A Neoproterozoic carbonate ramp and base-of-slope succession, the Andrée Land Group, Eleonore Bay Supergroup, North-East Greenland: sedimentary facies, stratigraphy and basin evolution. PhD Thesis 2001

Kasper Stefan Frederiksen

Publikation: Bog/rapportRapport (offentligt tilgængelig)

Abstrakt

The up to 1275 m thick Neoproterozic Andree Land Group crops out in the central fjord zone in the North-East Greenland Caledonides between latitudes 72°N and 74°30'N. It consists of limestones, dolomites, and mudstones representing deposition on a storm-dominated, north or north-eastward dipping grain-dominated carbonate ramp and base-of-slope environment. The Andree Land Group is subdivided into seven formations, which from below are the Skipperdal, Reservatet, Arbenz Kolle, Kap Mohn, Grejsdalen, Munotbjerg, and Waltershausen Gletscher Formations. In the lower five formations, sixteen facies are grouped into three facies associations: (1) microbial ramp, (2) pisolitic ramp, and (3) mid- to outer ramp facies association. Facies association 1 consists predominantly of microbialites which represent microbial reefs formed on an inner- to mid ramp. Facies association 2 consists of micrites, pisolites, peloidal calcarenites, and breccias, that collectively represent pisoid flats and shoals of the inner- to mid ramp. Facies association 3 predominantly consists of storm-produced limestone-mudstone couplets representing the mid- to outer ramp.

A sequence stratigraphic analysis was carried out on the basis of nine measured logs that collectively form a N-S orientated profile west of the Western Fault Zone. Eleven sequences, usually 50-100 m thick, are identified in the lower part of the Andree Land Group. The sequences reflect the changes in depositional pattern on the ramp during a cycle of relative sea-level change. They are from base to top composed of an early transgressive systems tract dominated by breccias and pisolites or microbialites, a limestone-mudstone couplet-dominated transgressive-to-early highstand systems tract, and a pisolite or microbialite-dominated late highstand systems tract.

The Andree Land Group includes seven ramp and basin stages: (1) a northward dipping homoclinal mixed siliciclastic-carbonate ramp, (2) a homoclinal carbonate ramp, (3) an aggradational to progradational carbonate ramp, (4) a differentially subsiding carbonate ramp, (5) a flooded carbonate ramp, (6) a drowned ramp, and (7) a re-established carbonate ramp now dipping southwards. Stages 6 and 7 (the Munotbjerg and Waltershausen Gletscher Formations) reveal an episode of rifting probably related to a pre-Vendian opening of the Iapetus Ocean. The Munotbjerg Formation mainly comprises graded carbonate siltstones and black, organic-rich, calcareous siltstones, which represent a base-of-slope environment. Their superposition on carbonate platform sediments reflects the drowning event. The W altershausen Gletscher Formation mainly consists of pisolitic limestones and limestone-mudstone couplets, which represent a reestablished carbonate platform. The drowning event was controlled by accelerated tectonic subsidence, where accumulation of coeval base-of-slope and carbonate platform sequences took place.

The Andree Land Group carbonate ramp records sedimentological aspects that are characteristic of Neoproterozoic carbonate platforms, including ramp architecture, significant influence of storms, large pisoids, molar-tooth structures, and microbialites containing calcified algae. Sedimentary features such as sea-floor precipitates and tidal flat tufas characteristic of Archaean, Palaeo- and Mesoproterozoic carbonate platforms are absent. The unique feature of the Andree Land Group ramp compared to other Precambrian and Phanerozoic examples is the presence of a channel facies belt. Inner ramp channels are known from modem carbonate ramps, suggesting that these should also be expected on ancient inner ramps. This study demonstrates that Neoproterozoic carbonates differ significantly from Archaean, Palaeo- and Mesoproterozoic carbonates. Precambrian analogues should therefore be used with the same caution as Phanerozoic and Modem analogues.

Later Palaeozoic tectonic activity related to the Caledonian orogeny and succeeding basin formation has implications for construction of Neoproterozoic palaeogeographical models in North-East Greenland; comparison between eleven measured profiles across the Western Fault Zone demonstrates that the relative positions of Andree Land Group and the overlying Tillite Group outcrops are changed because of post-depositional sinistral strike-slip movements of 80-90 km along the fault zone. These movements probably took place earlier than the Middle Devonian, and hence the fault zone was not a basin forming feature at least in its early history.
OriginalsprogEngelsk
UdgivelsesstedCopenhagen
ForlagGEUS
Antal sider248
Vol/bind2001
DOI
StatusUdgivet - 19 mar. 2001

Publikationsserier

NavnDanmarks og Grønlands Geologiske Undersøgelse Rapport
ForlagGEUS
Nr.27
Vol/bind2001

Emneord

  • Greenland

Programområde

  • Programområde 4: Mineralske råstoffer

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