriquecimiento en LREE, un patrón relativamente plano para las HREE y anomalía negativa de Eu. Los valores de CIA y PIA y el diagrama A–CN–K indican que las areniscas de la Formación Corral de Enmedio se derivaron de un área fuente que estaba sujeta a un bajo grado de meteorización química, mientras que las de la Arenisca Camas revelan meteorización química de intensidad baja a moderada en el área fuente. Las relaciones Al2O3/TiO2, así como diagramas bivariados y ternarios, comparaciones de patrones REE con patrones de rocas fuentes y cálculos de mezcla indican que las areniscas de la Formación Corral de Enmedio fueron derivadas predominantemente de rocas fuente de composición félsicas con una menor contribución de rocas de composición química intermedia, pero los sedimentos de la Arenisca Camas fueron derivados de las rocas fuente de composición félsicas.