The Somerset Island Formation: an upper Silurian to ?Lower Devonian intertidal/supratidal succession, Boothia Uplift region, Arctic Canada

1978 ◽  
Vol 15 (2) ◽  
pp. 181-189 ◽  
Author(s):  
A. D. Miall ◽  
J. Wm. Kerr ◽  
M. R. Gibling
Keyword(s):  
Lower Devonian ◽  
Alluvial Fan ◽  
Similar Sequence ◽  
Island Formation ◽  
Fine Grained ◽  
Rock Types ◽  
Sandstone Rock ◽  
Upper Silurian ◽  
Somerset Island ◽  
Cornwallis Island

The Somerset Island Formation of Somerset Island is a newly defined unit consisting of interbedded fine-grained, grey, planar-laminated dolomite and limestone, grey mottled limestone and dolomite, red quartzose siltstone and red dolosiltite. It forms a transitional unit between the limestone and dolomite of the underlying Read Bay Formation and the sandstone and conglomerate of the overlying Peel Sound Formation, and ranges in thickness from 150 to more than 400 m. The formation was formed predominantly in intertidal and supratidal environments and forms the lowest part of a regressive sequence that culminates in boulder conglomerates of alluvial fan origin in the Peel Sound Formation. The Somerset Island Formation is predominantly Pridolian in age, but may include some strata of Ludlovian and Gedinnian age.The regressive sequence reflects a major pulse of the Cornwallis Disturbance of Boothia Uplift. A similar sequence occurs in Prince of Wales Island, although the lower part of the succession there contains conglomerate and sandstone, rock types that are absent in Somerset Island. These rocks are formally assigned to the Lower Peel Sound Formation but are of similar age to the Somerset Island Formation of the type area.Rocks of similar facies to the Somerset Island Formation of Somerset Island comprise the upper member of the Drake Bay Formation on Russell Island and Member D of the Read Bay Formation on Cornwallis Island. The latter unit is younger than the Somerset Island Formation, reflecting a later commencement of regression in that area.

Atrypoidea zonation of the Upper Silurian Read Bay Formation of Somerset and Cornwallis Islands, Arctic Canada

1979 ◽  
Vol 16 (12) ◽  
pp. 2204-2218 ◽  
Author(s):  
Brian Jones
Keyword(s):  
Carbonate Rocks ◽  
Basal Part ◽  
Arctic Canada ◽  
Pressure Point ◽  
Species Overlap ◽  
Conodont Zone ◽  
Upper Silurian ◽  
Somerset Island ◽  
Cornwallis Island ◽  
Distinct Distribution

Species of the brachiopod genus Atrypoidea have a distinct distribution in carbonate rocks of the late Silurian Read Bay Formation of Arctic Canada. Atrypoidea phoca occurs in the basal part of the formation and this species is succeeded by Atrypoidea foxi forma B at higher levels. The ranges of the two species overlap, defining a third useful zone. Locally, as in the Pressure Point area of northwestern Somerset Island, Atrypoidea foxi forma B is succeeded by Atrypoidea foxi forma A. Atrypoidea foxi forma A is generally restricted to carbonates with a low content of detrital material and has a significantly larger shell than Atrypoidea foxi forma B. A higher zone is defined by Atrypoidea erebus which occurs in the basal part of the Somerset Island Formation on Somerset Island and in the basal part of member C of the Read Bay Formation at Goodsir Creek on Cornwallis Island. At the latter locality, Atrypoidea foxi forma A is found with Atrypoidea erebus, thereby demonstrating their overlapping ranges.The overlapping ranges of Atrypoidea phoca and Atrypoidea foxi forma B occur in the middle to late Ludlovian ploeckensis–siluricus conodont zones. On Somerset Island, Atrypoidea foxi forma B and Atrypoidea foxi forma A range through the ploeckensis–siluricus conodont zone. Atrypoidea erebus occurs in late Ludlovian and (or) early Pridolian strata.

SEDIMENTOLOGY AND CARBON ISOTOPE (δ13C) STRATIGRAPHY OF SILURIAN–DEVONIAN BOUNDARY INTERVAL STRATA, APPALACHIAN BASIN (PENNSYLVANIA, USA)

Palaios ◽  
2019 ◽  
Vol 34 (9) ◽  
pp. 405-423
Author(s):  
ANYA V. HESS ◽  
JEFFREY M. TROP
Keyword(s):  
New York ◽  
Carbon Isotope ◽  
Lower Devonian ◽  
Appalachian Basin ◽  
Sediment Supply ◽  
Fine Grained ◽  
Marine Strata ◽  
Central Pennsylvania ◽  
Storm Wave ◽  
Upper Silurian

ABSTRACT Silurian–Devonian boundary interval strata deposited during the expansion of land plants record a major perturbation of the carbon cycle, the global Klonk Event, one of the largest carbon isotope excursions during the Phanerozoic. In the Appalachian Basin, these marine strata record the regional buildup to the Acadian Orogeny. This study reports new sedimentologic, paleontologic, ichnologic, and carbon isotope data from an exceptional quarry exposure in central Pennsylvania, USA, a historically understudied area between better-documented outcrops >500 km away to the southwest (West Virginia, Virginia, Maryland) and northeast (New York). Facies spanning the continuous 113-m thick outcrop are dominantly carbonate and fine-grained siliciclastic strata interpreted as being deposited in supratidal through subtidal environments, including oxygen-limited environments below storm wave base. They record parts of three transgressive-regressive cycles, in the (1) upper Silurian Tonoloway Formation, (2) upper Silurian–Lower Devonian Keyser Formation through lower Mandata Member of the Old Port Formation, and (3) Lower Devonian Mandata through Ridgeley Members of the Old Port Formation. Micrite matrix δ13Ccarb analyses exhibit a large, positive δ13Ccarb excursion (>5‰ amplitude). Outcrops of this interval in the Appalachian Basin occur in two belts, between which correlation has been historically challenging. The regional correlation presented herein is based on carbon-isotope trends and is more consistent with published conodont biostratigraphy and volcanic ash ages, an improvement over published correlations based on lithostratigraphy. Transgressive-regressive trends at the central Pennsylvania study site are not consistent with regional trends, indicating that local controls (tectonics, sediment supply) rather than global (eustasy) dominated depositional patterns in the Silurian–Devonian boundary interval in the Appalachian Basin.

scholarly journals Paleomagnetism of Siluro-Devonian rocks from eastern Maine

1980 ◽  
Vol 17 (12) ◽  
pp. 1653-1665 ◽  
Author(s):  
Dennis V. Kent ◽  
Neil D. Opdyke
Keyword(s):  
Reasonable Agreement ◽  
Lower Devonian ◽  
Northeastern North America ◽  
Rock Types ◽  
Magnetic Carriers ◽  
Paleomagnetic Study ◽  
Intrusive Rocks ◽  
The Mean ◽  
Upper Silurian ◽  
Accurate Record

A diverse suite of rocks was collected for paleomagnetic study from two formations in the Eastport area of northeastern Maine: 18 sites (103 samples) from redbeds and diabase sills of the Hersey Formation (uppermost Silurian to Lower Devonian) and 14 sites (74 samples) from lavas, redbeds, and calcareous nodules of the Eastport Formation (Lower Devonian; Rb/Sr age 412 Ma). Characteristic magnetizations based on AF and thermal demagnetization analyses give mean directions, after simple correction for bedding tilt, of D = 163.6°, I = 41.3°, α95 = 6.3°, for N = 16 sites in the Hersey, and D = 179.3°, I = 38.0°, α95 = 9.4°, for N = 14 sites in the Eastport Formation. Baked contact relations, the presence of opposite polarities, and the similarity in directions over different rock types and magnetic carriers point to an acquisition of magnetization near to the time of rock formation. The mean directions correspond to (south) paleopole positions at 19.8°S lat., 308.8°E long. (δp, δm = 4.7°, 7.7°) for the Hersey and 23.7°S lat., 293.7°E long. (δp, δm = 6.6°, 11.1°) for the Eastport Formation.These paleopoles are removed from the Upper Silurian Bloomsburg Formation pole, but are in reasonable agreement with similar age results from central Newfoundland, suggesting that the Acadia displaced terrain encompassed these areas. Siluro-Devonian paleopoles from intrusive rocks in northeastern North America are generally widely divergent and these may not be providing an accurate record of paleomagnetic field in all cases.

Anatomy of an Upper Silurian transgressive–regressive cycle, Prince of Wales Island, Arctic Canada

1995 ◽  
Vol 32 (1) ◽  
pp. 24-36
Author(s):  
Paul S. Mortensen ◽  
Brian Jones
Keyword(s):  
General Pattern ◽  
Island Formation ◽  
Depositional Settings ◽  
The World ◽  
Influence Of Water ◽  
Shallow Subtidal ◽  
Main Factors ◽  
Upper Silurian ◽  
Somerset Island ◽  
Quartz Grains

The Ludlovian–Pridolian Cape Storm, Douro, and Somerset Island formations on eastern Prince of Wales Island form a transgressive–regressive succession that developed on the western flank of the active Boothia Horst. Sedimentation took place in a series of fault-bounded subbasins that were, at different times, characterized by abundant microbolites, rhodolites, brachiopods, and organisms that produced a diverse array of ichnofossils. Integration of paleoecological information from this succession provides a multifaceted paleoecological model, which can be applied to similar, lithologically monotonous successions throughout the world. Three main factors controlled the distribution of biota through the transgressive–regressive cycle. The most obvious factor was ever-changing depositional settings caused by progressive rise and fall in sea level. Superimposed on this general pattern, however, was the influence of water circulation and the influx of detrital quartz from the Boothia Horst. The microbolites and rhodolites were mutually exclusive; the microbolites developed in intertidal to shallow subtidal settings, whereas the rhodolites grew in subtidal settings. The exception is in the lower Somerset Island Formation, where oncolites and rhodolites are numerous, commonly in the same beds. The influx of detrital quartz grains into the intertidal and supratidal settings, common during the development of the lower part of the Cape Storm Formation and the upper part of the Somerset Island Formation, curtailed microbolite development. During the subtidal phase, circulation controlled the distribution of Atrypoidea-dominated brachiopod faunas, rhodolites, microbolites, and ichnofossils. Even subtle changes in the nature of the rhodolite associations were accompanied by changes in the Atrypoidea species and changes in the ichnofossil assemblages.

A subaerial arthropod trackway from the Upper Silurian Clam Bank Formation of Newfoundland

1995 ◽  
Vol 32 (3) ◽  
pp. 304-313 ◽  
Author(s):  
J. L. Wright ◽  
L. Quinn ◽  
D. E. G. Briggs ◽  
S. H. Williams
Keyword(s):  
Lower Devonian ◽  
Trace Fossil ◽  
Environment Analysis ◽  
Fine Grained ◽  
Body Drag ◽  
Upper Silurian ◽  
First Time ◽  
Parallel Series

Trackways are reported for the first time from Silurian rocks in Newfoundland. They occur in the Clam Bank Formation of the Port au Port Peninsula. At least one of the trackways represents one of the earliest known occurrences of a large subaerial arthropod trace fossil. It is preserved in hyporelief in a red fine-grained sandstone. The trackway, Diplichnites Dawson, 1873, consists of two parallel series of clearly defined imprints. It is attributed to a myriapod similar to the Lower Devonian Eoarthropleura. The sandstone contains halite pseudomorphs that indicate that the sediment horizon had been subject to desiccation immediately prior to the formation of the trackway. The arthropod walked on a red siltstone deposited in an alluvial flats environment. Analysis of the trackway suggests that the arthropod was approximately 23 cm long and had 17 pairs of walking appendages. It appears that a high-geared gait with a ratio of forestroke:backstroke of 8:2 was used in walking across the substrate, that is, approximately 20% of walking appendages were in contact with the substrate at any one time. This rapid gait, and the lack of a body drag mark, indicates that the arthropod was well adapted to subaerial locomotion. Knowledge of modern myriapod gaits has been used to extrapolate a theoretical trail, which compares well with the fossil trackway. Smaller, less well preserved trackways occur elsewhere in the Clam Bank Formation and may have been made by a similar arthropod.

scholarly journals Stauromatidium and Stauromatidiidae, new genus and family of Upper Silurian and Lower Devonian rugose corals

1982 ◽  
Author(s):  
A E H Pedder ◽  
W A Oliver
Keyword(s):  
Lower Devonian ◽  
New Genus ◽  
Rugose Corals ◽  
Upper Silurian

Valentia Slate, Co. Kerry, Ireland: a Global Heritage Stone Resource proposal

2021 ◽  
Author(s):  
Patrick Wyse Jackson ◽  
Louise Caulfield ◽  
Aidan Forde ◽  
Iseult Conlon ◽  
Peter Cox ◽  
...  
Keyword(s):  
Metamorphic Grade ◽  
Alluvial Fan ◽  
Mining Company ◽  
Small Surface ◽  
Red Sandstone ◽  
Fine Grained ◽  
Paris Opera ◽  
Underground Workings ◽  
Opera House ◽  
Pale Green

<div><span>Valentia Slate from the southwest of Ireland, is herein proposed as a Global Heritage Stone Resource. This Middle Devonian (Givetian) purple to pale green-coloured</span><span>, </span><span>fine-grained siltstone comprises the Valentia Slate Formation, part of the Old Red Sandstone which extensively crops out in southern Ireland.  The unit</span><span>, </span><span>which developed as an alluvial fan, has a thickness of over 3000m </span><span>and shows a well developed cleavage and low metamorphic grade imposed during the Variscan which produced its slaty fabric. Although quarried from small surface openings from the late eighteenth century, the commercial value of certain horizons of the Valentia Slate Formation was first recognised by the local landowner The Knight of Kerry who commenced its extraction at Dohilla in 1816 for use as roofing slates.  The operation was expanded from the 1820s by the Hibernian Mining Company and later by the Valentia Slab Company and its successor</span><span>, </span><span>the Valentia Slate Company</span><span>, </span><span>which continued to quarry the stone until the late 1870s. Initally stone was extracted from surface workings but since 1840 it has been exclusively obtained from underground workings. From the 1880s the quarry went into decline due to competition from Wales and extraction ceased altogether in 1911 following a large rockfall at the opening to the quarry.  It was revived in the 1980s and recent investment has resulted in </span><span>being able to provide </span><span>this quality stone to widespread markets. Although not easily split into thin slates Valentia Slate was first used locally for roofing and general building. However</span><span>, </span><span>as it could be cut into slabs of a variety of thicknesses and lenghts of up to 3m it was more readily adopted</span><span>, </span><span>both nationally and internationally</span><span>, </span><span>for use in buildings for window cills, steps, domestic fittings in bathrooms and kitchens, and paving both externally and internally as in the Houses of Parliament in London, the Paris Opera House, and for flagging in </span><span>a </span><span>number of British railway termini.  The stone </span><span>was susceptible to </span><span>and held sharp carving, and it it was also fabricated into headstones, memorials, garden furniture, and shelving. Stone was even exported in the 1870s to Brazil for use as railway sleepers. Craftsmen also </span><span>fabricated </span><span>lamps </span><span>and </span><span>birdhouses from the material and its most celebrated use was for billiard and snooker tables, a number of </span><span>which </span><span>were highly decorative having been enamelled.  During the height of production over 500 men were employed quarrying and working Valentia Slate. The first tramway in an Irish quarry was installed in about 1816 and was used to transport stone and sawn slabs from the quarry to Knightstown</span><span>, </span><span>some 4km away</span><span>, </span><span>where it was further fabricated if required in a dedicated stoneyard prior to exportation from the adjacent slate quay.  Today extraction continues and the stone is used for a variety of restoration, decorative and construction purposes. The longevity of its extraction, its versatility of use, and the extent of the exportation of the Valentia Slate makes it worthy to be proposed as a Global Heritage Stone Resource.</span></div>

Formation of the hour-glass structure in augite

1969 ◽  
Vol 37 (288) ◽  
pp. 472-479 ◽  
Author(s):  
D. F. Strong
Keyword(s):  
Glass Structure ◽  
Coarse Grained ◽  
Crystal Face ◽  
Thin Sections ◽  
Rapid Crystallization ◽  
Fine Grained ◽  
Rock Types ◽  
The Common

SummaryA study of augite in over three hundred thin sections of mainly alkalic rocks permits the distinction of two main types of hour-glass structure. The common ‘swallow-tailed’, sometimes skeletal augite crystals are found in the fine-grained groundmass of many rock types, and it is suggested that rapid crystallization alone accounts for their formation. Hence, this type of hour-glass structure has been called ‘quench hour-glass’. The hour-glass structures of larger augite crystals of porphyritic and coarse-grained rocks are commonly described as hour-glass ‘zoning’, as they result primarily from compositional differences between the different sectors. These were formed under conditions of relatively slower cooling than the ‘quench hour-glass’, and thus cannot be explained in the same way. They are thought to have formed by a process involving adsorption of impurities on a particular crystal face so as to impede growth of these faces, producing an initial skeleton of hour-glass form, which is completed by later crystallization of augite richer in FeO, Na2O, TiO2, and Al2O3. This hypothesis also explains the patchy zoning of other augite crystals, casting doubt on some petrogenetic interpretations of such zones as core zones.

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