A History of Crockerland – The Little Arctic Terrane that Could

Ashton Embry

Crockerland is conceived as an allochthonous terrane which accreted to the Laurentian margin in the Devonian and remained an important source area until the latest Triassic. The history of Crockerland has been interpreted from tectonic analyses, facies analyses, sediment composition, and ages of detrital zircons. It is interpreted that the Crockerland Terrane originated to the east as a fragment of fused Baltica and Laurentia crust on the basis of the common occurrence of both Timanide (500-700 MA) and Caledonide (440-420 MA) zircons in Late Devonian sandstones. The Caledonide-derivation of Crockerland fits well with escape tectonics and the westward migration of terranes in response to the collision of Laurentia and Baltica. Crockerland initially docked in earliest Devonian and the final convergence with Laurentia near the Devonian-Carboniferous boundary is recognized as the climax of the Ellesmerian Orogeny. In Early Carboniferous, the highly deformed portion of the Franklinian succession was affected by extension and the post-Devonian history of Crockerland is recorded in the sediments of the Sverdrup Basin. Substantial amounts of siliciclastic sediment were derived from Crockerland during the Permian. Sediment input increased through the Triassic and Late Triassic, Crockerland-derived sandstones contain numerous detrital zircons of Middle Triassic and Carnian age. This indicates that the drainage systems reaching the Sverdrup Basin stretched all the way to the tectonically active, Pacific margin of Crockerland. Sediment influx reached a zenith in the Norian when Crockerland-derived siliciclastic deposits were up to a kilometre thick and extended over the entire basin. The ages of detrital zircons occurring in the Norian strata indicate that the sediment source included the distant, tectonically active, Pacific margin of Crockerland. Notably, the ages of detrital zircons from Triassic sandstones of Chukotka are very similar to those found in the Late Triassic strata of the Sverdrup Basin suggesting a Crockerland source for the sediments of that area. In latest Triassic, sediment input from Crockerland became very minor. It is interpreted that Crockerland began to rift in the early Rhaetian resulting in a disruption of regional drainage patterns and a huge reduction of sediment supply. Rifting of Crockerland continued throughout the Jurassic and ages of detrital zircons indicate that only local streams from nearby rift shoulders supplied the northern margin of the Sverdrup Basin. In Early Cretaceous the Amerasia Basin opened by the counter clockwise rotation of the Arctic Alaska-Chukotka microplate. Crockerland was dismembered during sea floor spreading and its fragments now form the basement of: 1) the continental shelf and slope adjacent to the northern Canadian Arctic Archipelago, 2) the Chukotka-East Siberia continental margin of Russia, and 3) Chukchi Borderland.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013