Greywacke Sandstone Research Articles

A new tectonic model for the Itmurundy Zone, central Kazakhstan: linking ocean plate stratigraphy, timing of accretion and subduction polarity

The Itmurundy Zone of Central Kazakhstan is a key structure in the core of the Kazakh Orocline representing a typical Pacific-type orogenic belt hosting accretionary complex, ophiolite massifs and serpentinite mélange. The main controversies in the existing tectonic models of the Itmurundy Zone are about the timing of subduction and accretion, the direction and kinematics of subduction and the number of oceanic plates. A new model for the early Paleozoic tectonic story of the Itmurundy Zone is postulated in this paper, based on new detailed geological and U–Pb detrital zircon age data, combined with previously documented geological, U–Pb age, microfossil, geochemical and isotope data from igneous rocks, deep-sea sediments and greywacke sandstones. The present study employs the Ocean Plate Stratigraphy (OPS) model to explain the tectonic processes involved in the evolution of the Itmurundy Zone and to present a holistic story of Ordovician oceanic plate(s), which accretion formed an accretionary complex. The detailed mapping allows distinguishing three types of OPS assemblages: (1) Chert-dominated, (2) OIB-hosting, and (3) MORB-hosting. The U–Pb ages of detrital zircons from sandstones of OIB and Chert types show unimodal distributions with similar main peaks of magmatism at 460–455 Ma in the provenance, and their maximum depositional ages (MDA) span 455–433 Ma. Two samples from OPS Type 3 show the peaks of magmatism both at ca. 460 Ma and the MDA of 452 Ma and 459 Ma, respectively. The MDA of sandstones and microfossils data from chert show the younging of strata to the south and SE in Types 1 and 2 and to NEE for Type 3 (in present coordinates) suggesting double-sided subduction to the NNW and SEE and, accordingly, the co-existence of pieces of two oceanic plates in Ordovician time. The U–Pb zircon data from both igneous and clastic rocks indicate a period of subduction erosion in early Ordovician time. As a whole, the accreted OPS units of the Itmurundy Zone record the timing of subduction and accretion from the early Ordovician to the early Silurian, i.e., 60 Ma at shortest.

Survived and disappeared intra-oceanic arcs of the Paleo-Asian Ocean: evidence from Kazakhstan.

This paper reviews published and presents new data on U-Pb detrital zircon ages, and petrographic, geochemical and isotope (Sm-Nd, Lu-Hf) compositions obtained from greywacke sandstones of Kazakhstan in order to reconstruct fossil intra-oceanic arcs that once existed at Pacific-type convergent margins of the Paleo-Asian Ocean (PAO) in Paleozoic time. We focus on orogenic belts of central Kazakhstan (Itmurundy and Tekturmas) and eastern Kazakhstan (Zharma and Char) in the western Central Asian Orogenic belt. These orogenic belts host accretionary complexes with greywacke sandstones of early Paleozoic (central Kazakhstan) and middle-late Paleozoic (eastern Kazakhstan) ages. First, we evaluate general perspectives for studying sandstones to reconstruct survived and disappeared magmatic arcs, taking into account episodes of subduction erosion. Then we discuss the analytical data from sandstones to make conclusions about the ages and formation settings of their igneous protoliths and define maximum deposition ages. Finally, we discuss the role of serpentinite mélanges in tectonic reconstructions. We argue that sandstones hosted by accretionary complexes are typically greywackes deposited close to their igneous sources and buried rapidly. The provenances of the studied greywacke sandstones of central and eastern Kazakhstan were dominated by mafic to andesitic igneous protoliths derived from juvenile mantle sources. The igneous rocks in the provenances were emplaced in an intra-oceanic arc setting. The sandstones were deposited in fore-arc/trench basins or, to a lesser degree, in back-arc basins. The data from both sandstones and serpentinite mélanges reconstruct middle-late-Cambrian, Ordovician, late-Devonian and Carboniferous arcs of the western PAO. The middle-late Cambrian arcs were fully destroyed by subduction erosion, whereas the Ordovician and Carboniferous arcs survived. The late-Devonian arcs were also eroded, but partly. Both the early and late Paleozoic active margins of the PAO were characterized by alternating periods of accretionary growth and subduction erosion.

Sandstones of the Itmurundy accretionary complex, central Kazakhstan, as archives of arc magmatism and subduction erosion: Evidence from U-Pb zircon ages, geochemistry and Hf-Nd isotopes

Sandstones hosted by Pacific-type orogenic belts and related accretionary complexes carry records of their source intra-oceanic or continental magmatic arcs. Study of arc-derived sandstones is important for reconstructing tectonic evolution of Pacific-type convergent margins in case such arcs get partly or completely eroded during subduction. In this paper, we present first U-Pb detrital zircon ages and Hf-in-zircon isotope ratios and whole-rock geochemical and Nd data from Ordovician to early Silurian clastic sediments (sandstones) of the Itmurundy Pacific-type orogenic belt and its hosted accretionary complex (AC). The Itmurundy AC is located in the northern Balkhash area of central Kazakhstan and includes sandstones of the Itmurundy and Kazyk fms. (central segment) and Tyuretai Fm. (eastern segment). The U-Pb ages of detrital zircons from Group 1 sandstones show unimodal distributions with major peaks at ca. 467–456 Ma and the youngest clusters of ages from 442 to 439 Ma Ma suggesting post-Llandovery deposition. The distributions of the U-Pb ages of detrital zircons from Group 2 sandstones are polymodal with major peaks at ca. 462–461 Ma and subordinate peaks at 788, 992, 2472 Ma. The Group 2 zircons yielded two youngest clusters of U-Pb ages: 458 Ma and 424 Ma suggesting post-middle Ordovician and post-Ludlow maximum depositional ages. According to petrographic classifications, both Group 1 and 2 sandstones are poorly-sorted and poorly-rounded greywacke or litharenite. The chemical compositions imply that these sandstones are immature and weakly weathered sediments. The Group 1 greywackes are characterized by relatively low SiO2 (63 wt%) compared to Group 2 greywackes (SiO2 = 66 wt% in average). The major and trace element compositions of both groups of sandstones resemble those of supra-subduction andesitic to dacitic volcanic rocks. The positive values of whole-rock ɛNd(t) (+1 to + 5.3) and zircon ɛHf(t) (+9.8 to +17.5) obtained from the Group 1 greywackes suggest juvenile igneous rocks in the source area. On the contrary, the negative values of ɛNd(t) (−7.2) and variable values of zircon ɛHf(t) (−24.5 to +11.5) from the Group 2 sandstones suggest that their parental igneous rocks were derived from mantle sources possessing both juvenile and recycled characteristics. Conclusively, the greywacke sandstones of both groups formed by erosion of an Ordovician intra-oceanic volcanic arc once existed at an active margin of the Paleo-Asian Ocean, however those of Group 1 deposited in a fore-arc basin and trench, while those of Group 2 deposited in a back-arc basin.

Subduction-controlled temporal and spatial variations in early Palaeozoic sedimentary and volcanic record of the Mongol-Altai Domain

The early Palaeozoic volcano–sedimentary evolution of the Khovd and Gobi-Altai zones of the Mongol–Altai Domain was investigated by quantitative petrographic analysis of sediments, whole-rock geochemistry of volcanic rocks, and U–Pb zircon dating. Three evolutionary stages were identified in the Khovd Zone: (1) Cambrian–mid Ordovician basaltic (Nb/Yb = 0.09–1.25) and rhyodacitic (Nb/Yb = 4.36) volcanism and sedimentation of immature greywackes in the fore-arc basin in front of the juvenile continental arc, (2) late Ordovician flysch-type sedimentation accompanied by a volcanic gap coincided with Barrovian metamorphism in footwall sequences reflecting a compressional stage, and (3) Silurian–Devonian within-plate bimodal volcanism (with a strong asthenospheric imprint; Nb/Yb = 4.45–20.34) followed by mature siliciclastic deposition interpreted as transformation of the former fore-arc region into a back-arc domain associated with HT metamorphism. In the Gobi-Altai Zone the three stages were: (1) Cambro–Ordovician marginal greywacke–sandstone succession adjacent to a mature continental arc (mafic rocks Nb/Yb = 0.71–4.36), (2) Silurian siliciclastic sedimentation associated with migration of the volcanic gap and Barrovian metamorphism, and (3) Lower Devonian deep-marine sedimentation followed by shallow-marine carbonate sedimentation, initially accompanied by calc-alkaline basalts (Nb/Yb = 0.74–4.57) and andesites to rhyolites (Nb/Yb = 0.69–4.87), evolving in the mid–late Devonian to within-plate alkali basalts (Nb/Yb = 11.05) thus reflecting back-arc basin development. These temporal and spatial variations in the Mongol-Altai Domain are interpreted as a diachronous sequence of retreating and advancing subduction modes instead of juxtaposition of suspect terranes as proposed in previous studies.

Origin and Characteristics of the Shwetagun Deposit, Modi Taung-Nankwe Gold District and the Kunzeik and Zibyaung Deposits, Kyaikhto Gold District in Mergui Belt, Myanmar: Implications for Fluid Source and Orogenic Gold Mineralization

The Mergui Belt of Myanmar is endowed with several important orogenic gold deposits, which have economic significance and exploration potential. The present research is focused on two gold districts, Modi Taung-Nankwe and Kyaikhto in the Mergui Belt comparing their geological setting, ore and alteration mineralogy, fluid inclusion characteristics, and ore-forming processes. Both of the gold districts show similarities in nature and characteristics of gold-bearing quartz veins occurring as sheeted veins, massive veins, stockworks to spider veinlets. These gold deposits are mainly hosted by the mudstone, slaty mudstone, greywacke sandstone, slate, and slaty phyllite of Mergui Group (dominantly of Carboniferous age). The gold-bearing quartz veins generally trend from NNE to N-S, whereas some veins strike NW-SE in all deposits. The gold-bearing quartz veins are mainly occurred within the faults and shear zones throughout the two gold districts. Wall-rock alterations at Shwetagun are mainly silicification, chloritization, and sericitization, whereas in Kyaikhto, silicification, carbonation, as well as chloritization, and sericitization are common. At Shwetagun, the gold occurred as electrum grains in fractures within the veins and sulfides. In Kyaikhto, the quartz-carbonate-sulfide and quartz-sulfide veins appeared to have formed from multiple episodes of gold formation categorizing mainly as free native gold grains in fractures within the veins or invisible native gold and electrum within sulfides. At Shwetagun, the ore minerals in the auriferous quartz veins include pyrite, galena, and sphalerite, with a lesser amount of electrum, chalcopyrite, arsenopyrite, chlorite, and sericite. In Kyaikhto, the common mineralogy associated with gold mineralization is pyrite, chalcopyrite, sphalerite, galena, pyrrhotite, arsenopyrite, marcasite, magnetite, hematite, ankerite, calcite, chlorite, epidote, albite, and sericite. At Shwetagun, the mineralization occurred at a varying temperature from 250 to 335°C, with a salinity range from 0.2 to 4.6 wt% NaCl equivalent. The Kyaikhto gold district was formed from aqueous–carbonic ore fluids of temperatures between 242 and 376°C, low to medium salinity (<11.8 wt% NaCl equivalent), and low CO2 content. The ore-forming processes of the Shwetagun deposit in the Modi Taung-Nankwe gold district and the Kyaikhto gold district are remarkably comparable to those of the mesozonal orogenic gold systems.

Geology and distribution of heavy metals in topsoil, Kuala Krai, Kelantan

The study for geology of Guchil, Kuala Krai, Kelantan was carried out approximately 25 km2 in and around Guchil. Preliminary research and field studies conducted to produce geological map of Guchil, Kuala krai, Kelantan. Based on the field study carried, carbonaceous mudstone interbedded with greywacke sandstone, shale and ignimbrite distribution of rock found in this study. Meanwhile, investigation on distribution and potential heavy metals (Cu, Fe, Mn, Pb and Zn) in topsoil Guchil, Kuala Krai, Kelantan was conducted. Total of nine soil sample in and around Guchil undergo soil digestion and analyzed by Inductively Coupled Plasma Spectroscopy (ICP-OES). The heavy metals concentration in the topsoil was varied between 21176-138962; 649-8411; 11-505; 43-455; and 11-115 mg/kg for Fe, Pb, Mn, Zn and Cu respectively. The average concentration of heavy metals in this study followed the order of Fe > Pb > Mn > Zn > Cu. The spatial distribution pattern shows similar distribution pattern of heavy metals in residential area. The concentration of Cu, Fe, Mn, Pb and Zn from the soil samples compared with naturally occurring value of contaminated land management and control guidelines of Department of Environment Malaysia (DOE), 2009 and Barceloux (1999) as well as with permissible limit values in soil of Polish Ministry of the Environment, 2002. From this assessment method, highly potential element was Pb followed by Zn and Cu. Besides that soil characteristic of this study shows that soil pH which is acidic condition with low total organic matter. The soil fractions tend to dominated by clay fraction in topsoil.

Deformation mechanism of boudin structures at the Bulukuning area, Banjarnegara

The greywacke sandstone in the Bulukuning area, Banjarnegara where was previously proposed as the Bulukuning Formation is part of the Luk Ulo Mélange Complex. In general, these molassic deposits show alternation between siltstone and siltstone with thin bedding deposited in the foreland basin. The Eocene sandstones are in some parts associated with the boudin structure, folded and cut by faults in the contractional regime. This study aims to determination of boudin type, structural orientation is highly correlated with deformation mechanism. This mechanism of deformation can be formed in different deformation periods. The correlation between the orientation of the systematic fault P-foliation, Y-shear, and R shows that the formation of boudinage is thought to be affected by the presence of a right movement (dextral), which follows the principle of the riedel shear. The deformation mechanism in the formation of sandstone boudin structures embedded in the scaly clay matrix is thought to be affected by plastic (ductile) by following the simple shear principle.

The Precambrian Hazara Formation from Hazara Mountains, Northern Pakistan

The late Neoproterozoic Hazara Formation along the Lora Maqsood Road near Haripur, Lesser Himalayas, North Pakistan, is studied for sedimentology, petrography, and major and trace element analysis to determine the paleoenvironment, provenance, paleoweathring intensity, and tectonic settings. The Hazara Formation is characterized by greywacke sandstone, siltstone, shale, argillite, claystone, limestone, and coarsening and finning upward turbidite lithofacies. Based on bedding style, grain size, and sedimentary structures, 11 types of lithofacies were identified within the sequence. The macroscopic studies indicate that the sequence has undergone through slight metamorphism although the texture is altered sedimentary features and bed geometries are well preserved. Compaction seems to affect the part of argillaceous sediments of an enormous thickness of the Hazara Formation to make slate-like appearance which may preferably be called argillites. The same effect is seen on sandstone to make it so hard to name it orthoquartzite. Petrographic analysis of limestone reveals that the limestone is micritic in nature; stylolites and pressure solution structures are also present in the limestone. The petrographic analysis of sandstone categorized it as feldspathic greywacke in the QFR diagram. The quartz content is higher in sandstone and may reach to 70% which indicates a weathered felsic source. The petrographic analysis suggests a continental block provenance with stable craton and an uplifted basement source. The Chemical Index of Alteration and the Chemical Index of Weathering values indicate moderate to high weathering conditions with a warm and moist climate in the source region. A sedimentary-tectonic model based on the geochemical data of sandstone indicates deposition along with active continental margin tectonic settings. The paleocurrent flow analysis indicates that the dominant source region of the sediments of the Hazara Formation was situated south to southeast, which may probably be the central Indian craton, Aravali orogeny, and Bundelkhand craton of southern India.

A Combined Petrographic-Geochemical Provenance and Tectonic Setting Study of Palaeozoic Rocks, in East Johor Basin, Peninsular Malaysia

DOI: 10.17014/ijog.8.1.11-24Several greywacke sandstones considered as Paleozoic rocks are found in three different formations, i.e. the Dohol, Linggiu, and Tanjung Leman Formations within the Palaeozoic East Johor Basin. The compositions of twenty-nine sandstone samples were identified using petrographical and geochemical methods to determine the provenance of sandstones as well as the tectonic setting of pre-and syn-sedimentation. Seven samples of them were examined using point counting method to obtain the mineralogical compositions. This petrographical point counting was done by plotting composition percentages to QFL and QmFLt triangular diagrams, The results showed a magmatic arc for Dohol Formation, a change from a magmatic to a recycled orogen for Linggiu Formation, and a recycled orogen for Tanjung Leman Formation. The recycled orogen tectonic setting of Linggiu and Tanjung Leman may have come from the underlying metamorphic and sedimentary rocks of Mersing and Murau Formations. Meanwhile, twenty-two samples were examined using a geochemical method by utilizing the ratio of K2O/Na2O and SiO2. The samples suggest a tectonic setting from both passive continental margin (PM) and active continental margin (ACM). Based on these findings, it is interpreted that the sedimentary rocks in East Johor were deposited in a subduction-related basin, such as fore-arc, magmatic arc, and back-arc.

Revisiting the “Gercus Basalt within the Eocene Gercus Formation”: Implications for sedimentary origin of a basaltic body, Kurdistan Region, Northern Iraq

• A previously described intrusive basaltic body is re-studied. • The re-study proved that it consists of sedimentary rocks (greywacke sandstone). • The greywacke transported from remote volcanic source to its present area. • More than ten evidences are found to prove its sedimentary origin. • These evidence are such as content of bitumen, conglomerate imbricated pebbles. • Other evidences are presence of graded beds, parallel and planer bedding and ooids. • More evidences are absence of basaltic flows and chilled borders and others. Recently, a basaltic body is described geochemically and mineralogically by previous authors within the Gercus Formation, in the Bekhair Anticline (Duhok Governorate, Northern Iraq). They indicated feldspar, anorthoclase, diopside, forsterite and olivine as main minerals of the body with many accessary ones. They added that the body is anorogenic (non-tectonic), extruded on continental crust of Arabian Plate and affected by pervasive alteration with a thickness of 16 m and a width of 4 km. The present study discussed in detail the sedimentary origin of the claimed basaltic body, contesting its intrusive or extrusive igneous origin. We proved that the body consists of a volcaniclastic succession (greywacke), which was derived from remote volcanic source areas and deposited by running water in the basin of the Gercus Formation. These sediments had been transported from a northeastern source area toward southwestern by streams to the deltaic basin of the Eocene basin. For proving its sedimentary origin, we presented many field and petrographic evidences such as content of bitumen, ooid bed, thick or thin planar layers (with parallel and sharp contacts), graded bedding, conglomerate, imbricated pebbles and hosting limestone beds in addition to absence of contact metamorphism, lack of structures such as pillow lava, basaltic flow, crystals zoning, xenoliths, peperites, digitation into host rocks and dilatations features. The previous authors depended on the geochemical and thin section studies for proving its igneous origin but these methods cannot prove if the constituents (whole or broken minerals) of the body are transported or indigenous. While accurate field survey and boundary conditions studies can indicate its origin. The proof of the sedimentary origin is achieved via conjugating evidences of the body boundary, those from its internal architecture and composition. Therefore, we are sure 100% that the body is sedimentary succession not basaltic one.

Nickel in Buli Coastal Area, East Halmahera

Fragments of ultramafic, metamorphic, basalt and serpentine compose coastal sediments. These fragments derived from outcrops in hinterland as well as the coast. Existence of greywacke sandstone through microscopic observation in coastal sediments indicate deep sea derivation. Marine sediments also show almost the same composition with coastal sediments.Rock fragment abundances of ultramafic (10-47%), serpentine (12-24%) and metamorphic (3-12%) in stream and coastal sediments which have direct relation with the presence of nickel metal in the research area were resulted from petrographic analyses. While mineralographic analyses of heavy mineral concentrate from wooden pan show the existence of ferro nickel (Fe-Ni) and nickeline (Ni-As) in coastal and stream sediments. XRF analyses show nickel contents in seabed sediments 0.0140 to 0.793 %, chromite 0.0179 to 0.1128% and iron 1.2 to 6.85%. Coastal water nickel distribution is controlled by local trapped waves in Buli Bay that excite by equatorial Pacific Ocean waves propagate westward. Nickel occurrences in marine sediments would be an interesting further research.

Clast transport history influences Schmidt hammer rebound values

AbstractThe Schmidt hammer (SH) is widely used in geomorphology for relative‐ and calibrated‐exposure age dating surfaces and deposits within landforms. This study employs a laboratory‐based methodology to assess the effects of surface roughness, clast roundness, and clast volume on SH rebound values (R‐values) by analyzing samples from three modern depositional environments (i.e. river, alluvial fan, talus). Each environment contains clasts of Torlesse supergroup greywacke sandstones with distinct roundness and micro‐scale roughness characteristics. Roundness, surface roughness, and clast volume were all found to influence R‐values significantly. The R‐values from different deposit types are statistically significant and could potentially create an apparent age divergence of several thousand years for samples with the same exposure‐age. © 2020 John Wiley & Sons, Ltd.

Batupasir “Bulukuning” Pada Lempung Berisik Di Daerah Banjarnegara, Jawa Tengah; Studi Petrologi, Provenan dan Implikasi Tektonik

Sandstone unit in the Bulukuning area, Banjarnegara known and even once proposed as the Bulukuning Formation were formerly referred to as the greywacke sandstones as part of the Luk Ulo Melange Complex which is believed as Early Cretaceous-Paleocene in age. The sandstones are lightly metamorphosed and observed in many places to be inclunded in the exotic blocks within the scaly clay which is generally considered as matrix of melange. This study examines the details of lithological characteristics, their provenances and tectonic implications. Undeformed sequences of the Bulukuning Sandstones represented by well bedded sandstones and siltstones. Determinations of fossil species and association of these sandstones yield Paleo-Nummulites and nanno fossil matrices which strongly suggest Middle-Late Eocene (NP15-16). The highly deformed sequence of Bulukuning Sandstones often show block in matrix characters while others develop more boudinage structures as a result of rigid deformation. Analysis of the scaly clay matrix using the illite crystallinity (IC) value suggested that the deformation controlled the formation of scaly clay and boudinage structures occurred at temperatures around 205.916o - 223.014oC (± 30°). The provenance study of the sandstones confirms that these are resulted from recycled orogens related to the Micro-Continent collision of East Java with the southeast margin of the Sundaland during the Late Eocene-Early Oligocene period. The collision was subsequently followed by the exhumation of Karangsambung accretion complex, previously formed volcanic rocks and several Sundanese land blocks.

Early Cretaceous greywacke from Colville Knolls, New Zealand

ABSTRACTBlocks of greywacke sandstone were dredged from the Colville Knolls, on the margin of the Zealandia continent, in 1989. Re-examination shows them to be quartz-poor feldspathic litharenites similar to those recorded from the basement, rather than sedimentary cover, of the North Island. U-Pb dating of detrital zircons reveals significant age populations at 107, 115, 122, and 245 Ma. These compositions and ages best match those of Waipapa Composite Terrane greywacke basement on nearby Great Barrier Island. As such, an earlier Waipapa correlation is preferred, but Colville Knolls detrital petrography and zircon ages also resemble those from some Early Cretaceous Torlesse Composite Terrane greywackes. Irrespective of terrane correlation, Colville Knolls is a submarine outcrop of Cretaceous greywacke deposited at the toe of the Gondwana Mesozoic accretionary wedge, and likely represents the outer, northeastern margin of Zealandia continental crust.

The Itmurundy Accretionary Complex, Northern Balkhash Area: Geological Structure, Stratigraphy and Tectonic Origin

The Itmurundy zone of the northern Balkhash area is a Pacific-type orogenic belt. It possesses a complex geological structure and hosts rocks of mantle, accretionary and post-orogenic associations. The volcanic and sedimentary rocks of the accretionary association belong to three suites: Itmurundy (O1-2), Kazyk (O2-3) and Tyuretai (O3-S1). The suites are separated by tectonic unconformities or faults of three orders: 1) large regional faults; 2) medium faults separating mantle and oceanic accreted rocks; 3) small faults separating packages consisting of oceanic sediments. The Itmurundy Fm. (O1-2) is the most lithologically variable consisting of oceanic basalt, pelagic chert, hemipelagic siliceous mudstone and siltstone, and trench greywacke sandstone. The packages, each consisting of chert-siliceous mudstone, are separated from each other by 2nd and 3rd order faults of probably thrust nature, i.e. they are parts of duplex structures. The presence of duplex structures and the high degree of deformation of Itmurundy Fm. rocks are typical of accretionary complexes. The associations of volcanic and sedimentary rocks under study represent a full section of oceanic plate stratigraphy (OPS): basalt (MORB, OIB)—chert (pelagic)—siliceous mudstone, siltstone and shale (hemipelagic)—trench sandstones (greywacke). The structural position and the lithology of Itmurundy rocks accord well with the model of formation of accretionary complexes at Pacific-type convergent margins, in particular, those in the western Pacific.

Petrographic Characteristics and Depositional Environment Evolution of Middle Miocene Sediments in the Thien Ung - Mang Cau Structure of Nam Con Son Basin

DOI: 10.17014/ijog.4.3.143-157This paper introduces the petrographic characteristics and depositional environment of Middle Miocene rocks of the Thien Ung - Mang Cau structure in the central area of Nam Con Son Basin based on the results of analyzing thin sections and structural characteristics of core samples. Middle Miocene sedimentary rocks in the studied area can be divided into three groups: (1) Group of terrigenous rocks comprising greywacke sandstone, arkosic sandstone, lithic-quartz sandstone, greywacke-lithic sandstone, oligomictic siltstone, and bitumenous claystone; (2) Group of carbonate rocks comprising dolomitic limestone and bituminous limestone; (3) Mixed group comprising calcareous sandstone, calcarinate sandstone, arenaceous limestone, calcareous claystone, calcareous silty claystone, dolomitic limestone containing silt, and bitumen. The depositional environment is expressed through petrographic characteristics and structure of the sedimentary rocks in core samples. The greywacke and arkosic sandstones are of medium grain size, poor sorting and roundness, and siliceous cement characterizing the alluvial and estuarine fan environment expressed by massive structure of core samples. The mixed calcareous limestone, arenaceous dolomitic limestone, and calcareous and bituminous clayey siltstone in the core samples are of turbulent flow structure characterizing shallow bay environment with the action of bottom currents. The dolomitic limestones are of relatively homogeneous, of microgranular and fine-granular texture, precipitated in a weakly reducing, semi-closed, and relatively calm bay environment.

Landslides caused by the Mw7.8 Kaikōura earthquake and the immediate response

Tens of thousands of landslides were generated over 10,000 km2 of North Canterbury and Marlborough as a consequence of the 14 November 2016, Mw7.8 Kaikōura Earthquake. The most intense landslide damage was concentrated in 3500 km2 around the areas of fault rupture. Given the sparsely populated area affected by landslides, only a few homes were impacted and there were no recorded deaths due to landslides. Landslides caused major disruption with all road and rail links with Kaikōura being severed. The landslides affecting State Highway 1 (the main road link in the South Island of New Zealand) and the South Island main trunk railway extended from Ward in Marlborough all the way to the south of Oaro in North Canterbury.
 The majority of landslides occurred in two geological and geotechnically distinct materials reflective of the dominant rock types in the affected area. In the Neogene sedimentary rocks (sandstones, limestones and siltstones) of the Hurunui District, North Canterbury and around Cape Campbell in Marlborough, first-time and reactivated rock-slides and rock-block slides were the dominant landslide type. These rocks also tend to have rock material strength values in the range of 5-20 MPa. In the Torlesse ‘basement’ rocks (greywacke sandstones and argillite) of the Kaikōura Ranges, first-time rock and debris avalanches were the dominant landslide type. These rocks tend to have material strength values in the range of 20-50 MPa.
 A feature of this earthquake is the large number (more than 200) of valley blocking landslides it generated. This was partly due to the steep and confined slopes in the area and the widely distributed strong ground shaking. The largest landslide dam has an approximate volume of 12(±2) M m3 and the debris from this travelled about 2.7 km2 downslope where it formed a dam blocking the Hapuku River. The long-term stability of cracked slopes and landslide dams from future strong earthquakes and large rainstorms are an ongoing concern to central and local government agencies responsible for rebuilding homes and infrastructure. A particular concern is the potential for debris floods to affect downstream assets and infrastructure should some of the landslide dams breach catastrophically.
 At least twenty-one faults ruptured to the ground surface or sea floor, with these surface ruptures extending from the Emu Plain in North Canterbury to offshore of Cape Campbell in Marlborough. The mapped landslide distribution reflects the complexity of the earthquake rupture. Landslides are distributed across a broad area of intense ground shaking reflective of the elongate area affected by fault rupture, and are not clustered around the earthquake epicentre. The largest landslides triggered by the earthquake are located either on or adjacent to faults that ruptured to the ground surface. Surface faults may provide a plane of weakness or hydrological discontinuity and adversely oriented surface faults may be indicative of the location of future large landslides. Their location appears to have a strong structural geological control. Initial results from our landslide investigations suggest predictive models relying only on ground-shaking estimates underestimate the number and size of the largest landslides that occurred.

Sediment provenance and tectonics on the Laurentian margin: implications of detrital zircons ages from the Central Belt of the Southern Uplands–Down–Longford Terrane in Co. Monaghan, Ireland

The Ordovician–Silurian meta-sedimentary rocks of the Southern Uplands–Down–Longford terrane were deposited at the Laurentian margin and structurally emplaced in an accretionary prism during subduction of Iapetus Ocean lithosphere. Within the terrane, a Central Belt consists of repeated structural tracts in which Ordovician–Silurian mudstone and sandstone (Moffat Shale Group) are overlain by Silurian greywacke (Gala Group). A Moffat Shale Group sandstone and Gala Group greywacke sandstones from Co. Monaghan, Ireland were sampled in order to examine, for the first time, detrital zircon spectra with a view to elucidating sediment provenance and tectonic evolution of this sector of the Laurentian margin. Detrital zircon ages from Gala Group greywacke sandstones include variable abundance of Precambrian zircons with ages typical of Laurentia, but are dominated by two Ordovician peaks at c. 462 Ma and c. 474 Ma. These Ordovician ages equate to magmatism in the local Laurentian margin in Ireland. The age spectra are distinct from those of equivalent rocks of the Southern Uplands of Scotland. There is no evidence from detrital zircon ages that a Gondwana-derived terrane had accreted to the Laurentian margin before or during sedimentation. Zircons from a Moffat Shale Group sandstone include a middle Cambrian component that may be derived from Ganderia. Supplementary material: The complete U–Pb data table is available at http://doi.org/10.6084/m9.figshare.c.3270848

Bedload composition, transport and modification in rivers of Westland, New Zealand, with implications for the distribution of alluvial pounamu (jade)

River bedload surveyed at 50 sites in Westland is dominated by Alpine Schist or Torlesse Greywacke from the Alpine Fault hanging wall, with subordinate Pounamu Ultramafics or footwall-derived Western Province rocks. Tumbling experiments found ultramafics to have the lowest attrition rates, compared with greywacke sandstone and granite (which abrade to produce silt to medium-sand), or incompetent schist (which fragments). Arahura has greater total concentrations (103–105 t/km2) and proportions (5–40%) of ultramafic bedload compared with Hokitika and Taramakau catchments (101–104 t/km2, mostly <10%), matching relative areas of mapped Pounamu Ultramafic bedrock, but enriched relative to absolute areal proportions. Western Province rocks downthrown by the Alpine Fault are under-represented in the bedload. Enriched concentrations of ultramafic bedload decrease rapidly with distance downstream from source rock outcrops, changing near prominent ice-limit moraines. Bedload evolution with transport involves both downstream fining and dilution from tributaries, in a sediment supply regime more strongly influenced by tectonics and the imprint of past glaciation. Treasured New Zealand pounamu (jade) is associated with ultramafic rocks. Chances of discovery vary between catchments, are increased near glacial moraines, and are highest near source-rock outcrops in remote mountain headwaters.

Lithologic-petrographic characterization of Silurian rocks in the Niestachów profile (Holy Cross Mountains)

The Niestachów profile is located in the southwestern part of the Holy Cross Mountains and exposes lower Ludlovian greywacke sediments of the Niewachlów Beds that occur above graptolitic claystones of the Prągowiec Beds. Within the sequence of lithologically diversified Niewachlów Beds, more than 400 m thick, 11 characteristic lithologic complexes were identified. The lower and upper parts of the Niewachlów Beds comprise fine- and medium-grained greywacke sandstones with mudstone interbeds, whereas the middle part contains coarse-grained greywacke sandstones and conglomerates. The sediments were transported by “turbiditic currents” from the southwest. Petrographic examination of the upper part of the Prągowiec Beds and the Niewachlów Beds indicates that the greywacke conglomerates and sandstones of the Niewachlów Beds are composed primarily of volcanic and sedimentary lithoclasts, with subordinate metamorphic and scarce plutonic lithoclasts. The sandstones and conglomerates were derived from an orogen containing sandstones and mudstones as well as from the magmatic rocks of a continental volcanic arc, characterized by acidic-intermediate volcanism.