Exploring New Ways to Reconstruct the Forma Urbis Romae: An Archaeometric Approach (CL Color and Stable Isotope Analyses)

The Forma Urbis Romae (F.U.) was a 3rd-century-AD monumental map of ancient Rome consisting of 151 rectangular marble slabs. Several efforts have been made to reconstruct it from its current incomplete and fragmentary condition. In this paper, we explore the potential of an archaeometric approach to serve this purpose. Almost a hundred F.U. fragments have been characterized, particularly focusing on cathodoluminescence (CL) microscopy and stable isotopes (δ18O and δ13C). Different statistical methods have been used to quantify the similarity between samples. The central assumption is that samples from a given slab share similar CL colors and isotopic ratios. The assumption has been verified for samples from single fragments and then it has been used to check ten debated reconstruction hypotheses. The measured isotopic ratios confirm the Proconnesian nature of the F.U. marble, except for a fragment. Beyond provenance, the results cast doubts on four out of the ten checked reconstruction hypotheses and support the other six. The reconstruction of the F.U. remains a fascinating challenge, and both isotopic and CL analyses have demonstrated their potential to tackle it. Further research could extend the presented methodology to a higher number of samples. The innovative use of CL to reconstruct a fragmented artwork could be applied to other projects.

Mid-Late Holocene Stalagmite δ18O and δ13C Records in Naduo Cave, Guizhou Province, China

Global warming and climate anomalies have attracted worldwide attention. The study of global climate change has received increasing attention from all countries and fields worldwide. Paleoclimate research is an important way to understand past global change and environmental evolution and to simulate and predict future climate development. A stalagmite ND3 collected in Naduo Cave was used to reconstruct the history of local climate and environmental changes from 0.55 to 5.07 ka BP based on the data of 13 230Th ages and 642 groups of oxygen and carbon stable isotopes. First, according to correlation analysis, δ18O and δ13C were significantly correlated (correlation coefficient r = 0.308, n = 318, P < 0.001 ) during the 5.07–2.00 ka BP period. However, during the period of 2–0.55 ka BP, there was no significant correlation P > 0.05 . The δ18O and δ13C data indicate that the climatic environment changed asynchronously during the period of 2.00–0.55 ka BP. During the period of 5.07–2.00 ka BP, the influence of human activities was weak, and δ18O and δ13C indicate similar climatic and environmental conditions, both of which changed in the same direction (positive correlation). In other words, when δ18O was positive, it indicated weak summer monsoons and lower precipitation, which led to declines in vegetation, weakened biological activity, and decreased soil CO2 and positive δ13C. The reverse patterns were also true. Since 2.0 ka BP, the intensity of human activities and the transformation and influence of surface vegetation have increased, and native vegetation has been destroyed in large quantities. Therefore, the climatic and environmental significance indicated by δ13C and δ18O has been well demonstrated. Second, the δ18O records showed that stalagmite ND3 responded to the weak monsoon drought events of 4.2 ka BP and 2.8 ka BP in the Holocene in a discontinuous deposition manner, which brings up new directions for future research.

Identification of seasonal varves in the lower Pliocene Bouse Formation, lower Colorado River Valley, and implications for Colorado Plateau uplift

The cause of Cenozoic uplift of the Colorado Plateau is one of the largest remaining problems of Cordilleran tectonics. Difficulty in discriminating between two major classes of uplift mechanisms, one related to lithosphere modification by low-angle subduction and the other related to active mantle processes following termination of subduction, is hampered by lack of evidence for the timing of uplift. The carbonate member of the Pliocene Bouse Formation in the lower Colorado River Valley southwest of the Colorado Plateau has been interpreted as estuarine, in which case its modern elevation of up to 330 m above sea level would be important evidence for late Cenozoic uplift. The carbonate member includes laminated marl and claystone interpreted previously in at least one locality as tidal, which is therefore of marine origin. We analyzed lamination mineralogy, oxygen and carbon isotopes, and thickness variations to discriminate between a tidal versus seasonal origin. Oxygen and carbon isotopic analysis of two laminated carbonate samples shows an alternating pattern of lower δ18O and δ13C associated with micrite and slightly higher δ18O and δ13C associated with siltstone, which is consistent with seasonal variation. Covariation of alternating δ18O and δ13C also indicates that post-depositional chemical alteration did not affect these samples. Furthermore, we did not identify any periodic thickness variations suggestive of tidal influence. We conclude that lamination characteristics indicate seasonal genesis in a lake rather than tidal genesis in an estuary and that the laminated Bouse Formation strata provide no constraints on the timing of Colorado Plateau uplift.

Beachrock as a Paleoshoreline Indicator: Example from Wadi Al-Hamd, South Al-Wajh, Saudi Arabia

The present study concerns the Holocene inland beachrocks that are exposed in the Red Sea coastal plain at the mouth of Wadi Al-Hamd, South Al-Wajh City, Saudi Arabia, and their utility as an indicator for Holocene climate and sea level changes. In addition, the framework composition, and carbon and oxygen isotopic data, are employed to interpret the origin of their cement. The beachrock consists mainly of gravel and coarse-grained terrigenous sediments dominated by lithic fragments of volcanic rocks, cherts and rare limestones along with quartz, feldspars and traces of amphiboles and heavy minerals. In addition, rare skeletal remains dominated by coralline algae, benthic foraminifera and mollusca remains are recognized. The allochems are cemented by high Mg-calcite (HMC) formed mainly in the intertidal zone under active marine phreatic conditions. The cement takes the form of isopachous to anisopachous rinds of bladed crystals, micritic rim non-selectively surrounding siliciclastic and skeletal remains, and pore-filling micrite. Pore-filling micrite cement occasionally displays a meniscus fabric, suggesting a vadose environment. The δ18O and δ13C values of carbonate cement range from −0.35‰ to 1‰ (mean 0.25‰) and −0.09‰ to 3.03‰ (mean 1.85‰), respectively, which are compatible with precipitation from marine waters. The slight depletion in δ18O and δ13C values in the proximal sample may suggest a slight meteoric contribution.

Holocene environmental evolution and climate variability inferred from multi-proxy coastal sediment records of southern Greece

This thesis presents a multi-proxy reconstruction from 5 different coastal wetlands of southern Greece spanning in the Holocene period and an in-depth review and application of non-destructive systems (CT scanning, X-ray Fluorescence) in paleoenvironmental research. During this thesis, the acquired dataset used consisted of a) X-ray Fluorescence scanning (XRF), b) Computed Tomography (CT) scanning, c) Stable isotopes δ18O and δ13C, d) micropaleontology (foraminifera, ostracods, diatoms, pollen), e) mineralogical analysis, and f) standard sedimentological techniques (grain size, magnetic susceptibility (MS), Total Organic Carbon (TOC), carbonates content). The chronological framework for the sediment cores was established through 14C radiocarbon dating. The wetlands studied are Aliki salt pond (NE Gulf of Corinth), Klisova lagoon (SW Greece), lake Vouliagmeni (E Gulf of Corinth), Agoulinitsa marsh field (W Peloponnese) and Pappas lagoon (NW Peloponnese). The sites form an E-W transect of southern Greece, an area with high climatic and environmental spatial variability, whereas human occupancy on all areas is recorded from antiquity. Non-destructive, high-resolution techniques used in this thesis have been established as standard in the last decades and have been a great asset in geosciences. Computed Tomography (CT) was conducted in lake Vouliagmeni, Agoulinitsa marsh and Pappas lagoon cores. In contrast, XRF was performed on all core sections except for Pappas lagoon core, where the high assemblage of bivalve shells could lead to bias of Ca. The fundamental parameter behind CT analysis is the Hounsfield units that reflect relative density variations in the sediment. Correlation between HU values and heavy elements like Zr has been detected in all cores, whereas distinct sedimentological facies were recorded according to HU variations. In Agoulinitsa and Pappas lagoon, microstructural characteristics like shells/sediment ratio and root remnants were examined through 3D sections, in which HU boundaries were set accordingly. Lake Vouliagmeni sediment core was characterized by extreme stratigraphic variations with lamination structures alternating with homogenous deposits and event layers. Laminae thickness and boundaries were recorded through 3D rendered volumes with HU boundaries. Micro CT scanning and thin section analysis was also performed to cross-check possible variations. Event sedimentation layers were distinguished through the combined use of CT scanning, XRF and MS, with layers responding to increased HU, MS and Mn values. Statistical assessment of elemental distribution and HU revealed 3 different clusters. Cluster A responded to sedimentation during enhanced evaporation in the area, Cluster B emulated sedimentation during increased chemical weathering in the catchment, and Cluster C reflected the homogenous deposits. Aliki salt pond is located in a highly tectonic region, at the northeast part of the Gulf of Corinth in Greece. Beachrock deposits that form a barrier between the salt pond and the marine environment play an essential role in the evolution of the area. The chronological framework was set at ca. 3100 cal BP by four 14C radiocarbon dates and the established evolutionary model indicate four different changes taking place during this period in the study area. From around 3100 to 1600 cal BP, a transition from a closed to an open lagoonal environment, was identified, interrupted by a terrestrial fluvial deposit at ca. 2500 cal BP. A shift toward a closed lagoonal system at around 1600 cal BP and the establishment of a salt pond environment seem to correlate with tectonic activity. The study provides important information about the evolution of the coastal landscape in such an active tectonic region and points the interaction between regional human activity and climatic changes during the late-Holocene period.Klisova lagoon is located in the eastern part of Messolonghi-Etoliko wetland, the biggest lagoonal complex of Greece and an area of great environmental interest. For the last 4700 cal BP, the freshwater influx, the progradation of the Evinos river delta and related geomorphological changes control the environmental conditions (e.g. depth and salinity) in the lagoon system. Considering the centennial temporal resolution of our analyses, small offsets of c.a. 50 years due to the lack of regional reservoir correction do not impact the reported radiocarbon ages considerably. Prior to 4000 cal BP, a relatively shallow water depth, significant terrestrial/freshwater input and increased weathering in the lagoon area are inferred. Elemental proxies and increased dinoflagellate and foraminifera abundances, which indicate marine conditions with prominent freshwater influxes, point to the gradual deepening of the lagoon recorded at the drilling site up to 2000 cal BP. The marine and freshwater conditions equilibrium sets at 1300 cal BP, and the lagoonal system seems to reach its present state. Maxima of anthropogenic pollen indicators during the Mycenaean (3200 cal BP), Hellenistic (2200 cal BP) and Late Byzantine (800 cal BP) periods suggest intervals of increased anthropogenic activities in the study area. Lake Vouliagmeni is subjected to intense climatically and tectonic forces, causing stratigraphic variations, with laminated sediments frequently interrupted by homogenous and event sedimentation deposits. Lamination couplets consist of aragonite layers alternating with detrital and organic residues and form during periods of seawater intrusion and stratification of the lake water. The discontinuous occurrence of laminated deposits excludes a varve based chronology from being established but still highlights the susceptibility of the lake to record environmental and climatically driven changes. Our synthesis model for regional climatic reconstruction and local environmental changes derives from δ18O and δ13C data from the laminated and homogenous sediments studied separately depending on the dominant carbonate mineral. This is further strengthened by high-resolution geochemical proxies, diatom and sedimentological data. Regional climatic trajectories from key sites and possible links to the lake Vouliagmeni record are explored in response to atmospheric circulation patterns variations. Phases of overall humid conditions are recorded by the increased inflow of siliciclastic material in the lake and negative δ18Obulk values. In contrast, periods of marine intrusion and enhanced evaporation are recorded by aragonite precipitation, increased δ18OAr values and laminations. The driving mechanism behind laminae formation seems to be marine intrusions, leading to pycnocline stabilization and increased evaporation of lake surface waters during summer months. Climatic oscillations recorded during the Holocene, apart from their duration, do not exceed events of the last millennia.

Variability in Neogloboquadrina pachyderma stable isotope ratios from isothermal conditions: implications for individual foraminifera analysis

Individual foraminifera analysis (IFA) holds promise to reconstruct seasonal to interannual oceanographic variability. Even though planktonic foraminifera are reliable recorders of environmental conditions on a population level, whether they also are on the level of individuals is unknown. Yet, one of the main assumptions underlying IFA is that each specimen records ocean conditions with negligible noise. Here we test this assumption using stable isotope data measured on groups of four shells of Neogloboquadrina pachyderma from a 16–19 days resolution sediment trap time series from the subpolar North Atlantic. We find a within-sample variability of 0.11 and 0.10 ‰ for δ18O and δ13C respectively that show no seasonal pattern and exceed water column variability in spring when conditions are homogeneous down to 100s of metres. We assess the possible effect of life cycle characteristics and delay due to settling on foraminifera δ18O variability with simulations using temperature and δ18Oseawater as input. These simulations indicate that the observed δ18O variability can partially be explained by environmental variability. Individual N. pachyderma are thus imperfect recorders of temperature and δ18Oseawater. We estimate the excess noise on δ18O to be 0.11 ± 0.06 ‰. The origin and nature of the recording imprecision require further work, but our analyses highlight the need to take such excess noise into account when interpreting the geochemical variability among individual foraminifera.

Depositional system and lake-stage control on microbialite morphology, Green River Formation, eastern Uinta Basin, Colorado and Utah, U.S.A.

ABSTRACT Lake-margin lacustrine carbonates of the Green River Formation, in the eastern Uinta basin of Colorado and Utah, occur interbedded with fluvial and shoreline-parallel sandstone and shale. Microbial bindstones were deposited in a saline-alkaline lake during and after the Early Eocene Climate Optimum (EECO) (52–50 million years ago) that is characterized by global hot-house conditions, elevated atmospheric CO2, and highly fluctuating climate conditions. The stratigraphic architecture, chemostratigraphy, and morphology of the microbialites and other associated carbonate beds can be related to these climatic conditions. Three facies associations are recognized in the carbonate units across the lake margin from upper littoral to lower sublittoral environments: facies association 1, delta proximal non-microbial carbonates, characterized by quartzose bioclastic, peloidal, intraclastic packstones and grainstones–rudstones, quartose peloid wackestones and sandy oil shale; facies association 2, microbialite associated non-microbial carbonates, composed of ostracod, ooilitic, peloidal packstones–grainstones and intraclastic packstones, grainstones and rudstones; and facies association 3, microbial carbonates, consisting of diverse forms of stromatolitic and thrombolitic lithofacies. Multiple scales of carbonate cyclicity are suggested by shifts of δ18O and δ13C stable isotopes and deepening-upward microbialite facies. High-frequency cycles, on the order of 1 to 5 m thickness, are characterized by positive shifts in stable isotopes and interpreted deepening trends from littoral to lower sublittoral conditions. Large-scale trends, on the order of tens to hundreds of meters thickness record long-term lake changes, including: 1) sparse microbialite deposition during initial fresh conditions in lake stage 1, with low macro-structure diversity and light δ18O and δ13C isotope values; 2) transitional lake stage 2 corresponding to moderate macro-structural diversity, large meter-scale biostromal and biohermal buildups, and a positive shift in δ18O and δ13C isotope values that suggest increasing saline and alkaline conditions; 3) a highly fluctuating lake stage 3 that contains the highest microbialite macro-structural diversity and marks the interval of heaviest δ18O and δ13C isotope values, suggesting the greatest lake restriction, and the highest salinity and alkalinity conditions; and 4) a rising lake stage 4 that marks the lowest microbialite macro-structure diversity and a reversal in trend of δ18O and δ13C isotope values, that indicate deepening and freshening conditions.

Novel method for determining ²³⁴U–²³⁸U ages of Devils Hole 2 cave calcite (Nevada)

Uranium–uranium (234U–238U) disequilibrium dating can determine the age of secondary carbonates over greater time intervals than the well-established 230Th–234U dating method. Yet it is rarely applied due to unknowns in the initial δ234U (δ234Ui) value, which result in significant age uncertainties. In order to understand the δ234Ui in Devils Hole 2 cave, Nevada, we have determined 110 δ234Ui values from phreatic calcite using 230Th–234U disequilibrium dating. The sampled calcite was deposited in Devils Hole 2 between 4 and 590 ka, providing a long-term look at δ234Ui variability over time. We then performed multi-linear regression among the δ234Ui values and correlative δ18O and δ13C values. The regression can be used to estimate the δ234Ui value of Devils Hole calcite based upon its measured δ18O and δ13C values. Using this approach and the measured present-day δ234U values of Devils Hole 2 calcite, we calculated 110 independent 234U–238U ages. In addition, we used newly measured δ18O, δ13C, and present-day δ234U values to calculate 10 234U–238U ages that range between 676 and 731 ka, thus allowing us to extend the Devils Hole chronology beyond the 230Th–234U-dated chronology while maintaining an age precision of ∼ 2 %. Our results indicate that calcite deposition at Devils Hole 2 cave began no later than 736 ± 11 kyr ago. The novel method presented here may be applied to future speleothem studies in similar hydrogeological settings, given appropriate calibration studies.