Publication Date:
2023-09-11
Description:
Stable isotope (δ18O), sedimentological and mineralogical analyses were carried out along three sediment cores from the open North Atlantic and the Portuguese continental margin. The core sites are at the far eastern and southern margin of the presumed flow paths of icebergs which flooded the glacial North Atlantic during periods of ice sheet instability resulting in periodic surges of the Laurentide ice sheet. These surges resulted in massive inputs of ice rafted debris (IRD) to the sea floor and are commonly referred to as 'Heinrich' events. The sedimentary composition of the IRD and 'normal' pelagic samples was examined using XRD, DTA, TGA, coarse/clay fraction analyses and abundances of planktonic foraminiferal species. The data show that the IRD layers found in core Ml5612-2 from the mid-Atlantic ridge are clearly coeval with 'Heinrich' events: i.e. they are marked by high amounts of detrital carbonate (2-13% dolomite) and minimum abundances of planktonic foraminifers which are dominated by Neogloboquadrina pachyderma (sin.). On the other hand, the IRD layers in cores from the Portuguese margin often do not carry the characteristic signals of the 'Heinrich' layers in that detrital carbonates and abundances of distinct foraminiferal species are missing from the sedimentaryrecord. However, the mineralogy of three IRD layers 1, 2 and 4 off Portugal is similar to the open North Atlantic 'Heinrich' events Hl, H2 and H4 even though the quantities of the various detrital fragments from cores off Portugal are relatively lower. This suggests that the icebergs passed along the Portuguese margin were of the same rigin as those which led to formation of 'Heinrich' events Hl, H2 and H4 in the open North Atlantic. But the other IRD layers in cores from the Portuguese margin, which could not be equivalent to the 'Heinrich' events, are distinctly different from the 'Heinrich' layers which may be used to infer that during periods of these IRD depositions the icebergs off Portugal may have originated in a different, possibly Scandinavian source.
Type:
Thesis
,
NonPeerReviewed
Format:
text
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