Papers by Luis Ariel Gonzalez
Quaternary Research, 2000
Speleothems from a well-ventilated dolomitic cave in the Pokhara Valley, central Nepal, preserve ... more Speleothems from a well-ventilated dolomitic cave in the Pokhara Valley, central Nepal, preserve a mineralogic record of Indian summer monsoon variability over the past 2300 yr. Annually deposited aragonite layers formed between 2300 and 1500 yr B.P., indicating reduced monsoon precipitation and increased cave aridity, whereas alternating calcite/aragonite laminae deposited after 1500 yr B.P. record elevated summer monsoon precipitation and increased cave humidity. Dense, optically clear calcite layers deposited from 450 ± 5 to 360 ± 20 yr B.P. (1550 to 1640 A.D.) indicate a less-evaporative cave environment and suggest moister and/or cooler conditions, possibly related to climatic change associated with the onset of the Little Ice Age.
Geology, 1999
Isotopic analyses of three stalagmites from Cold Water Cave, northeast Iowa, United States, revea... more Isotopic analyses of three stalagmites from Cold Water Cave, northeast Iowa, United States, reveal nearly identical δ 13 C trends from ca. 7 to 2 ka. However, δ 18 O patterns differ by as much as 3‰ from 5.7 to 3.2 ka. These disparate δ 18 O values reflect evaporative 18 O enrichment in meteoric water prior to infiltration, suggesting that previously calculated temperatures based on a single Cold Water Cave stalagmite overestimated middle Holocene warming. The coincidence of elevated middle Holocene growth rates in the stalagmites with the lowest oxygen isotopic compositions indicates that the middle Holocene was marked by a predominance of coolweather precipitation during a period of increased overall aridity.
Geology, 2004
Quantitative estimates of increased heat transfer by atmospheric H 2 O vapor during the Albian gr... more Quantitative estimates of increased heat transfer by atmospheric H 2 O vapor during the Albian greenhouse warming suggest that the intensified hydrologic cycle played a greater role in warming high latitudes than at present and thus represents a viable alternative to oceanic heat transport. Sphaerosiderite ␦ 18 O values in paleosols of the North American Cretaceous Western Interior Basin are a proxy for meteoric ␦ 18 O values, and massbalance modeling results suggest that Albian precipitation rates exceeded modern rates at both mid and high latitudes. Comparison of modeled Albian and modern precipitation minus evaporation values suggests amplification of the Albian moisture deficit in the tropics and moisture surplus in the mid to high latitudes. The tropical moisture deficit represents an average heat loss of ϳ75 W/m 2 at 10؇N paleolatitude (at present, 21 W/m 2 ). The increased precipitation at higher latitudes implies an average heat gain of ϳ83 W/ m 2 at 45؇N (at present, 23 W/m 2 ) and of 19 W/m 2 at 75؇N (at present, 4 W/m 2 ). These estimates of increased poleward heat transfer by H 2 O vapor during the Albian may help to explain the reduced equator-to-pole temperature gradients.
Developments in Sedimentology, 2004
Geophysical Research Letters, 1991
t. The Toa Baja Well drilled in northern Puerto Rico to a depth of 2705 m (8872 ft.) penetrated o... more t. The Toa Baja Well drilled in northern Puerto Rico to a depth of 2705 m (8872 ft.) penetrated over 550 m (1800 ft.) of Tertiary carbonates. The limestone-dominated portion of the well consists mostly of shallow-water backreef carbonates. Metastable carbonates have been either calcitized, dolomitized or dissolved. The petrographic character of the Tertiary carbonates in the Toa Baja Well, and those reported by Monroe [1980], the cathodoluminescence petrography, and the stable isotopic compositions indicate that these carbonates were rapidly cemented in the marine environment (limiting compaction), that replacement of metastab!e carbonates by calcite and precipitation of sparry calcite took place mostly in meteoric diagenetic environments and dolomitization probably occurred in a meteoric-marine mixing zone. Given the history of numerous drainage systems that dissected the Tertiary carbonates throughout their depositional history [Monroe, 1980] and the repeated Cenozoic sea level oscillations [Monroe, !980; Seiglie and Moussa, 1984], it is likely that alteration of metastable carbonates took place during lowstands. Interstratified fluvial deposits suggest the continued influence of meteoric fluids in local highlands [Monroe, !980]. introduction The Toa Baja #1 well was drilled to evaluate the depositional history of the northem Puerto Rico sedimentary sequence and to assess postdepositional changes in these •ents. Major questions posed for the shallow carbonate dominated sediments of the Toa Baja #1 well (Figure 1) are: what type of diagenetic modifications are involved, when these occurred (early vs. late), whether diagenetic modifications involved hot (burial) fluids, and the fate of organic matter and possible hydrocarbon generation or involvement. In an attempt to clarify the nature of diagenetic modification of the Middle Tertiary carbonates present in the Toa Baja #1 well petrographic and stable isotope studies have been undertaken. The limestone-dominated portion of the Toa Baja Well ranges from 25 m (80 ft.) down to 570 meters (1875 ft.) in depth. The carbonates consist mostly of shallow-water backreef carbonates of Tertiary age [Montgomery et al., 199!]. Detrital influx is prominent in various portions of the stratigraphic sequence in the well (Figure 1). Most of these detrital sediments are fluvial in origin, and record the evolution 0fpaleodrainage systems that were periodically active throughout the Tertiary [Monroe, 1980]. The penetrated carbonates outcrop throughout the north coast of Puerto Rico and are described by Monroe [1980]. From the known
Journal of Sedimentary Research, 2010
Geosciences, 2022
We report estimated stable isotope compositions of depositional waters and paleoprecipitation fro... more We report estimated stable isotope compositions of depositional waters and paleoprecipitation from the Cretaceous Arctic to further elucidate the role of the global hydrologic cycle in sustaining polar warmth during that period. Estimates are based on new hydrogen isotopic analyses of n-alkane biomarkers extracted from Late Cretaceous and mid-Cretaceous terrestrial deposits in northern Alaska and the Canadian High Arctic. We integrate these new results with earlier published work on oxygen isotopic analyses of pedogenic siderites, dinosaurian tooth enamel phosphates, and pedogenic clay minerals from the same field areas. Average Late Cretaceous δD values of −143‰ VSMOW corresponded with average δ18O values of −24.1‰ VSMOW, and average mid-Cretaceous δD values of −106‰ VSMOW corresponded with average δ18O values of −22.1‰ VSMOW. The distributions of water isotope δD and δ18O values from Cretaceous Arctic deposits do not intersect with the Global Meteoric Water Line, suggesting an app...
Current Research in Earth Sciences, 2010
The Cretaceous Dakota Formation in the areas of Kansas, Nebraska, and Iowa contains a rich and we... more The Cretaceous Dakota Formation in the areas of Kansas, Nebraska, and Iowa contains a rich and well-preserved microflora of fossil palynomorphs. A comprehensive listing of these taxa is presented in this publication as part of a continuing effort to develop a refined biostratigraphic scheme for mid-Cretaceous terrestrial deposits in North America. The Dakota Formation in this region contains four distinctive Albian-Cenomanian palynostratigraphic zones that are used to partition the unit into successive depositional cycles, and each zone records deposition in fluvial-estuarine environments. The late Albian Kiowa-Skull Creek depositional cycle at the base of the Dakota Formation is recognized throughout the study area, and is also recognized in other parts of the Cretaceous North American Western Interior basin. The overlying newly recognized latest Albian "Muddy-Mowry Cycle" is formally defined for the first time in this paper and correlates with depositional cycles recogni...
New Frontiers in Paleopedology and Terrestrial Paleoclimatology: Paleosols and Soil Surface Analog Systems, 2013
Pedogenic siderite is a carbonate mineral that forms in the reducing groundwaters of poorly drain... more Pedogenic siderite is a carbonate mineral that forms in the reducing groundwaters of poorly drained soils and paleosols in zonal climatic belts with strongly positive precipitation-evaporation balances. Microcrystalline and spherulitic forms of siderite are commonly recognized in micromorphologic studies of hydromorphic paleosols. Ancient paleosol sphaerosiderites commonly occur with diameters in excess of 1 mm, while modern pedogenic siderite crystal dimensions in excess of 100 lm are rare. Pedogenic siderites have been widely reported from Late Paleozoic, Mesozoic, and Cenozoic paleosols. The carbon and oxygen isotopic compositions of pedogenic siderites have been widely used as proxies for the oxygen isotopic composition of paleoprecipitation for their respective paleosols. Modern process studies of historic pedogenic siderites are yielding a more refined understanding of the stable isotopic systematics of low-temperature siderite. These works will lead to a future change in usage of published siderite-water 18 O fractionation equations.
Journal of Sedimentary Research, 2014
We investigate the regional climatic effects of the formation of the ''Nevadaplano'' plateau duri... more We investigate the regional climatic effects of the formation of the ''Nevadaplano'' plateau during the Sevier Orogeny in an overall warming world. Paleohydrology was reconstructed from 590 individual measurements of phosphate O isotopes in continental faunas of the Lower Cretaceous Cedar Mountain Formation, Utah, U.S.A. Semi-aquatic (turtles, crocodiles) and terrestrial (dinosaurs) taxa are compared to coeval pedogenic carbonates to interpret changing water sources over time. Samples were grouped into four stratigraphic faunas (lower Yellow Cat, upper Yellow Cat, Ruby Ranch, and Mussentuchit members). Resulting isotopic values were converted to d 18 O w values using established d 18 O p -d 18 O w and d 18 O c -d 18 O w relationships. At a formation scale, turtles (d 18 O p = 14.1 to 15.7% V-SMOW) and crocodiles (d 18 O p = 15.0 to 19.2%) document water compositions of 28.1 to 26.1% and 27.7 to 24.2%, respectively, within the zonal range for formation-scale meteoric water at 34u N paleolatitude (27.1 to 24.8%) established by pedogenic carbonates (d 18 O c = 22.0 to 23.5% V-SMOW). These data suggest that, like soil carbonates, turtle and crocodile phosphate isotopes can be used as proxies for meteoric water isotopic composition. Dinosaur d 18 O p (sauropods: 19.7 to 21.9%, ornithischians: 16.6 to 21.7%, small theropods: 16.9 to 18.2%, and large allosauroids: 19.1 to 20.3%) values generally exceed those of semi-aquatic taxa. Using mass-balance equations for modern terrestrial animals adjusted for size and inferred dinosaur physiology, ingested water is calculated for the above dinosaur groups. On a member scale, when meteoric-water values are compared with calculated dinosaur drinking water, values are equal to or lighter than meteoric water for most herbivorous groups (as low as 215.5% for ornithischians) and equal to or heavier than meteoric water for most carnivorous groups (as high as 22.0% for allosauroids). Changes in d 18 O meteoric water , d 18 O dinosaur ingested water , faunal assemblages, and sedimentology, from member to member, correlate to thrusting events of the Sevier Orogeny. High elevations in the orogeny attenuated the influences of Pacific moisture, causing rainshadow-induced aridity on the leeward foreland basin during upper Yellow Cat time, and hosted seasonal snow accumulation by the end of Ruby Ranch time, as suggested by 18 O-enriched water (e.g., up to an average of 22.0% from an allosauroid tooth) and extremely 18 O-depleted water (e.g., 215.5% for ornithischians) in the Ruby Ranch Member. By Mussentuchit-time, delivery of the Western Interior Seaway-dominated moisture to the region, despite continued rise of the Sevier Mountains.
Paleozoic sequence stratigraphy; views from the North American Craton, 1996
The Decorah Formation of eastern Iowa was deposited on an open-marine subtidal shelf near storm w... more The Decorah Formation of eastern Iowa was deposited on an open-marine subtidal shelf near storm wave base. Maximum transgression is represented in organicrich strata of the Guttenberg Member. Brachiopod-derived marine carbonate isotopic compositions from the Decorah are approximately δ 13 C = +1‰ and δ 18 O = -3.5‰; these data are consistent with a recently recognized long-term secular increase in the δ 18 O of Middle Ordovician marine carbonates. Decorah carbonates lithified in early diagenetic modified-marine phreatic environments. Isotopic data from diagenetic components show that the Spechts Ferry Member lithified in a more fluid-dominated diagenetic system than the immediately overlying Guttenberg Member, which was characterized by a rock-dominated system. Whole-rock carbonate δ 13 C shifts in the Decorah Formation are carried by micritic components. A positive shift in the Guttenberg to micrites with δ 13 C values up to +2.5‰ indicates that some of the micrite isotopic signal is primary and not of benthic origin and/or that early diagenetic marine phreatic fluids in the organic-rich Guttenberg were affected by bacterial methanogenesis. Subtidal shallowing-upward depositional cycles in the Decorah are internally characterized by micrites with stratigraphically upward trends toward 13 C depletion as a consequence of increasing diagenetic water/rock ratios. Decoupling between coeval carbon isotopic signals carried by open-marine brachiopod carbonate and those of organic carbon and micrite indicates that the positive carbon isotopic excursion in the Guttenberg resulted from an episode of increased photosynthetic productivity near the sea surface. This event was a consequence of quasiestuarine circulation associated with marine transgression during deposition of the Guttenberg Member. Results from this study suggest that the extinct organic-walled microfossil Gloeocapsomorpha prisca, the principal source of organic carbon in the Decorah Formation, was a phytoplanktic organism.
Sedimentology, 2004
Meteoric sphaerosiderite lines (MSLs), defined by invariant δ18O and variable δ13C values, are ob... more Meteoric sphaerosiderite lines (MSLs), defined by invariant δ18O and variable δ13C values, are obtained from ancient wetland palaeosol sphaerosiderites (millimetre‐scale FeCO3 nodules), and are a stable isotope proxy record of terrestrial meteoric isotopic compositions. The palaeoclimatic utility of sphaerosiderite has been well tested; however, diagenetically altered horizons that do not yield simple MSLs have been encountered. Well‐preserved sphaerosiderites typically exhibit smooth exteriors, spherulitic crystalline microstructures and relatively pure (> 95 mol% FeCO3) compositions. Diagenetically altered sphaerosiderites typically exhibit corroded margins, replacement textures and increased crystal lattice substitution of Ca2+, Mg2+ and Mn2+ for Fe2+. Examples of diagenetically altered Cretaceous sphaerosiderite‐bearing palaeosols from the Dakota Formation (Kansas), the Swan River Formation (Saskatchewan) and the Success S2 Formation (Saskatchewan) were examined in this study...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2002
A latitudinal gradient in meteoric N 18 O compositions compiled from paleosol sphaerosiderites th... more A latitudinal gradient in meteoric N 18 O compositions compiled from paleosol sphaerosiderites throughout the Cretaceous Western Interior Basin (KWIB) (34^75 ‡N paleolatitude) exhibits a steeper, more depleted trend than modern (predicted) values (3.0x [34 ‡N latitude] to 9.7x [75 ‡N] lighter). Furthermore, the sphaerosiderite meteoric N 18 O latitudinal gradient is significantly steeper and more depleted (5.8x [34 ‡N] to 13.8x [75 ‡N] lighter) than a predicted gradient for the warm mid-Cretaceous using modern empirical temperature^N 18 O precipitation relationships. We have suggested that the steeper and more depleted (relative to the modern theoretical gradient) meteoric sphaerosiderite N 18 O latitudinal gradient resulted from increased air mass rainout effects in coastal areas of the KWIB during the mid-Cretaceous. The sphaerosiderite isotopic data have been used to constrain a mass balance model of the hydrologic cycle in the northern hemisphere and to quantify precipitation rates of the equable 'greenhouse' Albian Stage in the KWIB. The mass balance model tracks the evolving isotopic composition of an air mass and its precipitation, and is driven by latitudinal temperature gradients. Our simulations indicate that significant increases in Albian precipitation (34^52%) and evaporation fluxes (76^96%) are required to reproduce the difference between modern and Albian meteoric siderite N 18 O latitudinal gradients. Calculations of precipitation rates from model outputs suggest mid^high latitude precipitation rates greatly exceeded modern rates (156^220% greater in mid latitudes [2600^3300 mm/yr], 99% greater at high latitudes [550 mm/yr]). The calculated precipitation rates are significantly different from the precipitation rates predicted by some recent general circulation models (GCMs) for the warm Cretaceous, particularly in the mid to high latitudes. Our mass balance model by no means replaces GCMs. However, it is a simple and effective means of obtaining quantitative data regarding the mid-Cretaceous hydrologic cycle in the KWIB. Our goal is to encourage the incorporation of isotopic tracers into GCM simulations of the mid-Cretaceous, and to show how our empirical data and mass balance model estimates help constrain the boundary conditions.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2008
Stable isotope mass-balance modeling results of meteoric δ 18 O values from the Cenomanian Stage ... more Stable isotope mass-balance modeling results of meteoric δ 18 O values from the Cenomanian Stage of the Cretaceous Western Interior Basin (KWIB) suggest that precipitation and evaporation fluxes were greater than that of the present and significantly different from simulations of Albian KWIB paleohydrology. Sphaerosiderite meteoric δ 18 O values have been compiled from the Lower Tuscaloosa Formation of southwestern Mississippi (25°N paleolatitude), The Dakota Formation Rose Creek Pit, Fairbury Nebraska (35°N) and the Dunvegan Formation of eastern British Columbia (55°N paleolatitude). These paleosol siderite δ 18 O values define a paleolatitudinal gradient ranging from -4.2‰ VPDB at 25°N to -12.5‰ VPDB at 55°N. This trend is significantly steeper and more depleted than a modern theoretical siderite gradient (25°N: -1.7‰; 65°N: -5.6‰ VPDB ), and a Holocene meteoric calcite trend (27°N: -3.6‰; 67°N: -7.4‰ VPDB). The Cenomanian gradient is also comparatively steeper than the Albian trend determined for the KWIB in the mid-to high latitudes. The steep latitudinal trend in meteoric δ 18 O values may be the result of increased precipitation and evaporation fluxes (amount effects) under a more vigorous greenhouse-world hydrologic cycle. A stable-isotope mass-balance model has been used to generate estimates of precipitation and evaporation fluxes and precipitation rates. Estimates of Cenomanian precipitation rates based upon the mass-balance modeling of the KWIB range from 1400 mm/yr at 25°N paleolatitude to 3600 mm/yr at 45°N paleolatitude. The precipitation-evaporation (P-E) flux values were used to delineate zones of moisture surplus and moisture deficit. Comparisons between Cenomanian P-E and modern theoretical siderite, and Holocene calcite latitudinal trends shows an amplification of low-latitude moisture deficits between 5-25°N paleolatitude and moisture surpluses between 40-60°N paleolatitude. The low-latitude moisture deficits correlate with a mean annual average heat loss of 48 W/m 2 at 10°N paleolatitude (present, 8 W/m 2 at 15°N). The increased precipitation flux and moisture surplus in the mid-latitudes corresponds to a mean average annual heat gain of 180 W/m 2 at 50°N paleolatitude (present, 17 W/m 2 at 50°N). The Cenomanian lowlatitude moisture deficit is similar to that of the Albian, however the mid-latitude (40-60°N) precipitation flux values and precipitation rates are significantly higher (Albian: 2200 mm/yr at 45°N; Cenomanian: 3600 mm/yr at 45°N). Furthermore, the heat transferred to the atmosphere via latent heat of condensation was approximately 10.6× that of the present at 50°N. The intensified hydrologic cycle of the mid-Cretaceous greenhouse warming may have played a significant role in the poleward transfer of heat and more equable global conditions. Paleoclimatological reconstructions from multiple time periods during the mid-Cretaceous will aid in a better understanding of the dynamics of the hydrologic cycle and latent heat flux during greenhouse world conditions.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2011
This study aims to investigate the global hydrologic cycle during the mid-Cretaceous greenhouse b... more This study aims to investigate the global hydrologic cycle during the mid-Cretaceous greenhouse by utilizing the oxygen isotopic composition of pedogenic carbonates (calcite and siderite) as proxies for the oxygen isotopic composition of precipitation. The data set builds on the Aptian-Albian sphaerosiderite δ 18 O data set presented by by incorporating additional low latitude data including pedogenic and early meteoric diagenetic calcite δ 18 O. used the proxy data derived from the North American Cretaceous Western Interior Basin (KWIB) in a mass balance model to estimate precipitation-evaporation fluxes. We have revised this mass balance model to handle sphaerosiderite and calcite proxies, and to account for longitudinal travel by tropical air masses. We use empirical and general circulation model (GCM) temperature gradients for the mid-Cretaceous, and the empirically derived δ 18 O composition of groundwater as constraints in our mass balance model. Precipitation flux, evaporation flux, relative humidity, seawater composition, and continental feedback are adjusted to generate model calculated groundwater δ 18 O compositions (proxy for precipitation δ 18 O) that match the empirically-derived groundwater δ 18 O compositions to within ±0.5‰. The model is calibrated against modern precipitation data sets. Four different Cretaceous temperature estimates were used: the leaf physiognomy estimates of Wolfe and Upchurch (1987) and , the coolest and warmest Cretaceous estimates compiled by and model outputs from the GENESIS-MOM GCM by . Precipitation and evaporation fluxes for all the Cretaceous temperature gradients utilized in the model are greater than modern precipitation and evaporation fluxes. Balancing the model also requires relative humidity in the subtropical dry belt to be significantly reduced. As expected calculated precipitation rates are all greater than modern precipitation rates. Calculated global average precipitation rates range from 371 mm/year to 1196 mm/year greater than modern precipitation rates. Model results support the hypothesis that increased rainout produces δ 18 O-depleted precipitation. Sensitivity testing of the model indicates that the amount of water vapor in the air mass, and its origin and pathway, significantly affect the oxygen isotopic composition of precipitation. Precipitation δ 18 O is also sensitive to seawater δ 18 O and enriched tropical seawater was necessary to simulate proxy data (consistent with fossil and geologic evidence for a warmer and evaporatively enriched Tethys). Improved constraints in variables such as seawater δ 18 O can help improve boundary conditions for mid-Cretaceous climate simulations.
Journal of Sedimentary Research, 2001
The MD 80-08 coal exploration core from the Albian Boulder Creek Formation of northeastern Britis... more The MD 80-08 coal exploration core from the Albian Boulder Creek Formation of northeastern British Columbia contains 90 m of alluvial strata that underwent extensive pedogenic modification. Gleyed colors, pedogenic slickensides, clay coatings, mottling, sphaerosiderite, and sedimentary pyrite characterize the paleosols. The isotopic compositions of 30 sphaerosiderite-bearing horizons commonly show trends of invariant ␦ 18 O and variable ␦ 13 C values. Equal-area plots of ␦ 18 O vs. ␦ 13 C were used to construct meteoric sphaerosiderite lines (MSLs). The MSLs indicate that meteoric groundwater compositions ranged from approximately Ϫ11‰ to Ϫ16‰ (SMOW). The sphaerosiderite ␦ 18 O values indicate formation in shallow groundwaters predominantly recharged by local precipitation. The sphaerosiderite isotopic compositions are a proxy record of mid-Cretaceous precipitation, and are useful for quantifying changes in the hydrologic cycle during humid ''greenhouse'' periods. Micromorphology of a 1.15 meter interval (69.75-68.6 m), with a ؉1.31‰ increase in the average ␦ 18 O values, records a polygenetic history of paleosol development. The pedocomplex has a four-stage developmental history characterized by: (1) an initial well-drained phase, with wet-dry cycles and relatively low baselevel; (2) erosion, baselevel rise and coarser-grained sedimentation; (3) saturated, reducing soil conditions, high baselevel, with some marine influence on pedogenesis; and (4) meteoric-water-dominated hydromorphic soil conditions, high baselevel, and sphaerosiderite precipitation. The ␦ 18 O excursion recorded through this interval reflects minor mixing of marine and meteoric groundwaters. The modal abundance of pyrite, and increased Mg/(Ca ؉ Mg) and Mg/Fe cation ratios in the sphaerosiderites further substantiate marine influence on pedogenesis. The alluvial section of the Boulder Creek Formation is aggradational, and several changes in baselevel recorded in the paleosols are interpreted to have been driven by minor (parasequence-scale) changes in relative sea level.
Journal of Sedimentary Research, 2010
Recent studies utilize the oxygen isotopic composition of pedogenic carbonates (siderite and calc... more Recent studies utilize the oxygen isotopic composition of pedogenic carbonates (siderite and calcite) to evaluate empirically the global hydrologic cycle during the Cretaceous. Pedogenic carbonates are used as a proxy for the isotopic composition of meteoric waters in order to estimate precipitation rates in the Aptian-Albian via a mass-balance model. These modeling studies have previously been limited to mid-latitude to high-latitude data, and thus a more extensive latitudinal data set is needed to produce a more globally constrained model. This study provides an equatorial (, 2u S paleolatitude) data set from pedogenic sphaerosiderites of the Caballos Formation from the Upper Magdalena Valley, Colombia. In addition, macroscopic and microscopic morphological features of paleosols were used to identify ancient soil conditions. The gleyed appearance and presence of sphaerosiderites suggest that soils were dominated by water-saturated conditions, with occasional incursions of marine-influenced water resulting in pyrite precipitation. This observation constrains the sampling sites to paleoelevations near sea level. Paleosols are interpreted to have been Entisols, Inceptisols, and Ultisols similar to soils in coastal equatorial regions of modern Colombia. Relatively invariant d 18 O values and more variable d 13 C values produce vertical trends in d 13 C vs. d 18 O space called meteoric sphaerosiderite lines. The average oxygen isotopic composition for these trends is 24.41 ± 0.37% (VPDB). The average oxygen isotopic composition of meteoric waters precipitating the sphaerosiderites is estimated at 24.56 ± 0.38% (VSMOW). These are slightly more enriched than modern and modeled Cretaceous estimates of equatorial precipitation d 18 O but are generally in agreement with expected oxygen isotopic compositions of precipitation for this paleolatitude.
Journal of Sedimentary Research, 2010
Nodular carbonates (''calcretes'') in continental foreland-basin strata of the Early Cretaceous C... more Nodular carbonates (''calcretes'') in continental foreland-basin strata of the Early Cretaceous Cedar Mountain Formation (CMF) in eastern Utah yield d 13 C and d 18 O records of changes in the exogenic carbon cycle related to oceanic anoxic events (OAEs), and terrestrial paleoclimate. Chemostratigraphic profiles of both forebulge and foredeep sections show two prominent positive d 13 C excursions, each with a peak value of 23% VPDB, and having background d 13 C values of about 26% VPDB. These excursions correlate with the global early Aptian (Ap7) and late Aptian-early Albian (Ap12-Al1) carbon isotope excursions. Aptian-Albian positive d 13 C excursions in the CMF also correspond to 3-4 per mil increases in carbonate d 18 O. These phenomena record local aridification events. The chemostratigraphic profile on the thinner forebulge section of the CMF is calibrated, for the first time, by a radiogenic U-Pb date of 119.4 ± 2.6 Ma on a carbonate bed, and by detrital zircon U-Pb dates on two bounding sandstone units (maximum depositional ages of 146 Ma and 112 Ma). Petrographic observations and diagenetic analyses of micritic to microsparitic carbonates from nodules indicate palustrine origins and demonstrate that they crystallized in shallow early meteoric phreatic environments. Meteoric calcite lines derived from CMF carbonates have d 18 O values ranging between 28.1 to 27.5% VPDB, supporting an estimate of zonal mean groundwater d 18 O of 26% VSMOW for an Aptian-Albian paleolatitude of 34u N. Furthermore, our two chemostratigraphic profiles exhibit a generally proportionate thinning of correlative strata from the foredeep on to the forebulge, suggesting that there were consistently lower rates of accumulation on the forebulge during the Aptian-Albian. Identification of the global Aptian-Albian d 13 C excursions in purely continental strata, as demonstrated in this paper, opens a new avenue of research by identifying specific stratigraphic intervals that record the terrestrial paleoclimatic impacts of perturbations of the global carbon cycle.
Journal of Sedimentary Research, 2005
The Albian Stage of the mid-Cretaceous was a time of equable climate conditions with high sea lev... more The Albian Stage of the mid-Cretaceous was a time of equable climate conditions with high sea levels and broad shallow epeiric seas that may have had a moderating affect on continental climates. A Late Albian landscape surface that developed during a regression and subsequent sealevel rise in the Western Canada Foreland Basin is reconstructed on the basis of correlation of paleosols penetrated by cores through the Paddy Member of the Peace River Formation. Reconstruction of this landscape refines chronostratigraphic relationships and will benefit future paleoclimatological studies utilizing continental sphaerosiderite proxy records. The paleosols developed in estuarine sandstones and mudstones, and they exhibit evidence of a polygenetic history. Upon initial exposure and pedogenesis, the Paddy Member developed deeply weathered, well-drained cumulative soil profiles. Later stages of pedogenesis were characterized by hydromorphic soil conditions. The stages of soil development interpreted for the Paddy Member correlate with inferred stages of pedogenic development in timeequivalent formations located both basinward and downslope (upper Viking Formation), and landward and upslope (Boulder Creek Formation). On the basis of the genetic similarity among paleosols in these three correlative formations, the paleosols are interpreted as having formed along a single, continuous landscape surface. Results of this study indicate that the catena concept of pedogenesis along sloping landscapes is applicable to ancient successions. Sphaerosiderites in the Paddy Member paleosols are used to provide proxy values for meteoric d 18 O values at 52u N paleolatitude in the Cretaceous Western Interior Basin. The meteoric d 18 O values are used to refine existing interpretations about the mid-Cretaceous paleolatitudinal gradient in meteoric d 18 O values, and the mid-Cretaceous hydrologic cycle.
Geology, 2001
We present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid-lati... more We present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid-latitude North America based on the oxygen isotopic composition of sphaerosiderites found in middle Cretaceous wetland paleosols. Our reconstructed middle Cretaceous ␦ 18 O values of precipitation are ϳ4‰ less than values from comparable modern low-elevation coastal settings free of monsoons. The data fit a conceptual model in which the precipitation source for the eastern margin of the Cretaceous Western Interior Seaway of North America is an 18 O-enriched oceanic coastal jet. In this subtropical-tropical setting, mid-Cretaceous precipitation rates are interpreted to range from ϳ2500 to ϳ4100 mm/yr.
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Papers by Luis Ariel Gonzalez