Yamanaka et al. Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-020-00359-7(2020) 7:49

METHODOLOGY

Progress in Earth andPlanetary Science

Open Access

Visualization of the morphology and modeof occurrence of Cenomanian rudists withina drillcore by X-ray CT scanning and 3Dmodeling
Motoyoshi Yamanaka1*, Shin-ichi Sano2, Hamad Bu Alrougha Al Zaabi3, Hiroshi Fujioka4 and Yasufumi Iryu4

Abstract
Rudists are a group of bizarrely shaped marine bivalves that lived in the Tethys Ocean from the Late Jurassic to thelatest Cretaceous. They are morphologically variable, including snail-like, cup-like, and horn-like shapes. In the
Middle East, Cretaceous carbonates with rudists and rudist fragments are well exposed in many outcrops as well as
oil and gas fields. For rudist-bearing carbonates in the subsurface, knowledge of rudist morphology and mode ofoccurrence must be derived from observation of drillcores; however, understanding the three-dimensional (3D)
geometry of rudists from observation of core surfaces is difficult. In paleontological studies of rudists, X-ray
computerized tomography (CT) scans have been carried out to reconstruct the inside texture of rudist shells for the
purpose of taxonomic research. In contrast, in the oil and gas industry, application of X-ray CT scanning technology
is generally focused on direct measurement of reservoir properties. Studies of rudist fossils within drillcores bymeans of X-ray CT have not yet been conducted. We have developed a new protocol to observe core interiors
using X-ray CT. We obtained high-resolution 3D images of rudists in a drillcore by means of surface rendering,volume rendering, and 3D printing. X-ray CT and 3D modeling is a novel method for non-destructive analyses ofthe morphology and mode of occurrence of fossils within drillcores.
Keywords: X-ray CT scan imaging, Surface rendering, Volume rendering, 3D modeling, Drillcore, Rudist, Abu Dhabi,
Cretaceous

1 Introduction
The Late Cretaceous was the only time interval in Earthhistory when bivalves were one of the major components
of carbonate platforms. The bivalves were rudists, agroup of bizarrely shaped marine bivalves living in the
Tethys Ocean from the Late Jurassic to the latest
Cretaceous. They are morphologically variable, including
snail-like, cup-like, and horn-like shapes. Cretaceous
rudist-bearing carbonates are proven exploration targets
for hydrocarbons and form the reservoirs of a number of* Correspondence: motoyoshi.yamanaka@inpex.co.jp
1
JODCO Exploration Limited, 10th Floor, Tower 3, Etihad Towers, P.O. Box
2659, Abu Dhabi, UAE
Full list of author information is available at the end of the article

giant fields, including the Bu Hasa, Fateh, Fahud, Idd El
Shargi, Rumaila, Shaybah, Shah, and Umm Al-Dalkh fields(Neo 1987, 1996; Scott 1990; Alsharhan and Nairn 1993;
Alsharhan 1995; Al-Zaabi et al. 2010; van Buchem et al.
2011; Yamamoto et al. 2016; Kojima et al. 2017; Yamanaka
et al. 2018, 2019a). In the case of the Cenomanian–lower
Turonian Mishrif Formation, which is an importantreservoir rock throughout the Middle East, high porosityand permeability are restricted to the rudist-bearing facies,
which therefore constitute the main oil-producing reservoir zones in this formation. (Alsharhan 1995). The modeof occurrence (presence/absence, distribution, whether autochthonous or allochthonous, and sedimentologicalroles) of rudists in carbonate platforms is of scientific© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give
appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate ifchanges were made. The images or other third party material in this article are included in the article's Creative Commonslicence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commonslicence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain
permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Yamanaka et al. Progress in Earth and Planetary Science(2020) 7:49

importance. The depositional environment of rudistbearing carbonates and their porosity and permeability areclosely related and, thus, important for oil/gas exploration(e.g., Yamanaka et al. 2019b). This is the case for Upper
Cretaceous platform carbonates in the southern Arabian
Peninsula including at Abu Dhabi (Burchette and Britton
1985; Burchette 1993; Skelton et al. 1995; Cestari and Sartorio 1995; Özer et al. 2009).
Cretaceous rudist-bearing carbonates are widespreadin the Arabian Peninsula in outcrop and in the subsurface. Observations regarding rudist morphology andtaxonomy have been mainly derived from outcrop
studies (Skelton and Masse 2000; Schumann 2000), andthis knowledge is the starting point for use of rudists for
sedimentological and paleontological analyses of drillcores. However, in drillcore analyses, observations arelimited to the two-dimensional (2D) core surface and itis therefore very difficult to obtain three-dimensional(3D) information on the sedimentary structure andmorphology of macrofossils, including rudists.
To increase the amount of information that can beobtained from core observation, a 3D imaging techniqueusing X-ray computerized tomography (CT) has been
introduced to the fields of sedimentology (Seard et al.
2010) and paleontology (e.g., Sutton et al. 2014; Racicot
2016), and successful outcomes have already beenachieved.
Hughes et al. (2004) attempted to analyze the outerand inner morphology of rudists within drillcores using
X-ray CT images. However, it was very difficult to delineate the morphology of carbonate shells embedded in a
carbonate matrix with CT values achievable at that time,and only a dim outline of the outer morphology was distinguished. Subsequent studies (Molineux et al. 2007;
Molineux et al. 2010) of rudist morphology using X-ray
CT images dealt with silicified material isolated from a
carbonate matrix. Recently, the spatial resolution of Xray CT images has been greatly increased and newimage-processing techniques such as surface renderingand volume rendering have been invented and markedly
improved. In addition, 3D printers can create precise
plastic figures of objects at low cost. In this article, theseadvanced techniques are applied to rudist-bearing coresamples, yielding clearly delineated 3D images. Here, we
demonstrate the first use of 3D images of rudists for
identification of rudisit taxa and characterization of fossil
occurrences. These advanced techniques will be applicable to many types of fossil and, thus, are expected tosignificantly facilitate progress in paleontology.

2 Methods/experimental
2.1 Material

In this study, one core was collected from Cenomaniancarbonates in the “A field” located offshore of the United

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Arab Emirates (UAE) and 20 km northeast of Abu Dhabi
City (Fig. 1). A reservoir horizon in the A field consistsof Cenomanian shallow water, rudist-bearing carbonates(Neo 1987; Al-Zaabi et al. 2010; Yamamoto et al. 2016).
Five radiolitid genera (Sphaerulites, Praeradiolites,
Eoradiolites, Sauvagesia, and Durania) and one ichthyosarcolitid genus (Ichthyosarcolites) comprise most of therudist occurrences in the Cenomanian carbonate
platform outcrops of northern Oman (Philip et al. 1995).
Similar rudist assemblages are known from Cenomanianstrata in Sinai, Egypt (Saber et al. 2009; Zakhera 2011).
Broken and intact rudist shells belonging to these taxa
are common to abundant and are locally associated with
autochthonous specimens in the high-energy platformmargin/barrier facies of the Cenomanian–lower Turonian sequences on the eastern Arabian Plate (e.g.,
Alsharhan and Nairn 1993; van Buchem et al. 2011).
Therefore, radiolitid and ichthyosarcolitid rudists were
expected to occur in the studied cores.
A core drilled and recovered from shoal facies in thisfield comprised grainstone–packstone–wackestone containing common gravel-sized rudists and fragments of
those rudists. The studied material was a one-third splitof a seven-inch-diameter core (hereafter termed “thecore”; 8 cm long, 7 cm wide) of the packstone (Fig. 2a–e). Rudist fragments were randomly scattered on thecore surface.
The studied material is stored in the Technical Research Center of INPEX Corporation at Tokyo, Japan.
2.2 Work flow

The work flow followed in the present study is summarized in Fig. 3. X-ray CT scanning of the core wasundertaken after initial visual observation of the coresurface, followed by detailed visual study of fossil
rudists on the core surface taking into account the Xray CT scan results. We used a third-generation dualsource medical X-ray CT scanner (SIEMENS,
SOMATOM Definition Flash, Munich, Germany) at theTechnological Research Center of the Japan Oil, Gas
and Metals National Corporation, Chiba, Japan. A
single-source X-ray was utilized with tube voltage optimized to 140 kV and a scanning interval of 0.5 mm.
Approximately 160 slice images were obtained from thestudied core. A “CT value” represents the relative density of an object relative to water (zero) and air (− 1000)
and is expressed in Hounsfield units. For example, CT
values of hard tissues such as bones and teeth range
from 300 to > 1000. In typical X-ray CT images calculated from CT values, darker colors represent soft tissues or porous areas such as pores, whereas lighter
colors indicate hard tissues or dense (non-porous) areas
such as rock. As a result, gray-scale slice images can beobtained at a resolution of 0.2 mm pixel–1.

Yamanaka et al. Progress in Earth and Planetary Science(2020) 7:49

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Fig. 1 Location, schematic cross-section, and lithostratigraphy of the “A field”. a Location of the A field, indicated by a yellow star. b Stratigraphic
outline of the Upper Cretaceous succession in the Abu Dhabi to Dubai area (modified from Al-Zaabi et al. 2010 and Yamamoto et al. 2016). The
stratigraphic interval examined in this study is indicated (red square). A, rudist-bearing porous limestone facies comprising mainly rudist-bearing
rudstone and floatstone with a matrix of grainstone–packstone–wackestone; B, organic-rich dark-gray mudstone–wackestone–mudstone, partially
stylolitized; C, siliciclastic sediments extensively filling the remaining accommodation space in the preceding intrashelf basin; D, platform facies
comprising argillaceous limestone in central and western Abu Dhabi; E, dark grayish-brown to black shale, locally interbedded with dense
limestone. Note that the facies C, D, and E were not deposited in eastern Abu Dhabi, due to uplift of this area. c Schematic cross-section of the A
field (orange color denotes limestone-shoal facies, yellow upper-slope facies, green lower-slope facies, and blue basinal facies). Diagram modified
from Neo (1996)

We applied “surface rendering” and “volume rendering” to X-ray CT scan data to visualize 3D structuresusing Molcer Plus software (White Rabbit Ltd., Tokyo,
Japan). Surface rendering is a method for viewing thesurfaces of masses above a certain threshold of CT value.
Volume rendering is a method for changing opacity tomake the interior contents visible. Surface rendering is adrawing of the “equality surface,” which is a closed surface that allows voxel data to be double-valued at a certain threshold and corresponds to the topographic

contours of the material. Surface rendering is usuallycomposed of a collection of triangular polygons, while
volume rendering displays all voxel values. We createdvolume-rendering images following three steps: at firsttime, determine any one direction, from this voxel column, (1) display the highest value; (2) add a back-sidevoxel value to a front-side voxel value continuously in aline voxel and change the color (pseudo-color) andtransparency on the basis of the voxel values; and (3)prioritize where the voxel values change abruptly. One

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Fig. 2 Core photographs and X-ray CT images. a–e External appearance of the core. Note that rudists A–D, F, H. and I are indicated. a, d Side
view of the external core surface. b, e Side view of the split core surface. c Top view. f, g Vertical slice images of the core obtained by X-ray CT. f
Side view. g Side view of the core at ~ 0.5 cm from the external surface. Horizontal slice images of the numbered horizons (43, 62, 112, 134, 139,
and 153) are shown in Fig. 4. α, Radiolitidae α with a thick outer layer; β, Radiolitidae β with a thin outer shell layer; i, Ichthyosarcolites

3D-printed model was made to identify the growth
history of a rudist based on the results of the surface
rendering (for more details regarding the surface andvolume rendering, see Additional file 1: Document S1).
The rudist (rudist B; see below) had a thick outer shelllayer and was preserved in growth position near the center of the core sample. We created a transparent resin
model with a 3D printer (Objet500 Connex3, Stratasys
3D printer, Tokyo, Japan) at the Tokyo Metropolitan Industrial Technology Research Institute, Tokyo, tovisualize the internal structure of the core. We used atransparent resin, Veroclear (Stratasys Ltd., Eden Prairie,
MN, USA). The outer and the inner shell layers were
produced in different colors; magenta for the inner andcyan for the outer. The mold was polished using acompound to remove the modeling marks. The resin
model is stored in INPEX Corporation at Tokyo, Japan.

3 Results and discussion
By comparing the visual core surface observation,
surface rendering, volume rendering, and 3D modeling,
we discriminated four types of rudists: (1) Radiolitidae α
with a thick outer layer; (2) Radiolitidae β with a thinouter shell layer; (3) Radiolitidae γ, characterized by its
large size; and (4) Ichthyosarcolites (Figs. 2, 4, and 5).
Ten individual rudists assigned to the four types wereidentified in the core, with the following succession fromthe bottom to the top: I, Ichthyosarcolites; A, Ichthyosarcolites; B, Radiolitidae α, showing its early growth stage;
D, Radiolitidae β; E, Radiolitidae β; G, Radiolitidae β; F,Yamanaka et al. Progress in Earth and Planetary Science(2020) 7:49

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Fig. 3 Flow chart of the X-ray CT image analysis conducted in the present study.Two steps of image analysis were conducted for rudists in thestudied core. Step 1 was visual observation of rudists at the core surface (A). Step 2 included direct observation (1, B) and processing of X-ray CT
images of rudists in the core interior. To understand rudist morphology and spatial configuration, two techniques were adopted for X-ray CT
image processing: surface rendering (2) and volume rendering (3) (further details of the surface rendering and volume rendering are provided in
Additional file 1: Document S1). From the results of the surface rendering, one 3D-printed model was made (4). By integrating all results, we
visualized the morphology and mode of occurrence of the rudists

Ichthyosarcolites; C, Radiolitidae α; H, Radiolitidae α;
and J, Radiolitidae γ.
3.1 Visual observation of the core surface and X-ray CT
scan imaging

Seven rudists were identified during initial visual observation of the core surface: four on the external core surface (rudists B, C, H, and I; Fig. 2d) and four on the split
core surface (rudists A, C, D, and F; Fig. 2e). Of these,
two rudists (B and C) were relatively more noticeable.
Rudist B lay in the center part of the external core surface (Fig. 2d, e). This rudist had a conical external shape,
grew upward, and exhibited visible celluloprismatic

structure in its outer shell layer. The growth of rudist C
was directed downward, suggesting an allochthonousmode of occurrence (Fig. 2e).
X-ray CT scan images enabled us to clearly differentiate rudists, matrix, and dissolution cavities even if therudists were somewhat broken and fragmented (Fig. 2f,g). A series of slice images obtained from the X-ray CT
scan was useful in revealing outer shapes, internal
structures, and configurations of rudists in the core. We
describe the rudists in detail below (Additional file 2:
Figure S1).
Three slice images were obtained from the upper(slice numbers 43, 62, and 112; Fig. 4a–c) and lower

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Fig. 4 Horizontal slice images obtained by X-ray CT. a Upper-upper slice (slice number 43 in Fig. 2). Note mesh-like (celluloprismatic) structure in
the center. b Upper-middle slice (slice number 62 in Fig. 2). Note rudist C on the left-hand side. c Upper-lower slice (slice number 112 in Fig. 2).
Note rudists B and C. d Lower-upper slice (slice number 134 in Fig. 2). Four rudists (rudists B, D, E, and G) are present. e Lower-middle slice (slice
number 139 in Fig. 2). Three rudists (rudists B, D, and E) are present. f Lower-lower slice (slice number 153 in Fig. 2). Three rudists (rudists A, D,
and B) are discernible. Rudist B possesses the thick outer shell layer (red arrows in c, d, and e). Yellow arrows in b–f indicate individual rudists(slice numbers 134, 139, and 153; Fig. 4d–f) parts ofthe core. Mesh-like (celluloprismatic) shell structure(rudist C) was recognized in the central part of theuppermost slice (slice number 43; Fig. 4a). Rudist C
occurred also in the left-hand side of the uppermiddle slice (slice number 62; Fig. 4b), which was 9.5mm below slice number 43. In the upper-lower slice(slice number 112; Fig. 4c), two rudist shells (rudists
B and C) were recognized. Rudist B had a thick outershell layer (red arrows in Fig. 4). Four rudist shells(rudists B, D, E, and G) occurred in the lower-upperslice (slice number 134; Fig. 4d); of these, rudist B
preserved a thick outer shell layer. In the lowermiddle slice (number 139; Fig. 4e), which was 2 mm
below the lower-upper slice, three rudist shells(rudists B, D, and E) were discernible. Rudist B still
possessed a thick outer shell layer. Three rudist shells(rudists A, D, and B) were present in the lowermost
slice (number 153; Fig. 4f).

An outer shell layer was not recognized in rudist A.
The slice images indicated that rudist B was preserved in an upright position and had a thick outershell layer. The boundary between the inner andouter shell layers could be easily recognized, although
the inner shell layer was mostly dissolved. The
lattice-like (celluloprismatic) outer shell layer of rudist
C was not apparent in the X-ray CT scan images,
although it could be detected by visual core surface
observation. This difference in the visibility of thestructure is related to X-ray CT resolution. Because
the scanning interval of the X-ray CT image was 0.5
mm per slice, detail that is less than this size, such as
the celluloprismatic structure of the outer shell layer,
cannot be detected.
From visual observation of the core surface and X-ray
CT scan imaging, nine rudists (rudists A–I) were identified. These rudists were grouped into two types on theslice images: rudists possessing a thick outer shell layer(rudists B, C, and H) and rudists lacking a thick shell

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Fig. 5 X-ray CT images processed with a surface-rendering technique. a Surface-rendering-processed images of the studied core. The images areshown in clockwise rotation from the external core surface (left) to the split core surface (right). Orange color indicates rudists inside the core. b
Surface-rendering-processed image (left) and its interpretation (right). Red lines and dots indicate the growth directions and spats from which theshell growth started, respectively. c Occurrences of rudists detected by the surface-rendering technique (left: external core surface, right: split
core surface)layer (rudists A, D–G, and I). Rudist C had a thick outershell layer, which was confirmed to be present by visualobservation of the core but not by X-ray CT imaging.
3.2 Surface rendering

Evaluation of the whole morphology of rudists in drillcores based on the limited and fragmentary information
obtained by visual core surface observation is difficult. It
is possible, by applying a surface-rendering technique to
X-ray CT images of drillcores, to connect such limited
and fragmentary information together to yield a single
image and to understand how the shells of individual
rudists developed (Fig. 5; Additional file 3, Figure S2).
This new information will facilitate taxonomic andpaleoecological studies of rudists.
The images produced by applying the surfacerendering technique show that rudist B, which is cone-

shaped, was located in the central part of the studied
core (Fig. 5), in close proximity to rudist A below andrudist C above. The images also indicate that rudist A
grew obliquely to the sea bottom and may have retained
its growth position in bioclastic sediments during burial.
Rudist B settled on a hard substrate (see “volume rendering”) immediately adjacent to rudist A shortly after
settlement of the latter judging from the short distance
between the base of the two rudists. Rudist B grew in a
conical shape while developing the thick outer shelllayer. It is noteworthy that the surface-rendering technique made apparent the isolation of rudist B fromrudists A and C; in other words, the outer layer of rudist
B was not connected with those of rudists A and C. Rudist C was an allochthonous, fragmented shell in an
inverted position overlying rudist B, suggesting postmortem transportation of the former. The reconstructedYamanaka et al. Progress in Earth and Planetary Science(2020) 7:49

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Fig. 6 X-ray CT images processed with a volume-rendering technique. a Volume-rendering-processed images of rudist B in the studied core. The
images are shown in clockwise rotation from the external core surface (left) to the split core surface (right). b Enlarged images of the spat ofrudist B

succession indicates that three rudists did not bud fromindividuals located below (in other words, did not settle
on individuals located below) but grew independently.
The images produced with the surface-rendering technique also demonstrate that rudists D and E started to
grow on the flank of rudist B near its base (Fig. 5c).

3.3 Volume rendering

Volume rendering, unlike surface rendering, makes it
easier to recognize objectives as hologram images (Fig.
6a; Additional file 4: Figure S3). Volume rendering
revealed two modes of rudist occurrence in the core: inthe original growth position (four rudists: rudist A andFig. 7 Three-dimensional modeling of rudist B. a External surface of the studied core seen diagonally from the bottom right. b, c 3D model ofrudist B seen from the external core surface (b) and the split core surface (c). Magenta and cyan colors indicate the inner and outer shelllayers, respectively

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possibly rudists B, D, and G); and fragmented and in astanding or inverted position (e.g., rudist C; Fig. 5).
The detailed images (Fig. 6b) of the basal part of rudist
B clearly indicate that its growth began from the settlement of a juvenile (spat in Figs. 5 and 6) on a hardsubstrate such as a rock or a shell fragment. This finding
is consistent with the direct observation of settling ofjuvenile specimens onto gravel or the shells of adultrudists (Gili and Götz 2018).
This type of growth process is generally difficult toinfer from visual observation of core surfaces because
the observable area is very limited (8 cm long and 7 cmwide), and the interior of the core is not visible. Volume
rendering enables rotation of 3D images, which is usefulin taxonomic identification and analysis of the mode ofoccurrence of rudists. However, experience of the technique is required to determine the threshold at which
CT values should be rejected as noise on the image ofthe rudist surface during 3D modeling.
3.4 3D printer modelingTo visually understand the relationship between the
inner shell layer and the outer shell layer (Fig. 7;
Additional file 5: Figure S4), we made a 3D-printed
model using the surface-rendering technique for rudist
B, which is preserved in an upright position and has arelatively thick outer shell layer (Fig. 8). The created 3Dprinted model yielded information on the growth historyof rudist B. Figures 7 and 8 indicate that the outer shelllayer started to be developed from 7 mm above the baseof the inner shell layer, and subsequently extended upward to wrap around the inner shell layer. Finally, bothinner and outer shell layers grew upward together.
The 3D-printed model also clearly shows the settlement of the juvenile of rudist B. This is the first detection of a rudist spat in the interior of a core.
3.5 Evaluation of X-ray CT imaging and image processing

We show, in Fig. 9, a comparison of the occurrence ofrudists detected by visual observation of the core (Fig.
9a, b), the surface-rendering technique (Fig. 9c, d), andthe 3D-printed model (rudist B, Fig. 9e). We identified
seven rudists by means of visual observation of the coresurface and extracted limited information on theirmorphology and mode of occurrence (preservation state,
spatial distribution, and growth history). However, thecombination of several methods allowed identification of
10 rudists assigned to four types in the studied core.
Surface and volume rendering were useful in identifying
the initiation (settlement), development, and successionof rudists in the core interior. The volume-rendering
technique and the making of a 3D model from a transparent resin allowed observation of the rudists from all
directions.

Fig. 8 Three-dimensional printed model of rudist B. Photographs ofthe studied core (left) and images of the 3D model of rudist B(right). a High-angle images. b Images of the external core surface. c
Images of the split core surface. Magenta and cyan colors indicate
the inner and outer shell layers, respectively

4 Conclusions
X-ray CT imaging, combined with surface rendering,volume rendering, and 3D modeling, allows us to obtainvarious types of information on rudists, such as theirmorphology (including the presence/absence of pores/
voids within shells), mode of occurrence (including

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Fig. 9 Visualization of the morphology and mode of occurrence of rudists in the studied core. Comparison of the occurrences of rudists detectedby visual observation: a external core surface, b split core surface; and the surface-rendering technique: c external core surface, d split coresurface. The 3D model of rudist B is also shown (e). Magenta and cyan colors indicate the inner and outer shell layers, respectively

preservation states), and distribution in core samples.
This information will be useful in analyzing the sedimentary facies and paleoenvironment of rudist-bearing
carbonates and the paleoecology of rudists. We consider
that, if X-ray CT images become part of the routine
work of core analysis, this process will yield an important database for taxonomic, phylogenetic, and functional
morphological research on many fossils as well as sedimentological analysis of various deposits regardless of
their geological ages.
Application of X-ray CT imaging to petroleum engineering has already led to advances in our understanding of quantitative representation of the porosityand permeability of oil and gas reservoir rocks. The
combination of X-ray CT imaging with the threetechniques for visualizing the CT data allows us toclarify the morphology and vertical and spatial development of rudist bioherms/biostromes and delineate
their initiation, development, and demise. This information is essential for creating and improving geological models for oil/gas exploration. In addition, ournew techniques for studying core samples, in combination with direct visual observation, enable identification of rudists at the species level if they are in agood state of preservation, which will facilitate futurestudies of rudist biostratigraphy. Furthermore, we canaccurately estimate the number of rudists in a sample
and delineate their occurrence (e.g., autochthonous or
allochthonous), which is essential for reconstructing
rudist paleoecology.
Our study clearly indicates that X-ray CT imaging
and related techniques can yield new visual data thathave not yet been collected. This source of new

information will potentially expand our paleontologicaland paleoecological knowledge as well as assist in development of oil and gas exploration technology. Many
drillcores have been obtained for oil and gas exploration in many fields, leaving numerous core samples
that have been left uninvestigated after conventional
measurements and analysis. Our results highlight thepotential of such cores as an important data source for
future studies in Earth science.

5 Supplementary information
Supplementary information accompanies this paper at https://doi.org/10.
1186/s40645-020-00359-7.
Additional file 1: Document S1 Notes on the surface and volume
rendering techniques.
Additional file 2: Figure S1 Movie file of X-ray CT imaging.
Additional file 3: Figure S2 Movie file of X-ray CT imaging processedwith a surface-rendering technique.
Additional file 4: Figure S3 Movie file of X-ray CT imaging processedwith a volume-rendering technique.
Additional file 5: Figure S4 Movie file of the 3D model of rudist B.

Abbreviations
3D: Three-dimensional; CT: Computed tomography

Acknowledgements
The authors thank ADNOC Offshore and INPEX Corporation/Japan Oil
Development Company (INPEX/JODCO) for their support and permission to
publish this work. The authors also thank the Japan Oil, Gas and Metals
National Corporation (JOGMEC) and White Rabbit for their support andassistance with the core observation, sampling, and 3D image modeling. The
manuscript was significantly improved by the comments and suggestions of
K. Endo (editor) and two anonymous reviewers.

Yamanaka et al. Progress in Earth and Planetary Science(2020) 7:49

Authors’ contributions
MY and SS conceptualized and designed this study. MY conducted the X-ray
CT imaging and image processing. SS performed paleontological analysis. SS,
HAZ, HF, and YI collaborated with the corresponding author in the interpretation of the data and the construction of the manuscript. All authors readand approved the final manuscript.
Funding
This work was partly supported financially by JODCO Exploration Limited
and Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS KAKENHI) to Y.I. (26302008).
Availability of data and materials
Please contact the corresponding author regarding data requests.
Competing interests
The authors declare that they have no competing interests.
Author details
1
JODCO Exploration Limited, 10th Floor, Tower 3, Etihad Towers, P.O. Box
2659, Abu Dhabi, UAE. 2Department of Earth System Science, School of
Sustainable Design, University of Toyama, Gofuku, Toyama 930-8555, Japan.
3
Satah & Umm Al Dalkh Field Development Division, ADNOC Offshore, P.O.
Box 303, Abu Dhabi, UAE. 4Institute of Geology and Paleontology, Graduate
School of Science, Tohoku University, Aobayama, Sendai 980-0856, Japan.
Received: 13 February 2020 Accepted: 6 August 2020

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