ABI40 Image Data Processing

IODP-MSP drilling and logging contractor: ESO

Hole: M0028A

Expedition: 313

Location: New Jersey (NW Atlantic)

Latitude: 39°33.9427′ N

Longitude: 73°29.8348′ W

Logging date: June 05, June 16-18, 2009

Sea floor depth (driller's): 52.42 m DRF

Sea floor depth (logger's): 52.00 m WRF

Total penetration: 668.66 m DSF

Total core recovered:  385.50 (80.82 % of cored section)

Oldest sediment recovered: Early Micoene

Lithologies: Clays to gravels

ABI40 Lower Section 1: 637.97 – 656.32 m WSF

ABI40 Lower Section 2: 550.58 – 637.97 m WSF

ABI40 Lower Section 3: 426.30 – 550.58 m WSF

ABI40 Middle Section: 396.04 – 429.17 m WSF

The acoustic images show the acoustic hardness of the lithologies within the depositional sequence.

In M0028A, acoustic images have been recorded in the lower and middle sections of the borehole. In the lower interval the tool was run without centralisers as these were too large to fit through the diameter of the small HQ bit. In this section the images were acquired with a resolution of 72 samples x 4 mm, which results in a pixel size of less than 5 (horizontal) x 4 (vertical) mm. For a small interval at the bottom of the lower section the resolution was changed to 144 samples x 4 mm (keeping the same logging speed) as a test. Due to the large size of the image files the data was acquired in three separate files: the processed files were not merged due to small jumps in average amplitude and travel time across each break that can occur when acquisition is halted.

In the middle interval the HQ pipe had been pulled up entirely and so the acoustic tool could be run with centralisers. It was run with a resolution of 288 samples x 2 mm in order to acquire as much information as possible in an interval with poor core recovery. The slower acquisition speed and good centralisation resulted in images of high qualit. However, the orientation of the images to the magnetic north should be treated with caution, due to the close positioning of the centralisers to the magnetometer. There may be a thin mud cake present on the borehole walls. The raw acoustic images were acquired in two separate files but the processed image spectrum data have been combined into a single file due to total coherency across the file break.

The acoustic caliper values were obtained by assuming an acoustic wave velocity of 1495 m/s through borehole fluid and taking the mean value of the measurements at every sample.

The images of the borehole wall (360°), corrected for decentralization effects when possible, are displayed into a two-dimensional view as an unwrapped borehole cylinder. A dipping plane in the borehole will appear as a sinusoid on the image with the amplitude of this sinusoid proportional to the dip of the plane. The images are oriented with respect tothe magnetic north, hence the strike of dipping features can also be determined. A "static" normalization of the images has been applied to enhance structure visualization. Images are provided in PDF format at two different scales. The travel time and amplitude data for each interval logged have also been output in ASCII format.

Additional information about the drilling and logging operations can be found in the Operations section of the Site Chapter in IODP Proceedings of Expedition 313. For further questions about the data, please contact:

Jennifer Inwood

University of Leicester

Phone: 011-44-116-252-3327

Fax: 011-44--116-252-3918

E-mail: iodp@le.ac.uk

Johanna Lofi

University of Montpellier 2

Phone: 033- 467-149- 309

Fax: 033- 467- 143- 244

For any web site-related problem please contact:

E-mail: logdb@ldeo.columbia.edu