Ferruginous Deposits Research Articles

Characteristics, distribution, and origin of ferruginous deposits within the Late Ordovician glaciogenic setting of Arabia

Ferruginous deposits are iron-rich sediments or sedimentary rocks found in various sizes, shapes, and compositions within sedimentary strata in different depositional settings. This study investigates the characteristics, distribution, and origin of ferruginous deposits found in the Late Ordovician glaciogenic Sarah Formation and surrounding deposits in central Saudi Arabia. Several types of ferruginous deposits have been identified through field observations and laboratory investigations, including thin-section petrography, geochemical, surface, and bulk mineralogical analyses, and computed tomography scans. The identified ferruginous deposits include solid and rinded concretions, pipes, layers, ferricretes, liesegang bands, and fracture infills. They were associated with the periglacial and proglacial facies of the Sarah Formation. For instance, ferruginous deformed layers were mainly observed in subglacial facies, while rinded concretions occurred in bleached glaciofluvial facies. Ferruginous deposits were also found in the uppermost parts of non-glacial facies, such as the shallow marine Quwarah Member of the Qasim Formation and the braided deltaic Sajir Member of the Saq Formation. Compositionally, goethite was the dominant iron oxide mineral in all ferruginous deposits, and it is mostly distributed as cement, filling pore spaces. In comparison to ferruginous deposits reported in different depositional settings on Earth and Mars, the studied ferruginous deposits in an ancient glaciogenic setting exhibit different mineralogical characteristics. Specifically, the studied solid concretions are less abundant and primarily amalgamated, while the rinded concretions appear to be more mature than those reported in other depositional environments. This study suggests that the weathered basement rocks of the Arabian Shield were the primary source of iron. The iron-bearing rocks were eroded and transported by Hirnantian glaciation and deglaciation processes.

Features of soils of the natural park “Scherbakovsky” Volgograd region

The paper presents the results of a study of the soil cover of the Shcherbakovsky Nature Park in the Kamyshinsky district of the Volgograd region. To achieve the results 12 soil sections were laid along the studied soil catena (1.5 km), so that morphological and chemical features of the soils of the study area were investigated. Variety and diversity are due to vertical zonality and geological and hydrological peculiarities. So, in the gullies and in massive forest plantations various dark humus and gley soils have become widespread. On steppe, slope and watershed areas lithosolic light humus luvisols and light humus lithozems were formed. On areas with open sand surface, humus psammozems with protohumus horizons W, as well as light humus (AJ-C) and humus soils (A-C), and a variety of soil-forming rocks of the natural park were found. In relief depressions they are represented mainly by gleyed sandy, as well as proluvial-deluvial deposits with inclusions of large fragments of opokas. On steppe and steep-slope areas, the soil-forming rocks are thick layers of opoka deposits. Their upper boundary varies from 20 to 60 cm depth depending on the meso- and microrelief. On the watersheds, the soilforming rocks are represented by sandy, ferruginous deposits with new formations of clay and pseudofibres. The parent rock is registered starting from 100 cm depth and consists of large blocks of hardened sandstone. The chemical properties of the studied soils are characterized by a neutral or slightly acidic pH. Easily soluble salts are leached from all soil horizons. The maximum values of Сorg are typical of humus and transitional horizons. The studies conducted in the Shcherbakovsky Nature Park are of greatest importance for monitoring the state of soils, and also allowed us to identify the features of the genesis of underdeveloped soils and luvisols of the dry-steppe natural zone.

Geochemistry and Mineralogy of Rare-Earth Elements in Ferruginous Deposits and Bottom Sediments of the Laptev Sea

Abstract —The geochemical and mineralogical aspects of the distribution of rare-earth elements (REE) in ferruginous deposits (FD) and bottom sediments of the southeastern Laptev Sea are analyzed. The FD are dominated by biomorphs developed after polychaete tubes. The REE patterns depend on the proportion of ore and non-ore substances. The ore substance is represented mainly by iron hydroxides (limonite). It is a product of suboxic diagenesis enhanced by bioturbation and determines the slight enrichment of FD in MREE and cerium deficiency (Cean = 0.94). The non-ore substance comes from terrigenous sediments and has an (alumino)silicate composition. It controls the scandium content and is the source of REE mineral grains, among which monazite-(Ce) prevails. The sediments demonstrate a common similarity in REE patterns to shales and suspended material transported to the Laptev Sea by the Lena River, with elevated LREE and MREE contents and the value of Ce anomaly almost equal to unity (Cean = 1.06). In the sediments, REE minerals occur mostly in the silt fraction (<63 μm in size). The high content of organic matter (Corg of up to 2.15%) of predominantly terrigenous origin (OMter of up to 85%) in the sediments explains the oxygen deficiency and weak diagenetic mineral formation with low accumulation of trace elements, including REE, in the FD. The total REE content in the FD is lower than that in the sediments (on average, 173 ppm against 206 ppm).

A one-million-year isotope record from siderites formed in modern ferruginous sediments

Abstract Ancient iron formations hold important records of environmental conditions during the Precambrian eons. Reconstructions of past oceanic systems require investigation of modern ferruginous analogs to disentangle water column and diagenetic signals recorded in iron-bearing minerals. We analyzed oxygen, iron, and carbon isotopes in siderite, a ferrous carbonate phase commonly used as an environmental proxy, from a 100-m-long record spanning a 1 Ma depositional history in ferruginous Lake Towuti, Indonesia. Combining bulk sediment and pore water geochemistry, we traced processes controlling siderite isotope signatures. We show that siderite oxygen isotope compositions (δ18O) reflect in-lake hydrological and depositional conditions. Low iron isotope values (δ56Fe) record water column oxygenation events over geological timescales, with minor diagenetic partitioning of Fe isotopes by microbial iron reduction after deposition. The carbon isotope compositions (δ13C) reflect the incorporation of biogenic HCO3–, which is consistent with sediment organic matter remineralization lasting over ca. 200 ka after burial. Positive δ13C excursions indicate an increased production of biogenic methane that escaped the sediment during low lake levels. Diffusion across the sediment–water interface during initial formation of siderites tends to align the isotope signatures of bottom waters to those of pore waters. As microbial reduction of ferric iron and oxidation of organic matter proceed and saturate pore water conditions with respect to siderite, overgrowth on nuclei partially mutes the environmental signal inherited from past bottom waters over ca. 1 Ma. Because high depositional fluxes of ferric iron and organic matter in early oceans would have promoted similar microbial processes in ferruginous deposits prior to lithification, the environmental record contained in siderite grains can successively integrate depositional and early diagenetic signals over short geological timescales.

Mineralogical and hydrogeological study of "pouhons" in the lower Palaeozoic formations of the Stavelot-Venn Massif, Belgium

Numerous naturally CO2-rich mineral water springs, locally called pouhons, occur in the Stavelot-Venn Massif. These water springs show a particular composition with a high content of iron, manganese and lithium, and are characterised by a red-orange colour resulting from iron hydroxide precipitation near the land surface. Radon measurements have shown that these ferruginous deposits are weakly radioactive. The Upper Cambrian black shales of the La Gleize Formation are also known to display radioactive anomalies. These rocks show enrichment in HFSE (Pb, U, Y, Ce, Zr, Ti, Nb) and are depleted in transition metals (Co, Ni, Cu, Zn). Specific minerals such as florencite-(Ce), monazite-(Ce), xenotime-(Y) and zircon have been identified and are probably at the origin of the radioactive anomalies. Uranium was gradually leached from these minerals, transported in solution, and finally concentrated in ferruginous muds. These muds are mainly composed of goethite (most often amorphous), residual quartz and calcite in some samples. The most probable hypothesis is that uranium is adsorbed in small concentrations on the goethite surface. On the other hand, the Ottré Formation (Ordovician) appears to be the main source of lithium, iron and manganese. Pouhon waters have therefore probably leached rocks of various mineralogy and chemical composition during their sub-surface circulation.

Geochemical background concentrations of potentially toxic elements in soils of the Carajás Mineral Province, southeast of the Amazonian Craton.

The objective of this study was to establish background concentrations of potentially toxic elements (PTEs) in soils from the Carajás Mineral Province (CMP), southeastern Amazonian Craton. The PTEs Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, and Zn were digested in microwaves and quantified by optical emission spectrometry (ICP OES). The variability of physical-chemical and mineralogical attributes contributed to variation in PTE concentrations. High background concentrations of Al, Fe, Cr, Mn, Mo, Ni, Ti, and V and, in particular, the PTE concentrations of Cd, Cu, Cr, Ba, and Co were greater than the prevention values defined by the Brazilian National Council of Environment. Soil quality reference values (QRVs) were greater than those determined for most Brazilian states and soils in the state of Pará. The high background concentrations and QRVs of PTEs show that the region is strongly influenced by the source material, rich in ferruginous deposits and other associated minerals. The results are an important tool for establishing soil quality standards and public policies for environmental protection in regions naturally PTE enriched.

Symbiotic Association of the Bivalve Tellimya fujitaniana (Galeommatoidea) with the Heart Urchin Echinocardium cordatum (Spatangoida) in the Northwestern Pacific.

The bivalve Tellimya fujitaniana ( Yokoyama, 1927 ) (Galeommatoidea, Heterodonta) was described based on a fossil shell. Until now, the biology of living animals has not been reported. In this study, we found T. fujitaniana in a commensal relationship with the heart urchin Echinocardium cordatum (Pennant, 1777) (Spatangoida, Echinoidea) on the intertidal mud flats of the Seto Inland Sea, Japan. We investigated the morphology, host associations, and reproductive biology of this bivalve species. The elongate-ovate shell is covered by a reddish-brown ferruginous deposit. The mantle is exposed anteriorly to form a temporal siphon, while posteriorly one pair of short tentacles is exposed. Small individuals (shell length, SL, ≤ 2.1 mm) were attached to the host's body surface; middle-sized individuals (SL 3.0-3.2 mm) were attached to or stayed close to larger T. fujitanianathat were living freely in the host burrow. Nearly all the large individuals (SL ≥ 4.8 mm) lived freely in the host burrow, behind the urchin. This suggests that the host utilization pattern of T. fujitanianachanges with development. Specimens with SL ≥ 4.8 mm had mature gonads, mostly occupied by ova, and some individuals were brooding eggs or veliger larvae in the gills. This species was previously assigned to Fronsella. However, the morphology and ecology of this bivalve are very similar to those of Tellimya ferruginosa (the type species of the genus Tellimya) in the northeastern Atlantic Ocean. Thus, we have reassigned this species to genus Tellimya. We also confirmed that T. fujitaniana and T. ferruginosa can be genetically distinguished using the mitochondrial COI gene.

Planktonic marine iron oxidizers drive iron mineralization under low-oxygen conditions.

Observations of modern microbes have led to several hypotheses on how microbes precipitated the extensive iron formations in the geologic record, but we have yet to resolve the exact microbial contributions. An initial hypothesis was that cyanobacteria produced oxygen which oxidized iron abiotically; however, in modern environments such as microbial mats, where Fe(II) and O2 coexist, we commonly find microaerophilic chemolithotrophic iron-oxidizing bacteria producing Fe(III) oxyhydroxides. This suggests that such iron oxidizers could have inhabited niches in ancient coastal oceans where Fe(II) and O2 coexisted, and therefore contributed to banded iron formations (BIFs) and other ferruginous deposits. However, there is currently little evidence for planktonic marine iron oxidizers in modern analogs. Here, we demonstrate successful cultivation of planktonic microaerophilic iron-oxidizing Zetaproteobacteria from the Chesapeake Bay during seasonal stratification. Iron oxidizers were associated with low oxygen concentrations and active iron redox cycling in the oxic-anoxic transition zone (<3μm O2 , <0.2μm H2 S). While cyanobacteria were also detected in this transition zone, oxygen concentrations were too low to support significant rates of abiotic iron oxidation. Cyanobacteria may be providing oxygen for microaerophilic iron oxidation through a symbiotic relationship; at high Fe(II) levels, cyanobacteria would gain protection against Fe(II) toxicity. A Zetaproteobacteria isolate from this site oxidized iron at rates sufficient to account for deposition of geologic iron formations. In sum, our results suggest that once oxygenic photosynthesis evolved, microaerophilic chemolithotrophic iron oxidizers were likely important drivers of iron mineralization in ancient oceans.

An in situ shelly fauna from the lower Paleozoic Zapla diamictite of northwestern Argentina: Implications for the age of glacial events across Gondwana

A shelly fauna from the upper part of the Zapla glacial diamictite includes the lingulate brachiopod Orbiculoidea radiata Troedsson, the rhynchonelliforms Dalmanella cf. testudinaria (Dalman) and Paromalomena sp., the bivalve Modiolopsis? sp., and the trilobite Dalmanitina subandina Monaldi and Boso. Both taphonomic and paleoecologic data indicate a lack of transport reflecting the original community. The assemblage is closely comparable to the widespread latest Ordovician Hirnantia-Dalmanitina fauna. The Hirnantian age of the Zapla diamictite is further corroborated by the record of the northern Gondwana chitinozoans Spinachitina cf. oulebsiri Paris and Desmochitina minor typica Eisenack. The graptolites and chitinozoans from the overlying Lipeón Formation indicate that the postglacial transgression took place in the earliest Llandovery (Parakidograptus acuminatus Biozone). According to the tectonosedimentary evidence, the Early Silurian age of the Cancañiri and San Gabán diamictites of north–central Bolivia and south Peru based on their palynological record is more likely the age of posglacial gravity flows and not that of the glaciation. We support the hypothesis that the weakly lithified glacigenic deposits of Hirnantian age were reworked and redistributed by high-energy marine processes during the postglacial transgression and then transported to the adjacent deep-marine trough. Iron-rich horizons have been recognized in many basins of southern South America reflecting eustatic and paleoclimatic fluctuations. Most of them formed during the early stages of the postglacial transgression at the Ordovician/Silurian transition and are associated with low sedimentation rates and condensed intervals. The mild maritime postglacial climate, the increasing atmospheric CO2, and possibly the presence of incipient vegetated areas led to extensive weathering of glacigenic sediments supplying iron into the marine system to form ferruginous deposits. The sea level fall related to the peak of glaciation is recorded by both paleovalley incision and a sharp subaerial to subglacial unconformity. The transgressive systems tract starts with fluvio-estuarine deposits within incised valleys followed by widespread deposition of subtidal to open marine organic-rich shales onlapping regionally the basement rocks. The recognition of key stratigraphic markers (e.g. sequence boundary, flooding surface, ferruginous beds), alongside reliable micro and macropaleontological evidence allow a more accurate correlation between the Central Andean Basin of Peru, Bolivia and NW Argentina, the W Puna region, the Paraguayan and Brazilian sectors of the Paraná Basin, the Precordillera Basin of W Argentina, and the Cape Basin of South Africa.

Early Cretaceous Paleoclimate Characteristics of China: Clues from Continental Climate‐indicative Sediments

AbstractThe Cretaceous was one of the most remarkable ‘greenhouse’ climate periods in geological history. Most of the reported studies of the Cretaceous paleoclimate are based upon marine sedimentary records. Large spatial scale paleoclimatic reconstruction, which has a higher time resolution based upon continental sediments in China, is rarely found. This study presents paleoclimate reconstruction for the six time periods of the Early Cretaceous in China by employing continental climate‐indicative sediments, including calcareous deposits, coal, oil shale, gypsum, halite, desert sedimentary systems, ferruginous deposits and laterite, copper‐bearing deposits, limestone and dolomite. Based on the distribution of the association of climate‐indicative sediments and the influences of paleotopography and orogenic belts (or important structural belts) on climate, seven climatic zones have been identified: 1) a warm and humid zone; 2) a warm and humid‐warm and arid zone; 3) a warm and arid zone; 4) an arid and hot zone; 5) the Tibet hot and humid zone; 6) a hot and arid‐semiarid zone; and 7) a hot and humid‐hot and arid one. It is found that the Early Cretaceous climatic zones of China were nearly latitudinally distributed from northwest to southeast. The arid‐hot climatic zone expanded in the Aptian, suggesting that a hotter and drier climate prevailed in later period of the Early Cretaceous. Conversely, the humid climatic zone expanded in the Albian, indicating that a wetter climate appeared at the end of the Early Cretaceous. The overall distribution pattern of the seven climatic zones indicates that a hot‐warm and arid climate was predominant in China; this coincides with a global ‘greenhouse climate’ background. However, palaeogeographic features and specific geologic events, such as the existence and disappearance of the eastern high plateau, and the uplift and denudation of Yinshan, Yanshan, Tianshan, Qinling and Dabie Mountains, led to distinctive regional climatic features of the Cretaceous in China.

Natural radionuclides and activity concentrations in the calcareous and ferruginous deposits of hot springs in Akita and Aomori Prefecture

Natural radionuclides and activity concentrations in the calcareous and ferruginous deposits of hot springs in Akita and Aomori Prefecture

A study on the interaction between ferric ion and silicic acid in hydrosphere: Si-containing ferruginous deposits formed in neutral hot spring waters

Five ferruginous deposit samples formed from neutral hot springs were analyzed to determine whether they consisted of a mixture of silica, hydrous iron oxide or iron silicate by differential thermal analysis (DTA), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), and 57Fe Mossbauer spectroscopy. The Si/Fe atomic ratios of the deposits ranged from 0.25 to 0.45, and were smaller than those of hisingerite (1–2), but apparently close to those of siliceous ferrihydrite (0.25–0.5). Si was confirmed to be present as monomeric or oligomeric silicate from the Si-O stretching vibration frequencies on the IR spectra. Judging from the results of DTA, which minerals starting to produce after heating, and a relationship between Si-O stretching vibration frequency and Si/Fe atomic ratio proposed by Henmi et al. (1981), all the deposits in this study were concluded to be mixtures of various siliceous ferrihydrites with low and high Si/Fe atomic ratios. Moreover, by comparing the chemical properties of hot spring waters, the formation conditions of siliceous ferrihydrite were also discussed.

Palaeoenvironmental implications of ferruginous deposits related to a Middle–Upper Jurassic discontinuity (Prebetic Zone, Betic Cordillera, Southern Spain)

The Middle–Upper Jurassic boundary in the westernmost Tethyan basins is marked by a discontinuity. A thin iron crust with ferruginous ooids and pisoids and an overlying ferruginous oolitic limestone lithofacies occur in a genetic relationship to this discontinuity with a reduced thickness (< 50 cm) and very local distribution in the Prebetic Zone (Betic Cordillera). The ferruginous coated grains are subdivided into two types. Type A ooids are characterised by thin, regular lamination in concentric layers enclosing a nucleus; they are dominant in the top of the iron crust (100% of the ferruginous ooids) and in the ferruginous oolitic limestone (82%). Type B ooids typically have thick, irregular lamination in a few discontinuous concentric layers enclosing a variable nucleus including bioclasts and foraminifera; they are exclusive to the ferruginous oolitic limestone (18% of the ferruginous ooids). The bulk chemical composition varies between 80% Fe 2O 3 by weight in the iron crust and 67% by weight in the coated grains. In the ferruginous ooids, the contents in SiO 2 (5.4%), Al 2O 3 (6.5%), P 2O 5 (3.6%), and CaO (4.7%) are higher than in the crust. Trace elements (V, Cr, Co, Ni, Zn, Y, Mo, and Pb) in both the crust and ooids show enriched values compared with the bulk composition of the upper continental crust. The mineral composition of the iron crust and ooids is primarily goethite, with small amounts of Al-hydroxide (bohemite) and apatite, whereas hematite is identified only in the iron crust. The Type A ooids are interpreted as having an origin related to the iron crust. Since there is no evidence to support a marine genesis for the iron crust, the possibility of a subaerial origin is presented here. The crust has characteristics (chemical and mineralogical composition) similar to those of ferruginous pisolitic plinthite (highly weathered redoximorphic soil), and goethite shows an Al-substitution range (5–10 mol%) that indicates pedogenic conditions. Soil processes under periodic hydrous conditions are suggested; groundwater soils with hydrous conditions are congruent with the formation of the Type A ferruginous ooids and pisoids. In this situation, a coastal plain with periodically flooded soils would be the likeliest scenario. Callovian shallow carbonate shelf was possibly emerged and weathered, followed by marine sedimentation during the Middle Oxfordian, associated with major flooding of the Prebetic shelf and the erosion of ferruginous pisolitic plinthite. The first marine deposit was ferruginous oolitic limestones. Fragments of iron crust and Type A ferruginous ooids were reworked and incorporated into the marine sediments. A second phase of ferruginous ooids (Type B) with clear marine features developed, benefiting from iron-rich microenvironments due to the redistribution from iron crust fragments and Type A ferruginous ooids.

A Medieval Bloomery Mound in Glen Docherty, Kinlochewe, Highland

Summary An iron-working bloomery mound was excavated by CFA Archaeology Ltd in 2004 at the head of Glen Docherty, near Kinlochewe, Achnasheen, Highland. A mound of waste material was excavated and dated to the 15th–17th centuries on the basis of radiocarbon analysis. A solidified bed of ferruginous deposit was revealed during the bloomery mound excavations but was found to be of an earlier date (1050–1285 AD). There was no further evidence for metalworking installations. A charcoal-burning platform was also excavated in Glen Docherty in 2005 and radiocarbon dated to the 15th–17th centuries. The above provide evidence for a long involvement with iron making in this part of the western Highlands and prior to the 17th century when the area, and the north shore of Loch Maree in particular, became known as the location for the installation of the first charcoal-operated blast furnace in Scotland.

Precipitation of iron in a poorly drained alluvial soil

Abstract Ferruginous deposits from the outfall and backfill of a newly‐installed drainage scheme in a poorly drained alluvial soil have been characterised using selective chemical dissolution, X‐ray diffraction, and chemical analysis and compared with the iron (Fe) deposits found in various micro‐environments within the soil profile. In the drainage ditch and on the permeable backfill around the drainage pipes, the mineralogy of the ferruginous deposits is dominated by the poorly ordered mineral, ferrihydrite, whereas within the soil environment the hydrous iron oxides display a wider range of structural order. It is probable that the initial precipitation product is poorly‐ordered material but that within the soil transformation to a more well ordered mineral, goethite, can occur.

Tethyan ferromanganese oxide deposits from Jurassic rocks in Hungary

Fossil manganese nodules and encrustations from ‘seamount’ and ‘basin’ localities in the Transdanubian Central Mountains of Hungary are lithologically, mineralogically and chemically similar to some modern marine ferromanganese oxide deposits, and show no evidence of postdepositional changes other than cementation. Five groups of deposits were encountered: Fe/Mn nodules, encrusted shells, pavements, stains, and Fe oxide encrusted intraclasts, the first three of which are specific to the 'seamount' environment and the last to the ‘basins’. Optical and electron microprobe investigation of the samples shows them to exhibit many similarities with modern ferromanganese oxide deposits, and that many of the nodules are surrounded by a halo of dispersed ferromanganese oxides, strongly suggesting that they continued to accrete metals through the pore waters of unlithified sediments for a period after burial. By contrast, pavements which appear to have grown on hardgrounds at the sea floor show little or no evidence of derivation of metals from underlying sediments. Geochemical investigations on the deposits show the ‘seamount’ varieties to be closer in composition to most modern nodules and crusts than the ‘basin’ varieties, and that the latter are essentially manganese and trace-element-poor ferruginous deposits. Nevertheless, all can be more or less compositionally equated with modern ferromanganese oxide deposits forming in marginal Atlantic environments, which would be in accord with the proposed depositional environment of the Transdanubian Central Mountains based on other evidence

Origin and composition of the ferruginous oolites and laterites of North-Western Nigeria

The ferruginous deposits of north-western Nigeria occur extensively capping sediments which outcrop over thousands of square kilometers. These deposits could be subdivided into 3 major groups: i) Ferruginous oolites; ii) Crusty/Concretionary laterites; iii) Ferruginous sandstones.

Aspects of Mesozoic Shelf in Western Europe: ABSTRACT

During the Mesozoic, the major paleogeographic units of western Europe were the Tethyan Ocean on the south, where predominantly calcareous marine sediments were deposited, and a shelf zone on the north, where dominantly arenaceous and argillaceous marine sediments and nonmarine intercalations were deposited. Clear-cut distinctions cannot be made between the two units because of gradational changes and fluctuations in space and time. An additional complicating factor is the fact that in some parts of the section, particularly in lower Mesozoic strata, extensive Tethyan deposits on the margins of the present-day Meditteranean apparently were laid down in shallow water. Within the areas of sedimentation there can be distinguished a series of basins, such as the Lower Saxony, Paris, and Wessex basins, characterized by relatively thick, continuous sequences, and swells which are areas of relatively thin, discontinuous sequences which in many places correspond to the margins of Precambrian or Paleozoic massifs, e.g., Scandinavia, Scottish Highlands, Brittany, Massif Central, and Harz Mountains. These massifs were transgressed by the sea only to a limited extent before Late Cretaceous time. The Triassic of the northern shelf zone is composed largely of continental redbeds with subordinate evaporites. However, there is a marine intercalation, the Muschelkalk, between the Bunter and Keuper of Germany and the southern North Sea region. The Muschelkalk consists of limestone and dolomite with a restricted fauna suggesting abnormal salinity. The Triassic deposits of the southern (Tethyan) zone are thick and largely marine; particularly striking are several thousand meters of Carnian, Norian, and Rhaetian shallow-water limestone and dolomite. Just before the Jurassic, the sea began to transgress progressively northward across the shelf zone. Except for some minor regressions, the transgression persisted until late Oxfordian-early Kimeridgian time and was accompanied by the gradual northward spread of shallow-water, calcareous, relatively open-sea deposits at the expense of terrigenous clastic and ferruginous deposits laid down close to river deltas. Salinity probably controlled the regional faunal distribution. The latest Jurassic and Early Cretaceous was a time of widespread regression when nonmarine deposits (Purbeckian-Wealden) were laid down from southern England across northern France to Germany. Renewed transgression in Aptian-Albian time preceded the major Mesozoic transgression in the Late Cretaceous, when great th cknesses of chalk were deposited. During the deposition of the ancient coccolith ooze, most of western Europe was, for the first time, a deep shelf. Mesozoic history ended with a Cretaceous regression. End_of_Article - Last_Page 720------------

An X-ray examination of an exceptionally well crystallized kaolinite

SummarySpecimens of kaolinite have been found in inclusions in the ferruginous deposits on the Yorkshire Coast, just north of Scalby. The excellent quality of the X-ray powder pattern suggests that this kaolinite is better crystalline than kaolinites from other localities. Although the lattice constants of the Scalby material are considered to be identical with those previously published for kaolinite, minor differences in the intensities of the X-ray reflections do occur and may be due to a less distorted structural layer in the Sealby kaolinite.

Ferruginous bauxite deposits in northwestern Oregon

Ferruginous bauxite deposits in northwestern Oregon