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GSA Data Repository Item 2017086. Samples, Analytical conditions and methods.

GEOLOGIC SETTING OF THE STEEN RIVER IMPACT STRUCTURE

The Steen River impact structure (SRIS) is a buried complex crater of the central uplift type in NW Alberta, Canada (Figure DR1) and is named after the river that runs across its eastern boundary. The SRIS is located approximately 710 km NW of Edmonton, and lies within 40 km of the Zama oil and gas field. At the time of impact the target rocks included a 70 m layer of Mississippian calcareous shale underlain by ~1530 m of Devonian carbonates, evaporites and shales belonging to the Wabamun Group, Hay River shale and Elk Point Group. This ~1.6 km sequence of generally flat-lying sedimentary rocks unconformably overlies Lower Proterozoic rocks of the Great Bear Magmatic Arc and Hottah Accreted terrain, thought to be joined along a faulted contact (Figure DR 1). The diameter is not well constrained in the public domain but is widely cited as 25 km diameter. An irregular disturbed zone extends out from this structural rim. The age of the crater was originally quoted by Carrigy and Short (1968) to be 95 ± 7 Ma, which can be recalculated to 91 ± 7 Ma using more recent decay constants. This age is based on K-Ar whole rock data from a single sample described as a “pyroclastic vesicular rock” and the SRIS therefore remains a candidate for additional isotopic analyses to confirm the timing of impact.

There is no surface expression as the SRIS is completely covered by post-impact sedimentary rocks. Geophysical and drilling techniques have been used to explore the structure; however the geophysical data is proprietary and generally not publically available. The SRIS was discovered in 1963 by petroleum exploration drilling on a geophysical anomaly, undertaken by what was then Imperial Oil Enterprises. This hole (12-19-121-21W5; Figure DR2), generally cited as the crater center, penetrated ~185 m of Loon River Shale, followed by “suevitic breccia” which contains clasts showing a range of shock deformation features include planar features in quartz and feldspar. Large blocks of granitic rocks from the Precambrian basement were intersected by the core and are interbedded with brecciated zones (some described as melt-bearing). The hole bottomed in what was described by Carrigy and Short (1968) as green-colored impact glass. This central hole was only partially cored in irregular intervals. The following year (1964) a second well was drilled ~8 km west of 12-19 by Imperial Oil Enterprises (16-19-121-22W5). This well passed through ~215 m of steeply dipping Devonian and Mississippian (?) beds, before encountering a “normal” Devonian sequence. However, these normal Devonian rocks were down dropped ~600 m from levels in holes outside of the structure. Thin beds of “tuff” are described within the Cretaceous sediments but it is unclear whether these are related to the SRIS. A ~1 m layer of breccia containing clasts from sedimentary and igneous rocks was also described from this core. Three continuous but shallow diamond drill core – ST001, ST002 and ST003 – were collected by New Claymore Resources in 2000. These core were drilled in an effort to assess the precious and base metal mineral potential of the SRIS and are currently housed at the Mineral Core Research Facility in Edmonton, Alberta. These core were logged and details of their petrography, mineralogy, geochemistry and geophysical analyses were published in an open file report by the Alberta Geologic Survey in 2001 (Molak et al.).

This outline of the geology of the SRIS was drawn largely from the work presented in Carrigy and Short (1968), Molak et al. (2001) and Grieve (2006).

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Figure DR1. The location and size of the SRIS including the sites of cored and partially cored wells in close proximity to the crater (map modified from Molak et al., 2001). The sketch of the base map is taken from the Geological Atlas of the Western Canada Sedimentary Basin (Burwash et al., 1994) with some important modifications. The inner circle has been simplified to show a smoothed outline of the central uplift, with ST003 at the margin of this feature. The outer solid circle denotes the structural rim of the crater and has also been smoothed with cross cutting normal faults omitted. The down-dropped zone, which is a little inside the main 22-25 km structural boundary of the crater has been removed to declutter the sketch. The cross-section of the SRIS runs approximately E-W (B-B’) and is modified from Molak et al. (2001) with extrapolations of the crater fill deposits removed. Instead the thickness of the crater fill deposits is derived from their thickness in ST003 and 12-19-121-21W5, as well as cores ST001 and ST002 (not shown in the cross section). The core studied (ST003) penetrated the allochthonous impactites of the crater-fill deposits and the side of the central uplift.

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Figure DR2. Simplified core log of ST003 showing upper 206 meters of post-impact sediments – mostly lower Cretaceous marine shale and sandstone of the Shaftesbury, Loon River Shale and Bluesky Formations logged by Molak et al., (2001) and the underlying, older impactites which form the crater-fill deposits of the Steen River impact structure. The bottom 11 m of the core penetrated a shock-veined plagioclase-orthoclase-quartz-pargasite-annite gneiss, as studied by Walton et al., (2016). Open circles show sampled core depths from which polished thin sections were prepared but not reported on in this study. Black circles show sampled depths from which the detailed mineralogy and petrology performed on polished thin sections form the basis of this study. The numbers adjacent to the circles (1-30 with increasing depth) are referenced in table DR1 which provides a basic core description and the specified depth.

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PETROGRAPHY. Seventy two thin sections were prepared from the ST003 core sampled below a depth of 206 m to the bottom of the hole (381 m). Preliminary investigation of these thin sections using transmitted light microscopy with a ZEISS Axio Imager petrographic Microscope in reflected and transmitted light facilitated the identification of shock microstructures in quartz and feldspar grains (planar features), and documentation of lithic clasts. The matrix comprises small grains of a widely disseminated, dark to light green, high birefringence mineral which was confirmed through Raman spectroscopy and EMP spot analyses, to be high-Ca pyroxene. Other matrix minerals include feldspar, titanomagnetite, titanite, grossular, andradite, calcite, quartz, magnesioferrite and fine-grained clay minerals, identified through a combination of composition, spectroscopic and optical properties.

SCANNING ELECTRON MICROSCOPY

Back-scattered electron (BSE) and secondary electron (SE) images of polished thin sections were obtained using a Zeiss EVO MA LaB6 filament SEM equipped with a Si diode detector and a ZEISS Sigma Field Emission SEM equipped with a high resolution Bruker dual detector energy dispersive X-ray spectroscopy system (University of Alberta, UAb). These instruments were operated under conditions of 20 kV (accelerating voltage) and an 8-10 mm working distance. The BSE images were imported into a commercial image analysis program to make accurate measurements of features such as grain, fragment and melt thickness. These measurements were made in the two dimensions provided by the thin section and therefore represent apparent dimensions.

ELECTRON MICROPROBE ANALYSIS

Major and minor element geochemical analyses were carried out at the University of Alberta on a Cameca SX100 and a JEOL 8900 electron microprobe analyzer (EMPA) using a 1 µm beam, an accelerating voltage of 15 kV and a beam current of 10 nA for minerals. Count times were 30 s on peaks and 15 s on the background (Table DR1). Natural and synthetic silicate and oxide standards were used for calibration. Raw data were corrected for matrix, absorption, stopping power and fluorescence with the ZAF procedure. For oxides and titanite, the total iron was measured as FeO (wt% oxide) and the proportions of ferric and ferrous iron was calculated following the method of Droop (1987) based on overall charge balance. This necessitates 3.000 cations per 4.000 anions. Major and minor element geochemistry from EMPA analyses is given in Table DR1.

LASER ABLATION INDUCIVELY COUPLED PLASMA MASS SPECTROMETER

Trace element geochemistry of spinel group minerals were carried out at the University of Alberta on a New Wave 213 nm Laser Ablation ICP-MS. A Nd-YAG laser was focused on individual grains to a spot size of 40 μm. In total 27 magnesioferrite grains were analyzed for Cr,

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Ni, Cu, Ga, As, Ru, Rh, Pd, W, Re, Os, Ir, Pt and Au. For some elements, more than one isotope was measured; however, the value reported is not the concentration of just that isotope but the entire weight of the element. Elements with disparate isotope results are interpreted to result from interference and are excluded. Data are reported in ppm together with the 2-sigma internal measurement error which was determined by taking the standard error of the mean from all the mass sweeps for each individual isotope:

𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑒𝑠𝑠𝑒𝑠 =𝑠√𝑠

Where s = standard deviation and n = number of sweeps for each mass range. Each sweep of the mass range takes ~1 s. Acquisition for analyses varied from 17 s to 30 s depending on the analyses which the shorter duration analyses resulting from complete ablation of the grain. The limits of detection (LOD) are calculated by averaging the reported LOD for all the analyses and standards (excluding null values). For highly siderophile elements of interest (e.g., Ir) the LOD was ~0.2 ppm. These elements (Os, Ir, Ru, Ph, Pt, Pd, Re and Au) are of particular interest for magnesioferrite because they can be used to indicate a component of the chondritic projectile. Magnesioferrite grains found in the K-Pg boundary clays contain 29 ± 11 ppb Ir (Bohor et al., 1986), which is taken to indicate a component of the projectile in the vapor plume from which the grains condensed. Such low concentrations are not detectable using the system employed in this study.

RAMAN SPECTROSCOPY

Micro-Raman spectra of various mineral and glass phases were obtained with point measurements by means of a Bruker SENTERRA instrument at MacEwan University. An Olympus BX51 petrographic microscope was used to focus the excitation laser beam (532 nm line of Ar+ laser) and to collect the Raman signal in the backscattered direction. With the 100X objective lens, the focal spot size was ~1 µm in diameter. The spectrometer was operated in confocal model with the real volume resolution assessed to be better than 1.5 µm laterally and 2-3 µm in depth. The wavenumber accuracy (calibrated using a Ne lamp emission) was and the spectral resolution was 2-3 cm-1. A sequence of two-10 s exposures was acquired using a laser power of 10 mW. These multiple exposures were then summed to achieve the final spectrum. Backgrounds of the spectra were graphically reduced using commercial software.

MODAL ABUNDANCE

Volume % abundance of the various components of the 120 m breccia unit as intersected by the ST003 drill core are based on image analysis using commercial software. Measurement of the volume% abundances of matrix, mineral and lithic fragments, as well as impact melt clasts

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were made on photographs of the cut and polished surface of the sampled core. The core measured (sampled at depths of 251.5 m, 268 m, 279 m, 290 m and 304 m) avoided larger lithic clasts (decimeter-size) visible in the core and therefore the % abundances drastically underestimate the clasts proportion in the 120 m thick breccia unit as a whole. Proportions of the matrix component (<1 mm size crystals of pyroxene, oxides, feldspars, quartz, impact melt and interstitial clay + pore space) were made on SEM BSE images acquired at 150X magnification on thin sections from the same sampled depths. The greyscale contrast between alkali feldspar and plagioclase was not sufficient to discriminate between these two minerals and the modal abundance therefore reports this simply as “feldspar”. The image analysis also could not distinguish between feldspar clasts inherited from target rocks and newly formed crystals in the matrix. Material interstitial to matrix minerals comprises clays and open space. It is assumed that much of the pore space was originally occupied by clays, but that this soft material was lost during the sampling process (cutting with the rock saw and subsequent polishing). The results are compiled in Table DR3.

Table DR1. SIMPLIED ST003 CORE LOG. THE NUMBERS (1 TO 30) REFER TO VARIOUS SAMPLED CORE DEPTHS SHOWN SCHEMATICALLY IN FIGURE DR1.

Number in Figure DR1

Depth meters (feet)

General Description

1 210 (688.5) Grey, friable portion of the core, mineralogy dominated by matrix calcite and carbonate clasts, rare shocked granite. Evidence for carbonate melting in the form of carbonates intergrown with lechatelierite spherules. Rare clasts of pale grey impact melt are noted.

2 214 (703) Grey, friable portion of the core, mineralogy dominated by matrix calcite and carbonate clasts, rare shocked granite. Evidence for carbonate melting in the form of carbonates intergrown with lechatelierite spherules. Rare clasts of pale grey impact melt are noted.

3 220 (722) Core becomes more coherent (compared to upper, more friable portions of the core – 210 / 214) as clasts of pale (beige / grey) impact melt increase in abundance. The mineralogy is dominated by calcite in the matrix and carbonate clasts, some clasts of shocked granite and shale / mudstone. Evidence for carbonate melting in the form of carbonates intergrown with lechatelierite spherules.

4 222 (728) Core color is predominately beige with a patchy reddish tinge. Samples collected at this interval contain several larger (mm-size) clasts of shocked granite and carbonates. Pale clasts of contorted impact melt are abundant.

5 226 (742) Core color is predominately beige with a patchy reddish tinge. Core sampled at this interval contains several larger (mm-size) clasts of shocked granite and carbonates. Pale clasts of contorted impact melt are abundant.

6 230 (753.5) Core color is predominately beige with patchy reddish tinge. Core sampled at this interval is rich in clasts of pale beige to reddish impact melt. Lithic clasts of carbonates and basement granites are noted, as are clasts of impact melt.

7 237 (777) Core color has a distinctly reddish coloration. Clasts of impact melt are dark brown / reddish brown. Lithic clasts of carbonates and basement granites are noted.

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8 240 (786) Core color has a distinct red coloration. Clasts of impact melt are dark brown / reddish brown. Most impact melt clasts are amoeboid shape, one larger mm-size clast of impact melt possesses an angular shape. Lithic clasts of carbonates and basement granites are noted.

9 242 (794) Core has a distinct green color. Matrix mineralogy is dominated by widely disseminated poikilitic clinopyroxene, feldspar and oxides (Ti-magnetite). Pyroxene exhibits a skeletal morphology. Clasts of dark (black) impact melt become abundant. Some clasts of pale impact melt are noted. One mm-size carbonate clast is present.

10 251.5(825) Core takes on a distinct green color. Matrix mineralogy is dominated by widely disseminated poikilitic clinopyroxene, feldspar and oxides (Ti-magnetite). Pyroxene has a skeletal morphology. Clasts of dark (black) impact melt become abundant. The first crystal clusters of magnesioferrite are observed in thin section 825B.

11 268 (878) Green matrix (clinopyroxene + feldspar and oxides in clay) with granitic fragments (mostly highly altered feldspars, can only tell by remnant twinning), large amount of black glass mostly amoeboid shape, a few angular glassy clasts (quenched impact melt). Matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite) and magnesioferrite are observed throughout the matrix.

12 12 (cont’d)

279 (914.5) 279 (914.5) cont’d

Core is distinctly green colored. This sample contains the contact between a cm-size granite fragment enrobed by grey-colored, foliated (flow-banding parallel to clasts margin) impact melt in contact with green matrix containing clasts of dark impact melt (opaque to cloudy grey color). Mineral and lithic fragments from granitic basement rocks. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite) and magnesioferrite (plus associated minerals including pyroxene, calcite and quartz) are observed throughout the matrix.

13 284 (933) Core is distinctly green colored. The core sample contains the contact between matrix and a larger (cm-size) granitic fragment. Unlike 279 (914.5) this lithic clast is not enrobed by impact melt. Green matrix defines the color of the core attributed to wide spread calcic pyroxenes (diopside, hedenbergite and augite) + feldspar (zoned) + oxides (zoned) have crystallized. Amoeboid shape black / opaque glass (now devitrified). Mineral and lithic fragments from granitic basement. One partially decomposed carbonate clast (granoblastic calcite) is noted in this interval mantled by a rim of clay minerals. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

14 285.5 (937) Core is distinctly green colored. The core sampled at this interval contains the contact between green matrix and two larger (cm-size) granitic clasts. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

15 290 (950.5) Core is distinctly green colored containing clasts of black impact melt with flow textures and largely quartz fragments. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

16 301 (987) Core is distinctly green colored. The core sampled at this interval represents the contact between a cm-size granitic clast at the matrix. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and

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oxides. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

17 304 (997) Core is distinctly green colored. The core sampled at this interval represents the contact between a cm-size granitic clast at the matrix. The granite clast is partially mantled by black impact melt and is cut across (intruded by impact melt). The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

18 324.5 (1064.5) Core is distinctly green colored. Sample contains matrix between two granitic fragments. Matrix contains black glassy impact melt. Granitic fragments contain mica and amphibole which have decomposed to an oxide + pyroxene + feldspar assemblage associated with apatite and titanite. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Zeolite minerals (epistilbite) noted as radiating transparent crystal clusters filling a larger mm-size vug in the core.

19 336 (1102) Flow textured margin of a granitic clast in contact with green matrix. Glasses are of feldspar and quartz composition.

20 344 (1129) Centimeter-size shocked granitic clast embedded in green colored matrix. 21 21 cont’d

353.5 (1160) 353.5 cont’d

Core is distinctly green colored. Impact melt clasts are pale colored (beige) in this interval. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

22 355.5 (1166) Core is distinctly green colored containing opaque clasts of impact melt and shocked granitic basement rocks. The matrix mineralogy is dominated by euhedral poikilitic crystals of clinopyroxene feldspar, titanite and oxides. Zeolite minerals (epistilbite) noted as radiating transparent crystal clusters filling a larger mm-size vug in the core. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed throughout the matrix.

23 360.5 (1183) Melt-rich portion of the core (distinctly dark brown colored). Clasts of ballen quartz are noted in this interval. The matrix contains fine microlites of feldspar with interstitial clinopyroxene and oxides. Clasts of shocked granitic basement contain toasted quartz with planar fractures. Along their edges and at interstices, thin seams of matrix groundmass are recognizable so that this might be best described as impact melt agglomerate, rather than a coherent lens of impact melt. Heterogeneously-distributed crystal clusters of garnet (andradite), magnesioferrite, magnetite and granular pyroxene + feldspar+ oxide assemblages are observed.

24 362.5 (1189) Centimeter-size clast of shocked granitic basement rock. 25 365 (1197) Melt-rich portion of the core (distinctly dark brown colored). Clasts of ballen quartz

are noted in this interval. The matrix contains feldspar laths (K-spar zoned to albite rims) interstitial clinopyroxene and oxides. Clasts of shocked granitic basement contain toasted quartz with planar fractures. Along their edges and at interstices, thin seams of matrix groundmass are recognizable so that this might be best described as impact melt agglomerate, rather than a coherent lens of impact melt.

26 369 (1210) Core is distinctly green colored but the matrix is truly clastic, composed of angular fragments of quartz, feldspar and zircon. Clasts of angular micro and amphibole are opaque in transmitted light; in BSE images they appear to be fine-grained crystals of pyroxene + feldspar + oxide interpreted to represent a thermal decomposition

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product of the original mineral. Clasts of dark impact melt are abundant. Heterogeneously-distributed crystal clusters of garnet (andradite) and magnesioferrite are observed throughout the matrix.

27 370 (1214-5) Core is distinctly green colored but the matrix is truly clastic, composed of angular fragments of quartz, feldspar, zircon, titanite, pargasite, biotite, chlorite and epidote. Clasts of dark impact melt are abundant. Heterogeneously-distributed crystal clusters of garnet (andradite) and magnesioferrite are not observed.

28 371.5 (1219) Sample of shocked granitic basement rock near the bottom of the drill hole. 29 378.5 (1242) Shock-veined gneiss (refer to Walton et al., 2016 for details). 30 380 (1247) Shock-veined gneiss (refer to Walton et al., 2016 for details).

FIGURE DR3. Photomicrographs of larger quartz and feldspar clasts within the recrystallized breccia taken in plan light (A, C) and under crossed polars (B, D). A: A large mm-size quartz clast exhibiting a brown or “toasted” appearance with multiple sets of closely-spaced planar fractured. B: Higher magnification image of planar fractures in quartz. C: Several examples of quartz clasts with a ballen texture in S365. D: Overview of shock deformation (mosaicism / planar fractures) in quartz and feldspar from a cm-size clast of granitic basement rock within the recrystallized breccia (S362.5).

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FIGURE DR4. BSE images showing zircon in the ST003 core. A, B: Zircon occurs in the matrix as pulverized fragments derived from crystalline basement rocks. The brighter speck in (A) is dust. C, D: Zircon also occurs in the core as partially or completely decomposed clasts entrained within impact melt.

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Figure DR5. Photomicrographs taken in plane polarized light using an optical microscope (A, B) and BSE images of impact melt clasts which form a matrix component in the ST003 core between 242‒370 m depth.

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Figure DR6. Additional BSE images of magnesioferrite-bearing crystal clusters heterogeneously distributed throughout the matrix of S290. A: Magnesioferrite (bright grains) + calcite assemblages. B: Higher magnification image of rounded magnesioferrite grains surrounded by a corona of clinopyroxene. C: Rounded magnesioferrite crystal cluster with clay minerals surrounded by clinopyroxene. The matrix texture is defined by euhedral titanomagnetite (Ti-mag) laths, clinopyroxene (cpx) and euhedral feldspar (albite) as single crystals, crystals enclosed by clinopyroxene or nucleating on the rim of entrained mineral clasts. D: Higher magnification image of a magnesioferrite + calcite + quartz (qtz) cluster, note that quartz in this image is euhedral and unshocked (lacks planar fractures).

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Figure DR7. Additional BSE images of garnet-bearing crystal clusters heterogeneously distributed throughout the matrix of S285.5 (A, B) and S290 (C) with accompanying Raman spectra. Raman spectra coupled with EDS measurements were implemented to identify the small inclusions observed in some garnet grains which include anhydrite and clinopyroxene. The andradite cores are enriched in Al (wt% oxide) compared to the rim; spectra from the rim contain a stronger peak at 877 cm-1 Raman shift. A: Euhedral andradite single crystals in a groundmass of clay minerals and clinopyroxene. B: Andradite crystal clusters (bright grains in image). C: Darker grossular cores zoned to brighter andradite rims, surrounded by a corona of clinopyroxene crystals. Albite has also been observed as an inclusion in garnet but is not shown in these images.

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Figure DR8. BSE images of annite (A, B) and pargasite (C, D) which have partially thermally decomposed to form assemblages of feldspar + pyroxene + oxide. A: Former annite grain which has partially decomposed. Note that the decomposition products are coarser at the rim compared to the center of the grain and the trace of the original (001) cleavage can still be discerned (orientated roughly NE-SW). B: Higher magnification image of pyroxene (grey), oxide (bright) and feldspar (dark) showing a good topotactic relationship with the original mica grain. C, D: Partially decomposed pargasite grain with intact core surrounded by a rim of albite, clinopyroxene and Ti-magnetite. D: Higher magnification of the pargasite core (upper portion of the image) and thermally decomposed rim forming oxides (bright) + albite (dark) + clinopyroxene (intermediate greyscale) (lower portion of the image).

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Figure DR9. BSE images and Raman spectra of titanite grains in S290 (A, C) and S284 (B). Titanite grains which formed by subsolidius recrystallization in the matrix (A, B) are easily distinguished by inherited titanite grains from basement rocks (C). New titanite grains are fine-grained (≤20 μm) and euhedral, occurring as single grains (A) or completely or partially enclosed by clinopyroxene (B). A: BSE image of several titanite grains partially enclosing albite (dark) and clinopyroxene (grey). B: Titanite inclusions in clinopyroxene. C: Inherited titanite grain from basement rocks which is vesiculated, fractured and partially decomposed at the margin. Raman spectra were also useful in distinguishing newly formed versus inherited grains as those new mineral show sharp peaks characteristic of well-crystalline material whereas inherited grains show a distinct peak broadening attributed to deformation, most likely due to shock.

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Figure DR10. Temperature estimate for matrix and impact melt clasts.

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TABLE DR2. RESULTS OF MAJOR AND MINOR ELEMENT ABUNDANCE DETERMINERATION USING THE ELECTRON MICROSCOPE

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TABLE DR3. DATA REPOSITORY DATASET: LA-ICP-MS ANALYSIS OF MAGNESIOFERRITE

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TABLE DR3 CONT’D. DATA REPOSITORY DATASET: LA-ICP-MS ANALYSIS OF MAGNESIOFERRITE

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TABLE DR3 CONT’D. DATA REPOSITORY DATASET: LA-ICP-MS ANALYSIS OF MAGNESIOFERRITE

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TABLE DR4. DATA REPOSITORY DATASET: MODAL ABUNDANCE OF ST003 CORE COMPONENTS AT VARIOUS DEPTH INTERVALS

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Alberta Geological Survey (2015): Alberta Table of Formations; Alberta Energy Regulator, URL <https://www.aer.ca/documents/catalog/TOF.pdf.> [March 3rd, 2016]

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Burwash, R.A., McGregor, C.R. and Wilson, J.A. 1994. Precambrian basement beneath the Western Canada Sedimentary Basin; in Geological Atlas of the Western Canada Sedimentary Basin, G.D. Mossop and I. Shetsen (ed.); Canadian Society of Petroleum Geologists, Alberta Research Council, Chapter 5. p. 49–56

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Carrigy, M.A., and Short, N.M., 1968, Evidence of shock metamorphism in rocks from the Steen River structure, in French B.M., and Short, N.M., eds., Shock metamorphism of natural materials: Baltimore, Maryland, Mono Book Corporation, p. 367–378.

Droop G.R.T., 1987, A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analysis, using stoichiometric criteria: Mineralogical Magazine, v. 51, p. 431─435.

Grieve, R. A. F., 2006, Steen River: in Impact Structures in Canada, Geological Association of Canada, St John’s, Newfoundland, pp. 157‒160.

Locock, A.J., 2008. An Excel spreadsheet to recast analyses of garnet into end-member components, and a symposis of the crystal chemistry of natural silicate garnets: Computers & Geosciences, v. 34, p. 1769─1780, doi: 10.1016/j.cageo.2007.12.013.

Locock A.J., 2014, An excel spreadsheet to classify chemical analyses of amphiboles following the IMA 2012 recommendations: Computers & Geosciences, v. 62, p. 1─11.

Molak B., Balzer, S. A., Olson, R. A., and Waters, E. J., 2001, Petrographic, mineralogical and lithogeochemical study of core from three drillholes into the Steen River Structure, Northern Alberta: Alberta Geologic Survey, Earth Sciences Report 2001-04, http://ags.aer.ca/reports/earth-sciences-reports.

Thiéblot, L., Téqui, C., and Richet, P., 1999, High-temperature heat capacity of grossular (Ca3Al2Si3O12), enstatite (MgSiO3) and titanite (CaTiSiO5): American Mineralogist, v. 84, p. 848─855.

Walton, E.L., Sharp, T.G., and Hu, J., 2016, Frictional melting processes and the generation of shock veins in terrestrial impact structures: Evidence from the Steen River impact structure, Alberta, Canada: Geochimica et Cosmochimica Acta, v. 180, p. 256─270, doi: 10.1016/j.gca.2016.02.024.

*Note the following industry open file reports for the Steen River impact structure:

Brown, J.M.I., 1995, Steen River Prospect, Alberta: Alberta Energy and Utilities Board, Industrial and Metallic Mineral Assessment Report 19950015.

Germundson, R.K., and Fischer, P.A., 1978, Steen River diamond drill program, Alberta, NTS 84N: Alberta Energy and Utilities Board, Industrial and Metallic Mineral Assessment Report 19780015.

McCleary, J., 1997, Metallic and Industrial Mineral Assessment Report on the Steen River Impact Crater: Alberta Energy and Utilities Board, Alberta Geological Survey, Metallic and Industrial Mineral Assessment Report 1997-0004.