The lithostratigraphy of sand injection complexes (SICs) is governed by the architectural and petrological relationships between depositional parent units and intrusive networks. During the formation and evolution of SICs, diverse geological processes can modify mineral assemblages and textures, offering opportunities to evaluate genetic mechanisms and support petrological correlations. This study integrates field mapping with heavy mineral analysis of the Paleogene succession in the San Joaquin Basin, specifically targeting the upper Eocene Tumey Giant Injection Complex (TGIC) to investigate provenance of depositional and intrusive sandstones and processes associated with injection emplacement. Statistical analysis of heavy mineral assemblages and provenance-sensitive indices (MZi, GZi, CZi and RZi) confirms the genetic link between the slope channel-fills of the Kreyenhagen Formation and sandstone intrusions. These assemblages indicate derivation from granitic and metasedimentary sources derived from the Sierra Nevada Province to the east. In contrast, the underlying shallow-marine Domengine Formation reveals mixed sourcing, with significant blueschist-facies minerals (lawsonite and glaucophane) likely supplied by the Franciscan Complex accretionary prism to the west. While low ZTR values in the parent channel-fills and most intrusions indicate mineralogical immaturity, specific intrusive facies exhibit high ZTR and low ATi, suggesting mechanical degradation of less durable grains during sand injection. Qualitative grain morphology analysis reinforces this, showing a higher degree of grain damage within intrusions in comparison to parent unit. Furthermore, density-controlled ZTi index reveals hydraulic segregation, evidenced by the progressive settling of denser zircon grains through a km-scale wing-like intrusion. The petrological signature of the TGIC is thus a function of parent unit composition, intra-granular mechanical interaction, and hydraulic sorting under dynamic fluid-flow conditions. Despite the inherent 3D architectural complexity of the intrusive networks, this study provides robust methodological tools for investigating the evolution of injectites in diverse geodynamic settings.

Wing-like intrusions are some of the most prominent architectural elements identified within subsurface sand injectite complexes. These structures are composed of discordant inner wing zones and bedding-concordant outer wing zones, which can crosscut hundreds of metres of stratigraphy and extend laterally for several kilometres. Their large-scale geometry makes them discernible on seismic data; however, the inability to detect associated smaller intrusions can lead to underestimates of their significance within a basin. To support subsurface analysis, this study integrates field and digital mapping analyses of two wing complex outcrops from two giant injection complexes of the San Joaquin Basin. The Dosados Canyon wing, of the Panoche Giant Injection Complex (PGIC), features a single 14 m thick stepped inner intrusion that bifurcates into outer sills. The wing extends laterally over 1.5 km, crosscutting ca. 300 m of mudstones. Up to 64% of the sandstones are associated with sub-seismic intrusions (< 3 m thickness). The Tumey Hill wing within the Tumey Giant Injection Complex (TGIC) intrudes vertically > 200 m of mudstones and extends laterally for at least 1.3 km. It comprises laterally stacked inner intrusions (up to 12 m thick) transitioning to a highly connected outer sill zone. A total of 225 intrusions (0.15 m to 8 m thick) are identified within the composite wing structure, adding sand volume and providing excellent connectivity. Comparison with the Volund and Varadero fields within the North Sea reveals intrusions with similar scale and geometry, underscoring the value of the outcrops as analogues for characterisation of subsurface reservoirs and to aid the understanding of sand intrusion formation within different basin settings.

Summary Sand injection complexes are important components of petroleum systems. They form sub-vertical and sub-horizontal networks of permeable sandstone reservoirs, which often contain commercial hydrocarbons. In the subsurface, defining the geometry and distribution of sandstone intrusions and their reservoir quality is challenging, and constitutes a high level of uncertainty in subsurface models. The Tumey Giant Injection Complex (TGIC) is a well-exposed, excellent analogue for subsurface injection complexes. Herein, outcrop of a km-scale wing intrusion is used to create a 2D geological template as the basis for static and seismic reservoir models. The 2D and 3D static models combined outcrop geometries, injectite facies, and rock properties data to demonstrate spatial relationship between injectite facies and to derive pore volume and their distribution. Seismic modelling used the geological template and petrophysical well data as input for 2D point-spread function (PSF) based seismic modelling to create 2D synthetic seismic data. Results show that seismic data fail to image substantial "sub-seismic" reserve volumes, and that the reservoir geometry is oversimplified. Our models confirm subsurface experience that sandstone intrusions enhance reserve volumes and recovery factors and show that well placement strategy must be cognisant of intrusion architecture to optimize volumetric estimates and hydrocarbon recovery.

Zircon U-Pb geochronology was applied to investigate the provenance, depositional ages, and paleogeography of the southwestern Gondwana in detrital and ash fall sediments from Carboniferous to Jurassic succession of the southern Paraná Basin. Four detrital age populations suggest provenance from local and distal sources located to the south, southeast, and southwest: (i) Archean to Paleoproterozoic zircons from the Rio de La Plata Craton, Nico Peres and Taquarembó terranes; (ii) Grenvillian zircons from the basement of the Gondwanides and Namaqua–Natal belts; (iii) Neoproterozoic grains from the Don Feliciano Belt; and (iv) Phanerozoic populations from Paleozoic orogenic belts and related foreland systems in Argentina, as well as eroded units of the Paraná Basin. The paleogeographic reconstruction indicates an evolution in three distinct stages: (1) a gulf open to the Panthalassa Ocean during the Carboniferous; (2) an epicontinental sea with the rise of the Gondwanides Orogeny during the Permian; and (3) continental deposits controlled by an intra-plate graben system during the Triassic. Permian–Triassic volcanogenic zircons provide constrained maximum depositional ages and attested persistent volcanism, related to the Choiyoi magmatism and effects of the climate change episodes. During the Triassic, the extensional graben system recorded the uplift of the basement through regional northwest and northeast fault systems, and the recycling of Permian zircons, modifying source-to-sink relationships.

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 The Tumey Giant Injection Complex (TGIC) is a regionally developed sandstone intrusion complex emplaced into the deep-water Kreyenhagen Shale (Eocene) in the San Joaquin Basin, Central California. Detailed geological mapping, stratigraphic reconstruction and outcrop description, supported by structural analysis, allowed the architectural characterization of the TGIC. The complex is described as two main stratigraphically constrained intervals: (1) a lower interval (250 m thick) emplaced into clay-rich mudrock, consisting dominantly of sills with stepped and multilayered geometry; and (2) an upper interval (200 m thick) characterized by injection breccia and large wing-like intrusions (c. 600 m width × 100 m high) emplaced within predominantly biosiliceous mudrock strata. The intrusions in both intervals were derived from turbiditic channel fills intensely modified by sand fluidization. Sandstone intrusions and fractures affecting host strata are dominantly oriented sub-parallel to the basin axis striking between NW–SE and N–S, mainly dipping to NE and forming asymmetric saucer-shaped intrusions, suggesting structurally driven hydraulic fracturing and sand emplacement. The absence of a deep aquifer and potential sand sources underlying the complex suggests a lateral contribution of fluid flow. The TGIC occurs at a scale similar to injection complexes recognized in the subsurface and is a valuable reservoir analogue for hydrocarbon accumulations associated with sand injectites.

The presence of sand injections has been shown to enhance the likelihood of hydrocarbon traps within siliciclastic successions. Through the development of large interconnected networks of sills and dykes, sand injection complexes provide a volume of porous and permeable rocks within the low permeability host units. Overall, the formation of sand injection complexes requires extensive fracturing and hydrofracturing, which can be particularly pronounced when sand injections are coupled with brittle tectonic deformation. In some circumstances, this process may threaten the integrity of the reservoir top seal thereby preventing further hydrocarbon accumulation. Studying exceptional exposures along the coastal area of Santa Cruz in California, we report evidence for top seal failure associated with injection episodes. Two distinct sand injection episodes are proposed. The first event, datable to the Late Miocene, resulted in large volumes of sand being emplaced within the top-seal units, and was followed by accumulation of hydrocarbons within the newly injected sandstones. Later, a series of brittle tectonic events, associated with the San Andreas/San Gregorio Fault System, caused remobilization and accumulation of sand along newly formed fault planes. Our case study documents this combination of pervasive brittle deformation and sandstone injection along fault structures, which can ultimately disrupt the integrity of a host unit leading top seal failure and leakage of hydrocarbons.

Despite the potential of sandstone-filled normal faults to significantly influence fluid transmissivity within reservoirs and the shallow crust, they have to date been largely overlooked. Fluidized sand, forcefully intruded along normal fault zones, markedly enhances the transmissivity of faults and, in general, the connectivity between otherwise unconnected reservoirs. Here, we provide a detailed outcrop description and interpretation of sandstone-filled normal faults from different stratigraphic units in central California. Such faults commonly show limited fault throw, cm to dm wide apertures, poorly-developed fault zones and full or partial sand infill. Based on these features and inferences regarding their origin, we propose a general classification that defines two main types of sandstone-filled normal faults. Type 1 form as a consequence of the hydraulic failure of the host strata above a poorly-consolidated sandstone following a significant, rapid increase of pore fluid over-pressure. Type 2 sandstone-filled normal faults form as a result of regional tectonic deformation. These structures may play a significant role in the connectivity of siliciclastic reservoirs, and may therefore be crucial not just for investigation of basin evolution but also in hydrocarbon exploration.

A análise estrutural e as relações de contato entre o Metagranito Capané (MC) e as rochas metavulcanosedimentares neoproterozoicas do Complexo Porongos (CP) são discutidas a partir da integração entre o mapeamento geológico de detalhe e análise microtectônica. A área de estudo está situada na região centro-sul do estado de Rio Grande do Sul, na Antiforme Capané, estrutura regional com caimento para SW. As unidades do CP foram intensamente deformadas e metamorfisadas durante a etapa final da formação do Cinturão Dom Feliciano, entre 600 e 570 Ma. O Metagranito Capané, posicionado no flanco oeste da antiforme é um aegirina pertita granito milonítico com textura equigranular hipidiomórfica média localmente preservada e foliação milonítica (Sm) bem desenvolvida. O corpo apresenta forma alongada e concordante com a foliação S2 dos xistos pelíticos e das rochas metavulcânicas encaixantes. A Sm possui direção NNE e mergulha em média 30º para WNW, e a lineação de estiramento (Lx) tem baixo ângulo de caimento (<10º) para SSW. As microestruturas observadas são típicas de milonitos de grau médio, condição equivalente às encaixantes metassedimentares. Os indicadores cinemáticos, como pares SC e a assimetria de porfiroclastos deformados, indicam transporte tectônico de topo para SSW com cinemática sinistral. Essa milonitização está associada à geração de zonas de cisalhamento oblíquas de direção NE-SW durante o período pós-colisional de formação do Cinturão Dom Feliciano.

The Permian deglaciation of Gondwana caused a global icehouse/greenhouse transition, leading to increased aridity over large parts of this continent during the Lopingian, contributing to the overall scarcity of plant bearing localities. Despite a continuous increase of reports of fossil charcoal as direct evidence for palaeo-wildfires from Late Palaeozoic deposits, such records from low-latitude and arid to semi-arid areas are still rare. In order to contribute to the discussion about palaeoenvironmental conditions that dominated low latitudinal portions of the globe during that period and especially the occurrence of wildfires, the present contribution reports on charcoal recovered from sandstones from the Andradina Outcrop, Late Permian (Lopingian), Motuca Formation, in the Parnaíba Basin, Northern Brazil. This locality is part of the Northern Tocantins Petrified Forest, which is classified as one of the most important Permian assemblages of permineralized plant remains from warm temperate palaeobiomes of the Southern Hemisphere. The results presented here provide the first evidence for the occurrence of palaeo-wildfires in the western part of the Gondwanan palaeo-tropics during the Lopingian.

The Varzea do Capivarita Complex is composed of pelitic gneisses with subordinate calc-silicate rock, marble and rare quartzite. It is part of the neoproterozoic Dom Feliciano Belt, in southern Brazil. The gneisses are associated to veins and tabular leucogranite bodies, which are the product of anatexis of the pelitic gneiss. The paragneisses of the Varzea do Capivarita Complex are tectonically juxtaposed to orthogneisses of the Arroio dos Ratos Complex. This,complex is exposed as megaxenoliths in granites of the Encruzilhada do Sul Suite and as smaller fragments in the Quiteria and Cordilheira Granites, all part of the Pelotas Batholith. The metamorphic foliation is oriented to N30 degrees W, with dips between 35 and 55 degrees to the SW and mineral lineation is suborizontal with rake ranging from 15 degrees to 30 degrees and down dip to NW and SE, suggesting deformation associated with a transpressive system. Based on the paragenesis garnet-cordierite-sillimanite-biotite, metamorphism occurred at 720-820 degrees C and pressure of 8-9 kbar, characterizing it as of intermediate pressure and high temperature series. Zircon grains of one sample of garnet cordierite sillimanite-biotite gneiss and one of peraluminous leucogranite was dated by the U-Pb SHRIMP method. The paragneiss metamorphic zircon yielded an age of 619 +/- 43 Ma interpreted as an age of the main metamorphic event, whereas igneous zircon grains from the leucogranite indicates that magma crystallization took place at 620 +/- 6.3 Ma. The main metamorphic foliation (S2) of the paragneiss and the leucogranite magmatic foliation (S-0) are parallel to each other, indicating that they were formed during the same event. This suggests that anatexis of the paragneisses of the Varzea do Capivarite Complex generated the peraluminous leucogranites right after the climax of the collisional metamorphism. (C) 2015 Elsevier Ltd. All rights reserved.

O Complexo Várzea do Capivarita está representado por paragnaisses dispostos como megaxenólitos nos granitos da Suíte Encruzilhada do Sul e como fragmentos menores nos granitos Quitéria e Cordilheira. Essas unidades graníticas afloram no extremo norte do Batólito Pelotas, porção leste do Cinturão Dom Feliciano, próximo a Encruzilhada do Sul. O complexo é constituído por gnaisses pelíticos, com ocorrência subordinada de gnaisses calci-silicáticos, mármores, gnaisses quartzo-feldspáticos e raros quartzitos. Os gnaisses pelíticos possuem injeções de corpos tabulares de muscovita leucogranitos peraluminosos com espessuras centimétricas a métricas. Neste trabalho foram feitas análises petrográficas e microestruturais de seções delgadas representativas das litologias do complexo e a caracterização estrutural da área de estudo. A integração desses dados permitiu avaliar a migmatização dos paragnaisses e a geração das injeções leucograníticas. As condições metamórficas estabelecidas com base nas paragêneses identificadas indicam temperaturas da ordem de 850 a 1000°C e pressões entre 6 e 10 kbar, caracterizando um metamorfismo orogênico de fácies granulito, da série de pressão intermediária e de ultra-alta temperatura (UAT). A concordância estrutural entre o bandamento (S2) dos paragnaisses e a foliação ígnea (S0 ) do leucogranito indica que ambas foram formadas no mesmo evento, implicando que a migmatização dos paragnaisses do Complexo Várzea do Capivarita gerou os leucogranitos peraluminosos durante o ápice do metamorfismo orogênico colisional.

This study focuses on the provenance, volcanic record, and tectonic setting of the Paleozoic Ventania System, a geologic province which comprises the Cambro-Devonian Ventania Fold Belt and the adjoining Permo-Carboniferous Claromeco Foreland Basin, located inboard the deformation front. The Ventania Fold Belt is formed of the Curamalal and Ventana groups, which are composed mainly of mature quartzites that were unconformably deposited on igneous and metamorphic basement. The Pillahuinco Group is exposed as part of the Claromeco Basin and it has lithological and structural features totally distinct from the lowermost groups. This group is composed of immature arkoses and subarkoses with intercalated tuff horizons, unconformably overlaying the quartzites and associated with glacial-marine deposits of the lower Late Carboniferous to Early Permian section. The petrography, as well as major and trace elements (including rare earth elements) support that the Ventania quartzites were derived from cratonic sources and deposited in a passive margin environment. For the Pillahuinco Group, we suggest a transition between rocks derived from and deposited in a passive margin environment to those with geochemical and petrographical signatures indicative of an active continental margin provenance. LA-MC-ICP-MS analysis performed on euhedral and prismatic zircon grains of the tuffs revealed an age of 284 +/- 15 Ma. The geochemical fingerprints and geochronological data of the tuffs found in the Claromeco Basin support the presence of an active and widespread Lower Permian pyroclastic activity in southwestern Gondwana, which is interpreted as part of the Choiyoi Volcanic Province in Argentina and Chile. (C) 2013 Elsevier Ltd. All rights reserved.