v.378P

Stratigraphic correlation support (SCORS) User Guide
Peter Blum, 8 October 2016
V378P

Introduction

Stratigraphic correlation in the context of JOIDES Resolution shipboard operations refers to the construction of a core composite depth below sea floor (CCSF) depth scale for multiple adjacent holes, and a sampling splice composed of core intervals from multiple holes at a site. The CCSF depth scale overcomes many of the inadequacies of the original core depth below sea floor, method A (CSF-A) depth scale. The CSF-A scale is unique to each hole and derives from the length that the drill string advanced. In perfect layer cake stratigraphy, a stratigraphic feature has different CSF-A depths in each hole by up to a few meters because of ship heave (not compensated for in APC coring), tidal variations in sea level, and other sources of error. Furthermore, soft sediment cores regularly show core expansion due to stretching during coring, and elastic rebound and gas expansion upon recovery, resulting in "stratigraphic overlap", or >100% recovery. This means the bottom of an expanded core extends beyond the top of the next core at the CSF-A depth scale. In addition, we know from many multi-hole sites that in fact recovery gaps exist between cores as a result of the coring process, typically ranging from 0.5-2 m. To make things worse, the top of most cores is contaminated with material that fell from the borehole walls into the bottom of the hole and is stratigraphically useless (typically 10-40 cm). It is therefore impossible to recover a complete stratigraphy in a single hole and the most effective approach to achieve a continuous section is to develop a CCSF scale from multiple holes.
Shipboard stratigraphic correlation can be broken down into four (optionally, five) processes, each supported with specific software applications (Figure 1).
1: Download correlation data from the expedition (LIMS) database using the SCORS Downloader.
2: Correlate the downloaded data to create affine table and splice interval table (SIT) files. The affine table file results from depth-shifting cores relative to the CSF-A scale and is used to define a CCSF scale in LIMS. Because of core expansion, the CCSF depths are typically 10%–15% deeper than their CSF-A depths. The SIT results from defining core intervals that best represent the stratigraphy of a site when spliced together. This task is accomplished using the Correlator application or any other program of choice as long as the affine and SIT files are produced to LIMS specifications.
3: Upload affine table (and SIT) to the expedition (LIMS) database. LIMS internal computations store the cumulative offset of each core in the relevant database table and create a CCSF depth scale that can be applied to any data in LIMS.
4: (Optional) (A) Take the user-defined SIT file and use the top and bottom depth (CCSF) of each splice interval to compute core, section, offset, and CSF-A for a "corrected" SIT file (.CORR). Also create a difference report (.DIFF) if any of the aforementioned information is inconsistent between input and output files. This task is accomplished with the SpliceFileFixer program developed to correct and diagnose errors that originated in an earlier version of Correlator. This step is optional now that this aspect of Correlator has been fixed. (B) Upload the (corrected) SIT to the expedition (LIMS) database. LIMS internal computations store identities of the splice interval boundaries in the relevant tables so data can be retrieved by splice.
5:Use LIMS Reports to retrieve uploaded files and LIMS-computed data sets: (A) Lists of existing affine tables and splice interval tables, with links to uploaded user files, as well as the detailed, LIMS-computed affine and splice interval tables; (B) CCSF (alternate) depths for any data set; (C) data sets by selected splice.
Figure 1: Overview of SCORS tools and data flow, and the processes they are associated with. Blue shapes are JRSO supported user applications extracting and/or loading data from/to the LIMS database. Yellow shapes are data files. The green shape is the actual wiggle correlation tool, which may be a generic tool such as Excel, a custom tool such as Correlator, or any application users choose, and which interacts with the LIMS via files that must meet content and format specifications.

Scientists preparing before the cruise on shore can:

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