Calcareous Paleosols Research Articles

Characterization of the Carnian Pluvial Episode in the Argana Basin (Western High Atlas, Morocco): An approach based on sedimentology, clay mineralogy and paleosols

We report on a multi-proxy study of the Carnian Pluvial Episode in the continental Argana Basin (Morocco) based on mineralogy, geochemistry, paleosols and sedimentary features. The study focus on two sections of the Irohalene Member (unit t5) of the Timezgadiouine Formation dated as late Julian-early Tuvalian through clam shrimp (conchostracan) associations. The sedimentary study of the Irohalene Member defines three parts: lower, middle and upper (t5.1, t5.2, t5.3 respectively). The base of the lower part comprises channels with gravel and sandy bars related to proximal areas, and fluvial meandering systems, overbank and floodplain deposits developing upwards. Extensive floodplains showing the development of siliciclastic and carbonate lakes mostly represent the t5.2 and t5.3 parts, although the sedimentary characteristics of the former reflect more humid and permanent water conditions. These more humid characteristics are also indicated by the drastic change from calcareous paleosols in t5.1 to smectitic Vertisols in t5.2, which occur in relation to thin layers of lacustrine carbonates, greenish lutites, and hybrid oolitic sandstones of palustrine environments. Stable carbon and oxygen isotope data are consistent with a general tendency towards the arid conditions observed in the Tadart Ouadou t6 Member of the Bigoudine Formation, of fluvial-eolian origin and younger in age. This general tendency is interrupted by at least two humid yet hot intervals characterized by pedogenic carbonates featuring lighter isotope compositions and lacustrine carbonates precipitated under conditions of high temperatures and evaporation rates.

Mesoproterozoic calcareous paleosols from Montana

Calcareous soils are widespread in aridlands today, and common as Phanerozoic paleosols, but rare among Precambrian paleosols. Their geological antiquity is relevant to reconstructing Precambrian atmospheric CO2 and soil microbiomes. This contribution documents in detail calcareous paleosols (Calcids) and other paleosols dated to 1460 Ma (Calymman) from the Spokane Formation of the Belt Supergroup near Wolf Creek, Montana. Dolomitic Calcids may be as old as Paleoproterozoic (2403 Ma), or perhaps Archean (2600 Ma), but these Mesoproterozoic paleosols are the oldest known calcitic Calcids. Chemical data and Bk metrics are evidence that these paleosols formed in a temperate, semiarid climate with pronounced seasonality. A stable isotope paleobarometer for the carbonate is evidence of atmospheric CO2 levels of 1798 ± 502 ppm, compatible with the greenhouse effect needed at that time to offset the faint young sun. Comparable levels of CO2 can also be calculated from consumption of cationic bases during soil formation. Redox element distribution in the paleosols is evidence of O2 levels of <1%, barely adequate for respiration of eukaryotes, but there is evidence of a microbial earth terrestrial ecosystem from phosphorus depletion, nodule distribution, and stable isotopic correlation.

Multiproxy Paleosol Evidence for Jurassic Paleoclimate Fluctuations in the Sichuan Basin, SW China

AbstractPaleoclimate reconstruction of continental environments has been hampered by the limited evidence. A thick sequence of Jurassic continental deposits in the Sichuan Basin, Southwest China yields abundant paleosols that may offer valuable insights regarding Jurassic climate scenarios. A succession of 169 paleosols belonging to Protosols, Calcisols, and Argillisols from 23 detailed stratigraphic sections was recognized and characterized macro‐ and micromorphologically and assessed for mineral and geochemical compositions. Quantitative paleoclimate reconstructions using bulk geochemical proxies, the depth to and the stable oxygen isotopic composition of paleosol carbonates indicated a predominant alternation of semiarid and arid cool/warm‐temperate climatic conditions punctuated by several episodes of subhumid and humid climates that generally prevailed in the Sichuan Basin during the Jurassic. The estimated paleoatmospheric CO2 concentrations (pCO2) from calcic paleosols yielded a low range of ∼104 ± 58 to ∼610 ± 152 ppmv during the Middle Jurassic. The terrestrial paleotemperature changes in the Sichuan Basin coincided with the pCO2 variations, which probably resulted from global geological events (e.g., volcanic activities, magmatic and oceanic events, and the ephemeral caps development) in the Middle Jurassic. Jurassic climatic fluctuations in the basin were likely attributed to true polar wander due to global plate motion, megamonsoon effect linked to global and regional paleogeography, and regional paleotopography.

Alluvial fans in the latest phase of the Messinian Salinity Crisis: An example from the Chaabet Et Tabbela Formation, northern Tunisia, Central Mediterranean

Alluvial fan deposits record important information about paleoclimate, tectonic setting, and paleogeography that can be deciphered with detailed sedimentological analysis. The late Messinian Chaabet Et Tabbela Formation, in the western part of the Kechabta Basin in northern Tunisia, shows excellent examples of alluvial fans deposited during the latest phase of the Messinian Salinity Crisis, the Lago Mare event. This exposure provides the opportunity to investigate terrestrial depositional conditions during this period. The Chaabet Et Tabbela Formation was investigated through sedimentological logging and detailed facies analysis at eight locations. Sixteen facies types were identified and interpreted along with variation in clast compositions. These facies were further grouped into four facies associations: (1) proximal alluvial fan, dominated by gravity-driven processes, (2) medial alluvial fan, which mainly comprises a mix of debris flow and high-sediment load streamflow deposits, (3) distal alluvial fan, which consists of laterally continuous sheetflood and subordinate channels deposits, and (4) playa and floodplain, which are made of red mudstones with calcareous paleosols. Clast composition of these fan deposits comprises Triassic, Jurassic, and Cretaceous bedrock suggesting that sediment was sourced from the surrounding Maghrebian mountain chain. Two laterally adjacent alluvial fans were identified along the N-S Messeftine Fault. These fans have prograded during the Late Messinian, with an estimated radius of ca 2 km.The evolution of these alluvial fans is related to a complex interplay of allogenic processes. The uplift related to intra-Messinian tectonic event and climate variation contributed to the formation of these fans during the late Messinian. Although, these deposits are relatively limited in extension, similar continental deposits form synchronously in different marginal Mediterranean basins during the Lago Mare stage, suggesting that the alluvial fans of the Chaabet Et Tabbela Formation should be placed in a context of regionally change climactic and paleogeographic conditions.

Late Pennsylvanian Calcareous Paleosols from Central New Mexico: Implications for Paleoclimate

We document calcareous paleosols from Upper Pennsylvanian (lower Virgilian) strata of the Burrego Member of the Atrasado Formation in the Cerros de Amado of Socorro County, New Mexico. The Burrego paleosols are an excellent example of a scarce, climate-sensitive lithology in the Pennsylvanian strata of New Mexico. These paleosols contain mostly stage II to III carbonate horizons, and their overall morphology suggests deposition and pedogenesis under subhumid, seasonally dry conditions. This conclusion is consistent with paleobotanical and other data that indicate such climate conditions were widespread on Late Pennsylvanian Pangea. The mean value of the oxygen-isotope ratios from Burrego paleosol carbonates compares well with the values from Virgilian paleosols of the San Juan, the eastern Midland and Chama basins of New Mexico-Texas, suggesting similar conditions of temperature and paleoprecipitation. Application of the diffusion-reaction model to the mean carbon-isotope composition of the carbonate suggests a paleo-pCO2 of approximately 400 ppmV, which is also consistent with estimates from correlative carbonate deposits that formed farther east in Late Pennsylvanian Pangea.

Zebra rock and other Ediacaran paleosols from Western Australia

Zebra rock is an ornamental stone from the early Ediacaran, Ranford Formation, around and in Lake Argyle, south of Kununurra, Western Australia. It has been regarded as a marine clay, liquid crystal, groundwater alteration, unconformity paleosol or product of acid sulfate weathering. This study supports the latter hypothesis and finds modern analogues for its distinctive red banding in mottling of gleyed soils. Other acid sulfate paleosols of desert playas (Gypsids) are also are found in the Ranford Formation, as well as calcareous desert paleosols (Calcids). The megafossil Palaeopaschnicnus also found in associated grey shales may have been a chambered protozoan, but Yangtziramulus in calcic paleosols is most like a microbial earth lichen. Soil climofunctions are evidence of an arid, cool temperate climate during the early Ediacaran. KEY POINTS Ornamental stones known as ‘zebra rock’ are interpreted as Ediacaran gleyed soils. Gypsum desert-rose beds are interpreted as Ediacaran acid sulfate soils (Gypsids). Calcareous nodular loess beds are interpreted as Ediacaran desert soils (Gypsids).

Calcic Vertisols in the upper Daptocephalus Assemblage Zone, Balfour Formation, Karoo Basin, South Africa: Implications for Late Permian Climate

ABSTRACT The fully continental succession of the Beaufort Group, Karoo Basin, South Africa, has been used in the development of environmental models proposed for the interval that spans the contact between the Daptocephalus to Lystrosaurus Assemblage Zones, associated by some workers with the end-Permian extinction event. An aridification trend is widely accepted, yet geochemical data indicate that the majority of in situ paleosols encountered in this interval developed in waterlogged environments. To date, the presence of calcic paleosols in the latest Permian can be inferred only from the presence of calcite-cemented pedogenic nodules concentrated in fluvial channel-lag deposits. Here, we report on the first empirical evidence of in situ calcic Vertisols found in the upper Daptocephalus Assemblage Zone near Old Wapadsberg Pass, one of eight classic localities in which the vertebrate turnover is reported in the Karoo Basin. Seven discrete intervals of calcic Vertisols, exposed over a very limited lateral extent, occur in an ∼ 25 m stratigraphic interval. Estimates of mean annual temperature and mean annual precipitation are calculated from geochemical measurements of one paleosol, and these estimates indicate that the prevailing climate at the time of pedogenesis was seasonally cold and humid. Correlation with adjacent stratigraphic sections indicates that the late Permian landscape experienced poorly drained and better-drained phases, interpreted to reflect a climate that varied between episodically dry and episodically wet. In contrast to a paleoenvironmental reconstruction of unidirectional aridification from strata in the Wapadsberg Pass region, this study provides new evidence for a wetting trend towards the Daptocephalus–Lystrosaurus Assemblage-Zone boundary.

Late Miocene drying of central Australia

A back to the future approach to climate change refines Neogene records of paleoclimatic cooling and drying as future climate states for a warming world. Near Alcoota station in central Australia is a late Miocene fossil mammal site for Alcoota (10 Ma) and Ongeva (8 Ma) local faunas. The Alcoota fauna includes the largest known land bird (Dromornis stirtoni) and early diprotodontid (Kolopsis torus), but the geologically younger Ongeva fauna has a larger diprotodontid (Zygomaturus gilli). These faunas are evolutionary predecessors of Australian Pleistocene megafauna. Calcareous paleosols recorded a marked turn toward aridity compared with underlying thick lateritic duricrusts which lack fossils. Laterites of likely middle Miocene age are evidence of wet (>1100 mm mean annual precipitation) tropical (>17 °C mean annual temperature) paleoclimates, but these were deeply eroded and redeposited by the time of the late Miocene mammals. A succession of 19 paleosols of 5 pedotypes were recognized in the 19 m thick section, with shallow calcareous nodule (Bk) horizons as evidence of mean annual precipitation ranges from 100 to 400 mm, and mean annual range of precipitation of 50 mm, very similar to the modern climate of Alcoota (296 mm precipitation with 56 mm difference between wet and dry month). This was neither a rainforest nor monsoonal paleoclimate, and vegetation inferred from paleosols was open woodland and gallery woodland similar to that of today. Central Australia was not covered by monsoon rainforest during the late Miocene and its paleoclimatic history of Neogene desertification matches well that of other parts of the world.

Oxygen and Carbon Stable Isotope Composition of Cretaceous to Pliocene Calcareous Paleosols in the Tian Shan Region (Central Asia): Controlling Factors and Paleogeographic Implications

The Late Mesozoic–Cenozoic topographic and climate evolution of Central Asia remains highly debated. The final retreat of the proto-Paratethys Sea from the western Tarim Basin is thought to correspond in time with the onset of tectonic uplift in the Pamir, Tian Shan and Altai ranges, as well as with regional aridification. The oxygen and carbon isotope compositions of the sediment deposits in the various Central Asian basins have already been used to decipher both the topographic and climatic changes that occurred in that region during the Cenozoic, generally concentrating on one sedimentary section and/or on a limited time range and either using multiple-type samples including sandstone calcitic cements, marine carbonates, fossils, or paleosols. In order to get a homogeneous dataset, minimizing variations in the isotopic composition of the material depending on its type and/or depositional environment, we selected only calcareous paleosols sampled in several continuous sections covering a wide time range from the Late Jurassic to the Pliocene. Our sampling also covers a wide area encompassing the whole Tian Shan region, which allows detecting regional variations in the δ18O and δ13C values. We show that the influence of the distance to the proto-Paratethys Sea on the paleosol δ18O record was not significant. Besides local factors such as the occurrence of large lakes that can have a significant effect on the isotopic composition of the calcareous paleosols, the long-term evolution of both the δ18O and δ13C values possibly reflects the hypsometry of the river drainage systems that bring water to the basins. However, as it is commonly accepted that the δ18O of soil carbonates is controlled by the δ18O of in-situ precipitation, this last conclusion remains to be further investigated.

Late Cretaceous–Palaeogene topography of the Chinese Tian Shan: New insights from geomorphology and sedimentology

The Cenozoic growth of the intra-continental Tian Shan Range initiated during the late Eocene–Oligocene, and led to a tectonic reactivation of the complex Palaeozoic and Mesozoic lithospheric structure. Due to the very low erosion rates linked to the semi-arid climate that characterised the Tian Shan region during most of the Cenozoic, the topography of the range is not at equilibrium with deformation. Fragments of pre-orogenic low relief surfaces are preserved among the Late Cenozoic Alpine-type topography. Using field observations and satellite image mapping of those fragments, as well as sedimentology and biostratigraphic analysis, we show that the pre-Oligocene topography of the Tian Shan region was indeed complex, combining hundreds of metres to one-and-a-half kilometre-high reliefs with a multi-phased Mesozoic planation surface incised by Late Mesozoic paleo-valleys. The occurrence of several metres-thick Late Cretaceous–Palaeogene calcareous paleosols, in the basins surrounding the range further implies a semi-arid climate, very low subsidence rates and no uplift at that time. Late Cretaceous and early Miocene fossil records in the northern Tian Shan suggest a possible connection, even if episodic, between the drainage system of the south Junggar foreland basin and the proto-Paratethys Sea to the west. A renewed late Eocene–early Oligocene sedimentation probably marks the onset of the Tian Shan uplift. We argue that in addition to the growth of the Pamir and Western Kunlun ranges, this incipient uplift was one of the driving mechanisms for the final retreat of the proto-Paratethys Sea from the Tarim Basin. This regression apparently did not change the climate in the studied area because semi-arid conditions seem to prevail at least since the Late Cretaceous. Finally, the Tian Shan uplift remained very limited up to the Miocene as revealed by the occurrence of Burdigalian lake deposits preserved in the paleo-valleys inside the present day range. In contrast, post-early Miocene deformation of the northern Tian Shan has produced 4000 to 5000 m of differential vertical movement between the uplifted range and the subsiding proximal foreland basin.

Isotopic evidence for ecological and climate change in the richly fossiliferous Plio-Pleistocene Upper Siwalik deposits exposed around Chandigarh, India

The Plio-Pleistocene Siwalik deposits around Chandigarh, well known for their great wealth of mammalian fossils, preserve a continuous record of calcareous paleosols ranging in age from ∼2.7 to ∼0.6 Ma. The carbon isotope composition (δ13C relative to Vienna Peedee belemnite [VPDB]) of 140 pedogenic carbonates from Ghaggar and Nadah sections and 13 gastropod samples from Nadah section record a landscape primarily occupied by C4 grasses during this interval. However, a mixed C3–C4 vegetation between 2.15 and 1.7 Ma and a progressive increase in the percentage of C3 plants from ∼1.1 to ∼0.6 Ma has been recorded. Most of the pedogenic carbonate δ18O values (VPDB) in the Ghaggar River Section range between −5.29 and −8.93‰ indicating the dominance of monsoon climate. These δ18O values exhibit somewhat consistent trend in relation to δ13C values suggesting influence of climate on the vegetation. At two instances ∼1.07 and ∼0.66 Ma, there is significant depletion in carbonate δ18O and δ13C values, suggesting monsoon intensification and a synchronous development of C3 vegetation. Pedogenic carbonate and gastropod δ18O values (VPDB) in the Nadah paleoswamp, also exhibit consistent trends in relation to δ13C values, indicating steady relationship between short-term climatic fluctuations in terms of warm-humid and cool-dry conditions and the abundance of C3/C4biomass on the landscape nearly 1.8 Ma ago. The vegetation change on the Siwalik landscape during Early and Middle Pleistocene appears to have been influenced mainly by the regional tectonics, sedimentation patterns and monsoonal rains rather than global climate changes.

Large mammal burrows in late Miocene calcic paleosols from central Argentina: paleoenvironment, taphonomy and producers.

Large cylindrical sediment-filled structures interpreted as mammal burrows occur within the loess-paleosol sequence of the late Miocene Cerro Azul Formation of central Argentina. A total of 115 burrow fills from three localities were measured. They are typically shallowly dipping, subcylindrical, unbranched structures with rounded ends and lacking enlargements. The horizontal diameter of the burrows range between 0.15 and 1.50 m, with most of the burrows in the interval of 0.39 to 0.98 m. Geometric morphometric analysis of transverse cross-sections support their distinct subcircular and elliptical (horizontally flattened) shapes. Burrow fills are typically laminated in the lower part and massive in the upper part. The laminated intervals reflect pulses of flowing water entering the abandoned burrow during moderate rains, whereas massive intervals reflect mass flow input of dense sediment-water mixtures during heavy rains that produced sheet floods. Approximately 1% of the burrows contained fragmentary, disarticulated and weathered mammal bones that were introduced in the open burrow by currents along with other sedimentary particles. Analysis of the tetrapod burrow fossil record suggests that Miocene burrows, including those studied herein, reflect a remarkable increase in the average size of the fossorial fauna. We conclude that large late Miocene mammals dug burrows essentially as a shelter against environmental extremes and to escape predation. The simple architecture of the burrows suggests that the producers essentially foraged aboveground. Several mammal groups acquired fossorial habits in response to cold and seasonally dry climatic conditions that prevailed during the late Miocene in southern South America. The considerable range of horizontal diameters of the studied burrows can be attributed to a variety of producers, including dasypodids, the notoungulate Paedotherium minor, Glyptodontidae and Proscelidodon sp.

ORIGIN OF THE CARNEGIE QUARRY SANDSTONE (MORRISON FORMATION, JURASSIC) AT DINOSAUR NATIONAL MONUMENT, JENSEN, UTAH

The Carnegie Quarry at Dinosaur National Monument was excavated in the Quarry Sandstone bed of the Brushy Basin Member of the Morrison Formation (Jurassic). The Quarry Sandstone is a discontinuous, lenticular, heterolithic unit that rests upon drab, greenish-gray claystones and is capped by reddish-brown mudstones. The underlying drab claystones are interpreted as being deposited in an overbank interfluvial wetland or lacustrine environment. By tracing the sandstone and studying detailed measured stratigraphic sections along its 1.8-km outcrop belt, this interval can be shown to be a complex of intergrading sandstone bodies and mudstone units. The Quarry Sandstone interval is reinterpreted as being deposited within a crevasse splay complex. The lowest part of this deposit is a laterally continuous, tabular unit composed of polymictic sandstone and granule conglomerate that directly overlies lacustrine claystones. This unit contains re-sedimented carbonate clasts from the surrounding Brushy Basin, displays a gradational to sharp basal contact, and is interpreted as the initial crevasse splay deposit. Overlying the tabular basal unit are numerous, laterally continuous, upward-coarsening sandstone bodies interpreted as distributary mouth bars. The interpreted distributary mouth bar deposits are cut by lenticular, trough cross-bedded, upward fining sandstone units exhibiting erosional bases. These sandstone lenses are interpreted as distributary channels within the crevasse splay. They, in turn, are overlain by discontinuous sandstone bodies that interfinger with, and are overlain by reddish brown and variegated, rooted mudstones containing calcic paleosols. The Carnegie dinosaur quarry was excavated in one of the main distributary channels of this splay complex.

Paleoecological crisis in the steppes of the Lower Volga region in the Middle of the Bronze Age (III–II centuries BC)

Diagnostic features of a catastrophic aridization of climate, desertification, and paleoecological crisis in steppes of the Lower Volga region have been identified on the basis of data on the morphological, chemical, and microbiological properties of paleosols under archeological monuments (burial mounds) of the Middle Bronze Age. These processes resulted in a certain convergence of the soil cover with transformation of zonal chestnut (Kastanozems) paleosols and paleosolonetzes (Solonetz Humic) into specific chestnut-like eroded saline calcareous paleosols analogous to the modern brown desert-steppe soils (Calcisols Haplic) that predominated in this region 4300–3800 years ago.1 In the second millennium BC, humidization of the climate led to the divergence of the soil cover with secondary formation of the complexes of chestnut soils and solonetzes. This paleoecological crisis had a significant effect on the economy of the tribes in the Late Catacomb and Post-Catacomb time stipulating their higher mobility and transition to the nomadic cattle breeding.

Stable isotope paleohydrology and chemostratigraphy of the Albian Wayan Formation from the wedge-top depozone, North American Western Interior Basin

Understanding of the role of atmospheric moisture and heat transport in the climate system of the Cretaceous greenhouse world represents a major challenge in Earth system science. Stable isotopic paleohydrologic data from mid-Cretaceous paleosols in North America, from paleoequatorial to paleoArctic latitudes, have been used to constrain the oxygen isotope mass balance of the Albian hydrologic cycle. Over the range from 40°–50°N paleolatitude, sideritic paleosols predominate, indicating paleoenvironments with positive precipitation-evaporation (P-E) balances. Local exceptions occur on leeward side of the Sevier Orogen, where calcic paleosols in the wedge-top depozone record paleoenvironments with negative P-E balances in the orographic rain shadow. Stratigraphic sections in the Wayan Formation of Idaho (WF) were sampled from the wedge-top depozone. The units consist of stacked m-scale mudstone paleosols separated by m-scale sandstone-siltstone beds. Sections were sampled for organic carbon isotope profiles, and B-horizons from 6 well-developed paleosols were sampled for detrital zircons to determine maximum depositional ages. The first of these from the WF has produced a U-Pb concordia age of 101.0±1.1 Ma. This same WF section has produced a stratigraphic trend of upwardly decreasing δ13C values ranging from–24‰ upwards to–27‰ VPDB, suggesting correlation to the late Albian C15 C-isotope segment. Pedogenic carbonates from the WF principally consist of micritic calcite, with carbon-oxygen isotope values that array along meteoric calcite lines (MCLs) with δ18O values that range from–9.47‰ up to–8.39‰ VPDB. At approximately 42°N paleolatitude, these MCL values produce calculated paleoprecipitation values of–8.12‰ to–7.04‰ VSMOW, a range that is consistent with the estimates produced from other proxies at the same paleolatitudes across North America. These results indicate that despite the orographic rain shadow effect, the processes of meridional atmospheric moisture transport in this locale were similar to those in more humid mid-latitude paleoenvironments elsewhere in the continent.

The Celliforma ichnofacies in calcareous paleosols: An example from the late Miocene Cerro Azul Formation, La Pampa, Argentina

Invertebrate trace fossils from the late Miocene Cerro Azul Formation (La Pampa, Argentina) are described and compared with known paleosol ichnofacies. The formation is a loess succession punctuated by numerous calcareous paleosols. Trace fossils were recovered from thirteen localities distributed in a wide latitudinal and longitudinal range within La Pampa Province. Paleosols from the northwestern localities display clastic dikes and pedogenic slickensides and are compared with calcic vertisols, which are typical of strongly seasonal and semiarid climate. Paleosols from the remaining localities have a Bt horizon with blocky or prismatic peds and can be compared with mollisols. The depth to the Bk horizon for all paleosols averages 0.54m, suggesting a mean annual precipitation of 450mm (±147mm), also pointing to semiarid climatic conditions during soil formation. The trace fossil assemblage from the Cerro Azul Formation is of low diversity and abundance and is typified by the presence of the insect trace fossils Celliforma, Rosellichnus, Rebuffoichnus, Fictovichnus and Teisseirei. The ichnospecies recorded are: Celliforma germanica, Celliforma cf. rosellii, Celliforma isp., Rosellichnus isp., Rebuffoichnus casamiquelai, Fictovichnus cf. sciuttoi, Fictovichnus isp., Teisseirei barattinia, Taenidium barretti, and cylindrical burrow fills. These trace fossils (along with Attaichnus kuenzelii, vertebrate burrows and medium–sized rhizoliths described in previous works) are considered comparable with the Celliforma ichnofacies. This ichnofacies is indicative of well-drained calcareous paleosols developed under low vegetation coverage. For the analyzed succession the vegetation was probably dominated by scrubs with minor participation of herbaceous plants. Coprinisphaera ispp. (including Coprinisphaera lazai, Coprinisphaera murguiai, and Coprinisphaera isp.) showing a cementation similar to associated late Miocene trace fossils were only recorded, along with Celliforma isp., in two localities. This trace fossil assemblage is comparable with the Coprinisphaera ichnofacies, suggesting dominance of herbaceous communities and wetter climate than those of the Celliforma ichnofacies. Some specimens of uncemented Coprinisphaera ispp. were produced during post-Miocene times and are not considered as a part of the trace fossil assemblage of the Cerro Azul Formation.

Lower Cretaceous paleosols and paleoclimate in Sichuan Basin, China

Abundant Lower Cretaceous (Berriasian–Hauterivian) paleosols have been recognized in the Sichuan Basin, along with the preserved pedogenetic features, e.g., soil horizons, soil structure, root traces and pedogenic nodules. Chemical, geochemical and mineralogical analyses were used to examine the paleosols. These paleosols were classified as Entisols, Inceptisols, Aridisols and Alfisols in terms of the modern soil taxonomic system. Early Cretaceous paleoprecipitation and paleotemperature in the Sichuan Basin were estimated from the degree of chemical weathering for non-calcareous paleosols, and from the depth to the calcic horizon and stable oxygen isotopic composition of pedogenic carbonates in calcareous paleosols, respectively. A temperate semi-arid climate generally prevailed in the Sichuan Basin as a part of the South China Block (SCB) and was controlled by subtropical high-pressure and a rain-shadow effect because the humid air masses from the Paleo-Pacific were impeded by the highlands of the South China Block. Further, several intervals of sub-humid paleoclimate occurred due to strengthened monsoonal circulation in the Early Cretaceous. Using the paleosol barometer, the paleoatmospheric CO2 levels of the Early Cretaceous are estimated to range from ∼120 to ∼520 ppmv, with a mean of 305 ppmv. Regional temperature is generally coupled with atmospheric CO2 concentration and is roughly consistent with the sea level fluctuation.

Refining the pedogenic carbonate atmospheric CO2 proxy and application to Miocene CO2

Quantifying uncertainty is essential for any paleoenvironmental proxy. Recent work on propagating error through the equation used to determine atmospheric CO2 concentrations from paleosol carbonates yields conflicting results. Small magnitude uncertainty from Gaussian error propagation contrasts with larger magnitude uncertainty from Monte Carlo error propagation. The discrepancy is reconciled here by revising partial differential equations for the Gaussian approach. Uncertainties calculated using the two approaches are compared and applied to Miocene calcic paleosols. Monte Carlo-propagated errors are asymmetrical but otherwise agree with Gaussian errors. Three methods for assigning soil-respired CO2 concentrations (S(z)) to paleosols are also compared. A revised calibration of depth to the Bk horizon as a direct proxy for S(z) is presented and although it results in lower atmospheric CO2 concentrations than the original calibration, it results in significantly higher calculated atmospheric CO2 than the use of mean annual precipitation as a proxy for S(z) or assigning S(z) values based on soil order. Averaging atmospheric CO2 concentrations calculated using soil-order based S(z) values from >10 penecontemporaenous and independent paleosols will likely result in useful constraints on Earth system sensitivity. The improvement of proxies for S(z) is needed to increase the accuracy and precision and to resolve potential volatility in CO2 time series.

Quantitative reconstruction of early cretaceous paleoclimate using paleosol carbonates in China

In this study, an attempt to quantitatively rebuild the Early Cretaceous paleoclimate was executed by employing calcareous paleosols (fossil soils), which have a horizon of pedogenic carbonate accumulation within the profile, in the central Sichuan Basin of southwestern China and Jinlingshi-Yangshan Basin of northeastern China, using the relationships between the climate and geochemical proxies, depth to calcic horizon and oxygen stable composition of pedogenic carbonates in modern soils. During the early Valanginian and early-middle Berriasian ages in the central Sichuan Basin, the climate was dominantly cold and dry, with a mean annual temperature (MAT) within 5 and 9 °C (standard error (S.E.) = ±5.8 °C) and mean annual precipitation (MAP) within ~190 and ~320 mm. During the late Barremian age (~126 Ma), the MAP was within ~200 and ~380 mm, and MAT was between 9 and 13 °C (S.E. = ±5.8 °C) in the Jinlingsi-Yangshan Basin. Noticeably, for the paleosols which formed under the arid climate, alkali and alkaline earth cations were weakly leached from the soil profile, and even accumulated on the soil surface. Therefore, geochemical indices (such as the chemical index of alteration (K2O-free) and alkaline index) to evaluate the chemical weathering, including base cations (Ca2+, Mg2+, Na+ and K+), as the functions of precipitation and air temperature, are unsuitable for paleoclimate reconstruction of paleo-aridisols.

Stable isotope record in pedogenic carbonates in northeast Iran: Implications for Early Cretaceous (Berriasian–Barremian) paleovegetation and paleoatmospheric P(CO2) levels

The Shurijeh Formation (Early Cretaceous) consists of siliciclastic, evaporate, and carbonate facies with associated calcareous paleosols in the Kopet-Dagh basin. These calcareous paleosols (pedogenic carbonate nodules) include specific macromorphological and micromorphological features. Based on macroscopic and microscopic properties, the Shurijeh Calcareous paleosols are divided into pedogenic and non-pedogenic (ground water) types that are each formed under specific conditions. Estimated δ13C values of plant-CO2 for Shurijeh vegetation range from −20.75‰ to −22.14‰ (with an average=−21.31‰). These values are consistent with plant type C3. The contribution of atmospheric CO2 in δ13C values of plant-CO2 of studied calcareous paleosols was 25 to 30%. The Neocomian (Berriasian–Barremian) paleoatmospheric PCO2 gap was reconstructed by interpretation from measured carbon isotopic compositions of the Shurijeh Formation pedogenic carbonates. The paleoatmospheric CO2 levels of the Shurijeh Formation are estimated to be 1226–2196ppmv. The general trend of Early Cretaceous estimates matches the modeled value trends for these times.