For the first time detailed downhole and core logging measurements have been made on lithologically variable, upper Paleocene, low-latitude sections containing the LPTM. Exact core-log integration is accomplished by detailed correlation of FMS data and continuous high-resolution core log data that allows the construction of a composite core from adjacent holes and correlation between two widely separated sites. The definition of composite sections was also essential for defining postcruise core sampling that verified the recovery of the LPTM by its characteristic negative shift in carbon isotope values.
The LPTM is identified by narrow (short term), co-varying anomalies in core logging data and continuous downhole measurements, which marks an abrupt, distinct, and long-term difference in physical and chemical properties of the strata above and below the LPTM.
With the exception of the FMS log at Site 1001, all downhole logs and high-resolution core logs show no evidence for gradual change preceding the LPTM, while above the LPTM the core-log data do show a gradual transition to pre-LPTM values.
The logging data alone support a multiphase LPTM, including a nearly instantaneous onset followed by a uniform, but very much altered, set of physical and chemical conditions of short duration referred to as the LPTM clay. The LPTM clay is succeeded by a longer transition to a new, more permanent environmental mode called the LPTM interval. The estimated duration of these "phases" relies on assumptions of sedimentation rates, and are consistent with paleontological and isotopic studies of the LPTM.
Whole-core high-resolution XRF data show that the LPTM interval is characterized by an abrupt shift to uniformly low Ca intensities (i.e., carbonate) which is interpreted to reflect a rapid shoaling of the CCD and lysocline. Ca intensities reach minimum values within 4 cm indicating an initiation of the LPTM of less than a few thousand years.
The minimum duration of the LPTM interval and LPTM clay defined by logging anomaly thicknesses and shipboard-derived sedimentation rates range from 21 to 30 k.y. and from 8 to 11 k.y., respectively.
The exact depth placement of the LPTM clay using FMS data coupled with polarity reversal stratigraphy from downhole measurements (V. Louvel and B. Galbrun, unpubl. data), and shipboard-derived sedimentation rates indicate an onset time for the LPTM early in C24r at 55.54 Ma.
The data indicate the presence of unrecovered, discrete ash layers within and surrounding the LPTM interval, which add to the already numerous recovered ash layers that define a late Paleocene-early Eocene pulse of explosive volcanism in the Caribbean region.