Hyalotuff deltaic deposits in the Ballantrae ophiolite of SW Scotland: evidence for crustal position of the lava sequence

1982 ◽  
Vol 72 (4) ◽  
pp. 217-228 ◽  
Author(s):  
B. J. Bluck
Keyword(s):  
Shallow Water ◽  
Hot Spots ◽  
Oceanic Islands ◽  
Lava Flows ◽  
Marked Contrast ◽  
Marginal Basin ◽  
Ocean Ridges ◽  
Water Origin ◽  
Lava Sequence ◽  
Radiometric Ages

ABSTRACTHyalotuff deltaic deposits, a high proportion of volcanogenic sediment and a repeated occurrence of conglomerate with well-rounded clasts constitute evidence for the shallow-water origin of spilitic lavas and volcanogenic sediments in an Ordovician ophiolite at Ballantrae, SW Scotland. One section, >1.5 km thick, shows repeated evidence for a shallow-water origin. This implies accumulation in a subsiding area. In this sense the sequence at Ballantrae is in marked contrast to those found in oceanic islands (hot spots) which are known to grow from deep into shallow water. Neither does it compare well with those from ocean ridges which usually begin in deep water and move, with cessation of vulcanicity, into even deeper water.The lava sequence at Ballantrae compares well with oceanic island-arc and remnant arc deposits where uplift and subsidence is common. This, the occurrence of intermediate and acidic lavas and clasts, and the restricted palaeontological and radiometric ages support an arc-marginal basin origin for the lavas. Diversity in the chemical composition of the lavas may reflect diverse origins within the marginal basin.An upward coarsening sedimentary sequence was built by a hyalotuff delta which formed in front of advancing lava flows. As the lavas advanced over the sediments so a sequence was generated where these sediments have a source in lava flows which were eventually to overlie them.Clasts of tholeiite were derived from lavas which are now spilite. This, together with the presence of spilitic lava clasts and tuff immediately beneath the flow suggests that the spilitisation resulted from metasomatic activity associated with the convective circulation of trapped water, with the lava as a heat source.

scholarly journals Shallow-Water Foraminifera and Other Microscopic Biota of Clipperton Island, Tropical Eastern Pacific

2019 ◽  
Author(s):  
Mary L McGann ◽  
Robert W. Schmieder ◽  
Louis-Philippe Loncke
Keyword(s):  
Shallow Water ◽  
Geographic Location ◽  
Oceanic Islands ◽  
Tropical Pacific ◽  
Eastern Pacific ◽  
North Equatorial Current ◽  
Tropical Eastern Pacific ◽  
Foraminiferal Assemblage ◽  
Island Endemic ◽  
The North

<p></p><p>The recent foraminiferal fauna and associated microbiota of Clipperton Island (10.2833°N, 109.2167°W) were investigated at 20 sites collected in the intertidal zone around the perimeter of the island and from the edge of the inner brackish-water lagoon. Due to the island’s geographic location in a low productivity zone, a lack of variable habitats on and surrounding the island, and heavy surf that pounds the exposed land, a depauperate fauna was recovered although mixed biogeographic affinities are represented. The shallow-water foraminiferal assemblage has no endemics but primarily tropical Indo-Pacific and eastern Pacific (Panamic) affinities, as well as one species of Caribbean affinity. The most abundant taxa are <i>Sorites</i> spp. and <i>Quinqueloculina</i> spp. Noticeably absent are any species of <i>Amphistegina, </i>despite the fact that they are considered ubiquitous in the tropical Pacific. The molluscan fauna has Clipperton Island endemics, a tropical Pacific/Inter-Island endemic, and tropical eastern Pacific oceanic islands/Panamic Molluscan affinities. The ostracods included endemics found restricted to Clipperton Island lagoon, as well as Indo-Pacific and Panamic Province species. The foraminifera, mollusks, and ostracods are thought to disperse to Clipperton Island by way of the North Equatorial Countercurrent and North Equatorial Current, suggesting that the island is indeed a stepping stone for migration both east and west across the Eastern Pacific Barrier.</p><br><p></p>

Le Miocene marin du revers septentrional du bassin du Hodna (partie orientale) (department de Constantine, Algerie)

1952 ◽  
Vol S6-II (4-6) ◽  
pp. 275-281
Author(s):  
Jacques Bertraneu ◽  
Magne Jean
Keyword(s):  
Shallow Water ◽  
Northern Flank ◽  
Lower Miocene ◽  
Water Origin

Abstract The Miocene microfaunas of the thick marine series on the northern flank of the eastern Hodna basin, Constantine, Algeria, show that it is of shallow-water origin and lower Miocene age. The existence of an important basin of subsidence in the region in Miocene time is thus established.

Stone rosettes as indicators of ancient shorelines: examples from the Precambrian Belcher Group, Northwest Territories

1979 ◽  
Vol 16 (9) ◽  
pp. 1887-1891 ◽  
Author(s):  
B. D. Rlcketts ◽  
J. A. Donaldson
Keyword(s):  
Shallow Water ◽  
Northwest Territories ◽  
Close Packing ◽  
Desiccation Cracks ◽  
Cross Bedding ◽  
Vertical Arrays ◽  
Water Origin ◽  
Shallow Subtidal ◽  
Shore Platforms

Flat-pebble conglomerates in the McLeary Formation of the Belcher Group display close packing of intraformational slabs in near-vertical arrays that appear distinctively polygonal in sections parallel to bedding. Such arrangements of flat pebbles, known by names such as stone rosettes and slone packings, are common on modem beaches, especially within the swash and backwash zone of shore platforms. Association of the McLeary stone rosettes with sedimentary features suggestive of shallow subtidal to supratidal origin (herringbone cross-bedding, reactivation surfaces, desiccation cracks, tepee structures, gypsum casts, oncolites, stromatolites, and probable beachrock) supports a hydrodynamic origin for these polygonal arrays of flat pebbles, an origin that has been demonstrated for modern occurrences. Where associated structures corroborate interpretation of a shallow-water origin, such stone rosettes provide evidence for ancient strandlines, and the designation "beach rosettes" is suggested as appropriate to distinguish them from stone rosettes formed by periglacial processes.

Timing of events in an Early Cretaceous island arc–marginal basin system on South Georgia

1979 ◽  
Vol 116 (3) ◽  
pp. 167-179 ◽  
Author(s):  
P. W. G. Tanner ◽  
D. C. Rex
Keyword(s):  
Continental Crust ◽  
Island Arc ◽  
Magmatic Arc ◽  
South Georgia ◽  
Marginal Basin ◽  
Early Mesozoic ◽  
Mafic Complex ◽  
Minimum Age ◽  
Radiometric Ages ◽  
Basin System

Summary19 new K–Ar mineral ages of 78-201 Ma and 3 Rb–Sr whole rock isochron ages of 81 ± 10, 127±4 and 181±30 Ma are presented from units of continental crust, mafic complex and island arc assemblage on South Georgia. The Drygalski Fjord Complex, part of the possible floor of the marginal basin in the southern part of the island, includes granodiorite and gabbro plutons of minimum age 180–200 Ma. Together with older metasediments they have been affected by a major thermal event at about 140 Ma, thought to have resulted from the emplacement of a mafic complex (Larsen Harbour Formation) during the initial opening of the marginal basin. Rocks of the Larsen Harbour Formation are cut by the Smaaland Cove intrusion dated by Rb–Sr whole rock isochron at 127±4 Ma. An island arc assemblage exposed to the SW of South Georgia consists of pyroclastic rocks cut by monzodiorite and andesite intrusions, which give radiometric ages of 81–103 Ma. These data suggest that the marginal basin opened during the late Jurassic (pre-140 Ma); that part of an earlier (early Mesozoic) magmatic arc is preserved in continental crust making up part of the floor of the basin; and that subduction continued beneath the island arc until at least the Senonian time. The younger plutons in the arc were emplaced at roughly the same time as turbidite facies rocks at deep levels in the marginal basin were being affected by penetrative deformation and metamorphism. The timing of events on South Georgia agrees closely with that deduced for the continuation of the same island arc–marginal basin system in South America. The 180–200 Ma plutons correlate with an older suite of plutonic rocks reported from the Antarctic Peninsula and southern Andes; they are part of a once-continuous magmatic arc related to subduction of the Pacific plate beneath Gondwanaland during the early Mesozoic.

scholarly journals Ba, Rb and Cs in the Earth's Mantle

1983 ◽  
Vol 38 (2) ◽  
pp. 256-266 ◽  
Author(s):  
Albrecht W. Hofmann ◽  
William M. White
Keyword(s):  
Mobile Phase ◽  
Aqueous Fluid ◽  
Oceanic Islands ◽  
Primitive Mantle ◽  
Partial Melt ◽  
Ocean Ridges ◽  
The Earth ◽  
Isotopic Abundances ◽  
Oceanic Basalts ◽  
Relative Abundances

Abstract In 166 isotope dilution analyses of Ba, Rb, Cs on fresh basalts from mid-ocean ridges and oceanic islands, Ba/Rb and Cs/Rb ratios are nearly constant. From this, we conclude that Ba/Rb and Cs/Rb ratios are essentially constant in the present-day mantle in spite of large differences in the degree of source depletion or enrichment. As it appears improbable that these ratios could be both constant and non-primitive, we propose that they are representative of the primitive mantle and of the present-day crust-mantle system. We explain this uniformity of relative abundances as follows: the mantle is depleted by subtraction of a mobile phase such as a partial melt or an aqueous fluid. In either case, a significant amount of the mobile phase remains in the residue. Ba, Rb and Cs are among the most highly incompatible elements. Therefore the mobile phase cannot fractionate these elements relative to one another but retains the source ratios of Ba/Rb and Cs/Rb. Also, the amount of mobile phase remaining in the residue is enough to dominate the Ba, Rb and Cs concentrations in the residue. Consequently, neither the mobile phase nor the residue, nor any other portion of the mantle that may be enriched by addition of the mobile phase, will be changed in their relative abundances of Ba, Rb and Cs, even though the absolute abundances of these elements may change by orders of magnitude.The primitive Ba/Rb = 11.3 and Cs/Rb = 12.6 x 10-3 lead to the following estimates for the primitive mantle: Ba = 6.9 ppm (taken from Jagoutz et al. [1]). Rb = 0.61 ppm and Cs = 7.7 ppb.Assuming the earth has a chondritic Sr/Ba ratio of 3.08, we calculate a Rb/Sr ratio of 0.029 for the earth. This corresponds to a present-day 87Sr/ 86Sr of 0.7045. This value lies near the lower limit of the ratios estimated from the correlation of Nd and Sr isotopic abundances in oceanic basalts.The Cs/Rb ratios is about a factor of ten lower than the Cl-chondritic ratio and a factor of three lower than the lunar ratio. This low terrestrial Cs/Rb ratio should be matched by similar values in the continental crust. However, the large range of Cs/Rb ratios found in the crust prevent us from obtaining a meaningful mass balance.

Lacustrine Sedimentation in a Semiarid Alpine Setting: An Example from Ladakh, Northwestern Himalaya

1989 ◽  
Vol 31 (3) ◽  
pp. 332-350 ◽  
Author(s):  
Monique Fort ◽  
Douglas W. Burbank ◽  
Pierre Freytet
Keyword(s):  
Shallow Water ◽  
Debris Flows ◽  
Arid Environment ◽  
Alpine Lakes ◽  
Marked Contrast ◽  
Semiarid Environment ◽  
Lacustrine Sedimentation ◽  
Carbonate Sedimentation ◽  
Semi Arid

AbstractThe Lamayuru lacustrine strata in Ladakh typify many of the carbonate-rich Pleistocene alpine lakes found in the semiarid environment of the northern Himalaya. Created by a 200-m-thick landslide, the lake was in existence by at least 35,000 yr ago, and may have persisted until 500–1000 yr ago. Represented in the center by thin turbidites and laminated muds, the lacustrine sedimentation along the lake margins and low-relief deltas characteristically displays a marked contrast between (1) clastic lenses representing rapid, sporadic, matrix-poor debris flows and periglacial inputs from the alpine slopes and (2) abundant, diverse, shallow-water, biologically dominated carbonate strata, among which organism-rich, chalky beds and oncolithic and encrusted stem-rich strata predominate. Resemblances of the Lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the Greater Himalayan crest suggest that the alpine, semi-arid environment would favor diversified, spacially restricted carbonate sedimentation punctuated by occasional clastic influxes. Such a depositional regime contrasts strongly with that found immediately south of the Himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes.

Sedimentology of the Partry Series in the Partry Mountains, Co. Mayo, Eire

1967 ◽  
Vol 104 (6) ◽  
pp. 585-607 ◽  
Author(s):  
John McManus
Keyword(s):  
Shallow Water ◽  
Marine Environment ◽  
Volcanic Rocks ◽  
Sedimentary Structures ◽  
Welded Tuff ◽  
Water Origin ◽  
Red Bed

AbstractThe Lettereeneen fault, a newly recognized structure, brings the Mweelrea and Maumtrasna Groups of the Partry Series (Caradocian-Llandeilian age) into contact. The stratigraphy of the Mweelrea Group, of red bed facies, is followed from the presence of welded tuff horizons; no such markers exist in the Maumtrasna Group which lies unconformably upon the former.Sedimentary structures of shallow water origin occur in each group. Three types of conglomerate recognized in the area are examined. The immature feldspathic sandstones increase in arkosity upwards.A proluvial or proluvio-marine environment of deposition is suggested, with debris derived from an eastward extension of the metamorphosed Dalradian rocks of the Connemara Cordillera and foothills of sedimentary and volcanic rocks.

Quelques aspects des conditions de depot du flysch

1962 ◽  
Vol S7-IV (1) ◽  
pp. 41-48 ◽  
Author(s):  
Marguerite Rech-Frollo
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Organic Material ◽  
Detrital Material ◽  
Water Origin ◽  
The Moment ◽  
Bird Tracks ◽  
Marine Basin

Abstract Analysis of the Niesen flysch between Le Sepey and Mosses lake does not confirm the deep-water bathymetry commonly attributed to flysch deposits. The juxtaposition of organic material over continental alluvium--a typical flysch characteristic--was observed only at shallow depths. The muddy sands, source of the flysch deposits, are actually formed at shallow depths. Bird tracks reported from certain flysch beds also suggest shallow-water origin for the deposits. Cross currents produced after periodic disruption of tectonic and climatic equilibria in parts of a marine basin corresponding to the continental platforms explain the mechanical sorting of the organisms and detrital material as well as the granoclastic structure of the flysch. After deposition of the flysch and before its compaction orogenic mobility at the bottom of the basin affected the petrography of the flysch causing corrosion of the quartz and feldspars at the moment of consolidation. Evidence presented by proponents of a deep-water origin for the flysch deposits--based on foraminifera and the petrographic and paleo-oceanographic characters of the deep-water sands--is reviewed.

Community structure of Harpacticoida and Canuelloida (Crustacea, Copepoda) on the Great Meteor Seamount (North-east Atlantic Ocean)

2019 ◽  
Vol 99 (06) ◽  
pp. 1325-1342 ◽  
Author(s):  
Karin Richter ◽  
Kai Horst George
Keyword(s):  
Community Structure ◽  
Atlantic Ocean ◽  
Shallow Water ◽  
Oceanic Islands ◽  
Species Level ◽  
North East ◽  
Analysis Of Similarity ◽  
Distribution Ranges ◽  
First Time ◽  
Great Meteor Seamount

AbstractDuring the expedition POS397 ‘GroMet’ in 2010 the sediments of the Great Meteor Seamount (GMS) plateau were sampled quantitatively for the first time, allowing statistical analysis of the community structure of Harpacticoida and Canuelloida. Analysis of similarity revealed no differences between three geographic regions at family/species level. Analysis of diversity indicated slightly greater diversity in the south, with more species belonging to more genera/families. Dispersal opportunities possibly occurring at the plateau (emergence, erosion, rafting) are discussed. Of 18 investigated families 106 species were identified, but only 5.66% were already scientifically known and widely distributed. Within the investigated families, 37.74% of the species belonged to shallow-water genera, leading to the conclusion that the plateau was once connected to shallow-water habitats, perhaps functioning as a stepping stone, but is now geographically isolated. This isolation is most likely due to seafloor spreading of the Atlantic Ocean and descending of the GMS. On the plateau, six species with wider distribution ranges were present, indicating that species may arrive accidentally, but their means of settlement remains unknown. Comparisons of the identified GMS plateau fauna with that of other seamounts and mid-oceanic islands revealed similar communities at family level, but at species level the GMS shares only one species with the Seine Seamount; all other elevations had more species in common. Hence, the GMS plateau is considered to be isolated regarding benthic Copepoda but may play an important role in meiofaunal species distribution, as it represents a shallow-water habitat within the deep sea.

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