Introduction and Overview

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INTRODUCTION AND OVERVIEW

Each heavy mineral grain is a unique messenger of coded data, carrying the details of its ancestry and the vicissitudes of its sedimentary history Clastic sediment packages are geological archives that record and preserve signatures of past geological events in source provinces, during transit, and at the depocentre. Their high-density grains represent the detrital occurrence of essential rock-forming minerals (e.g. garnet, pyroxenes, micas) or accessories (e.g. zircon, tourmaline, apatite) with densities 42.8: thus they are termed ‘heavy minerals’ (Mange and Maurer, 1992). They typically comprise 1% of siliciclastic sediments, so to study them effectively, they must be concentrated. This is normally carried out after rock disaggregation by mineral separation, using ‘heavy’ liquids, for example bromoform or tetrabromoethane, with specific gravities of 2.89 and 2.97, respectively. Alternatively, non-toxic sodium polytungstate or other LST products with adjustable densities may be used. Heavy minerals sink in these liquids, which permits their complete segregation from the less dense framework components (Mange and Maurer, 1992). The recognition of heavy minerals in sands probably dates back to the times when prospecting started for placer deposits, gold and minerals of economic importance. The first known publication was by Dick (1887), as a result of his heavy mineral explorations in North Wales, while Artini (1898) provided the first thorough descriptions of heavy minerals in quantitative analyses of River Po sands. From the late 19th century to the beginning of the Second World War, heavy mineral studies were de rigueur and always a critical part of any serious sedimentary petrographic analysis, as described in Milner’s (1929, 1962) and Boswell’s (1933) classic texts. However, a subsequent decline in popularity resulted from the recognition that hydraulic effects can cause selective sorting according to size, shape and density, compounded by the realisation that other phenomena, such as inherited grain size dependence and post-depositional dissolution, could also affect heavy mineral compositions. Knowledge of the behaviour of heavy minerals in a wide range of sedimentary environments, both surficial and diagenetic, increased in parallel with the growing understanding of sedimentary processes and factors operating in depositional environments. This led to the re-emergence of heavy mineral studies as a valuable investigative tool. Insights into such processes explained the ‘enigmatic’ response of heavy minerals during the rock cycle in, for example, selective grain sorting in transit, dissolution of unstable minerals in the pedogenesis zone during alluvial storage and the post-burial effects of ‘intrastratal dissolution’. A revival in heavy mineral studies followed rapidly, and the recognition of their value is reflected in the increasingly diverse range of problems to which they have been applied, not only within earth sciences but also in the cross-disciplinary areas of forensic and

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soil sciences, and geoarchaeology. Moreover, heavy minerals are probably even more frequently used than in past decades, stimulated by cutting-edge, instrument-oriented technologies that exploit the unique properties of individual minerals. The history of any mineral begins during the petrogenesis of its parent rock. Crystallisation is a highly complex and prolonged process that includes a series of phases during which minerals are generated in accordance with their stability fields, and inherit the parameters of their particular phase. This is manifested in the properties of crystal structure, morphology, colour, chemical and optical zoning, inclusions, twinning and many other characteristics. Parent rocks may pass through episodes of progressive crystallisation, instability, retrogression, metamorphic overprint and other geochemical processes which can either generate new minerals or leave an imprint on existing ones. Examples include pyroxenes rimmed by amphiboles, sodic amphiboles surrounded by calcic amphibole rims, tourmaline cores preserving a pre-existing phase, garnet zoning and, probably the most well-known, the complex internal structure and overgrowths of zircons. The effects of transport, climate, alluvial storage, re-entrainment, deposition, burial diagenesis and, not uncommonly, recycling are preserved within the inherited morphology, structural properties and surface textures of a particular heavy mineral grain. Recognising these chemical and physical signatures enables the researcher to critically assess and interpret the information encoded within the heavy mineral assemblage. It is, however, important to establish a link between the component heavy minerals of the host sediment, the geological setting of their origin and their sedimentary history. The analyst also needs to have a sound knowledge of igneous and metamorphic petrology and the geology of the study area! Optical mineralogy provides an overview of the heavy mineral assemblages and will prompt the researcher to invoke, if necessary, other instrumental techniques for further information, higher resolution and clarification. With the widespread availability of increasingly sophisticated modern instruments (EDS–SEM electron microprobe, laser ablation multicollector MC–ICP–MS, sensitive high-resolution ion microprobe (SHRIMP) to mention only a few), the heavy mineral technique can reach the highest level of precision. In all cases, however, the whole assemblage must be considered before conclusions are drawn. Heavy mineral assemblages yield unique information, not provided by any other means, but that information is held in coded form that only the right keys can unlock. In assembling this volume, we have tried to provide examples of the usefulness and validity of heavy minerals in an expanding field of applications. We hope that the collation of seminal and innovative studies in pure and applied research in this volume will reveal the debt that we owe to early workers, while recognising the importance of recent advances and providing a much-needed and authoritative resource for researcher and practitioner alike. ‘Heavy Minerals in Use’ comprises a series of contributions across a wide spectrum of geological and related disciplines in which heavy mineral analysis played a decisive role, either alone or as part of a holistic approach with other techniques. The book is subdivided into sections to reflect, thematically, the diverse applications in which heavy mineral analysis has been used.

PART I: Heavy Minerals in the Study of Siliciclastic Sediments

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PART I: HEAVY MINERALS IN THE STUDY OF SILICICLASTIC SEDIMENTS: PRINCIPLES, PROCESSES AND PRODUCTS Part I deals with fundamental processes, the principal factors that control the nature and composition of heavy mineral suites. Chapters here provide an insight into the main physical and chemical controls on heavy mineral abundances and composition in sediments, and the means by which heavy minerals can be studied. From the moment when heavy minerals are liberated from their host rock, along with framework components and lithic fragments, they are subjected to a series of mechanical and chemical weathering processes that persist until the assemblages are extracted from a sediment for study. These processes make their first impact on mineral detritus that accumulates temporarily in close proximity to the parent rocks. Once entrainment commences, heavy minerals, either in pristine form or affected by a degree of dissolution, enter the sedimentary cycle and are subjected to the effects of sediment transport. 1.1. Entrainment, Transport and Deposition: Hydraulic Control Transported sediments commonly exhibit spatial mineralogical trends resulting from hydraulic processes. Paul D. Komar reviews the contrasting hydrodynamic properties of heavy minerals and quartz and feldspar grains related to differences in the ranges of particle sizes and shapes. He shows how differential rates of transport are reflected in distinct patterns of deposition related to particle attributes. He concludes that a better understanding of the physical processes that bring about mineral sorting is necessary to assist in provenance interpretations of heavy mineral analyses. Omran E. Frihy examines modern physical processes in which waves and currents sort and concentrate the heavy mineral grains according to their densities, sizes and shapes during transport of beach sand between eroding and accreting shores along the Nile Delta. These two environments have distinctive heavy mineral assemblages, with garnet and zircon decreasing exponentially with distance from the site of erosion at a river mouth, while augite and hornblende show an opposite trend. Distinctive cross-shore patterns are also detected, with the densest minerals being most concentrated in the inner surf zone, and decreasing in concentration towards winnowed sediment sinks offshore that may be almost entirely free of detrital heavy minerals. Thus the suite of heavy minerals found in delta coastal sands can be used as natural tracers of sand movement related to large-scale shoreline change. The third case study dealing with the operating factors in dynamic aquatic regimes is by Joa˜o Cascalho and Catarina Fradique, who discuss processes on the Portuguese continental margin. They identified a main association, comprising biotite, andalusite, tourmaline, amphibole, garnet, staurolite, zircon and apatite, and a second, subordinate, suite that includes orthopyroxene, clinopyroxene and olivine. The latter is present only in the outer shelf and upper slope south of Porto canyon. The distribution patterns of the mineral species in the main association indicate that these terrigenous assemblages were delivered to the shelf by rivers in a highly selective manner, constrained by the hydraulic behaviour of the different grains. They found that mobile grains, such as biotite and the most platy amphiboles, are excellent sedimentary tracers of the present shelf transport dynamics, whereas the

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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. 1.2. From Surface Weathering to Burial Diagenesis Chemical weathering is a fundamental process in the geological cycle that operates not only on exposed rocks in the source area, but also on mineral grains in transit, at the depositional site and in the environment of diagenesis. It is responsible for the formation of soils and, being highly selective in its effects, it ultimately controls the composition of heavy mineral suites, affecting especially those which experienced a long geological history under substantial burial. Weathering processes and their products are extensively studied in earth and soil sciences by chemists, soil scientists, sedimentologists, geochemists and heavy mineral specialists. Seven contributions are presented, with case studies from different geological settings and at different stages of the sedimentary cycle. Michael A. Velbel describes the effects of the weathering process by examining the surface textures of pyroxenes and amphiboles at different stages of dissolution. He investigates all aspects of heavy mineral responses and chemically produced surface features. Velbel concludes that surface textures on detrital heavy mineral grains can be used to infer weathering processes in soils and weathered regoliths, provenance and sedimentary environments, and intrastratal dissolution during burial diagenesis. He shows that the significance of etch pits and other surface textures on heavy minerals in a soil or regolith depends on the rates at which they form in that regolith, and how long the grains have been subject to such reactions (i.e., the age of the soil) in the weathering environment. Comparison of ranges of dissolution textures on pyroxenes and amphiboles in modern sediments with those of intrastratally dissolved grains in clastic sedimentary rocks indicated that these features are similar. Richard M. Bateman and John A. Catt cover a wide range of themes in their evaluation of weathering processes affecting surficial sediments. They identify five stages in the sedimentary cycle, with six processes that may potentially modify the original sediment composition. Their work suggests that the boundary between superficial pedochemical and deeper geochemical weathering is largely artificial, and that the effects of biotic processes may be underestimated. Their holistic approach integrates multivariate ordinations, mineral depletion curves and different data sources to interpret patterns of variation in heavy mineral assemblages that can then inform the reconstruction of provenance and palaeoenvironments. Bateman and Catt also make a number of excellent observations on mitigating the risks of applying new techniques to heavy mineral analysis by constructing a conceptual framework for data interpretation, and on the potential for the better exploitation of existing data through rigorous statistical analysis. A.J. (Tom) van Loon and Maria A. Mange deal with the rarely discussed environment of extreme weathering and the ‘in situ’ dissolution of heavy minerals. Diverse processes during the sedimentary cycle and extreme weathering imparted an unusual bulk and heavy mineral composition to the Tertiary Dutch and German ‘silver sands’ (sands that consist almost exclusively of quartz) which are devoid of clear provenance signatures. The study provides a new insight into the impact of

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‘in situ’ weathering on heavy mineral assemblages and shows that understanding its end-products may be helpful in drawing stratigraphic boundaries between units with originally comparable heavy mineral compositions. Andrew C. Morton and Claire Hallsworth explore the environment of burial diagenesis, and apply their knowledge and experience to show how heavy mineral assemblages respond to increasing burial depth through the progressive dissolution of unstable components. Case studies from sedimentary basins worldwide show a uniform pattern of relative mineral stability. Increasing pore fluid temperatures, accompanied by changes in pore fluid composition, are responsible for progressive mineral dissolution. Morton and Hallsworth show that an indirect relationship exists between mineral diversity and burial depth in sedimentary basins worldwide. However, the depths at which individual minerals disappear vary markedly between basins, largely because of differences in pore fluid temperature gradients. Geological time is another significant factor in mineral depletion. Kitty L. Milliken takes the reader to the Gulf of Mexico Basin which, because of the well-documented provenance and simple burial history, serves as a natural laboratory for research into the nature of processes by which provenance information is ‘erased’ and otherwise complicated by diagenesis. She proposes a generalised model for basinal diagenesis of heavy minerals, characterised first by acid hydrolysis or weathering processes. At depths that overlap the ultimate completion of the subsurface weathering process, authigenic minerals, including a number of high-density phases, form by reactions that can be described as acid-releasing or reverse weathering. Finally at depths near the limit of coring (45 km), the surviving ultrastable detrital heavy mineral assemblage (mostly zircon, tourmaline and rutile) is accompanied by a variety of high-density authigenic minerals (including anatase and titanite). Gian G. Zuffa and Francesca Serra’s 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 3300 m deep Escanaba Trough of the Juan de Fuca Plate, and shows the effects of hydrothermal fluid circulation on heavy minerals in a highly active geochemical environment. Their results provide an insight into the environment of circulating hydrothermal pore fluids that cause severe etching and the dissolution of heavy minerals at various depths, especially the chemically highly unstable ortho- and clinopyroxenes. These specific geochemical conditions also generated new minerals, mainly titanite, iron-rich magnesite, barite and pyrite. The length of time during which the sediments were affected by pore fluid movements is constrained by the Late Pleistocene (60 ka) age of the sediments. This section concludes with the contribution by Rikke Weibel and Henrik Friis, presenting a case study on the alteration of opaque heavy minerals from different depositional and diagenetic environments and various geochemical regimes in Denmark and the island of Helgoland. These include Triassic red beds with early oxidising conditions, the weakly reducing conditions of the Miocene Odderup Formation and the strongly reducing environment of the Gassum Formation, where abundant iron and organic matter, and thus related sulphate reduction, have influenced the alteration products. Extreme sulphur-dominated local environments are represented by Holocene carbonate-cemented sandstone pillars.

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1.3. Heavy Minerals and Grain Size Sceptics argue that the effect of grain size may impart a strong bias to interpretation of heavy mineral data because it causes selective sorting by weight, size and shape. This influence can be alleviated, largely, by dense sampling and by the understanding of ‘hard’ rocks and the nature of their mineral phases. Grain size and shape is usually inherited because a number of heavy mineral species have an affinity to certain grain sizes and crystal forms, a factor controlled primarily by conditions of crystallisation. Therefore, many heavy minerals enter the sedimentary cycle with their ‘inherited’ size and shape. For example, zircon usually occurs as small, frequently, euhedral or subhedral grains, whereas staurolite, kyanite, sillimanite, andalusite, topaz, and in many deposits, garnet, tourmaline and pyroxenes appear as relatively large grains with a variable shape. During the sedimentary cycle, a variety of processes modify the original grain size and shape, and, as a result, heavy minerals can have an ‘acquired’ grain size and shape. Differentiating between inherited and acquired characteristics may be possible by analysing the imprint of the process(es) responsible for the grain’s size and shape, while the surface texture of the grains may prove useful for environmental reconstruction. In this section, Alice R.A. Thomas integrates heavy mineral analysis with systematic grain size measurements on Palaeocene sediments of the London Basin. Her analysis reveals that grain size and heavy mineral characteristics show variations between two end-members: a tourmaline-dominated sediment with a 3.5 phi grain size mode and a zircon-dominated sediment with a 3 phi grain size mode. Grain size trends also reflect reworking of older sediments into a younger formation, whereas other beds show signs of pedogenic modification, and/or strong bioturbation. Her contribution indicates that combined grain size and heavy mineral studies of outcrop and borehole-derived material can improve our stratigraphic understanding of poorly preserved and bioturbated strata, despite the restrictions of poor exposures, small sample size and limited borehole distribution. Matthew W. Totten and Mark A. Hanan challenge some of the preconceptions about heavy minerals in shales, including hydraulic equivalency, and stress the importance of using the heavy mineral fraction to complement the geochemical study of shales, while acknowledging that we do not yet fully understand the mechanism by which they were deposited. Whereas the mineralogical source of most trace elements in shales is attributed typically to clays, the frequently reported correlation between clay–mineral percentage and trace elements in whole-rock analyses is not always borne out in studies, and the variation may be due to geochemical variations of certain trace elements in component heavy minerals. An alternative explanation offered is the dilution of trace elements and clay minerals by quartz. 1.4. Miscellaneous Techniques This section is an overview of techniques that take heavy mineral analyses beyond the light microscope and broaden knowledge of the assemblages by adding geochemical and/or optical information. Maria A. Mange and Andrew C. Morton review the benefits of single-mineral geochemical (varietal) analysis conferred by continuing

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technological advances that provide increasingly higher levels of analytical precision. Virtually all detrital heavy minerals can now be subjected to a range of sophisticated geoanalytical techniques that can determine their isotopic composition, map the distribution of major and trace elements and identify their crystal chemistry. Mange and Morton present case studies on garnet, tourmaline, chrome spinel, apatite, pyroxenes, amphiboles and ilmenite, from a wide variety of geological settings and brief references are given to those that have, so far, received only minor interest. The sharp, high-resolution images of the scanning electron microscope (SEM) have attracted heavy mineral specialists for over 30 years. Equipped with energy dispersive X-ray spectrometer (EDS) the SEM also provides a quick and easy way to increase information on heavy mineral species besides revealing great details of their surface characteristics at various stages of corrosion. It is probably the most frequently used auxiliary instrument in heavy mineral studies. This is reflected by the two substantial contributions of Grenville Turner and Andrew Morton, and by Michael A. Velbel, Jennifer T. McGuire and Andrew S. Madden. Kitty L. Milliken, Richard M. Bateman and John A. Catt and David Smale also illustrate the interpretation of their case study by high-resolution SEM images. Maria A. Mange and David T. Wright discuss the principles of high-resolution heavy mineral analysis (HRHMA). They emphasise the complexity of heavy mineral assemblages and caution against recording grains of a particular species with differing characteristics (reflected by their appearance, physical and optical properties) as one category. Different varieties of a species may have marked differences in petrogenesis and provenance; thus not categorising varietal characteristics which occur at species level can generate misleading information and incorrect interpretations, while the full history of a sediment and the accurate reconstruction of its provenance remains concealed. 1.5. Numerical Data Analysis Although a visual inspection of tabulated data and figures allows the detection of the more obvious mineral trends, less marked differences can be overlooked; hence, using advanced numerical techniques is of considerable importance if data assessment is to be objective. Imbrie and Van Andel (1964) were the first to numerically evaluate heavy mineral data by Q-mode factor analysis. This analysis is most applicable in studies involving complex and remote source regions and far-travelled, mixed sands, enhanced by maps showing regional variability patterns to reveal the aerial distribution of mineral assemblages. This method continued to be used for large databases (e.g., Frihy and Lofty, 1997; Carriquiry and Sa´nchez, 1999; Wong, 2002). Principle Component Analysis (PCA) finds a wide application in geology and is successfully used to analyse and interpret complex heavy mineral data (Pirkle et al., 1985; Svendsen, 2002). Because heavy mineral studies are generally data-intensive, they are particularly suitable for numerical data analysis. In this volume three case studies focus on numerical analysis of large heavy mineral datasets. Several authors in other sections in this volume also include statistical evaluation of their data (e.g., Bateman and Catt, Frihy, Malone, Poulsen et al., and Smale). Of the case studies presented in this section, Alexander N. Derkachev and Natalia A. Nikolaeva demonstrate the value of multivariate statistics using an extremely

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large heavy mineral database generated by the analysis of samples from basins in the western Pacific (Bering, Okhotsk, Japan, East China, Philippine, Banda, etc.) and from the Tonga and Vanuatu Trenches. Results allowed identification of several mineralogical provinces, linked to distinct hinterland complexes and associated tectonic controls. Q-mode factor analysis differentiates four major groups of assemblages of distinctive provenance. R-mode factors help to define representative mineral associations, which best characterise the mineral composition of the sediments of the individual marginal seas, and lead to the delineation of eight provinces, tied to distinct source provinces and associated tectonic controls. Despite the large latitudinal and environmental range of the study basins, the complexity of source rocks and volcanic signatures is clearly reflected in the distribution of heavy mineral assemblages. Paul D. Ryan, Maria A. Mange and John F. Dewey developed new statistical techniques for treating the substantial heavy mineral data, produced over a 10-year period, from Ordovician rocks of the South Mayo Trough, western Ireland. They aimed at providing an independent and objective way to elucidate the stratigraphy and tectonic history of the region. A new method is presented for plotting normalised scores to emphasise stratigraphic trends of heavy minerals and specific heavy mineral varieties, which are shown to be largely non-normally distributed, with significant variation between formations. Also, a method is developed for testing significance of variation within a formation using non-parametric tests. PCA is used to identify major source regions throughout the life of this basin. Edit Thamo´-Bozso´ and Lajos O´.Kova´cs introduce the thick Quaternary successions of the central part of the Hungarian Plain to the reader and discuss the evolution of the fluvial network during the Quaternary. They benefited from a large heavy mineral database, obtained on borehole and modern river samples. Cluster analysis and PCA reveal appreciable similarities between the heavy mineral compositions of modern river sediments and those from borehole samples, resulting in a more refined reconstruction of the Quaternary fluvial network and sediment provenance. PCA has provided a clear differentiation of the garnet-rich sediments of the two main modern rivers flowing from opposite directions (Danube and Tisza), but uncertainties remain with the older sands probably because of changing source areas and/or intermixing the loads of different palaeo-rivers with time. Using PCA, a comparison of the heavy mineral composition of modern river sands and those deposited by their ancestors has revealed some differences, interpreted as the impact of tectonic and erosional changes during the Pleistocene.

PART II: PROVENANCE, TRANSPORT, DEPOSITION, EXHUMATION 2.1. Regional Studies—Modern and Ancient Environments This section encompasses a wide spectrum of research commencing with a comprehensive study on modern sediments. These provide analogues that lead to the better understanding and faithful reconstruction of the history of ancient successions. Authors from different countries and continents present their case

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studies, ranging from the Alps to Antarctica, demonstrating the potential of heavy mineral analyses in a variety of cratonic and dynamic plate-tectonic settings. Eduardo Garzanti and Sergio Ando` point out the genetic link between heavy mineral concentrations in sediments and the chemistry and tectono-stratigraphic level of rocks in source terranes. However, although mantle peridotites, lower crustal gabbros and high-grade metamorphic rocks yield more abundant heavy minerals than igneous and sedimentary rocks of the upper crust, depleted heavy mineral assemblages may result from severe diagenetic dissolution in ancient sandstones, for example, in Alpine and Himalayan foreland basins. Conversely, hydraulic sorting in the sediment cycle can concentrate and segregate heavy minerals within distinct grain size fractions in different, high-energy sedimentary environments. Garzanti and Ando` show that in modern sands, the concentration of heavy minerals from different geodynamic settings depends primarily on the chemical composition and density of the source rocks. A good example is where heavy mineral concentrations of sediments increase upsection in a basin during the unroofing of progressively deeper tectono-stratigraphic levels within a source terrane. By applying heavy mineral concentration indices in conjunction with heavy mineral density and stability ratios, they are able to assess the effect of hydraulic sorting in sedimentary environments or that of diagenetic dissolution in ancient sandstones. John Malone compares the heavy mineral ‘fingerprint’ from sediments of local rivers with that of seabed sediments to determine whether seabed sands off southeastern Ireland were derived from the Irish land mass. Perhaps surprisingly, Malone found that both the beach sands and offshore suites were rich in augite, which is not found with any frequency in river sediment, indicating that beach sands are largely derived from offshore sources. Malone supports his observations with multivariate statistical analyses to quantify differences in sediment provenance. Garnets present in the rivers confirm that the offshore sediments in the Irish Sea were not derived from the Irish landmass, but were delivered from Northern Ireland and Scotland by glacial processes. Glaucophane in offshore and some beach sediments indicates the high-pressure-ophiolite subduction complex of Anglesey, northwestern Wales, as a possible source perhaps delivered by an ice lobe. In New Zealand, David Smale similarly reports how evidence from heavy minerals indicates that the silting of the harbours was caused largely by sediments transported from offshore, rather than from discharging rivers. In his review, Smale demonstrates his experiences with a variety of heavy mineral applications, that range from tracing the onset of volcanism and forensics, and notes how an increasing diversity of heavy minerals can be tied to the inception of the modern plate boundary system in the Miocene. He argues that optical examination must continue to underpin any heavy mineral study, adding that ‘‘to attempt not to do so is like studying petrology without thin sections’’. The discovery of the persistence of identical heavy mineral assemblages from Pleistocene through to the modern sands in Willapa Bay, Washington State, allows Gretchen Luepke Bynum to conclude that the pattern of estuarine sedimentation in Late Pleistocene deposits closely resembles that of the modern Bay, with the same sediment source areas. However, the presence of a heavy mineral suite enriched in epidote in a few older Pleistocene units, associated with southwest-directed foresets in cross-bedded gravel, indicates derivation from the northeast, perhaps from an

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area of glacial outwash. The presence of this suite in ancient estuarine sands exposed on the northeast side of the bay suggests that input from this northerly source may have intermittently dominated Willapa Bay deposition in the past. Jill S. Schneiderman and Zhongyuan Chen studied drill core samples to document the Quaternary tectonic and palaeoenvironmental history of the southern Yangtze delta in China and to integrate the data with other studies to predict sedimentation rates and patterns, following the construction of the Three Gorges Dam on the Yangtze River. Heavy mineral data indicate a southward migration of the Yangtze River channel and deltaic depocentre to its present position. During the Quaternary, the Yangtze River flowed only across the northern delta plain, so that the southern delta plain received heavy minerals from local sources delivered by proximal rivers. However, heavy mineral assemblages in the upper portion of the core indicate that with continued subsidence, the Yangtze River channel shifted south and deposited sediments transported from distal source areas. Future planning requires a comprehensive understanding of the history of the development of the Yangtze delta plain. Giorgio Gandolfi, Luigi Paganelli and William Cavazza integrate old and new heavy mineral analyses from 567 turbidite sandstone samples to provide the first basin-wide stratigraphic and sedimentological framework of the Miocene Marnosoarenacea Formation of the Northern Apennines, Italy. They conclude that the turbidites are the product of distinct detrital inputs from opposing directions and source areas, and that these were deflected along the main axis of the basin, flowing side by side with only minor mixing, as exemplified by marker beds traceable over long distances. Tuvia Weissbrod and Ron Bogoch employ heavy minerals to break down the apparent homogeneity of the Nubian Sandstone of the Arabo-Nubian Shield (ANS) and its northern periphery. The Nubian Sandstone is one of the largest siliciclastic sediment bodies preserved on earth, long considered to be a single unit because of its lack of useful biostratigraphic data and its laterally continuous lithological markers. Sharp changes in the heavy mineral assemblages, indicating unconformities and shifts of provenance, contrast with the presence or disappearance of metastable heavy minerals that may reflect changes in climate. Combined with sedimentological and palaeogeographic data and detrital zircon geochronology, Weissbrod and Bogoch have identified three major depositional sequences in the Nubian Sandstone ranging from Neoproterozoic to Mesozoic. The Neoproterozoic sequences were derived largely from a Pan-African igneous/metamorphic terrain within the ANS, while Early Palaeozoic sequences were derived mostly from Pan-African and older crust outside the ANS in the Gondwana interior. An ultrastable heavy mineral assemblage of the Late Palaeozoic-Early Mesozoic reflects mature sands mostly sourced from reworked internal siliciclastics, but which also incorporate detritus from extensive exposures of the ANS basement. Far from the Nubian Desert, Sandra Passchier records the value of heavy minerals in reconstructing ice-sheet drainage patterns of the East Antarctic ice-sheet and glacial events in the Transantarctic Mountains. These demonstrate that the glacial tills can be subdivided into at least two end-member petrofacies of Caenozoicglaciogenic sediments of the Sirius Group that represent different ice-sheet drainage patterns, with the tills deposited during consecutive stages of denudation of a rift

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margin. Heavy mineral assemblages also demonstrate that the Sirius Group resulted from multiple glacial events, and enable the determination of palaeo-ice flow direction through source rock signatures from outcrops several 100 km upstream. Goran Durn, Dunja Aljinovic´, Marta Crnjakovic´ and Bosˇ ko Lugovic´ tackle the long-standing problem of the nature and relationship of terra rossa in the Istrian peninsula, Croatia, to underlying carbonates, and test the theory that it has developed from the insoluble residue of the carbonate rocks. The heavy mineral assemblage of amphiboles, zircon, tourmaline, garnet, kyanite, clinopyroxene and orthopyroxene, present in both loess deposits and in the terra rossa, clearly establish a link with Late Pleistocene loess. Heavy mineral data indicate that material was also derived from Istrian flysch, and that air-fall of particles from the Roman-Campanian Volcanic Province may also have contributed. Durn et al. conclude that the external contributions to the terra rossa, predominantly Middle Pleistocene loess with some from flysch and tephra, may constitute up to 50% of the polygenetic sediment, the rest coming from insoluble residues of presumed limestone and dolomite source formations. Late Pleistocene loess may have become incorporated in the upper parts of already formed terra rossa. 2.2. Tectonogenic Sediments: The Use of Heavy Minerals in Active Geodynamic Settings In their second contribution, Eduardo Garzanti and Sergio Ando` build on the conceptual models developed by earlier researchers and apply high-resolution heavy mineral and petrographic analyses to detrital heavy mineral assemblages from contrasting modern terrigenous geodynamic settings to diagnose sediment provenance. Because statistical techniques cannot easily identify valid end-members of the wide variety of mineral species in the sands, Garzanti and Ando` employ all the evidence and information provided by raw datasets. They define ten standard groups of heavy minerals from different tectonic settings with similar provenance implications, which may be combined into supergroups and plotted for general conclusions, or split into subgroups for more detailed work. This enables them to determine the relationships between plate-tectonic setting and both framework silicates and heavy mineral assemblages. Commonly, heavy minerals are essential for deciphering the provenance signals of the sediments in orogenic belts, because the composition of the source terrain cannot always be reconstructed from the framework constituents. For example, ophiolitic complexes or blueschist belts in pre-existing source terrains can only be proved through their diagnostic heavy minerals. Peter Faupl, Andreas Pavlopoulos and George Migiros, working in mainland Greece and the Peloponnese, use heavy mineral studies to help track Maastrichtian-Miocene flysch sedimentation in the Hellenides synorogenic basin during the destruction of the Tethys Ocean, and synthesise the results to build a geodynamic model of the Hellenides. Pavel V. Markevich, Alexander I. Malinovsky, Marianna I. Tuchkova, Sergei D. Sokolov and Vladimir N. Grigoryev translate and report the work of Russian researchers who have used heavy minerals to reconstruct the provenance and source lithologies of Mesozoic-Caenozoic sedimentary complexes of the Far East and the western Pacific Ocean, and to identify their plate-tectonic settings. Their overview

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Introduction and Overview

also documents important findings from several hundred samples obtained during numerous marine geological expeditions. Markevich et al. integrated heavy mineral analyses with framework components, volcanics (lava, tuffs and tephra) and bulk chemical compositions to identify source rocks and link them to the plate-tectonic setting of the depositional area. For example, magnetite and chromite compositions were used to identify, and differentiate between, assemblages sourced from different types of ophiolites, while the chemistry of detrital pyroxenes identified the main types of volcanic arc sources. Working in the eastern segment of the Himalayas, Ashraf Uddin, Pranav Kumar, Jogen N. Sarma and Syed H. Akhter, report heavy mineral analyses of representative Oligocene to Pleistocene sandstones from the Assam Basin, and compare these with existing heavy mineral data from coeval Caenozoic sequences in the Bengal Basin to help constrain the unroofing history of the eastern Himalayas and the Indo-Burman Ranges. Uddin et al. conclude that during the Oligocene, heavy minerals in the Assam Basin were derived from incipient uplifts in the Himalayas, whereas in the Bengal Basin supply was from Indian cratonic sources. However, heavy mineral contents in Miocene and younger sequences suggest that both the Bengal and Assam Basins were sourced from the Himalayan and Indo-Burman orogenic hinterlands to the north and east. They conclude from distinct heavy mineral associations that the Assam Basin appears to represent an earlier and more proximal repository of detritus, shed from Himalayan convergence, whereas the Bengal Basin was a downstream and somewhat younger depocentre.

PART III: INTEGRATED AND INTERDISCIPLINARY HEAVY MINERAL APPLICATIONS 3.1. Heavy Mineral Studies Integrated with Other Geoanalytical Techniques This chapter consists of two sections. The first includes studies that invoke a variety of geoanalytical techniques. The second demonstrates the potential of heavy minerals in interdisciplinary research. The first contribution in this section is by Andrew Carter who reviews the intimate links between data of heavy mineral studies and fission-track analysis. He emphasises the mutual benefits of the fission-track analysis; detrital apatite and zircon provide complementary information on timing and rates of source exhumation that helps place heavy mineral evidence within a temporal framework. While combined heavy mineral—fission-track analyses strengthen provenance studies, the effects of lithological bias, small datasets and non-uniqueness of fission-track ages (and thermochronometric ages in general) can limit or hinder interpretation. Carter discusses these issues and presents new approaches that link high-precision geochemical data from single detrital grains with sediment composition and detrital age structure. Combined geochemical and isotopic signatures extracted from single grains permit more detailed resolution of source composition and evolution that strengthen the role of heavy mineral studies and fission-track thermochronometry. D. Johannes Huisman and Gerard Th. Klaver obtained data from an extensive database of an earlier large-scale work that used heavy mineral compositions to

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systematically distinguish lithostratigraphic units in single boreholes or borehole transects in The Netherlands. Huisman and Klaver use sophisticated computer software and create multiple contour maps of heavy mineral concentrations, with stacked threshold maps and colouring codes for depths that give an effective overview of the temporal and spatial distributions of sediments derived from various sources to the area. They use spatial variations of single minerals, as opposed to mineral assemblages, to illustrate the geometry of sediments on a countrywide scale. Distributions of selected heavy minerals (zircon, augite, hornblende, garnet and topaz) reflect ancestral flow paths of the modern major rivers. Hilmar Von Eynatten provides a brief review of heavy mineral research on the Swiss Molasse Basin and summarises the results of recent studies. His contribution integrates heavy mineral analysis with high-resolution single-grain chemistry and thermochronological studies ( 40Ar/ 39Ar laser-probe dating of white mica, fissiontrack dating of zircon). These techniques are applied to Rupelian to Serravallian (31–13 Ma) sandstones from two composite sections of the Swiss Molasse Basin, one in the east (Honegg-Kronberg-Ho¨rnli) and one in the central part (HoneggNapf). Their data indicate that the east experienced a normal unroofing sequence of the Austroalpine-Penninic nappe stack, whereas in the central part, erosion of basement rocks started significantly earlier; sediments younger than 20 Ma document increasing cooling rates of their source rocks, reflecting accelerated exhumation in the hinterland. Geoffrey M.H. Ruiz, Diane Seward and Wilfried Winkler apply an integrated heavy mineral and zircon fission-track analysis to unravel the evolution of the Amazon basin in Ecuador. 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 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. They measured lag times of the zircons, which range from 400 to 0 Ma. In their study, they combine zero lag times with lithological and mineralogical datasets that have been used to identify volcanic events in the hinterland, thus enabling establishment of the stratigraphic age of the enclosing sediments more precisely. 3.2. The Use of Heavy Minerals in Interdisciplinary Research 3.2.1. Forensic Science—Evidence from Heavy Minerals in Criminal Investigation Heavy minerals yield vital clues in criminal investigations and are highly appreciated by the forensic scientist. Their potential has been proved numerous times in court when comparative analyses provided the missing evidence. Of the two contributors to this section, Skip Palenik is a forensic microscopist and Wayne C. Isphording uses his geological knowledge and expertise in criminal investigations. Both provide an insight into the principles and practicalities of evidence gathering, and also indicate precautions that must be observed when working under legal scrutiny. They conclude with examples that illustrate how a mineral component that commonly comprises less than 1% of a typical sample, can provide the geoscientist with information that is critical in a wide variety of forensic investigations.

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Because often only traces of material are available for study, special techniques are necessary to recover the minute quantities of accessory minerals that may be used in evidence. In describing these special techniques, Palenik provides useful guidance for geoscientists who in special cases can obtain only limited, even minute, amounts of sample material (such as samples from deep boreholes/wells, cuttings contaminated by excessive drilling mud and archaeological material that may be available in minute pieces, etc.).

3.2.2. Geoarchaeology Archaeology and geology have long enjoyed a mutual interdependence because archaeological raw materials have a predominantly geological origin. Therefore, artefacts made of stone or clay, the principal inorganic raw materials of ancient times, can be best analysed by techniques used in geological laboratories. Pottery sherds are amongst the most abundant artefacts at archaeological sites and are suitable for heavy mineral analysis because they always include a certain portion of sand, called ‘temper’. This is added to the clay during manufacturing to improve cohesion during working and firing and to increase durability in use. Heavy minerals of the sandy temper can thus provide information on the source and location of the raw material, and manufracturing practices. Comparative studies of potteries from different sites may indicate trade and transport routes in ancient times. Two contributions demonstrate the use of heavy minerals in geoarchaeology. William R. Dickinson analysed prehistoric ceramics from a series of islands in Pacific Oceania and discovered a diverse array of volcanic sand tempers used by the ancient potters. Their heavy mineral suites allowed their sources to be linked to beach placer sands that reflect the phenocryst mineralogy of bedrock on the islands where pottery was made. Island groups within the region of ceramic cultures were found to extend from western Micronesia to western Polynesia with the temper recording hotspot, arc, postarc and backarc geotectonic settings. Because the relative proportions of heavy mineral species in Oceanian placer tempers correlate with the nature of restricted bedrock sources on individual islands, they serve as diagnostic evidence for temper origins wherever pottery was transported between islands. Maria A. Mange and Tama´s Bezeczky analysed sherds of amphorae from the Roman period, excavated in pottery workshops, owned by the Roman Laecanius family, on the peninsula of Istria, Croatia. Their distinctive heavy mineral asemblages furthered the characterisation of the amphorae and pointed to the source of the raw material used for the clay and sandy temper. Heavy mineral signatures in amphorae produced in other workshops facilitated their distinction from the Laecanius sherds. Comparative heavy mineral analysis of terra rossa, taken from an outcrop close to the workshop, indicates that terra rossa was the major source of the paste. Modern Adriatic sponge spicules found in the majority of Laecanius amphora sherds and the temper-derived, generally immature, heavy mineral assemblages suggest that the sandy material for the temper was obtained largely from Adriatic deposits. Results of both contributions prove that the heavy mineral technique is a powerful archaeometric tool.

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PART IV: INDUSTRIAL APPLICATION: RESERVOIR CHARACTERISATION, ECONOMIC HEAVY MINERAL DEPOSITS, DIAMOND PROSPECTING 4.1. Reservoir Characterisation Contributions of heavy mineral studies to solve problems in basin analysis, petroleum exploration and reservoir management have long been appreciated. When allied with other sedimentological and/or stratigraphical and geochemical techniques, they have much to offer towards a better understanding of sediment provenance and the history of a given basin. Heavy mineral assemblages prove especially informative when used in lithologically uniform successions, which are devoid of lithological and/or biostratigraphical markers. Systematical changes in heavy mineral compositions can reveal heterogeneity, caused either by shift in transport, changes in tectonics, climate, depositional mechanism or basin configuration. These impart particular signatures to the assemblages that are usually reflected by distinct heavy mineral zones. Heavy mineral zones with similar characteristics in related sand packages permit well-to-well or basin-wide correlation. Andrew C. Morton, Rob Herries and Mark Fanning apply heavy mineral analysis to the construction of a correlation framework for the Triassic succession in the Strathmore Field, west of Shetland. They describe how correlation is dependent on the identification and quantification of parameters that are sensitive to changes in provenance, but are unaffected by other processes of the sedimentary cycle. Care must therefore be exercised when considering provenance signals, which may be overprinted by the effects of hydrodynamic, weathering and diagenetic processes on heavy mineral suites. Ratios of abundances of stable minerals having similar density and hydraulic behaviour, in a limited size range, can provide an accurate provenance indicator. An alternative approach uses the range of varietal parameters within a single-mineral group (e.g., zircons) that thus reflects provenance characteristics without significant hydrodynamic or diagenetic modification. Morton and his co-authors use integrated heavy mineral, mineral chemical and zircon age data to show that Triassic sandstones in the Strathmore Field were derived from different sources. The Early Triassic Otter Bank Formation is linked to recycled DevonianCarboniferous rocks of Upper Clair Group, with contributions from Lewisian orthogneisses, on the eastern (British) margin of the Faeroe-Shetland rift. The overlying Middle-Late Triassic Foula Formation is interpreted to have been derived from high-grade metasedimentary/charnockitic basement rocks, thought to be located in the Nagssuqtoqidian belt of southern East Greenland, on the western side of the rift. Maria A. Mange, Peter Turner, David Ince and David T. Wright, in a combination of high-resolution heavy mineral and palaeomagnetic studies on onshore type sections and cored interbedded sandstone and mudstone samples from the Triassic Sherwood Sandstone Group, generated a heavy mineral magnetostratigraphy. Heavy mineral zones are identified and tied to specific magnetostratigraphic Chrons. A reference section, combined with data from surface exposures and cored wells, is used to interpolate the defined heavy mineral and magneto zones to uncored

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successions of nine wells in the East Irish Sea. The combined technique has yielded vital information on sediment provenance and dispersal within the basin. The assignment of absolute ages to the identified heavy mineral zones generates a timestratigraphic framework for the Triassic of the East Irish Sea Basin and adjacent areas, within which basin evolution may be better reconstructed. The significance of this combined approach is its potential for the dating, subdivision and correlation of uncored wells and sedimentary successions that are barren or stratigraphically poorly constrained. Mette Lise K. Poulsen, Henrik Friis, Johan B. Svendsen and Christian B. Jensen explore Palaeocene reservoirs in the Siri Canyon (Danish North Sea), comprising sands interbedded with deep marine muds and remobilised and/or injection deposits. The sands are subdivided into a series of flow units by interpreting Zr, Th and TiO2 trends on the geochemical logs, and by heavy mineral grain size sorting. Distinct cycles, interpreted as reflecting systematic heavy mineral variations, have been recognised in homogenous, massive sands on the basis of elemental trends, gamma ray and grain density logs, and in factor score depth plots calculated by PCA. Poulsen et al. argue that each cycle represents a single surge within a larger flow event, and that the sediments were sorted by suspension fallout during deposition. They suggest that suspension fallout sorting of heavy mineral grains may be a common feature in concentrated density flow deposits, allowing the recognition of individual flow units within thick massive sands. Andrew C. Morton develops an application of heavy mineral analysis as a realtime geosteering and correlation tool for horizontal wells that can be considered as an alternative to biostratigraphic methods where these have inadequate resolution. Morton points out that heavy mineral-directed geosteering is dependent on discovering recognisable stratigraphically significant variations in provenance between the pay zone and overlying and underlying units of the target succession, and requires the establishment of a robust correlation scheme prior to drilling. The technique has been successfully applied in a variety of depositional environments, including fluvial/aeolian, shallow and deep marine, in the Clair, Ross and Hannay Fields of the UK Continental Shelf. 4.2. Mineral Exploration and Mining Scientific analysis of heavy minerals grew out of the prospecting for alluvial deposits containing gold, other precious metals or precious stones, dominantly diamonds. Exploitable sands are usually placer deposits which are described as ‘‘a surficial mineral deposit, formed by mechanical concentration of mineral particles from weathering debris. The mechanical agent is usually alluvial, but can also be marine, aeolian, lacustrine or glacial, and the mineral is usually a heavy metal such as gold’’ (Gary et al., 1972). Placer minerals are all heavy minerals, with specific gravities greater than 2.58; this is slightly lower than that of bromoform (2.9), the standard liquid used for separating heavy minerals from a heterogeneous mixture (Els and Eriksson, 2006). Several of the world’s important mineral commodities have been obtained from placers, for example, gold, diamond, cassiterite, etc. Certain indispensable industrial minerals occur in sandy placers informally known as ‘black sands’, ‘heavy mineral

References

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sand deposits’ or ‘heavy mineral sands’. Valuable heavy minerals associated with sand deposits are rutile, zircon, ilmenite, leucoxene, cassiterite, monazite, kyanite, tourmaline, sillimanite and garnet. They are exploited from coastal sand deposits in many parts of the world, for example, in Australia, Canada, India, Kenya, Madagascar, Mozambique, South Africa. (Harben and Bates, 1990; Force, 1991). Worldwide interest in heavy mineral deposits and the potential of mining commodities from heavy mineral sand is reflected by international heavy mineral conferences and by the monthly reports and annual reviews issued by the Perthbased consulting group TZ Minerals International Pty. Ltd. Fredric L. Pirkle, William A. Pirkle and E.C. Pirkle present a concise review of the heavy mineral sands of the Atlantic and Gulf Coastal Plains, USA. Their contribution includes the history of prospecting and mining which started in this region in 1916, when ilmenite was first mined from the heavy mineral sands (Frontispiece A and B: Chapter 46). Their contribution provides a detailed description of the properties and development of all major deposits. They also outline the problem that heavy mineral mining industry faces along both the Atlantic and Gulf coastal plains, due to demands for land uses, such as forestry, residential and resort development and environmental concerns. 4.3. The Role of Tracer Heavy Minerals in Diamond Exploration This volume would not be complete without including a review on the significance of particular heavy minerals as pathfinders in searching for diamonds. Tom E. Nowicki, Rory O. Moore, John J. Gurney and Mike C. Baumgartner provide an overview of kimberlite, a variety of ultramafic- and sub-volcanic rock, which is the dominant source of diamonds worldwide. Diamonds were formed in the deep ancient lithospheric keels of Archaean cratons and kimberlites are the transporting agents that ‘‘sample’’ deep, occasionally diamond-bearing, mantle material and rapidly convey it to surface. Along with diamonds, kimberlites pick up large quantities of other mantle minerals, commonly referred to as kimberlitic indicator minerals. From an exploration point of view, the most important indicator minerals are garnet, chromite, ilmenite, Cr-diopside and olivine. Several of these minerals display diagnostic visual and compositional characteristics, making them ideal pathfinders for kimberlite. The more chemically resistant minerals (garnet, ilmenite and chromite) are particularly useful due to their greater ability to survive weathering in the surface environment. Thus, prospecting for surface materials to recover kimberlitic indicator minerals and tracing these back to their source is a key component of most diamond exploration programs. REFERENCES Artini, E., 1898. Intorno alla composizione mineralogical delle sabbie di alcuni fiumi del Veneto, con applicazione ai terreni di transporto. Riv. Miner. Crist. Italiana 19, 33–94. Boswell, P.G.H., 1933. On the Mineralogy of Sedimentary Rocks. Murby & Co., London, 393pp. Carriquiry, J.D., Sa´nchez, A., 1999. Sedimentation in the Colorado River delta and Upper Gulf of California after nearly a century of discharge loss. Marine Geology 158, 125–145.

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Dick, A.B., 1887. On zircon and other minerals contained in sand. Nature 36, 1–92. Els, G., Eriksson, P., 2006. Placer formation and placer minerals. Ore Geology Reviews 28, 373–375. Force, E.R., 1991. Geology of Titanium-Mineral Deposits. Geological Society of America Special Paper 259, 112. Frihy, O.E., Lofty, M.F., 1997. Shoreline changes and beach-sand sorting along the northern Sinai coast of Egypt. Geo-Marine Letters 17, 140–146. Gary, M., McAfee, R. Jr., Wolf, C.L. (Eds.), 1972. Glossary of Geology. American Geological Institute, Washington DC. Harben, P.W., Bates, R.L., 1990. Industrial Minerals Geology and World Deposits. Industrial Minerals Division, Metal Bulletin plc, Surrey, UK. Imbrie, J., Van Andel, Tj.H., 1964. Vector analysis of heavy mineral data. Bulletin of the Geological Society of America 75, 11131–11156. Mange, M.A., Maurer, H.F.W., 1992. Heavy Minerals in Colour. Chapman and Hall, London, 147pp. Milner, H.B., 1929. Sedimentary Petrography, 2nd rev. ed. Murby, London, 521pp. Milner, H.B., 1962. Sedimentary Petrography, Vol. 1, Methods in Sedimentary Petrography, 4th Edition. George Allen and Unwin, London, 643pp. Pirkle, F.L., Pirkle, E.E., Pirkle, A., Dichs, S.E., 1985. Evaluation through correlation and principal component analyses of delta origin for the Hawthorne and Citronelle sediments of peninsular Florida. Journal of Geology 93, 493–501. Svendsen, J.B., 2002. Sedimentology and High-Resolution Stratigraphy of Fluvial-Aeolian Sequences Using Integrated Elemental Whole Rock Geochemistry. Ph.D. thesis. University of Aarhus, Denmark. Wong, F., 2002. Heavy mineral provinces of the Palos Verdes margin, southern California. Continental Shelf Research 22, 899–910.

Maria A. Mange and David T. Wright