Blocks Of Conglomerate Research Articles

Tips on the SW-Gondwana margin: Ordovician conodont-graptolite biostratigraphy of allochthonous blocks in the Rinconada mélange, Argentine Precordillera

The Rinconada Formation is a mélange that crops out in the eastern margin of the Argentine Precordillera, an exotic terrane accreted to Gondwana in Ordovician times. Its gravity-driven deposits have been studied by means of conodont and graptolite biostratigraphy, and complemented with stratigraphic analyses. 46 rock samples (85 kg total weight) were obtained from blocks of limestones and of carbonate-cemented quartz-arenites, and from limestone clasts included in conglomerate blocks and debrites. 16 of these samples were productive after standard laboratory acid procedures, yielding 561 conodont elements. The specimens occur in variable number per sample and are frequently fragmented, but they reveal the occurrence of phantom stratigraphic units in the Darriwilian of the Precordillera. Lithological and fossil evidence from the Rinconada Formation provide new constraints on the biostratigraphy, palaebiogeography and tectonostratigraphic history of the southwestern margin of Gondwana during the Ordovician to Lower Devonian times.

Dynamic analysis of rock slopes using the distinct element method: A case study at the right abutment of the Upper Gotvand Dam, Iran

This paper reviews the dynamic stability of the right abutment of the Gotvand Dam, the highest earth fill dam located at the southwest of Iran, using the distinct element method. The right abutment comprises a soft clayey layer called the Lower Mudstone Siltstone interlayer (LMST) covered by disturbed conglomerate blocks. According to the results of the dynamic numerical analyses, no collapse will occur at the right abutment area. However, the residual shear displacement of disturbed blocks on the LMST layer will be 20–60 fcm for Maximum Credible Earthquake (MCE) loading. Such a displacement can cause cracking in the cut-off wall, and hence it was considered the main indicator of the right abutment instability. Investigating different solutions, such as buttressing and excavation, showed that these approaches are not effectively preventing abutment shear displacement. Therefore, the designing process was carried out by accepting the risk of cut-off wall cracking in seismic loading conditions. However, some pre-remedial solutions (as discussed thoroughly in the text) have been considered in the construction process to minimize the risk of water seepage from the cut-off wall.

Morpho-structural heterogeneity of shallow-water coralligenous in a Pleistocene marine terrace (Le Castella, Italy)

Coralligenous is the most volumetrically significant type of autochthonous carbonate build-up in the Mediterranean, but its range of morphological variability at the macroscale, and potential link with environmental factors have not been fully documented. Well-preserved examples of coralligenous are exposed in shallow marine carbonate deposits from the Upper Pleistocene Le Castella marine terrace (Southern Italy). The coralligenous build-ups occur in the lower part of an unconformity-bounded, transgressive-regressive sequence. They show high structural and morphological heterogeneity in terms of framework type and build-up size, over a distance of several hundred meters. In northern exposures, coralligenous forms banks up to 4m high, with a dense, coralline-dominated framework, laterally adjacent to paleo-channels devoid of build-ups and filled by coeval infra-circalittoral biogenic packstone. To the south, build-ups are smaller (up to 1.8m high), with an open algal framework and local predominance of the coral Cladocora caespitosa as primary framework builder. At both locations, the most important framework-building coralline species is Mesophyllum philippii; Titanoderma pustulatum also occurs. Analysis of sedimentary structures, paleo-topographic indicators, faunal composition of associated mollusk assemblages, and predominance of M. philippii suggest the algal builds-ups grew within a shallow-water, possibly infralittoral setting, competing for space with other biocoenoses. Suitable substrate availability in the form of conglomerate blocks or shell accumulations was the primary factor controlling the inception and spatial distribution of coralligenous. Differences in hydrodynamism and water turbidity determined variability in size and internal composition between the northern and southern locations. To the south, abundant supply of fine suspended sediment resulted in smaller build-ups with more open framework, the growth of which was terminated abruptly by sediment burial. Eventually, relative sea level fall during regression prevented further growth of the coralligenous even in the northern area. This study contributes to a better understanding of the relationship between coralligenous morphology and environmental factors, highlighting the role of suitable substrate availability, turbidity, and sediment burial in influencing spatial and temporal variability of coralligenous assemblages.

The failure mechanism of a Late Glacial Sturzstrom in the Subalpine Molasse (Leckner Valley, Vorarlberg, Austria)

A number of prehistoric landslides and rock avalanches occurred in the folded and faulted section of the Molasse Zone in Vorarlberg, Austria. Some developed into a Sturzstrom, defined as a ‘rapidly moving fluidised mass movement of large volumes of rock, derived from the disintegration of a falling rock mass, that spread under the influence of gravity’. Their impact on the landscape usually is related to obstruction of rivers and valleys. In this paper, we analyse the geomorphology and the failure mechanism of a relative small ‘Sturzstrom’. The failure mechanism can be described as a ‘buckling failure’. The morphological situation indicates that failure took place after local deglaciation by the end of the Upper Würm. The period of failure coincides with glacial and ice-marginal remnants, which developed between 15.000 and 14.600 BP. The lithological sequence and rock structure, as well as the impact of the processes related to the former glacial environment, were major causal conditions. The rock sequence consists of conglomerates, sandstone layers, and marls. Next to glacial scouring, which increased the inclination of the valley slopes, the effect of late-glacial unloading and postglacial processes, such as weathering and fluvial erosion, subsequently weakened the mass rock fabric until failure occurred. Discontinuity orientation measurements, geostructural and geomechanical conditions, and the former hydrological and geomorphological conditions support bucklings failure. In fact, three-hinge buckling may have occurred. The frontal section of the Sturzstrom consists mainly of large conglomerate blocks, averaging 1.5 m 3 in volume, although megablocks, reaching of up to 4000 m 3, are present as well. The volume of the entire Sturzstrom equals approximately 10×10 7 m 3. Present activity is only restricted to minor rock falls derived from the conglomerates and mudflows originating from the marl layers.

The Building Stone at the Roman Religious Complex, Lydney Park, Gloucestershire: Character and Fate

The lower walls of the temple and bath house survive above ground at the Roman religious complex in the high ground of Lydney Park. They are composed almost exclusively of roughly dressed, coursed blocks of the red-stained, petrographically distinct Drybrook Sandstone (Lower Carboniferous), which outcrops within a few hundred metres nearby. Blocks of conglomerate from the Quartz Conglomerate (Upper Old Red Sandstone) and limestones from the Carboniferous Limestone Series are also present but very rare. The Norman Great Tower of Chepstow Castle, claimed to have been built largely of material robbed from Lydney Park, presents a markedly different suite of building materials in terms of rock-type, relative abundance and block shape, and was sourced from elsewhere.

Cretaceous Basin-to-Shelf Transition in Northern Alaska: Deposition of the Fortress Mountain Formation: ABSTRACT

The Fortress Mountain Formation (Albian) is a sequence of shale, sandstone, and conglomerate exposed as isolated synclinal outcrops in the southern foothills province of the Brooks Range. The formation overlies a variety of severely deformed older rocks, particularly the Okpikruak Formation of Neocomian age. The unit records a significant change in the depositional architecture of the North Slope Cretaceous and is closely tied to the evolution of the Brooks Range orogenic belt. Detailed stratigraphic and sedimentologic studies of the Fortress Mountain Formation within the type region and at easternmost exposures have demonstrated a systematic change in lithology and bedding style. The lower 40% of the Fortress Mountain is transitional with the Torok Formation and is composed of thick (up to 2,000-m) intervals of gray to black shale with thin, rhythmically interbedded, fine-grained sandstone beds. This succession is interrupted periodically by allochthonous blocks of conglomerate and conglomeratic sandstone. The sequences record a transition from basin plain to slope sedimentation. The middle 30-40% of the formation is composed of thick conglomerate and conglomeratic sandstone lenses that thin toward the north and are arranged in multiple upward-coarsening se uences and megasequences. End_Page 660------------------------------ Regional dispersal patterns indicate these beds accumulated within the midfan environment of a northward-prograding submarine fan complex. The upper 20-30% of the Fortress Mountain rests above a conspicuous angular discordance and is composed of upward-fining channel sequences of conglomerate, sandstone, and shale. This phase of deposition records progradation of fan-delta and fluvial environments. The regional depositional architecture of the Fortress Mountain records the buildup and sedimentologic evolution of the Cretaceous shelf, which ultimately allowed progradation of overlying deltaic and interdeltaic complexes of the Nanushuk Group and related strata. End_of_Article - Last_Page 661------------

The 1957 explosive eruption on Iwo Jima, Volcano Islands

An explosive eruption occurred without warning on March 28, 1957, near the center of Iwo Jima, a small volcanic island midway between Guam and Tokyo, Japan. The eruption of steam, volcanic sand, and volcanic sandstone and conglomerate blocks began suddenly at 11:55 A.M. local time, continued for 65 min., and ended abruptly. Coarse ejecta were thrown as high as 150 ft.; dust and steam rose to heights of 200 to 300 ft. No juvenile material was ejected. An elliptical crater 90 to 110 ft. in diameter and 45 ft. deep resulted. Deposits were concentrated to the western (lee) side where they ranged in thickness from 22 ft. near the crater to less than one inch 300 ft. to the W. About 50 min. after the eruption a second crater formed by collapse 75 ft. NW. of the eruption crater. The circular collapse crater was 115 ft. in diameter and 55 ft. deep. Many ground cracks and small faults with displacements up to 8 in. were formed nearby during and following the eruption. Steam and other gases issued from the craters, faults, and cracks following the eruption, and some sublimates were deposited. No significant change of fumarolic activity was noted on other parts of the island before, during, or after the eruption. The eruption resulted from the sudden release of an underground accumulation of steam under high pressure beneath artificial fill adjacent to an abandoned airfield. The eruption does not seem to indicate an increase in volcanic activity on Iwo Jima.

Paradox Formation: ABSTRACT

The principal occurrence of the Paradox formation is in a northwest-southeast trending basin west of the Uncompahgre uplift, chiefly in southwest Colorado and adjacent portions of southeast Utah. It extends, roughly, from Barker Dome on the Colorado-New Mexico line, northwestward to the vicinity of Green River, Utah. It is approximately 200 miles long and 115 miles wide. The town of Monticello, Utah, is near the geographical center. It is a structural basin lying between the Uncompahgre-San Juan Mountains on the east and the San Rafael-Circle Cliffs upwarps on the west. It is separated from the San Juan basin on the south by a relatively low saddle, and perhaps from the Uinta basin to the north by a similar saddle. The Paradox is a depositional wedge, within the Hermosa formation. It is lower Pennsylvanian in age. Similar sediments of black shale, gypsum, and anhydrite of Pennsylvanian age occur in the Eagle-Glenwood Springs area, east of the Uncompahgre and on the east flank of the White River uplift. While these sediments probably are equivalent to the Paradox formation, there is no evidence to indicate that the basins were ever connected, and the term Paradox formation has not been applied, officially, to the sediments in the Eagle basin. The chief exposures of the Paradox occur in Gypsum Valley, Paradox Valley, Sinbad Valley, in Colorado, and in Moab-Spanish Valley, Onion Creek, and Cache Creek-Salt Valley in Utah; all of which are commonly referred to as breached salt anticlines. In these exposures the Paradox consists of irregular beds of gypsum, limestone, dark shales and some find sands. In many places these beds are highly contorted and brecciated, indicating flowage from a deeper source, and contain blocks of foreign material dragged up from below. The maximum thickness of the Paradox is unknown, but in one occurrence it exceeds 10,800 feet, although this undoubtedly represents flowage rather than depositional thickness. Several wells which have drilled a normal section have had in excess of 2,000 feet. The section is so irregular that no correlation horizons which can be used for more than local work have been established. In the salt anticlines the section is so garbled and twisted that little bedding remains, and thickness cannot be established. No exposure out in the basin exhibits the base, but in Salt Valley blocks of conglomerate, believed to have been dragged up with the salt, may represent the underlying formation. End_of_Article - Last_Page 962------------

Notes on the submergence of Scotland

1. The old red blocks of Morayshire and its vicinity do not occur in the interior of the country, but the blocks belonging to the interior are strewed all over the plains of Moray, and the ridges of the Black Isle. Most of the blocks perched upon the S.W. and S. sides of the Strathnairn hills are not native, but evidently belong to the basin of the Ness. The S.W. slope and summit of Doune Daviot are strongly glaciated. Its talus spreads out to N.E. Two round hummocks (700 feet), of fine sand are situated upon this talus, and they are strewed with large blocks of conglomerate and Doune Daviot gneiss, all streaming eastwards or across the line pursued by the land ice. Along the N. ridge of Strathnairn we see how the old red sandstone beds were torn up by continental ice. The old red blocks are strewed along the line of junction of the old red and the gneiss, and rest chiefly on the gneiss. Many of these blocks have been moved only a few inches in their native beds. But among them may be found blocks which are not native. These are also strewed over the sandy ridges in long streams to the E. or nearly so. No blocks could be deposited upon continental ice, but they would fall down when the valleys were well filled with glaciers, upon which they would be carried along. It is thus evident that the blocks of the Ness basin, which