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Author Topic: The Nares Strait thread  (Read 481978 times)

Tor Bejnar

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Re: The Nares Strait thread
« Reply #1550 on: April 17, 2019, 05:38:20 PM »
Quote
The Nares Strait is, I believe, bordered by extremely hard limestones and dolomites.
This is "true" as far as it goes. 
Here is a partial 'grab' of rock types associated with each group of formations identified on first map from Denmark (yes, lots of dolomite, some of it 'hard') [some great photographs showing examples of outcrops]:
  • ‘Ellesmere Island – Inglefield Land belt’:  used to describe occurrences of the same gneiss, supracrustal and igneous suites on both sides of Smith Sound (Dawes 1988).
  • The Thule Basin is defined by a thick sedimentary-volcanic succession.  K-Ar ages of 676 and 627 Ma
  • Palaeozoic Franklinian Basin
    • Dallas Bugt Formation: Red to purple-brown arkosic sandstones with con-glomerates form the basal strata, overlain by white to pale yellow weathering, crossbedded sandstones, and topped by finer grained sandstones interbedded with green bioturbated mudstones
    • Humboldt Formation: basal fluvial sandstones and conglomerates, are succeeded by cross-bedded, bioturbated, shallow marine clastics of tidal origin, with the upper interbedded sandstone and mudstone
    • Ryder Gletscher Group: carbonate and siliciclastic deposits:  cliff-forming dolomites, crossstratified dolomites, hard grey dolomite, grey dolomites, with some thin silty horizons, mottled lime mudstones with silty laminations and horizons, together with dolomite-filled burrows and small mounds, locally dolomitised burrowed lime mudstones and minor conglomerates with some interbeds of grey, often glauconitic, calcareous finegrained sandstones; in the south-west glauconitic sandstones and siltstones dominate, with some more resistant limestone beds, uniform and hard, locally dolomitised oolitic limestone, bedded platy lime mudstone with silty laminae, and laterally extensive beds of intraformational flat-pebble conglomerate, massive thin bedded dolomites, stromatolitic mounds, siltstones and bituminous limestones, grainstones and white, brown-weathering sandstones, cliff-forming, burrow-mottled, grey lime mudstones with subordinate intermixed stromatolitic to thrombolitic limestones, sponge mounds and flat-pebble conglomerates, shaly dolomites, laminated lime mudstones and shales with both algal and wave-formed lamination, and dolomitic sandstones. Conspicuous beds of laminated to massive anhydrite and gypsum.
    • Morris Bugt Group: cliff-forming dolomitic limestones, with one distinctive recessive argillaceous unit
    • Washington Land Group: reef-derived deposits, lime mudstones, dolomitic limestones, dolomites and resedimented limestone conglomerates, together with subsidiary siltstones and shales.
    • Peary Land Group: siltstone and sandstone turbidites

The second map is from a Geologic Map of the Arctic from Canada with a few place names added in red.  A plate-boundary transverse fault (with complications) runs through the Strait.
« Last Edit: April 17, 2019, 05:58:05 PM by Tor Bejnar »
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b_lumenkraft

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Re: The Nares Strait thread
« Reply #1551 on: April 17, 2019, 05:42:05 PM »
Great job pivoting on topic again Tor. Well done and thanks for the infos. ;)

Sailaway

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Re: The Nares Strait thread
« Reply #1552 on: Today at 12:27:19 PM »
The way to calculate the high of a tide at any given point uses the "Rule of 12th.

The rule states that over the first period the quantity increases by 1/12. Then in the second period by 2/12, in the third by 3/12, in the fourth by 3/12, fifth by 2/12 and at the end of the sixth period reaches its maximum with an increase of 1/12. The steps are 1:2:3:3:2:1 giving a total change of 12/12. Over the next six intervals the quantity reduces in a similar manner by 1, 2, 3, 3, 2, 1 twelfths.