ALBERT

Description: This paper presents fission-track ages and confined track-length measurements from detrital apatites recovered from Ocean Drilling Program Leg 116 Site 717 and 718 cores. We interpret these data in terms of the post-depositional thermal history at these two sites and the thermotectonic history of apatite source areas. Composite apatite samples were derived by combining fine-grained sand samples from Sites 717 and 718 cores over 70- to 120-m intervals over the total depth penetrated at Sites 717 (T.D. = 820 mbsf) and 718 (T.D. = 960 mbsf). Thirty apatite grains per composite sample from ten samples (at least every other sampled interval) were dated and track-length measurements (20-50 per sample) were obtained for all samples. Mean track lengths from Site 717 samples are statistically identical, ranging from 14.4 ± 0.4 to 14.8 ± 0.3 ?m (all errors are the 95% confidence interval), and mean fission-track ages increase monotonically downhole from 4.8 ± 1.1 to 14.3 ± 2.3 Ma. For Site 718, located approximately 7 km to the south of Site 717 on an adjacent fault block, mean track lengths to 560 mbsf are equivalent to those measured from Site 717 samples. A decrease in mean track length (14.6 ± 0.3 to 13.2 ± 0.4 µm) and a corresponding decrease in mean fission-track age (21.1 ± 2.9 to 15.8 ± 2.4 Ma) with depth for samples between 560 and 960 mbsf from Site 718 indicates that post-depositional downhole shortening of fission tracks at elevated temperatures has taken place. Track-length shortening, based on mean track lengths relative to an unannealed mean track length of 16.3 µm, is approximately 10% for all Site 717 samples and for samples from the upper 560 m of Site 718. The total amount of shortening of the lowermost sample from Site 718 is approximately 20%. Based on extrapolation of published laboratory annealing experiments, maximum isothermal time-temperature condition extremes that could produce this degree of annealing at the base of Site 718 are estimated to range from 50°C for a duration of 17 m.y. (since deposition) to 55°C for a duration of 7.5 m.y. (since the onset of deformation). These estimates argue against regional thermal conduction as the only mechanism for post-depositional heating and support seafloor heat flow and shipboard geochemical evidence for local convective heat transfer in the vicinity of Site 718. In terms of source-area implications, dated samples have mean apatite fission-track ages that are only 0 to 10 m.y. older than depositional ages. These young ages imply rapid transport of sediment to the distal Bengal Fan and source areas characterized by high denundation rates (〈300 m/m.y.). These rates suggest that source areas similar to parts of the present-day Himalayas supplied sediment to the distal Bengal Fan since at least 17 Ma.

Description: Oxygen and carbon isotopic records have been developed for the Cenozoic carbonate oozes of Sites 752, 754, 756, and 757 based on the analysis of monospecific benthic foraminifers. The intent of this report is to provide a basic isotopic stratigraphy for use in other paleoceanographic studies. The oxygen isotope record displays the enrichments associated with cooling or ice volume buildup at the Eocene/Oligocene boundary, in the middle Miocene, and in the upper Pliocene. The carbon isotopic record contains the Chron 16 enrichment in the lower Miocene and the Chron 6 depletion in the uppermost Miocene.