Figure 1. A map of the Caribbean Sea, showing the location of ODP Leg 165 sites and sites drilled during DSDP Leg 15.
Figure 2. Summary of correlations between seismic stratigraphy, depths, logging units, lithologic units, and ages at Site 998. Velocities shown are averages derived from the sonic velocity tool within each logging unit. The 1.65 km/s velocity is an average of 1.5 km/s at the seafloor and the first log velocity of 1.8 km/s at 180 mbsf. Although total depth at Hole 998B is 904.8 mbsf, Logging Unit 5 is only defined to 880 mbsf. The bottom of Hole 998B at 904.8 mbsf corresponds to 5 s twt, and volcanic basement lies at 5.15 s twt.
Figure 3. Turbidite frequency and the median and total bed thicknesses vs. age at Site 998.
Figure 4. The distribution of volcanic ash layers at four sites drilled during Leg 165, Site 999 on the Kogi Rise in the Colombian Basin, Site 998 on the Cayman Rise, Site 1000 on the upper Nicaraguan Rise, and Site 1001 on the Hess Escarpment. The figure shows the accumulation rate of megascopic volcanic ash layers as cm/m.y. The data are not corrected for core recovery, as, in general, core recovery was excellent and close to complete in much of the cored section. The distribution of volcanic ash layers defines five volcanic episodes: (1) early to mid-Miocene, (2) mid- to late Eocene, (3) late Paleocene to earliest Eocene, (4) early Paleocene, and (5) late Campanian.
Figure 5. The dispersed ash and terrigenous component in sediments drilled during Leg 165 calculated on the basis of geochemical normative models.
Figure 6. Correlation between %CaCO3 and magnetic susceptibility data for pelagic carbonates at Site 998 and comparison with the Miocene "carbonate crash" equatorial Atlantic (Leg 154) and Pacific (Leg 138) sites from prior ODP legs.
Figure 7. Summary of correlations between seismic stratigraphy, depths, logging units, lithologic units, and ages at Site 999. The location of Site 999 marked on this profile is 800 m west of the actual site location determined by GPS. Correlations with the reflection seismic record were constrained by calculations of two-way traveltime vs. depth derived from compressional velocities measured by downhole logging and laboratory instruments. Velocities shown are averages derived from the downhole sonic tool within each major logging unit. The total depth at Hole 999B of 1066.4 mbsf corresponds to 4.722 twt. The depth of volcanic basement is approximately 1400 mbsf if average velocities measured within seismic unit CB5 are extended to 4.936 s twt.
Figure 8. An overview of the Cretaceous/Tertiary boundary at Site 999. At left is a lithostratigraphic summary of the boundary. The second column from the left shows a photograph of the core sections including and adjacent to the boundary (Sections 165-999B-59R-3, 59R-CC, and 60R-1). In the right center is an image of the boundary from the Formation MicroScanner log (FMS) of the hole. In this image the limestone above the boundary appears light gray (a low conductivity layer), whereas the claystone above and below the boundary is dark (high conductivity layers). The FMS image shows a claystone layer at the base of the limestone, which is about 8 cm thicker than the recovered claystone deposit. We propose that this represents the portion of the boundary deposit that was not recovered. On the far right is magnetic susceptibility log of the recovered core.
Figure 9. Mass accumulation rates for the carbonate and non-carbonate components for the interval bounding the middle/late Miocene "carbonate crash" at Sites 998, 999 and 1000.
Figure 10. Correlation between %CaCO3 and magnetic susceptibility data for pelagic carbonates at Sites 998, 999, and 1000.
Figure 11. Summary of correlations between seismic stratigraphy, depths, logging units, lithologic units, and ages at Site 1000. Correlations with the reflection seismic record were constrained by calculations of two-way traveltime versus depth derived from compressional velocities measured by downhole logging and laboratory instruments. Velocities shown are averages derived from the downhole sonic tool within each major logging unit.
Figure 12. Alkalinity in Site 1000 interstitial waters compared to bulk calcium carbonate contents of sediment. Arrow indicates mean ocean bottom water sulfate composition.
Figure 13. Summary of correlations between seismic stratigraphy, depths, logging units, lithologic units, and ages at Site 1001. Velocities above basement are interval velocities derived from two-way traveltimes to the two prominent reflections "A" and "B" and from drilling depths to each of these seismic horizons. In lithologic Unit IV (volcanic basement) the average velocity from laboratory measurements is given (4.672 km/s) and is used to calculate total depth at 4.736 s twt. An approximately 2-km portion of EW9417 SCS line 10 is displayed with a vertical exaggeration of 10x.
Figure 14. The Cretaceous/Tertiary boundary at Site 1001 on the lower Nicaraguan Rise. On the left is a lithostratigraphy description of the recovered boundary deposit in Section 165-1001B-18R-5. In the center is a core photograph of the unsplit Section 165-1001B-18R-5, (15-55 cm). Note that the dark specks on the surface of the upper Maastrichtian limestone are smectite particles that have been eroded from the basal part of the boundary deposit during drilling. On the right is the Formation MicroScanner downhole log of the K/T boundary interval. The FMS record shows a high-resistivity band (bright to white), which we interpret to reflect the hard limestone immediately above the K/T boundary. It is underlain by a 30-cm-wide zone of low to very low (dark) resistivity, which we interpret as the K/T boundary deposit. The interpretation of downhole magnetic susceptibility logging data of Hole 1001A (See "Physical Properties" section, chapter 1001) and comparison with the magnetic susceptibility log of the recovered cores are also consistent with a 20-to-30 cm-thick in situ boundary deposit at this site. Thus approximately only a third of the deposit was recovered by drilling.
Figure 15. Drilling during Leg 165 recovered volcanic ash layers in Caribbean sediments that have originated by two modes of deposition. Silicic ash layers in the Colombian Basin (A; Sites 999 and 1001) and on the Nicaraguan Rise (Site 1000) are dominantly derived as co-ignimbrite ash fallout from major ignimbrite-forming explosive eruptions in the Central American arc to the west. They are deposited from eruption plumes that are transported to the east in the lower stratosphere. In contrast, many of the Eocene ash layers recovered on the Cayman Rise (B; Site 998) are volcaniclastic turbidites, derived from a relatively local source. We propose that they owe their origin to Eocene activity of the Cayman volcanic arc to the south.
Figure 16. The plate tectonic setting of the Cayman Ridge volcanic arc and the Cayman Rise in the Eocene, based on the results of Site 998 drilling, and from dredging in the Cayman Trough (Perfit and Heezen, 1978). Relations in southeastern Cuba and north Hispaniola are based on Pindell and Bartlett (1990). The Cayman arc is attributed to a northerly subduction of the leading edge of the Caribbean Plate, after collision of the Cuban arc with the Bahamas platform has choked off subduction beneath the Cuban arc. The Eocene (and Paleocene?) subduction beneath the Cayman arc may also have led to backarc rifting of the Yucatan Basin. The middle Eocene cessation of Cayman arc volcanism is taken as the timing of choking of the Cayman arc trench by the thicker component of the Caribbean Plate, leading to a change in the North American-Caribbean plate boundary from one of subduction to one of strike-slip, with the initiation of the Cayman Trough in the middle to late Eocene (Rosencrantz and Sclater, 1986).