Alluvial Conglomerates Research Articles

Long-term stability of sediment routing on an active continental margin: Insights from detrital zircon U-Pb ages and measured stratigraphy of Carboniferous to Miocene strata, Sierra de Narváez, NW Argentina

The complex Phanerozoic tectonic evolution of the western margin of South America, including extensional, neutral, and contractional deformation regimes, provides an opportunity to test how sedimentary systems were affected by variable tectonics on a long-lived active margin. Here, we report new geologic mapping, measured stratigraphic sections, paleocurrent measurements, and detrital zircon U-Pb ages from the Fiambalá area, NW Argentina, that together constrain the evolution of sediment routing and basin systems of the northern Sierras Pampeanas during Carboniferous to Miocene time. Carboniferous to Triassic strata of the Paganzo Group include fluvial, lacustrine, and eolian intervals deposited in an extensional setting with SSW-directed paleocurrent orientations. The Mesozoic El Pedernal Formation consists of a lower, basalt interval and an upper, conglomerate and sandstone interval, which has a new detrital zircon maximum depositional age of ca. 88 Ma. Observed strata of the Miocene Tambería Formation include fluvial to eolian sandstones of the lower member of the formation and alluvial conglomerates of the middle member. Whereas lower member Tambería fluvial strata have SSW-oriented paleocurrents, middle member conglomerates indicate broadly E-directed paleoflow.Detrital zircon age distributions of the Paganzo Group, El Pedernal Formation, and Tambería Formation are remarkably consistent, with dominant age peaks ca. 1.3–0.9 Ga and ca. 660-450 Ma. The ages and relative magnitudes of these peaks are consistent with derivation from igneous sources associated with Choiyoi magmatism (330-215 Ma), the Famatinian (490-450 Ma) and Pampean (540-510 Ma) orogens, basement of the MARA block (ca. 1.3–0.9 Ga), and recycling of Neoproterozoic to Cambrian sedimentary successions derived from central Gondwana (ca. 1.3–0.9 Ga, 650-590 Ma, 540-510 Ma).The consistent paleocurrent orientations and detrital zircon U-Pb ages of the Carboniferous Paganzo Group to the Miocene lower member of the Tambería Formation suggest that a S-directed axial drainage network with a consistent sediment source area persisted in the region for ∼300 Myr. This axial drainage network was succeeded by an E-directed transverse drainage network initiated between 15 Ma and 8 Ma due to growth of the Andean thrust wedge, coeval with tectonic compartmentalization and drainage modification of nearby foreland depocenters. These findings highlight the potential for long-term persistence of drainage networks on continental margins under changing tectonic regimes.

Detrital zircon and apatite U-Pb provenance and drainage evolution of the Newark Basin during progressive rifting and continental breakup along the Eastern North American Margin, USA

Abstract Mesozoic rift basins of the Eastern North American Margin (ENAM) span from Florida in the United States to the Grand Banks of Canada and formed during progressive extension prior to continental breakup and the opening of the north-central Atlantic. The syn-rift strata from all the individual basins, lumped along the entire margin into the Newark Supergroup, are dominated by fluvial conglomerate and sandstone, lacustrine siltstone, mudstone, and abundant alluvial conglomerate and sandstone lithofacies. Deposition of these syn-rift sedimentary rocks was accommodated in a series of half grabens and subsidiary full grabens situated within the Permo-Carboniferous Appalachian orogen. The Mesozoic ENAM is commonly depicted as a magma-rich continental rift margin, with magmatism (Central Atlantic magmatic province [CAMP]) driving continental breakup. However, the southern portion of the ENAM shows evidence of magmatic breakup (e.g., seaward-dipping reflectors), and rifting and crustal thinning appeared to start ~30 m.y. prior to CAMP emplacement in the Jurassic. This study provides extensive new detrital zircon and apatite U-Pb provenance data to determine the provenance and reconstruct the paleodrainages of the Newark Basin during progressive rifting and magmatic breakup and the implications for the overall rift configuration and asymmetry during progressive rifting along the ENAM rift margin. Detailed new detrital zircon (N = 21; n = 3093) and apatite (N = 4; n = 559) U-Pb results from sandstone outcrop and core samples from the Newark Basin indicate a distinct provenance shift, with relatively older Carnian syn-rift strata predominately sourced from the hanging wall of the basin bounding fault in the east while relatively younger Norian strata were regionally sourced from both the hanging wall and footwall. The syn-rift strata at the Triassic-Jurassic boundary were sourced from the hanging wall before a transition to local footwall terranes. These results suggest two major provenance changes during progressive rifting—the first occurring during Carnian crustal necking and rift flank uplift as predicted by recent numerical models and the second occurring at the onset of the Jurassic due to regional and local thermal uplift during CAMP magmatism as seen along other magma-rich margins, such as the North Atlantic and the southern portion of the South Atlantic margin.

Controls on Late Miocene to Early Quaternary continental sedimentation during the development of the Sohag basin, Nile Valley, Egypt

Sohag Basin is a Late Cenozoic rift basin that follows the course of the River Nile and contains a sequence of Early Miocene to Quaternary times. The present study outlines the impact of the allocyclic factors controlling a sequence of a fluvio-lacustrine succession dated from the Late Miocene to the Early Pleistocene and is subdivided into Units II and III. Unit II is made mostly of fluvial siliciclastic sediments (FA1), interpreted as channels and floodplains. Unit III consists of alluvial conglomerates (FA2) followed upwards by lacustrine carbonates (FA3) covering the whole basin. These two units are arranged in two depositional sequences (DSQ-1 and DSQ-2), bounded by sequence boundaries. Both sequences are composed of the Low- and High-Accommodation System Tracts (LAST, HAST), and they are distinguished primarily by the facies associations and the nature of the contacts that separate them. Allogenic controls strongly influenced the general evolution of the fluvio-lacustrine system. Tectonics determined the variations in thickness and lithofacies of Units II and III, where the basin was affected by the reactivation of basin-bounding faults, and suggested that the basin physiography changed from the full-graben to half-graben stage. The variation in the lacustrine facies associations and the pedogenic features show the response to tectonics and local climate conditions. Provenance played a role in the drainage pattern evolution. Using the Facies architecture and sequence stratigraphic framework, a depositional model was constructed and strongly influenced by tectonic subsidence and uplift of the basin concurrent with the reactivation of the Gulf of Suez-Red Sea rifting.

Paleogeographic and sedimentary evolution of North Calabrian basins during the Messinian Salinity Crisis (South Italy)

The Rossano and Crotone basins in North Calabria represent key areas for the study of the Messinian Salinity Crisis (MSC) in the central Mediterranean. The integrated analysis of the outcropping successions coupled with well-borehole stratigraphies and seismic profiles permitted the stratigraphic and paleogeographic reconstruction of the MSC as follows:During the late Tortonian-early Messinian, open normal marine conditions typified the studied basins, as the deposition of deep-water claystones followed by diatomites (Tripoli Fm). The first basin restriction occurred during the early Messinian (5.96 Ma) when a relative sea-level still-stand triggered the formation of a carbonate platform system (Calcare di Base Fm − CdB). This latter was characterized by sabkha to shallow-water environments passing into a gentle slope to basin setting.A successive relative sea-level drop (ca. 5.60 Ma) induced a general exposure of the CdB platform systems and the creation of a marked erosional surface linkable with the Messinian Erosional Surface (MES). Consequently, progradational early LST forced regression wedges deposited and, as the reduction of open-sea connections, more severe restricted conditions took place. Later on, during the late LST, the massive deposition of salt dominated bodies brought to the sedimentary filling of the basins and to the consequent leveling of the paleobathymetric differences. Afterwards, a transgression phase (TST) inundated again the basins, causing firstly the sedimentation of clay dominated deposits, and successively, during a further sea-level still-stand (HST), the reestablishment of evaporitic conditions with deposition of widespread shallow-water sulphate deposits. Lastly, a new severe sea-level drop (LST) exposed again all the previous deposits and alluvial conglomerates deposited along incised paleovalleys above the HST sulphate deposits. This event marks the transition to the Lago-Mare phase that typifies the last stage of the MSC, before the base-Pliocene reflooding of the Mediterranean (ca. 5.33 Ma).

Sedimentary evolution of a foreland basin from the northeastern Qilian Mountains based on the integration of geomorphological and luminescence dating of alluvial conglomerates and fluvial terrace sediments

Sedimentary deposits in the foreland basin of the northeastern Qilian Mountains are crucial documents recording tectonic activity and climate changes on the Tibetan Plateau. In this study, luminescence dating was used to date alluvial conglomerates and fluvial terrace sediments collected from the Beida River in the Jiuquan Basin, a foreland basin in the Hexi Corridor, northeastern Qilian Mountains. Detailed sedimentology and luminescence ages reveal that alluvial conglomerates accumulated from before 620 ka to 12 ka and that sediment accumulation rates increased at ∼330 ka and ∼35 ka, coinciding with the dates of two tectonic events (∼350 and ∼50 ka) and followed by climate cooling (from marine isotope stage (MIS) 9 to MIS 8 and from MIS 3 to MIS 2). This reveals that variations in the sediment accumulation rates are controlled by the coupling of tectonic uplift and climate cooling. The highest terrace (T7) that developed on the alluvial conglomerate base formed at ∼ 12 ka. The incision rate in the early Holocene was ∼2.1 mm/yr and increased to ∼14.6 mm/yr during the middle and late Holocene. The variations in the river incision rate provide geomorphic evidence for Holocene climate patterns in arid and semiarid areas. Luminescence dating offers a credible temporal framework for the deposits and reveals climate and tectonic effects on the evolution of the foreland basin, northeastern Qilian Mountains.

U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden

To constrain the tectonothermal evolution of the type locality for iron oxide-apatite deposits, we have obtained U-Pb zircon, titanite, and apatite age data for the Kiruna mining district in northernmost Sweden. The results indicate that the host basin initiated in an overall extensional regime as indicated by the deposition of alluvial conglomerates and greywackes. A volcanic intercalation in a conglomerate unit approximately 1 km northwest of the Luossavaara iron oxide-apatite deposit yields a U-Pb zircon concordia age of 1887 ± 3 Ma representing the timing of the earliest Orosirian volcanism in the central Kiruna mining district coinciding with the onset of basin development. In-situ analysis of titanite sitting on hydrothermally altered fracture planes within a cataclastic fault damage zone (c. 270 m from the fault core system associated with the Luossavaara iron oxide-apatite deposit) yields complex U-Pb data. Applying a strict discordance filter yields seven analyses (<1.5 % relative discordance which included six common Pb-corrected analyses and one analysis where no significant common Pb was detected) that yield a 207Pb/206Pb weighted average age of 1889 ± 26 Ma that we interpret as the most probable minimum age of fault initiation. The overlap in age of the host volcanic rock and the fault implies that during basin development, contemporaneous volcanism and syn-volcanic faults may have played an important role during iron ore emplacement. A U-Pb lower intercept age of apatite from the Nukutus iron oxide-apatite deposit provides a first indication that the area was subsequently buried and metamorphosed under upper greenschist-facies conditions and later tectonically exhumed and cooled below the apatite closure temperature at 1805 ± 26 Ma. Further temporal constraints on exhumation and basin inversion is given by syn-tectonic titanite along a brittle-ductile reverse shear zone to the east of the study area that shows limited presence of significant common Pb and is part of a sodic-calcic + Fe + Cl hydrothermal alteration assemblage. Titanite grains that show a well-developed zonation yield a U-Pb concordia age of 1812 ± 3 Ma, which we interpret as the onset of basin inversion. Titanite grains from the same sample that show less pronounced zonation yield a U-Pb concordia age of 1802 ± 8 Ma, tentatively indicating that the tectonothermal activity lasted up to c. 20 m.y.

Tectonic uplift along the northeastern margin of the Qinghai–Tibetan Plateau: Constraints from the lithofacies sequence and deposition rate of the Qaidam Basin

The uplift processes of the Qinghai–Tibetan Plateau is of great significance for understanding the tectonic dynamics and monsoons in East Asia. In this study, the spatiotemporal characteristics of the tectonic uplift along the northeastern margin of the Qinghai–Tibetan Plateau are discussed from a basin–orogen coupling perspective on the basis of detailed analyses of stratigraphy and sedimentology of the Qaidam Basin and comparisons with those of the Xining, Lanzhou, Linxia, Guide–Xunhua, and Jiuquan basins. The asynchronous tectonosedimentary events characterized by alluvial conglomerates at the Early Jurassic–Cretaceous, ~53 Ma, ~40 Ma, ~22 Ma, ~15 Ma, and <2.5 Ma have been preserved in wells at different locations. Consistently, the deposition rates indicate three episodes of accelerated deposition at ~40 Ma, ~20 Ma, and ≤5 Ma in the Cenozoic. Therefore, we believe that the orogenic uplift along the northeastern margin of the Qinghai–Tibetan Plateau can be divided into four stages: Jurassic–Cretaceous, ~40–20 Ma, ~20–5 Ma, and <5 Ma. During the Jurassic–Cretaceous, tectonic activation and uplift occurred in the ancient Qilian orogenic belt, which formed in the Early Paleozoic. By ~40 Ma, the deformation due to the growth of the “proto-Tibetan Plateau” had propagated to the Qiman Tagh Shan–East Kunlun Shan–Ela Shan–West Qinling Mountain chain. Controlled by the tectonic thrusting of the eastern Kunlun Mountains, the Qaidam Basin entered a stage of comprehensive development. At ~20 Ma, the deformation front of the Qinghai–Tibetan Plateau reached the Qilian Shan. The unified Paleogene compressional basin in the northern West Qinling Mountains split into secondary basins, such as the Xining, Lanzhou, Linxia, Guide–Xunhua, and Gonghe basins, which evolved independently. At ~5 Ma, the entire Qinghai–Tibetan Plateau entered a rapid uplift stage, and the large lacustrine basins in and around the plateau shrank and disappeared.

Palaeoclimatic and palaeoenvironmental evolution of the Lower Pleistocene Arda River succession

The Arda River marine succession, cropping out in western Emilia (northern Italy) represents an excellent site to study past ecosystems dynamics in the frame of Early Pleistocene climate change and tectonic activity. This one-day excursion leads the participants to discover the palaeoclimatic and palaeoenvironmental evolution of the Lower Pleistocene Arda River marine section, unraveled through an integrated use of sedimentological, palaeoecological (molluscs and trace fossils) and geochemical tools. Upsection, the succession was deposited in progressively shallower water and colder climate during phases of advance of fan deltas affected by hyperpycnal flows. It culminates at the top with clast supported alluvial conglomerates and freshwater/terrestrial biota indicating a sea level drop and the establishment of a continental environment. It is very rich in fossils: in the marine part molluscs, brachiopods, corals and echinoderms, besides well preserved trace fossils, are abundant; whereas in the continental part a mammal fauna and freshwater/terrestrial molluscs are occasionally found. Sclerochemical analyses undertaken on bivalve shells indicate that seawater temperature seasonality was the main variable of climate change within the study area during the Early Pleistocene. In particular, strong seasonality and low winter palaeotemperatures were assumed to be the main drivers for the widespread establishment of Arctica islandica populations in the palaeo-Adriatic Sea around 1.80 Ma. During the excursion not only fossils are shown, but also interesting biocalcarenitic bodies with a complex geometry cropping out in the town of Castell'Arquato. The excursion is complemented by the visit to the Giuseppe Cortesi geological and palaeontological museum, housing vertebrate and invertebrate fossil collections.

Tajik Basin and Southwestern Tian Shan, Northwestern India‐Asia Collision Zone: 3. Preorogenic to Synorogenic Retro‐foreland Basin Evolution in the Eastern Tajik Depression and Linkage to the Pamir Hinterland

AbstractThe Tajik basin archives the orogenic evolution of the Pamir hinterland. Stratigraphic‐sedimentologic observations from Cretaceous‐Pliocene strata along its eastern margin describe the depositional environment and basin‐formation stages in reaction to hinterland exhumation and basin inversion. During the Late Cretaceous‐Eocene (preorogenic stage: ~100–34 Ma), a shallow‐marine to terrestrial basin extended throughout Central Asia. An alluvial plain with influx of conglomerate bodies (Baljuvon Formation) indicates a first pulse of hinterland erosion and foreland‐basin formation in the late Oligocene‐early Miocene (synorogenic stage Ia: ~34–23 Ma). Further hinterland exhumation deposited massive alluvial conglomerates (Khingou Formation) in the early‐middle Miocene (synorogenic stage Ib: ~23–15 Ma). Westward thickening growth strata suggest transformation of the Tajik basin into the Tajik fold‐thrust belt in the middle‐late Miocene (synorogenic stage IIa: ~15–5 Ma). Increased water supply led to the formation of fluvial mega‐fans (Tavildara Formation). Latest Miocene‐Pliocene shortening constructed basin morphology that blocked sediment bypass into the central basin from the east (Karanak Formation), triggering drainage‐system reorganization from transverse to longitudinal sediment transport (synorogenic stage IIb: &lt; ~5 Ma). Accelerated shortening (~27–20 Ma) and foreland‐directed collapse (~23–12 Ma) of Pamir‐plateau crust loaded the foreland and induced synorogenic stages Ia and Ib. Coupling of Indian and Asian cratonic lithospheres and onset of northward and westward delamination/rollback of Asian lithosphere (i.e., lithosphere of the Tajik basin) beneath the Pamir at ~12–11 Ma transformed the Tajik basin into the Tajik fold‐thrust belt (synorogenic stage IIa). The timing of the sedimentologically derived basin reconfiguration matches the thermochronologically derived onset of Tajik‐basin inversion at ~12 Ma.

Constraints on the early Mesozoic denudation of the Qinling orogen from Upper Triassic-Lower Jurassic successions in the Zigui Basin, central China

The Qinling mountains are situated in central China and mark the collisional assembly between the North and South China blocks. To understand the early Mesozoic evolution of the Qinling orogenic belt, we present new paleocurrent data, sandstone petrology and detrital zircon U-Pb ages for Upper Triassic-Lower Jurassic sedimentary successions in the Zigui Basin in the northern margin of the South China block. The deltaic sandstones in the Upper Triassic Jiuligang Formation have high concentrations of quartz grains and the basal alluvial conglomerates of the Lower Jurassic Tongzhuyuan Formation contain abundant chert gravels with sandy matrixs rich in quartz grains. Both the Upper Triassic sandstones and Lower Jurassic conglomerate have two major detrital zircon U-Pb age groups of 2100–1700 Ma and 950–700 Ma with very few Phanerozoic ages. The overlying fluvial sandstones of the Tongzhuyuan Formation display relative enrichment in volcanic and metamorphic rock fragments. They are characterized by primary zircon U-Pb age groups of 250–200 Ma and 950–700 Ma. Consistent with the northwestward paleocurrents, zircon grains of 2100–1700 Ma and 900–700 Ma were likely derived directly or recycled from the Paleoproterozoic and Neoproterozoic basement of the South China Block, with the latter also possibly sourced from the Qinling orogen. The 250–200 Ma age group is understood to be associated with volcanic rock fragments and, considering the southward paleocurrents, indicates a volcanic source within the Qinling orogen. Along with the increased low-grade metamorphic rock fragments in sandstones, this significant provenance change in the Early Jurassic indicates the initial massive erosion and rapid southward propagation of the south Qinling orogen.

LATE PERMIAN PALEOENVIRONMENTAL CHANGES IN THE XINGCHENG AREA, LIAONING PROVINCE, CHINA: SEDIMENTARY SUCCESSION AND ROOT SYSTEMS

ABSTRACT During the late Permian, an alluvial environment prevailed along the northern margin of the North China Plate in the Xingcheng area, Liaoning Province, China. In this region, the middle–late Permian Shihhotse Formation and the late Permian Hamashan Formation record this transition from previous swamp-dominated settings. The two formations are mainly coarse-grained deposits and can be correlated with the Pingdingshan Sandstone, which developed as widespread alluvial facies in the central and southern parts of the North China Plate. Tectonic uplift around the plate due to Variscan orogenic activities probably contributed to the onset of alluvial prevalence, but the sedimentary characteristics in the Xingcheng area indicate that aridification was also an important driver. This is supported by the presence of root systems composed of rhizoliths in the Shihhotse Formation and Stigmaria fossils at the top of the alluvial conglomerate of the Hamashan Formation. Viewed at a larger scale, this basin-wide alluvial episode on the North China Plate was contemporaneous with the Wuchiapingian extreme aridity and followed a short humid interval. The overlying Changhsingian–Induan redbeds mark a paleoclimatic change to semiarid and arid again. The paleoenvironmental changes recorded in the upper Permian and Lower Triassic strata of the North China Plate, therefore, provide essential information for the understanding of late Paleozoic terrestrial evolution.

Origin of beaded tafoni in cliffs of Danxia landscapes, Longhushan Global Geopark, South China

The tafoni that develop in sandstone cliffs have attracted the interest of both scientists and the general public. A necklace-like tafone system, referred to here as beaded tafoni, has developed in the prominent cliffs of the Danxia landscapes within the Longhushan Global Geopark in the subtropical zone of South China. This paper presents a new model of the formation of this system of extraordinary beaded tafoni. The cliffs of the Danxia landscapes of the study area are composed of an alluvial conglomerate (i.e., red beds). These Danxia landscapes have subrounded summits that are covered by vegetation and experience a nearly vertical water flow induced by gravity. Erosion and collapse of the outsized gravels and concentrated pebbles in the red beds give rise to the initial development of the beaded tafoni. The tafoni then become rounded and beaded as a result of reworking and decay by fluvial outwash. During storms, intense water flows run vertically down the cliffs and generate a whirling motion in the tafoni. Consequently, the inside walls of the tafoni gradually become wider and smoother. During the late development stage, the beaded tafoni tend to become indistinct or disappear because of the interconnection of the tafoni and subsequent merging with the bedding-controlled cavities.

Proveniência e paleocorrentes de conglomerados e arenitos do Grupo Santa Bárbara (Ediacarano) no Vale do Piquiri, Sub-bacia Camaquã Oriental, RS: implicações tectônicas

A Sub-bacia Camaquã Oriental compreende exposições da borda leste da Bacia do Camaquã, como o Vale do Piquiri, pertencentes ao Grupo Santa Bárbara (Ediacarano). Estudos estratigráficos de fácies, sistemas deposicionais, proveniência e paleocorrentes conduziram à subdivisão do Grupo Santa Bárbara na Sub-bacia Camaquã Oriental em duas unidades: (i) Formação Passo da Capela, formada por turbiditos de leques subaquosos; e (ii) Formação Rincão dos Mouras, constituída por arenitos e conglomerados de leques aluviais e sistemas fluviais entrelaçados. Este artigo propõe formular um modelo de evolução de altos estruturais durante o preenchimento de uma bacia rifte. Conglomerados de leques subaquosos da Formação Passo da Capela apresentam composição do arcabouço derivada da própria bacia (arenitos), indicando autofagia, além de rochas do embasamento (quartzitos, xistos, metarriolitos). Análises de paleocorrentes indicam dispersão dos sedimentos segundo NNE, compatível com litotipos do Complexo Porongos (quartzitos, metarriolitos, milonitos). A norte, análises de proveniência dos conglomerados indicam derivação principalmente do Sienito Piquiri, e também de outras litologias. Esse fato sugere que a proveniência reflete contribuição do embasamento adjacente (clastos do Sienito Piquiri), com pouco ou nenhum transporte. Conglomerados aluviais da Formação Rincão dos Mouras contam com proveniência diversificada. Na base ocorrem clastos metamórficos do Complexo Porongos (metarriolitos) e da própria bacia (arenitos). Análises de proveniência sugerem denudação do Complexo Porongos (altos de embasamento) e da bacia. A porção intermediária apresenta clastos de granitos róseos/muscovita leucogranitos correlacionáveis ao Batólito Pelotas, e litologias do Complexo Porongos. Sienitos e traquitos aparecem em pequena proporção, assim como arenitos. Análises de proveniência, aliadas às de paleocorrentes, indicam que áreas a leste estavam sendo soerguidas e erodidas, como Batólito Pelotas e Complexo Porongos, comportando-se como altos de embasamento fornecedores de sedimentos para a bacia. No topo predominam fragmentos do Complexo Porongos (mármores). Análises de paleocorrentes realizadas na Formação Rincão dos Mouras sugerem controle tectônico importante durante o preenchimento da unidade, com mudanças de fontes de detritos para a bacia e soerguimento de altos internos. As análises de proveniência levadas a efeito em todas as unidades (i) indicaram sempre fonte adjacente aos depósitos sedimentares; (ii) demonstraram as fontes de detritos; e (iii) auxiliaram na diferenciação entre as formações Passo da Capela e Rincão dos Mouras. A ocorrência na Formação Rincão dos Mouras de fragmentos de mármore e o aumento considerável da proporção de clastos do Granito Encruzilhada do Sul, situado a ENE da região do Vale do Piquiri, foi mais um dos critérios utilizados na separação das unidades, sobretudo quando conglomerados estratificados de ambas se acham contíguos.

Diagenetic Preservation and Modification of Porosity in Aptian Lithic Reservoirs from the Sergipe–alagoas Basin, Ne Brazil

Research Article| November 14, 2017 Diagenetic Preservation and Modification of Porosity in Aptian Lithic Reservoirs from the Sergipe–alagoas Basin, Ne Brazil Argos B.S. Schrank; Argos B.S. Schrank Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Search for other works by this author on: GSW Google Scholar Sabrina D. Altenhofen; Sabrina D. Altenhofen Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Search for other works by this author on: GSW Google Scholar Luiz F. De Ros Luiz F. De Ros Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Search for other works by this author on: GSW Google Scholar Author and Article Information Argos B.S. Schrank Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Sabrina D. Altenhofen Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Luiz F. De Ros Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil e-mail: argosssb@hotmail.com Publisher: SEPM Society for Sedimentary Geology First Online: 14 Nov 2017 Online Issn: 1938-3681 Print Issn: 1527-1404 Copyright © 2017, SEPM (Society for Sedimentary Geology) Journal of Sedimentary Research (2017) 87 (11): 1156–1175. https://doi.org/10.2110/jsr.2017.64 Article history First Online: 14 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Argos B.S. Schrank, Sabrina D. Altenhofen, Luiz F. De Ros; Diagenetic Preservation and Modification of Porosity in Aptian Lithic Reservoirs from the Sergipe–alagoas Basin, Ne Brazil. Journal of Sedimentary Research 2017;; 87 (11): 1156–1175. doi: https://doi.org/10.2110/jsr.2017.64 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Sedimentary Research Search Advanced Search Abstract Litharenites composed of sedimentary and low-grade metamorphic rock fragments are rarely good hydrocarbon reservoirs. Most of their primary porosity is lost by ductile grain deformation during mechanical compaction. However, the lithic Carmópolis Member of the Muribeca Formation from the Sergipe–Alagoas Basin, NE Brazil, is one of the most important oil reservoirs of the country. The high reservoir quality of the Carmópolis Member, despite its unusual composition rich in low-grade metamorphic fragments, indicates the occurrence of effective porosity preservation processes. The understanding of the occurrence and distribution of these porosity preservation processes are of paramount importance to optimize the recovery from producing oilfields, for the further development of these reservoirs, and for the exploration for similar reservoirs. The Carmópolis Member consists of alluvial conglomerates and sandstones intercalated with fine-grained lacustrine and alluvial-plain sediments deposited during the Aptian, in an arid environment. Detailed petrographic analyses were performed on 135 thin sections taken from cores of six wells, with support from SEM and EDS analyses. The reservoirs correspond mainly to conglomerates and to medium- to coarse-grained conglomeratic sandstones, classified as litharenite phyllarenites, subordinately feldspathic litharenites, and lithic arkoses. Dolomite is the most abundant cement. Other volumetrically significant processes are K-feldspar and calcite precipitation, feldspar dissolution, and deformation of ductile grains due to compaction. Twenty reservoir petrofacies were defined, based on the main aspects of primary composition and texture and diagenesis that control the porosity. Although partial dolomite cementation was previously considered as the main process of porosity preservation in the Carmópolis reservoirs, the present study suggests that other mechanisms such as early oil saturation may have been important for preserving their quality. Variations in depositional texture and composition, and in the distribution of these processes, resulted in the various defined reservoir petrofacies. Oil and the fluids that precipitated dolomite migrated up along major faults from deeply buried fine sediments to the shallow reservoirs. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Interaction of an antecedent fluvial system with early normal fault growth: Implications for syn‐rift stratigraphy, western Corinth rift (Greece)

AbstractContinental ‘overfilled’ conditions during rift initiation are conventionally explained as due to low creation of accommodation compared with sediment supply. Alternatively, sediment supply can be relatively high from the onset of rifting due to an antecedent drainage system. The alluvial Lower Group of the western Plio–Pleistocene Corinth rift is used to investigate the interaction of fluvial sedimentation with early rifting. This rift was obliquely superimposed on the Hellenide mountain belt from which it inherited a significant palaeorelief. Detailed sedimentary logging and mapping of the well‐exposed syn‐rift succession document the facies distributions, palaeocurrents and stratigraphic architecture. Magnetostratigraphy and biostratigraphy are used to date and correlate the alluvial succession across and between fault blocks. From 3·2 to 1·8 Ma, a transverse low sinuosity braided river system flowed north/north‐east to east across east–west‐striking active fault blocks (4 to 7 km in width). Deposits evolved downstream from coarse alluvial conglomerates to fine‐grained lacustrine deposits over 15 to 30 km. The length scale of facies belts is much greater than, and thus not directly controlled by, the width of the fault blocks. At its termination, the distributive river system built small, stacked deltas into a shallow lake margin. The presence of a major antecedent drainage system is supported by: (i) a single major sediment entry point; (ii) persistence of a main channel belt axis; (iii) downstream fining at the scale of the rift basin. The zones of maximum subsidence on individual faults are aligned with the persistent fluvial axis, suggesting that sediment supply influenced normal fault growth. Instead of low accommodation rate during the early rift phase, this study proposes that facies progradation can be controlled by continuous and high sediment supply from antecedent rivers.

Cosmogenic nuclide burial dating of an alluvial conglomerate sequence: An example from the Hexi Corridor, NE Tibetan Plateau

Abstract The thick alluvial conglomerate sequences around the Tibetan Plateau have been notoriously difficult to date. Here we use the cosmogenic nuclide burial dating method to date the Yumen and Jiuquan formations, a ∼900 m thick fanglomerate found in the Hexi Corridor, the foredeep of the Qilian Shan, and exposed in the Laojunmiao anticline. We date 16 sites with simple burial dating and 2 sites with isochron burial dating, and use these dates to reinterpret the magnetostratigraphy of the section. We suggest that the bottom of the Yumen Formation, defined by a progressive unconformity, is around 5 My. Taking this timing as the initiation of anticline growth, the long-term crustal shortening rate at the ramp zone in western Qilian Shan is about 0.72 mm/yr, consistent with those obtained from middle and eastern Qilian Shan. The boundary between the Yumen and Jiuquan Formations is near ∼1.2 My. Three other angular unconformities are dated to ∼2.6–3.1, ∼2.2–2.5, and ∼1.2–1.7 My, respectively. Burial dating offers a robust chronology for these deposits, and when combined with paleomagnetic stratigraphy offers much tighter precision.

Paleoenvironmental reconstruction of the coal- and oil shale-bearing interval in the lower Cretaceous Muling Formation, Laoheishan Basin, northeast China

The Laoheishan Basin in northeast China has been filled with Lower Cretaceous coal- and “oil shale”-bearing sediments. The basin fill includes from base to top alluvial conglomerate (lower member of Muling Formation), fan delta sediments interbedded with coal and oil-prone mudstone (denominated as “oil shale”) layers in the upper member of Muling Formation, and volcaniclastic rocks (Dongshan Formation). In the present study, the maturity of organic matter, oil shale quality, and paleoenvironment of the coal and oil shale accumulation are investigated based on macro- and micropetrographic data, proximate and ultimate analyses, bulk geochemical parameters, biomarkers analysis and stable isotope geochemistry.In the Laoheishan Basin, both coal and “oil shale” layers are derived from land plant organic matter. This contrast the “oil shale” of this basin from oil shale/coal intercalations in fault-related basins, in which oil shale has been found to be of algal origin. The coal is sub-bituminous in rank, hydrogen-rich and oil-prone. The “oil shale” is of low-medium grade and the relatively low oil yield may relate to the abundant resinite and sporinite, because of their lower generation potential compared with alginite. Accumulation of the high-ash coal commenced in low-lying mire, drowned during frequent floodings. Subsequently high-ash, low-sulfur coal was deposited in a stable low-lying mire, under oxic conditions and limited bacterial activity. Afterwards the mire was drowned and formed a freshwater, dysoxic to oxic shallow lake, in which “oil shale” layers accumulated. Finally, the depositional environment returned to low-lying mire but probably with a brackish influence, as indicated by elevated sulfur contents in the uppermost samples. Petrography- and biomarker-based proxies indicate that gymnosperms dominated the paleovegetation of the mire, accompanied by variable amounts of herbaceous plants, such as ferns.

Cenozoic tectonic and geomorphic evolution of the Longxi region in northeastern Tibetan Plateau interpreted from detrital zircon

The Longxi region contains different kinds of Cenozoic sediments, including eolian deposits, reworked loess, fluvial and lacustrine deposits. The provenance evolution of these sediments is of great significance in exploring the uplift, tectonic deformation and associated with geomorphic evolution of the Northeastern Tibetan Plateau. In this paper, we used the single-grain zircon provenance analysis to constrain the provenances for the Paleogene alluvial conglomerates and for the Neogene fluvial-lacustrine sediments, and compared them with results from the loess deposits since the Miocene. The results show that: (1) the Paleogene alluvial conglomerates contain a large number of detrital zircons ranging from 560 to 1100 Ma that were derived from the Yangzi Block. However, the sediments of early Miocene have much fewer zircons of this age span, which are characterized by an abundance of zircon ages in the ranges of 200–360 Ma. This indicates that the Paleogene alluvial conglomerates mainly come from the middle and/or southern West Qinling, and the early Miocene sediments are primarily from the northern West Qinling; (2) Late Neogene fluvial sediments (11.5 Ma onward) in Tianshui-Qinan region are dominated by zircon ages of 380–450 Ma. This zircon population is similar to that of the exposed intrusive rocks of southern part of the Liupan Mountains, implying that the southern part of Liupan Mountains probably had already uplifted by 11.5 Ma; (3) Late Miocene lacustrine sediments in Tianshui region have a zircon age spectra that is remarkably different from coeval fluvial deposits, but is similar to the zircon age distributions of the Miocene loess in Qinan region, late Miocene-Pliocene Hipparion red clay and Quaternary loess. This indicates that fine particles within these Miocene lacustrine sediments in Tianshui region may be dominated by aeolian materials. This study reveals that provenance changes of Cenozoic sediments in Tianshui-Qinan region and its geomorphic evolution are closely related to the multi-stage uplift of the Northeastern Tibetan Plateau. In particular, the major uplift of the Northern Tibetan Plateau during late Oligocene-early Miocene may have not only provided the source areas and wind dynamic conditions for the deposits of the Miocene loess, but also provided the geomorphic conditions for its accumulation.

Tectonosedimentary evolution model of an intracontinental flexural (foreland) basin for paleoclimatic research

Intracontinental flexural (foreland) basin sediments are now frequently used as archives for detailed paleoclimatic and sedimentary environmental reconstruction, fossil and stratigraphic correlation, and tectonic evolution and uplift of basin and orogen. However, sedimentologic characteristics vary considerably in time-space with the evolution of flexural basin, apt to cause misinterpretation of climatic change and stratigraphic correlation. Based on high resolution fossil mammal and magnetostratigraphic constraints and sedimentary facies analysis, here we took the Linxia Basin at the front of the NE Tibetan Plateau as a case to demonstrate and figure out a model how sedimentology and stratigraphy vary temporospatially with the evolution of such flexural basin. The results show that the Linxia Basin is a type intracontinental foreland basin subjected to two phases of flexural deformation exerted by the West Qin Ling (Mts.) and NE Tibetan Plateau to the south. Phase I began latest at the beginning of the Miocene (23.3Ma), indicated by a balanced fast flexural subsidence and mostly fine sediment infilling giving rise to the early underlying unconformity. It manifests as an obvious sediment wedge with high filling rate, thickening toward mountains and an occurrence of a mountains-parallel big river – shallow lake system along the foredeep, suggesting a less high mountain topography. In the late Phase I, from ~13Ma to 8Ma, the subsidence and thickening rates began to decrease, accompanied by faults and deformation propagating gradually into the basin, causing gradual basinward migration of the foredeep and its accompanying river-lake system. Since ~8Ma in Phase II, the West Qin Ling and NE Tibetan began to uplift rapidly and thrust/load onto the Linxia Basin, causing strong mountain erosion, thrust-fold belt propagation and basin overfilling. This forced the mountains-parallel river - lake system to turn to the mountains-perpendicular alluvial - braided river system, and finally to an outflow system by the Quaternary onset of the Yellow River in the basin. Concurrent are rapid rotation of the basin, occurrence of growth strata and late unconformities, widespread expansion of boulder conglomerates, great decreasing and increasing sedimentation rates above and before the hanging wall of the fault-fold system and new supplementary provenance from the thrust-fold system. This demonstrates that in stable climate, same lithologic units such as distinct lacustrine sediments and alluvial conglomerates will migrate basinwards with the foredeep moving into basin, causing a great diachroneity and often misleads to recognize the same lithologic unit in space as one unit in time. A dynamic model is presented that should help to avoid such pitfalls in tectonic basin evolution, especially concerning stratigraphic correlation and paleoclimatic change research.

Facies control on seismites in an alluvial–aeolian system: The Pliocene dunefield of the Teruel half-graben basin (eastern Spain)

The recognition of seismically induced soft-sediment deformation structures (SSDS) in sedimentary successions characterized by different facies, and hence by different rheology, is challenging. This is the case for high porosity and high permeability aeolian facies interbedded with muddy wet interdune deposits and alluvial conglomerates and sandstones. Several types of SSDS have been studied in two exposures of the Upper Pliocene (2.9–2.6Ma) sediments of a fault-bounded intracontinental aeolian dune field in the Teruel Basin (Iberian Chain, eastern Spain). Among SSDS, load and fluid-escape structures, apart from several animal tracks, have been recognized. Those structures show an irregular distribution through the studied stratigraphic sections, being scarce in homogenous aeolian sands and frequent in water-related facies. A detailed study of the distribution and geometry of SSDS and their relationships with respect to the stratigraphic architecture and facies has allowed a critical discrimination of trigger mechanisms, i.e. biological or physical overloading vs. earthquakes. The seismically induced structures are concentrated into seven deformed beds, showing an uneven lateral distribution and geometry closely controlled by the hosting sedimentary facies and their rheology. These seismites resulted from liquefaction during moderate earthquakes (estimated magnitude from 5.0 to 6.8). The most probable seismogenic source was the Sierra del Pobo normal fault zone, located 2km to the East. Results show how an appropriate recognition of sedimentary facies is crucial to understand the lateral variability of seismites in sedimentary environments characterized by sharp facies changes.