The rock-magnetic signature of high-latitude northern hemispheric deep-sea sediments and their relationships to Quaternary glacial cycling

• Main Author: Hall, Frank Reginald
• Format: Text
• Language: English
• Published: DigitalCommons@URI 1990
• Subjects: Geology|Oceanography; Alpha Ridge; Arctic; Arctic Ocean; Baffin Bay; Fogo; alpha ridge; Baffin; Ice cap; Labrador Sea; North Atlantic; Polar Ice Cap
• Online Access: https://digitalcommons.uri.edu/dissertations/AAI9120421

Rock-magnetic analyses were performed on sediments from three high-latitude sites and one middle-latitude site of the northern hemisphere. These data were compared with sedimentologic and microfossil information to determine the relationships between magnetic-mineral fluctuations and glaciation in the deep-sea environment. At ODP Hole 645C (Baffin Bay), the magnetic-mineral grain-size parameter $\chi\sb{\rm ARM}$/$\chi$ was shown to fluctuate with respect to the % clay content of the hole. ODP Site 645 represents the oldest sediments studied (Miocene at the base) in this dissertation. The magnetic-mineral concentration ($\chi$), and grain size ($\chi\sb{\rm ARM}$/$\chi$) parameters, along with the % carbonate and $>$ 250 $\mu$m size fraction, show significant peaks above background at 460 mbsf, near the base of the Gauss Chron. From these data, the initiation of northern-hemispheric ice formation was inferred to be approximately 3.4 Ma. Correlation using rock-magnetic parameters of core CESAR83-14 with two cores in the central Arctic Ocean (FL-353 and FL-419) taken nearby at deeper sites on the Alpha Ridge, suggest that a hiatus, which includes the Olduvai subChron, lasting as long as approximately 0.8 my, may be present in the deeper cores. The absence of calcareous microfossils in this interval make it difficult to assign a more accurate length to this apparent hiatus. This hiatus may represent increased bottom current activity resulting from the formation of the polar ice cap. The down-hole variations of rock-magnetic properties at ODP Site 646 (Labrador Sea) were compared with the SPECMAP oxygen isotope curve; an indicator of glacial cycling. During interglacial periods, $\chi$ and $\chi\sb{\rm ARM}$/$\chi$ values are low. These data are probably related to increased biogenic productivity and bottom activity, respectively. Furthermore, the results of cross-correlation analyses suggest that rock-magnetic parameters are in-phase with the oxygen-isotope curve in sediments older than ca. 0.4 Ma but lag the curve in sediments younger than ca. 0.4 Ma. Rock-magnetic analyses performed on sediments from the Fogo Seamounts (western North Atlantic) suggest that two distinct rock-magnetic units can be seen downcore. Unit 1 consists of fine-grained magnetite dominated sediment derived from the Labrador Current and Western Boundary Undercurrent. Unit 2 consists of coarse-grained, hematite dominated sediment derived from the Laurentian Channel. When deposited, unit 2 sediments are seen either during peak glacial times or during glacial-interglacial transitions. The presence of tropical fauna in unit 2 sediments suggest that the Gulf Stream was an important transporting agent.