Upper Proterozoic 'Limestone Unit', Northern Dogtooth Mountains, British Columbia

1973 ◽  
Vol 10 (2) ◽  
pp. 292-305 ◽  
Author(s):  
T. P. Poulton
Keyword(s):  
British Columbia ◽  
Sea Level ◽  
Continental Margin ◽  
Sea Level Fluctuations ◽  
Metasedimentary Rocks ◽  
Upper Proterozoic ◽  
Clastic Sediments ◽  
Carbonate Deposition ◽  
Stratigraphic Position

The Upper Proterozoic 'Limestone Unit' of the Horsethief Creek Group in the northern Dogtooth Mountains consists of deformed sedimentary and metasedimentary rocks with complex depositional and erosional relationships. They are interpreted to represent a westwardly prograding terrigenous and carbonate wedge in a continental margin situation. Shoaling resulted in differential carbonate deposition on top of a largely pelitic succession. Sea level fluctuations produced a complex unit characterized by alternating erosion and sedimentation, in different fades from east to west. This was succeeded by terrigenous clastic sediments with easterly or southeasterly provenance. The last recognizable events produced a widespread carbonate and sandstone blanket.A carbonate unit of similar stratigraphic position occurs in several locations north–northwest of the Dogtooth Mountains, approximately along a line paralleling the trend of Phanerozoic fades belts.

Pleistocene carbonates from Dobrogea (E Romania) and their relationship with Black Sea level fluctuations

2020 ◽  
Author(s):  
Virgil Dragusin ◽  
Silviu Constantin ◽  
Vasile Ersek ◽  
Dirk L. Hoffmann ◽  
Alex Hotchkies
Keyword(s):  
Isotopic Composition ◽  
Sea Level ◽  
Black Sea ◽  
Underground Water ◽  
The Black Sea ◽  
Sampling Area ◽  
Sea Level Fluctuations ◽  
Water Tables ◽  
Carbonate Deposition ◽  
The Town

<p>The eastern part of Romania, bordering on the Black Sea, is generally poor in speleothems and only Piatra Cave has important speleothem occurrences. This cave is positioned close to the present-day shoreline, forcing the local aquifer to completely flood it when it rose synchronously with sea level. The flooding of the cave prevented speleothem formation. Conversely, sub-aerial carbonate deposition took place when the sea level was lower than today and the cave was dry. The study of speleothems from Piatra Cave could bring more insight on past Black Sea level fluctuations, as well as on the isotopic composition of percolating water.</p><p>Some 50 km to the south of Piatra Cave, around the town of Mangalia, botryoidal calcite has been deposited inside small voids formed between Sarmatian limestone beds. Such calcite formations are considered to form close to the water table, at the contact with the underground atmosphere. If so, they could be used to track the position of past water tables, as well as the isotopic composition of those waters. Moreover, as these samples are found only close to the present-day shoreline, they might have been deposited from underground water whose level was directly controlled by the sea.</p><p>Here we present the results of δ<sup>18</sup>O and δ<sup>13</sup>C measurements on 75 samples and sub-samples of botryoidal calcite. We explore the implications of their isotopic variability, by comparison with speleothems from Piatra Cave as well as to other speleothems from Romania. Moreover, we explore their isotopic variability across the sampling area, in order to better assess their possible use as sea level markers.</p>

U–Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska

1991 ◽  
Vol 28 (8) ◽  
pp. 1285-1300 ◽  
Author(s):  
George E. Gehrels ◽  
William C. McClelland ◽  
Scott D. Samson ◽  
P. Jonathan Patchett
Keyword(s):  
Continental Margin ◽  
North American ◽  
Detrital Zircons ◽  
Northern Coast ◽  
Coast Mountains ◽  
Metasedimentary Rocks ◽  
The North ◽  
Upper Proterozoic ◽  
Two Samples ◽  
Cordilleran Margin

Metamorphic rocks within and west of the northern Coast Mountains in southeastern Alaska consist of an Upper Proterozoic(?) to upper Paleozoic continental margin assemblage that we interpret to belong to the Yukon-Tanana terrane. U–Pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of ~495 Ma, ~750 Ma, 1.05–1.40 Ga, 1.75–2.00 Ga, ~2.3 Ga, 2.5–2.7 Ga, and ~3.0 Ga. Multigrain fractions from two samples yield upper intercepts between 2.0 and 2.3 Ga, but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of < 2.0 and > 2.3 Ga grains. Zircons in these rocks generally overlap in age with (i) detrital zircons in metasedimentary rocks of the Yukon–Tanana terrane in eastern Alaska and Yukon, (ii) detrital zircons in strata of the Cordilleran miogeocline, and (iii) plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata. In addition, the pre-1.7 Ga grains overlap in age with dated crystalline rocks of the western Canadian Shield. These similarities raise the possibility that metaclastic rocks in the northern Coast Mountains accumulated in proximity to western North America. The younger zircon populations were likely shed from mid-Proterozoic to early Paleozoic igneous rocks that now occur locally (but may have been widespread) along the Cordilleran margin. Recognition of a continental margin assemblage of possible North American affinity in the Coast Mountains raises the possibility that some arc-type and oceanic terranes inboard of the Coast Mountains may be large klippen that have been thrust over the North American margin.

Stratigraphic framework for the Cambrian–Ordovician rift and passive margin successions from southern Quebec to western Newfoundland

2003 ◽  
Vol 40 (2) ◽  
pp. 177-205 ◽  
Author(s):  
Denis Lavoie ◽  
Elliott Burden ◽  
Daniel Lebel
Keyword(s):  
Sea Level ◽  
Continental Margin ◽  
Passive Margin ◽  
Early Cambrian ◽  
Sea Level Fluctuations ◽  
Late Cambrian ◽  
Head Groups ◽  
Stratigraphic Framework ◽  
Lower Ordovician ◽  
First Time

The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the rift–drift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in early–middle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (Tremadocian–Arenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession.

Detrital zircon geochronology and regional correlation of metasedimentary rocks in the Coast Mountains, southeastern Alaska

1998 ◽  
Vol 35 (3) ◽  
pp. 269-279 ◽  
Author(s):  
G E Gehrels ◽  
P A Kapp
Keyword(s):  
Continental Margin ◽  
Detrital Zircon ◽  
Lower Paleozoic ◽  
Coast Mountains ◽  
Detrital Zircon Geochronology ◽  
Metasedimentary Rocks ◽  
Upper Proterozoic ◽  
Regional Correlation ◽  
Upper Paleozoic ◽  
Detrital Zircon Ages

U-Pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the Coast Mountains in southeastern Alaska. These rocks belong to the Port Houghton assemblage, which consists of upper Paleozoic pelitic and psammitic schist, metaconglomerate, metabasalt, and marble. The Port Houghton assemblage rests unconformably(?) on metamorphosed and deformed mid-Paleozoic arc-type volcanics (Endicott Arm assemblage), which gradationally overlie upper Proterozoic(?) - lower Paleozoic continental margin strata (Tracy Arm assemblage). Three main clusters of ages are present: 330-365 Ma (19 grains), 1710-2000 Ma (27 grains), and 2450-2680 Ma (6 grains). Additional grains are approximately 2334, 2364, and 3324 Ma. Comparison of these ages with detrital zircon ages in other Cordilleran assemblages supports previous interpretations that metasedimentary rocks in the Coast Mountains (i) form a southwestern continuation of the Yukon-Tanana terrane of eastern Alaska and Yukon, (ii) are not correlative with strata of the Alexander terrane, and (iii) contain detritus that was probably shed from cratonal rocks in the Canadian Shield to the east. Several scenarios exist to explain the occurrence of these continental margin rocks west (outboard) of arc-type and ocean-floor assemblages such as the Stikine, Cache Creek, Quesnel, and Slide Mountain terranes.

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