Lithic Fragments Research Articles

Age and depositional setting of the Paleoproterozoic Gantaohe Group in Zanhuang Complex: Constraints from zircon U–Pb ages and Hf isotopes of sandstones and dacite

The Gantaohe Group, located in the Zanhuang area, contains typical North China Craton Paleoproterozoic strata, and is one of the best-preserved examples of these rocks. It is therefore a significant area for deciphering evolutionary process in the trans-North China Orogen. In this paper, we present petrologic, detrital and volcanic zircon U–Pb ages and Lu–Hf isotopes from three formations of the Gantaohe Group. The zircons from a conglomerate at the base of the Gantaohe Group yielded a young population of ca. 2.1Ga. Dacite from the upper section of the Nansizhang Formation yielded zircon 207Pb/206Pb ages of 2090±14Ma. Thus, the initial deposition of the Gantaohe Group occurred at ∼2.1Ga. The Group underwent greenschist to low amphibolite facies metamorphism, identical to regional 1.87–1.85Ga metamorphism in Zanhuang Complex. Therefore, we propose that the Gantaohe Group was deposited in the period between 2.1Ga and 1.9Ga. Sandstones in the Gantaohe Group are dominated by Q (monocrystalline and polycrystalline quartz) and F (K-feldspar and plagioclase) with only minor lithic fragments, suggesting that detrital components were mainly derived from a cratonic source. Detrital zircons from sandstones exhibit a dominant population of 2.55–2.5Ga grains with minor contributions of ∼2.7Ga and ∼2.1Ga grains, which further indicate they were dominantly sourced from ∼2.5Ga TTG gneisses, late Archean Zanhuang and late Archean to Paleoproterozoic Guandu Groups, with subordinately input from ∼2.7Ga TTG gneisses and the Paleoproterozoic Xuting granite. Given that the sandstone clastic components chiefly comprise quartz and feldspar, there is a lack of volcanic lithics, and the major detrital zircons are 400Ma older than the initial deposition age, we propose that the Gantaohe Group was deposited in a rift-related setting far from any back-arc basin at ∼2.1Ga or 1880–1810Ma syn-collisional processes. A few 2.5–2.7Ga zircons have positive εHf(t) values identical with the contemporaneous depleted mantle and the 207Pb/206Pb ages are similar to their single stage model ages (TDM1), which suggests some degree of 2.5–2.7Ga crustal growth. Most ∼2.5 zircons, however, show 207Pb/206Pb ages that are much younger than the Hf single stage model ages, which indicates intensive crustal reworking in the late Neoarchean. The zircons collectively present two stage model ages ranging from 2.6 to 2.9Ga. Therefore, we suggest that the 2.6–2.9Ga periods represents a time of intensive crustal growth in the Zanhuang Complex.

Sediment Composition of the Thakuran River Basin of the Sunderbans

Thakuran River sediments are typical estuarine. Lithogenic constituents are dominant with about 85-90% in bulk and biogenic components constitute the rest (10-15%). Quartz, feldspars, mica, lithic fragments and some heavy minerals are the main terrigenous constituents. Secondary overgrowth of quartz with multiple rims of inclusions suggests their derivation from sedimentary rocks of different cycles of sedimentation. The heavy mineral assemblage in the sediments lead to conclude that the sediments have been derived from the acid igneous rocks of the Himalayas in the north and the metamorphic rocks of the Precambrian shields of the west and north-west of Bengal Basin. Benthic foraminiferal assemblage indicates a shallow water, moderate to low salinity environment of deposition.

Conduit enlargement during the precursory Plinian eruption of Aira Caldera, Japan

Increase in magma flux as the result of conduit enlargement is one of the key processes that triggered caldera collapse and eruption of the Ito ignimbrite from Aira Caldera at ~29 ka. We examine the total volume of the pumice fall deposit, vertical variations in grain size of pumice, and the lithic content in the Osumi pumice deposit to investigate the trigger for caldera collapse. Wider distribution of the later-stage unit and the upward coarsening of grain size throughout the Osumi pumice fall deposit indicate an increase in magma discharge toward the onset of collapse. The total volume of lithic fragments in the Osumi pumice fall deposit is estimated as ~1.6 km3, based on the lithic content in several representative outcrops and the total volume of the Osumi pumice fall deposit. The lithic fragments in the Osumi pumice fall deposit indicate intense mechanical erosion of the conduit during the Plinian eruption prior to caldera collapse. Caldera collapse requires decompression of the magma chamber by withdrawal of magma; effective enlargement of the conduit diameter during precursory eruptive phases is one of the important processes that subsequently allow the rapid discharge of a large volume of magma, which in turn facilitates decompression of the reservoir and induces caldera collapse.

Sedimentology, diagenesis and reservoir quality of the upper Abu Gabra Formation sandstones in the Fula Sub-basin, Muglad Basin, Sudan

Successful hydrocarbon exploration of the Lower Cretaceous Abu Gabra Formation has established the need to understand the diagenesis and reservoir quality of the sandstones reservoirs in the area. Therefore, this study contains a subsurface facies analysis based on description of three conventional cores from the Moga21-2 well. Methods include wireline log analysis, a petrographic study with both thin sections and scanning electron microscope investigations, grain-size, X-ray diffraction (XRD), and heavy minerals analysis of the Abu Gabra sandstone.Sedimentary composition and facies sequences of the well logs indicate a complex fluvial channel paleo-environment. Grain-size analysis revealed that the sandstone is a mixture of mainly sand-size (<0.01–2.00 mm) along with minor amount of silt and clay size (<0.063 mm). Alternation of coarse to medium-grained, massive to cross-bedded sandstones with fine-grained ripple laminated sandstones shows a sequence of fluvial channel fill or sand deposits of channel bars. The finer-grained facies association, predominantly mudstone and siltstone, represents overbank deposits or floodplain sediments.Petrographically, the sandstones are classified (based on standard rock classification schemes) into, subfeldspathic arenites, and feldspathic arenite lithofacies. Quartz grains are the most abundant detrital components in the samples (both polycrystalline and monocrystalline), followed by feldspars (mainly K-feldspar), micas, and detrital and authigenic clays with carbonatic detritus. Although, lithic fragments, iron oxides and heavy minerals occur in minor amounts, presence of sillimanite, epidote and hornblende (compared to zircon, tourmaline and rutile), as well as the presence of chlorite, the dominance of polycrystalline quartz and high crystallinity of kaolinite could be responsible for the low grade metamorphism. Kaolinite is an authigenic component, while quartz overgrowths occur in variable quantity and carbonates (calcite and siderite) in a relatively minor amount. Pore types are basically primary and secondary interparticle, with few secondary intraparticle pores due to the dissolution of feldspars. Although porosity ranges from 9.20 to 31.20%, the presence of kaolinite, carbonate, and quartz overgrowth cement reduce the porosity of the samples.Analyzed samples are characterized by poor to very good pore interconnectivity. Despite the fact that most of the sandstones display point, concavo-convex, and long contacts with poor to good compaction, few sutured grain contacts (which reflect a higher degree of compaction) still exist. XRD and SEM analyses show that kaolinite, chlorite, illite, smectite, and illite/smectite mixed layer clay are the common clay minerals in the studied samples. The presence of vermiform morphology, besides the sharp peak pattern of the kaolinite, in most of the XRD pattern indicates that part of the kaolinite was authigenically formed.

Magmatic versus phreatomagmatic fragmentation: Absence of evidence is not evidence of absence

Fragmentation processes in eruptions are commonly contrasted as phreatomagmatic or magmatic; the latter requires only fragmentation of magma without external intervention, but often carries the connotation of disruption by bubbles of magmatic gas. Phreatomagmatic fragmentation involves vaporization and expansion of water as steam with rapid cooling and/or quenching of the magma. It is common to assess whether a pyroclast formed by magmatic or phreatomagmatic fragmentation using particle vesicularity, shape of particles, and degree of quenching. It is widely known that none of these criteria is entirely diagnostic, so deposit features are also considered; welding and/or agglomeration, particle aggregation, lithic fragment abundance, and proportion of fines. Magmatic fragmentation yields from rhyolite pumice to obsidian to basaltic achneliths or carbonatitic globules, making direct argument for magmatic fragmentation difficult, so many have taken an alternative approach. They have tested for phreatomagmatism using the fingerprints listed above, and if the fingerprint is lacking, magmatic fragmentation is considered proven. We argue that this approach is invalid, and that the criteria used are typically incorrect or incorrectly applied. Instead, we must consider the balance of probabilities based on positive evidence only, and accept that for many deposits it may not be possible with present knowledge to make a conclusive determination.

Petrography and geochemistry of Cenozoic sedimentary sequences of the southern Samar Island, Philippines: Clues to the unroofing history of an ancient subduction zone

The Cenozoic sedimentary sequences of southern Samar Island in eastern Philippines were examined to understand the unroofing history of an ancient arc terrane. Petrographic and geochemical data revealed varying degrees of inputs from the ophiolite basement and differences in modal compositions. The sedimentary units are mostly made up of lithic fragments. The Late Oligocene to Early Miocene Daram Formation contains more chert and volcanic fragments whereas the late Middle Miocene to Early Pliocene Catbalogan Formation is dominantly composed of ultramafic components. These variances are correspondingly reflected in the geochemical signatures of these two sedimentary formations. The Catbalogan Formation clastic rocks have higher volatile-free MgO and Fe2O3 values (average: 8.4% for both oxides) compared to the Daram Formation samples (average: 5.1 and 6.3%, respectively). Geochemical variations are also reflected in the Co, Cr and Ni values: the Catbalogan Formation samples reflect higher concentrations (Co: 15–57ppm; Cr: 231–1094ppm; Ni: 84–484ppm) compared to the Daram Formation samples (Co: 24–32ppm; Cr: 234–418ppm; Ni: 212–323ppm). These observations suggest that the Daram Formation eroded and transported more of the crustal portions of the ophiolite, while the younger Catbalogan Formation represents a later exhumation and subsequent erosion of the ultramafic section. An oceanic island arc (OIA) setting is proposed for the two formations based on several tectonic discrimination diagrams (e.g., Th-La-Sc, La vs. Th). The OIA signature is further supported by their smooth chondrite-normalized rare earth element (REE) patterns with no obvious Eu anomaly as well as LREE enrichment which are typical of sediments deposited in OIA setting. Based on the dominantly ophiolitic provenance of the Daram and Catbalogan formations, the post-emplacement history of the nearby Samar Ophiolite is constrained during the Late Oligocene to Early Pliocene period.

Permian exhumation of the Montagne Noire core complex recorded in the Graissessac‐Lodève Basin, France

AbstractThe paleogeographic reconstruction of the Variscan Mountains during late Carboniferous‐Permian post‐orogenic extension remains poorly understood, owing to the subsequent erosion and/or burial of most associated sedimentary basins during the Mesozoic. The Graissessac‐Lodève Basin (southern France) preserves a thick and exceptionally complete record of continental sedimentation spanning late Carboniferous through late Permian time. This section records the localized tectonic and paleogeographic evolution of southern France in the context of the low‐latitude Variscan Belt of Western Europe. This study presents new detrital zircon and framework mineralogy data that address the provenance of siliciclastic strata exposed in the basin. The ages and compositions of units that constitute the Montagne Noire metamorphic core complex (west of the basin) dictate the detrital zircon age populations and sandstone compositions in Permian strata, recording rapid exhumation and unroofing of the Montagne Noire dome. Cambrian‐Archean zircons and metamorphic lithic‐rich compositions record derivation from recycled detritus of the earliest Paleozoic sedimentary cover and Neoproterozoic‐early Cambrian metasedimentary Schistes X, which formerly covered the Montagne Noire dome. Ordovician zircons and subarkosic framework compositions indicate erosion of orthogneiss units that formed a large part of the dome. The youngest zircon population (320–285 Ma) reflects derivation from late Carboniferous‐early Permian granite units in the axial zone of the Montagne Noire. This population appears first in the early Permian, persists throughout the Permian section and is accompanied by sandstone compositions dominated by feldspar, polycrystalline quartz and metamorphic lithic fragments. The most recent migmatization, magmatism and deformation occurred ca. 298 ± 2 Ma, at ca. 17 km depth (based on peak metamorphic conditions). Accordingly, these new provenance data, together with zircon fission‐track thermochronology, demonstrate that exhumation of the Montagne Noire core complex was rapid (1–17 mm year−1) and early (300–285 Ma), reflecting deep‐seated uplift in the southern Massif Central during post‐orogenic extension.

Stratigraphic units overlying the Zambales Ophiolite Complex (ZOC) in Luzon, (Philippines): Tectonostratigraphic significance and regional implications

The Zambales Ophiolite Complex (ZOC) on the island of Luzon, Philippines is one of the most well-studied crust-mantle sequences in the region. Several massifs comprise the ZOC, one of which is the Coto Block overlain by clastic sedimentary units previously dated as Eocene. Geochronologic studies from diabase, granodiorites and other late-stage magmatic products similarly yielded the same age. Succeeding tectonic models have therefore all been grounded on the assumption that the entire ZOC is Eocene.Recent investigations, however, revealed the presence of chert blocks within the Early to Middle Miocene clastic formation overlying the Acoje Block in the northern part of the ophiolite complex. Radiolarians extracted from the cherts yielded a stratigraphic range that suggests a Late Jurassic to Early Cretaceous age. The recognition of a much older age than previously reported of the ZOC warrants a re-examination of its actual distribution and genesis. Correlating with other similarly-aged ophiolites, we suggest defining a western Mesozoic ophiolite belt, largely extending from the west-central portion of the archipelago to the northeastern tip of Luzon island. Tentatively, we attribute the Mesozoic ophiolitic and associated rocks in western Luzon to an arc-continent collision involving the Philippine Mobile Belt and the Palawan Microcontinental Block.In addition, differences in the clastic compositions of the Cenozoic sedimentary formations provide material not only for deciphering the ZOC’s unroofing history but also for constraining the timing of province linkage. The intermittent appearance of lithic fragments and detrital minerals from the ophiolite in the units of the Middle Miocene Candelaria Limestone and the Late Miocene to Early Pliocene Sta. Cruz Formation indicates significant but geographically variable contributions from the ophiolite complex. In the northern Zambales Range, the Sta. Cruz Formation caps the Coto Block and the Acoje Block of the ZOC, providing a minimum age for their amalgamation.

Provenance of volcaniclastic beach sand in a magmatic-arc setting: an example from Lipari island (Aeolian archipelago, Tyrrhenian Sea)

AbstractLipari, an active volcanic island in the Aeolian magmatic arc, is an excellent area to determine the effects of multiple source lithology, climate, weathering, transport and depositional environment on epiclastic sand composition. Volcaniclastic sand samples from 12 modern beaches were petrographically characterized using the Gazzi–Dickinson method, and the proportions of source rocks in combination with topography in associated coastal drainage basins were quantified using GIS. Several types of bedrock in the 12 drainage basins that are the likely prominent sources for sand at each sampled beach were recognized, and divided into two categories of provenance lithotypes: lavas and pyroclastic rocks ranging in composition from basaltic andesitic, to andesitic, to rhyolitic. Volcanic lithic fragments from Lipari beach sand consist of colourless and black glassy volcanic fragments with lathwork, felsitic, vitric and microlitic textures. Moreover, high amounts of detrital less durable minerals, such as pyroxene, olivine and Fe oxides, illustrate how the analysed sands preserve the source rock(s) provenance signals. Applying the concept of Sand Generation Index we see that these lithotypes have different propensities to create detritus, in terms of both grain-size and composition. Clastic contribution from pyroclastic rock outcrops such as pumice is not found in the size ranges studied, suggesting that these pumiceous source rocks probably only produce gravel or very fine sand and silt. This finding has implications for the stratigraphic record because pumice clasts, ranging from medium to fine grain-size, could be underrepresented in older volcaniclastic deposits and overrepresented in other size fractions.

Provenance of Triassic and Jurassic sandstones in the Banda Arc: Petrography, heavy minerals and zircon geochronology

Quartz-rich sandstones in the Banda Arc Islands are thought to be equivalent of Mesozoic sandstones on the Australian NW Shelf where they are important proven and potential reservoirs. Previous studies suggested that rivers draining Australia provided most of the sediment input and there have been suggestions of a northern provenance for some Timor sediments. We present results from a provenance study of Triassic and Jurassic sandstones of the Banda Arc between Timor and Tanimbar, which used several methodologies, including conventional light and heavy mineral point counting, textural classification and laser ablation (LA-ICP-MS) U–Pb dating of detrital zircons. Most sandstones are quartz-rich and detrital modes suggest a recycled origin and/or continental affinity, consistent with an Australian source. However, many of the sandstones are texturally immature and commonly contain volcanic quartz and volcanic lithic fragments. In the Tanimbar Islands and Babar, acid igneous material came from both the Australian continent and from the Bird's Head, whereas sandstones in Timor have a greater metamorphic component. Heavy mineral assemblages are dominated by rounded ultra-stable minerals, but mixed with angular grains, and indicate an ultimate origin from acid igneous and metamorphic sources. Detrital zircon ages range from Archean to Mesozoic, but variations in age populations point to differences in source areas along the Banda Arc both spatially and temporally. Significant zircon populations with ages of 240–280Ma, 1.5Ga and 1.8Ga are characteristic and are also common in many other areas of SE Asia. We interpret sediment to have been derived mainly from the Bird's Head, Western and Central Australia in the Triassic. In the Jurassic local sources close to Timor are suggested, combined with recycling of NW Shelf material.

An Early Bronze Age pile-dwelling settlement of discovered in Alepu lagoon (municipality of Sozopol, department of Burgas), Bulgaria

A new pile-dwelling settlement has been discovered during coring investigations on the shores of the Alepu lagoon (municipality of Sozopol, department of Burgas), on the western Black Sea coast, in Bulgaria. A multi-disciplinary methodology was applied to analyze the archaeological dataset, composed of wood piles, abundant charcoals and wood fragments, seeds, fish and shell remains, a few small bone fragments, some lithic fragments and potsherds. The piles were trimmed from oak trees and sunk into lagoonal muds, and currently lie 5.8 to 6.8 m below mean sea level. It highlights a wooden building at the edge of Alepu palaeo-lagoon. Charcoal remains confirm the use of oak tree as a dominant timber resource, consistent with pollen data for this period. Palaeo-botanic remains highlight gathering activities and the consumption of wild grapes, raspberries and figs. The herbaceous assemblage evokes deforestation activities. Exploitation of coastal resources is well attested by the great density of fish remains, dominated by anchovy (61%), highlighting possible preservation of fish products. Five radiocarbon dates constrain the age of the site to between 3350 and 3000 cal. BC.The Alepu piles-dwelling settlement sheds new light on the very beginning of the Early Bronze Age in coastal Bulgaria. Adding fresh information to the local archaeological record, it completes the well-discussed issue of the protohistoric submerged settlements, revealing in turn the economic strategies of the societies at the end of the transitional period. Considerations about geomorphological settings of these sites underline the evolution of the regional settlement patterns, as well as the importance of lagoonal locations. Lagoon contexts not only offer abundant fish resources, as attested by our data from Alepu, but also good conditions for anchorage. These sites were later drowned, preserved and buried following the relative rise of the Black Sea level.

Petrography, geochemistry and U-Pb detrital zircon dating of the clastic Phu Khat Formation in the Nakhon Thai region, Thailand: Implications for provenance and geotectonic setting

The purpose of this paper is to determine the provenance and tectonic setting of the Phu Khat Formation and get a better understanding of the tectonic evolution of the Nakhon Thai region using the petrography and whole-rock geochemistry integrated with the U-Pb detrital zircon dating. The sandstone of the Late Cretaceous to Early Tertiary Phu Khat Formation is chiefly characterized by unsorted texture and highly unstable volcanic lithic fragments. The formation overlies unconformably on a high textural and mineral maturity of clastic sandstone of the Late Cretaceous Khao Ya Puk Formation. Geochemically, the tectonic setting discrimination (K2O/Na2O-SiO2, Al2O3/SiO2-Fe2O3+MgO, and Th-Sc-Zr/10) and the petrography indicate that the Phu Khat Formation was accumulated in a passive margin tectonic setting which is the same as the Khao Ya Puk Formation but with a different depositional environment. The plots of geochemical provenance discrimination (La/Th-Hf, Th/Sc-Zr/Sc, Eu anomaly Eu/Eu* 0.42 to 0.74) and the petrography reveal that the provenance of the Khao Ya Puk Formation is mainly recycled sedimentary rocks while the Phu Khat Formation consists primarily of recycled sedimentary rocks associated with minor felsic volcanic rocks from the old continental island arc of the uplifted either western or eastern continental terranes or both. However, the U-Pb detrital zircon dating indicates a unique provenance of the Phu Khat Formation from the terrane west of the Nakhon Thai region where the volcanic continental arc is active predominantly in the Middle to Late Triassic. The results indicate that while the Phu Khat Formation was accumulated in Nakhon Thai region, the western terrane was uplifted by reactivation of the preexisting structure probably since the Maastrichtian time to be the source area of sediments. Meanwhile, the eastern terrane (mainly Loei-Phetchabun fold belt) had not been uplifted probably until, the accumulation of the Phu Khat Formation terminated. Subsequently, the whole region began to uplift forming a high mountainous area since the Ypresian time when the Greater India collided with the Eurasia.

The effect of freeze–thaw process on the physical and mechanical properties of tuff

In this study, we used a decay function to predict the long-term durability of tuffs against freeze–thaw (F–T) processes that are responsible of most of damages in natural building stones. The model proposed by Mutluturk et al. (Int J Rock Mech Min 41:237–244, 2004) provides meaningful parameters (including decay constant and half-life) for assessing the integrity loss of stones against freeze–thaw action. After their mineralogical characterization, six different types of tuffs were submitted to freeze–thaw cycles. Their deterioration was investigated by determining the physical (including effective porosity and P-wave velocity) and mechanical properties (including Brazilian tensile strength and uniaxial compressive strength) 10 cycles of F–T up to 70 cycles. Slake durability test was performed after 15, 30 and 60 cycles of F–T action. Results showed that slake durability index cannot be used for assessing the effect of F–T processes on the durability of the samples being studied. The decay model applied to the data indicated that, due to difference of petrographical characteristics of studied samples, decay constant and half-life were different for all types of tuffs. As with increase in lithic fragments and grain size of samples, their decay constant will increase (half-life will decrease) and, consequently, durability will decrease. Furthermore, based on achieved results from values of decay constant and half-life of the different tuff types, the destructive effect of F–T process on tensile strength was higher than on compressive strength. Brazilian tensile strength is a more relevant measurement to assess long-term durability of rocks to F–T.

Detrital mode and whole-rock geochemistry of the Miocene-Pliocene fluvial succession, Pishin Belt, Pakistan: implications on provenance and source area weathering in peripheral foreland basins

Detrital mode and geochemical composition of sandstones and mudstones of the Miocene Dasht Murgha Group (DMG) and Pliocene Malthanai Formation (MF) of the Pishin Belt, northwestern Pakistan, have been examined to identify their provenance and source area weathering. Sandstones of the Dasht Murgha Group and Malthanai Formation are lithic to sublitharenites, rich in quartz, and metamorphic and sedimentary lithic fragments, indicating a recycled orogenic source. LmLvLs plots show that the Dasht Murgha Group is rich in sedimentary and metamorphic lithic fragments (Lm35Lv18Ls47), while samples of the Malthanai Formation are overwhelmingly rich in sedimentary fragments (Lm14Lv10Ls76). Eocene Nisai Formation and Oligocene Khojak Formation within the Pishin Belt were mainly providing the sedimentary/metasedimentary detritus. High content of monocrystalline quartz (DMG 28.21 %; MF 30.7) and higher SiO2/Al2O3 ratios in sandstones (DMG 9.86; MF 11.98) also indicate high maturity of sandstones due to recycling of source terrain in collision orogens. High Cr/Ni (DMG 5.23; MF 6.17) and moderate Cr/V (DMG 3.96; MF 3.88) ratios suggest significant contributions from mafic and ultramafic detritus derived from Muslim Bagh-Zhob Ophiolite. Malthanai Formation has higher CIA and CIW values (68.96 and 77.53) than Dasht Murgha Group (63.87 and 70.93); however, they both indicate low to moderate weathering intensities. Dasht Murgha Group and Malthanai Formation have higher ICV values which indicate abundance of aluminous silicates, hence, showing moderate weathering of the source area. In A-CN-K diagrams, the samples make linear trend towards illite which suggests that the sediments were derived from a tectonically active source going through non-steady-state weathering, where the detritus has been derived from different zones of weathering profiles.

Mineralogy and geochemistry of sands along the Manzanillo and El Carrizal beach areas, southern Mexico: implications for palaeoweathering, provenance and tectonic setting

AbstractThe provenance of sands from the Manzanillo (MN) and El Carrizal (CAR) beach areas along the Mexican Pacific coast (southern Mexico) was investigated based on their modal composition, mineralogy and geochemical data. The average quartz, feldspar and lithic fragment (QFL) ratios revealed that the proportion of quartz is higher in CAR sands than in MN sands. In comparison with MN, the CAR sands are enriched in SiO2 content with higher SiO2/Al2O3 ratio indicating that sediment recycling is greatest for the CAR sands. The variation in K2O/Al2O3 and Na2O/K2O ratios between the MN and CAR sands specified a difference in the relative proportion of plagioclase. The chemical index of alteration (CIA) and Plagioclase Index of Alteration (PIA) values revealed a moderate weathering intensity in the source areas. The MN sands are characterized by a low degree of rare earth element (REE) fractionation (LaCN/YbCN = ~6–7), whereas the CAR sands define fractionated REE patterns (LaCN/YbCN = ~8.8–16.8). The fractionated REE pattern with elevated total low REE (∑LREE) content of the CAR sands suggested that sediment sorting is higher for the CAR than MN sands. Small negative and positive Eu anomalies (Eu/Eu* = ~0.91–1.23) of MN sands indicated the derivation of sediments from felsic‐intermediate source rocks. The CAR sands showed higher concentration of ∑LREE than total heavy REE (∑HREE) and characterized by a significant negative Eu anomaly (Eu/Eu* = ~0.46–0.78), suggested that the source rock is felsic type. The result obtained by the comparison of REE patterns of the beach sands to the probable source rocks is also consistent with this observation. The compositional differences identified between the MN and CAR beach areas suggested that longshore current in the mixing and homogenization of sands is not significant. The new tectonic discriminant‐function‐based multidimensional diagrams showed an arc setting (active) for the MN sands and a rift setting (passive) for the CAR sands, which is consistent with the regional geology of southern Mexico. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Facies controls on the distribution of diagenetic alterations in fan delta deposits: a case study from the Lower Cretaceous sandstone, Chagan Sag, Inner Mongolia, China

AbstractBy integrating diagenesis and sedimentary facies, the distribution of diagenetic alterations and their impacts on reservoir quality were investigated within a lacustrine fan delta depositional environment in the Lower Cretaceous of the Western sub‐sag in the Chagan Sag, Yin‐E Basin, northern China. Core observation and analyses of petrography and geochemistry of the sandstones revealed that the eogenetic alterations display spatial and temporal distribution patterns associated with sedimentary facies, including distributary channels of a fan delta front (DC), distributary bays (DB) and sheet sands (SS) and mouth bar (MB) (SS and MB are collectively referred to as S). Percolation of meteoric waters occurring in high permeability DC sandstones resulted in leaching of feldspar, the formation of kaolinite, as well as mechanical infiltrated clays around detrital grains. Conversely, the DB deposits containing abundant ductile lithic fragments were subjected to mechanical compaction and thus the development of a pseudomatrix. During a long burial residence time (the Early Cretaceous period) in a lacustrine environment, abundant early carbonate cements were precipitated, especially in the distal S sandstones. The sandstones lacking eogenetic cements were subjected to stronger mechanical compaction. Additionally, eogenetic alterations have an important impact on the distribution of the mesogenetic alterations. Sandstones containing few eogenetic cements or thin or discontinuous infiltrated clay rims around the detrital grains were subjected to quartz cementation. However, during the hydrocarbon generation stage, the most efficient percolation of meteoric waters and organic acid dissolved feldspar minerals and carbonate cements, resulted in DC sandstones having more intragranular and intergranular porosity. Owing to high matrix contents and early calcite cement contents, the DB and S sandstones had lower permeability and were rarely dissolved. During the late mesogenetic stage, late carbonate cements occurred in all sedimentary facies and iron and magnesium ions were released from the transformation from kaolinite to illite or to chlorite. The results from this study show possible diagenetic evolutionary pathways in the reservoir sandstones within the fan delta depositional environment, which in turn provides some insights into the controls on reservoir potential. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Provenance of sandstone on the western flank of Anambra Basin, Southwestern Nigeria

Petrographic and heavy mineral studies were carried out on clastic deposits that crop out in Ikpeshi, Auchi and Fugar localities in order to determine the provenance of the sediments and the tectonic setting of the source area. The localities are in the western flank of the Anambra basin, southwestern Nigeria. Petrographic study shows that the sandstone deposits are composed of variable amounts of quartz, feldspars and lithic fragments with minor occurrence of authigenic silica and chlorite cements. Quartz is the predominant detrital mineral in all the samples accounting for over 87 % of the total framework composition. The representative samples from all the localities contain 88-94 % quartz, 1-8 % lithic fragment, 1-4 % cement and 0-4 % matrix. Feldspar is present in small amount only in samples from Fugar locality. The sandstones each classify as quartz arenites and sublitharenites. Both opaque and transparent heavy minerals occur in the sandstones. The opaques are magnetite, ilmenite and leucoxene. Together, they account for 35 – 55 % of the total heavy mineral abundance. The transparent heavy minerals are zircon, tourmaline, rutile, staurolite, and apatite listed in order of decreasing abundance. The heavy mineral assemblages in the localities are similar except for the absence of rutile from the sediments of Ikpeshi locality. The heavy mineral grains are subangular to rounded. The zircon-tourmaline-rutile (ZTR) index for the sediments from the three localities are generally high and range from 90.5 to 100% indicating high degree of mineralogical maturity of the sandstones. The heavy mineral suites and the petrographic signatures of the sandstones suggest derivation mainly from acid igneous rocks, gneisses and older sandstones in both stable tectonic and recycled orogenic settings. However, the absence of rutile in sandstone from Ikpeshi may suggest derivation from lithologically more restricted provenance.

The island of Elba (Tuscany, Italy) at the crossroads of ancient trade routes: an archaeometric investigation of dolia defossa from the archaeological site of San Giovanni

Dolia are large pottery containers used in Roman times for the storage and fermentation of wine. They were produced in specialized pottery workshops (figlinae) and were typically marked with specific epigraphical stamps, which represent a major tool to unravel their provenance and trade. In this work we present the preliminary results of a study of two dolia defossa, recently found at San Giovanni (Portoferraio, island of Elba, Italy) during 2012–2014 archaeological excavations in a Roman farm (late 2nd cent. BC-1st cent. AD), devoted to wine production and probably constituting the antecedent archaeological phase of the adjacent “Villa delle Grotte”. Based on archaeological (epigraphic) evidence, five different production areas have been hypothesized: 1) Elba island, where the dolia have been found; 2) the municipal figlinae in the Pisa territory; 3) the middle catchment of the Tiber river (central Latium) where “urban” figlinae occurred; 4) the figlinae of Minturno (southern Latium), a locality known both for wine production and exportation and for the presence of ancient figlinae; 5) the municipal figlinae in the Volterra territory. Archaeometric analysis of tempering agents intentionally added to the clay for the manufacturing of the dolia, particularly magmatic lithic fragments and clinopyroxene crystals, allowed us to suggest that the watershed of the central Tiber Valley - including different volcanic centres belonging to both Tuscany Magmatic Province (Monti Cimini) and Roman Magmatic Province (Monti Vulsini and Vico volcano) - could have been the most likely sites of production of the dolia found at San Giovanni. Alternatively, the site of Minturno (southern Latium) could be proposed.

Petrography and geochemistry of the Late Cretaceous redbeds in the Gan-Hang Belt, southeast China: implications for provenance, source weathering, and tectonic setting

ABSTRACTThe distinct basin and range tectonics in southeast China were generated in a crustal extension setting during the late Mesozoic. Compared with the adjacent granitoids of the ranges, the redbeds of the basins have not been well characterized. In this article, provenance, source weathering, and tectonic setting of the redbeds are investigated by petrographic and geochemical studies of sandstone samples from the Late Cretaceous Guifeng Group of the Yongchong Basin in the Gan-Hang Belt, southeast China. Detrital grains are commonly subangular to subrounded, poorly sorted, and are rich in lithic fragments. The variable pre-metasomatic Chemical Index of Alternation (CIA* = 62–85), Chemical Index of Weathering (CIW = 70.90–98.76, avg. 85.62), Plagioclase Index of Alteration (PIA = 60.23–98.35, avg. 79.91), and high Index of Compositional Variability (ICV = 0.67–3.08, avg. 1.40) values collectively suggest an overall intermediate degree of chemical weathering and intense physical erosion of the source rocks, but a relatively decreased degree of chemical weathering during the late stage (Lianhe Formation) of the Guifeng Group is observed. Several chemical ratios (e.g. Al2O3/TiO2, La/Th, Cr/Th, Th/Sc, Zr/Sc) also suggest a dominant felsic source nature, significant first-cycle sediment supply, and low sedimentary recycling. Such features are consistent with active extension tectonic setting. Sandstone framework models and geochemical characteristics suggest the provenance is related to passive margin (PM), active continental margin (ACM), and continental island arc (CIA) tectonic settings. Sediment derivation from the Neoproterozoic metamorphic rocks and Silurian–Devonian granites indicates a PM provenance, whereas sediments derived from the Early Cretaceous volcanic-intrusive complexes suggest an ACM and CIA nature. Therefore, the Late Cretaceous redbeds were deposited in a dustpan-like half-graben under the back-arc extension regime when southeast China was possibly influenced by northwestward subduction of the Palaeo-Pacific plate beneath East Asia.

Internal Domains of Natural Porous Media Revealed: Critical Locations for Transport, Storage, and Chemical Reaction.

Internal pore domains exist within rocks, lithic fragments, subsurface sediments, and soil aggregates. These domains, termed internal domains in porous media (IDPM), represent a subset of a material's porosity, contain a significant fraction of their porosity as nanopores, dominate the reactive surface area of diverse media types, and are important locations for chemical reactivity and fluid storage. IDPM are key features controlling hydrocarbon release from shales in hydraulic fracture systems, organic matter decomposition in soil, weathering and soil formation, and contaminant behavior in the vadose zone and groundwater. Traditionally difficult to interrogate, advances in instrumentation and imaging methods are providing new insights on the physical structures and chemical attributes of IDPM, and their contributions to system behaviors. Here we discuss analytical methods to characterize IDPM, evaluate information on their size distributions, connectivity, and extended structures; determine whether they exhibit unique chemical reactivity; and assess the potential for their inclusion in reactive transport models. Ongoing developments in measurement technologies and sensitivity, and computer-assisted interpretation will improve understanding of these critical features in the future. Impactful research opportunities exist to advance understanding of IDPM, and to incorporate their effects in reactive transport models for improved environmental simulation and prediction.