Abstract Sandstone intrusions in giant injection complexes are characterized by texturally immature sand with common micro-fractured framework grains. Individual micro-fractures are distinctive in geometry and unaligned within or between grains, thus differentiating them from micro-fractures formed by shock metamorphism or tectonics. Individual grains preserve histories of multiple impacts. The geometry of micro-fractures and their textural association makes them diagnostic of high-energy inter-granular collisions during sand injection. Mudstone clasts have sand-propped micro-fractures associated with hydraulic fracturing and individual sand grains embedded in clasts by corrasion, which is diagnostic of high grain velocity. Heavy mineral assemblages record abrasion of apatite and hydrodynamic segregation of zircon (both relative to abundance of tourmaline) upward through the injection complex. Granular abrasion and hydrodynamic segregation are consistent with turbulent flow during sand injection. Collectively the petrographic and mineralogical data support the interaction of high-velocity grains in turbulent flow during sand injection in which the granular content is likely to be dilute.

Abstract Sediment provenance studies concern the origin, composition, transportation and deposition of detritus, and are therefore an important part of understanding the links between basinal sedimentation, and hinterland tectonics and unroofing. Such studies can add value at many stages of hydrocarbon exploitation, from identifying regional-scale crustal affinities and sediment-dispersal patterns during the earliest stages of exploration to detailed correlation in producing reservoirs and understanding the impact of mineralogy on reservoir diagenesis. This Special Publication records 20 of the papers given at the conference titled ‘Sediment Provenance Studies in Hydrocarbon Exploration and Production’ organized by the Petroleum Group of the Geological Society of London, and held in London from 5 to 7 December 2011. The observations drawn in this introductory section reflect the volume editors’ experience, presentations at the conference and papers within this volume.

Abstract Three distinct analytical approaches are embraced in mineral–chemical stratigraphy: mineralogy, whole-rock geochemistry and single-grain geochemical analysis. Mineralogical studies identify and quantify the clastic components of sandstone, even though any clast category may be geochemically diverse. Whole-rock geochemical studies (sometimes referred to as chemostratigraphy), by contrast, quantify the abundance of major and trace elements in sandstone, but provide no information on the distribution and location of the elements in minerals. These approaches are linked by single-grain geochemical analysis, which enables further characterization and subdivision of individual mineralogical components, and identifies sites where specific major and trace elements reside. In this paper, we consider the relationships between minerals, mineral chemistry and whole-rock composition, before exploring the value of mineral–chemical stratigraphy for lithostratigraphic correlation and evaluation of sediment provenance, using published examples from the North Sea region, where the great majority of such studies have been undertaken. We conclude by discussing the important role that alluvial basins play in controlling mineral–chemical signatures.

Abstract Detrital garnet suites have been demonstrated to be reliable indicators of the mineralogical and lithological characteristics of sediment source areas. This study applies garnet analysis to the Paleocene to Eocene Sele Formation deep-water sandstone units of the central North Sea. These stratigraphic units are economically important as they represent one of the main hydrocarbon reservoir intervals in this mature basin. The routing of turbidity currents into the Central Graben has been demonstrated to be related to axial fans (ultimately sourced from Lewisian and Moine basement rocks and Triassic sandstones to the NW) and lateral fans (ultimately sourced from the Dalradian basement rocks to the west). Garnet analysis suggests the majority of samples can be attributed to the axial fan system and that the lateral system contributed little to sandstone deposition east of the Gannet Fields. This contradicts previous seismic mapping work, which suggested that the lateral fan system dominated sedimentation as far east as the Merganser Field. This reinterpretation is potentially important for our understanding of sediment routing and its impact on the distribution of reservoir quality, particularly as this is believed to relate directly to proximity to the shelf.

Abstract A heavy mineral, mineral chemical and detrital zircon study of Jurassic–Cretaceous (Bathonian–Valanginian) sandstones of the Andøya B borehole, Lofoten–Vesterålen, northern Norway, has revealed the existence of significant differences within the succession. These are related partly to changes in source and partly to variations in the extent of weathering during alluvial storage. Three mineralogical units have been identified. The main change takes place within the Bathonian, and is interpreted as marking a switch from eastern (West Troms) to western (Andøya–Lofoten High) sourcing, consistent with previously published sedimentological models. U–Pb age data indicate that most of the zircons were derived from Palaeoproterozoic rocks ( c. 1750–1860 Ma), with a subordinate Archaean group ( c. 2600–2800 Ma) and a small early Palaeozoic group (mostly in the 435–446 Ma range). These groups can all be tied back to lithological components of the Lofoten–Vesterålen and West Troms regions, including Palaeozoic rocks hosted in Caledonian allochthons. The provenance characteristics of the Andøya succession have no counterpart in Cretaceous and Paleocene sandstones of the Vøring Basin. This suggests that sediment fed into the basin from Lofoten–Vesterålen was of minor importance, and that prospective Cretaceous–Paleocene hydrocarbon reservoir sandstones in the Vøring Basin were mainly derived from either northern Nordland or northern East Greenland. Supplementary material: Zircon isotopic compositions and ages are available at http://www.geolsoc.org.uk/SUP18616 .

Abstract Amphibole and garnet are among the most widespread heavy minerals in orogenic sediments. Their chemical composition and optical properties vary markedly and systematically with temperature and pressure conditions during growth, and thus provide important information on the metamorphic evolution of source areas that is crucial in palaeotectonic and palaeogeodynamic reconstructions. This study investigates the chemical composition of detrital amphiboles and garnets derived from parent rocks of progressively increasing metamorphic grade through a well-studied composite section across the Central and Southern Alps, including the granulite-facies core of the Late Palaeozoic orogen exposed in the Ivrea–Verbano Zone and the amphibolite-facies core of the Cenozoic orogen exposed in the Lepontine Dome. We specifically focus on metamorphic grade because it represents the best proxy for tectono-stratigraphic crustal level, and hence degree of unroofing of source areas. In river sands collected between metamorphic isograds corresponding to crystallization temperatures ranging from c. 500 °C to c. 850 °C, TiO 2 gradually increases in detrital amphibole while its colour progressively changes from blue-green in the lower amphibolite-facies where actinolite, hornblende and tschermakite are most abundant, to brown in the granulite facies where pargasite is dominant. Detrital garnets display moderate gradual changes across the amphibolite-facies Lepontine Dome, where low-Mg ‘type B’ garnets predominate. Almandine-spessartine is spatially associated with abundance of pegmatites while entering the zone of anatexis (Southern Steep Belt), where grossular or grossular-andradite-spessartine are occasionally found. A sharp change occurs while reaching granulite-facies in the Ivrea–Verbano Zone, where high-Mn garnets disappear and ‘type A’ almandine-pyrope (from ‘stronalite’ metasediments) and ‘type C’ almandine-pyrope-grossular (from metagabbros of the Mafic Complex) predominate. Also redefined in this article are a series of numerical indices based on amphibole colour and relative abundances of diverse key minerals (chloritoid, staurolite, andalusite, kyanite, fibrolitic and prismatic sillimanite), useful to accurately assess the average metamorphic grade of meta-igneous and metasedimentary source rocks. Supplementary material: Chemical composition of detrital amphiboles and garnets and full information on the location and mineralogical composition of studied samples is available at http://www.geolsoc.org.uk/SUP18618 .

Abstract Detrital zircon dating has proven to be an effective way to constrain ages of submerged basement terranes on the margins of the northern Rockall Basin, a region where direct evidence of crustal affinities is scarce or absent. Zircons have been dated from sandstones of Paleocene–Oligocene age known to have been derived from the east (Hebridean Platform) and west (Rockall and George Bligh highs). The results show that the Hebridean Platform is a westward extension of the Lewisian Complex, with Archaean and Palaeoproterozoic ages that can be directly correlated with events identified in the Outer Hebrides and NW Scotland. The detrital zircons derived from the Hebridean Platform also provide evidence for a Mesoproterozoic thermal event and two phases of intrusions in the Palaeozoic. The Rockall High consists of a Palaeoproterozoic terrane dated as c. 1760–1800 Ma, similar to ages previously determined from both basement samples and detrital sediment. The data also provide evidence for the subsequent intrusion of alkaline igneous rocks in the Paleocene–Eocene. The George Bligh High represents an Archaean terrane heavily affected by Palaeoproterozoic tectonothermal events, and was also the site of intrusion of alkaline igneous rocks during Paleocene time.

Four different sand types (termed FSP1, FSP2, FSP3, and FSP4) have been recognized in the Paleocene succession of the Faroe-Shetland Basin, NE Atlantic, on the basis of conventional heavy mineral analysis, major element geochemistry of garnet, trace element geochemistry of rutile, U-Pb dating of detrital zircon, and palynofloral analysis. Sand types FSP1, FSP2, and FSP4 were all sourced from the eastern margin of the basin, whereas FSP3 was supplied from the west. No single technique discriminates all four sand types. Conventional heavy mineral analysis discriminates FSP3 from the other three sand types but does not discriminate FSP1, FSP2, and FSP4. Garnet geochemistry distinguishes FSP1, FSP2 and FSP4, but FSP3 garnet populations overlap those of FSP1 and FSP2. Rutile geochemistry distinguishes FSP2 from FSP1 and FSP4 but cannot be easily applied to FSP3 owing to the scarcity of rutile in this sand type. Zircon age spectra in FSP1, FSP2, and FSP4 are similar to one another, but FSP4 can be recognized on the basis of a higher proportion of Archean zircons. Some of the individual techniques have certain limitations: e.g., one of the key conventional heavy mineral parameters is the presence of clinopyroxene, but this is not always reliable owing to the instability of this mineral during burial diagenesis. Likewise, garnet geochemistry cannot be applied to the most deeply buried sandstones in the Faroe-Shetland Basin owing to complete garnet dissolution. Furthermore, care is required when interpreting garnet data from sandstones that have undergone partial garnet dissolution, as there may have been modification of the range of garnet compositions as a result of the greater instability of Ca-rich garnets compared with Ca-poor types. Finally, the “Greenland flora,” which occurs in association with sand type FSP3, has been found in some wells that lack FSP3 sandstones. This discrepancy is attributed to the difference in hydrodynamic behavior of palynomorphs compared with sand particles. This chapter illustrates the importance of adopting an integrated approach, as significant detail would have been lost if only one technique had been applied, and integration of a number of different techniques overcomes limitations associated with individual approaches. An integrated approach also builds a more comprehensive picture of source area characteristics.

Upper Jurassic sandstones deposited in a shallow-marine deltaic setting in the Piper Field of the Outer Moray Firth area, North Sea, show high-frequency fluctuations in apatite:tourmaline ratios that appear to be related to sea-level change. Because apatite and tourmaline are both stable during burial diagenesis and have similar hydraulic behavior, variations in the apatite:tourmaline ratio indicate either differences in sediment provenance or in the extent of floodplain weathering, apatite being unstable during weathering. Other provenance-sensitive heavy mineral ratios (rutile:zircon, monazite:zircon, chrome spinel:zircon) and mineral-chemical data from detrital garnet assemblages show that sandstones with high apatite:tourmaline have the same provenance as sandstones with low apatite:tourmaline. Fluctuations in apatite:tourmaline ratios are therefore attributed to the extent of weathering during floodplain residence prior to the sediment entering the marine system. Sedimentological data indicate that sandstones with high apatite:tourmaline were deposited during sea-level highstands, whereas sandstones with low apatite:tourmaline were deposited during lowstands. The implication of this observation is that during sea-level lowstands, sediment undergoes more prolonged floodplain residence than during highstands, apparently the direct result of the increase in areal extent of the floodplain. The fluctuations in apatite:tourmaline offer an opportunity for high-resolution correlation in the Piper Field. If similar patterns become apparent in other areas, variations in apatite:tourmaline ratios could also provide a basis for identifying highstand and lowstand events, and help establish whether deep-water submarine fan sandstones were deposited during highstands or lowstands.

Abstract The Devonian–Carboniferous Clair Group reservoir succession in the Clair Field, located west of Shetland on the UK continental shelf, comprises over 1000 m of clastic sediment deposited in a range of fluvial, lacustrine, and eolian environments. Owing to the unfavorable depositional conditions, palynomorphs and microfossils are almost entirely absent, precluding development of a high-resolution biostratigraphic framework for reservoir correlation. An alternative approach to reservoir subdivision and correlation is therefore necessary in order to establish a viable reservoir model prior to field development. Heavy-mineral analysis, which subdivides clastic successions on the basis of changes in provenance and sediment transport history, has proved successful in establishing a high-resolution correlation framework for the Clair Field. This paper concentrates on the heavy-mineral stratigraphy of the Lower Clair Group, which is the target for the first phase of the field development. The key parameters that have been used to erect the correlation framework are provenance-sensitive ratios of heavy minerals (notably garnet:zircon, rutile:zircon, and apatite:tourmaline), grain morphology (apatite roundness), and mineral chemistry (garnet composition). The Lower Clair–Upper Clair boundary is a major heavy-mineral event related to a fundamental change in provenance. Six major units (I–VI) and a number of subunits have been recognized within the Lower Clair Group, boundaries being related to more subtle changes in provenance and sediment transport history. The successful application of integrated heavy-mineral analysis in the Clair Field demonstrates that the method can be reliably applied to correlation of clastic hydrocarbon reservoirs. The technique is successful because it generates data that are independent of factors such as hydrodynamics and diagenesis, and therefore directly reflect correlatable geological events such as changes in provenance, sediment transport history, and climate. Furthermore, the method can be used on the full range of geological samples acquired during hydrocarbon exploration, since data are acquired from the constituent components of the sample rather than from the bulk sample, thereby enabling contamination from drilling additives and caving to be filtered out. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 183–199.

Abstract Field-based investigation of ‘Infracambrian’ rocks cropping out on the eastern flank of Al Kufrah Basin (area 500 000 km 2 ) reveals a an approximately 500 m-thick clastic succession of massive and cross-bedded sandstones, separated by 60 m-thick mudrock intervals. New zircon age data indicate a maximum age of deposition of approximately 950 Ma; furthermore, the absence of zircons of Pan-African age suggests a minimum depositional age older than the Pan-African Orogeny. Previously unreported folding and spaced cleavage affects these deposits to produce a pronounced NE–SW-striking tectonic grain that is interpreted to result from NW–SE-directed orthogonal compression during the Pan-African Orogeny. These Infracambrian rocks are therefore unlikely to be suitable analogues for weakly deformed strata shown to exist beneath the Cambro-Ordovician strata of the Al Kufrah Basin. Earlier work mapped a series of Infracambrian marble outcrops along strike of the clastic deposits; thin section petrography reveals that some of these are basic igneous rocks metamorphosed to greenschist facies. Interpretation of gravity data over the Al Kufrah Basin shows NE–SW-striking faults, parallel to outcrop structures, and secondary NW–SE faults. The data do not support earlier interpretations of a rhomboidal geometry in the deep subsurface of the basin, which has previously been attributed to strike-slip (pull-apart) processes. This research impacts on earlier suggestions that the Al Kufrah Basin opened as one of a series of en echelon pull-apart basins situated along a 6000 km-long shear zone known as the Transafrican Lineament, stretching from the Nile to the Niger Delta.

Single-grain, laser-ablation inductively coupled plasma–mass spectrometry analyses of detrital apatites from Pliocene sandstones in the South Caspian Basin (Azerbaijan) and Devonian-Carboniferous sandstones from Clair oil field, west of Shetland (UK), demonstrate that apatite geochemistry has significant potential in provenance analysis. Apatites in Pliocene sandstones deposited by the paleo-Kura River system, which drained the Lesser Caucasus region, were derived largely from mafic to intermediate and alkaline rocks. Apatite populations in Pliocene sediments transported by the paleo-Volga River system, which drained the Russian Platform, show greater compositional diversity and indicate supply from granitoids or other acidic rocks together with subordinate mafic to intermediate and alkaline rocks. Apatites in the Devonian-Carboniferous succession west of Britain were derived predominantly from acidic rocks, either directly from Archean gneisses or indirectly from metasedimentary rocks. In the two case studies, the most useful discriminators of apatite provenance proved to be La/Nd and La + Ce/ΣREE. Since apatite is stable during burial in sedimentary basins, apatite geochemistry can be used to determine provenance of sandstones from the full range of diagenetic environments, although the instability of apatite during weathering means that the method will be difficult to apply to sandstones with prolonged weathering history. At present, identification of provenance using apatite geochemistry is limited by the lack of a comprehensive database on apatite compositions in some of the potential source rocks, particularly those of metamorphic origin. The role played by sediment recycling is another factor that requires consideration when reconstructing source areas on the basis of apatite compositions.