Ramon Mercedes-Martín

Autonomous University of Barcelona | UAB · Department of Geology

The origin of spherical-radial calcite bodies – spherulites – in sublacustrine, hyperalkaline and saline systems is unclear, and therefore their palaeoenvironmental significance as allochems is disputed. Here, we experimentally investigate two hypotheses concerning the origin of spherulites. The first is that spherulites precipitate from solutions...

The South Atlantic Aptian ‘Pre-salt’ reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcrop analogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic c...

Understand the origin of the exotic strontium-rich calcite/magnesium-rich clay/silica deposits formed during the Early Cretaceous in the South Atlantic Pre-salt lakes is challenging our ability to comprehend the chemical evolution of alkaline volcanic lakes. Here we present a new hydrochemical model based on an open basin concept, thermodynamic equ...

Lacustrine non-skeletal carbonates exhibit a diversity of petrographies due to interactions between physico-chemical and biologically influenced mechanisms. Despite the suggestion that evaporative concentration was involved in the formation of spherulite and shrubby-bearing carbonate successions in the Pre-Salt Cretaceous alkaline lakes of the Sout...

Ancient and recent terrestrial carbonate-precipitating systems are characterised by a heterogeneous array of deposits volumetrically dominated by calcite. In these environments, calcite precipitates display an extraordinary morphological diversity, from single crystal rhombohedral prisms, to blocky crystalline encrustations, or spherulitic to dendr...

The combined sedimentological and palaeoecological analysis of charophyte-rich carbonate microfacies is proven to be a useful methodology for the palaeoenvironmental reconstruction of continental settings. However, the integration of these charophyte assemblages with geochemical proxies has not been explored, yet. In the present work, the charophyt...

The combined taxonomic and palaeoecological analysis of charophyte-rich carbonate microfacies is proven to be a useful methodology for the palaeoenvironmental reconstruction of continental settings. However, the integration of these charophyte assemblages with geochemical proxies has not been explored, yet. In the present work, the charophyte-rich...

The chemostratigraphy of the growth strata related to the growth of the Sant Corneli-Bóixols anticline, reveals the sedimentary environment evolution of these syn-orogenic sediments. The decrease of Y/Ho ratios throughout the succession from typical open marine values to nearshore values indicates the shallowing upward trend of the growth strata an...

The lithographic limestone of La Pedrera de Meià (LPM) in south-central Pyrenees (NE Spain) is considered one of the best preserved lacustrine-coastal successions of the Early Cretaceous in Europe, hosting a taxonomically diverse record of Barremian biota. While this Konservat-Lagerstätte has been extensively surveyed for paleontological purposes,...

Ancient and recent terrestrial carbonate-precipitating systems are characterised by a heterogeneous array of deposits volumetrically dominated by calcite whose formation takes place in hydrochemically challenging environments. While sedimentologists and geochemists acknowledge that early formed carbonate crystals may suffer a range of diagenetic pr...

Understanding the flow of carbon through hyperalkaline lakes is a key means of understanding their biogeochemistry, sedimentology, and their paleoenvironmental and paleoclimatic records. Furthermore, understanding how mineral precipitation is regulated in these lakes can provide insights into how their sequestration of carbon can be managed. We rep...

La Pedrera de Meià (LPM) fossil site, discovered in the 19 th century, is an important Barremian Konservat-Lagerstätte located at the southern slope of the Montsec range (Lleida province, Spain). LPM is comparable in fossil preservation with other European lithographic limestones lagerstätten sites such as Solnhofen (Germany), Cerin (France) or Las...

Core recoveries are often incomplete, hampering sedimentological descriptions and their interpretations. To solve these limitations, chemostratigraphy is a reliable tool that provide information about the evolution of buried sedimentary systems, which can be applied to both continuous conventional core data and drill cuttings. Furthermore, chemostr...

The Ladinian-Carnian transition in the Tethys domain was accompanied by an important environmental change representing a milestone in the climate evolution of the Triassic. However, estimations on paleodiversity composition and paleoenvironmental conditions across this interval are scarce in marine settings due to the lack of fossil-bearing succes...

This study aims to compare the fabrics of anthropogenic carbonates downstream of lime and steel disposal sites with models of carbonate precipitation from natural systems to elucidate potential drivers, precipitation mechanisms, morphological similarities, predictability in 3D facies distributions and depositional models of these systems. For this...

Ancient and recent terrestrial carbonate-precipitating systems are characterised by a heterogeneous array of deposits volumetrically dominated by calcite. In these environments, calcite precipitates display an extraordinary morphological diversity, from single crystal rhombohedral prisms, to blocky crystalline encrustations, or spherulitic to dendr...

The recent discovery of significant hydrocarbon reserves in microbial carbonate reservoirs from the Cretaceous Pre-salt layers in the Santos Basin (Brazil) has renewed the interest in the study of modern and ancient microbialite deposits. Understand the factors controlling the facies heterogeneities and depositional processes involved in microbial...

The Middle Triassic (Ladinian) deposits of the Catalan Basin (Spain) are essentially represented by extensive marine carbonate platforms developed in a rift tectonic setting. During the Ladinian, a regional sea-level drop led to a significant paleogeographic reorganisation of the depocentres of eastern Iberia producing a relevant shift in the distr...

O ver the last decennia, alkaline leachates from the weathering of legacy steel slag disposal sites have affected the surrounding soils and drainage streams. The hyperalkaline and hypersaline conditions around these sites are comparable to extreme paleo environments such as alkaline lakes in rift volcanic settings. Investigating the carbonate depos...

The timing of recovery after the end‐Permian mass extinction has been a matter of debate, with some authors favouring a more rapid faunal recovery during the Early Triassic and others considering a more protracted biotic reestablishment spanning until the Middle Triassic. In this work, we investigated the lowermost Middle Triassic (Ladinian) carbon...

The South Atlantic Aptian "Pre-salt" shrubby carbonate Formations of Brazil and Angola are of major interest for the oil industry due to their potential hydrocarbon accumulations. Although the general sedimentology of these deposits is associated to saline, alkaline lakes in rift volcanic settings, the specific genesis of shrubby carbonate morpholo...

The Cretaceous 'Presalt' lakes of the South Atlantic margins (Brazil-Angola) display an unusual co-occurrence of chemical precipitates typically accumulated in extensive hyper-alkaline volcanic environments (Sr-rich spherulitic calcite, dolomite, Mg-rich smectites and silica). Despite previous hydrogeochemical models have contributed to rethink the...

The South Atlantic Aptian “Pre-Salt” shrubby carbonate successions offshore Brazil and Angola are of major interest due to their potential hydrocarbon accumulations. Although the general sedimentology of these deposits is widely recognized to be within saline, alkaline lakes in rift volcanic settings, the specific genesis of shrubby carbonate morph...

Understand the origin of the exotic Sr-rich spherulitic calcite/ Mg-rich clay/ silica deposits accumulated in the South Atlantic Cretaceous Presalt lakes is challenging our ability to comprehend the chemical evolution of alkaline volcanic lacustrine systems. Here we present a new hydrochemical model based on an open basin concept, thermodynamic equ...

The Permian-Triassic rifting represents the first of the two Mesozoic rifting stages recorded in the Iberian Peninsula. Its first phases of development started during the Early Permian, and were linked to the beginning of the break-up of Pangea, the large, unique and rheologically unstable supercontinent that mainly resulted from the collision of G...

The Cretaceous 'Presalt' lakes of the South Atlantic margins (Brazil and Angola) display an unusual co-occurrence of chemical precipitates typically accumulated in extensive freshwater and hyper-alkaline volcanic environments, i.e. spherulitic calcite, dolomite, Mg-rich smectites and silica. The origin and distribution of these mineral assemblages...

Understanding the physical, chemical and environmental thresholds affecting skeletal producers is crucial to build refined facies models and predict the basin-scale depositional architectures. Extensive research in the last decades has focused on comprehend the way metazoan biotas interact with the environment to produce specific carbonate accumula...

Lacustrine carbonate chimneys are striking, metre‐scale constructions. If these were bioinfluenced constructions, they could be priority targets in the search for early and extraterrestrial microbial life. However, there are questions over whether such chimneys are built on a geobiological framework or are solely abiotic geomorphological features p...

The Late Permian and Mesozoic evolution of Iberia can be divided into three major rift cycles and post-rift stages. The Late Permian-Triassic rift cycle broadly affected the eastern part of the Iberian plate generating fault-driven basins that were filled with sediments attributed to the Germanic facies during the Late Permian and Triassic. In Iber...

What would continental carbonate rocks look like in a world without microorganisms? Which macro-to nano-scale features would change, and which would be the same? Theoretical abiotic physicochemical processes may be invoked to explain many terrestrial carbonate rock-forming processes, but microbes influence crystal nucleation and growth even where t...

Lacustrine carbonate deposits with spherulitic facies are poorly understood, but are key to understanding the economically important “Pre-Salt” Mesozoic strata of the South Atlantic. A major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite-dominated deposits which are known in outcrop. Stratigra...

Phase diagrams are extremely powerful interpretive tools for converting qualitative observations about a sediment into quantitative constraints on the environment in which it was deposited. We present a new phase diagram for growth forms in non-marine calcite sediments, showing the competing influence of the chemical " driving force " (saturation i...

The ability to distinguish the features of a chemical sedimentary rock that can only be attributed to biology is a challenge relevant to both geobiology and astrobiology. This study aimed to test criteria for recognizing petrographically the biogenicity of microbially influenced fabrics and fossil microbes in complex Quaternary stalactitic carbonat...

The role of extracellular polymeric substances (EPS) and aminoacids in the nucleation of calcium carbonate spherulites and associated carbonate species is well-known, but still poorly constrained. Moreover, alkaline and saline lacustrine carbonate environments are also prone to generate authigenic hydrated magnesium clays (stevensite group). Here w...

Although carbonate spherulites are well known to form in a wide range of carbonate environments, the environmental conditions that underpin their origin are poorly constrained. To understand the sedimentology of spherulitic carbonate deposits, we must disentangle the chemistry and origin of the water involved in the precipitation of these sort of f...

Understanding the geochemical origin and timing of formation of unusual non-marine carbonate precipitates formed in highly alkaline and saline sublacustrine settings is a hot topic of research in carbonate sedimentol-ogy. The East Kirkton Limestone (West Lothian, Lower Carboniferous, Scotland) is constituted by an interesting array of uncommon fres...

Non-marine carbonates comprise a hugely diverse family of deposits, which reflect a constellation of forcing factors from local hydraulics to regional climatology. However, the two dominant controls on precipitation are solution chemistry and benthic microbial biogeochemistry. Here, we present a unifying concept for understanding how these controls...

The fault-block carbonate ramps of the Ladinian (Middle Triassic) Catalan Basin hosted a wide variety of microbial deposits which formed during a syn-rift stage. Stratigraphical and sedimentological analyses of these microbialites allow us to reconstruct two depositional models for such microbial deposits. Moreover new insights into the interplay b...

The Ladinian sedimentary record represents a major marine transgressive pulse over the Mediterranean region (northeastern Iberia) during the Middle Triassic. This record is arranged in two transgressive-regressive sequences formed by two steepened microbial-dominated carbonate ramp systems. Syn-rift subsidence, which controlled the creation of acco...

The Ladinian sedimentary successions record a major transgressive pulse of northeastern Iberia during the Middle Triassic. This record is arranged in two transgressiveeregressive (TeR) sequences formed by two fault-block microbial and shoal-dominated carbonate ramps. The main factor controlling the creation of accommodation space is the differentia...

The Upper Muschelkalk sedimentary record constitutes a major transgressive pulse of north-eastern Iberia during the Ladinian. This record is arranged in two transgressive–regressive (T–R) sequences formed by two stepped microbial-dominated carbonate ramp systems where accommodation was mainly controlled by extensional faults. This study seeks to ga...

During the Triassic, western and central Europe underwent crustal extension due to the break-up of Pangea and westward expansion of the Neotethyan Ocean. This propagation of Neotethys along eastern and southern margins of Iberian plate drowned the Paleozoic palaeotopography during Ladinian times. Siliciclastic supplies and evaporites increased duri...