Geological constraints for tectonic models of the alpha ridge

Initial interpretations of the CESAR geological samples are re-examined in light of new data from the Alpha Ridge and circum-Arctic region. A composite stratigraphy for the CESAR and Fletcher Island (T-3) pre-Neogene cores shows a sequence of Campanian-Maastrichtian organic-rich terrigenous mud overlain by Maastrichtian-Eocene biosiliceous marine deposits with a low organic content, terminating in volcanoclastic mudstone of Late Eocene age. CESAR core 6 contains a transition zone in which biosiliceous sediment is replaced by volcanoclastic and terrigenous sediment of Paleocene-Eocene age. Palynomorphs provide a Late Eocene age for the volcanic outcrop dredged from Northern Alpha Ridge. Textural and geochemical studies of laminated biosiliceous sediments were made with special techniques for quantitative analyses of very small samples (1-10 mg) and particle sizes of less than 5 microns. Results show that the laminated sediments were deposited very slowly in an oxidizing environment. Laminae in CESAR core 6 mainly reflect cyclical variations in the formation and/or accumulation of particulate iron, probably due to periodic hydrothermal venting. Absence of detrital sediment, sparsity of pyroclastic material and lack of diagenetic alteration of the biogenic sediments suggest that the eastern Alpha Ridge was not an area of major tectonic activity during the Eurekan Orogeny, from ca. 80-40 Ma.