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![(A–H) Chemofacies results visualized on selected core box photographs from the Lloyd Hurt No. 1 core. The top depth for each core photograph is shown. The white numbered x-ray fluorescence stickers illustrate the 2-in. (5-cm) resolution of analysis reported in this study and the colored squares over each sticker are the results from the supervised neural network model classification in this study. Colors represent chemofacies 1–8: chemofacies 1 = blue; chemofacies 2 = orange; chemofacies 3 = green; chemofacies 4 = red; chemofacies 5 = brown; chemofacies 6 = pink; chemofacies 7 = purple; chemofacies 8 = gray.]()
![A chemofacies comparison of the three-component Si–Al–Ca chemical system where each pie chart (A–D) represents an individual chemofacies as labeled. Elemental x-ray fluorescence (XRF) measurements are normalized to Si + Al + Ca = 100 wt. % and averaged over the data subset for each respective chemofacies. This facilitates a quantitative comparison of the chemical compositions between chemofacies. For chemofacies 1, 3, and 4 (A, C, and D), Si is the most abundant chemical component. In chemofacies 2 (B), Ca is the most abundant component, aligning with the assumption that Ca cements are the identifying feature of chemofacies 2 samples. A minor component in chemofacies 2 and 3, Al is considered to represent extrabasinal grain components. Further comparison of the chemical compositions representing each chemofacies is described in the main text.]()
![Element crossplots of all portable energy-dispersive x-ray fluorescence data collected for the Lloyd Hurt No. 1 core grouped according to chemofacies clusters predicted from the supervised neural network model. (A) Concentrations of Si versus Al highlighting the siliciclastic mixing trend and chemofacies with excess Si. (B) Element concentrations of Ni versus Al highlighting elevated Ni in chemofacies 8, 5, and 6. (C) Element concentrations of Mo versus V highlighting distinct chemistries of chemofacies 5 and chemofacies 6. (D) Element concentration of K versus Al illustrating two different siliciclastic mixing trends for chemofacies 3 and 8 (high K/Al trend) versus chemofacies 1 and 4 (low K/Al trend). (E) Molybdenum versus total organic carbon (TOC) illustrating chemofacies 5 plotting along a Mo-enriched trend distinct from the other chemofacies.]()
![Cross-plots between data on XRF-derived brittleness index and unconfined compressive strength (UCS) collected with a Procep Equotip rebound hammer (UCS data from Jaramillo (2024)), colored by chemofacies. It suggests that calcareous and detrital chemofacies are the most brittle intervals, while oxic–suboxic and anoxic argillaceous chemofacies are more ductile.]()
![Elemental ternary and histogram distributions of chemofacies. (A) A calcium (Ca)–silicon (Si)–aluminum (Al) oxide ternary diagram (modeled after Brumsack, 1989). Elemental distributions indicate a dominantly binary depositional system between clay and carbonate minerals with a small silt fraction (which plots closer to the SiO2 end member). Carbonate dilution line indicates increasing compositions of carbonate from an average shale defined by Wedepohl (1970). (B) Total organic carbon (TOC) distributions indicate that the calcareous, organic matter (OM)–rich chemofacies is the most enriched in OM. Conversely, the argillaceous, OM-poor chemofacies is the most depleted in OM. The calcareous, OM-moderate chemofacies demonstrates the widest range of TOC distributions because of the diagenetic fabrics of this chemofacies (Figure 12) that irregularly overprint primary organic-rich mudstone with organic-poor calcite cements and replacive dolomite. (C) Distributions of manganese (Mn) concentrations indicate that the argillaceous, OM-poor and calcareous, OM-rich chemofacies are the most- and least-oxygenated chemofacies, respectively. (D) Distributions of enrichment factor molybdenum (EF Mo) values indicate that the calcareous, OM-rich chemofacies is significantly enriched in Mo and the most oxygen-restricted chemofacies. (E) Distributions of EF nickel (EF Ni) values indicate that the argillaceous, OM-poor and calcareous, OM-rich chemofacies represent the lowest and highest amounts of paleoproductivity, respectively. (F) Distributions of bioturbation index measurements (Table 3) made from petrographic observation of 233 thin sections indicate that the argillaceous, OM-poor and calcareous, OM-rich chemofacies are the most and least bioturbated chemofacies, respectively. (G) Distributions of sediment energy index (Table 4) interpreted from petrographically observed sedimentary textures indicate that the argillaceous, OM-poor and calcareous, OM-rich chemofacies were deposited under the most and least bottom-water energy, respectively, at the time of deposition.]()
![A) Interpolated grain-size data extracted from the digitization of the core description shown in Figure 2. B) Histogram and probability of density function (PDF) of grain-size distributions of each chemofacies. Calcareous chemofacies show bimodal data distribution, indicating strong diagenesis that is confirmed petrographically. Those four chemofacies represent different grain-size distributions from coarser grains to finer grains: detrital, calcareous, oxic–suboxic argillaceous, and anoxic argillaceous. C) Sediment-unit facies distribution of each chemofacies, ranging from the highest to the lowest sedimentary energy. In general, the calcareous and siliciclastic HEBs are widespread in the more proximal parts of the submarine lobe, and followed by the predominantly laminated mudstone and background mudstone in the distal parts.]()
![Results from mechanical index testing (E*) shown in ternary compositional space for each chemofacies. The axes (Si, 5xAl, and 2xCa) are normalized such that the summation of each multiplied component equals 100%. (A) The x-ray fluorescence (XRF) measurements are plotted in ternary space to show the spatial relationships between chemofacies where chemofacies 1 is blue; chemofacies 2 is red; chemofacies 3 is black; and chemofacies 4 is yellow. In (A)–(D), formation is differentiated by shape where the Spraberry Formation (Fm.) is circles, and the Wolfcamp formation (fm.) is squares. Please note that only those measurements with a collocated impulse hammer measurement are shown in this figure, (A)–(D). (B–D) The XRF measurements from each chemofacies are plotted on a respective ternary figure and labeled accordingly. Measurements are colored by E* value and presented with two accompanying core images (numbered 1–6 for reference). Core scale and E* values are described in the legend. Each core image inset (numbered 1–6) represents 0.3 ft of continuous core and an approximate location (dashed box) and measurement range (dashed bars) over which mechanical index measurements were taken (after the method described in Rathbun et al., 2014). Arrows and labels help to correlate core images with respective E* measurement and chemofacies.]()
![Core box photographs and predicted chemofacies for Wolfcamp A illustrating carbonate-dominated HEBs and calcareous turbidites. Chemofacies colors are provided in Table 1 and consistent with chemofacies attributes shown in Figures 4, 5, 8 and 9.]()
![A) Siliciclastic HEB model (H1, H2, H3, LM) with pseudonodules transition to oxic–suboxic mudstone and overlain by laminated mudstone. Bioturbated laminated mudstone and slurry deposits are more common in this deposit. The chemofacies provide significant geomechanical interface predictability. B) Schematic diagram of chemofacies and depositional models in a deep marine environment with elemental proxies of detrital and clay minerals. It shows multiple various sediment sources from siliciclastics-rich and carbonates-rich surrounding the study area of the Wolfcamp XY interval. Chemofacies variability from the proximal to distal part correlates to the sediment-unit facies that vary across turbidite fans. Based on elemental data composition, Si and Ca decrease toward the distal part, whereas Al and K content increase with distance (Hardisty et al. 2021). C) Grain-size distribution through statistical measurement of each chemofacies to support the schematic facies model. The chemofacies of detrital, calcareous, oxic–suboxic argillaceous, and anoxic argillaceous show grain-size variability that ranges from the coarser to finer grains. D) Calcareous-HEB model (H1, H3, H5) with pseudonodules larger than in siliciclastic HEBs and abundant load structures. Anoxic-rich mudstones are more common in this deposit.]()
![Stratigraphic designation of the chemofacies defined using HCA of XRF samples from the YCYV1112 core, in the context of TOC and EF-As. The dominant chemofacies designations, based on elemental enrichments, are color coded to match XRF-, XRD-, and visually observed changes in lithology. Chemofacies 1−4 are all sandstone and siltstone facies, largely reflective of the feldspathic/quartzose and quartzose/feldspathic argillaceous arkose facies defined by Ruppel et al. (this volume). These chemofacies are here called sandstones (Ss) and siltstones (ss), and they are largely separated according to the amount of %Ca (a proxy for calcite) in each sample. The calcite occurs as variable quantities of cement in the coarser-grained facies. Chemofacies 5 is a silty mudstone, and it is associated with higher TOC concentrations. Chemofacies 6 and 7 are pyritic mudstones. Note that Chemofacies 7 generally occurs in intervals characterized by the highest values of EF-As (pyrite proxy). The gray horizontal intervals denote TOC-rich strata (Figure 4). The brown-shaded intervals denote depositional intervals associated with enrichment in RSTEs, and they are labeled as sustained meromixis intervals SM1–SM6 (Figure 9). LT-SM denotes intervals that are low-trace-element sustained meromixis.]()
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![The x-ray fluorescence (XRF) core measurements are plotted in log-log space to compare chemical ratios as indicators of cement and grain content. The circles indicate measurements from the Spraberry Formation (Fm.) and the squares represent those from the Wolfcamp formation (fm.). Annotated XRF measurements represent those with accompanying thin-section samples selected for petrographic or scanning electron microscope (SEM) imaging (refer to Table 1 for detailed compositional information) in this study. Samples annotated in red represent those with SEM imaging and quantitative cement mapping referenced in this paper. Each chemofacies field (numbered 1–4) is annotated, along with the 1:1 line where anything plotting above this line will be enriched in Al-normalized Ca with respect to Si. The two dashed lines represent approximate iso-compositional lines for Al weight percent concentrations. As described in the text, Ca, Si, and Al are chemical proxies for calcite, quartz, and clay mineral content, respectively. When plotted as elemental ratios against Al, increasing Ca (y axis) and Si content (x axis) is interpreted to represent increases in intrabasinal and authigenic grain components (i.e., cements). The breakdown of the 440 XRF measurements presented in this study is as follows: chemofacies 1 = 212 measurements, chemofacies 2 = 42 measurements, chemofacies 3 = 8 measurements, chemofacies 4 = 58 measurements. The primary identifying features of each chemofacies are as follows: (1) siliciclastic detrital grain components, (2) calcite cements; (3) mixed carbonate and microcrystalline quartz cements, and (4) microcrystalline quartz cements. Derivation of each chemofacies field is described in the text.]()
![Random forest chemofacies classification results for cored wells A, B, and C. The Meramec reservoir zones, GR log, actual core-based chemofacies log, and the classified chemofacies log from the random forest blind test are shown in the tracks from left to right. Log data from the wells were divided into two halves with the representative chemofacies percentages. One half was used to build the random forest model and was further divided into a training and testing sets for cross validation. The model was applied to the second half of the original data set for a blind test. The overall accuracy for wells A, B, and C was 75.3%, 77.2%, and 82.6%, respectively.]()
![Bulk organic parameters (%TOC, C/N, δC13org) for the core YCYV1112 compared with the stratigraphic shifts in the HCA-defined chemofacies. Here, the chemofacies have been amalgamated as coarser-grained SS-sS chemofacies and finer-grained mS chemofacies. The gray horizontal intervals denote TOC-rich strata (Figure 4). The brown-shaded intervals denote depositional intervals associated with enrichment in RSTEs and are labeled as sustained meromixis intervals SM1 through SM6 (Figure 9). LT-SM denotes intervals that are low-trace-element sustained meromixis.]()
![Chemofacies show siliciclastic HEB (H2, H3) overlain by thin-bedded bioturbated laminated mudstone (LM). Calcareous HEB with skeletal-rich siltstone (H1), followed by the variability of detrital, oxic–suboxic argillaceous, and calcareous-rich pseudonodular siltstone (H3). The chemofacies variability in this profile is visually interpreted as calcareous HEBs.]()
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Journal Article
Depositional-process controls on chemofacies in mixed-lithology submarine lobe deposits: a high-resolution core study from the Permian Wolfcamp XY Formation, Delaware Basin, Texas, U.S.A. Available to Purchase
Journal: Journal of Sedimentary Research
Publisher: SEPM Society for Sedimentary Geology
Published: 30 January 2025
Journal of Sedimentary Research (2025) 95 (1): 63–85.
... that chemofacies derived using unsupervised machine learning correlate with event-bed interpretations and reservoir-property distribution. Unsupervised k -means clustering and principal-component analysis on 17 XRF-derived elemental concentrations derive four chemofacies that characterize geochemical heterogeneity...
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Journal Article
Machine learning classification of Austin Chalk chemofacies from high-resolution x-ray fluorescence core characterization Available to Purchase
Journal: AAPG Bulletin
Publisher: American Association of Petroleum Geologists
Published: 01 June 2023
AAPG Bulletin (2023) 107 (6): 907–927.
... to characterize the geochemistry of core samples at a resolution that captures thin–layered heterogeneity common to mudrock systems. Here, we developed a training data set using a semisupervised chemofacies clustering approach that is explored with a deep neural network model to predict chemofacies across...
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Journal Article
Classification of elemental chemofacies as indicators of cement diagenesis in mudrocks of the Permian Spraberry Formation and Wolfcamp formation, western Texas Available to Purchase
Journal: AAPG Bulletin
Publisher: American Association of Petroleum Geologists
Published: 01 June 2023
AAPG Bulletin (2023) 107 (6): 863–886.
... cementation in grain-supported packing arrangements, whereas samples dominated by intrabasinal grain components show pervasive cementation in matrix-supported grain assemblages. We present a novel workflow using correlative relationships between elemental Si, Al, and Ca to classify mudrocks into chemofacies...
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Journal Article
A novel integrated approach for chemofacies characterization of organic-rich mudrocks Available to Purchase
Journal: AAPG Bulletin
Publisher: American Association of Petroleum Geologists
Published: 01 February 2022
AAPG Bulletin (2022) 106 (2): 437–460.
...Junwen Peng; Toti E. Larson ABSTRACT A novel integrated approach for chemofacies characterization of organic-rich mudrocks was developed using principal components analysis of 25 elements from core-based energy-dispersive x-ray fluorescence (ED-XRF) measurements and k -means clustering. Using...
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Journal Article
Stratigraphic variability of Mississippian Meramec chemofacies and petrophysical properties using machine learning and geostatistical modeling, STACK trend, Anadarko Basin, Oklahoma Available to Purchase
Journal: Interpretation
Publisher: Society of Exploration Geophysicists
Published: 09 August 2021
Interpretation (2021) 9 (3): T987–T1007.
... and Si/Al). We used an unsupervised K-means classification to cluster elemental data from which we interpret three chemofacies: (1) calcareous sandstone, (2) argillaceous-calcareous siltstone, and (3) detrital mudstone. We used random forest to relate core-derived chemofacies to well logs and classify...
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(A–H) Chemofacies results visualized on selected core box photographs from ... Available to Purchase
in Machine learning classification of Austin Chalk chemofacies from high-resolution x-ray fluorescence core characterization
> AAPG Bulletin
Published: 01 June 2023
Figure 5. (A–H) Chemofacies results visualized on selected core box photographs from the Lloyd Hurt No. 1 core. The top depth for each core photograph is shown. The white numbered x-ray fluorescence stickers illustrate the 2-in. (5-cm) resolution of analysis reported in this study and the colored
Image
A chemofacies comparison of the three-component Si–Al–Ca chemical system wh... Available to Purchase
in Classification of elemental chemofacies as indicators of cement diagenesis in mudrocks of the Permian Spraberry Formation and Wolfcamp formation, western Texas
> AAPG Bulletin
Published: 01 June 2023
Figure 4. A chemofacies comparison of the three-component Si–Al–Ca chemical system where each pie chart (A–D) represents an individual chemofacies as labeled. Elemental x-ray fluorescence (XRF) measurements are normalized to Si + Al + Ca = 100 wt. % and averaged over the data subset for each
Image
Element crossplots of all portable energy-dispersive x-ray fluorescence dat... Available to Purchase
in Machine learning classification of Austin Chalk chemofacies from high-resolution x-ray fluorescence core characterization
> AAPG Bulletin
Published: 01 June 2023
Figure 4. Element crossplots of all portable energy-dispersive x-ray fluorescence data collected for the Lloyd Hurt No. 1 core grouped according to chemofacies clusters predicted from the supervised neural network model. (A) Concentrations of Si versus Al highlighting the siliciclastic mixing
Image
Cross-plots between data on XRF-derived brittleness index and unconfined co... Available to Purchase
in Depositional-process controls on chemofacies in mixed-lithology submarine lobe deposits: a high-resolution core study from the Permian Wolfcamp XY Formation, Delaware Basin, Texas, U.S.A.
> Journal of Sedimentary Research
Published: 30 January 2025
Fig. 17. Cross-plots between data on XRF-derived brittleness index and unconfined compressive strength (UCS) collected with a Procep Equotip rebound hammer (UCS data from Jaramillo (2024) ), colored by chemofacies. It suggests that calcareous and detrital chemofacies are the most brittle
Image
Elemental ternary and histogram distributions of chemofacies. (A) A calcium... Available to Purchase
in Depositional environment and source rock quality of the Woodbine and Eagle Ford Groups, southern East Texas (Brazos) Basin: An integrated geochemical, sequence stratigraphic, and petrographic approach
> AAPG Bulletin
Published: 15 April 2021
Figure 8. Elemental ternary and histogram distributions of chemofacies. (A) A calcium (Ca)–silicon (Si)–aluminum (Al) oxide ternary diagram (modeled after Brumsack, 1989 ). Elemental distributions indicate a dominantly binary depositional system between clay and carbonate minerals with a small
Image
A ) Interpolated grain-size data extracted from the digitization of the cor... Available to Purchase
in Depositional-process controls on chemofacies in mixed-lithology submarine lobe deposits: a high-resolution core study from the Permian Wolfcamp XY Formation, Delaware Basin, Texas, U.S.A.
> Journal of Sedimentary Research
Published: 30 January 2025
Fig. 7. A ) Interpolated grain-size data extracted from the digitization of the core description shown in Figure 2 . B) Histogram and probability of density function (PDF) of grain-size distributions of each chemofacies. Calcareous chemofacies show bimodal data distribution, indicating strong
Image
Results from mechanical index testing ( E* ) shown in ternary compositional... Available to Purchase
in Classification of elemental chemofacies as indicators of cement diagenesis in mudrocks of the Permian Spraberry Formation and Wolfcamp formation, western Texas
> AAPG Bulletin
Published: 01 June 2023
Figure 10. Results from mechanical index testing ( E* ) shown in ternary compositional space for each chemofacies. The axes (Si, 5xAl, and 2xCa) are normalized such that the summation of each multiplied component equals 100%. (A) The x-ray fluorescence (XRF) measurements are plotted in ternary
Image
Core box photographs and predicted chemofacies for Wolfcamp A illustrating ... Available to Purchase
in A machine-learning workflow to integrate high-resolution core-based facies into basin-scale stratigraphic models for the Wolfcamp and Third Bone Spring Sand, Delaware Basin
> Interpretation
Published: 18 October 2023
Figure 7. Core box photographs and predicted chemofacies for Wolfcamp A illustrating carbonate-dominated HEBs and calcareous turbidites. Chemofacies colors are provided in Table 1 and consistent with chemofacies attributes shown in Figures 4 , 5 , 8 and 9 .
Image
A) Siliciclastic HEB model (H1, H2, H3, LM) with pseudonodules transition ... Available to Purchase
in Depositional-process controls on chemofacies in mixed-lithology submarine lobe deposits: a high-resolution core study from the Permian Wolfcamp XY Formation, Delaware Basin, Texas, U.S.A.
> Journal of Sedimentary Research
Published: 30 January 2025
Fig. 18. A) Siliciclastic HEB model (H1, H2, H3, LM) with pseudonodules transition to oxic–suboxic mudstone and overlain by laminated mudstone. Bioturbated laminated mudstone and slurry deposits are more common in this deposit. The chemofacies provide significant geomechanical interface
Image
Stratigraphic designation of the chemofacies defined using HCA of XRF sampl... Available to Purchase
in Chemostratigraphic insights into fluvio-lacustrine deposition, Yanchang Formation, Upper Triassic, Ordos Basin, China
> Interpretation
Published: 16 February 2017
Figure 12. Stratigraphic designation of the chemofacies defined using HCA of XRF samples from the YCYV1112 core, in the context of TOC and EF-As. The dominant chemofacies designations, based on elemental enrichments, are color coded to match XRF-, XRD-, and visually observed changes in lithology
Journal Article
A machine-learning workflow to integrate high-resolution core-based facies into basin-scale stratigraphic models for the Wolfcamp and Third Bone Spring Sand, Delaware Basin Available to Purchase
Journal: Interpretation
Publisher: Society of Exploration Geophysicists
Published: 18 October 2023
Interpretation (2023) 11 (4): SC91–SC104.
...Figure 7. Core box photographs and predicted chemofacies for Wolfcamp A illustrating carbonate-dominated HEBs and calcareous turbidites. Chemofacies colors are provided in Table 1 and consistent with chemofacies attributes shown in Figures 4 , 5 , 8 and 9 . ...
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Image
The x-ray fluorescence (XRF) core measurements are plotted in log-log space... Available to Purchase
in Classification of elemental chemofacies as indicators of cement diagenesis in mudrocks of the Permian Spraberry Formation and Wolfcamp formation, western Texas
> AAPG Bulletin
Published: 01 June 2023
cement mapping referenced in this paper. Each chemofacies field (numbered 1–4) is annotated, along with the 1:1 line where anything plotting above this line will be enriched in Al-normalized Ca with respect to Si. The two dashed lines represent approximate iso-compositional lines for Al weight percent
Image
Random forest chemofacies classification results for cored wells A, B, and ... Available to Purchase
in Stratigraphic variability of Mississippian Meramec chemofacies and petrophysical properties using machine learning and geostatistical modeling, STACK trend, Anadarko Basin, Oklahoma
> Interpretation
Published: 09 August 2021
Figure 10. Random forest chemofacies classification results for cored wells A, B, and C. The Meramec reservoir zones, GR log, actual core-based chemofacies log, and the classified chemofacies log from the random forest blind test are shown in the tracks from left to right. Log data from the wells
Image
Bulk organic parameters (%TOC, C/N, δ C 13 org ) fo... Available to Purchase
in Chemostratigraphic insights into fluvio-lacustrine deposition, Yanchang Formation, Upper Triassic, Ordos Basin, China
> Interpretation
Published: 16 February 2017
Figure 13. Bulk organic parameters (%TOC, C/N, δ C 13 org ) for the core YCYV1112 compared with the stratigraphic shifts in the HCA-defined chemofacies. Here, the chemofacies have been amalgamated as coarser-grained SS-sS chemofacies and finer-grained mS chemofacies
Image
Chemofacies show siliciclastic HEB (H2, H3) overlain by thin-bedded bioturb... Available to Purchase
in Depositional-process controls on chemofacies in mixed-lithology submarine lobe deposits: a high-resolution core study from the Permian Wolfcamp XY Formation, Delaware Basin, Texas, U.S.A.
> Journal of Sedimentary Research
Published: 30 January 2025
Fig. 10. Chemofacies show siliciclastic HEB (H2, H3) overlain by thin-bedded bioturbated laminated mudstone (LM). Calcareous HEB with skeletal-rich siltstone (H1), followed by the variability of detrital, oxic–suboxic argillaceous, and calcareous-rich pseudonodular siltstone (H3). The chemofacies
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