At Site 991, the uppermost part of the sequence (lithostratigraphic Unit I, 0-2.05 mbsf) is an undisturbed late Pleistocene to ?Holocene nannofossil-rich clay that overlies a disturbed early Pliocene to late Pleistocene interval containing layers of clay conglomerates (Unit II, 2.05 mbsf to bottom of hole, 47.66 mbsf). At Site 992, a similar disturbed interval containing clay conglomerates extends from the seafloor to 9.10 mbsf and has a Pleistocene to ?Holocene age; in concordance with ODP convention, this becomes Unit I for Site 992, even though it more closely resembles Unit II of Site 991. Unit II at Site 992 is an interval of undisturbed, diatom- and nannofossil-rich clay, restricted to the middle late Miocene, and extending to the base of the hole at 50.75 mbsf.
Slumping and mass transport are indicated by the disturbed intervals represented by Unit II at Site 991 and Unit I at Site 992. These represent repeated slumping and transport events (at least three within the Miocene to Pleistocene at Site 991). Much of the section between the upper Miocene and the Pleistocene at Site 992 (which lies above the summit of the diapir) may have been removed downslope by repeated slumping. Site 991, which is located on the flank of the diapir, may have accumulated multiple mass-transport deposits from sediment failures further upslope on the diapir's crest. Alternatively, all of the mass-transport deposits at Sites 991 and 992 may have been emplaced as part of a larger Cape Fear Slide complex (Shipboard Scientific Party, 1996c).
At Site 991, the interval of increased susceptibility is restricted to the uppermost, undisturbed lithostratigraphic unit (Fig. 5). The susceptibility shows a single peak instead of the double or multiple peaks seen at Site 995. The DJH profile, however, is broadly similar to Site 995 (Fig. 6); DJH is a maximum in the shallowest sample (0.4 mbsf) with a value of 0.085, slightly lower than the maximum at Site 995 but still near the middle of the PSD field. DJH declines sharply below Unit I to a minimum of 0.006 at 3.6 mbsf, rises slightly between 6.5 and 13 mbsf to about 0.035, then settles down to less than 0.02 for the remainder of the hole. Coercivity spectra for pARM and dARM indicate an initial population with a peak at around 25-40 mT at 0.4 mbsf, which becomes sharply left skewed at 3.4 mbsf, and exhibits a bimodal coercivity distribution for some samples deeper in the hole (Fig. 7).
Susceptibility at Site 992 forms a broader initial high (Fig. 5), with a series of peaks between 0 and 6 mbsf. Paradoxically, DJH is a minimum near the seafloor (0.03 at 1.2 mbsf) and increases sharply within the interval of high susceptibility to values around 0.5 (Fig. 6), well within the SD field. Coercivity spectra in this interval mirror DJH, with strongly right-skewed pARM and dARM histograms indicating peak coercivities at about 65-70 mT (Figs. 8A, 8B). Below the susceptibility maximum DJH declines sharply to less than 0.03 (in the PSD field, near the boundary of the SPM/MD field), with the exception of a sample at 15.9 mbsf, where DJH lies near the middle of the PSD field, at about 0.08. Coercivity spectra in samples below the high-susceptibility interval all show weakly developed bimodal behavior (Figs. 8C, 8D).