Kentland Crater Bouguer Gravity: Digitization of Tudor's (1971) Contour Map

<p>The Kentland Crater is a well known complex impact structure (i.e. one with a central peak and rim faults) near the town of Kentland in NW Indiana near the Illinois border.  It is particularly notable due as it is the classic site in which the shock deformation indicator 'shatter cones' were found.  There have been numerous investigations of this crater, but Tudor's (1971) study is particularly notable in that it describes an extensive gravity survey covering 13.5 km X 13.5 km are centered on the Newton County Stone Quarry (40.75°N, 87.4°W) about 3 km east of the town of Kentland.  The central peak of the structure is exposed in the quarry (see Fig 1a).  Tudor (1971) collected 2600 measurements of gravity,  but to the best of our knowledge these original data sets have been lost.  His data, however, was reported in a series of large format plates that were scanned by personnel at the libraries at Indiana University in July, 2024.   The data set here consists of the manually digitized contours from Tudor's Bouguer map (his Plate 4).   The files include here are:</p>

<p>1. <strong>README.docx</strong> - a short document providing details of the files in the folder.</p>

<p>2. <strong>Tudor_Bouguer.tif</strong> - TIFF format image of Tudor's (1917) plate 4 used for extracting digitized contours.</p>

<p>3. <strong>outxyz.dat</strong> - ASCII csv format file containing the digitized contours.  Readers may use this file if they want to grid the data themselves.  The format of the file is  COL 1 - longitude, COL 2 - latitude, COL 3 - No data, COL 4 - individual digitized values of the Bouguer contours from Plate 4 (in mgal).  The digitization was carried out using the licensed software SURFER (Golden Software). </p>

<p>4. <strong>Cor_Bouguer.dat</strong> - ASCII (space delimited) format file containing the digitized contours with the latitudinal correction removed (see README.docx for details). The file is the same as <em>outxyx.dat </em>except for the addition of the 7th column that contains the latitudinal corrected values in mgal.</p>

<p>5. <strong>Grav_corrections.m </strong>- Matlab function that carries out the latitude corrections and produces the <em>Cor_Bouguer.dat </em>file.</p>

<p>6. <strong>Scanned_Maps_Tudor_July2024.pdf </strong>- the scanned images provided by Indiana University. </p>

<p>7. <strong>Corrected_Maps.srf </strong>- The Surfer project containing the information shown in the Figure below.  See README.docx for additional details.  Note that the uncorrected Bouguer data is a layer also in this project.</p>

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<p>Tudor, D. S. (1971). A geophysical study of the Kentland disturbed area. MSc thesis, Indiana University.</p>