Evaluating Reflux Dolomitization using a Novel High-Resolution Record of Dolomite

Transcription

1 1 GSA Data Repository Evaluating Reflux Dolomitization using a Novel High-Resolution Record of Dolomite Stoichiometry: A Case Study from the Cretaceous of Central Texas, U.S.A. Cameron J. Manche 1 and Stephen E. Kaczmarek 1 1 Department of Geological and Environmental Sciences, Western Michigan University, 1903 W. Michigan Ave., Kalamazoo, MI USA 7 Samples Acquisition Samples were collected using a 1-inch diameter, gas-powered core plugger. 217 samples (175 core plugs and 42 hand samples) were collected from 9 vertical transects that stair-step up section along the ca m tall outcrop (Fig. DR1). The total lateral distance between the 9 vertical transects is ca m. The number of samples collected from each transect are as follows: Transect A 18 core plugs; Transect B 16 core plugs; Transect C 16 core plugs; Transect D 27 core plugs and 2 hand samples; Transect E 20 core plugs and 4 hand samples; Transect F 29 core plugs; Transect G 26 core plugs; Transect H 23 core plugs; Transect RF 36 hand samples. Transect RF consists of hand samples that were collected by rappelling from the top of the outcrop. 102 core plugs were collected laterally across the Transect D to ca m from Transect E, covering a transect of 32.6 m at an interval of 0.3 m. The lateral transect was collected in the same interval that was also sampled for porosity and permeability data by Fullmer (2005) and Fullmer and Lucia (2010). 20 Analytical Procedures Standard powder X-ray diffraction (XRD) data were collected using a Bruker D2 Phaser Diffractometer with a CuKα anode. Data were collected using a 2θ range of 20 to 60, a step

2 size of 0.01 and a count time of 1 s/step. Peak positions were calibrated with a CaF 2 standard. For the data presented, X-ray determined dolomite (104) peak positions were reproducible with an analytical uncertainty of 0.15 mole % MgCO 3. The abundance of dolomite relative to calcite (i.e. percent dolomite), dolomite stoichiometry (mole % Mg), and the degree of cation ordering were calculated as follows. Dolomite stoichiometry, which is reported as mole % MgCO 3, was calculated using the calibrated position of the dolomite (104) reflection (Lumsden, 1979). Percent dolomite was determined using the peak-height ratio of the dolomite (104) peak divided by the dolomite (104) peak plus the calcite (104) peak (Royse et al., 1971). Cation ordering was determined using the ratio of the intensities of the dolomite (015) and (110) reflections (Goldsmith and Graf, 1958). X-ray determined dolomite (015) and (110) peak height ratios were reproducible with an analytical uncertainty of 0.03 (015/110) Bulk δ 18 O and δ 13 C were obtained from a Finnigan MAT 253 collector isotope ratio mass spectrometer at the University of Michigan Stable Isotope Laboratory. In total 66 samples were analyzed from the vertical transect and 11 samples were analyzed from the lateral transect. 10 µg of each sample were placed in stainless-steel boats. Samples were then transferred to individual borosilicate reaction vessels and reacted at 77 C ± 1 C with 4 drops of anhydrous phosphoric acid in a Finnigan MAT Kiel IV preparation device coupled directly to the inlet of a Finnigan MAT 253 triple collector isotope ratio mass spectrometer (IRMS). Limestones and dolomites were reacted for 8 and 12 min, respectively. O 17 data were corrected for acid fractionation and source mixing by calibration to a best-fit regression line defined by two standards (NBS 18 and NBS 19). All stable isotope data are reported in standard delta (δ) notation in per mil ( ) relative to the Vienna Peedee belemnite (VPDB) scale. Precision and accuracy were monitored through daily analysis of a variety of powdered carbonate standards, with at least four standards

3 46 47 reacted and analyzed daily. Measured precision was maintained at better than 0.1 for both carbon and oxygen Scanning electron microscope (SEM) analyses were performed on 40 rock chips and 20 standard petrographic thin sections using a JEOL JSM-IT100. Petrographic thin sections were also evaluated using a Zeiss Axioplan 2. Crystal size was measured along the long-axis of the crystal and were obtained from both the SEM (n=1,600) and petrographic microscope (n=800) Facies Analysis The Cretaceous Upper Glen Rose Formation exposed along Wild Basin Preserve and Highway 360 (Austin, Texas) consists of 5 facies: foram wackestone, foram packstone, coarse planar-e dolomite, dolomitic moldic packstone, dolomitic intraclastic wackestone. Facies analysis integrated observations from outcrop, hand samples, and thin sections were employed to document lithology, fossil content, rock fabric, sedimentary structures, and stratigraphic surfaces (Fig. 3) The foram wackestone and packstone facies vary from mud-to-grain supported, respectively. Components within the facies include miliolid foraminifera. Both facies represent a dolomitic limestone and is not pervasively dolomitized. In the foram wackestone and packstone facies the density of dolomite crystals varies from isolated to somewhat clustered, respectively. These facies are typically extensively burrowed based on observations from the road-cut. Based on the abundance of mud, miliolid foraminifera, and burrows it is interpreted that these facies were deposited in a subtidal environment The coarse planar-e dolomite facies is characterized as dolostone with no observable components such as skeletal and non-skeletal grains. Moldic pores are infrequently observed suggesting that

4 components were present during deposition but were subsequently dissolved. Dolomite crystals are observed to frequently contain cloudy cores which are suggested to be remnants of calcite that were entombed during dolomitization. The average crystal size for dolomite rhombs is ± µm. Based on the high degree of diagenetic alteration it is not possible to determine a specific depositional environment The dolomitic moldic packstone facies consists of abundant moldic pores with a fine crystalline dolomite matrix. This facies has been pervasively dolomitized and all components have been dissolved. Components were interpreted from the geometry of the molds to mostly represent bivalves and Turritella gastropods. The molds of the skeletal components were also observed to be bounded by microbial laminations. Based on the prevalence of skeletal components preserved as molds and the presence of microbial laminations it is interpreted that this was deposited in the inter-to-supratidal environment The dolomitic intraclastic wackestone facies was pervasively dolomitized and contains mud intraclasts. Intraclasts are interpreted to be mud-rip clasts resulting from times of exposure and were subsequently transported. No skeletal or other non-skeletal components were observed. Intraclasts contain some calcite while the matrix is entirely dolomite. Based on observations from the road-cut, cycle boundaries are marked by mud-cracks, rip-up clasts, gypsum molds, and terra rossa staining which are all features found within this facies. Based on the occurrence of mud-cracks and rip-up clasts mud it is interpreted that this facies was deposited in the supratidal environment. 88 DATA REPOSITORY REFERENCES 89 Fullmer, S., and Lucia, F.J., 2005, Burial history of central Texas Cretaceous carbonates:

5 90 University of Texas at Austin, 97 p Fullmer, S.M., and Lucia, F.J., 2010, Rate of Reflux Dolomitization Based on Hydrodynamic Modeling of a Glen Rose Dolostone, Austin, Texas: Gulf Coast Association of Geological Societies Transactions, v. 60, p Goldsmith, J.R., and Graf, D.L., 1958, Structural and compositional variations in some natural dolomites: The Journal of Geology, v. 66, p , doi: / Lumsden, D.N., 1979, Discrepancy between thin-section and X-ray estimates of dolomite in limestone: Journal of Sedimentary Research, v. 49, p , doi: /212f7761-2b24-11d c1865d Royse, C.F., Wadell, J.S., and Petersen, L.E., 1971, X-ray determination of calcite-dolomite; an evaluation: Journal of Sedimentary Research, v. 41, p , doi: /74d722a7-2b21-11d c1865d FIGURE CAPTIONS Figure DR1. A: Photo pan of the Wild Basin Preserve road cut, Austin, Texas, U.S.A. The road-cut measures ca m vertically, and ca. 236 m horizontally. Solid yellow lines show locations of the vertical transects. Dashed yellow line show the location of the lateral transect. B: Spliced photos to illustrate the height and distance between vertical transects. C: Photo pan of the lateral transect Figure DR2. Sample were collected from the dolomitic moldic packstone facies. A: Lateral road cut log showing dolomite stoichiometry and δ 18 O ( ). B: Lateral road cut log section dolomite cation ordering Figure DR3. Cross-plots of dolomite stoichiometry, dolomite cation ordering, and dolomite abundance. A: Cross-plots of dolomite stoichiometry and cation ordering. B: Cross-plots of

6 dolomite abundance and cation ordering. C: Cross-plots of dolomite abundance and stoichiometry. D: Cross-plots of δ 13 C and δ 18 O.

7 Fig. DR1

8 Fig. DR2

9 Fig. DR3

10 Table DR1. Raw mineralogical and geochemical data from the vertical transects. Transect ID Height (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) A % 0.52 A % 0.63 A % 0.65 A % 0.64 A % 0.62 A % 0.56 A % 0.57 A % 0.44 A % 0.46 A % 0.62 A-11B % A-11T % 0.37 A % 0.45 A % 0.56 A % 0.80 A % 0.50 A % A % 0.74 A % 0.71 B % 0.71 B % 0.39 B-3B % 0.49 B-3T % 0.45 B % 0.51 B % 0.51 B % 0.59 B % 0.54 B % 0.55 B % B % 0.50 B % 0.66 B % 0.71 B % 0.53 B % 0.50 B % 0.49 B % 0.56 C % C % 0.57 C % 0.50

11 Table DR1. (continued) Transect ID Height (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) C % 0.48 C % 0.50 C % 0.42 C % 0.47 C % C % 0.40 C % 0.40 C % 0.37 C % 0.36 C % 0.46 C % 0.42 C % 0.45 C % 0.52 C % D % D % D % D % D % D % D % D % D % 0.64 D % D % D % D % D % D % 0.44 D % D % D-18B % D-18T % D-19B % D-19T % D % D % D % D %

12 Table DR1. (continued) Transect ID Height (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) D % D % D % D % D % D % 0.41 E % 0.42 E % 0.49 E % 0.45 E % 0.37 E % E % 0.38 E % 0.39 E % 0.45 E % 0.43 E % 0.39 E % 0.49 E % 0.47 E % 0.48 E % 0.57 E % E % 0.70 E % 0.52 E-18B % 0.63 E-18T % No Ordering Peaks E-19B % No Ordering Peaks E % 0.84 E % 0.60 E % 0.48 F % 0.63 F % 0.46 F % 0.57 F % 0.50 F % F % 0.42 F % 0.46 F % 0.51 F % 0.47 F % 0.61

13 Table DR1. (continued) Transect ID Height (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) F % 0.62 F % 0.46 F % F % 0.51 F % 0.45 F % 0.50 F % 0.60 F % 0.76 F % 0.51 F % 0.77 F % F % 0.53 F % 0.52 F % 0.46 F % 0.55 F % 0.53 F % 0.40 F % 0.40 F-29B % F-29T % 0.40 G % G % 0.43 G % 0.49 G % 0.43 G % 0.42 G % 0.48 G % 0.50 G % 0.49 G % G % 0.53 G % 0.54 G % 0.59 G % 0.54 G % 0.57 G % 0.50 G % 0.54 G % 0.54 G % 0.50 G % 0.44

14 Table DR1. (continued) Transect ID Height (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) G % 0.32 G % 0.40 G % G % 0.38 G % 0.34 G % 0.39 H % 0.34 H % 0.33 G % 0.41 H % H % 0.39 H % 0.41 H % 0.48 H % 0.45 H % 0.42 H % 0.49 H % 0.42 H % RF % H % 0.46 H % 0.44 RF % 0.45 H % 0.45 H % 0.46 RF % 0.35 H % 0.52 RF % 0.41 H % 0.52 RF-24B % 0.44 H % RF-24T % 0.50 H % 0.39 H % 0.32 H % 0.47 RF % 0.47 RF-22B % 0.52 RF-22T % 0.55 RF % RF % 0.46

15 Table DR1. (continued) Transect ID Height (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) RF % 0.52 RF % 0.49 RF % 0.53 RF % 0.48 RF % RF % 0.45 RF % 0.56 RF % 0.46 RF % RF % 0.50 RF % 0.40 RF % 0.43 RF % 0.45 RF % RF % 0.44 RF % 0.53 RF % 0.63 RF % 0.44 RF % 0.65 RF % 0.44 RF % 0.53 RF % RF % 0.51 RF % 0.56 RF % 0.58 RF % RF % 0.52

16 Table DR2. Raw mineralogical and geochemical data from the lateral transect. Transect ID Lateral Distance (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) LDE-1A % 0.43 LDE-1B % LDE-1C % 0.53 LDE % 0.54 LDE % 0.52 LDE % 0.57 LDE % 0.55 LDE % 0.69 LDE-7A % 0.51 LDE-7B % LDE-7C % 0.50 LDE % 0.56 LDE % 0.56 LDE % 0.57 LDE % 0.53 LDE % 0.62 LDE-14A % 0.52 LDE-14B % LDE-14C % 0.56 LDE % 0.59 LDE % 0.61 LDE % 0.63 LDE % 0.50 LDE % 0.54 LDE % 0.45 LDE % 0.52 LDE % 0.58 LDE-23A % 0.46 LDE-23B % LDE-23C % 0.52 LDE % 0.58 LDE % 0.44 LDE % 0.55 LDE % 0.49 LDE % 0.57 LDE % 0.47 LDE-30A % 0.48 LDE-30B % LDE-30C % 0.51

17 Table DR2. (continued) Transect ID Lateral Distance (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) LDE % 0.52 LDE % 0.43 LDE % 0.44 LDE % 0.55 LDE % 0.60 LDE % 0.61 LDE-37A % 0.51 LDE-37B % LDE-37C % 0.60 LDE % 0.50 LDE % 0.68 LDE % 0.64 LDE % 0.59 LDE % 0.61 LDE % 0.56 LDE % 0.57 LDE % 0.55 LDE % 0.50 LDE % 0.51 LDE % 0.56 LDE % 0.60 LDE % 0.46 LDE % 0.54 LDE % 0.54 LDE % 0.58 LDE % 0.59 LDE % 0.51 LDE % 0.59 LDE % 0.63 LDE % 0.52 LDE % 0.50 LDE % 0.60 LDE % 0.57 LDE % 0.61 LDE % 0.61 LDE % 0.51 LDE % 0.65 LDE % 0.49 LDE % 0.55

18 Table DR2. (continued) Transect ID Lateral Distance (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) LDE % 0.59 LDE % 0.47 LDE % 0.52 LDE % 0.46 LDE % 0.51 LDE % 0.53 LDE % 0.46 LDE % 0.55 LDE % 0.48 LDE % 0.57 LDE % 0.61 LDE % 0.65 LDE % 0.57 LDE % 0.64 LDE % 0.68 LDE % 0.58 LDE % 0.70 LDE % 0.57 LDE % 0.47 LDE % 0.54 LDE % 0.47 LDE-89A % 0.54 LDE-89B % LDE-89C % 0.47 LDE-89D % 0.54 LDE % 0.60 LDE % 0.54 LDE % 0.58 LDE-93A % 0.47 LDE-93B % LDE-93C % 0.48 LDE % 0.56 LDE % 0.58 LDE-96A % 0.51 LDE-96B % LDE-96C % 0.52 LDE % 0.46 LDE % 0.54 LDE-99A % 0.52

19 Table DR2. (continued) Transect ID Lateral Distance (m) Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 13 C ( ) δ 18 O ( ) LDE-99B % LDE-99C % 0.51 LDE % 0.51 LDE % 0.48 LDE-102A % 0.49 LDE-102B % LDE-102C % 0.58

20 Table DR3. Mean mineralogical and geochemical data by facies. Facies Mole % MgCO 3 Dolomite Abundance (%) Cation Ordering (015/110) δ 18 O ( ) Foram Wackestone ± ± ± ± 0.55 Foram Packstone ± ± ± ± 1.03 Coarse Planar-e Dolomite ± ± ± ± 0.20 Moldic Dolomitic Packstone ± ± ± ± 0.25 Intraclastic Dolomitic Wackestone ± ± ± ± 0.28