Key Outcrops Research Articles

Outcrop-to-Subsurface Stratigraphic Correlations of the Upper Desmoinesian and Lower Missourian Stages (Pennsylvanian) in Eastern Kansas

Pennsylvanian (Upper Carboniferous) strata in eastern Kansas have been investigated for more than 120 years. We have determined, however, that discrepancies arising from emphases on either outcrop observations or subsurface data, as well as the loss of some key outcrops since their first descriptions, created major problems in prior stratigraphic interpretations. One particularly problematic stratigraphic interval contains the boundaries between units in the Marmaton (Desmoinesian) and Pleasanton (Missourian) groups, which encompasses the global Moscovian-Kasimovian stage boundary. We use 246 petrophysical well logs, especially gamma ray and neutron logs, to provide greater stratigraphic control among 22 previously described type outcrops, neostratotypes, and principal reference localities. Nine new stratigraphic cross sections resulting from our analysis of these data permit innovative interpretations of ancient facies belts as well as a reassessment of the geometry and structural history of the Cherokee–Forest City Basin. We make three recommendations regarding group boundaries on the basis of our analysis: 1) The boundary between the Cherokee and Marmaton groups should be placed at the base of the Excello Shale, thereby including the unit within the Marmaton Group. An unnamed limestone underlying the Excello Shale and observed in some areas should ideally be included within the Marmaton, but this unit will require further study. 2) The boundary between the Marmaton and Pleasanton groups should be placed at the base of the Nuyaka Creek Shale Member, as opposed to the standing placement at the base of the Hepler Sandstone. 3) The boundary between the Pleasanton and Kansas City groups should be maintained at the base of the Critzer Limestone Member of the Hertha Limestone. Additionally, we advocate the following changes to stratigraphic nomenclature in Kansas: 1) the Fort Scott Limestone should be revised to include the Excello Shale; 2) members of the Lenapah Limestone (the Idenbro Limestone Member, Perry Farm Shale Member, and Norfleet Limestone Member) should be abandoned because of prior miscorrelations; 3) the stratigraphic interval between the Lenapah Limestone and the Nuyaka Creek Shale Member correlates to either the Holdenville Shale or Memorial Shale—therefore, we leave this interval unnamed; and 4) with our proposal to place the lower boundary of the Pleasanton Group at the base of the Nuyaka Creek Shale Member, the lower boundary of the Lost Branch Formation should likewise be moved to that same level. The stratigraphic contexts of the Seminole, Tacket, and Shale Hill formations remain to be clarified by future work.

Facies Analysis and Sequence Stratigraphy of Plio-Pleistocene Fan Delta Deposits in the East Arm Sulawesi, a case study of Biak Formation, Luwuk, Banggai

Abstract Fan delta deposits were found widespread in the east arm of Sulawesi as the area experienced tectonic uplift during Plio-Pleistocene continental collision, known as Bongka Formation in the western part and Biak Formation in the eastern part. One of key outcrops for Biak Formation was observed in Biak Village, North Luwuk District, Banggai Regency, thus served as the lithotype location for the Biak Formation. The outcrop was a roadcut and had a 50 m long and 25 m high. In general it shows a coarse-grained heterolithic inclined strata dipping southward and overlain by horizontal strata of similar facies. Its sequence stratigraphy was analyzed by examine its facies, facies association, petrography, and paleontology, along a 1:100 scaled measured section. Six lithofacies were identified, namely conglomeratic coralline limestone, conglomeratic coralline limestone, parallel bedding – gradation conglomerate-sandstone, gravely sandstone, conglomerate-sandstone – conglomeratic corraline limestone and gradation conglomerate-sandstone with horizontal bedding. Their lithofacies deposited during Late Pliocene in a transition – inner neritic environment. Their facies association made several depositional system tracts, showing a complete cycle of Highstand System Tract (HST), Sequence Boundary/Correlative Conformity (SB/CC), Lowstand System Tract (LST), Transgressive System Tract (TST), Transgressive Surface (TS) later capped by younger HST and LST. Result of this study suggesting repetitive cyclic depositiona tracts dictated by sea-level eustacy and tectonic uplift. This location served as an ideal outcrop as a textbook example to study sequence stratigraphy in an outcrop scale.

An integrated stratigraphic framework for the uppermost jurassic to Lower Cretaceous interval of the Essaouira-Agadir Basin (Moroccan Atlantic margin) based on ammonites, calcareous nannofossils and calpionellids

The extensive exposures of Mesozoic rocks along the Atlantic Moroccan margin can offer the best and the most continuous record of Mesozoic sediments and Upper Jurassic – Lower Cretaceous deposits along the Atlantic margin. This study reports the results of high resolution sampling and sedimentary logging of key outcrops to allow for ammonite, calpionellid and nannofossil biostratigraphy, in order to build a new integrated biostratigraphic chart for the uppermost Tithonian to the lowermost upper Barremian. This has been correlated to the offshore record (DSDP Sites 370/416A), which has also been redated using newly described calcareous nannofossil assemblages that confirm a thick and previously undescribed upper Tithonian through Berriasian succession.Calpionellid assemblages, although sparse, show affinities to the Mediterranean Tethys assemblages. Ammonites also show affinities to the Mediterranean Tethys taxa, but the identification of two new species points to periods of endemism during the lower Hauterivian. Calcareous nannofossils show varied affinities; to the North Atlantic Tethys and Mediterranean Tethyan Realms, the Cental Atlantic and short, but distinct cold-water Boreal Realm exchanges during the Berriasian, lower Valanginian and upper Hauterivian which have necessitated the development of a local EAB nannofossil zonation. The faunal affinities, local morphological variations and periods of faunal endemism are attributed to relative sea level changes which influenced the connection between the Essaouira-Agadir Basin (EAB), Central Atlantic and the western Tethyan Realm.A major sedimentary hiatus in the middle part of the Berriasian is recognised in the studied sections based on the biostratigraphy. This is interpreted to record a middle Berriasian unconformity that can be correlated both regionally and globally, due to an important period of tectonic activity associated with the break-up stage of the Atlantic.This new biostratigraphy builds on recent published studies that have focused on a high resolution integrated stratigraphic framework for the upper Barremian - lower Albian interval (Lower Cretaceous) in the Essaouira-Agadir Basin of Morocco.

Remote Detection of Geothermal Alteration Using Airborne Light Detection and Ranging Return Intensity

The remote detection of hydrothermally altered grounds in geothermal exploration demands datasets capable of reliably detecting key outcrops with fine spatial resolution. While optical thermal or radar-based datasets have resolution limitations, airborne LiDAR offers point-based detection through its LiDAR return intensity (LRI) values, serving as a proxy for surface reflectivity. Despite this potential, few studies have explored LRI value variations in the context of hydrothermal alteration and their utility in distinguishing altered from unaltered rocks. Although the link between alteration degree and LRI values has been established under laboratory conditions, this relationship has yet to be demonstrated in airborne data. This study investigates the applicability of laboratory results to airborne LRI data for alteration detection. Utilising LRI data from an airborne LiDAR point cloud (wavelength 1064 nm, density 12 points per square metre) acquired over a prospective geothermal area in Bajawa, Indonesia, where rock sampling for a related laboratory study took place, we compare the airborne LRI values within each ground sampling area of a 3 m radius (due to hand-held GPS uncertainty) with laboratory LRI values of corresponding rock samples. Our findings reveal distinguishable differences between strongly altered and unaltered samples, with LRI discrepancies of approximately ~28 for airborne data and ~12 for laboratory data. Furthermore, the relative trends of airborne and laboratory-based LRI data concerning alteration degree exhibit striking similarity. These consistent results for alteration degree in laboratory and airborne data mark a significant step towards LRI-based alteration mapping from airborne platforms.

Mush Architecture and Processes in the Reservoirs of a Supereruption-Scale Magma System, Permian Ora Ignimbrite (Northern Italy)

Abstract The Ora Ignimbrite (~275 Ma) is a crystal-rich (~40%), heterogeneous, supereruption-sized (~1300 km3) rhyolite in northern Italy and the final eruptive product of the Athesian Volcanic Group (289–274 Ma), the largest Permian volcanic district in Europe. Two key outcrops, an intracaldera vitrophyre and an outflow vitrophyre, contain well-preserved, glass-bearing juvenile material. We investigate at what scale heterogeneities existed in the Ora magmatic system by studying the geochemical and petrological characteristics of crystal-rich (20–50%) and crystal-poor (<20%) fiamme from the Ora vitrophyres, allowing us to reconstruct critical aspects of Ora's magmatic architecture and pre-eruptive history and granting us further insight into the storage and dynamic processes that occur in large, crystal-rich, silicic systems. Textural analysis of fiamme reveals four types: the intracaldera vitrophyre has very coarse-grained crystal-rich (VCCR) and fine-grained crystal-poor (I-FCP) fiamme, while the outflow vitrophyre has coarse-grained crystal-rich (CCR) and fine-grained crystal-poor (O-FCP) fiamme. The diversity of crystal-poor (I-FCP & O-FCP) fiamme glass trace-element compositions suggests that multiple small crystal-poor magma bodies were dispersed throughout the Ora magmatic system. Compositionally and texturally distinct glass types in single O-FCP fiamme preserve evidence of variable degrees of magma mixing and record different mingling to eruption timescales, revealing that the Ora magmatic system experienced multiple silicic recharge events. In the crystal-rich (VCCR & CCR) fiamme, high crystal contents (VCCR: 40–50%; CCR: 20–40%), large crystals (max grain size: VCCR: 4–10 mm; CCR: 3–4 mm), and interlocking growth textures suggest that these fiamme contain parcels of disaggregated magma mush. High-silica rhyolite glass compositions (77.2–78.3 wt.% SiO2) and extremely depleted Sr (VCCR: <20; CCR: <5 ppm) and Ba (VCCR: <70; CCR: <20 ppm) glass trace-element concentrations indicate that the crystal-rich fiamme glasses represent highly fractionated melts. Crystal-rich fiamme glass trace-element compositions also form discrete, tightly clustered populations, suggesting that multiple crystal-rich, melt-dominated magma bodies existed prior to eruption. We propose that the coexistence of large-scale heterogeneity (e.g. deposit-scale and outcrop-scale) with small-scale homogeneity observed in crystal-rich fiamme is resolved by a model in which at least two separate magma reservoirs, each containing multiple melt-dominant magma bodies, erupted to form the Ora Ignimbrite.

Applying integrated Triassic biostratigraphy in Timor-Leste to unlock an under-sampled Gondwanan sector of the Tethys puzzle

The contribution to Tethyan and global Triassic studies from the Australian sector of southeastern Tethys is limited relative to that from the Himalayan sector. Whilst many of the Triassic successions from the Australian sector are located offshore, one succession is exposed on the island of Timor. This marine succession, dismembered during collision between the Australian continent and the volcanic Banda Arc, has been investigated for over 100 years but has also made limited modern contributions to Tethyan and global Triassic studies. To address this a new integrated Triassic biostratigraphic microfossil database (conodonts, palynomorphs and radiolarians) from Timor-Leste is presented here that compliments published foraminiferal data. This integrated data set 1) supports application in Timor of the endemic palynomorph zonal scheme from the North West Shelf of Australia whilst providing additional ties for this to the Geological Time Scale (GTS), 2) provides paleobiogeographic support for accumulation of the Timor-Leste Triassic succession within a southeast Tethyan Gondwanan basin and informs discussions about Tethyan paleobiogeography, 3) calibrates over 300 outcrops to the GTS enabling an improved reconstruction of the dismembered succession that will facilitate enhanced regional and local paleogeographic and tectonostratigraphic assessments, and 4) provides independent GTS calibration for published basinal foraminiferal assemblages which will assist understanding the biostratigraphic utility of these assemblages. This database identifies key outcrops, such as the first outcropping Permian-Triassic Boundary section from this sector of southeastern Tethys, that will facilitate targeted studies addressing a range of Tethyan and global Triassic issues unlocking insights from an under-sampled Gondwanan sector of Tethys.

KOMATIITE LAVAS FROM THE QUEBRA OSSO GROUP (RIO DAS VELHAS GREENSTONE BELT, SOUTHEAST BRAZIL): A FIELD GUIDE TO AN ARCHEAN FLOW FIELD

The Quebra Osso Group encompasses one of the best preserved Archean komatiite flows in the Quadrilátero Ferrífero region, southern São Francisco craton (Brazil). It is commonly associated with the base of the Rio das Velhas greenstone belt within the Santa Bárbara tectonostratigraphic block. The Quebra Osso rocks are well exposed along the valley of the homonymous river, near the Catas Altas city (Minas Gerais state), and in inactive serpentine quarries. In this field guide, we provide the descriptions of the key outcrops in this area, including a variety of komatiite flows, sedimentary rocks and pyroclastic rocks. Despite the pervasive alteration of primary mineral assemblages due to greenschist to amphibolite facies metamorphism, the ultramafic rocks exhibit diverse igneous textures and structures. Volcanic textures are recognizable due to the morphology of the original igneous olivine and pyroxene, which underwent pseudomorphosis by hydrous minerals – serpentine and chlorite. These features include distinctive spinifex and cumulate textures that provide clues of the conditions operating during emplacement and crystallization of the ultrabasic liquids. The predominance of thick-packages of massive flows suggests channelized lava flows, with subordinate thin marginal layered (spinifex-textured), pillowed, brecciated and pyroclastic flows. Volcanic breccias, pillow lavas and chemical sedimentary rocks indicate that these rocks erupted underwater. These multiple volcanic products characterize a unique komatiite flow field and their remarkable preservation distinguishes the Quebra Osso Group from the other ultramafic associations within the São Francisco Craton.

Facies analysis and depositional model for the Oxfordian Hanifa Formation, Central Saudi Arabia

The Jurassic was a time for major global changes in climate, tectonics, and oceanography, reflected in the southern Neo-Tethys Ocean by a distinct transition from carbonate-poor to carbonate-dominated sedimentation. To better constrain the effect of this turning point in the Late Jurassic, key outcrops of Oxfordian deposits of the Arabian Plate were investigated through detailed sedimentologic analysis. High-resolution (centimeter-scale) description and analysis of eight outcropping sections with a cumulative thickness of 461 m through the Oxfordian Hanifa Formation along a N–S 535 km-long transect in central Saudi Arabia are used to develop a comprehensive conceptual depositional evolution through time. Nine sedimentary lithofacies are interpreted and grouped into four facies associations. These associations include: I) outer-ramp association (FA1), II) mid-ramp association (FA2), III) inner-ramp grainy-facies association (FA3), and VI) inner-ramp reefal association (FA4). The lithofacies succession distinguishes two depositional phases, a middle Oxfordian homoclinal ramp (Phase 1) that corresponds to the Hawtah Member, and a late Oxfordian reef-bearing carbonate ramp (Phase 2) that corresponds to the Ulayyah Member. After being restricted to the high latitudes in the northern Neo-Tethys during early and middle Oxfordian ages, the carbonate ramp evolution within the Hanifa Formation reflects the expansion of scleractinian coral reefs over the southern Neo-Tethys passive margin in the late Oxfordian. However, the distribution of the corals in the Arabian Plate is mainly controlled by water salinity and siliciclastic input; they are absent northward due to hypersalinity and southward due to siliciclastic input. Furthermore, the differential subsidence and the resulting uneven topography, in addition to the eustatic sea level variation during the Oxfordian age, controls the distribution of different depositional styles over the Arabian Plate (homoclinal ramp, distally-steepened ramp, rimed shelf, and intrashelf basin).

A field guide to the excursion in the Maures Massif (southern France): a complete transect of the Southern European Variscan belt

In this guide key outcrops of the Maures Massif, the southernmost part of the Variscan belt in France, are described. Here the features acquired during the fundamental steps of the evolution of the southern European Variscan belt can be recognised. The field trip develops along a W to E transect, perpendicular to the main architecture of the belt. It is organised in eight stops that can be easily reached by car or by walking. The excursion can be completed in one day, but to better enjoy these spectacular outcrops, two days are suggested. The stops show significative outcrops of the low-grade rocks of the External Zone up to the high-grade migmatite of the Internal Zone. Particular focus is given on the tectonic contact between the Internal and External zones of the belt marked by a km-scale transpressional shear zone, known as the Cavalaire Fault, whose structural, lithological, metamorphic and geochronological aspects are described in detail. This structure is a branch of a crustal-scale system of late Carboniferous shear zones known at the regional-scale as the East Variscan Shear Zone. The several branches were interconnected and all recorded a common evolution characterised by transpressional deformation starting from ~330 My.

Portable XRF investigation of Stonehenge Stone 62 and potential source dolerite outcrops in the Mynydd Preseli, west Wales

The doleritic bluestone monoliths at Stonehenge have long been known to have been sourced from the Mynydd Preseli area in west Wales, some 225 km away. On geochemical grounds, based on a range of major and trace elements determined by laboratory-based X-ray fluorescence spectrometry, they have been divided into three groups (Groups 1–3). Subsequently, rare earth element data obtained by solution nebulization ICP-MS showed Group 2 Stone 45 to have been sourced from Cerrigmarchogion with Group 2 Stone 62 showing similarities to the outcrops of Carn Ddafad-las and Garn Ddu Fach. In order to test this possible link, portable XRF (pXRF) analyses were obtained in situ from Stone 62 at Stonehenge and from key outcrops in the Preseli.To obtain reliable results from heterogeneous coarse-grained igneous rocks using pXRF to enable comparisons between orthostats and possible sources, a robust analytical strategy was developed. For outcrops this involved a series of horizontal traverses through individual outcrops comprising 10 to 15 analyses a few centimetres apart, giving 60–175 independent analyses per outcrop. This gives a large, analysed surface area per outcrop providing representative data and also has potential to show any vertical variation in source outcrops. Analyses were taken from similarly weathered surfaces on orthostats and outcrops to minimise compositional changes from surface weathering, and a minimum of 20 analyses were taken from orthostats at various locations across the stone. This approach provides a set of well-determined elements which can reliably be used for provenance studies (including K, Fe, Mn, Zn, Rb, Sr, Zr, Nb, Ba). Nickel, Ti and V are affected slightly more by weathering but still prove useful in comparisons, but Cr, used in earlier studies as a compositional discriminant with Ni, here has poor accuracy by pXRF and is not used.The pXRF analyses show that Stone 62 sits within the same ‘compositional space’ (for multiple element concentrations and ranges) as analyses from Carn Ddafad-las and Garn Ddu Fach, two outcrops of the same intrusion which differ from all other analysed outcrops. More specifically, analyses from Stone 62 and Garn Ddu Fach overlap, these forming a subset of the analyses from Carn Ddafad-las, which shows a more extensive range of those same elements. On this basis it is suggested that Garn Ddu Fach is the likely source of Stonehenge non-spotted dolerite Stone 62, a suggestion supported by indistinguishable petrographic characteristics between Stone 62 and dolerite sample PGDF24 from Garn Ddu Fach.

Lithostratigraphy and structure of the Macael marbles (Betic zone, Spain)

A complex stack of tectonic imbricates is mapped and studied in the Nevado-Filábride Complex of the Macael-Cóbdar area of the Sierra de los Filabres. The lithostratigraphy and geological structure are unravelled, documenting key outcrops in the heavily quarried area that is famous for its pure white marble. Four principal successive stages of deformation are recognized, based on careful field work. Initial SW-verging folding and thrusting was followed by extensional, top-to-the-NW shearing. Late N-verging folding and thrusting is also prominent. The resulting lithostratigraphic and tectonic subdivision is compared with some of the previous investigations in the area, which span over 6 decades. The findings assert the importance of using detailed local field data and the difficulty to apply a simple stratigraphic or tectonic model for this part of the Betic Zone.

Geology aspects, sedimentation environments and oil-and-gas bearing capacity of Vendian and Cambrian deposits of Lena-Tunguska basin

At present time several dozen hydrocarbon fields are known in the Vendian-Cambrian complex of the Lena-Tunguska basin, which clearly does not exhaust its potential. The significant stratigraphic interval of the complex, its thickness (up to 3000 m), favorable properties laid down in sedimentogenesis, namely the presence of source, reservoir and seal deposits, allow us to hope for the discovery of new oil and gas deposits. Sedimentological studies of the Vendian-Cambrian complex, carried out using a network of key lithological sections and outcrops, made it possible to create a series of schematic maps of sedimentation environments on a scale of 1:5000000 for six time intervals (Nepa, Tira, Danilovo, Tommotian-Early Atdabanian, Botomian-Amgaian and Late Cambrian). The evolution of sedimentation of the Vendian-Cambrian complex is considered, as well as an assessment of its oil and gas properties, which are primarily associated with various sedimentation environments.

THE SHOREFACE - FAIRWEATHER WAVE BASE ENVIRONMENT OF THE MIDMIOCENE SANDSTONE IN THE CENTRAL PART OF THE MADURA ISLAND

As mentioned in the previous paper (Endharto, 2005) this paper is part of the series of the depositional model of the Ngrayong Sandstone, which takes part especially in the central part of the Madura Island. This study also examines physical evidence of the best exposure of the study area. The central part is located between 07 01' 18" S - 113 32' 56" E and 07 04' 55" S- 113 36' 54" E, covering the area of Tanjung - Pasean to the north and Mentok - Kertengeneh - Sentol to the south. (Figure 1). The Geological work was carried out during June - July 2005, where the particular attention was concentrated within the central region of the island. There are 3 major key outcrop areas were studied and assigned for the depositional setting of this area (i.e., Tanjung toward Pasean River, Mentok - Kertengeneh Oil Field and Sentol Daya sections). This worked has attempted to sort it out both vertical and horizontal sections with applying the stratigraphic measuring sections (outcrop/surface logs), horizontal distance using passing compass, supported by petrography and paleontology analysis, and trying to look at the internal sedimentological structures to get into broadly image of the depositional system within this area.

Metaconglomerate in the Pinerolo Unit (Dora Maira Massif, Western Alps): a key outcrop for Alpine geology and training structural geologists

Metaconglomerate in the Pinerolo Unit (Dora Maira Massif, Western Alps): a key outcrop for Alpine geology and training structural geologists

Revision of thelodonts, acanthodians, conodonts, and the depositional environments in the Burgen outlier (Ludlow, Silurian) of Gotland, Sweden

ABSTRACT Ludfordian strata exposed in the Burgen outlier in eastern Gotland, Sweden record a time of initial faunal recovery after a global environmental perturbation manifested in the Ludfordian Carbon Isotope Excursion (LCIE). Vertebrate microfossils in the collection of the late Lennart Jeppsson, hosted at the Swedish Museum of Natural History, hold the key to reconstruct the dynamics of faunal immigration and diversification during the decline of the LCIE, but the stratigraphic relationships of the strata have been debated. Historically, they had been placed in the Burgsvik Formation, which included the Burgsvik Sandstone and the Burgsvik Oolite members. We revise the fauna in the Jeppsson collection and characterize key outcrops of Burgen and Kapellet. The former Burgsvik Oolite Member is here revised as the Burgen Oolite Formation. In the Burgen outlier, back-shoal facies of this formation are represented and their position in the Ozarkodina snajdri Biozone is supported. The shallow-marine position compared to the coeval strata in southern Gotland is reflected in the higher δ13Ccarb values, reaching +9.2‰. The back-shoal succession includes high-diversity metazoan reefs, which indicate a complete recovery of the carbonate producers as the LCIE declined. The impoverishment of conodonts associated with the LCIE in southern Gotland might be a product of facies preferences, as the diverse environments in the outlier yielded all 21 species known from the formation. Fish diversity also returned to normal levels as the LCIE declined, with a minimum of nine species. In line with previous reports, thelodont scales appear to dominate samples from the Burgen outlier.

Widening of Hydrous Shear Zones During Incipient Eclogitization of Metastable Dry and Rigid Lower Crust—Holsnøy, Western Norway

AbstractThe partially eclogitized crustal rocks on Holsnøy in the Bergen Arcs, Norway, indicate that eclogitization is caused by the interplay of brittle and ductile deformation promoted by fluid infiltration and fluid‐rock interaction. Eclogitization generated an interconnected network of millimeter‐to‐kilometer‐wide hydrous eclogite‐facies shear zones, which presumably caused transient weakening of the mechanically strong lower crust. To decipher the development of those networks, we combine detailed lithological and structural mapping of two key outcrops with numerical modeling. Both outcrops are largely composed of preserved granulite with minor eclogite‐facies shear zones, thus representing the beginning phases of eclogitization and ductile deformation. We suggest that deformation promoted fluid‐rock interaction and eclogitization, which gradually consumed the granulite until fluid‐induced reactions were no longer significant. The shear zones widen during progressive deformation. To identify the key parameters that impact shear zone widening, we generated scale‐independent numerical models, which focus on different processes affecting the shear zone evolution: (i) rotation of the shear zones caused by finite deformation, (ii) mechanical weakening due to a limited amount of available fluid, and (iii) weakening and further hydration of the shear zones as a result of continuous and unlimited fluid supply. A continuous diffusion‐type fluid infiltration, with an effective diffusion coefficient around , coupled with deformation is prone to develop structures similar to the ones mapped in field. Our results suggest that the shear zones formed under a continuous fluid supply, causing shear zone widening, rather than localization, during progressive deformation.

Fossil vs. Active Geothermal Systems: A Field and Laboratory Method to Disclose the Relationships between Geothermal Fluid Flow and Geological Structures at Depth

Comparison between fossil and analogue active geothermal systems permit to obtain key-parameters to define a conceptual model of the area under exploration. The approach is based on structural, kinematic, and fluid inclusions analyses. The fossil system is investigated to describe the distribution of the hydrothermal mineralization as witness of the fluid flow through geological structures and bodies, at depth. Structural and kinematic data (to define the preferential direction of fluid flow) are collected in structural stations and by scan lines and scan boxes on key outcrops. Distribution, length, width of fractures, and hydrothermal veins bring to evaluate permeability in the fossil system and, by analogy, in the deep roots of the active system. Fluid inclusions analysis shed light on density, viscosity, and temperature of the paleo-fluids. Data integration provides the hydraulic conductivity. In active geothermal systems, fieldwork is addressed to paleo-stress analysis with data from recent faults (<2 Ma), to compare with local focal mechanisms. By this, indications on the present fluid pathways are given. The main advantage resides in obtaining parameters normally got after drilling, thus contributing to strengthen the strategy of exploration, de-risking unsuccessful boreholes.

Evolution of deformation bands, insights from structural diagenesis

The vast majority of deformation bands (Dbs) studies focus on structural analysis only and neglect chemical/diagenetic effects. Here we report the structural diagenesis of Dbs occurring in the Tucano Basin (NE-Brazil). Although the occurrence of these structures in this basin has been well registered in literature, none of the researches related to them addressed the linking between structural and diagenetic processes. To fill this gap, we performed a multiscale (macro, meso and microscopic) analysis. Some key outcrops were selected and sampled for microscopic studies in order to investigate the deformational mechanisms active during Dbs formation and the coeval diagenetic processes. The diagenetic analysis reveals that the sandstones attained a minimum burial depth around 3 km and a temperature ≥100 °C, which means they reached the deep mesodiagenesis field. The nucleation of Dbs in these rocks started in the transition between the late eodiagenesis and initial (shallow) mesodiagenesis. In such conditions, the active deformational regime was the hydroductile flow, expressed by the dragging (bending) of rocks’ bedding (S0) by the Dbs. In the syn-lithification stage, transitional bands (hydroductile-cataclastic) developed exhibiting SC-type patterns and sigmoidal fractures. During deep mesodiagenesis, the cataclastic bands were formed by the cataclastic flow. These types of Dbs developed after mesodiagenetic quartz overgrowth and before (or synchronically) to chemical dissolution processes. The formation of tectonic matrix at this stage, along with the siliceous/ferruginous cementations, enhanced the strength of these structures.

Tide-dominated deltas responding to high-frequency sea-level changes, Pre-Messinian Rifian Corridor, Morocco

ABSTRACTThe Rifian Corridor was an ancient sea strait that connected the Mediterranean Sea with the Atlantic Ocean during the Miocene. Key outcrop exposures of this corridor's sedimentary fill are exposed at the Ben Allou, El Adergha, and Driouate localities, in the Fez–Meknes region, Morocco. These display cyclic successions that formed immediately before the disappearance of the Rifian Corridor, and the associated isolation and desiccation of the Mediterranean Sea. Sedimentary cycles at Ben Allou consist of: facies 1, Organic-matter-bearing blue claystones; facies 2, gray marlstones intercalated with turbidites; and facies 3, yellow-brown, coarse-grained calcarenites. Based on their coarse grain size, presence of reactivation surfaces, bidirectional current structures, and mud drapes as well as microfossil, macrofossil and trace fossil assemblages, we interpret the calcarenites (facies 3) as prograding, strait-adjacent tide-dominated deltas transitioning from large subtidal compound dunes to intertidal sand sheets that are composed mostly of authigenic carbonate sediment. The two fine-grained facies were deposited in deeper prodelta (facies 2) and shelfal (facies 1) environments, as shown by our combined sedimentological and paleontological evidence. Cross-sectional channel geometries provide a means for reconstructing the delta's paleo–tidal range, suggesting that it was macrotidal, and likely amplified by the paleogeometry of the Southern Rifian Corridor, to at least 4.2 m. The cyclic succession of corridor fill exposed here likely is the result of three, roughly 70 m fluctuations of eustatic rise and subsequent fall, possibly linked to ∼ 100,000-year glacial–interglacial climate fluctuations. Broadly similar, contemporaneous sedimentary successions from the outcrop at El Adergha, 40 km east of Ben Allou, show that these sea-level variations affected a wide range of the Corridor, while rocks at the locality of Driouate, 9 km south of Ben Allou, show evidence for lagoonal environments on the landward side of the corridor, which were subject to periodic marine regressions and floodings. These results are reinterpretations of previous work on these sediments, with implications for depositional processes in the Rifian Corridor, Miocene paleoclimate, and the Messinian salinity crisis.

Guía de campo post-congreso, 21-24 de Octubre de 2019: Ediacárico y Terreneuviense en los alrededores del Geoparque de la UNESCO Villuercas-Ibores-Jara

Una de las esquinas de los mapas geográficos que enlazan las provincias de Badajoz, Cáceres y Toledo contiene unos afloramientos claves para entender el tránsito Ediacárico-Cámbrico de la Zona Centroibérica. En los núcleos del Anticlinorio Extremeño y de los Anticlinales de Ibor y Valdelacasa afloran el Supergrupo del Alcudiense inferior-Domo Extremeño (donde destacan las diamictitas de la Formación de Orellana), los arrecifes microbianos más espectaculares con Cloudina de la Formación de Villarta y la base paleoicnológica del Cámbrico en la Formación de Arrocampo (las dos últimas formaciones pertenecen al Grupo de Ibor). Los afloramientos que tradicionalmente se consideraban como representantes del límite Precámbrico-Cámbrico y base del piso regional Cordubiense se sitúan en el miembro inferior de la Formación del Pusa, suprayacentes al Grupo de Ibor y considerados actualmente como intra-terreneuvienses.