Clay mineral evidence of nepheloid layer contributions to the Heinrich layers in the northwest Atlantic

The clay fraction of four cores drilled in the north Atlantic Ocean was stu died at a very high resolution over the last 150 ka in order to record the mineralogical signature of Heinrich events. Factor analysis of clay mineral ogy establishes that three independent factors represent the main variation s: a 'detrital factor' (illite + chlorite + kaolinite), a 'smectite factor' , and a 'mixed-layer factor' (IVML: illite-vermiculite mixed-layered clay). The clay mineral fraction of core SU90-38 drilled in the northeastern Atla ntic basin did not record any Heinrich event, whereas large changes in the clay mineral fraction occurred during Heinrich events H1, H2, H4, and H5 in the three cores from the northwestern Atlantic basin (cores SU90-08, SU90- 11, and SU90-12). Heinrich layers are characterized by increases in the det rital factor in cores SU90-08 and SU90-11, and sharp increases in the mixed -layer factor in cores SU90-11 and SU90-12, The geographical setting of the cores, the pattern of surface, intermediate and deep water circulation, an d the main sources of clay minerals allow recognition of two major mechanis ms involved in the deposition of the Heinrich Layers: (1) an increased supp ly of detrital clay minerals by the icebergs; and (2) a specific input of i llite-vermiculite mixed-layer clay minerals by a nepheloid layer. (C) 1999 Elsevier Science B.V. All rights reserved.