Author Topic: ellesmere island syncline and the “Nares Strait problem” (gravity anomaly)  (Read 14007 times)

electrobleme

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ellesmere island syncline and the “Nares Strait problem” (gravity anomaly) - photographs and papers

synclines formation and ellesmere syncline formation is being discussed here



ellesmere island syncline


ellesmere island syncline has fossiliferous limestones



caledonian bay where the ellesmere island syncline and anticline are located - diagram


ellesmere island syncline (canada) surrounds with sandstones shales


ellesmere syncline and caledonian bay geology

Quote
geological investigations in ellesmere island, 1952

Scientific results - geology

The ridge immediately north of Caledonian Bay, on the east coast of
Canyon Fiord, mainly consists of a large anticline, which is built up of
unfossiliferous sandstones, slates, limestones, chert beds, and chert conglomerates.
The age of this sequence is unknown but may conceivably be Late
Precambrian.

South of Caledonian Bay there is a large syncline (Figs. 1 and 6), which
seems to be separated from the large anticline by a major fault. The syncline
is composed of fossiliferous limestones, shales, and sandstones (Fig. 7). On
the basis of lithological similarities and field identifications ofossils these
beds have tentatively been assigned to the following formations, which are
known from the unfolded sequence in north Greenland (Koch, 1929, pp.
238-42):
The Offley Island formation, of Middle Silurian (Late Llandovery; Clinton) age.
The Cape Tyson formation, of Late Silurian (Tarannon-Wenlock) age.
The Polaris Harbour formation, of doubtful Late Silurian (Ludlow) age.
Until the study of the collections has been completed this comparison cannot
profitably be carried any further, but it is certain that Silurian fossils occur
in the syncline.

Although the folding of the Lower Paleozoic strata around Caledonian
Bay has been rather intensive, no metamorphic rocks above the rank of slate
have been found. Neither were any intrusive rocks 0bserved.l Similar conditions
are known from northern Ellesmere Island (Troelsen, 1950a). There
are therefore good reasons for classifying those parts of the folded mountains
which have been examined as belonging to a miogeosyncline.

Around Caledonian Bay, Middle Carboniferous sandstones and limestones
(with Fusulina and Fusulinella) are found resting upon (1) the folded unfossiliferous
sedimentary strata north of the bay and ( 2 ) the folded Silurian
sedimentary strata south of the bay (Figs. 1 and 8 ). The low island in the
bay also consists of Carboniferous rocks. It was definitely proved that the
contact between the Carboniferous and the older rocks is an irregular erosion
surface overlain by a coarse conglomerate of water-worn pebbles.

River gravels, moraines, and the Carboniferous basal conglomerate were also searched unsuccessfully for intrusives and highly metamorphosed rocks.

The Carboniferous rocks truncate the older, folded rocks. At one place
north of Caledonian Bay, a small erosional valley that parallels the trend of
the old anticline was found to have been filled with Carboniferous sandstone.
I got the impression that by Carboniferous time a bay already existed in the
Caledonian Bay area (in this case, the assumed major fault was probably
formed before Carboniferous time). The bay was filled with Carboniferous
sediments, and later the whole structure was slightly warped. In comparatively
recent geological time erosional forces have re-excavated the bay to
form what is now Caledonian Bay and the large valley behind it. North of
Caledonian Bay the erosion has been so thorough that only small patches of
the Carboniferous strata have been left here and there on the hill sides.

For the first time in Ellesmere Island we thus have positive, irrefutable
evidence of a post-Silurian (or possibly Late Silurian) but pre-Middle Carboniferous
folding. This, together with what is now known about Peary
Land (Troelsen, 1950b), proves the essential correctness of Lauge Koch’s
theory as to the age of the folding.
extract from geological investigations in ellesmere island, 1952 (pdf)


the “Nares Strait problem” (gravity anomaly)


Quote
The Nares Strait gravity anomaly and its implications for crustal structure

H. R. Jackson and L. Koppen

Abstract: A negative free-air gravity anomaly is associated with Nares Strait, the waterway that separates Ellesmere Island and Greenland. Two east–west gravity profiles that cross Ellesmere Island and Nares Strait were collected. A low with values in the range of ?100 to ?120 mGal (?1000 to ?1200 ?m/s2) was observed, and two-dimensional crustal models were created to identify the cause of the anomaly. The gravity anomaly cannot be attributed wholly to the bathymetry of the strait or to the sedimentary rocks underlying the strait. Crustal models that reproduce the anomaly have a M discontinuity that slopes under Nares Strait towards Ellesmere Island so that the crust beneath Ellesmere Island is thickened. The anomaly is similar to those associated with ancient and modern suture zones, regions of collided continental crust. Plate reconstructions suggest Nares Strait is a collisional boundary between the North American Plate (Ellesmere Island) and the Greenland Plate. The gravity anomaly supports this interpretation of Nares Strait.
The Nares Strait gravity anomaly and its implications for crustal structure | web-p.cisti.nrc.ca

Quote
Structure of Palaeogene sediments in east Ellesmere Island: Constraints on Eurekan tectonic evolution and implications for the Nares Strait problem

Abstract

The “Nares Strait problem” represents a debate about the existence and magnitude of left-lateral movements along the proposed Wegener Fault within this seaway. Study of Palaeogene Eurekan tectonics at its shorelines could shed light on the kinematics of this fault. Palaeogene (Late Paleocene to Early Eocene) sediments are exposed at the northeastern coast of Ellesmere Island in the Judge Daly Promontory. They are preserved as elongate SW–NE striking fault-bounded basins cutting folded Early Paleozoic strata. The structures of the Palaeogene exposures are characterized by broad open synclines cut and displaced by steeply dipping strike-slip faults. Their fold axes strike NE–SW at an acute angle to the border faults indicating left-lateral transpression. Weak deformation in the interior of the outliers contrasts with intense shearing and fracturing adjacent to border faults. The degree of deformation of the Palaeogene strata varies markedly between the northwestern and southeastern border faults with the first being more intense. Structural geometry, orientation of subordinate folds and faults, the kinematics of faults, and fault-slip data suggest a multiple stage structural evolution during the Palaeogene Eurekan deformation: (1) The fault pattern on Judge Daly Promontory is result of left-lateral strike-slip faulting starting in Mid to Late Paleocene times. The Palaeogene Judge Daly basin formed in transtensional segments by pull-apart mechanism. Transpression during progressive strike-slip shearing gave rise to open folding of the Palaeogene deposits. (2) The faults were reactivated during SE-directed thrust tectonics in Mid Eocene times (chron 21). A strike-slip component during thrusting on the reactivated faults depends on the steepness of the fault segments and on their obliquity to the regional stress axes.

Strike-slip displacement was partitioned to a number of sub-parallel faults on-shore and off-shore. Hence, large-scale lateral movements in the sum of 80–100 km or more could have been accommodated by a set of faults, each with displacements in the order of 10–30 km. The Wegener Fault as discrete plate boundary in Nares Strait is replaced by a bundle of faults located mainly onshore on the Judge Daly Promontory.

Keywords: Arctic; Nares Strait; Eurekan Fold Belt; Palaeogene; Cenozoic; Palaeogene sedimentary basins; Strike-slip tectonics

Structure of Palaeogene sediments in east Ellesmere Island: Constraints on Eurekan tectonic evolution and implications for the Nares Strait problem  | sciencedirect.com


immense online map of canada and surrounding area including ellesmere island


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