Carbonate Diagenesis and Stratigraphy

Keywords:

Canning Basin;
Devonian;
Famennian;
Frasnian;
palaeokarst;
reefs

The Frasnian–Famennian boundary in the Canning Basin has long been associated with a shelf-wide, short-lived fall in relative sea-level. A near-planar palaeokarst surface, separating Frasnian proximal forereef and Famennian backreef facies, locally marks the boundary in the northwestern Lennard Shelf (Chedda Cliffs area, northern Napier Range). Surface and subsurface relationships between the Frasnian and Famennian strata suggest that a major episode of normal faulting and associated tilting in the latest Frasnian uplifted the platform margin to subaerially expose and erode all of the margin and uppermost forereef facies. Tectonic control on the development of this Frasnian–Famennian palaeokarst surface questions the interpretation of a simple, shelf-wide eustatically driven relative sea-level fall. Instead, a tectonic event affecting the northwestern Lennard Shelf, coupled with widespread recognition of a reduction in carbonate production at or very near the Frasnian–Famennian boundary elsewhere on the shelf, supports earlier interpretations of a major phase of basin-margin uplift related to extension along basin-bounding faults.

Cathodoluminescent petrography (CL) is a well established technique that can provide a means to examine fabrics, diagenetic phases and cement relationships in sedimentary rocks.  CL is very useful in the study of carbonate rocks because of the activators and quenchers.  Mn is the most important CL activator in carbonate minerals and concentrations of ca. 20 ppm can cause luminescence, although levels of just a few ppm may be enough to cause weak CL depending on the amount of Fe present.  Fe begins to quench luminescence at levels of ca. 200 ppm, and effectively quenches luminescence at levels of 103 ppm.  Mn and Fe both have divalent reduced forms that readily fit into trigonal carbonate crystal structures and they have different redox potentials, so the concentration of these cations provide a baseline for understanding oxygen levels of the pore fluids from which the carbonate precipitated.
Dolomite is an important sedimentary mineral that can be difficult to interpret because many dolostones are composed of multiple stages of dolomite that typically represent very different geochemical processes of replacement, recrystallization, and cementation.  Because these processes usually occur under different redox conditions, dolomites record these changes in their crystals.  Dolomites of the Permian Phosphoria Complex provide an excellent case example that contains petroleum source rocks in basinal facies and petroleum reservoir rocks in shallow water peritidal carbonate facies.  The shallow water facies were subjected to extreme arid conditions and evaporation that led to an early mimetic dolomitization of CaCO3 sediments.  This first phase experienced recrystallization and overprinting by burial phases that also are major cementing phases. Cement recognition is important in carbonate rocks, and especially dolomite, because of its importance in determining the hydrologic properties of carbonate aquifers and petroleum reservoirs.

El origen y formación de las dolomitas ha sido un enigma por parte de la comunidad científica en las últimas décadas. En este trabajo de investigación, se llevó a cabo un estudio geoquímico de una secuencia litoestratigráfica de diversas facies de calizas macrofosilíferas y dolomitas, correspondientes al Miembro Punceres de la Formación El Cantil en La Cantera El Vivero, Sector Pertigalete, Edo. Anzoátegui - Venezuela, con el propósito de establecer su origen, las condiciones paleoambientales presentes durante la depositación y su evolución diagenética durante el tiempo geológico. Para cumplir con los objetivos planteados, se colectaron un total de once (11) muestras de roca; de modo que, diez (10) correspondían al Miembro Punceres (Fm. El Cantil), y una (1) al posible Miembro Caripe (Fm. Chimana). A cada muestra de roca se les realizó una previa descripción macroscópica, un análisis instrumental por Fluorescencia de Rayos-X (FRX) para determinar la concentración elemental de Al2O3, SiO2, K2O y V (ppm), y un posterior análisis químico por valoración complexométrica con EDTA (ácido etilendiamino-tetraacético) con el propósito de determinar la concentración elemental de MgO, CaO, MnO y Fe2O3. Por medio de la interpretación de los datos obtenidos a partir del levantamiento litoestratigráfico, se definieron tres (3) unidades informales, correspondientes al Miembro Punceres (Fm. El Cantil) (Unidad I y II) y al posible Miembro Caripe (Fm. Chimana) (Unidad III). Asimismo, se identificó la presencia de cuatro (4) facies de carbonatos dentro de las unidades informales I y II: 1) Mudstones diagenética o Cementstone; 2) Floatstone diagenética; 3) Rudstone diagenética; 4) Dolomicrosparstone; de las cuales, se estableció que el posible ambiente de depositación del Miembro Punceres se vincula a un evento de evolución progresiva de un complejo arrecifal rudístico, dentro de un margen de plataforma interna o semi-protegido por algún banco o montículo arrecifal, bajo condiciones ligeramente anóxicas, condicionado por eventos episódicos de transgresión y regresión marina; aunque también, se estableció la posible hipótesis de que algún evento tectónico posterior pudo haber afectado dicha secuencia carbonática, separando la misma en dos entes distintos (Unidad I y II). Por otra parte, en la Unidad III se identificó solo una facies de carbonato: 1) Mudstone pelágica; estableciendo un entorno de depositación más anóxico y de mayor profundidad en esta unidad, posiblemente, dentro del margen de plataforma externa. A través del análisis geoquímico se determinó que las dolomitas del Miembro Punceres, posiblemente, se originaron durante una diagénesis de soterramiento, a través de la filtración por reflujo de aguas de alta salinidad ricas en Mg y, quizás, por influencia de aguas de formación modificadas por la interacción agua-roca de origen sedimentario. Dichas dolomitas presentaron elevadas concentraciones de Fe2O3, MnO y V, a comparación de las calizas, indicando la evidencia de posibles fluidos dolomíticos enriquecidos en Fe2+, Mn2+ y VO2+, bajo condiciones ligeramente anóxicas; estableciendo niveles más anóxicos en los fluidos diagenéticos que originaron la capa de dolomita M2 - M3 (Unidad I), a comparación de la capa de dolomita M7 (Unidad II). Asimismo, en bases a las relaciones elementales MgO/CaO y MnO/CaO, se estableció una posible dolomitización más avanzada y más completa en la capa de dolomita M7. La baja concentración de K2O y CaO y el aumento de MgO, MnO y Fe2O3 en las capas de dolomitas, indica una posible sustitución iónica o reemplazo y recristalización durante el avance diagenético; sin embargo, las concentraciones de K2O en las capas de dolomitas M2 - M3 y M7 y la capa de caliza M1 (Unidad I) se vinculan con mayor criterio a un aumento en la salinidad en la plataforma carbonática; aunque también, se estableció que las elevadas concentraciones de K2O en las capas de calizas M4 a M11 (Unidad I, II y III) se debe, principalmente, a la presencia de minerales arcillosos, destacado por la contenido significativo de SiO2 y Al2O3 en las mismas.

Owing to their tightness, intra reservoir barriers have the potential to prevent homogenization of reservoir fluids
and so cause compartmentalization. Identification of these barriers is an important step during reservoir evaluation.
In order to achieve this, three main approaches: i) detailed petrographic and core analysis, ii) petrophysical studies
(flow unit concept) and iii) geochemical analysis (strontium residual salt analysis) were applied systematically in
the Permo-Triassic carbonate reservoirs (Dalan and Kangan formations) of a supergiant gas reservoir located in
the Central Persian Gulf. Integration of these approaches has led to a full clarification of the intra reservoir barriers.
Petrographic examinations revealed the potential stratigraphic barriers to fluids flow created by various depositional/
diagenetic characteristics. Petrophysical data such as poroperm values, pore throat size distribution and scanning
electron microscopy (SEM) analysis were used to differentiate the reservoir flow units from non-reservoir rock.
According to different trends in 87Sr/86Sr ratios of residual salts, the existence of flow barriers was evaluated and
proved. Finally, by integrating these approaches, three intra reservoir barriers were introduced in the studied reservoir
interval. These intra reservoir barriers are depositional and diagenetic in nature and are located in stratal positions
with sequence stratigraphic significance. The possibility of reservoir compartmentalization was evaluated in the
studied wells, and then their existence was predicted at the adjacent fields. As shown in this study, integration of
petrographic examinations with flow unit determination in a sequence stratigraphic framework has the potential for
recognizing intra reservoir barriers and predicting compartmentalization of the studied Permo-Triassic reservoirs.

An evolutionary model is proposed to explain the spatio-temporal distribution of karstification affecting the Lower Jurassic shallow-marine carbonate succession (Coimbra Group) of the Lusitanian Basin, cropping out in the Coimbra-Penela region (western-central Portugal), in a specific morphostructural setting (Dolomitic Hills). Indeed, in the Coimbra Group, despite the local lateral and vertical distributions of dolomitic character and the presence of few thick sandy-argillaceous/shale and marly interbeds, some (meso)karstification was identified, including several microkarstification features. All types of karst forms are commonly filled by autochthonous and/or allochthonous post-Jurassic siliciclastics, implying a palaeokarstic nature.

The main aim of this work is to infer the interplay between depositional facies, diagenesis, syn- and postdepositional discontinuities and the spatio-temporal distribution of palaeokarst. Here, the palaeokarst concept is not limited to the definition of a landform and/or possibly to an associated deposit (both resulting from one or more processes/mechanisms), but is considered as part of the local and regional geological record.

Detailed field information from 21 stratigraphic sections (among several dozens of other observations) and from structural-geology and geomorphological surveys, was mapped and recorded on graphic logs showing the lithological succession, including sedimentological, palaeontological and structural data. Facies determination was based on field observations of textures and sedimentary structures and laboratory petrographic analysis of thin-sections. The karst and palaeokarst forms (both superficial and underground) were classified and judged on the basis of present-day geographic location, morphology, associated discontinuities, stratigraphic position and degree of burial by post-Jurassic siliciclastics that allowed to distinguish a exposed karst (denuded or completely exhumed) than a palaeokarst (covered or partially buried).

A formal lithostratigrafic framework was proposed for the local ca. 110-m-thick combined successions of Coimbra Group, ranging in age from the early Sinemurian to the early Pliensbachian and recorded in two distinct subunits: the Coimbra formation, essentially dolomitic; and the overlying S. Miguel formation, essentially dolomitic-limestone and marly-limestone.

The 15 identified facies were subsequently grouped into 4 genetically related facies associations indicative of sedimentation within supra/intertidal, shallow partially restricted subtidal-lagoonal, shoal and more open-marine (sub)environments - in the context of depositional systems of a tidal flat and a very shallow, inner part of a low-gradient, carbonate ramp. In some cases, bedded breccia bodies (tempestite/sismites) are associated to synsedimentary deformation structures (slumps, sliding to the W to NW), showing the important activity of N–S and NNE–SSW faults, during the Sinemurian. All these deposits are arranged into metre-scale, mostly shallowing-upward cycles, in some cases truncated by subaerial exposure events. However, no evidence of mature pedogenetic alteration, or the development of distinct soil horizons, was observed. These facts reflect very short-term subaerial exposure intervals (intermittent/ephemeral), in a semiarid palaeoclimatic setting but with an increase in the humidity conditions during the eogenetic stage of the Coimbra Group, which may have promoted the development of micropalaeokarstic dissolution (eogenetic karst).

Two types of dolomitization are recognized: one (a) syndepositional (or early diagenetic), massive-stratiform, of “penesaline type”, possibly resulting from refluxing brines (shallow-subtidal), with a primary dolomite related to the evaporation of seawater, under semiarid conditions (supra/intertidal) and the concurrent action of microbial activity; another (b) later, localized, common during diagenesis (sometimes with dedolomitization), particularly where fluids followed discontinuities such as joints, faults, bedding planes and, in some cases, pre-existing palaeokarstic features.

The very specific stratigraphic position of the (palaeo)karst features is understood as a consequence of high facies/microfacies heterogeneities and contrasts in porosity (both depositional and its early diagenetic modifications), providing efficient hydraulic circulation through the development of meso- and macropermeability contributed by syn- and postdepositional discontinuities such as bedding planes, joints and faults. These hydraulic connections significantly influenced and controlled the earliest karst-forming processes (inception), as well as the degree of subsequent karstification during the mesogenetic/telogenetic stages of the Coimbra Group. Multiple and complex karstification (polyphase and polygenic) were recognized, including 8 main phases, to local scale, integrated in 4 periods, to regional scale: Jurassic, Lower Cretaceous, pre-Pliocene and Pliocene-Quaternary. Each phase of karstification comprise a specific type of (palaeo)karst (eogenetic, subjacent, denuded, mantled-buried and exhumed).

Finally, geological, geomorphological and hydrogeological characteristics allowed to describe the local aquifer. The elaborated map of intrinsic vulnerability shows a karst/fissured and partially buried aquifer (palaeokarst) with high to very high susceptibility to the contamination.

Mollusk shells excavated from archeological sites have been used to reconstruct paleoenvironment, human foraging , and migratory patterns. To retrieve information on past environment or human behavior, chemical signatures such as oxygen stable isotopes (δ 18 O shell) are analyzed. Shell archeological remains usually represent food waste. Thermal treatments such as boiling and roasting may influence shell structure and biochemical composition. However, little is known about the relationship between changes at macro-, microstructural and chemical levels. This work is a calibration study on modern Phorcus (Osilinus) turbinatus shells. A simulation of two different cooking methods (boiling and roasting) was carried out at four temperatures (100 °C, 300 °C, 500 °C and 700 °C) for two durations (20 min and 60 min). The structure and biochemistry of shells boiled at 100 °C did not significantly change. However, treatments at higher temperatures strongly affected both the structure and the biochemistry of the shells. At 300 °C the external coloration, as well as nacre iridescence, were altered. Raman spectroscopy revealed that, at this temperature, the aragonite-calcite polymorphic transformation starts. Scanning electron microscope (SEM) analysis showed drastic changes in the microstructural organization also beginning at 300 °C. Furthermore, the isotopic δ 18 O shell values were significantly affected. Increasing cooking temperatures resulted in an enhancement of the above-mentioned alterations. These results provide a set of temperature-related morphological, structural and biochemical characteristics for investigating the thermal behavior of biocarbonates and for estimating different cooking treatments in archeological record.

The tectonic evolution, stratigraphy and mineralization of northern Iraq are strongly affected by the structural position of the country within the main geostructural units of the Middle East; Arabian part of the African platform and the Asian branches of the Alpine geosyncline; as well as by the structure of the country itself. During the Late Mesozoic and Early Cenozoic, sedimentation in the area of the present Mesopotamian Basin and Zagros Fold Belt was controlled by local tectonics, eustatic sea-level changes, and climate variations. From Triassic through Late Cretaceous, sea-level fluctuations in

A combination of high resolution cathodoluminsecnce-spectroscopy (HRS-CL) with spatial electron
microprobe analysis and optical microscopy is used to determine paragenesis and history of cementation
in the limestones and dolostones of Khurmala Formation which is exposed in many parts of Northern
Iraq. Khurmala Formation was subjected to different diagenetic processes such as micritization, compaction,
dissolution, neomorphism, pyritization and cementation that occurred during marine to shallow
burial stages and culminated during intermediate to deep burial later stages. Five dolomite textures
are recognized and classified according to crystal size distribution and crystal-boundary shape.
Dolomitization is closely associated with the development of secondary porosity that pre-and postdates
dissolution and corrosion; meanwhile such porosity was not noticed in the associated limestones. Microprobe
analysis revealed three types of cement, calcite, dolomite and ankerite which range in their luminescence
from dull to bright. Cathodoluminescence study indicated four main texture generations. These
are (1) unzoned microdolomite of planar and subhedral shape, with syntaxial rim cement of echinoderm
that show dull to red luminescence, (2) equant calcite cements filling interparticle pores which shows
dull luminescence and weak zonal growth, (3.1) homogenous intrinsic blue stoichiometric calcite with
dull luminescence and without activators, (3.2) coarse blocky calcite cement with strong oscillatory zoning
and bright orange luminescence which postdates other calcite cements, (4) ankerite cement with red
to orange, non-luminescence growth zonation which is the last formed cement.

The late Ypresian (early Eocene) Jdeir Formation was deposited in the Mesozoic-Cenozoic Gabes-Tripoli Basin, offshore Libya. The basin developed on the northern passive margin of the African Plate and was relatively unstable being affected by syn-sedimentGly tectonic movements. Deposition was coeval with a relative rise of sea-level and the subsequent highstand. A lower, thinly-developed nummulitic bank facies with restricted distribution records the transgressive event and is succeeded by more micritic sediments that record the time of maximum flooding. The succeeding sea-level highstand is represented by a thick, and widely developed, progradational-aggradational nummulitic sequence that displays lateral changes across WNEESE trending facies belts. Three major lithofacies are recognized in the Jdeir Formation: Nummulites packstonegrainstone, Alveolina-Orbitolites wackes tone-packs tone, and Fragmental-Discocyclina-Assilina wackestone-packstone, deposited in bank, back-bank, andf ore-bank environments, respectively. The formation passes to the NNE into the pelagic lithofacies of the Ha/lab Formation; landward, to the south, it passes into shoreline evaporiticfacies of the Taljah Formation. The lithofacies were structurally controlled by contemporaneous and/or syndepositional tectonic movements, with nummulitic facies tending to develop on uplifted areas. Petrographic and petrophysical studies indicate that porosity in the Jdeir Formation is controlled by depositional environment, tectonic setting and diagenesis. The combined effects of salt tectonics, a major unconformity at the top of the formation and meteoric diagenesis have produced excellent-quality reservoir facies at the Bouri oilfield and in other areas. Porosity is highest in the nummulitic bankfacies and lowest in the Alveolina-Orbitolites micrite facies. Good to excellent reservoir quality occurs in the upper part of the nummulitic packstone-grainstonefacies, especially where these sediments overlie structurally high areas. High rates of dissolution found at the crests of domes and anticlines suggest that early diagenetic processes and features are, in part, structurally controlled. Future exploration success will depend on investigation of similar structures within the Gabes-Tripoli Basin.
Both porosity initiation and preservation are related to early depositional and diagenetic I processes. The wide time-gap between hydrocarbon generation and reservoir formation points to the role of the seal in porosifYrpreservation and rules out the assumption that early emplacement of oil had preserved the porof ity.

The late Ypresian (early Eocene) Jdeir Formation was deposited in the Mesozoic-Cenozoic Gabes-Tripoli Basin, offshore Libya. The basin developed on the northern passive margin of the African Plate and was relatively unstable being affected by syn-sedimentary tectonic movements. Deposition was coeval with a relative rise of sea-level and the subsequent highstand. A lower, thinly-developed nummulitic bank facies with restricted distribution records the transgressive event and is succeeded by more micritic sediments that record the time of maximum flooding. The succeeding sea-level highstand is represented by a thick, and widely developed, progradational-aggradational nummulitic sequence that displays lateral changes across WE-ESE trending facies belts.Three major lithofacies are recognized in the Jdeir Formation: Nummulites packstone-grainstone, Alveolina-Orbitoliteswackestone-packtone, andFragmental-Discocyclina-Assilina wackestone-packstone, depositedin bank, back-bank, and fore-bank environments, respectively. The formation passes to the NNE into the pelagic lithofacies of the Hallab Formation; landward, to the south, it passes into shoreline evaporitic facies of the Taljah Formation. The lithofacies were structurally controlled by contemporaneous and/or syndepositional tectonic movements, with nummulitic facies tending to develop on uplifted areas.Petrographic and petrophysical studies indicate that porosity in the Jdeir Formation is controlled by depositional environment, tectonic setting and diagenesis. The combined effects of salt tectonics, a major unconformity at the top of the formation and meteoric diagenesis have produced excellent-quality reservoir facies at the Bouri oilfield and in other areas.Porosity is highest in the nummulitic bank facies and lowest in the Alveolina-Orbitolites micrite facies. Good to excellent reservoir quality occurs in the upper part of the nummulitic packstone-grainstone facies, especially where these sediments overlie structurally high areas. High rates of dissolution found at the crests of domes and anticlines suggest that early diagenetic processes and features are, in part, structurally controlled. Future exploration success will depend on investigation of similar structures within the Gabes-Tripoli Basin.Both porosity initiation and preservation are related to early depositional and diagenetic processes. The wide time-gap between hydrocarbon generation and reservoir formation points to the role of the seal in porosity preservation and rules out the assumption that early emplacement of oil had preserved the porosity.

Coelenterta berasal dari bahasa Yunani yaitu Coilos yang berarti rongga dan Enteron yang berarti usus. Jadi Coelenterata dapat diartikan sebagai hewan yang memiliki rongga yang berfungsi sebagai usus. Nama Filum Coelenterata lebih sering dikenal sebagai Cnidaria.Cnidaria berasal dari bahasa Yunani yaitu cnido yang berarti penyengat karena hewan ini memiliki sel penyengat (Pandhu, 2010).

"A thick sequence of late Dinantian (Asbian±Brigantian) carbonates crop out in the Buttevant area, North Co. Cork,
Ireland. A mud-mound unit of early Asbian age (the Hazelwood Formation) is the oldest unit described in this work.  This formation is partly laterally equivalent to, and is overlain by, over 500 m of bedded platform carbonates which belong to the Ballyclogh and Liscarroll Limestone Formations. Four new lithostratigraphic units are described within
the platform carbonates: (i) the early Asbian Cecilstown Member and (ii) the late Asbian Dromdowney Member in
the Ballyclogh Limestone Formation; (iii) the Brigantian Templemary Member and (iv) the Coolbane Member in the
Liscarroll Limestone Formation.
The Cecilstown Member consists of cherty packstones and wackestones that are inferred to have been deposited below
fair-weather wavebase. This unit overlies and is laterally equivalent to the mud-mound build-up facies of the Hazelwood
Formation. The Dromdowney Member is typi®ed by cyclic-bedded kamaenid-rich limestones possessing shell bands,
capped by palaeokarst surfaces, with alveolar textures below and shales above these surfaces. The carbonates of this unit
were deposited at or just below fair-weather wavebase, the top of each cycle culminated in subaerial emergence. The
Templemary Member consists of cyclic alternations of subtidal crinoidal limestones capped by subtidal lagoonal crinoid-
poor, peloidal limestones possessing coral thickets. Intraclastic cherty packstones and wackestones characterize the
Coolbane Member, which is inferred to have been deposited below fair-weather wavebase but above storm wavebase.
The early Asbian Cecilstown Member has a relatively sparse micro- and macrofauna, typi®ed by scattered Siphono-
dendron thickets, archaediscids at angulatus stage and common Vissariotaxis. Conversely, macro- and microfauna is
abundant in the late Asbian Dromdowney Member. Typical late Asbian macrofossils include the coral Dibunophyllum
bipartitum and the brachiopod Davidsonina septosa. The base of the late Asbian (Cf6g Subzone) is recognized by the ®rst
appearance of the foraminifers Cribrostomum lecompteii, Koskinobigenerina and the alga Ungdarella. The Cf6g Subzone
can be subdivided into two biostratigraphic divisions, Cf6g1 and Cf6g2, that can be correlated throughout Ireland.
Relatively common gigantoproductid brachiopods and the coral Lonsdaleia duplicata occur in the Brigantian units. The
base of the Brigantian stage (Cf6d Subzone) is marked by an increase in the abundance of stellate archaediscids,
the presence of Saccamminopsis-rich horizons, Loeblichia paraammonoides, Howchinia bradyana and the rarity of
Koninckopora species.
Changes in facies at the Cecilstown/Dromdowney Member and the Ballyclogh/Liscarroll Formation boundaries
coincide closely with the changes in fossil assemblages that correspond to the early/late Asbian and the Asbian/Brigantian
boundaries. These facies changes are believed to re¯ect major changes in relative sea-level on the Irish platforms. The sea-
level variations that are inferred to have caused the facies changes at lithostratigraphic boundaries also brought in the new
taxa that de®ne biostratigraphic boundaries. Moreover, many of the Dinantian stage boundaries that are de®ned bio-
stratigraphically in Great Britain, Belgium and the Russian Platform also coincide with major facies boundaries caused
by regressive and transgressive episodes. The integration of detailed biostratigraphic analyses with facies studies will lead
to better stratigraphic correlations of Dinantian rocks in northwest Europe."

Carbonate mounds are important and ubiquitous components of the sedimentary rock record throughout the Phanerozoic. Nevertheless, factors controlling their occurrence and growth remain enigmatic, in particular because the depositional depths of such mounds are poorly constrained and it is assumed that fossil examples lack modern analogues. Factors currently used to constrain thewater depth that ancient mounds grew in include water energy, occurrence of specific organisms that perform photosynthesis (particularly calcareous algae) and distinct non-biogenic components. In reviewing the main criteria used to delineate water depth of formation of fossil carbonate mounds, most (if not all) criteria traditionally used to assume shallow-water settings appear to be no longer substantiated in the light of current knowledge gained frommodern carbonate mounds. High energy, assumed to indicate shallow-water conditions, is ongoing in water as deep as > 1000 m. The occurrence of peloids and processes such as micritization is not diagnostic of water depth. Furthermore, virtually none of the calcareous algae assumed to indicate the photic zone have a taxonomically granted affiliation.
Over the last years, research in the deep ocean, in particular thanks to the deployment of new devices and techniques, provided a good database revealing a wide distribution of modern carbonate mounds. Reviewing the characteristics of ancient carbonate mounds, with emphasis on depositional settings, and confronting the criteria used with current knowledge from sub-recent and modern carbonate mounds, we conclude that for many ancient mounds a bathyal origin is (at least) as likely as a shallow-water origin. This conclusion iswell supported by the sedimentary records left by these modern mounds that are astonishingly similar to those seen in Palaeozoic and Mesozoic carbonate mounds.

We present the results of a multidisciplinary study on the relationships between the structural archi- tecture of an extensional fault system in poorly lithified shallow marine sands and the associated pattern of diagenetic carbonate concretions. Based on their shape, spatial distribution, cement texture and chemistry, and isotopic signature, carbonate concretions are grouped into (1) tabular (encompassing also nodular and lens- shaped) concretions developed within the fault zones, and (2) elongate and coalescent strata-bound concre- tions formed adjacent and mostly parallel to fault zones. Cement chemistry and morphology, as well as stable carbon–oxygen isotopic signatures, indicate that tabular concretions formed during early diagenesis in the vadose mixing marine–meteoric zone, possibly during coseismic rupture propagation and, in the interseismic periods, as a result of slow capillary suction along the low-permeability fault zones. On the other hand, elon- gate concretions formed after regional uplift and during telodiagenesis by precipitation from meteoric, phreatic water flowing parallel to the fault zones, which acted as a hydraulic barrier. The concretion patterns record the evolution of fluid flow orientation and the changing chemistry of fault-zone fluids, which were fundamentally driven by fault system propagation and resulting fault architecture during two major diagenetic stages.

The Cenozoic carbonates of the Bounty-Talisman region
can be divided into five major facies. From oldest to
youngest, these are: Paleocene to Eocene basinal facies,
Oligocene to Miocene slope-canyon facies, Oligocene to
Miocene shelf facies, Oligocene to Miocene near-shore
facies, and Pliocene-Quaternary shelf facies. This
represents a shallowing-upwards cycle up to the late
Miocene, followed by a significant transgression and a
return to more open marine conditions in the Pliocene-
Quaternary. The dominant geological processes
controlling sonic velocity in the Cenozoic carbonates are
physical compaction, burial calcite cementation,
dolomitisation, and anhydrite/gypsum cementation. In
the more open marine facies of the Cenozoic carbonates,
compaction and burial calcite cementation have been
the dominant geological processes that have controlled
sonic velocity. Large-scale carbonate content variations
associated with submarine canyon-fill sediments have
also produced lateral sonic velocity variations.
Dolomitisation and anhydrite cementation have produced
localised high velocity zones within the near-shore facies
of the carbonates

The Eocene sediments plays critical role in the evolution and development of the petroleum system in the Gulf of Suez region, where it is representing a self-source rock or self-reservoir or combination in some areas within the basin. Microfacies analysis and paleontological studies have not been conducted on these Eocene sediments in the area of the October oil field, which is mandatory for the formation characteristics assessment. Therefore, sidewall core and ditch-cuttings samples that was obtained from October Eocene carbonate sediments so far ascribed to the Thebes formation was studied in terms of sedimentology, paleontology and depositional environment. A total of 64 thin sections were analyzed petrographically, and three microfacies types recognized. Both Calcareous nanoplankton and Foraminifers were examined. The study of the Eocene carbonate facies in the October field revealed that the succession is composed of pelagic foraminiferal limestone of varied color, containing abundant planktonic foraminifers and minor traces of chert. Three microfacies are distinguished including wackestone of smaller planktonic foraminifera (50%), wackestone-packstone of planktonic foraminifera (40%) and packstone of planktonic foraminifera (10%). Nannoplankton and foraminifers indicate that the studied succession is of early Eocene to middle Eocene age. Microfacies and fossil assemblage of the studied section indicate a pelagic environment and deposition in deep basin at water depths of a few hundred meters. Finally, the current results were compared with data from previous publications on Eocene sediments in the region. It is revealed that the studied succession provides new data and contribution for the evolution of carbonate platform in the Ypresian-Lutetian age, and differs from the typical Thebes Formation and other Eocene Formations concerning facies, lithology, fossil content, age and depositional environment. Therefore, we suggest to abandon the term Thebes Formation for this Eocene car-bonate succession in the October field, and a new lithostratigraphic unit, named Radwany Formation, is formally introduced.

ABSTRAK
Gua Liyah 1 termasuk salah satu gua di Kawasan Karst Gombong Selatan, Kebumen, Jawa Tengah.
Kawasan batugamping terutama bentangalam karst terkaji memiliki keanekaragaman bumi yang
berukuran kecil (micro geodiversity) dan keanekaragam hayati (biodiversity) yang unik, langka dan
bersifat strategis sehingga harus dilestarikan keberadaannya. Surat Keputusan Menteri Pertambangan
dan Energi Nomor 1518 K/20/MPE/1999 tanggal 29 September 1999, yang selanjutnya diperbaiki
dalam Surat Keputusan Menteri Pertambangan dan Energi Nomor 1456 K/20/MEM/2000 tanggal 3
November 2000 tentang Pedoman Pengelolaan Kawasan Karst, merupakan momentum yang baik
untuk mensosialisasikan tentang nilai strategis yang dimiliki oleh suatu kawasan karst. Data-data
untuk mengetahui itu diperlukan survey lapangan, pemetaan gua grade 4B, analisis petrografi batuan,
dan dokumentasi. Gua Liyah 1 merupakan gua karst yang tersusun dari litologi batugamping
wackestone. Batugamping ini berumur Miosen Akhir, setara dengan Formasi Kalipucang. Gua Liyah 1
memiliki lorong gua yang mencapai 901.46 meter. Aspek yang paling bisa dimanfaatkan untuk
geowisata adalah aspek speleologi, selain itu keragaman biotanya. Aspek speleologi Gua Liyah 1
dilihat dari sisi ornamen gua seperti stalaktit, stalagmit, pilar, flowstone, gordyn, drapery, moonmilk,
soda straw, dan heliktit. Beberapa ornamen gua pertumbuhannya dipengaruhi oleh pelarutan air yang
masuk melalui rekahan yang ada. Aspek geologi dilihat dari adanya endapan batuan sedimen berupa
lumpur, pasir sampai kerikil terdapat di dalam gua. Beberapa lokasi di dalam lorong gua dapat
dimanfaatkan sebagai pembelajaran bidang paleontologi. Potensi air tanah yang dapat dimanfaatkan
oleh warga, terdapat sungai bawah tanah yang mengalir di atas batuan breksi vulkanik Formasi Gabon.
Kata Kunci : Micro Geodiversity, Biodiversity, Potensi Karst, Gua Liyah 1

A paleostress analysis was carried out on fault slip data collected at 13 sites distributed over a total of 135 km within the Canadian Rocky Mountains at a latitude of about N51º. Striae on brittle deformation structures were used to calculate paleostress states responsible for the observed deformation, and hence, to unravel the stress state evolution of the Cordilleran foreland fold-and-thrust belt in the study area. we identified five main paleostress states in the study area and interpret these as deformation events in the evolution of the foreland belt. Radial or pure (ENE-wSw) extension and oblique NE-Sw to ENE-wSw compression were derived from back-tilted data and were probably active during an early stage. While radial extension may result from increasing burial in the absence of significant horizontal compression, the compression phase may correspond to Middle Jurassic to Late Cretaceous tectonic convergence along the western border of the North American craton. The other three paleostress states include (i) NE-Sw to ENE-wSw compression, (ii) compressional NE-Sw or pure strike-slip and (iii) pure or strike-slip extension or extensional strike-slip. The NE-Sw to ENE-wSw compression and compressional or pure strike-slip phase correspond to the main tectonic compressive stress during Laramide orogeny, consistent with the stress field that caused the macrostructural thrust faults. The final extensional phase may relate to the Eocene regional extensional tectonics.

As part of the International Continental Scientific Drilling Program's Fennoscandian Arctic Russia–Drilling Early Earth Project (ICDP FAR-DEEP), Palaeoproterozoic diamictic and associated rocks were targeted and recovered in Hole 3A on the Kola Peninsula of NW Russia. In addition to the diamictites, carbonate sedimentary rocks and volcanic ash layers (all metamorphosed to greenschist grade) were encountered. Sedimentology and geochemistry suggest deposition of the diamictites in an open-marine aragonite-precipitating environment. Sampling of the core and of outcrops from the same geographical area yielded a number of zircons for analyses, the majority of which were inherited. However a tuff at 20.01 m core depth yielded zircons dated at 2434 ± 1.2 Ma (± 6.6 Myr including decay constant uncertainties) that we interpret as a magmatic age. These data, combined with dates from underlying intrusions, indicate deposition of the Polisarka Sedimentary Formation diamictites and underlying carbonates during an interval of time from ca. 2430 to 2440 Ma. The carbonate rocks, which likely originally included aragonitic limestones, were deposited mostly in a deep-water setting (i.e, at least below storm wave base) and occur below the diamictite. They record two inorganic carbon δ13C excursions, from values of ca. 0‰ to minima of ca. -5.4‰, as the contact with the overlying diamictite is approached. The older excursion occurs about 9 m below the base of the diamictic units and the younger one at 1 m below. Throughout that interval, Mg/Ca ratios correlate strongly with δ13C (n = 38, r = 0.85), and combined with petrographic observations, this indicates that the first (stratigraphically lower) excursion was modified by secondary alteration and the second is recorded in resedimented dolostone clasts. It is tempting to speculate that these dolostone clasts weredeposited in penecontemporaneous shallow-marine waters, and that their low δ13C values might reflect input of oxidised atmospheric methane to the ocean surface (and therefore the cause of the glaciation); the dolostones were subsequently resedimented into the deeper marine settings. However this must be left as a hypothesis to be tested when further age-constrained contemporaneous pre-glacial carbonate sections are found.

Mineralisation at the Courtbrown deposit in south-western Ireland is concentrated in the basal section of the Chadian Waulsortian Limestone, immediately above the Courceyan Ballysteen Limestone. Two episodes of sulphide deposition have been identified: an early stage of minor pyrite precipitation, and a later base-metal-rich mineralisation event. Sphalerite, galena and pyrite of the later mineralisation event occur predominantly as replacement phases along stylolites, dissolution seams, and within the micritic matrix of the host limestone. These sulphide minerals also occur as cements within late stage fractures.

The following diagenetic phases are present in the Waulsortian and Ballysteen Limestones in the Courtbrown area (from oldest to youngest): non-luminescent synsedimentary calcite cements, non-luminescent equant calcite cements, bright luminescent calcite cement, dull luminescent calcite cement, planar dolomite cement and replacement dolomite (regional dolomite), saddle dolomite cement, and fibrous dull luminescent calcite cement filling pressure-shadows around the sulphide minerals.

Homogenisation temperatures for primary fluid inclusions within dull luminescent calcite cements (precipitated penecontemporaneously with base-metal mineralisation) range from 160 to 200 °C, with a mode at 170–180 °C. These values are unlikely to be representative of mineralisation temperatures as the fluid inclusions may have been significantly affected by heating and/or deformation during late burial (maximum paleotemperatures from Ro and CAI data around 310 °C).

The observed paragenetic sequence indicates that mineralisation is completely epigenetic. As the earliest mineralisation is hosted by macro-stylolites, the sequence must have obtained a minimum burial depth of around 800 m prior to the onset of mineralisation. A burial depth of 800 m would correspond to an approximate early Chadian age for the Courtbrown area. Pressure-shadows around sphalerite further indicate that mineralisation preceded the major phase of Variscan deformation. Therefore, the base-metal mineralisation at Courtbrown is epigenetic, and the age of mineralisation is in the range of 350 to 307 Ma.

The late-Permian succession of the Upper-Indus Basin is represented by carbonate dominated Zaluch Group, which consists of Amb, Wargal and Chhidru Formations. These formations accumulated on the southwestern shelf of the Paleo-Tethys Ocean, north of hydrocarbon-producing Permian strata of the Arabian Peninsula. The reservoir properties of mixed clasticcarbonate Chhidru Formation are evaluated based on Petrography, Scanning Electron Microscopy (SEM), Energy Dispersive Xrays-Spectroscopy (EDX) and X-ray Diffraction (XRD) techniques. The diagenetic features, ranging from marine (isopachous fibrous calcite, micrite), through meteoric (blocky calcite-I, neomorphism and dissolution) to burial (poikilotopic cement, blocky calcite-II-III, fractures, fracture-filling and stylolites) are recognized. Major porosity types included fracture and moldic, while inter-and intra-particle porosities also existed. The visual porosity from 1.5-7.14% with an average of 5.15% was recognized. The sandstone facies (CMF-4) had the highest average porosity of 10.7%, while siliciclastic grainstone microfacies (CMF-3) showed average porosity of 5.3%. The siliciclastic mudstone microfacies (CMF-1) and siliciclastic wacke-packestone microfacies (CMF-2) showed the lowest porosity of 4.8% and 5.0%, respectively. Diagenetic processes like cementation, neomorphism, stylolitization and compaction have reduced the primary porosities. However, processes of dissolution and fracturing have produced secondary porosity. On average, the Chhidru Formation in Nammal Gorge (Salt Range) showed promising and at Gula Khel Gorge (Trans-Indus) lowest porosity.

I n t h e L a s t o u r s v i l l e b a s i n , l o c a t e d a t t h e c e n t e r of the Francevillian (~2.2 Ga), the FB unit consits with carbonates i n d o l o m i t i c m a t t e r , o r g a n i c m a t t e r e n r i c h e d b l a c k shales and mudstone dolomites surrounded by tabular cherts[1]. The unit, called "Lastoursville dolomites"[2] is based on fluviodeltaic FA sandstones. They are described as evaporitic dolomites formed [3]. The organic matter abundance observed in these rocks coupled with the recent discoveries of multicellular organisms fossilized in Franceville [4] and Okondja [5] FB formations, imply an abondant biological activity in this paleoproterozoic environment.

This article presents a set of Late Pleistocene marine mollusk radiocarbon (AMS) age estimates of 30-50 14 C kyr BP, whereas a MIS5 age (>75 ka) is indicated by quartz and feldspar OSL dating, biostratigraphy, U-Th dating, and age-depth relationships with sea level. These results indicate that the 14 C dates represent minimum ages. The age discrepancy suggests that the shells are contaminated by younger carbon following shell death. The enigmatic 14 C dates cannot be "solved" by removing part of the shell by stepwise dissolution. SEM analysis of the Late Pleistocene shells within a context of geologically younger (recent/modern, Holocene) and older (Pliocene) shells shows the presence of considerable amounts of an intracrystalline secondary carbonate precipitate. The presence of this precipitate is not visible using XRD since it is of the same (aragonitic) polymorph as the original shell carbonate. The combination of nanospherulitic-shaped carbonate crystals, typical cavities, and the presence of fatty acids leads to the conclusion that the secondary carbonate, and hence the addition of younger carbon, has a bacterial origin. As shell material was studied, this study recommends an assessment of possible bacterial imprints in other materials like bone collagen as well.

After more than forty-five years of hydrocarbon exploration and production, the Cretaceous Chalk Group in the Danish North Sea is still an attractive target. Most of the production is from four-way dip closures in the Danian Ekofisk Formation and the Maastrichtian Tor Formation. On a field-scale their stratigraphy is well understood. The Chalk Group, however, consists of more than these two high-flyers and it is in this remainder of the Chalk where additional exploration targets may be found.
To help find these targets the stratigraphic framework for the Chalk Group has been updated and is being refined. We used chemostratigraphy and detailed SEM petrography of cuttings and core from eight wells and integrated this with a recently established seismic stratigraphic framework. In this framework, which spans a large part of the Danish Central Graben, the eight wells provide a reference section.
Using seismic morphology as context, our observations from cores further confirm that chalk sedimentation was dynamic. Large facies variability including coccolith-debris dominated chalk, lithoclastic chalk and foram-packstones indicate that besides gentle pelagic settling, mass-wasting and strong bottom currents were common. Silica-altered hardgrounds with sponge borings further suggest the existence of current swept areas where marine cementation stabilized the substrate. This variability in depositional facies and early diagenetic alteration affected reservoir and seal properties as is indicated by the variability in poretypes found in different facies.
Geochemistry further refines the stratigraphic framework beyond seismic and biostratigraphic resolution. The carbon isotopic signal appears to be well preserved and can be correlated with published on-shore UK reference sections. Major and minor trace elements provide detail of detrital input of K- and Al rich clays. Si-elemental variations, in lieu of these detrital markers, indicate the importance of silica-diagenesis in the chalk. SEM petrography indicates that this silica is commonly present as sub-micron scale spherical aggregates, which precipitated during or soon after deposition of the chalk.
Based on the integration of multi-scale data we are refining the Chalk stratigraphy. With this framework we are defining new play concepts which will help in unlocking the remaining hydrocarbon potential of the Danish Central Graben and the North Sea Basin.

May, A. (1997a): Verwitterungsbeständigkeit und Verwitterung von Naturbausteinen aus Kalkstein. - Geologie und Paläontologie in Westfalen, vol. 48: p. 3-185, 94 figs., 2 tabs., pl. 1-11; Münster.

Abstract: Weathering durability and weathering process of natural building stones from the Lower Muschelkalk, the Upper Muschelkalk, and the Devonian have been investigated. Various properties of each building stone and its limestone material are measured (microscopy, SEM, porosity, ultrasonic velocity, geochemical methods). Defined microfacies types show clear differences in their weathering durability. The quantities of the cold water absorption, the Schurecht ratio (= ratio cold/boiling water absorption), and the residue insoluble by hydrocloric acid strongly affect the weathering durability. Together with the investigation of thin-sections, these properties enable prognoses about the weathering durability. A diagram of correlation between coldwater absorption and Schurecht ratio is developed, which is able to discriminate more durable and less durable limestones by a boundary line (Fig. 59-60).The limestones are mainly damaged by fissures which harm the unity of the stone. Probably these fissures are mainly based on frost phenomena. Connections between the sedimentary environment and the weathering durability are recognizable: generally limestones of the agitated (shallow) marine are more durable than other limestones.

Kurzfassung: Es wurden die Unterschiede in der Verwitterungsbeständigkeit zwischen verschiedenen Varietäten jeweils eines Kalksteins untersucht. Beprobt wurden Kalksteine des Muschelkalks im Raum Osnabrück-Bielefeld und des Devons im Sauerland in Bauwerken und Aufschlüssen. Eine neue Klassifikation des Verwitterungszustandes von Kalkstein-Mauersteinen wurde entwickelt. Die Oberflächenschäden auf der Außenseite sind nur ± gering und stellen bloß ein "kosmetisches" Problem dar. Die Stärke der Schädigung des inneren Zusammenhaltes des Mauersteins durch Risse ist viel wichtiger, da sie die Sicherheit und Stabilität des Bauwerks gefährdet. Die Untersuchung von Dünnschliffen ermöglichte es, insgesamt 17 Mikrofaziestypen zu definieren und erstmalig Unterschiede in der Verwitterungsbeständigkeit zwischen den verschiedenen Mikrofaziestypen eines Kalksteins zu erkennen. Kalksteine, die in ± turbulentem (und damit ± flachem) Meereswasser abgelagert wurden, sind tendenziell verwitterungsbeständiger als solche aus anderen Ablagerungsräumen. Mit der Auftriebsmethode wurden wichtige Porositätsparameter festgestellt. Freiwillige Wasseraufnahme und Schurecht-Ratio (= Quotient freiwillige Wasseraufnahme / effektive Porosität) beeinflussen die Verwitterungsbeständigkeit sehr stark, wenn ihre Größe zunimmt, nimmt die Verwitterungsbeständigkeit ab. Die Ultraschall-Untersuchungen zeigten, daß in Kalksteinen Spannungen viel weiter geleitet werden als in Sandsteinen und deshalb zu (lang aushaltenden) Rissen führen. Die rasterelektronenmikroskopische Untersuchung erlaubte Aussagen über einzelne Aspekte des Verwitterungsprozesses. Die im salzsäurelöslichen Gesteinsanteil gemessenen Element-Konzentrationen spielen keine Rolle für die Verwitterungsbeständigkeit der Kalksteine.  Die Verwitterungsbeständigkeit der bearbeiteten Kalksteine wird am stärksten von freiwilliger Wasseraufnahme und Schurecht-Ratio beeinflußt. Der Einfluß des Gehaltes an salzsäureunlöslichem Rückstand ist erheblich geringer. Darüber hinaus spielen auch die Merkmale Feinschichtung und Kristallgröße (Mikritl Sparit) eine gewisse Rolle. Die Entwicklung von Stylolithen hat nur nachrangige Bedeutung. Einen sehr großen praktischen Nutzen für Prognosen über die Verwitterungsbeständigkeit verspricht die erstmalig ermittelte Grenzlinie Schurecht-Ratio/freiwillige Wasseraufnahme, die unabhängig vom Probenkollektiv überdurchschnittlich und unterdurchschnittlich verwitterungsbeständige Kalkstein-Mauersteine mit ziemlich großer Schärfe voneinander trennt. Darauf aufbauend wurden leicht durchzuführende Verfahren zur Auswahl besonders verwitterungsbeständiger Kalksteine entwickelt. Im Gegensatz zur vorherrschenden Literaturmeinung werden Kalksteine im wesentlichen durch Risse geschädigt, die wahrscheinlich aufgrund von Frosterscheinungen (bzw. Frost-Tau-Wechsel-Prozessen) entstehen und hauptsächlich durch Frostsprengung vergrößert werden. Da die Schädigung der Gesteinsoberfläche ± gering ist, kann die chemische Verwitterung für Kalksteine nicht wichtig sein. Hierdurch unterscheiden sich Kalksteine in ihrem Verwitterungsverhalten sehr stark von Kalksandsteinen.

Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary and Olenellus biostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to r...

The rift succession of the Araripe Basin can be subdivided into four depositional sequences, bounded by regional unconformities, which record different palaeogeographic and palaeoenvironmental contexts. Sequence I, equivalent to the Brejo Santo Formation, is composed of fluvial sheetflood and floodplain facies association, while Sequence II, correspondent to the lower portion of the Missão Velha Formation, is characterised by braided fluvial channel belt deposits. The fluvial deposits of Sequences I and II show palaeocurrents toward SE. The Sequence III, correspondent to the upper portion of Missão Velha Formation , is composed of fluvial sheetflood deposits, which are overlain by braided fluvial channel deposits displaying a palaeocurrent pattern predominantly toward SW to NW. Sequence IV, equivalent to the Abaiara Formation, is composed of fluvioedeltaicelacustrine strata with polimodal paleocurrent pattern. The type of depositional systems, the palaeocurrent pattern and the comparison with general tectono-stratigraphic rift models led to the identification of different evolutionary stages of the Araripe Basin. Sequences I, II and III represent the record of a larger basin associated to an early rift stage. However, the difference of the fluvial palaeocurrent between sequences II and III marks a regional rearrangement of the drainage system related to tectonic activity that compartmentalised the large endorheic basin, defining more localised drainage basins separated by internal highs. Sequence IV is associated with the renewal of the landscape and implantation of half-graben systems. The high dispersion of palaeocurrents trends indicate that sedimentary influx occurs from different sectors of the half-grabens.

Article: Origin and timing of siderite and calcite concretions in late Palaeogene non- to marginal-marine facies of the Te Kuiti Group, New Zealand
Heather A. Middleton, Campbell S. Nelson
[Hide abstract]
ABSTRACT: The Late Eocene-earliest Miocene Te Kuiti Group represents an overall transgressive sequence of formations ranging upwards from non-marine coal measure facies through marginal-marine low-energy shoreline siliciclastic sediments to fully-marine mixed siliciclastic-carbonate deposits. Concretionary structures are common in the lowest formations of the group, being dominantly sideritic in the non-marine to brackish sediment facies (Waikato Coal Measures and Glen Afton Claystone) and calcitic in the more marine-influenced sediments (Rotowaro Siltstone). The geochemistry of the carbonate cements within these early diagenetic concretions records the change from carbonate precipitation from purely meteoric fluids to precipitation from marine fluids, and a shifting source of carbonate carbon across this transition.Siderite precipitation in the Waikato Coal Measures concretions and hardpans was initiated and often largely completed in the methanogenic zone, within the upper 20 m of the sediment pile over a period possibly lasting 100–300 ka. Precipitation continued at a reduced rate to burial depths of 300 m or more when septarian cracking occurred in some siderite concretions and was healed by calcite vein cements that probably derived carbonate from the oxidation of methane ascending from the maturing coal seams directly below.Siderite precipitation in the concretions and hardpans of the overlying brackish-marine Glen Afton Claystone was completed in the topmost few metres of sediment, possibly a few 10 ka. Stable-isotope values near zero support a marine carbonate carbon source, suggested to be from remobilised shell material as evidenced by the common occurrence of shell casts in the formation and the high degree of Mg and Ca substitution in the siderites.The overlying marginal-marine to low-energy marine Rotowaro Siltstone contains calcite concretions precipitated from pore waters enriched in bicarbonate derived from the sulphate-reduction zone, largely within the upper 8 m of sediment, and possibly growing over a few 100 ka. Concretion development continued at a reduced rate to burial depths of several tens of metres and in some cases septarian cracks developed during the later stages of concretion growth. The precipitation of septarian vein calcites with more depleted δ18O values and more enriched δ13C signatures than central concretions cements, may be due to increasing burial temperatures, and the progressive introduction of carbonate sourced from shell dissolution.

Thorium-232-lead-208 and uranium-238-lead-206 radiometric ages for ore-stage calcite show that Mississippi Valley-type (MVT) ore deposits can form in distinct tectonic settings. An age of 251 ± 11 million years for the Jumbo Mine in Kansas, United States, is in agreement with other ages for MVT deposits in the midcontinent of North America. The similarity of ages of these deposits supports the concept that they formed in response to fluid flow during the late Paleozoic Alleghenian-Ouachita orogeny. An age of 351 ± 15 million years for Twelve Mile Bore and Bloodwood-Kapok deposits in Australia indicates that these MVT ores were deposited in a rifting environment.

Twenty-nine sections were measured along a 135 km distance, in the Cyrenaican Miocene of Ar-Rajmah Group carbonate rocks, northeast Libya. Four sections were sampled every 0.5 m for sequence stratigraphy, stable isotope (δ18O and δ13C) chemostratigraphy, and diagenesis. Petrographic study helped to identify facies based on texture, grain types, mud content, cements, porosity types and amount, dolomitization, dedolomitization, silicification, and recrystallization. Combined sequence stratigraphy, chemostratigraphy, and petrography indicates two supersequences separated by a sequence boundary and two different diagenetic patterns. The Miocene Ar-Rajmah Group carbonate rocks record two 2nd-order supersequences with a 97 m maximum thickness; six 3rd-order sequences, and 10 parasequences. The Ar-Rajmah Group depositional facies are grouped into peritidal facies, ramp crest facies, and subtidal facies. The peritidal facies includes evaporites, microbialites, pelletal wackestone/packstone,...

Lime plaster and mortar are pyrotechnological materials that have been employed in constructions since prehistoric times. They may nucleate as calcite and/or aragonite under different environmental settings. In nature, aragonite and calcite form through biogenic and geogenic processes that lead to different degrees of atomic order. The latter is a result of defects in the crystal lattice, which affect the properties of crystals, including their interaction with infrared light. Using Fourier transform infrared spectrometry (FTIR) with the KBr pellet method, it is possible to exploit these differences and assess the degree of atomic order of aragonite and calcite crystals and thus their mechanisms of formation. Here we use FTIR to characterize the degree of short-range atomic order of a pyrogenic form of aragonite recently observed in experimental and archaeological lime binders. We show that pyrogenic aragonite has a unique signature that allows its identification in archaeological sediments and lime binders of unknown origin. Based on these results, we developed a new FTIR-based method to assess the integrity and degree of preservation of aragonite and calcite when they occur together in the same material. This method allowed a better assessment of the diagenetic history of an archaeological plaster and finds application in the characterization of present-day conservation materials, such as lime plaster and mortar, where different polymorphs may nucleate and undergo recrystallization processes that can alter the mechanical properties of binders.

The pivotal idea of this study is to unravel the processes that control heterogeneity in the attributes of the pore space in carbonate rocks (i.e. stiffness, connectivity and tortuosity), and, in turn, in the transport and elastic properties. We use starting rocks of variable fabric (i.e. a deposi-tional-dependent microstructure) to induce a specific process (e.g. chemical dissolution under stress) and then observe the development of the microstructure, permeability, porosity and velocity due to the induced chemomechanical processes. We find that the changes in the two end members of the analysed rock types (mudstones and packstones) can lead to two different evolutionary trends of permeability and velocity, depending on the effectiveness of dissolution with respect to compaction. The balance between the two depends on: (a) the fraction of the carbonate phases characterized by large surface area; and (b) the pore stiffness of the rock. Packstones are characterized by low pore stiffness and compact significantly upon dissolution. This behaviour leads to a decrease in velocity because of a reduction in the stiffness at the grain contacts and a slight increase in permeability. The latter is curbed by the ongoing compaction. Mudstones are characterized by higher pore stiffness, experiencing minimal or negligible compaction. This behaviour leads to a slight change in porosity and velocity. However, large permeability changes are observed, related to enhanced connectivity or decreased tortuosity of the pathways.

Beachrocks are coastal sedimentary formations resulting from a relative rapid cementation of beach sediments
by the precipitation of carbonate cements. These lithified structures are not usually observed at
temperate settings. The present work is focused on the occurrence of a significant intertidal cementation
in sand-gravel beaches formed among 43 ◦N latitude coastline, close to the Nerbioi-Ibaizabal
estuary (Bilbao, Bay of Biscay, North of Spain). Raman micro-spectroscopy combined with SEM-EDX
analyses and petrographic descriptions have been applied for the determination of the cement generations
and the cemented materials compositions of the beachrock outcrops. In general terms, the cements
described were: Cement Generation 1 (CG 1, aragonite, high-magnesium calcite and silicate mixtures),
Cement Generation 2 (CG 2, aragonite) and Cement Generation 3 (CG 3, mixtures of CaCO3 polymorphs
and iron oxides). The rest of the interstitial porosity of the rocks appeared either empty or filled with
heterogeneous cemented mixtures of previously reworked compounds. The mineralogy, the regular distribution
and the isopachous character of the carbonate cements together with the accurate cementation
at advanced seaward bands propose a possible marine-phreatic context for the beachrock formation.
However, the impure cements and the materials covering the interstitial porosity seem to be the result
of both, the weathering actions consequences and the surface alterations of specific grains. Moreover,
the presence of modern cemented materials (e.g. slag, bricks and pebbles) suggest a recent formation of
the phenomenon.

Carbonate-sulphide cement stratigraphic relationships in the host rock and ore have been used to constrain the age of mineralisation at the Silvermines zinc-lead-barium deposit. The base-metal sulphides post-date planar dolomite and replace stylolites. Furthermore, the pre-mineralisation planar dolomites also replace stylolites. These and other diagenetic observations indicate that the base-metal sulphides formed at burial depths greater than 800 m, but probably predate the Variscan deformation (since pressure shadows overgrow base metal sulphides). This indicates that the sulphides are of epigenetic origin, constraining the age of mineralisation to between the late Chadian (≈347 Ma) and the late Westphalian (≈307 Ma). However, the most likely age for mineralisation, (based on widespread macro-stylolite development) is Asbian (≈339 Ma) or younger. No evidence of synsedimentary sulphides (in the form of hydrothermal chimneys, vent faunas, or sulphides intergrown with marine cements) was observed at Silvermines. Mineralised breccias (black matrix breccias), late-stage internal sediments, and dissolution zones within the carbonate cements all appear to be produced by hydrothermal karsting that occurred during the mineralisation process. Fluid inclusion homogenisation temperatures for ore-stage calcites (up to 300 °C) approach the peak temperature estimates derived from regional maturation parameters (270 to 310 °C from conodont alteration indices and vitrinite reflectance). This suggests that homogenisation temperatures represent maximum heating temperatures (probably during Variscan time) rather than mineralisation temperatures.