Amino Acid Racemization Research Articles

A question of time: historical overview and modern thought on Quaternary dating methods to produce fluvial chronologies

Since its early stage one century ago, Quaternary geochronology has witnessed major progress with the development of a vast array of relative, correlation and numerical dating methods. Fluvial geomorphologists have simultaneously striven to quantitatively assess processes on very different timescales (101-106 years). Dating fluvial/alluvial landforms and/or associated material/archives rapidly turned out to be one of the main challenges accordingly. Here, a bipartite reflection is proposed on how Quaternary dating methods have allowed the production of fluvial chronologies over the last century, including at the present time. Firstly, a progressive methodological shift has been witnessed. Whilst age controls were mostly attained via relative and correlation dating until the late xxth century, numerical dating methods have increasingly taken over the prevailing role since the last two or three decades. Two explanatory causes are then proposed. The bipartite evolution of relative dating methods over the last decades is explored: whilst some methods were further developed in the fluvial context (e.g., amino-acid racemization), some others were vehemently questioned (e.g., lichenometry). The late flourishing of radiometric dating methods during the second half of the xxth century is also considered. Secondly, the current status of Quaternary geochronology is doubly questioned: (i) Is the die cast for “disused” relative dating methods? and (ii) Can radiometric dating methods solve all chronological issues related to fluvial environments? Surface exposure dating of alluvial surfaces via cosmogenic nuclides is then thoroughly discussed in this respect, focusing on some methodological issues. A rehabilitation of some methods fallen into disuse, such as weathering indicators, is then proposed to support numerical age outputs. Finally, geochronological approaches based on multiple dating tools, either by crosschecking the outputs of different methods or coupling numerical dating methods, are fostered.

Last Interglacial sea-level data points from Northwest Europe

Abstract. Abundant numbers of sites and studies exist in NW Europe that document the geographically and geomorphologically diverse coastal record from the Last Interglacial (Eemian, Ipswichian, Marine Isotope Stage 5e). This paper summarises a database of 146 known Last Interglacial sea-level data points from in and around the North Sea (35 entries in the Netherlands, 10 Belgium, 23 in Germany, 17 in Denmark, 9 in Britain) and the English Channel (24 entries for the British and 25 for the French side, 3 on the Channel Isles) believed to be a representative and fairly complete inventory and assessment from ∼80 published sites. The geographic distribution (∼1500 km SW–NE) across the near field of the Scandinavian and British ice sheets and the attention paid to relative and numeric age control are assets of the NW European database. The research history of Last Interglacial coastal environments and sea level for this area is long, methodically diverse and spread through regional literature in several languages. Our review and database compilation effort drew from the original regional literature and paid particular attention to distinguishing between sea-level index points (SLIPs) and marine and terrestrial limiting points. We also incorporated an updated quantification of background rates of basin subsidence for the central and eastern North Sea region, utilising revised mapping of the base Quaternary, to correct for significant basin subsidence in this depocentre. As a result of subsidence, lagoonal and estuarine Last Interglacial shorelines of the Netherlands and the German Bight are preserved below the surface. In contrast, Last Interglacial shorelines along the English Channel are encountered above modern sea level. This paper describes the dominant sea-level indicators from the region compliant with the WALIS database structure and referenced to original data sources (https://doi.org/10.5281/zenodo.6478094, Cohen et al., 2021). The sea-level proxies are mostly obtained from locations with good lithostratigraphic, morphostratigraphic and biostratigraphical constraints. Most continental European sites have chronostratigraphic age control, notably through regional pollen association zones with duration estimates. In all regions, many SLIPs and limiting points have further independent age control from luminescence, uranium series, amino acid racemisation and electron spin resonance dating techniques. Main foreseen usage of this database for the near-field region of the European ice sheets is in glacial isostatic adjustment modelling and fingerprinting Last Interglacial ice sheet melt.

Rapid Radiolytic Degradation of Amino Acids in the Martian Shallow Subsurface: Implications for the Search for Extinct Life.

Amino acids are fundamental to life as we know them as the monomers of proteins and enzymes. They are also readily synthesized under a variety of plausible prebiotic conditions and are common in carbon-rich meteorites. Thus, they represent a reasonable class of organics to target in the search for prebiotic chemistry or chemical evidence of life on Mars. However, regardless of their origin, amino acids and other organic molecules present in near-surface regolith and rocks on Mars can be degraded by exposure to cosmic rays that can penetrate to a depth of a few meters. We exposed several pure amino acids in dry and hydrated silicate mixtures and in mixtures of silicates with perchlorate salts to gamma radiation at various temperatures and radiation doses representative of the martian near-subsurface. We found that irradiation of amino acids mixed with dry silica powder increased the rate of amino acid radiolysis, with the radiolysis constants of amino acids in silicate mixtures at least a factor of 10 larger compared with the radiolysis constants of amino acids alone. The addition of perchlorate salts to the silicate samples or hydration of silicate samples further accelerated the rate of amino acid destruction during irradiation and increased the radiolysis constants by a factor of ∼1.5. Our results suggest that even low-molecular-weight amino acids could degrade in just ∼20 million years in the top 10 cm of the martian surface regolith and rock, and even faster if the material contains elevated abundances of hydrated silicate minerals or perchlorates. We did not detect evidence of amino acid racemization after gamma radiation exposure of the samples, which indicates that the chirality of some surviving amino acids may still be preserved. Our experimental results suggest serious challenges for the search of ancient amino acids and other potential organic biosignatures in the top 2 m of the martian surface.

From Microorganisms to Biosignatures: Subcritical Water Extraction as a Sample Preparation Technique for Future Life Detection Missions

AbstractAmino acids are important targets in the search for life beyond Earth. The types of amino acids, their relative abundances, and enantiomeric excess all serve as biosignatures. To detect such biosignatures, identification and quantification of individual amino acids are required. Regardless of the analytical workflow used, it is critical to release amino acids from the sample without altering their molecular distributions. Subcritical water extraction (SCWE) is a promising technique for the release of organics from a variety of samples that has been under development for flight implementation for over 20 years. However, there is a risk of racemization and/or degradation of amino acids during extraction that could alter their distributions. This work demonstrates for the first time that SCWE (200°C for 30 min) can release amino acids from bacterial cells and spores, while maintaining their native distributions and enantiomeric excess.

Enantioseparation of amino acid and mandelic acid enantiomers using Garphos derivatives as chiral extractants.

In this paper, Garphos with different substituents were employed as chiral extractants to enantioseparate racemic amino acid and mandelic acid. The influences of metal precursors, pH of aqueous solution, Garphos-metal concentration, extraction temperature, and substituent effect on extraction were investigated. The results indicated that the substituent groups significantly affected the π-π interaction between extractant and substrate. And the separation factors (α) for Garphos could be remarkably improved by regulating substituent groups. Garphos-II-Pd, Garphos-VI-Pd, Garphos-III-Pd, Garphos-I-Cu, Garphos-VI-Cu, and Garphos-V-Pd were the most efficient extractants for phenylalanine (Phe), homophenylalanine (Hphe), 4-nitrophenylalanine (Nphe), 3-chlorophenylglycine (Cpheg), mandelic acid (MA), and 2-chlormandelic acid (CMA) with α values of 2.40, 2.37, 5.37, 1.59, 5.98, and 3.69, respectively. This work provided an important reference for the design of efficient chiral extractants in future work.

Compilation of Last Interglacial (Marine Isotope Stage 5e) sea-level indicators in the Bahamas, Turks and Caicos, and the east coast of Florida, USA

Abstract. This paper provides a summary of published sea-level archives representing the past position of sea level during the Last Interglacial sea-level highstand in the Bahamas, Turks and Caicos, and the eastern (Atlantic) coast of Florida, USA. These data were assembled as part of a community effort to build the World Atlas of Last Interglacial Shorelines (WALIS) database. Shallow marine deposits from this sea-level highstand are widespread across the region and are dominated by carbonate sedimentary features. In addition to depositional (constructional) sedimentary indicators of past sea-level position, there is also evidence of erosion, dissolution, and/or subaerial exposure in places that can place an upper limit on the position of sea level. The sea-level indicators that have been observed within this region and attributed to Marine Isotope Stage (MIS) 5e include corals, oolites, and other coastal sedimentary features. Here we compile a total of 50 relative sea-level indicators including 36 in the Bahamas, three in West Caicos, and a remaining 10 for the eastern seaboard of Florida. We have also compiled U-Th age data for 24 fossil corals and 56 oolite samples. While some of these archives have been dated using U-Th disequilibrium methods, amino acid racemization, or optically stimulated luminescence, other features have more uncertain ages that have been deduced in the context of regional mapping and stratigraphy. Sedimentary archives in this region that constrain the elevation of the past position of sea level are associated with uncertainties that range from a couple of decimeters to several meters. Across the Bahamas and on West Caicos, one of the observations that emerges from this compilation is that estimation of sea-level position in this region during Marine Isotope Stage 5e is complicated by widespread stratigraphic evidence for at least one sea-level oscillation. This evidence is defined by submarine features separated by erosion and subaerial exposure, meaning that there were likely multiple distinct peaks in sea level rather than just one. To this end, the timing of these individual sea-level indicators becomes important when compiling and comparing data across the region given that different archives may have formed during different sub-orbital peaks in sea level. The database can be found at https://doi.org/10.5281/zenodo.5596898 (Dutton et al., 2021).

Late Quaternary land snail faunas of the Desertas Islands (Madeira): high diversity and endemism followed by recent impoverishment and extinction

ABSTRACT Late Quaternary deposits containing fossil snail shells were sampled from nine sites on Deserta Grande and three on Bugio, two of the three Desertas Islands in the oceanic Madeiran archipelago. In total, 3,432 shells representing 45 species or subspecies were retrieved. Calibrated amino acid racemization yielded ages ranging from >45 to 6 ka, with variation by site often confounded by reworking of mostly colluvial deposits. The assemblages found are compared with the extant fauna, itself a subject of intensive recent study. Of the 45 taxa, 18 are apparently extinct, and a further 5 no longer survive on the Desertas. A similar pattern emerges when each island is considered separately. The level of local extinction (c. 50%) is greater than seen on the larger, nearby islands of Madeira and Porto Santo. There are few endemic species in the extant fauna not represented in the fossil assemblages, but there are a number of possibly adventitious species, some with wide distributions in Europe. There is little evidence of faunal change within the limits of the age range available, and extinction seems to be concentrated in the later Holocene. It is attributed to the massive habitat destruction that occurred subsequent to human occupation from the 15th century CE onwards. The study emphasizes the depauperate nature of many extant island faunas subject to human disturbance.

Long-term preservation of amino acid racemization interlaboratory comparison samples

This report summarizes the present status and future preservation of four Interlaboratory Comparison Samples (ILC) used in the Amino Acid Racemization (AAR) community over the past 40 years. The ILC samples are now housed in the archival collection of Lamont-Doherty Earth Observatory.

Chiral Bicyclic Imidazole-Catalyzed Direct Enantioselective C -Acetylation of Indolones

Chiral Bicyclic Imidazole-Catalyzed Direct Enantioselective <i>C</i> -Acetylation of Indolones

Holocene evolution and depositional model of a bayhead delta, Lake Illawarra, Australia

AbstractExtensive research into the evolution of wave‐dominated estuaries has been documented since the 1960s. However, there has only been limited research on the prograding bay‐head deltas that are the primary drivers for the rate and stage of estuary evolution. This paper presents the findings of a high‐resolution spatial study into the evolution of the Macquarie Rivulet bayhead delta in the Lake Illawarra barrier estuary. The delta’s evolution has been established based on sedimentological analysis of 74 cores, two14C ages and 45 amino acid racemization ages. This study intersected two Pleistocene and 10 Holocene sedimentary facies associations representing both the retrogradational and progradational phases of delta development. The distribution of bayhead delta facies associations in shallow barrier estuaries is initially controlled by the antecedent morphology, but, in contrast to deeper estuaries, this influence decreases as sedimentation proceeds. Changing relative sea level also has a major control on facies distribution with transgressive facies deposited as relative sea‐level rises being replaced by prograding deltaic facies during the highstand and subsequent minor relative sea‐level fall. Fluvial sediment supply and river flood events affect the rate of delta progradation, and produce low and high flow sediment deposits within the overall deltaic sequence. The low tidal flux in barrier estuaries, the muddy cohesive nature of the sediments and the prevalence of bioturbation means that primary sedimentary structures are rarely preserved in these bayhead delta facies. The depositional model of bayhead delta evolution shown by the Macquarie Rivulet delta would be widely applicable to other similar barrier estuary settings.

Development of the marine Holocene environment in a drowned paleovalley with final anthropic influence in the Cartagena Bay (Murcia, SE Spain)

Sedimentological, paleobiological, mineralogical, and geochemical analyses of a sediment core retrieved on the seafront of Cartagena Bay were performed after high-resolution sampling. A wide series of dates obtained through radiocarbon and amino acid racemization proved that the Holocene record on the analyzed core began at ca. 7300 yr cal BP. Reinterpretation of the marine seismic profiles indicated that the beginning of this transgression was channeled along erosive paleochannels excavated on a coastal plain of, at least, MIS5c age. The Holocene paleoenvironmental evolution consisted of a first period marked by marine conditions with strong inputs from a fan delta linked to the reorganized fluvial network that occurred after the sudden rise of the base level, which caused a growing sedimentary prism. Later, the full marine environment was reflected in the development of a Posidonia- Cymodocea meadow hosting a rich biodiversity of marine species (mollusks, foraminifera, ostracoda). Around 3800 yr cal BP, the area underwent a profound change and a silting process started to alter the conditions, turning the area into a paucispecific brackish marsh environment in which mud deposition was dominant. Since Carthaginian times, arrangement works locally affected the record, allowing the arrival of some marine species due to port work (dredging) undertaken to gain depth and showing anthropic influence.

The Whale Point Formation: A stratigraphic record of high-frequency climate and sea-level fluctuations in the Bahamas during Marine Isotope Stage 5a (ca. 80 ka BP)

In this paper, we formally define a series of bioclastic eolianites and protosols exposed on high-energy bank margins throughout the Bahamas archipelago as the Whale Point Formation (WPF). The position of this new lithostratigraphic unit above and seaward of deposits dated to Marine Isotope Stage (MIS) 5e and below Holocene sediments constrains its age to the latest Pleistocene, more precisely to MIS 5a (ca. 88–74 ka BP). This age is further corroborated by amino-acid racemization data calibrated with UTh ages. Based on their sedimentological characteristics, the WPF eolianites are interpreted as landward-advancing dunes decoupled from their source beaches. Relying on the faunal content, the maximum elevation of relative sea level during MIS 5a can be roughly estimated at ca. 9 ± 2 m below the present stand. The WPF includes two phases of eolian deposition separated by an interval of negative sediment budget and pedogenesis. These different facies possibly reflect millennial-scale sea-level and climate instability during MIS 5a, the latter being likely related to shifts in the mean annual position of the intertropical convergence zone and associated rainfall belt.

50 years of chiral liquid Chromatography. How it started

The birth of modern chiral liquid chromatography can be traced back to the years 1968–71 when the first complete resolution of a racemic amino acid was obtained and presented in the literature. Extreme enantioselectivity was achieved due to the introduction of ligand exchange principle, i.e. participation of a copper ion in the solute-sorbent interactions. Simultaneously, first microporous (hypercrosslinked) polymeric matrixes were introduced, thus enhancing the chromatographic efficiency of the process.

Synthesis of Levofloxacin based Chiral Reagent and its Application in Determination of Optical Purity of Essential Racemic Amino Acids using RP-HPLC

In this report, the activated chiral reagents of the (S)- levofloxacin (CR-Lfx) were prepared via coupling reaction of N-hydroxysuccinimide and characterised by UV, IR, HRMS, NMR and CHNS. Three essential racemic amino acids were chosen for the chiral recognition study. The diastereomeric derivatives of the chosen amino acids were prepared under microwave heating conditions, using highly reactive activated reagents (CR-Lfx). RP-HPLC was used to separate the prepared diastereomeric derivatives. The effect of varying mobile phase concentrations and sample concentrations was optimised. The density functional theory calculations were performed using Gaussian 09 rev A.02 and hybrid density functional B3LYP with 6-31G* basis set software to create the lowest energy optimised structures of diastereomeric derivatives. LOD (0.208 ng mL−1), LOQ (0.624 ng mL−1), calibration range (0.02-2.0 mg mL−1), correlation coefficient (0.998) and recovery were the validation parameters for our method (99.54 and 99.89 percent for intra-day assay and 99.87 and 99.32 percent for inter-day assay).

Lipid biomarkers and metal pollution in the Holocene record of Cartagena Bay (SE Spain): Coupled natural and human induced environmental history in Punic and Roman times

We reconstructed the palaeoenvironmental conditions of Cartagena Bay during the Holocene after a multidisciplinary study to identify natural variations and the anthropic processes of this coastal area. A total of 119 samples were recovered for amino acid racemization dating, 3 for radiocarbon dating (14C), and four sets of 80 samples for sedimentological and palaeontological determination, mineralogical content, biomarker and trace elements quantification. Two natural scenarios were identified from the variations of n-alkane indices and palaeobiological content. The first period (6650–5750 yr cal BP) was marked by the development of euhaline marine conditions with strong inputs from aquatic macrophytes and high biodiversity. After a hiatus, the area underwent a profound change, becoming a paucispecific brackish marsh environment with increasing inputs from land plants, with possible episodes of emersion with a greater presence from terrestrial gastropods (3600–300 cal yr BP). By combining trace element abundance and stanol distributions, our study also provides a novel approach to identify the predominant influence of anthropogenic factors in the last three millennia in the coastal record of Cartagena Bay. Findings confirmed that Pb mining and metallurgy began during the Bronze Age, with considerable inputs of this heavy metal into the atmosphere during Phoenician, Punic and particularly Roman times compared to the Middle Ages. Pollution by Cu and Zn was also observed during Punic and Roman times, and was first documented in the Middle Ages. In addition, faecal stanols, such as coprostanol, derived mainly from humans, and 24-ethylcoprostanol from herbivores were present, thereby indicating for the first time a continuous presence of human populations and significant pollution input since 3600 yr cal BP, this being greater in the late Bronze Age and Phoenician, Punic and Roman times than during Late Antiquity and the Middle Ages, when the city was in decline.

Theoretical Investigation of Racemization of Amino Acid using Organic Catalysts

Racemization of amino acid catalyzed by aldehyde and carboxylic acid has been proposed and widely used. Herein, we investigated the detailed racemization mechanism of alanine catalyzed by salicylaldehyde and acetic acid. Quantum chemistry calculations based on the density functional theory demonstrated that the dehydration reaction is the rate-determining step, and this dehydration step is enhanced by surrounding water molecules. We also discussed the dependence of the reaction rates on the type of amino acid.

Construction of carbazole-based unnatural amino acid scaffolds via Pd(II)-catalyzed C(sp3)-H functionalization.

We report the synthesis of carbazole-based unnatural α-amino acid and non-α-amino acid derivatives via a Pd(II)-catalyzed bidentate directing group 8-aminoquinoline-aided β-C(sp3)-H activation/functionalization method. Various N-phthaloyl, DL-, L- and D-carboxamides derived from their corresponding α-amino acids, non-α-amino acids and aliphatic carboxamides were subjected to the β-C(sp3)-H functionalization with 3-iodocarbazoles in the presence of a Pd(II) catalyst to afford the corresponding carbazole moiety installed unnatural amino acid derivatives and aliphatic carboxamides. Carbazole motif-containing racemic (DL) and enantiopure (L and D) amino acid derivatives including phenylalanine, norvaline, leucine, norleucine and 2-aminooctanoic acid with anti-stereochemistry and various non-α-amino acid derivatives including GABA have been synthesized. Removal of the 8-aminoquinoline directing group, deprotection of the phthalimide moiety and the preparation of carbazole amino acid derivatives containing free amino- and carboxylate groups are shown. The carbazole motif is prevalent in alkaloids and biologically active molecules and functional materials. Thus, this work on the synthesis of carbazole-based unnatural amino acid derivatives would enrich the libraries of unnatural amino acid derivatives and carbazoles.

An Attempt to Extract Ancient DNA from the Petrous Part of the Temporal Bones and Roots of Teeth of Skeletal Remains Found in the Intermediate Climatic Zone in Sri Lanka

Ancient DNA (aDNA) is used to explore the genetic landscape of the past and investigate the movement, mixture, and adaptation events that shaped present-day patterns of human genetic diversity. The present study was designed to explore the genetic composition of the ancient people of Sri Lanka. Despite the low amino acid racemization often found in skeletal remains of Sri Lanka, we attempted to extract DNA from skeletal remains of 5 individuals found from several sites in intermediate climatic zone in Sri Lanka by using methodologies particularly designed for highly damaged and degraded DNA. We attempted to extract and sequence DNA from the petrous part of the temporal bones and tooth roots of remains excavated from Sigiriya <em>Potana, Pellemalala</em> (4,500 YBP) and <em>Mini-atheliya</em> (1,000 – 5,000 YBP) in Sri Lanka. The bone processing, DNA extraction and amplification were performed in three separate rooms with dedicated equipment as accordance to the recommendation for analysis of aDNA. All measures were strictly taken to minimize contamination with modern samples. Using the DNA extracts, we prepared dual-indexed single-stranded libraries treated with uracil-DNA glycosylase (UDG) to reduce the rate of ancient DNA damage. Prior to sequencing, in-solution target hybridization was used to enrich the sequences that overlap the mitochondrial genome and about 1.24 million genome-wide SNPs. Sufficient data passing quality control standards for any of the five individuals studied was not obtained. Coverage of the mitochondrial genome ranged between 0.04-0.45x, with damage rates at the terminal nucleotide that were not indicative of authentic ancient DNA. A range of 453-2,838 SNPs out of ~1.24 million targets were covered across the nuclear genome, translating to a maximum coverage of 0.004x. The damage rates at the terminal nucleotide were not indicative of authentic ancient DNA. The low numbers of SNPs hit on the X and Y chromosomes precluded the confident assessment of genetic sex in all individuals but it is possible that the ancient skeletal sample represented by Sigiriya <em>Potana</em> is a female individual. Although the recent published work on using the petrous part of the temporal bone has generated many times more data than other skeletal elements, even this technique did not work to generate aDNA on this set of prehistoric skeletal remains found in the intermediate climatic zone in Sri Lanka. It is possible that other sites might provide better taphonomic preservation conditions than the sites we analysed, and in addition a priority should be to attempt ancient DNA analysis from skeletal remains found in Sri Lanka’s dry zone.

Assessment of prospective geological hazards in Torrevieja-La Mata coast (western Mediterranean) based on Pleistocene and Holocene events

The coastal zone in which the lagoons of La Mata and Torrevieja (Eastern Spain) developed can be described as a compilation of geo-hazards typical of the Mediterranean realm. This study has focused mainly on those linked to recent tectonics. Extensive use of the amino acid racemization dating method allowed us to establish the evolution of all the geomorphological units differentiated in the area, the most striking manifestation being at the La Mata Lagoon Bar, where MIS 5 deposits settled on MIS 7 sediments along a marked erosive unconformity, thereby attesting coastal uplift between these two stages. In addition, recent uplift processes were reflected on stepped abrasion platforms and, in some cases, enormous boulders were transported over these platforms by extreme surge waves. Furthermore, we obtained feasible evidence that, during the end of MIS 5, an earthquake with an offshore epicenter linked to Torrevieja Fault, Bajo Segura Fault or the set of faults linked to the former, was responsible for tsunami surge deposits represented in accumulations of randomly arranged and well-preserved Glycymeris and Acanthocardia shells. Recent catastrophic effects linked to the earthquakes were also detected. In this regard, comparison of the paleontological and taphonomic analyses allowed us to discern between wave and tsunami surge deposits. Therefore, evidence of these hazards undoubtedly points to important future (and present) erosive and/or catastrophic processes, which are enhanced by the presence of tourist resorts and salt-mining industry. Thus, these sites are also threatened by future increases in sea level in the context of warmer episodes, attested by raised marine fossil deposits. At the north of Cervera Cape, beaches will be eroded, without any possibility of sediment input from the starved Segura River delta. At the south of this cape, waves (and tsunamis) will erode the soft rocks that built up the cliff, creating deep basal notches.

Surficial and Shallow Subsurface Geology of the Northern and Central Exuma Cays, The Bahamas

The surface and subsurface geology of the Exuma Cays in the central Bahama Islands records sea-level cyclicity that extends back to the Jurasssic, however the focus of this paper is the Plio-Pleistocene, since approximately 1–3 million years ago. During the 1990s, the first author surveyed a large number of the islands by boat, mapped the geology on 1:25,000 topographic maps with the aid of air photos, and more recently complemented these mapping studies using Google Earth Pro. In 1994, two 33 m cores were extracted from Norman's Pond Cay and Lee Stocking Island in the southern group of the Exuma Cays. The outcropping rocks throughout the Cays are characterized by a mix of nearly pure bioclastic and oolitic sediments and limestone units. Generally, the highstand limestone deposits are capped with lowstand terra rossa paleosols, red-stained micritic limestone, calcrete, or karst surfaces. From surface and subsurface geology, a minimum of seven stratigraphic units are recorded, yet many cycles are obviously missing. Three broad eustatic intervals are evident from the δ18O record. These are associated with the Pliocene-early Pleistocene (“PP” >1.2 Ma), Mid-Pleistocene Transition (“MPT” ∼1.2–0.7 Ma), and the mid-late Pleistocene (“MLP” ∼0.7 Ma to present). A combination of physical stratigraphy, geomorphology, paleomagnetism, and amino acid racemization (AAR) provide a general age framework for these deposits. Pliocene beds at -25 m in only one core appear to indicate slow subsidence of the Bahama Banks. An interval of prolonged bank marginal or lower sea stands of the MPT are indicated by a cluster of dense, clayey red paleosols. Many MLP rocks on the islands and in the cores retain sufficient amino acids to establish a relative chronology for the MLP. The geomorphic and stratigraphic succession from the Exumas shows very rapid progradation of the over-steepened bank margin toward Exuma Sound by several km since the Plio-Pleistocene. The purpose of this paper is to: 1) characterize the geology of the existing Exuma rocks and cays; 2) demonstrate the shallow-subsurface stratigraphy in two 33-m long cores; and 3) provide some examples of how the Exuma Cays and their margins have evolved over the past 1–3 million years.