Unstable Heavy Minerals Research Articles

Distribution pattern of heavy minerals assemblages in recent sediments of Lesser Zab River Basin (LZRB), NE Iraq

The Lesser Zab River (LZR), the largest tributary in Iraq, with a catchment area of about 20,000 km2, and majority of its basin lying in Iraq, drains into the Tigris River. It runs through highly folded and faulted igneous and metamorphic zone in the northeastern part of Iraq. We studied the heavy minerals in recent sediments of the Lesser Zab River Basin (LZRB) to determine their mineralogies, assemblages pattern, distribution manner, spatial variability, microtexture, provenance, and tectonic setting. We analyzed 24 sediment samples for heavy mineral assemblage determination, using the standard petrographic method. Scanning Electron Microscopy was used to determine the morphology of the grains of selected heavy minerals. Heavy minerals identified in the studied sediments include: dark color such as magnetite, ilmenite, hematite, and goethite; and transparent minerals represented by hornblende, tremolite–actinolite; pyroxenes, epidotes, zircon, tourmaline, rutile, garnet, staurolite, kyanite, and layered minerals assemblage such as muscovite, chlorite, biotite, and phlogopite. The studied sediments are considered immature, because they have the lowest concentration of ultrastable minerals compared to unstable heavy minerals, which confirms that the surface sediments of LZR and its sub-basin tributaries were deposited in an active continental-margin tectonic setting.

Heavy-mineral provenance signatures during the infill and uplift of a foreland basin: An example from the Jaca basin (southern Pyrenees, Spain)

ABSTRACT In the Jaca foreland basin (southern Pyrenees), two main sediment routing systems merge from the late Eocene to the early Miocene, providing an excellent example of interaction of different source areas with distinct petrographic signatures. An axially drained fluvial system, with its source area located in the eastern Central Pyrenees, is progressively replaced by a transverse-drained system that leads to the recycling of the older turbiditic foredeep. Aiming to provide new insights into the source-area evolution of the Jaca foreland basin, we provide new data on heavy-mineral suites, from the turbiditic underfilled stage to the youngest alluvial-fan systems of the Jaca basin, and integrate the heavy-mineral signatures with available sandstone petrography. Our results show a dominance of the ultrastable Ap-Zrn-Tur-Rt assemblage through the entire basin evolution. However, a late alluvial sedimentation stage brings an increase in other more unstable heavy minerals, pointing to specific source areas belonging to the Axial and the North Pyrenean Zone and providing new insights into the response of the heavy-mineral suites to sediment recycling. Furthermore, we assess the degree of diagenetic overprint vs. provenance signals and infer that the loss of unstable heavy minerals due intrastratal dissolution is negligible at least in the Peña Oroel and San Juan de la Peña sections. Finally, we provide new evidence to the idea that during the late Eocene the water divide of the transverse drainage system was located in the North Pyrenean Zone, and areas constituted by the Paleozoic basement were exposed in the west-Central Pyrenees at that time. Our findings provide new insights into the heavy-mineral response in recycled foreland basins adjacent to fold-and-thrust belts.

Unravelling the widening of the earliest Andean northern orogen: Maastrichtian to early Eocene intra‐basinal deformation in the northern Eastern Cordillera of Colombia

AbstractThe onset of deformation in the northern Andes is overprinted by subsequent stages of basin deformation, complicating the examination of competing models illustrating potential location of earliest synorogenic basins and uplifts. To establish the width of the earliest northern Andean orogen, we carried out field mapping, palynological dating, sedimentary, stratigraphic and provenance analyses in Campanian to lower Eocene units exposed in the northern Eastern Cordillera of Colombia (Cocuy region) and compare the results with coeval succession in adjacent basins. The onset of deformation is recorded in earliest Maastrichtian time, as terrigenous detritus arrived into the basin marking the end of chemical precipitation and the onset of clastic deposition produced by the uplift of a western source area dominated by shaly Cretaceous rocks. Disconformable contacts within the upper Maastrichtian to middle Palaeocene succession document increasing supply of quartzose sandy detritus from Cretaceous quartzose rocks exposed in eastern source areas. The continued unroofing of both source areas produced a rapid shift in depositional environments from shallow marine in Maastrichtian to fluvial‐lacustrine systems during the Palaeocene‐early Eocene. Supply of immature Jurassic sandstones from nearby western uplifts, together with localized plutonic and volcanic Cretaceous rocks, caused a shift in Palaeocene sandstones composition from quartzarenites to litharenites. Supply of detrital sandy fragments, unstable heavy minerals and Cretaceous to Ordovician detrital zircons, were derived from nearby uplifted blocks and from SW fluvial systems within the synorogenic basin, instead of distal basement rocks. The presence of volcanic rock fragments and 51–59 Ma volcanic zircons constrain magmatism within the basin. The Maastrichtian–Palaeocene sequence studied here documents crustal deformation that correlates with coeval deformation farther south in Ecuador and Peru. Slab flattening of the subducting Caribbean plate produced a wider orogen (>400 km) with a continental magmatic arc and intra‐basinal deformation and magmatism.

Phanerozoic Quartz Arenite Formation and Sequence-Analytical Patterns: Indirectly Relating to Major Impacting and Super Plume Volcanism, Jordan, Arabian Plate

This paper deals with indirect effects of major impacting throughout the Early Paleozoic resp. with those of super plume activity during the Early Cretaceous, both applied to the siliciclastic series of Jordan deposited on the Arabian Platform, Arabian Plate. Its focus is mainly directed on gases released by both processes (CO2, SO2, NOx, HCl, HF) and the relating acids, challenged by experiments and microscopic analysis of grain mounts and thin sections that reveal chemical instability of quartz and ultrastable heavy minerals (i.e. tourmaline) under high acidity (pH °C - 90°C). According to Lopatin’s Time/Temperatur-Index the Lower Cambrian reached the onset of hydrocarbon generation (liquid window) during the Lower Early Cretaceous. Unstable heavy minerals (apatite, garnet, hornblende, epidote, zoisite/clinozoisite) are generally absent in quartz arenites while in arkosic sandstones of marine environment carbonate cement and primary clay minerals (illite) provide conservation. As known since the eighties, the K/T-event’s indirect effects had global influence on Earth’s surface sediments and atmospheric chemistry by wildfires, hot whirl storms, acidic “sturz rain”, dust, soot, darkness, loss of photosynthesis, toxic metals, gases and relating acids. All of them are here concerned and applied to major impacting throughout the Early Paleozoic using the impact data of Price (2001); while superplume volcanism during Cretaceous led to the opening of the South Atlantic accompanied by the cyclic outflow of the Para?a/Etendeka Flood Basalts and relating gases in a gigantic scale (137 - 127 Ma). Assuming that the gases cause similar global effects on Earth’s surface sediments, an according result may be expected in form of quartz arenites and their sequence-analytical patterns (cyclic SBs, MFSs).*

A giant sandy sediment drift in early Silurian (Telychian) and its multiple sedimentological prosess

Abstract This study describes a regional-scale sedimentary feature in the Upper Yangtze region of China that is identified as a Telychian age (438 Ma) sediment sandy drift that is 500–800 km long, 100–150 km wide, and 10–20 m thick. Graptolite zones is applied to recognize Telychian sandstone beds and reconstruct an isochronal stratigraphic framework for the study area. It is possible to observe numerous traction structures in Telychian sandstone beds, including ripples, cross-bedding, cross-laminations, wavy-laminations and horizontal-laminations and Bouma sequence. The palaeocurrent direction is towards SSW (200°–240°), which is measured by sedimentary structures (cross-bedding, cross-laminations and ripples) in outcrops. Besides, the alignment of elongate particles in thin section, and the distribution characteristics of heavy minerals also indicate a SSW palaeocurrent direction. This direction is parallel to palaeo-coastline, which is a characteristic feature of bottom current. A multiple sedimentary processs is identified based on analysing facies of each sections. Contourite-dominated sequences are observed in channel-related seaway while turbidite sequences are observed in shelf near palaeo-coastline. Based on provenance analysis, the Telychian drift (channel reworked sandy drift) is the production of a mixed depositional system (first turbidite deposition and then bottom current deposition). The turbidite sand on the shelf provides material source for the sandy drift, and the deposit is transported from the shelf to the channel (parallel to ancient coastline). The provenance direction is identified by analyzing the distribution of heavy minerals. The unstable heavy minerals content is higher in the turbidites samples (near provenance region) than the channel reworked sandstone samples (far away from provenance region). This Telychian deposit is a rare example of an ancient channel reworked sandy drift.

Provenance of heavy minerals from recent sediments of Balakyan River, Kurdistan Region, Iraq

Heavy mineral assemblages of the sediments in Balakyan River have been studied to determine their concentrations and provenance. Twelve sediment samples were analyzed for heavy mineral assemblage determination. The unstable heavy minerals (pyroxene and amphibole) represent more than 50%. The mineral chemistry and petrographic studies refer to the predominant clinopyroxene mineral is diopside. Actinolite, tremolite, and magnesiohornblende are common calc-amphibole in the sediments. The ultrastable heavy minerals are present in trace amounts. According to the mineral chemistry the clinopyroxene is derived from basic igneous rocks crystallized at 1150-1220⁰C and low pressure. Amphibole and epidote crystallized under low temperature and/or formed under low grade metamorphism. The detrital chromian spinel is derived from basic and ultrabasic igneous rocks of Alpine type peridotite formed in fore-arc. The probable source of these assemblages is Ophiolite Complex to the north of the studied area (north Iraq) and igneous parts of Walash Series and Red Bed Series also the sedimentary rocks of Shiranish and Tanjero formations.

A comparison of heavy mineral assemblage between the loess and the Red Clay sequences on the Chinese Loess Plateau

Abstract QEMSCAN-based (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) heavy mineral analysis has recently been demonstrated an efficient way to allow a rapid extraction of provenance information from sediments. However, one key issue to correctly obtain a provenance signal using this technique is to clearly separate effects of diagenetic alteration on heavy minerals in sediments, especially in fine-grained loess. Here we compare heavy mineral assemblages of bottom Quaternary loess (L33) and upper Pliocene Red Clay of three sites on the Chinese Loess Plateau (CLP). Two sites (Chaona and Luochuan) with similar modern climate conditions show similar heavy mineral assemblages but contain much less of the unstable heavy mineral amphibole than the drier Xifeng site. This result provides strong evidence supporting that climate-caused diagenesis is an important factor controlling heavy mineral assemblages of fine-grained loess. However, heavy mineral assemblages are similar for loess and paleosol layers deposited after 0.5 Ma on the Chinese Loess Plateau regardless of climate differences, suggesting that time is also a factor controlling heavy mineral assemblages of loess and Red Clay. Our high resolution sampling of the upper Miocene-Pliocene Chaona Red Clay sequence reveals similar heavy mineral compositions with a minor amphibole content, different from the drier Xifeng site results of the same age. This result indicates that the monsoonal climate pattern might have been maintained since the late Miocene. Furthermore, it indicates that the heavy mineral method is promising in tracing provenance for sites northwest of the Xifeng site on the Loess Plateau.

Provenance of sands from the confluence of the Amazon and Madeira rivers based on detrital heavy minerals and luminescence of quartz and feldspar

Source-to-sink systems are poorly known in tropical rivers. For the Amazonian rivers, the majority of the provenance studies remain focused on the suspended load, implying a poor understanding of the processes governing production and distribution of sands. In this study, we perform heavy mineral and optically stimulated luminescence (OSL) analysis to cover the entire spectrum (heavy and light minerals fraction) of 29 sand samples of the Lower Madeira river region (Amazon and Madeira rivers), of which the main goal was to find provenance indicators specific to these rivers. Despite the tropical humid climate, the sands of the Amazon and Lower Madeira rivers are rich in unstable heavy minerals as augite, hypersthene, green hornblende and andalusite. The Madeira river is highlighted by its higher content of andalusite, with source attributed to the Amazon Craton (medium-to-high grade metamorphic rocks), while the Amazon river, upstream of the Madeira river mouth, has a signature of augite and hypersthene, that suggests an Andean provenance (volcanic rocks). Sands from the Madeira river can be tracked in the Amazon river by the increasing concentration in andalusite. OSL analysis of the light minerals fraction was used as an index of feldspar concentration and sedimentary history of quartz grains. Lower feldspar concentration and quartz grains with longer sedimentary history (higher OSL sensitivity) also point to a major contribution of cratonic sources for the sands in the Madeira river. While the sands from the Lower Madeira would be mainly supplied by cratonic rocks, previous work recognised that suspended sediments (silt and clay) are derived from Andean rocks. Therefore, we interpret a decoupling between the sources of sand and mud (silt and clay) under transport in the Madeira river. Andean sands (rich in augite and hypersthene) would be trapped in the foreland zones of the Beni and Mamoré tributaries. In the Amazon river sands, the low OSL sensitivity of the quartz, higher content of feldspar and unstable heavy mineral assemblage dominated by augite and hypersthene suggest both a fast transport from Andean sources with fine sediment bypass over foreland areas.

Distribution pattern and controlling factors of heavy mineral assemblages in surficial seafloor sediments offshore of the Eastern Shandong Peninsula (Yellow Sea)

The source and processes controlling the deposition of the sand fraction of muddy seafloor sediments remain poorly understood. Surficial seafloor sediments were collected offshore of the Eastern Shandong Peninsula and were analyzed regarding their detrital heavy mineral constituents and grain size distributions to determine their spatial distribution patterns, sand fraction provenance, and transport pathways. Five sediment types were identified in the study area: clayey silt, silt, sandy silt, silty sand, and sand. Each of these sediment types displayed distinct grain size parameters of their corresponding sand fractions. Moreover, three statistical clusters of sand grains were identified, suggesting variations in provenances and sedimentary processes from one cluster to the next. Twenty-five species of detrital heavy minerals in the sand fraction were identified and then assigned to four categories based on their mineral stability (i.e., ultrastable, stable, moderately stable, and unstable). The sandy sediments were enriched in ultrastable and stable heavy minerals, indicating that these sand grains mostly originated from coastal erosion of granitic and/or metamorphic rocks. In contrast, the muddy sediments were characterized by unstable heavy minerals dominated by hornblende and epidote. The results of principal component analysis further suggested that these sand grains are similar in terms of their provenance (coastal erosion) but have undergone complex sedimentary processes. Relative sea level changes during the late Quaternary caused shifts in the sediment sources and supplies, which were the primary factors controlling the grain sizes of the sand fractions and heavy mineral assemblages in the surficial sediments of the study area.

Provenance of Late Paleozoic-Mesozoic Sandstones, Taimyr Peninsula, the Arctic

The sedimentary and provenance characteristics of seven Permo-Carboniferous and two early Cretaceous samples from the Taimyr Peninsula provide information about the latest evolution of Uralian orogeny and the opening of the Amerasian Basin. The Permo-Carboniferous samples have a mixed provenance of recycled and first cycle sediment, sourced from metamorphic and igneous terranes. U-Pb detrital zircon ages represent a mixture of Precambrian-Paleozoic grains with euhedral, penecontemporaneous late Carboniferous and Permian grains consistent with derivation from the Uralian Orogen, plus additional Timanian and Caledonian material presumably derived from Baltica. Differences between the late Permian sample and the other Carboniferous and early Permian samples are interpreted to reflect the final collisional stage of Uralian orogeny. Early Cretaceous sediments deposited at the time of the Amerasian Basin opening preserve a mixed provenance of mainly first cycle metamorphic and igneous source material, as well as an unstable heavy mineral assemblage dominated by staurolite, suggesting local derivation. Detrital zircon ages fall almost exclusively into one late Permian-early Triassic cluster, indicating a Siberia Trap-related magmatic source. The detrital zircon age spectra support a passive margin setting for Taimyr during the opening of the Amerasian Basin in the early Cretaceous.

Grain size and heavy minerals of the Late Quaternary eolian sediments from the Imbituba–Jaguaruna coast, Southern Brazil: Depositional controls linked to relative sea-level changes

The stratigraphic subdivision and correlation of dune deposits is difficult, especially when age datings are not available. A better understanding of the controls on texture and composition of eolian sands is necessary to interpret ancient eolian sediments. The Imbituba–Jaguaruna coastal zone (Southern Brazil, 28°–29° S) stands out due to its four well-preserved Late Pleistocene (eolian generation 1) to Holocene eolian units (eolian generations 2, 3, and 4). In this study, we evaluate the grain-size and heavy-mineral characteristics of the Imbituba–Jaguaruna eolian units through statistical analysis of hundreds of sediment samples. Grain-size parameters and heavy-mineral content allow us to distinguish the Pleistocene from the Holocene units. The grain size displays a pattern of fining and better sorting from generation 1 (older) to 4 (younger), whereas the content of mechanically stable (dense and hard) heavy minerals decreases from eolian generation 1 to 4. The variation in grain size and heavy-mineral content records shifts in the origin and balance (input versus output) of eolian sediment supply attributable mainly to relative sea-level changes. Dunefields submitted to relative sea-level lowstand conditions (eolian generation 1) are characterized by lower accumulation rates and intense post-depositional dissection by fluvial incision. Low accumulation rates favor deflation in the eolian system, which promotes concentration of denser and stable heavy minerals (increase of ZTR index) as well as coarsening of eolian sands. Dissection involves the selective removal of finer sediments and less dense heavy minerals to the coastal source area. Under a high rate of relative sea-level rise and transgression (eolian generation 2), coastal erosion prevents deflation through high input of sediments to the coastal eolian source. This condition favors dunefield growth. Coastal erosion feeds sand from local sources to the eolian system, including sands from previous dunefields (eolian generation 1) and from drowned incised valleys. Therefore, dunefields corresponding to transgressive phases inherit the grain-size and heavy-mineral characteristics of previous dunefields, leading to selective enrichment of finer sands and lighter minerals. Eolian generations 3 and 4 developed during a regressive-progradational phase (Holocene relative sea level highstand). The high rate of sediment supply during the highstand phase prevents deflation. The lack of coastal erosion favors sediment supply from distal sources (fluvial sediments rich in unstable heavy minerals). Thus, dunefields of transgressive and highstand systems tracts may be distinguished from dunefields of the lowstand systems tract through high rates of accumulation (low deflation) in the former. The sediment source of the transgressive dunefields (high input of previously deposited coastal sands) differs from that of the highstand dunefields (high input of fluvial distal sands). Based on this case study, we propose a general framework for the relation between relative sea level, sediment supply and the texture and mineralogy of eolian sediments deposited in siliciclastic wet coastal zones similar to the Imbituba–Jaguaruna coast.

Heavy Minerals and Rare Earth Elements in Coastal and Inland Dune Sands of El Vizcaino Desert, Baja California Peninsula, Mexico

A heavy mineral (HM) study and light and heavy rare earth elements (LREE and HREE) analysis were performed in coastal and inland dune sands, El Vizcaino Desert, Central Baja California Peninsula, Mexico. Our study shows high abundances of hornblende and apatite in the El Vizcaino dune sands, suggesting a dominance of granodiorites/intermediate plutonic rocks and marine authigenic phosphorite in the dune sands. There is a relationship between unstable heavy minerals like hornblende, pyroxenes, and sphene, and heavy rare earth elements (HREE) that suggests that unstable heavy minerals are potential carriers of HREE in the dune fields. However, there is a slight depletion of HREE in relation to LREE, especially in one locality of the inland dunes probably associated with the wind regime and weathering of unstable heavy minerals in the sands. Inland, transitional, and coastal dune fields can be observed as different dune provinces by means of grouping HM and REE data in two separate dendograms. It seems that HREE are correlated with fine-grained sand sizes and correlated with high CIA values linked to slightly weathered sands.

Stability of Detrital Heavy Minerals on the Norwegian Continental Shelf as a Function of Depth and Temperature

Abstract Petrographic analysis of 1931 thin sections from sandstones of Pliocene to Devonian age on the Norwegian continental shelf indicate that the heavy minerals zircon, tourmaline, rutile, apatite, and spinel survive to depths exceeding 5000 m and to temperatures of around 200°C without showing signs of intrastratal dissolution. On the other hand, the maximum depth and temperature of occurrence for amphibole are 841 m and 40°C, around 1500 m and 55°C for sphene when 0.5 km of probable uplift is taken into account, 2231 m and 92°C for kyanite, 2559 m and 95°C for epidote, 2810 m and 109°C for staurolite, and 4589 m and 175°C for garnet. Initial signs of garnet dissolution occur at around 2000 m depth, and all garnets are partially dissolved at depths greater than 3500 m. Monazite is present down to 4858 m and 182°C and chloritoid to 3811 m and 149°C. It is, however, uncertain whether this is due to the low number of samples deeper than 4858 m and to the rare occurrence of chloritoid, or to intrastratal dissolution. The same sequence of heavy-mineral stability is found when volume of quartz cement is used as a proxy for time-temperature exposure. Quartz cement is not found in samples containing amphibole or detrital sphene. A maximum of a fraction of a percent quartz cement is found in samples containing kyanite, up to 1% together with epidote, up to 6% with staurolite, up to 24% with chloritoid, up to 25% with garnet, whereas maximum values of 25–35% are present together with zircon, tourmaline, rutile, patite, spinel, and monazite. The sequence of persistence of heavy minerals versus depth found in this study is very similar to results from several previous studies, although unstable heavy minerals survive to greater depths in very young and rapidly buried sandstones, and there are some differences regarding the stability of sphene and epidote. Heavy mineral dissolution has created secondary pores and possibly has contributed to precipitation of kaolinite, illite, quartz, and carbonates in the studied sandstones, but these reactions are of very limited volumetric importance.

Temporal Variations of Mesozoic Sandstone Compositions in the Qiangtang Block, Northern Tibet (China): Implications for Provenance and Tectonic Setting

Abstract One hundred and forty-four and fifty-two Mesozoic sandstone samples from the Qiangtang block (ca. 32° 20'–35° N, 85°–93° E; northern Tibet, China) were conducted for analysis of detrital modes and heavy-mineral spectra, respectively, in an attempt to evaluate their provenance and the type of tectonic setting in which they were deposited. The Lower–Middle Triassic sandstones in central Qiangtang are characterized by complex derivations from both recycled orogen and continental block provenances. Most of the Upper Triassic and Jurassic sandstones are dominated by a recycled-orogen origin. However, sandstones derived from a continental-block source also occur in Upper Triassic strata in the southern margin of southern Qiangtang, and in Lower Jurassic strata in the southern margin of northern Qiangtang. Although the heavy-mineral spectra of the Upper Triassic and Jurassic sandstones are occupied mostly by the stable heavy minerals zircon, tourmaline, and rutile (ZTR), most of the samples are generally accompanied by unstable heavy minerals, such as apatite, chlorite, chrome spinel, amphibole, epidote, garnet, and pyroxene, except for those from Upper Triassic strata in the southern margin of southern Qiangtang and from Lower Jurassic strata in the southern margin of northern Qiangtang. The detrital modes and heavy-mineral spectra of the Mesozoic sandstones, along with the lithologic evidence, indicate that the central Qiangtang anticlinorium must have been elevated and eroding due to orogenesis and most likely has contained rolling topographic relief at least since Early Triassic time. It could have contained abundant ophiolitic fragments as evidenced by rich chrome spinel, amphibole, and other readily decomposed ferromagnesian minerals across the entire anticlinorium. These mafic minerals may point to the presence of the Shuanghu suture along the entire central Qiangtang anticlinorium. The blueschist-bearing metamorphic complexes in central Qiangtang could be accommodated in a large-scale enclave in an irregular central Qiangtang continental margin. The Upper Triassic–Jurassic recycled-orogen-derived sandstones in northeastern Qiangtang suggest continued orogenesis due to the suturing between Qiangtang and Asia. Such a contractional background does not support models that relate a tensile mechanism for back-arc spreading along the Bangong–Nujiang belt.

Composition and trace-element geochemistry of detrital clay and heavy-mineral suites of the lowermost Amazon River; a provenance study

ABSTRACT Compositions of clays and heavy minerals as well as trace-element geochemistry of the lowermost Amazon sediments reflect source regions and the intense chemical weathering conditions. Illite and montmorillonite indicate mountainous sources under physical weathering conditions, whereas kaolinite is related to the soil composition under humid tropical conditions, where chemical weathering predominates. The suite of unstable heavy minerals, on the other hand, reflects some sediment transport from the Andes, more supply from tributaries draining the basic and metamorphic rocks from the Southeastern Guiana Shield, and strongest influence of the upstream Amazon and Solimoes areas. These source signals are damped by transitional storage and intense lateral sediment exchange between channel and floodplain. The Brazilian Shield contribution (via the Xingu River) seems to be of minor importance, although the Alter do Chao and the Barreiras Formations, which are products of erosion of the shields, supply suites of stable heavy minerals that reflect recycling. Rare-earth and trace-element data from the clay and heavy-mineral fractions provide additional clues to the source areas: in the downstream direction, superimposed upon provenance of sediments from an undifferentiated arc, the Andes, is provenance from strongly weathered continental crust, the Precambrian shields, as well as sedimentary recycling. Small-scale provenance can be delineated by the most immobile elements. Heavy rare earth elements in the heavy-mineral fraction increase downstream toward Estreitos (to the Para River).

Provenance of the Sardona Flysch, eastern Swiss Alps: example of high-resolution heavy mineral analysis applied to an ultrastable assemblage

The Sardona Flysch of eastern Switzerland was deposited in the northern sector of the embryonic Alpine Foreland Basin, the so-called North Penninic Trough, during the Late Cretaceous-Early Tertiary. The flysch sediments consist of quartz arenites, sublitharenites and arkosic arenites, plus polygenic, pebble to boulder conglomerates. The Sardona Flysch was sourced by a single petrologic province composed of plutonic, Variscan granitoids, gneisses and low-grade, quartzo-feldspathic schists, plus associated cover sediments throughout its sedimentary history. Its heavy mineral suite principally comprises zircon, tourmaline, rutile and varying amounts of apatite, whose distribution cannot be used to characterise the various lithostratigraphic units. However, recording the diagnostic varieties of ultrastable heavy minerals using a ‘high-resolution heavy mineral analysis’ (HRHMA) yielded conclusive results. The varietal distribution of zircon proved especially informative, demonstrating that changes in its distributional trends coincide remarkably well with lithostratigraphic subdivisions and reveal subtle variations in the provenance of the flysch. The limited number of heavy mineral species was predetermined by the low diversity of parent rock lithologies in the hinterland, rather than resulting from high sediment maturity, or progressive removal of unstable species during diagenesis. The basin was structurally confined by the South Helvetic and North Penninic Prättigau Swells, which defined its northern and southern margins, respectively; these structural highs may represent Mesozoic normal fault-blocks reactivated under compressive stresses within the European foreland. They provided detritus to the Sardona flysch basin and prevented the influx of material from the orogenic thrust wedge. Hence, garnet and unstable heavy minerals recycled from medium-grade metamorphic rocks within the mineralogically more diverse Austroalpine thrust wedge are absent from the flysch sediments.

Sedimentology and mineral composition of the Kurnub Sandstone in Wadi Qsieb, SW Jordan

The Kurnub Sandstone of Early Cretaceous age crops out in Wadi Qsieb (in the southwest of Jordan) with a thickness of 130 m. Moderately developed fining-upward cycles with irregular erosive bases, together with the presence of plant fragments and the absence of body or trace fossils, point to a fluviatile depositional environment, probably a river of intermediate sinuosity. Results of grain-size analysis confirm this interpretation. The sandstones are compositionally and texturally supermature quartz arenites formed mainly by recycling from Early Palaeozoc sandstones and less commonly by direct supply from the Arabian-Nubian Shield. The absence of feldspars and unstable heavy minerals is attributed to intense chemical weathering, attacking sands that were deposited with a low rate on a craton bordering the Tethys Sea. The thickness recorded here and the absolute absence of hornblende are in contradiction with what has been published by Nasir and Sadeddin (1989).

Linear Dunes Near the Orange River

Abstract The sands of the linear dunes studied in the vicinity of the Orange River were probably produced and deposited during arid climatic conditions. The presence of unstable heavy minerals of the pyroxene-amphibole suite as well as the red colouring of the sand indicate that the detrital material was produced and deposited during arid climatic conditions. The mineralogical similarity between the dunes to the north and to the south of the Orange River indicates that the sand was able to cross the river. probably during the arid phase(s) of the Quaternary. The original lithological source of the dune sand is uncertain but the mainly quartzose nature of the sediment points to a granitic and/or sandstone source. The presence of small amounts of unstable minerals suggests some addition of material from local weathering. A few small brown dunes near the Orange River apparently are formed by sand being blown from the banks of the river. Mineralogically the reddish and yellowish dunes to the south of the Oran...

Subsurface dissolution of heavy minerals, Frio Formation sandstones of the ancestral Rio Grande Province, South Texas

Oligocene sandstones (Frio Formation) of South Texas, deposited by the ancestral Rio Grande, contain a heavy mineral assemblage that is markedly altered, even in the shallowest sample examined (approximately 1 km depth). The weight fraction of detrital heavy minerals in the modern Rio Grande is approximately 1% whereas subsurface Frio sandstones contain as little as 0.1% (or less) heavy minerals. Modern Rio Grande sand contains a diverse and unstable heavy mineral assemblage dominated by pyroxenes, amphiboles, and an assortment of iron-titanium oxides; minor components include apatite, garnet, sphene, epidote, and zircon. Heavy minerals in subsurface Oligocene sandstones include abundant apatite, zircon, and titanium oxide among detrital components; minor iron-rich garnet also survives in the subsurface to depths of about 3 km. Other very stable, but also very minor, heavy minerals include tourmaline, chromite, spinel, and monazite. Locally, the heavy mineral fraction in the Frio is dominated by authigenic components such as siderite, pyrite, or barite. Authigenic sphalerite is also observed among the heavy minerals. Feldspars and rock fragments suggest that sediment deposited by the ancestral Rio Grande was more strongly dominated by volcanic detritus than is the modern river. It is reasonable to infer that the initial heavy mineral assemblage of the Frio Formation was likewise more unstable than that which appears today in the Rio Grande. Thus, heavy mineral loss determined by comparing subsurface Frio sandstones with the sand in the modern Rio Grande is conservative. Comparison of Sr and Nd concentrations in modern Rio Grande sands and subsurface Frio sandstones suggests that heavy mineral destruction in the subsurface does not cause major perturbations of whole rock isotopic systems involving these elements.

The effects of transport and weathering on heavy minerals from the Cascade River, New Zealand

The effects of transport and weathering processes on heavy mineral suites have been assessed by examining suites from the Cascade-Martyr river system (Westland, New Zealand) and its associated beach. These rivers drain a predominantly ultramafic source that supplies a large amount of unstable minerals, including forsteritic olivine, enstatite, diopside, actinolite-tremolite and Ti-rich brown amphibole. The weathering processes at outcrop, which take place in a wet temperate climate, have not caused a significant decrease in mineral diversity. The only variations in mineralogy that are detectable in the river samples reflect slight variations in catchment lithologies, suggesting that weathering processes on the floodplain have not affected heavy mineral suites during transit. This indicates that most coarse sediment movement takes place during floods and that coarse sediment does not reside for extensive periods on the floodplain. The suites found in the river sands do not differ appreciably from those in the beach, indicating that longshore drift does not introduce extraneous sediment to the Cascade detritus as it enters the beach. Furthermore, mechanical abrasion processes on the beach have not caused any significant decline in abundance of any of the constituent minerals, even of olivine, one of the most mechanically unstable heavy minerals. Therefore, neither mechanical abrasion nor weathering has had a marked effect on the heavy mineral suites in the Cascade-Martyr river system.