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The Eastern North American Titanium Province extends from Labrador to Florida and westward toward the Mississippi River. In the United States, this province covers the Atlantic Coastal Plain and a substantial portion of the Gulf Coastal Plain. Heavy minerals were first mined from surface and near-surface sands of the Atlantic Coastal Plain in 1916, when Buckman and Pritchard opened a mine on a beach near Mineral City, Florida, to recover ilmenite. Numerous heavymineral deposits have since been identified within the surface sands of the Atlantic and Gulf coastal plains. Although some of the deposits are now being mined, others are no longer active, or have been lost to mining because of cultural developments. Some are likely to be mined in the future. Significant heavy-mineral deposits have been or are being exploited in New Jersey, Virginia, South Carolina, Georgia, and Florida. Some important heavy-mineral deposits formed in beach ridges at the height of major marine transgressions, e.g., the Trail Ridge and Highland (Maxville) deposits along Trail Ridge, and the Yulee, Cabin Bluff, Altama, Aurora, and Chowan deposits along the Pamlico shoreline. Other deposits developed in beach ridges formed at times of temporary halts or during minor transgressions in periods of general regression, e.g., the Green Cove Springs, Boulougne, Folkston, and Lulaton deposits. Those formed in alluvial environments include Manchester, Lakehurst, and Camden, as well as those of the Virginia and North Carolina Fall Zone. The most significant heavy-mineral deposits of the onshore Atlantic and Gulf coastal plains, as far west as the Louisiana-Texas border, are reviewed. [ABSTRACT FROM AUTHOR]

The use of heavy mineral analysis on a 'real-time' basis at well site is a logical extension of the application of the method as a non-biostratigraphic correlation tool. To date, the method has been used to monitor the stratigraphy during drilling of horizontal wells in three fields on the UK continental shelf (Clair, Ross and Hannay), and in several cases heavy mineral data have been integral in deciding to amend well bore trajectories in order to remain within hydrocarbon-bearing zones, a process known as 'geosteering'. Heavy mineral analysis now has a positive track record for geosteering horizontal wells in a variety of depositional environments, from fluvial/aeolian to shallow and deep marine, and can therefore be genuinely considered as an alternative geosteering tool in circumstances where biostratigraphic methods have inadequate resolution. Heavy mineral data have been used in the decision-making process in a variety of situations, including whether to maintain angle, to steer up or to steer down, to sidetrack and to terminate drilling. Application of heavy mineral analysis at the well site requires establishment of a robust correlation scheme prior to drilling horizontal wells, using samples from offset wells adjacent to the proposed well track. Parameters used to monitor the geology during horizontal drilling include those conventionally used for reservoir correlation (principally, ratios of stable minerals with similar hydrodynamic behaviour), but other parameters have also proved useful in the particular circumstance associated with individual fields. For example, the abundance of unstable minerals is locally useful in the Clair Field, and ratios of minerals with contrasting hydrodynamic behaviour are useful in the Ross and Hannay Fields. [ABSTRACT FROM AUTHOR]

Integrated heavy mineral, mineral-chemical and zircon age data show that Triassic sandstones in the Strathmore Field result from the interplay of sediment derived from eastern and western sources. The Early Triassic Otter Bank Formation is interpreted as having a source on the British margin of the Faeroe-Shetland rift. Two main provenance components (recycled Devonian-Carboniferous Upper Clair Group in conjunction with Lewisian orthogneiss) were involved. The overlying Foula Formation (Middle-Late Triassic) was derived from high-grade metasedimentary/charnockitic basement rocks, interpreted as lying in the Nagssuqtoqidian belt of southern East Greenland on the opposite side of the rift. Zircon age data from the Foula Formation also provide evidence for an important Permian igneous event along the proto-northeast Atlantic rift. The switch in sediment supply from easterly-sourced to westerly-sourced detritus is the most clearly defined correlative event in the Triassic succession of the Strathmore Field. Variable supply from a subordinate zircon-rich component (probably of granitic origin) provides a basis for intra-Foula subdivision and correlation. The upper part of the Otter Bank Formation is characterised by a relatively high apatite/tourmaline ratio, believed to indicate the initial appearance of sediment from East Greenland. The construction of the correlation framework for the Triassic succession in the Strathmore Field depends crucially on identification and quantification of parameters that are sensitive to changes in provenance and insensitive to other processes that operate during the sedimentation cycle. [ABSTRACT FROM AUTHOR]

Many volcanic sand tempers used for the fabrication of prehistoric ceramics in Pacific Oceania are beach placer sands with heavy mineral contents that reflect the phenocryst mineralogy of bedrock on the islands where pottery was made. Island groups within the region of ceramic cultures extending from western Micronesia to western Polynesia include hotspot, arc, postarc, and backarc geotectonic settings. The abundance of opaque minerals is governed by intensity of placering and is not diagnostic of geotectonic temper class, but differing proportions of ferromagnesian silicate mineral grains faithfully reflect island provenance. Clinopyroxene is the most abundant non-opaque heavy mineral in nearly all tempers of volcanic derivation. Hotspot tempers are marked by relative abundance of olivine (>25%), which also occurs in subordinate amounts in selected arc and postarc tempers. Hornblende accompanies clinopyroxene in varying proportions in other arc and postarc tempers, and orthopyroxene accompanies clinopyroxene in arc tempers from New Britain and Tonga. Relative proportions of heavy mineral species in Oceanian placer tempers correlate with the nature of restricted bedrock sources on individual islands, and serve as diagnostic evidence for temper origins wherever pottery was transported between islands. [ABSTRACT FROM AUTHOR]

The retro-arc Andean Amazon Basin (AAB), a foreland basin located east of the evolving Andes, has been an active sediment depocentre since the late Early Cretaceous (Aptian-Albian). Heavy mineral analysis of the proximal shallow marine and continental deposits in the Sub-Andean Zone reveals an overall trend from ultrastable zircon, tourmaline and rutile (ZTR) dominated assemblages, to more complex heavy-mineral suites with metamorphic and mafic volcanic signatures. This reflects successive derivation from shallow to deep crustal rocks and, subsequently, from accreted oceanic terranes during formation of the proto-Andes. In parallel with heavy mineral analysis, detrital zircons were dated using fission-track methodology. The measured lag times of the zircons range from 400 to 0 Ma. Approximately zero lag times generally represent fast cooling events in the source region, while long lag times are the result of slow cooling or recycling in the source regions. In the present study, zero lag times combined with lithological and mineralogical data sets have also been used to identify volcanic events in the hinterland which, in turn, establishes the stratigraphic age of the enclosing sediments more precisely. Changes in source areas are identified by changes in lag times, which coincide with variations in the composition of the heavy mineral suites. During early stages of basin evolution (Aptian-Campanian), lag times of detrital zircons, occurring in the dominantly ultrastable ZTR mineral suite, allow the discrimination of sediment input from two different continental basement sources. Zircons, with very long lag times (E400 Ma), indicate input from the Amazonian Craton regions at the eastern margin of the basin, while comparatively short lag times (0-60Ma) in zircons infer coeval sediment flux from the primordial Cordillera Real to the west. Higher up in the succession, a switch in provenance to dominantly westerly sources to the evolving Cordillera Real occurred, where progressively higher grade metamorphics were eroded. In the uppermost, Miocene to Pliocene sections, the appearance of mafic minerals documents new sources associated with the uplift of accreted basement terranes of the Cordillera Occidental and the reworking of arc volcanics. [ABSTRACT FROM AUTHOR]

The study of heavy minerals can provide information of significance in forensic investigations involving microscopic trace evidence derived from sand, soil and dust. Special techniques are frequently necessary to recover the minute quantities of accessory minerals that are typical of such evidence and these are described along with the precautions that must be observed when working under legal scrutiny. Identification of the minerals themselves follows well-established petrographic methods. Several examples show the use of heavy mineral evidence in actual cases. [ABSTRACT FROM AUTHOR]

The Swiss Molasse Basin represents an ideal setting to study the sedimentary response to orogenic processes, because (1) the sediments of the Swiss Molasse Basin are chronostratigraphically well-calibrated and (2) the orogenic hinterland, the Central Alps, has been extensively studied. Heavy minerals are sensitive recorders of both tectonic and exogenic processes, and have been widely used to constrain the stratigraphy, transport, provenance and diagenesis of Swiss Molasse Basin sediments. After a brief review of almost a century of heavy mineral research in the Swiss Molasse Basin, this contribution focuses on modern analytical techniques including high-resolution single-grain chemistry and thermochronological studies ( 40Ar/ 39Ar laser-probe dating of white mica, fission-track dating of zircon). These techniques have been applied to Rupelian to Serravallian (∼31 to ∼13Ma) sandstones from two composite sections of the Swiss Molasse Basin, one in the east (Honegg-Kronberg-Hörnli) and one in the central part (Honegg-Napf). In the east, the data reflect a normal unroofing sequence of the Austroalpine-Penninic nappe stack, lacking any signal of rapid exhumation in the hinterland at any time. In the central part, erosion of basement rocks started significantly earlier, and sediments younger than ∼20Ma document increasing cooling rates of their source rocks, reflecting accelerated exhumation in the hinterland. The timing of maximum cooling as well as the cooling rates (up to ∼40 1C/Ma) correspond exactly with 40Ar/ 39Ar data obtained from the presently exposed Lepontine metamorphic dome. [ABSTRACT FROM AUTHOR]

This contribution classifies detrital heavy mineral assemblages produced in contrasting geodynamic settings, following the provenance scheme proposed by Dickinson and co-workers in the late 1970s. The vital link with bulk-sediment detrital modes was established by systematically coupling high-resolution heavy mineral and petrographic analyses on the same sample sets, in a series of actualistic provenance studies carried out in key geological areas, characterised by arid to semiarid climate. Quartzofeldspathic to quartzose sands of ''Continental Block Provenance'' contain either heavy-mineral-rich, hornblende-dominated assemblages derived from amphibolite-facies basements exposed along rift escarpments and in cratonic shields, or heavy-mineral-poor suites with commonly rounded ultrastable grains recycled from cover strata. Volcanic rifted margins shed lithofeldspathic detritus with clinopyroxene-dominated suites (largely lilac-brown Ti-rich augite) that commonly include olivine. Abundant clinopyroxenes (mostly green augite) and hypersthene, associated with olivine or dark-brown to reddish-brown hornblende (oxyhornblende), characterise feldspatholithic sands of ''Magmatic Arc Provenance''. The proportion of mainly blue-green hornblende increases progressively with erosion cutting deeper into the batholithic core of the arc massif. Quartzolithic sands of ''Orogenic Provenance'' include suites dominated by amphiboles, garnet, and epidote. The relative abundance of garnet (associated with subordinate staurolite, kyanite, and sillimanite) and blue-green to green-brown hornblende increases with increasing metamorphic grade of the sedimentary or igneous protoliths, respectively. Oman-type obduction orogens shed abundant heavy minerals, dominated by mafic and ultramafic minerals derived from the obducted ophiolite nappe. Apennine-type thin-skinned thrust belts provide heavy-mineral-poor assemblages recycled from accreted passive-margin successions or foredeep turbidites. Pyroxenes, derived from offscraped ophiolitic sequences, are locally present. The wealth of information heavy minerals provide on the geology of source areas makes their analysis an extremely powerful complementary tool in provenance studies of sediments not modified by diagenesis. [ABSTRACT FROM AUTHOR]

Heavy-mineral analysis is proven as a powerful tool in reconstructing ice-sheet drainage patterns and has been used in the past in both drift exploration and studies of ice-sheet dynamics. Although ice flow patterns can be extracted from morphological indicators such as striated and grooved bedrock surfaces, clast orientation in tills, or glacial landforms, these properties are not suitable to analyse the sequence of multiple ice-sheet events. Antarctica has been glaciated for the past 34 Myr and has experienced several glacial advances and retreats. Here a case study is presented in which heavy minerals were used to reconstruct East Antarctic glacial events in the Transantarctic Mountains that form an active rift margin. Heavy-mineral analyses demonstrate that the tills in these mountains should be subdivided into at least two end-member petrofacies. The first petrofacies is characterised by tills derived from the highest stratigraphic succession of the Transantarctic Mountains, which were deposited when ice was overriding the mountains. Tills of the second petrofacies originate from erosion and deposition within the glacial troughs that traverse the Transantarctic Mountains, and now form the drainage pathway for the outlet glaciers of the East Antarctic ice sheet. The two petrofacies represent different ice-sheet drainage patterns and the tills were deposited during consecutive stages of denudation of the rift margin. [ABSTRACT FROM AUTHOR]

Following the consolidation and erosion of the Arabo-Nubian Shield (ANS) in the Neoproterozoic, extensive siliciclastics were deposited above it and along its northern margins. These sediments consist of two thick successions, which are separated by an erosional surface representing a regional peneplain. They comprise Neoproterozoic-Early Cambrian orogenic, molasse-type, immature conglomerates and arkoses, and a Palaeozoic to Early Mesozoic succession of platformal, mature sandstones. The heavy mineral contents generally parallel those of the major framework components, e.g., a prevalence of unstable species in the lower, and dominantly ultrastable minerals in the upper succession. This maturation is controlled by provenance and chemical weathering at the source, during transportation or both. Environmental and climate changes are indicated by the presence or absence of detrital apatite, which disappears in the Late Palaeozoic and onward, reacting to acidic weathering in a warm climate, and in the abundance of garnet in the Middle Ordovician to Early Silurian successions due to colder climatic conditions with limited weathering. Authigenic apatite is present locally and is formed at a later phase, as a result of fluid migration during the early stages of the Tertiary Dead Sea Rift. The following three provenance-controlled heavy mineral suites may be distinguished. (1) An unstable heavy mineral assemblage of the Neoproterozoic immature, siliciclastic deposits, derived mostly from a Pan-African igneous/metamorphic terrain within the ANS. This records only mechanical abrasion and a short-distance of transport. (2) An ultrastable/stable heavy mineral assemblage of the Early Palaeozoic, mature, siliciclastic successions, derived mostly from Pan-African and older crust outside the ANS (interior of Gondwana), but with intermittent input from locally exposed basement rocks of the ANS. This assemblage underwent mainly chemical weathering over a long transport distance. (3) An ultrastable heavy mineral assemblage of the Late Palaeozoic-Early Mesozoic mature, siliciclastic sediments, sourced mostly from reworked older internal siliciclastics, and from beyond the ANS, but which also incorporate detritus from extensive exposures of the ANS basement. They were affected by chemical weathering and experienced long to moderate transport. [ABSTRACT FROM AUTHOR]

Heavy mineral concentration in sediments depends primarily on the chemistry and tectonostratigraphic level of rocks eroded within continental-block, arc, or orogenic source terranes. Detritus derived from mantle peridotites and lower crustal gabbros, as well as from high-pressure (oceanic or continental eclogite) and high-temperature (amphibolite, granulite) metamorphic rocks contains one to two orders of magnitude more heavy minerals than detritus derived from upper crustal rocks including granites and sedimentary successions. Concentrated heavy mineral assemblages, however, may result from density-sorting during erosion, transport, or deposition by tractive currents, which can very effectively segregate minerals with even small differences in density within distinct grain-size fractions and sedimentary environments (e.g., fluvial channel versus overbank, beach versus shelf). Conversely, depleted heavy mineral assemblages may result from severe diagenetic dissolution in ancient sandstones, a process that in Alpine and Himalayan foreland basins very extensively affected clastic wedges older than the Pleistocene. Through a series of key modern examples from various geodynamic settings in arid to semiarid climate, we stress the importance of giving full consideration to heavy mineral concentration while interpreting provenance of terrigenous sediments and sedimentary rocks. The concentration parameters introduced herein (Heavy Mineral Concentration index, Source Rock Density index), coupled with parameters based on heavy mineral species with either contrasting density (% opaque, % ultradense, % ZR) or chemical stability, allow us to reveal and quantify also the effects of hydraulic sorting in the depositional environment and of diagenetic dissolution in ancient terrigenous rocks. We document that in most modern sands, the relative abundance of chemically stable species (e.g., zircon, tourmaline, rutile, apatite, chrome spinel) is considerably less than the experience on ancient sandstones generally induces to believe, and show that the actualistic approach provides crucial insight for a correct interpretation of heavy mineral suites. [ABSTRACT FROM AUTHOR]

A wide-ranging study of heavy mineral grain surface textures using the scanning electron microscope has demonstrated that heavy mineral dissolution is widespread in sedimentary basins worldwide. Many heavy mineral grains, including andalusite, amphibole, chloritoid, epidote, garnet, kyanite, olivine, pyroxene, sillimanite, staurolite and titanite show dissolution textures, which range from pits, mamillated surfaces, facets and deep parallel grooves and furrows, to hacksaw terminations and skeletal forms. Dissolution has been observed in sedimentary basins from the North Sea, Faeroe-Shetland Basin, Rockall Trough, Norwegian Sea, Germany, France, Ivory Coast, Nigeria, south Caspian Basin, Bengal Basin, India, Borneo, US Gulf Coast and Trinidad. Heavy mineral grain surface texture studies therefore testify to the fact that intrastratal dissolution is a global, rather than a local, phenomenon. Some heavy minerals (apatite, monazite, rutile, spinel, tourmaline and zircon) rarely display surface corrosion during deep burial, and are considered to be essentially stable. However, tourmalines have been observed to develop etch facets under some deep burial circumstances, and both monazite and chrome spinel show signs of incipient corrosion in extreme burial situations. Apatite shows both overgrowth and corrosion textures in the subsurface, with overgrowths tending to develop as burial proceeds. Etched apatite generally coexists with unetched grains irrespective of burial depth, and the corrosion is therefore not related to in-situ diagenetic processes. Dissolution of apatite is considered to occur through weathering in the source area and during periods of alluvial storage during transport, rather than in-situ corrosion in the subsurface. Evaluation of the extent to which heavy mineral assemblages have undergone post-depositional modification by dissolution processes is crucial when evaluating provenance, and the scanning electron microscope has an important role to play in this regard. [ABSTRACT FROM AUTHOR]

Although shales dominate the sedimentary rock record, when compared to sandstones their heavy mineral fraction has received little attention. A principal reason for this disparity is the difficulty of density separations in rocks with high clay contents using organic liquids. These liquids work well for clean sandstones, but their effectiveness in clay-rich samples is limited by the adsorption of organic molecules onto clay minerals. Additionally, the small size of heavy mineral grains within shales demands advanced observational conditions, and considerable expertise that analysts must develop before undertaking these investigations. In this study heavy minerals were separated from the clay and light-mineral matrices of over 100 shale samples using lithium metatungstate (LMT), a non-organic heavy liquid. The sample sets include sites from Ordovician through Mississippian shales from the Ouachita Mountains of Oklahoma and Arkansas, USA, and Miocene through Pleistocene shales from the subsurface Gulf of Mexico (GOM). Heavy minerals include variable amounts of zircon, tourmaline, rutile, apatite, baryte, monazite, and xenotime. Opaque minerals are Fe, Ti, Fe-Mn, Ba-Mn, and Cr-Fe oxides, as well as Fe-rich micas. Comparisons with heavy-mineral contents of interbedded sandstones with the surrounding deep-water shales show that heavy minerals are equally plentiful and diverse in the finer-grained clastics. Tectonic and provenance interpretations based on trace-element geochemistry rely upon the assumption that signature elements are quantitatively transferred from the same source as the bulk of the sediments. Trace-element analyses of whole-rock and light-mineral separates indicate that heavy minerals are sometimes the dominant sites for some of the trace elements in shales. The potential control of signature trace elements by an accessory mineral phase, perhaps from a secondary, low-volume source terrain, needs to be addressed. We stress the importance of using the heavy-mineral fraction to complement the geochemical study of shales. Heavy minerals in shales can be as effective in determining sediment provenance as they have proven to be in sandstones. A source of some of the heavy minerals within shales could be from resistate mineral inclusions within both light and heavy host minerals. This is particularly important for zircon, rutile, and monazite, based upon their observed size in shales. This should be considered when using heavy minerals in shales for provenance studies. [ABSTRACT FROM AUTHOR]

Grain-size and heavy mineral data are presented for the Palaeocene strata of the London Basin, southeastern England. This succession comprises four main sedimentary units: the Thanet Sand, Upnor, Woolwich and Reading formations. Samples from two borehole sections (Coppermills and Hadley Road) and one exposure (Herne Bay) have been analysed. The boundary between the Thanet Sand and Upnor formations is clearly defined lithologically at the base of a transgressive pebble bed, but is also recognised by a change from a tourmaline-dominated to a zircondominated heavy mineral assemblage and a shift in grain-size mode from 3.5 to 3 phi. At Herne Bay, strata close to the lower and upper boundaries of the Upnor Formation display atypical mineral assemblages, suggesting, at least at the upper boundary, that bioturbation has masked these contacts. Samples from the Lower Mottled Clay Member of the Reading Formation show clear evidence of multiple provenance. Grain-size and heavy mineral characteristics show variation between two end-members: a tourmaline-dominated sediment with a 3.5 phi grain-size mode and a second zircon-dominated sediment with a 3 phi grain-size mode. The former may represent fluvially reworked Thanet Sand sediment and the latter either reworked Upnor sediment or continued sedimentation from the same source area (s) as the Upnor Formation. The Reading Formation, particularly the Upper Mottled Clay Member, shows signs of pedogenic modification. The results presented in this contribution indicate that combined grain-size and heavy mineral studies of borehole-derived material can improve our stratigraphic understanding of poorly preserved and bioturbated strata, despite the restrictions of small sample size and limited borehole distribution. [ABSTRACT FROM AUTHOR]

This short contribution deals with the behaviour and modification of heavy mineral assemblages in a 500 m-thick turbidite succession deposited in the rift valley of the 3300m deep Escanaba Trough of the Juan de Fuca Plate. To our knowledge, there have been no previous studies on the effects of hydrothermal fluid circulation on heavy minerals in such an active geochemical environment. The sediments were transported mainly from glacial lakes of the Columbia drainage basin by cataclysmic floods during the last 60 ka. Climatic and sediment transport conditions imply minor weathering of the source rocks, with little sorting and mechanical abrasion of heavy minerals during transit. Our results indicate that the heavy minerals experienced severe chemical etching and dissolution by circulating hydrothermal pore fluids that caused, at various depths, the complete loss of particular species, especially the chemically highly unstable ortho- and clinopyroxenes. These specific geochemical conditions also generated new minerals, mainly titanite, iron-rich magnesite, barite, and pyrite. However, at present there is insufficient data to fully constrain the kinetics of dissolution of the various minerals as a function of pH, temperature, composition of pore fluids, and sediment-permeability. The length of time during which the sediments were affected by pore fluid movements is constrained by the very young (Late Pleistocene, ∼60 ka) age of the sediments. [ABSTRACT FROM AUTHOR]

Detrital heavy-mineral assemblages respond to increasing burial diagenesis by progressive dissolution of unstable components. Case studies from sedimentary basins worldwide show a uniform pattern of relative stability. The order of stability during burial diagenesis is olivine (least stable) < orthopyroxene, clinopyroxene < sodic pyroxene < calcic amphibole, andalusite, sillimanite < epidote < titanite < kyanite < sodic amphibole < staurolite < allanite < garnet, chloritoid < tourmaline, monazite, spinel < rutile, anatase, brookite, zircon, apatite (most stable). Mineral dissolution can be recognised by corrosion textures on grain surfaces and by preservation of unstable minerals in low-porosity zones adjacent to friable sandstones with less diverse assemblages. Increasing pore fluid temperatures, accompanied by changes in pore fluid composition, are responsible for progressive mineral dissolution. There is, therefore, an indirect relationship between mineral diversity and burial depth in sedimentary basins worldwide. However, the depths at which individual minerals disappear vary markedly between basins, largely due to differences in pore fluid temperature gradients. Geological time is another significant factor in mineral depletion. Interpretation of provenance using heavy-mineral data from sandstones likely to have suffered burial diagenesis must carefully consider the possibility that some heavy-mineral species have been eliminated through dissolution. Evaluation of provenance under such circumstances must rely on parameters that are demonstrably unaffected by diagenesis. A combined approach, integrating provenance-sensitive ratio measurements with varietal data, either petrographic, geochemical or isotopic, is recommended. [ABSTRACT FROM AUTHOR]

A typical complete sedimentary cycle involves five phases (pre-erosional, in transit, post-depositional pre-burial, post-burial, exhumation) and six processes potentially modifying the original composition of the sediment. Some processes add mineral species to an assemblage, others subtract minerals, and yet others can both add and subtract minerals; moreover, some can operate in only one of the five phases, whereas others can affect up to three phases. Authigenic growth and anthropogenic addition are relatively easy to recognise and compensate for, occurring in predictable and limited environmental conditions. Although mechanical weathering can substantially alter heavy mineral assemblages, its effects also are predictable, and prolonged or intense abrasion is required. In contrast, differential sorting of minerals during transport can have a rapid and profound modifying effect on a heavy mineral assemblage that is less readily compensated for but does broadly follow the laws of physics. In an analogous effect, any contrasts between heavy mineral studies in the size fraction selected by each analyst can seriously undermine data comparison. The widely recognised boundary between superficial pedochemical weathering and deeper geochemical weathering is largely artificial. Both phenomena frequently and often profoundly modify heavy mineral assemblages, but the resulting patterns of depletion vary considerably. For example, intrinsic properties of minerals conferring vulnerability to acid pedochemical weathering include well-developed multiple cleavage planes and/or inclusions, high-energy lattices and high Fe2+ content. However, these properties are insufficient to accurately predict a stability series in any particular heavy mineral assemblage, as both relative and absolute depletion rates are strongly influenced in the post-depositional environment by both abiotic factors (e.g., pH, redox potential) and under-researched biotic factors. Five case-studies of heavy mineral assemblages in British Tertiary and Quaternary deposits are used to illustrate these principles and to demonstrate the benefits of (a) using multivariate methods to elucidate patterns of variation in heavy mineral assemblages, (b) characterising a weathering front using 90% depletion (D90) values and (c) integrating heavy mineral data with those derived from other geoanalytical and field-based techniques. This approach allows not only more accurate reconstruction of provenance but also of palaeoenvironments; both can then usefully inform correlation. [ABSTRACT FROM AUTHOR]

Knowledge of the transparent heavy minerals present in the sand fraction of sediments on the northern Portuguese continental margin rests on the study of 504 samples, obtained from the shelf and upper slope (358), and from the major rivers (146). Results show the main association comprising biotite, andalusite, tourmaline, amphibole, garnet, staurolite, zircon and apatite. A second, subordinate, suite includes orthopyroxene, clinopyroxene and olivine and is present only in the outer shelf and upper slope south of Porto canyon. These two distinctive assemblages indicate derivation from different primary sources: the main heavy mineral suite is sourced from metamorphic and igneous rocks, widespread in the drainage basins of all northern Portuguese rivers, whereas the minor one is of different origin and points to a basic igneous source, located probably elsewhere in the outer shelf or upper slope, south of Porto canyon. The distribution patterns of the mineral species in the major association indicate that these terrigenous assemblages were delivered to the shelf by rivers in a highly selective manner. Only biotite and other platy grains are able to reach the middle shelf that is constrained by the analysis of the hydraulic behaviour of the different grains. Mobile grains, such as biotite and the most platy amphiboles, are excellent sedimentary tracers of the present shelf transport dynamics. Their distribution patterns suggest the influence of a downwelling oceanographic regime, which predominantly affects the inner and middle shelves. Corresponding distribution patterns between the most mobile heavy mineral grains and fine-grained sediments (muddy patches) may indicate the similarity of their hydraulic behaviour. In contrast, the less mobile grains, such as coarse garnet, andalusite, tourmaline, staurolite and zircon, reach only the inner shelf. Polycyclic, rounded grains found in the middle shelf in coarse-grained deposits represent relict and palimpsest sediments and contrast with the angular forms characteristic of the modern river and inner-shelf sediments. [ABSTRACT FROM AUTHOR]