STRATIGRAPHIC AND PALEOGEOGRAPHIC EVOLUTION OF A CARBONATE PLATFORM IN AN EXTENSIONAL TECTONIC REGIME: THE EXAMPLE OF THE DOLOMIA PRINCIPALE IN LOMBARDY (ITALY)

Stratigraphic and sedimentologic studies of the norian succession outcropping in rhe Lombardy Basin allowed the reconstruction of the paleogeographic and strucural evolution oi this area, 1) restricted lagoon and tidal flat are the most common deposits ar the Carnian-Norian boundary (Lower Member of the Dolomia Principale); 2) these are overlain by a thick inner platform succession organized in shallowing upwards cycles (lower Dolomia Principale), with the exception of Idro Lake area where intraplatform basin already generated; 3) the overlying middle-upper Dolomia Principale is dissected by synsedimentary faults with subsequent widespread development of intraplatform basin, margin, and slope facies with marked asymmetric distribution; the inner platform was locally emerged; 4) in the uppermost Dolomia Principale buildup margins become more abundant and the platform partially prograded on the basins; 5) at last the platform drowns and terrigenous sedimentation becomes prevalent (Riva di Solto Shales). The drowning of the platform is favoured by the lack of carbonate production, due to clay pollution and climatic changes in an area with high subsidence rates. The observed asymmetric distribution of buildup margins and fault-scarp related breccias, which outcrop on the western side of the basins west of Iseo Lake and bounding the eastern side of the basins east of Iseo Lake, allows us to propose a model of norian ensialic asymmetric rifting for the Lombardy Basin. This asymmetric rifting could be explained by interpreting the Lombardy Basin as a pull-apart basin, linked to transtension with E-W trending faults

TEM INVESTIGATION OF THE SHELL OF THE BRACHIOPOD <em>THECOSPIRA TYROLENSIS</em> (LORETZ): A CLUE TO UNDERSTANDING GROWTH AND REPLACEMENT OF PRISMATIC AND/OR FIBROUS LOW MG-CALCITE?

The shell of Thecospira tyrolensis (Loretz) is characterized by three distinct layers consisting of low Mg-calcite. The primary layer consists of microcrystalline calcite and it is often diagenetically altered. The secondary layer is composed of imbricate fibres subparallel to the valve surface. The tertiary layer (prismatic) is made of calcite prisms perpendicular to the outer epithelium of the mantle and was formed by ephitelial cells that reverted to inorganic secretion. For this reason, as well as its morphology, the prismatic layer can be com­pared to some pore-filling low Mg-calcites, therefore we would expect it to follow inorganic nucleation and growth theory. Transmission electron microscopy allowed to recognize crystal defects (sets of microtwins and dislocations) which, by creating abutting surfaces and kinks, represent favourable sites where new "calcite seeds" attach themselves to the crystal surface. Stacking of (hkil) planes where growth is faster (in particular the basal piane), favoured by twinning, accounts for the prismatic habit

DOLOMITE FORMATION BY NANOCRYSTAL AGGREGATION IN THE DOLOMIA PRINCIPALE OF THE BRENTA DOLOMITES (NORTHERN ITALY)

Upper intra- to supratidal laminites in the Norian Dolomia Principale of the Brenta Dolomites (Northern Italy) commonly consist of aphanitic and partially peloidal dolomite previously interpreted as very early diagenetic or penecontemporaneous. Re-examination of a sample prepared by focused ion beam milling through high-resolution transmission electron microscopy (TEM) revealed that dolomicrite crystals may consist of ca. 5-nm-sized nanocrystals characterized by imperfectly aligned orientation. A similar type of dolomite was found in clay-rich Carnian laminites of the Travenanzes Formation (Venetian Alps, Northern Italy) and was interpreted as indication of primary precipitation. The observation of nanocrystals in both the Dolomia Principale and the Travenanzes Formation allows hypothesizing that dolomite mud formed directly from solution via a non-classical pathway involving nucleation and aggregation of nano-particles. Domains of nanocrystalline dolomite in the Dolomia Principale are embedded within, or cemented by, calcian dolomite showing coherent lattice at the micrometre scale and a modulated structure under the TEM. This new finding provides the first evidence that one of the largest dolomite bodies occurring in the geological record, the Dolomia Principale, commenced with deposition of sediment, consisting of dolomite mud formed from solution via non-classical crystallization, and was partially affected by later pervasive diagenetic dolomitization. Based on these new observations we propose that further nano-scale studies are necessary to substantiate the hypothesis that the formation of large dolomite bodies characterized by abundant dolomicrite may have commenced by non-classical nucleation and growth processes. This approach may provide insight on non-actualistic conditions in ancient environments that may have differed, in their boundary conditions, from their modern analogues

Sulphate concentration in cave dripwater and speleothems:long-term trends and overview of its significance as proxy for environmental processes and climate changes

Sulphate concentrations in speleothems identify major volcanic eruptions, provide useful information on soil and aquifer dynamics and, in similar fashion to the 14C bomb peak, its Anthropocene peak can be used to date recent cave formations. However, the transmission of S from the atmosphere to cave dripwater and its incorporation in speleothems is subjected to biogeochemical cycling and accurate studies of each cave site are needed in order to assess how the S atmospheric signal is modified and eventually encoded in speleothems. This study investigates the role of biogeochemical cycling and aquifer hydrology by utilising published and new dripwater and speleothem data from Grotta di Ernesto (ER) in northern Italy. Here we provide the first long-term record of sulphate concentration in cave dripwater based on over 20 years of measurements. Fast drip site st-ER1 is characterised by a continuous decrease in SO4 concentration from a high of 7.5 ± 0.8 mg/l in 1993–1994 to a low of 2.2 ± 0.2 mg/l in 2013–2014, and replicates with a delay of ∼15 years the decline in the atmospheric SO2 emissions. The S-series of slow flow ER78 site is further delayed by ∼4.5 years in relation to the S retention in the aquifer matrix. The dripwater data are used to extend the previously published S record (1810–1998 AD) of stalagmite ER78 and reconstruct the anthropogenic S-peak: this displays a delay of ∼20 years with respect to the atmospheric S emission peak due to biogeochemical cycling and aquifer storage. However, sulphur recycling above the cave did not operate with the same degree of efficiency through time, which resulted in a variable time delay between S deposition and incorporation into the stalagmite. In the pre-Anthropocene era, and in particular during the cold Little Ice Age, biogeochemical cycling was far less efficient than today, and the fast transmission of the atmospheric signal allowed capture of S released during major volcanic eruptions by stalagmites

The Ernesto Cave, northern Italy, as a candidate auxiliary reference section for the definition of the Anthropocene series

Annually laminated stalagmites ER77 and ER78 from Grotta di Ernesto provide an accurate annual record of environmental and anthropogenic signals for the last ~200 years. Two major transitions are recorded in the stalagmites. The first coincides with the year 1840 CE, when a change from porous and impurity-rich-laminae to clean, translucent laminae occurs. This is accompanied by a steady increase in the growth rate, a decrease in fluorescence and a sharp increase in δ13C values. These changes concur with the end of the Little Ice Age. The second transition takes place around the year 1960 CE and corresponds with an increase in both annual growth rate and sulfur concentration in stalagmite ER78 at 4.2 mm from the top, and with the deflection point in the 14C activity curve in stalagmite ER77 at 4.8 mm from the top. This latter is the stratigraphic signal proposed as the primary guide for the definition of the Anthropocene series. The following shift toward depleted δ34S–SO4 in stalagmite ER78 suggests that industrial pollution is a major source of sulfur. The interpretation of atmospheric signals (S, δ34S, 14C) in the stalagmites is affected by attenuation and time lags and the environmental signals are influenced by soil and ecosystem processes, while other anthropogenic signals (δ15N, 239Pu) are not recorded. For these reasons, the stalagmite record is here proposed as an auxiliary (reference) section rather than a global standard. In summary, Grotta di Ernesto contains one of the best stalagmite records documenting the Anthropocene, and one of only two stalagmite records where the S peak has been measured at high resolution

The influence of Antarctic subglacial volcanism on the global iron cycle during the Last Glacial Maximum

Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilisation of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestration from complementary Fe sources, such as the Antarctic ice sheet, due to the difficulty of locating and interrogating suitable archives that have the potential to preserve such information. Here we present petrographic, geochemical and microbial DNA evidence preserved in precisely dated subglacial calcites from close to the East Antarctic Ice Sheet margin, which together suggest that volcanically-induced drainage of Fe-rich waters during the Last Glacial Maximum could have reached the Southern Ocean (SO). Our results support a significant contribution of Antarctic volcanism to subglacial transport and delivery of nutrients with implications on ocean productivity at peak glacial conditions

Exploring the dating of “dirty” speleothems and cave sinters using radiocarbon dating of preserved organic matter

Speleothems and other carbonate deposits such as tufa containing high proportions of detrital material can be difficult to chemically date due to detrital thorium levels causing a high level of error in conventional U-Th disequilibrium dating. Here we investigate the use of an alternative technique centring on radiocarbon dating of organic matter preserved within the detrital fraction. Non-acid soluble humic, particulate and detritally absorbed organic matter was recovered from eight samples from a flowstone sinter formed within a roman aqueduct at Trento in Italy with a maximum age of 100 CE (1850 cal yr BP), and two repeat samples from a dripstone formed within the 20th Century on a wire fence at Lilly-Pilly Cave, Buchan Caves Reserve in Victoria, Australia. In the aqueduct samples the median calibrated 14C ages ranged from 2232 to 2889 cal yr BP, with 95.4% probability age range in the youngest and oldest samples of 2153–2337 and 2342–3449 cal yr BP respectively. The median age of the more modern dripstone was 336 cal yr BP, with a 95.4% probability age range of 148–486 cal yr BP. These results provide very approximate ball-park estimates of the age of the sample, but are consistently too old when compared to the known maximum ages of formation. It is hypothesised that this offset is due to a combination of the nature of the organic carbon transported from the source organic matter pools, and reworking of both modern and old organic carbon by in situ microbial communities

Modern speleothem oxygen isotope hydroclimate records in water-limited SE Australia

Dryland regions are generally projected to become drier under future climate change scenarios. Understanding the long-term natural variability of dryland regions via paleo-reconstructions is therefore highly desirable. The δ18O of two coeval modern speleothems from Cathedral Cave, Wellington, in semi-arid SE Australia are compared to the instrumental record to assess its efficacy as a proxy of past hydrological variability. Stalagmite δ18O was modulated by the frequency of recharge events and epikarst evaporation of storage water. Prolonged intervals between recharge events, such as droughts, resulted in higher stalagmite δ18O. Conversely, periods with more frequent recharge events and a positive water balance, resulted in lower δ18O. Disequilibrium cave processes are likely to be enhanced during dry conditions, although it is argued that these will modulate δ18Ospel in the same direction as epikarst evaporation, effectively amplifying the response of δ18Ospel. Extreme events, such as floods and droughts, were also captured in the stalagmite records, although potentially with a lag of several years. We verify that modern speleothems from semi-arid regions can be used to reconstruct hydroclimate due to variations in δ18Ospel modulated by karst processes. Such records are archives of past changes in recharge rather than precipitation amount or surface temperature, as is commonly applied to speleothem records from non-water-limited regions

Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition.

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth's climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration

Hydroclimate of the Last Glacial Maximum and deglaciation in southern Australia's arid margin interpreted from speleothem records (23-15 ka)

Terrestrial data spanning the Last Glacial Maximum (LGM) and deglaciation from the southern Australian region are sparse and limited to discontinuous sedimentological and geomorphological records with relatively large chronological uncertainties. This dearth of records has hindered a critical assessment of the role of the Southern Hemisphere mid-latitude westerly winds on the region's climate during this time period. In this study, two precisely dated speleothem records for Mairs Cave, Flinders Ranges, are presented, providing for the first time a detailed terrestrial hydroclimatic record for the southern Australian drylands during 23-15 ka. Recharge to Mairs Cave is interpreted from the speleothem record by the activation of growth, physical flood layering, and δ18O and δ13C minima. Periods of lowered recharge are indicated by 18O and 13C enrichment, primarily affecting δ18O, argued to be driven by evaporation of shallow soil/epikarst water in this water-limited environment. A hydrological driver is supported by calcite fabric changes. These include the presence of laminae, visible organic colloids, and occasional dissolution features, related to recharge, as well as the presence of sediment bands representing cave floor flooding. A shift to slower-growing, more compact calcite and an absence of lamination is interpreted to represent reduced recharge. The Mairs Cave record indicates that the Flinders Ranges were relatively wet during the LGM and early deglaciation, particularly over the interval 18.9-15.8 ka. This wetter phase ended abruptly with a shift to drier conditions at 15.8 ka. These findings are in agreement with the geomorphic archives for this region, as well as the timing of events in records from the broader Australasian region. The recharge phases identified in the Mairs Cave record are correlated with, but antiphase to, the position of the westerly winds interpreted from marine core MD03-2611, located 550 km south of Mairs Cave in the Murray Canyons region. The implication is that the mid-latitude westerlies are located further south during the period of enhanced recharge in the Mairs Cave record (18.9-16 ka) and conversely are located further north when greater aridity is interpreted in the speleothem record. A further comparison with speleothem records from the northern Australasian region reveals that the availability of tropical moisture is the most likely explanation driving enhanced recharge, with further amplification of recharge occurring during the early half of Heinrich Stadial 1 (HS1), possibly influenced by a more southerly displaced Intertropical Convergence Zone (ITCZ). A rapid transition to aridity at 15.8 ka is consistent with a retraction of this tropical moisture source.The stable isotope measurements on MC-S1 and MC-S2 were supported by Australian Research Council LIEF grants LE0989624 and LE0668400, and U-Th age measurements by Australian Research Council LIEF grant LE098906