CONTRASTING OXYGEN ISOTOPIC
COMPOSITIONS OF ALBIAN LOCAL vs. REGIONAL RECHARGE, CRATONIC
MARGIN, WESTERN INTERIOR BASIN
P.L. Phillips, G.A. Ludvigson, L.A. González, R.L. Brenner, and
B.J. Witzke
The Geological Society of
America
1998 GSA Annual Meeting
Toronto, Ontario, October 26-29, 1998
1998 Abstracts with Programs, v. 30, no. 7, p. A-332
Abstract
Comparisons are made between the stable isotopic compositions of early meteoric phreatic siderite cements in proximal coarse-grained braided fluvial sandstones of the Nishnabotna Member, Dakota Formation of NW Iowa and coeval sphaerosiderite nodules from a paleosol in the more distal fluvial-estuarine facies of the Terra Cotta Member, Dakota Formation of SE Nebraska. Both units correlate to the Late Albian marine Kiowa Shale in Kansas. Basal Nishnabotna sandstones of the Hawarden core (described by Witzke and Ludvigson, 1994, GSA SP 287:52-53) in NW Iowa contain spherulitic and prismatic siderite cements that occluded 31 to 47 % minus-cement porosity, indicating early diagenetic cementation. These cements have relatively invariant d18O (-6.08 ± 0.42 ‰ PDB) and d13C (-15.35 ± 0.23 ‰) values.
The sphaerosiderite horizon at the Camp Jefferson section in SE Nebraska (unit 6, locality 2 of Joeckel, 1987, Univ. Wyo. Cont. Geol. 25:95-102) occurs in a plinthic paleosol that immediately overlies estuarine strata with inclined heterolithic stratification containing marine palynomorphs. A positive covariant trend between d13C and d18O values in these sphaerosiderites is interpreted to record fluid mixing between meteoric phreatic and marine phreatic fluids. This fluid mixing curve converges on a Meteoric Sphaerosiderite Line (MSL) with a d18O value of –4.17 ± 0.28 ‰. The MSL at the Camp Jefferson section is interpreted as a proxy record of local Late Albian paleoprecipitation and recharge on the cratonic coastal plain of the Western Interior Basin. The lighter d18O values of the siderite cements in more proximal fluvial sandstones are interpreted to record the composition of regional recharge by inland paleoprecipitation that was depleted by continental effect over a large drainage basin including much of the area of NW Iowa and southern Minnesota.
| Aptian-Albian Paleogeography (121-98.5 Ma) |
 |
| Late Albian carbonate cements were sampled from three stratigraphic sections from the eastern margin of the Cretaceous Western Interior Basin. The Hawarden (D7) core (Sioux County, Iowa) provided access to intervals of siderite-cemented Nishnabotna Sandstone Member of the Dakota Formation. Sphaerosiderites from the Terra Cotta Member of the Dakota Formation were sampled at the Camp Jefferson section in Jefferson County, Nebraska. Calcite cements in the Cheyenne Sandstone were sampled from the KGS Stanton County core, Stanton County, Kansas. The above map is a reconstruction by Brian Witzke using the continental positions of Scotese (1991, Palaeo3:87:493-501). Map shows maximum extent of continental flooding by epeiric seas, and yellow lines show the limits of the minimum extent of epeiric seas. |
| Regional Stratigraphic Cross
Section of Cretaceous Strata: Northwest Iowa to Western Kansas |
 |
Regional onshore-offshore stratigraphic cross section of Albian-Cenomanian strata from the cratonic margin of the Western Interior Basin. The Cheyenne Sandstone, sampled from the KGS Stanton County core, is a fluvial unit directly underlying the Albian marine Kiowa Shale, and is older than the other units described in this study. Sampled intervals from the Camp Jefferson section and the Hawarden Core are also from Albian non-marine units whose deposition and early diagenetic fluids were influenced by the Kiowa marine transgression.
 |
| Sphaerosiderite collecting site at Camp Jefferson section in Jefferson County, Nebraska. Geologists Greg Ludvigson, Ty Hamid, and Matt Joeckel (left to right) examine a plinthic paleosol in the Terra Cotta Member, Dakota Formation. Prismatic vertical mottling zones of hematite in the paleosol are juxtaposed with bleached kaolinitic mudstones that contain sphaerosiderite. Carbonaceous beds to the lower right were deposited in lateral accretion sets in a unit with inclined heterolithic stratification. These carbonaceous mudstones contain marine palynomorphs and other zonally-significant forms demonstrating correlation to the marine Kiowa Shale, and were deposited on tidal point bars. The plinthic paleosol (an ancient lateritic soil) contains reduced iron minerals (sphaerosiderite and pyrite) that formed in reducing water-saturated environments, probably near the head of a paleoestuary. |
 |
 |
|
| Photomicrographs showing siderite cements from near the base of the Nishnabotna Member, Dakota Formation of the Hawarden core in northwest Iowa, sample at the 642.3’ level. Minus-cement porosity is approximately 39%. No pyrite cement inclusions present. (Plane polarized light to left, cross-polarized to right. Long axis of photomicrographs = 0.65 mm.) |
 |
 |
|
| Photomicrographs showing siderite and pyrite cements from the Nishnabotna Member of the Hawarden core in northwest Iowa, sample at the 614.4’ level. Minus-cement porosity is approximately 41%. About 1.67% pyrite cement inclusions present. (Plane polarized light to left, cross-polarized to right. Long axis of photomicrographs = 0.65 mm.) |
 |
 |
|
| Photomicrographs showing sphaerosiderite separates from the Camp Jefferson section in southeast Nebraska. (Plane polarized light to left, cross-polarized to right. Long axis of photomicrographs = 1.3 mm.) |
 |
 |
|
| Photomicrographs showing poikilotopic calcite cement in the upper Cheyenne Sandstone of the KGS Stanton County core in western Kansas, sample at the 221.8’ level. Minus-cement porosity is approximately 30%. Less than 1% pyrite cement inclusions present. (Plane polarized light to left, cross-polarized to right. Long axis of photomicrographs = 1.3 mm.) |
| Stable Isotopic Data from Late Albian Carbonate Cements |
 |
| Carbon and oxygen isotope plots for
Late Albian carbonate cements. These data are used to
interpret groundwater systems in different parts of the
eastern margin of the Cretaceous Western Interior Basin.
Siderite d18O data have been corrected for acid
digestion at 73 ºC, after Carothers et al. (1988, GCA
52:2445-2450). Time 1 data were isolated from calcite cement of the Cheyenne Sandstone, and plot on a trend with negative correlation between the two isotopes. We interpret this trend as the meteoric fluid end-member of a hyperbolic fluid mixing curve, indicating that the cement formed in a groundwater mixture between meteoric phreatic and modified marine phreatic fluids. Time 2 data were isolated from two approximately coeval units, the Terra Cotta and Nishnabotna members of the Dakota Formation, and both yield trends with positive correlation between the two isotopes. We interpret these trends as hyperbolic fluid mixing curves, indicating that the cements formed in mixtures of meteoric phreatic and marine phreatic fluids. Sphaerosiderites isolated from plinthic paleosols of the Terra Cotta Member (Camp Jefferson) include stable isotopic data which are interpreted as preserving a purely meteoric phreatic signal—the meteoric sphaerosiderite line (Ludvigson et al., 1998, Geology 26:1039-1042). Data from cements in the Nishnabotna Member become more enriched with increasing abundance of pyrite inclusions, which increase up-section. The presence of pyrite inclusions suggests that anaerobic sulfate reduction occurred in brackish pore fluids, and is consistent with the fluid mixing hypotheses outlined above. |
| Estimates of Groundwater Compositions |
 |
| Estimates of groundwater compositions for the respective cements are based on the interpreted freshwater end-members of the fluid-mixing curves for calcite in the Cheyenne Sandstone and siderite in the Nishnabotna Member, and by the meteoric sphaerosiderite line (MSL) from the paleosol in the Terra Cotta Member. These values are –11.01 ‰ (PDB) for calcite in the Cheyenne, and –6.61 ‰ (PDB) for siderite in the Nishnabotna. The MSL for the Terra Cotta Member is –4.17 ‰. Published 18O fractionation relations for calcite (Friedman and O’Neil, 1977, USGS PP 440-KK) and siderite (Carothers et al., 1988, GCA 52:2445-2450) can be used to calculate ranges of fluid d18O and temperature values that satisfy oxygen isotopic equlibrium for calcites and siderites of a given composition. All samples considered in this study were retrieved from localities with a paleolatitude of approximately 36º N, which corresponds to estimated Cretaceous mean annual temperatures ranging between 20 and 29 ºC (Barron and Washington, 1985, AGU Geophys. Mon. 32:546-553). Note that despite their widely different d18O values, meteoric phreatic calcite in the Cheyenne and meteoric phreatic siderite in the Nishnabotna yield similar estimates for groundwater compositions at the temperature range of interest. Moreover, the estimated groundwater compositions of these sandstone cements do not overlap with the range of groundwater compositions estimated from the MSL value from the Terra Cotta. We suggest that the difference between these differing proxy records results from the differing sizes of the catchment areas recharging the respective groundwater systems. Sphaerosiderites in the coastal paleosols formed in groundwaters that were locally recharged by coastal rainfall, whereas the sandstone cements formed in groundwaters recharged by both coastal and inland rainfall carried by rivers draining the eastern subcontinent. This groundwater system also integrated the recharge to alluvial aquifers from inland sites far upstream, and 18O depletions of this paleoprecipitation from continental effects are to be expected. |
| The following diagrams illustrate our interpretation of groundwater influences on the d18O of carbonate cements in Late Albian deposits of the eastern margin of the Western Interior Basin. |
 |
| In Time 1, the calcite cements were precipitated from groundwaters that were mixtures of fresh water and modified marine pore fluids. Continental effects leading to depletion of 18O in atmospheric water vapor that fell as inland paleoprecipitation is captured in the d18O composition of this cement. Regional recharge of groundwaters from cratonic source areas mixed with local coastal meteoric recharge and lesser amounts of seawater to produce cements with a light oxygen isotopic composition. |
 |
| Time 2 illustrates a scenario where two carbonate cements formed in sedimentary facies that sampled different portions of the same regional groundwater flow system. Both facies appear to have hosted groundwaters that resulted from mixing between fresh waters and seawater. The sphaerosiderites in paleosols formed within a few meters of the land surface, in small topographically-controlled local groundwater flow systems that were recharged only by local coastal paleoprecipitation. Conversely, the coeval siderite cements in sandstones of the Nishnabotna Member, Dakota Formation were precipitated within a regional paleoaquifer system. The lighter d18O values of these cements are interpreted to reflect the regional (fluvial bypass) recharge by inland paleoprecipitation. Continental effect (depletion of 18O in water vapor as it moves away from its source) is the primary agent in variations between the two meteoric phreatic siderite cement compositions. |
Conclusions
Early carbonate cements in siliciclastic deposits can be used as proxy records for paleoclimatic reconstructions.
Acknowledgements
This research supported by the National Science Foundation (EAR 96-28128), and seed grants by The University of Iowa Center for Global & Regional Environmental Research, and the Carver Scientific Research Initiative. We thank Tim White for assistance on this project, and Angela Murillo, Ron Metzger, and Kay Saville for aiding in preparation and extraction of samples. Special thanks are due to L. Wingate and K.C. Lohmann at the University of Michigan Stable Isotope Laboratory, where the isotope analyses were performed. We thank Pat Lohmann of the Iowa DNR Geological Survey Bureau for her assistance in preparing this poster. Our colleague R. Matt Joeckel has shared many important insights on the Cretaceous geology of eastern Nebraska. Finally, we thank the Kansas Geological Survey for access to curated drillcores.
References
Barron, E.J., and Washington, W.M., 1985, Warm Cretaceous climates: High atmospheric CO2 as a plausible mechanism, in Sundquist, E.T., and Broecker, W.S., eds., The carbon cycle and atmospheric CO2: Natural variations Archean to present: American Geophysical Union Geophysical Monograph 32, p. 546-553.
Carothers, W.W., Adami, L.H., and Rosenbauer, R.J., 1988, Experimental oxygen isotope relation between siderite-water and phosphoric acid liberated CO2-siderite: Geochimica et Cosmochimica Acta, v. 52, p. 2445-2450.
Friedman, I., and O’Neil, J.R., 1977, Compilation of stable isotope fractionation factors of geochemical interest: U.S. Geological Survey, Professional Paper 440-KK, p. KK1-KK12.
Joeckel, R.M., 1987, Paleogeomorphic significance of two paleosols in the Dakota Formation (Cretaceous), southeastern Nebraska: University of Wyoming Contributions to Geology, v. 25, no. 2, p. 95-102.
Ludvigson, G.A., González, L.A., Metzger, R.A., Witzke, B.J., Brenner, R.L., Murillo, A.P., and White, T.S., 1998, Meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology: Geology, v. 26, p. 1039-1042.
Scotese, C.R., 1991, Jurassic and Cretaceous plate tectonic reconstructions: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 87, p. 493-501.
Witzke, B.J., and Ludvigson, G.A., 1994, The Dakota Formation in Iowa and the type area, in Shurr, G.W., Ludvigson, G.A., and Hammond, R.H., Cretaceous Sedimentary Record of the Eastern Margin of the Western Interior Seaway, Geological Society of America, Special Paper 287, p. 43-78.
Presented as a poster at the 1998 Annual Meeting of The Geological Society of America, October 26-29, 1998, Toronto, Ontario.
Photomicrographs by Lee Phillips, The University of Iowa.