Conglomerate Beds Research Articles

Bedrock lithology control on contemporaneous alluvial fan facies, Oligo‐Miocene, southern Pyrenees, Spain

AbstractClimate and tectonics play important roles in controlling processes of transport and deposition on alluvial fans, but the bedrock lithology in the fan catchment area is also a significant, independent factor. Adjacent Oligo‐Miocene alluvial fan deposits on the northern margin of the Ebro Basin display contrasting depositional characteristics with one dominated by the deposits of debris flows and the other by deposition from flows of water. A difference in clast compositions indicates that the two studied fans (the Nueno and San Julián fans) had contrasting bedrock lithology in their drainage basins. The proximal facies of the Nueno fan body contains matrix‐supported conglomerate beds with up to 80% pebble clasts of gypsum in a matrix of gypsiferous sand, interbedded with gypsarenite beds. The drainage basin of this fan was dominated by Triassic bedrock consisting of beds of gypsum, marl and micritic limestone. The San Julián fan body comprises clast‐supported, polymict conglomerate beds containing pebbles from Triassic, Cretaceous and Palaeogene limestone units that are exposed in the adjacent part of the basin margin. The interfingering of the deposits of these two fans demonstrates that they were contemporaneous. Given the consistent climate, the differences in fan depositional processes must therefore be attributed to the contrasting bedrock lithology in their drainage basins. A drainage basin consisting mainly of marl and gypsum bedrock provided sufficient fine‐grained material to generate debris flows, whereas more dilute, water‐lain processes dominated where the drainage basin was largely limestone strata.

Discussion on evidence for a major Neoproterozoic orogenic unconformity within the Dalradian Supergroup of NW Ireland

Geoff Tanner writes: Firstly, I would like to congratulate the authors for presenting a very carefully documented, and splendidly illustrated, account of the origin of the Stralinchy conglomerates. The aim of this contribution is to focus on one important question: is their controversial model for the Donegal Dalradian supported by studies of the stratigraphically equivalent Dalradian rocks of the SW Highlands of Scotland? If an orogenic unconformity is present in the Dalradian Supergroup, evidence for this should be found at the base of, or within, the Easdale Subgroup in this region. The field relationships seen at this stratigraphical level in Scotland are reviewed briefly, and an attempt made to reconcile the results with the Donegal model. Jura Quartzite–Easdale Subgroup relationship in SW Highlands of Scotland. The contact between the Jura Quartzite and the Scarba Conglomerate Formation (which represents the base of the Easdale Subgroup) is best seen in excellent coastal exposures between Jura and Loch Creran. It is exposed on the SE side of the island of Jura; is excised by faulting on the islands of Scarba and Lunga; and re-appears on the SE side of the Rubha Aird Peninsula, 7 km north of Oban. At Lussagiven on Jura [NR 6387 8666], the top of the Jura Quartzite is marked by cross-bedded quartzite followed by 23 m of thinly bedded, commonly gritty, sandstones with conglomerate lenses. These beds, which display cross-lamination, graded bedding and channel structures, pass upwards with perfect conformity into a 36 m thick unit of laminated slate with sandstone ribs, the Jura Slate member of the Scarba Conglomerate Formation. Gritty sandstone and conglomerate beds up to 1 m thick, that characterize the Scarba Conglomerate, appear 280m farther up sequence They contain pebbles to 3 cm; rip-up clasts of mudrock; and less common rafts of sandy sediment up …

Tertiary alluvial fans at the northern margin of the Ebro Basin: a review

Abstract Tertiary alluvial fan deposits along the margin of the Ebro foreland basin north of Huesca, Spain, are remarkable for the range of sedimentological and tectonic features preserved within them. The fan deposits formed after the southern Pyrenean thrust front (the Guarga Thrust) was established in this area, forming steep topography at the basin margin in the mid-Oligocene. Some shortening continued during deposition of the earliest fans resulting in synsedimentary faults, folds and unconformities. Clast compositions in the fan conglomerate beds record unroofing of the thrust front and also reveal differences in bedrock provenance between adjacent, coeval fan deposits. Bedrock provenance also influenced processes of deposition, with fans built up of detritus derived from areas rich in gypsum and mudrock showing more evidence of debris-flow processes. Deposition by debris flows also dominated the smallest fan body, but the majority of the fans were the products of sedimentation from unconfined or poorly confined traction currents. These resulted in sheets of conglomerate in the more proximal areas. Within individual fan bodies the proportion of sandstone increases over a distance of up to 5 km to where the distal fan facies are seen as thin sandstone and mudstone beds. The fringes of the fan bodies interfinger with lacustrine and fluvial facies, which indicate a temperate-semi-aric palaeoclimate. Vertical aggradation of the fan deposits due to rising base level in the Ebro Basin in the Oligocene and early Miocene was followed by deep incision following a late Miocene base level-fall. This led to the partial erosion of the fan deposits and their spectacular exposure in the modern landscape.

Magnetostratigraphic chronology of a late Eocene to early Miocene glacimarine succession from the Victoria Land Basin, Ross Sea, Antarctica

Drilling offshore from Cape Roberts, Antarctica, has enabled recovery of a 1472-m cumulative record of late Eocene–early Miocene history of sedimentary basin development and climate change in the Western Ross Sea. In this paper, we synthesize the results of palaeomagnetic analyses carried out on the CRP-1, CRP-2 and CRP-3 sediment cores, and present a chronology for the recovered Eocene–Miocene succession. Stepwise demagnetization data demonstrate that secondary overprints have been successfully removed and that characteristic remanent magnetizations (ChRMs) have been clearly identified in most of the samples. A close sampling interval has allowed a detailed magnetic polarity stratigraphy to be established for the composite succession. Correlation with the geomagnetic polarity time scale (GPTS) has been constrained by a number of 40Ar/ 39Ar and 87Sr/ 86Sr ages, as well as by a recently developed Antarctic siliceous microfossil zonation, and by calcareous nannoplankton biostratigraphy. The basal sediments of the Eocene–Miocene succession rest unconformably on Devonian sandstones of the Beacon Supergroup. A basal sandstone breccia, which probably represents the onset of rifting in the Victoria Land Basin (VLB), is overlain by a succession of sandstones that are interbedded with thin conglomerate beds. These sediments give way to more clearly glacially influenced mudstones and diamictite facies in the mid Oligocene, and, by the Oligocene–Miocene boundary, coincident with the Mi-1 glaciation, a permanent glacial dominance was imprinted on the sedimentary record. Average sediment accumulation rates were initially rapid in the late Eocene–early Oligocene (up to 60 cm/k.y.), but reduced to only a few cm/k.y. in the early Miocene as basin subsidence slowed.

Flat‐pebble conglomerate: its multiple origins and relationship to metre‐scale depositional cycles

AbstractCarbonate flat‐pebble conglomerate is an important component of Precambrian to lower Palaeozoic strata, but its origins remain enigmatic. The Upper Cambrian to Lower Ordovician strata of the Snowy Range Formation in northern Wyoming and southern Montana contain abundant flat‐pebble conglomerate beds in shallow‐water cyclic and non‐cyclic strata. Several origins of flat‐pebble conglomerate are inferred for these strata. In one case, all stages of development of flat‐pebble conglomerate are captured within storm‐dominated shoreface deposits of hummocky cross‐stratified (HCS) fine carbonate grainstone. A variety of synsedimentary deformation structures records the transition from mildly deformed in situ stratification to buckled beds of partially disarticulated bedding to fully developed flat‐pebble conglomerate. These features resulted from failure of a shoreface and subsequent brittle and ductile deformation of compacted to early cemented deposits. Failure was induced by either storm or seismic waves, and many beds failed along discrete slide scar surfaces. Centimetre‐scale laminae within thick amalgamated HCS beds were planes of weakness that led to the development of platy clasts within partly disarticulated and rotated bedding of the buckled beds. In some cases, buckled masses accelerated downslope until they exceeded their internal friction, completely disarticulated into clasts and transformed into a mass flow of individual cm‐ to dm‐scale clasts. This transition was accompanied by the addition of sand‐sized echinoderm‐rich debris from local sources, which slightly lowered friction by reducing clast–clast interactions. The resulting dominantly horizontal clast orientations suggest transport by dense, viscous flow dominated by laminar shear. These flows generally came to rest on the lower shoreface, although in some cases they continued a limited distance beyond fairweather wave base and were interbedded with shale and grainstone beds. The clasts in these beds show no evidence of extensive reworking (i.e. not well rounded) or condensation (i.e. no rinds or coatings). A second type of flat‐pebble conglomerate bed occurs at the top of upward‐coarsening, metre‐scale cycles. The flat‐pebble conglomerate beds cap these shoaling cycles and represent either lowstand deposits or, in some cases, may represent transgressive lags. The clasts are well rounded, display borings and have iron‐rich coatings. The matrix to these beds locally includes glauconite. These beds were considerably reworked and represent condensed deposits. Thrombolites occur above the flat‐pebble beds and record microbial growth before initial transgression at the cycle boundaries. A third type of flat‐pebble conglomerate bed occurs within unusual metre‐scale, shale‐dominated, asymmetric, subaqueous cycles in Shoshone Canyon, Wyoming. Flat‐pebble beds in these cycles consist solely of clasts of carbonate nodules identical to those that are in situ within underlying shale beds. These deeper water cycles can be interpreted as either upward‐shoaling or ‐deepening cycles. The flat‐pebble conglomerate beds record winnowing and reworking of shale and carbonate nodules to lags, during either lowstand or the first stages of transgression.

Microfacies Analysis of Oligocene Formations in Butmah and Rafan Areas Northwest Iraq.

Oligocene deposits in Butmah and Rafan areas northwestern Iraq were penetrated by three core holes (BW-CH1, BE-CH1 and RF-CH1). The depositional basin evolved through two stages, generating two sedimentary cycles, which were separated by exposure surface as represented by conglomerate beds in core holes BW-CH1 and RF-CH1. Six microfacies were recognized in the Oligocene formations (Shurau Fn., Sheikh Alas Fn. and Bajwan Fn.), comprising three microfacies association allocated to: reef (Sa1) and back reef (Sh1, Sh2) in the first cycle (Early Oligocene), and back reef (B1, B2, B3) in the second cycle (Late Oligocene). Oligocene rocks have been affected by many diagenetic processes of cementation, dissolution, dolomitization (by mixing process) and dedolomitization. The paleogeographic distribution of the microfacies in conjunction to the previous work elucidates that the studied area is representing the eastern margin of the Sinjar Oligocene basin. ــــــــــــــــ ـــــــــــــ ــــــــــــــــ ـــــــــــ ﻕﺍﺭﻌﻟﺍ ﺏﺭﻏ لﺎﻤﺸ ﻥﺎﻓﺍﺭﻭ ﺔﻤﻁﺒ ﻲﺘﻘﻁﻨﻤ ﻲﻓ ﻥﻴﺴﻭﺠﻴﻟﻭﻻﺍ ﺕﺎﻨﻴﻭﻜﺘﻟ ﻲﻨﺤﺴﻟﺍ لﻴﻠﺤﺘﻟﺍ

Storms and tsunamis: evidence of event sedimentation in the Late Jurassic Tendaguru Beds of southeastern Tanzania

In Late Jurassic shallow marine siliciclastic sediments of the dinosaur-bearing Tendaguru Beds from the Mandawa Basin of southeastern Tanzania we identified several event deposits. Based on an analysis of their sedimentological and palaeontological features, a storm-induced origin can be assumed for the majority of these deposits. This interpretation is in agreement with the regional palaeogeography and palaeoclimatological data, and is further supported by the widespread evidence of Late Jurassic storm-controlled sedimentation in adjacent basins along the East African margin. A particularly striking feature is a laterally extensive, conglomeratic bed with gravel components up to 30 cm in diameter, and megaripples indicating southward transport directions. The troughs between ripples are filled by cross-bedded fine-grained sandstones and siltsones with inferred transport directions to the north. Giant bedforms, a mixture of clasts of marine and continental origin, and evidence of opposite current directions suggest that this chaotically deposited sediment may have formed from a tsunami. Within the available time resolution this event is synchronous with the Morokweng impact structure in South Africa. However, because of the considerable distance of Morokweng from the Jurassic sea, direct links between both events cannot be established. Alternative mechanisms such as a landslide-generated tsunami are plausible, but not yet supported by geophysical data.

The Lombardian Gonfolite Group in central Brianza (Como and Milano Provinces, Italy): Calcareous nannofossil biostratigraphy and sedimentary record of neo-alpine tectonics

The sedimentary succession cropping out in central Brianza, in an area embracing the territories of Besana Brianza, Briosco (Milan Province), Arosio and Inverigo (Como Province), is properly ascribed to the Lombardian Gonfolite Group. It consists of prevailing turbidite sandstones and marls, with conglomerate beds occurring in the central part of the section. A precise biostratigraphic dating of the succession was obtained through the analysis of calcareous nannofossils. The occurrence of reliable index species allowed us to recognise the NN3 to NN6 nannoplankton zones (Burdigalian to Serravallian). Since in the type-areas between Varese and Como the youngest dated units of the Gonfolite Group are Burdigalian in age, the studied succession documents a more recent part in the history of the south-alpine foredeep, that might have been recorded in outcrop elsewhere in Lombardy only by the ill-dated Gurone Sandstone and Bizzozzero Mudstone (Varese area). The deformation of the studied succession seemingly requires a single event of tectonic buckling, that is reliably constrained as late Serravallian to Tortonian (late “Lombardic Phase”). Provenance signals point to roughly contemporaneous exhumation of the Pennidic nappes and active stacking of thrust sheets in the uprising Southern Alps. This phase of tectonic activity took place around the Langhian/Serravallian boundary (early “Lombardic Phase”).

An Early Jurassic ammonite from a limestone conglomerate in the Kuzu Complex of the Ashio Belt

A specimen referable to an Early Jurassic ammonite, Cleviceras cf. chrysanthemum (Yokoyama, 1904), was discovered from a limestone conglomerate layer of the Kuzu Complex in the Ashio Belt, central Japan. Cleviceras chrysanthemum, a species comparable to the present specimen, is a diagnostic ammonite of early Toarcian age in the Circum-Pacific. The limestone conglomerate layer in question is a part of a sequence composed of, from top to bottom, siliceous shale, limestone conglomerate itself, calcareous sandstone, and again siliceous shale. The siliceous shale above and below the ammonite-bearing conglomerate bed carries radiolarian fossils which indicate the Unuma echinatus Assemblage Zone or Tricolocapsa plicarum Zone of Middle Jurassic age. The whole sequence is judged to be normally superposed by frequently observable normal graded bedding. Thus, the age indicated by the fossil ammonite for the limestone conglomerate is in contradiction with the age of the overlying and underlying beds. These facts suggest that the ammonitebearing pebble of Early Jurassic age is a fragment transported from elsewhere and redeposited in its present position during a Middle Jurassic time. The description of the ammonite is given.

Spatial distribution of road salt contamination of natural springs and seeps, Cuyahoga Falls, Ohio, USA

A total of 71 water samples were collected from 37 springs and seeps that flow from the Pennsylvanian aged Sharon Sandstone at Gorge Metro Park, Cuyahoga Falls, Ohio. The geology of the study area consists of natural springs and seeps emerging from fractures, thin conglomeratic beds and the contact between the Sharon Sandstone and underlying Meadville Shale. The springs were analyzed for discharge, temperature, conductivity, pH, major anions, and major cations.

Transition from debris flow to hyperconcentrated flow in a submarine channel (the Cretaceous Cerro Toro Formation, southern Chile)

ABSTRACT It is important to understand the exact process whereby very large amounts of sediment are transported. This paper reports peculiar conglomerate beds reflecting the transition of submarine debris flows into hyperconcentrated flows, something that has been well documented only in subaerial debris‐flow events until now. Voluminous debris flows generated along a Cretaceous submarine channel, southern Chile, transformed immediately into multiphase flows. Their deposits overlie fluted or grooved surfaces and comprise a lower division of clast‐supported and imbricated pebble–cobble conglomerate with basal inverse grading and an upper division of clast‐ to matrix‐supported, disorganized conglomerate with abundant intraformational clasts. The conglomerate beds suggest temporal succession of turbidity current, gravelly hyperconcentrated flow, and mud‐rich debris flow phases. The multiphase flows resulted from progressive dilution of gravelly but cohesive debris flows that could hydroplane, in contrast to the flow transitions in subaerial environments, which involve mostly non‐cohesive debris flows. This finding has significant implications for the definition, classification, and hazard assessment of submarine mass‐movement processes and characterization of submarine reservoir rocks.

Armored mudstone boulders in submarine debris-flow deposits, the Hunghae Formation, Pohang Basin: An evidence for the large-scale slumping of adjacent area of a submarine channel or scar wall

In the Hunghae Formation of the Pohang Basin, some heavily armored, calcareous mudstone balls (boulders) occur in a chaotic conglomerate bed which was deposited from debris flow on a steep slope. Sparsely armored or unarmored mudstone balls are also found in the same bed. Also some isolated armored mudstone boulders occur in a homogeneous mudstone bed of the formation which is interpreted as hemipelagite. The armored mudstone balls were most likely formed by retrogressive failures of submarine channel or scar wall and subsequent rolling over sand and pebble pavement along the submarine channel floor prior to incorporation into the debris flow. Their occurrence also suggests that a large-scale slumping should be happened on the upper slope apron or lower prodelta including the submarine channel and be evolved into debris flows, resulting in the corporation of the boulders into them. Some armored mud boulders rolled along and passed away the channelized gravel pavement, and deposited on hemipelagic mud in lower slope, not having been reworked.

From seamount to oceanic island, Porto Santo, central East-Atlantic

The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts. Two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions, pyroclastic fragmentation being subordinate. The lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called 'lapilli cone aprons'. Vertical growth due to accumulation of tephra, voluminous intrusions, and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion, as shown by conglomerate beds. Periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels. The loose tephra piles became stabilized by widespread syn-volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice. Shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions, accentuated by quench fragmentation, resulted in pumice- and crystal-rich deposits emplaced in a prominent submarine erosional channel. The dome must have produced an island as indicated by a collapse breccia comprising surf-rounded boulders of dome material. Subaerial explosive activity is represented by scoria cones and tuff cones. Basaltic lava flows built a resistant cap that protected the island from wave erosion. Some lava flows entered the sea and formed two distinct types of lava delta: 1. closely-packed pillow lava and massive tabular lava flows along the southwestern coast of Porto Santo, and 2. a steeply inclined pillow-hyaloclastite breccia prism composed of foreset-bedded hydroclastic breccia, variably-shaped pillows, and thin sheet flows capped by subhorizontal submarine to subaerial lava flows along the eastern coast of Porto Santo.The facies architectures indicate emplacement: 1. on a gently sloping platform in southwestern Porto Santo, and 2. on steep offshore slopes along high energy shorelines in eastern Porto Santo.Growth of the pillow-hyaloclastite breccia prism is dominated by the formation of foreset beds but various types of syn-volcanic intrusions contributed significantly. Submarine flank eruptions occurred in very shallow water on the flanks of the hyaloclastite prism in eastern Porto Santo. The island became consolidated by intrusion of numerous dikes and by emplacement of prominent intrusions that penetrate the entire volcanic succession. Volcanic sedimentation ended with the emplacement of a debris avalanche that postdates the last subaerial volcanic activity.

Origin of terraced hillslopes on active folds in the southern San Joaquin Valley, California

The northern-facing forelimbs of the active San Emigdio and Wheeler Ridge anticlines in the southern San Joaquin Valley (SSJV) are marked by numerous, sharply defined terracettes. Terracette treads and risers are 3–5 and 7–11 m wide, respectively. The terracettes are discontinuous along their length, with the longest being ∼300 m, although most terminate more abruptly forming lobate mounds. The terracettes form on 10–25° slopes underlain by loosely consolidated coarse conglomerate beds of the Pleistocene Tulare Formation that dip subparallel to terracette risers. Soil developed on the slopes is comprised of a 1- to 2-m-thick calcic Bk horizon, overlain by a 0.5-m-thick argillic claypan Bt horizon, followed by 1- to 3-m-thick AB and A horizons that have been extensively bioturbated. A number of hypotheses have been proposed for the genesis of similar terracettes. The two most viable tectonic models for our study area are based on growth of active fault-bend folds and include (i) sediment onlap with seismic folding and (ii) flexural slip faulting. We produced a very high-resolution digital elevation model (DEM) (1.67-m spatial resolution and ±5-cm vertical accuracy) using NASA's RASCAL (RAster SCanning Airborne Lidar) instrument and completed numerical modeling that we interpret to disprove both of the active fold growth models. The discovery and mapping of similar terracettes on NW- to NE-facing hillslopes on the Kettleman Hills anticline and Comanche Point in the northern Tehachapi Mountains suggest that a northern-facing aspect is an important factor contributing to terracette development. The terracettes are also present only on hillslopes that overlie blind or emergent thrust faults. We propose that a soil creep model based on flow-dominant mass wasting is the most likely cause of terracette development. Creep is confined to the thick A and AB cumulic soil horizons that delaminate above the rigid Bt claypan and occurs predominantly on northern-facing slopes due to increased soil moisture retention. The barrier to creep caused by the decrease in slope at the base of fold limbs leads to the development of terracettes that become more sharply defined in a downslope direction. We interpret the overthickened A and AB soil horizons to form preferentially on northern-facing slopes due to increased bioturbation and deposition of eolian silt. Strong ground motions produced by earthquakes may facilitate soil creep, and thereby contribute to the overall development of the terracettes.

Ancient denudational surfaces in the Gondwana sequences of Peninsular India

Gondwana basins of Peninsular India contain a thick pile of clastic sediments of predominantly fluvial origin. As expected in such a depositional milieu, the sedimentary pile is punctuated by numerous episodes of contemporaneous uplift, non-deposition and erosion. Most of these events are localised in nature and hence not correlatable from one basin to another. However, a few events of regional nature can be recognized. They comprise (a) basement surface with glaciated features like polishing, striations and frost wedging below the basal Talchir strata; (b) surface of angular and erosional unconformity between Permian/Triassic and Early Triassic/infra - Late Norian and (c) a major diastrophic episode resulting in reversal of palaeoslope between Late Jurassic and Early Cretaceous. Besides these, localized events represented by surfaces of contemporaneous subaerial exposure and oxidation showing characters of pedogenic (palaeosol) and lateritic (latosol) profiles have been recorded. These include Lower Barakar (Early Permian) of Hutar basin of Koel valley, Barren Measures (Late Permian) and Triassic/Jurassic contact of Rewa and Satpura basins, and Late Cretaceous Lometa Beds in Rewa Basin. Breaks represented by conglomerate beds occur in Early Permian Barakar strata of Talchir coalfield and Late Mesozoic Bagra Formation of Satpura basin. The palaeosols vary in thickness from 4 m to 25 m and are characterised by red brown clay with mottles, rootlets, slickensides, ferruginous concretions and calcareous veinlets. The palaeosols are hydromorphic and are developed under poorly drained to well drained groundwater conditions. Even where the palaeosols are not present, the bedrock displays evidences of deep weathering. These probably represent the earlier topographic positive areas affected by physical weathering and intense groundwater activity.

A possible Plio-Pleistocene tsunami deposit, Hornitos, northern Chile

A section equivalent to the Pliocene La Portada Formation exposed in the coastal cliff at Hornitos, northern Chile, contains a ca . 7-10 m thick conglomerate bed. The bed occurs within a succession of shallow marine sandstones and has an erosional contact with underlying strata. The largest boulders of basement (5 m) are angular to very angular and are set within a matrix of very poorly sorted fine to very coarse grained shell-rich sandstone. Also present are very well rounded granodiorite pebbles and shallow marine sandstone intraclasts (maximum 10 m). The clast size, erosional contact, associated facies and bed thickness suggests that the conglomerate bed is a shallow marine tsunami deposit. The angular clasts indicate limited transport and no marine reworking prior to deposition. They represent alluvial fan sediment incorporated into the bed during tsunami backflow. Intraclasts of shallow marine sandstone are thought to have been ripped up and included in the bed during the seaward passage of the tsunami across the shoreface.

Folding and the formation of bedding‐parallel faults on the western limb of Grey Valley Syncline near Blackball, New Zealand

Fresh roadside exposures of faults on the western limb of Grey Valley Syncline near Blackball (West Coast, South Island) provide new information on the kinematics of folding since c. 2.5 m.y. ago. These faults are parallel to, or dip within 10° of, steep bedding (60‐>90°) in Pliocene Old Man Group, and offset two gently dipping Quaternary gravel formations. Deformed gravel sequences record reverse‐fault displacements of 0.5‐c. 80 m and bed dips of 5–50°, which accumulated over the last c. 450 000 yr. The dip of Quaternary gravel beds and fault displacements decrease up‐sequence, suggesting that gravel deposition and deformation were synchronous. Bedding‐parallel faults in Old Man Group are typically located at the boundaries between mudstone beds and coarser grained sandstone or conglomerate beds. The bedding‐parallel orientations of the faults, fault slickenside striations approximately normal to the hinge of Grey Valley Syncline, and total fault displacement across the fold limb are consistent with these structures being flexural‐slip faults formed during folding. Small amounts of bedding‐parallel shortening and extension within Pliocene strata between faults indicate non‐rigid deformation of the limb and departure of folding from an ideal flexural‐slip model.

Comparison of the Ordovician-Carboniferous Boundary Between Korea and NE China: Implications for Correlation and Tectonic Evolution

There is a great hiatus between Ordovician and Carboniferous strata in the Northeast China and Korean Peninsula. In order to understand geology and tectonic evolution, and to find out the similarities and differences in both regions, two sections in the Western Hill near Beijing in NE China and several sections in the Korean Peninsula were selected to examine their geologic boundaries between Lower and Upper Paleozoic strata to compare their characteristic features. At four sites in the two sections in the Western Hill near Beijing were examined their contact relations. The Hui Yu section is the same horizon where one site is top of a quarry hill and the other of down hill. Mid-Carboniferous Qingshuijian Formation rests on the Ordovician Majiagou Formation. Limestone beds are more commonly intercalated with shale and sandstone at site 2 of the Hui Yu section, while at site 1, conglomerate beds are dominant. Site 1 of the Se Shu Fen section shows eroded and concealed karst topography and conglomerate beds are intercalated within shale beds. Silurian and Devonian strata are absent in these areas. In the Korean Peninsula, most O-C contacts occur between Ordovician limestone formation and Carboniferous strata, although Silurian strata occur beneath the Carboniferous strata in the Jeongseon area and Pyeongnam Basin. Most contact relations are parallel unconformity and angular unconformity is rarely seen. The O-C relations in both regions are similar to each other, and these indicate that the Korean Peninsula was located near or belonged to the Sino-Korean paraplatform during Paleozoic time.

Lithostratigraphy and biostratigraphy of the Mungok Formation (Lower Ordovician), Yongwol, Korea

The Mungok Formation in Yongwol area is divided into four members: i.e., Karam, Paeiljae, Chommal, and Tumok members in ascending order. The basal Karam Member (29–55 m thick) consists mainly of ribbon rock and grainstone to packstone with intercalation of thin limestone conglomerate beds and chert layers. The Paeiljae Member (28.6–35m thick) is a monotonous sequence of light gray to gray, massive to crudely-bedded dolostone. The Chommal Member (30–51 m thick) is characterized by alternation of ribbon rock and limestone conglomerate facies with occasional intercalation of grainstone to packstone beds in the upper part. The uppermost Tumok Member (41.2–77 m thick) comprises ribbon rock, grainstone to packstone, limestone conglomerate, and marlstone to shale. Trilobites occur in three stratigraphically separated intervals, which are herein referred to theYosimuraspis, Kainella, andShumardia zones, respectively. TheYosimuraspis Zone occurs at the lowermost part of the Karam Member and yieldsYosimuraspis, Jujuyaspis, andElkanaspis, indicating an early Tremadoc age. TheKainella Zone is established based on the occurrence ofKainella andLeiostegium from the basal part of the Chommal Member and is correlated with the middle Tremadoc of North America and Argentina. TheShumardia Zone has a relatively long stratigraphic range covering most of the Tumok Member and is dominated by cosmopolitan trilobite taxa with a few endemic species. This faunal assemblage is well correlated with the late Tremadoc faunas of North China and Australia.

Origin of the Peñalver Formation in northwestern Cuba and its relation to K/T boundary impact event

Abstract The uppermost Maastrichtian Penalver Formation and its equivalents in northwestern Cuba are characterized by thick, normal-graded calcarenite with distinct basal conglomerate, and have been suspected as deposits related to the Cretaceous–Tertiary boundary (K/T) impact. However, its depositional mechanism is not well understood and clear evidence for its association with the impact has never been presented. In this study, detailed field survey and petrographic observations were carried out on the Penalver Formation in order to clarify its sedimentary processes and to test its relation to the K/T impact. The Penalver Formation at the type locality near Havana is approximately 180 m thick and is subdivided into the Basal, Lower, Middle, Upper and Uppermost Members based on its lithology. The Basal Member consists of massive, poorly sorted, calcirudite with grain-supported fabric, which contains abundant macrofossils of shallow-marine origin and occasional large intraclasts of the underlying strata, suggesting that it was formed by a grain flow from a carbonate platform on the Cretaceous Cuban Arc. The Lower to Uppermost Members consist of massive calcarenite and calcilutite that show upward fining. Composition of the calcarenite is distinctly different from that of the Basal Member. The homogeneous appearance, coarse-tail normal grading, abundant water escape structures, and abundant reworked fossils in these members are consistent with those of the Mediterranean “homogenite”, a deep sea tsunami-induced deposit that was formed by settling from a high density suspension. Repetition of thin conglomerate beds in the Lower Member that contain well-sorted, well-rounded mud clasts and shallow marine fossils is considered to reflect intermittent lateral flow possibly induced by a series of tsunami waves during an early stage of settling of grains from a high density suspension. Altered vesicular glass of probable impact origin and shocked quartz are discovered in the Basal and the Lower to Upper Members, respectively. Together with the biostratigraphically constrained age of the Penalver Formation, this evidence suggests that the Penalver Formation has a genetic relation to the K/T impact. Distribution of altered vesicular glass and shocked quartz grains can explain the sequence of the initial grain flow and the following tsunami waves.