Carbonate Platform Development Research Articles

Geological Sites of the Anergui Region: Description and Place in the Alpine Geological History of the M'goun UNESCO Global Geopark (Morocco)

The M'goun UNESCO Global Geopark is located in the central part of the High Atlas Mountains in Morocco. Numerous studies have highlighted the richness of the geological heritage of this area. Despite these increased efforts in characterization, some areas, such as Anergui, remain underexplored. This mediation work aims to describe the most significant geological landscapes of this region and place them within the broader geological history framework of the UNESCO M'Goun Geopark, thereby enriching the list of geosites within this geopark and promoting geological awareness in the area. This study focused on describing 16 geosites selected based on scientific, educational and geotourism values. These geosites stand out for their geodiversity, showcasing both deep-seated and surface geological phenomena. They provide an excellent framework for understanding the alpine geological history of the M'Goun Geopark. Each site bears witness to one or several key stages of this history, highlighting the extension of the High Atlas basin, the development of carbonate platforms, Jurassic diapirism and magmatism, Late Cretaceous and Tertiary compression, Tertiary and Quaternary uplift, and erosion, resulting in a variety of geological features relating to deformation and alteration.

Architectural development of a land-attached carbonate platform in the African–Arabian Desert Belt: the late Pleistocene to Holocene evolution of the Al Wajh Platform, NE Red Sea, Saudi Arabia

ABSTRACT Carbonate platform architectures are indicators of environmental changes, such as sea level, climatic variations, and tectonic influence, which all control platform evolution. While analog studies on modern carbonate platforms have predominantly focused on tropical settings, limited attention has been given to arid and semiarid environments, although many ancient carbonate sequences were developed under these settings. This study aims to bridge this gap by investigating the Al Wajh carbonate platform lagoon in the NE Red Sea, Saudi Arabia, using geophysical and remote-sensing data to unravel its architecture and development since the last interglacial highstand (MIS 5e). We collected and analyzed sub-bottom profiles extending over 675 km and airborne lidar multibeam bathymetry data covering an area of 1700 km2. Surface sediment samples and vibracores with a maximum penetration of three meters were integrated to strengthen our interpretation. Furthermore, a recently published Red Sea sea-level curve was used to establish an age model and supplemented by available climate data to reconstruct depositional models. The Al Wajh lagoon is a “bucket” structure hosting five distinct depositional units since the late Pleistocene: U0 (pre-MIS 5e and MIS 5e), U1, U2, U3, and U4 (MIS 1), which are composed of five hydroacoustic facies, ranging from mounded to wavy laminated facies. Based on combining climate data, sea-level curves, and platform topography with our geophysical data, we conclude that the lagoon hosts carbonate, siliciclastic (fluvial and eolian), and potentially evaporitic deposits of open-marine and playa-lake origin. Intriguingly, karst architecture (i.e., sinkholes, caves, and collapsed cavities) is absent despite intermittent pluvial episodes and exposure during the late Pleistocene. Data analysis indicates that the Al Wajh lagoon architecture and development since the late Pleistocene are controlled by a combination of antecedent topography, sea-level variation, climate fluctuation, siliciclastic influx, carbonate production, and reef growth and drowning. Finally, insights from this study enhance our understanding of the architecture and sedimentary infill of ancient land-attached carbonate platforms deposited in a mature rift basin under alternating arid and pluvial climate settings.

Sequence stratigraphic architecture and depositional evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate successions, N Cyrenaica Promontory, NE Libya – Interplay of tectonics and eustasy

The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.

Effective application of geological process modeling for unravelling carbonate build-up complexity: A case study from the EX-Carbonate build-up in central Luconia Province, Malaysia

In the dynamic field of carbonate reservoir Exploration, the need for specialized models is vital, assisting as a key tool to facilitate interdisciplinary collaboration and enhance strategies for predicting reservoir behavior. This study examines the use of geological process (GPM), a standard tool to simulate forward stratigraphic modelling, particularly focusing on the Central Luconia Province in the South China Sea. Central Luconia Province stands out for its extensive carbonate build-ups and is recognized as a prolific hydrocarbon reservoir. Forward Stratigraphic Modelling (FSM) leads to a paradigmatic change in geological modeling. Unlike geostatistical models controlled by geometrical parameters, FSM relies on mathematical representations of the physical rules determining erosion, transport, and sedimentation in carbonate growth. This tool, supported by various researchers, has proven its ability in quantitative sedimentary system analysis across diverse temporal and spatial scales. This study located in EX Field showcases the ability of stratigraphic forward modeling in replicating sedimentary complexities and resulting stratigraphic architecture of the EX isolated carbonate platform. The methodology links parameters from existing literature with multiscale data. Additionally, carbonate production laws, contingent on water depth, play a pivotal role in the meticulous modeling process. This work illustrates the efficacy of geological process modelling as a transformative approach for unraveling the complexities of carbonate systems, particularly in regions with prolific hydrocarbon reservoirs like Central Luconia. The incorporation of literature-derived parameters and multiscale data serves as evidence of the model's ability to offer nuanced understandings of the dynamic evolution of carbonate platforms, thereby advancing our understanding of reservoir prediction and future management strategies.

Millennial-scale sedimentary evolution of carbonate platforms during the Permian–Triassic boundary hyperthermal event

The millennial-scale response of shallow-water carbonate platforms to the climatic upheaval at the Permian–Triassic boundary (PTB) remains unclear. This study presents three carbonate platform sections across the Permian–Triassic (P–T) boundary in South China and the Lhasa terrane. A total of 14 types of carbonate microfacies were identified, which show that the Liangfengya and Taiping sections in South China were deposited in an inner ramp, and the Wenbudangsang section on the Lhasa terrane was deposited in an outer ramp. Bulk carbonate carbon isotope patterns through the sections are generally characterized by negative excursions (−2.2 to −3.5‰) during the PTB hyperthermal event. These excursions can be divided into four phases (NC1 to NC4), with NC1 before the negative carbon isotope excursion (NCIE) event, NC2 during the initiation phase of the NCIE, NC3 during the body of the NCIE, and the NC4 marking the recovery stage of the NCIE. The pattern of sedimentary changes in each section through the PTB hyperthermal event, and the relationship between these changes and the carbon isotope stages, was established. In the studied sections, the onset of the NCIEs (NC2 stage) preceded evidence for a carbonate production crisis, with the occurrence of anachronistic facies developed after this crisis but prior to the NC3 stage. In detail, our data show that the carbonate production crisis occurred 11 kyr after the onset of the NCIE, and 47 kyr before the first Permian–Triassic mass extinction (PTME), and that the carbonate production crisis may have been closely related to the environmental stresses associated with greenhouse gas emission from the Siberian Traps Large Igneous Province (STLIP).

Late Cretaceous marine flooding and installation of a mangrove swamp environment in the Prebetic (Betic External Zones, SE Spain)

The Cenomanian (Upper Cretaceous) sedimentary rocks of the External Prebetic (Betic Cordillera) in the Sierra de Montearagón-Carcelén (SE Spain) record the transgression and flooding of continental deposits and the subsequent development of an inner shallow carbonate platform. The transgressive surface is densely colonized by infaunal trace-makers of the Glossifungites ichnofacies (Gastrochaenolites and Glossifungites), which indicate sediment starvation and erosion as well as colonization of a firmground. The first deposits were a thick calcarenite bar (2 to 11 m) with large-scale cross-bedding pointing to a high-energy environment in a shallow carbonate platform. The record of the Rosselia ichnofacies (Rosselia and Ophiomorpha) confirms a loose sandy bottom under high-energy conditions. The overlaying stratigraphic succession is characterized by subtidal laminated marly limestones and intertidal limestones with rhizoliths interpreted as a mangrove swamp environment. These facies are organized in shallowing-upwards sedimentary sequences. An episodic high-energy event is represented by bivalve-rich limestones representing shell lags of disarticulated valves. This facies could be related to a climatic perturbation evidenced by a negative excursion of δ13C and δ18O. The successive shallowing-upwards sedimentary sequences persisted thanks to subsidence related to the tectonically controlled depocenters located in the south of the Sierra de Montearagón-Carcelén. The differential subsidence, evidenced by the increasing thickness towards the south of the sector under study, suggests the activity of listric faults that controlled the depocenters. This is the first report of the Cenomanian transgression in this sector of the External Prebetic and the first record of the very extensive mangrove swamp that developed close to the land that emerged.

Ypresian–Lutetian platform evolution in the Indus Basin, Southwestern Pakistan: An interplay between local and regional tectonic changes

The present investigation aims to analyze the depositional environment, sequence stratigraphy, and geochemistry of the Early–Middle Eocene succession in the Laki Range of the Southern Indus Basin, Pakistan. The sequence is subsequently correlated with other sections within the Southern Indus Basin, Central Indus Basin, Upper Indus Basin, and Hazara Basin in Pakistan. For this study, the Lakhra and Laki formations were sampled from four sections in the Laki Range. Based on detailed outcrop observations, eight lithofacies were identified including four clastic lithofacies (CLF-1 to 4) and four limestone lithofacies (LLF-1 to 4). Similarly, based on detailed petrographic examination, seven microfacies were identified in limestone units. Considering the biotic paleoecology, facies texture, and chemical composition, depositional environments were assigned to the microfacies and lithofacies. All the microfacies, and the shale and sandstone lithofacies (CLF-1 and CLF-4) represent shallow inner to deeper outer-shelf settings whereas the other two lithofacies (CLF-2 and CLF-3) represent deltaic and tidal flat settings, respectively. All the microfacies and lithofacies information was used to establish sequence stratigraphy for the studied strata. The top of the Lakhra Formation and the whole of the Laki Formation in the Bara Nala Section (BNS) represent two complete, and two partial, third-order sequences, further divided into fourth order and small-scale cycles. The sequence's development is primarily influenced by regional and local tectonics. The regional correlation of the Indus Basin and Hazara Basin indicates that the regional basin's bathymetry and resultant depositional sequence were significantly influenced by the Himalayan Orogeny. The regional depositional pattern indicates that subsequent to India–Asia collision, the closure of eastern Tethys took place in a temporal succession from northwestern to the southwestern parts of the Indus Basin. In the Central Indus Basin, marine environments persisted until the Priabonian Stage (SBZ20) compared to those of the Upper (SBZ11–12) and Southern (SBZ13–14) Indus basins. This study offers valuable insights into both the local and regional depositional frameworks and the influence of local and regional tectonics on a carbonate platform evolution.

Devonian to Mississippian strata of the Shine Jinst region revisited: Facies development and stratigraphy in southern Mongolia (Gobi Altai Terrane)

AbstractThis report provides new stratigraphical and facies data from Devonian and Carboniferous rocks in the Shine Jinst region (Trans Altai Zone, southern Mongolia) with a special focus on the Lower Devonian Chuluun Formation, the Middle Devonian Tsagaankhalga Formation, and the Upper Devonian to Mississippian Heermorit Member of the Indert Formation. Facies development in the Shine Jinst region exhibits a fundamental break in the carbonate platform evolution in the Lower Devonian as reef building organisms were affected by a major regression and deposition of several metres-thick conglomerates at the base of the Tsakhir Formation (Lower Devonian). The overlying Hurenboom Member of the Chuluun Formation is composed of fossiliferous limestones. Reef building organisms, such as colonial corals and stromatoporoids show low diversity and exhibit limited vertical growth and lateral extension of individuals. Thus, they do not represent a real reef as proposed in previous publications but biostromal limestones instead. One reason might be the isolated position of the Shine Jinst region between an unknown continent and a volcanic arc in the early Middle Devonian that hampered the successful colonization in shallow-water areas. Bivalves of the Alatoconchid family were once grouped into reef builders or biostrome builders and they are known only from Permian rocks. The found bivalve biostomes in Mongolia may represent precursors, which would document the oldest record of Alatoconchids found in the world. Remarkable thicknesses of massive crinoidal grainstones (“encrinites”) are documented in many parts of the succession, which suggest rather stable environmental conditions of a carbonate ramp setting at different times. The occurrence of thick-bedded conglomerates in the Shine Jinst section is not restricted to the Lochkovian to Pragian interval (Tsakhir Formation), but also occurs in the Eifelian. A thick-bedded conglomerate, which is interpreted to represent braided fluvial or fan-delta to shallow-marine deposits occurs at the base of the Tsagaankhaalga Formation. A steep relief associated with uplift and volcanism seems to be a realistic scenario for deposition of these sediments. This succession points to a remarkable tectonic uplift or sea-level fall in the Middle Devonian. Conodont findings of the studied section confirm the occurrence of time-equivalent strata of the Choteč Event, the Dasberg Crisis, and the Hangenberg Event found elsewhere in the world, which are described from Mongolia for the first time. Sedimentological descriptions, revised biostratigraphical data, and U-Pb dating by LA ICP-MS of some volcaniclastic rocks from the Chuluun Formation are presented in this report. The studied section records a complex interaction of sedimentation, regional tectonics, sea-level changes and coeval volcanism, which is very similar to other regions in Mongolia. The new data provide the background for further scientific studies in this region. This is a contribution to the Special Series on “The Central Asian Orogenic Belt (CAOB) during Late Devonian: New insights from southern Mongolia”, published in this journal.

The evolution of the early Paleozoic carbonate platform in the Central uplift, Tarim Basin, northwestern China, and hydrocarbon accumulation

The evolution of the early Paleozoic carbonate platform in the Central uplift, Tarim Basin, northwestern China, and hydrocarbon accumulation

Neogene carbonate platform development in the southern South China Sea: Evidence from calcareous microfossils

Biogenic reefs are unique geologic bodies that are the products of biological activity in tropical and subtropical oceans and critical to global carbon cycling. The South China Sea (SCS) has developed largest carbonate platforms in the Western Pacific. The fully-cored Well NK-1, which is drilled through the reef complex on the Meiji Atoll, Nansha Islands, offers good opportunity for assessing the long-term evolutions of biogenic reefs in the SCS. The stratigraphic ages based on palaeomagnetic and Sr isotopic data are controversial in some intervals of core NK-1. To reveal the evolution history of Nansha Islands and their controlling factors, more credible age constraints on core NK-1 are needed. This research presents new records of calcareous microfossils (calcareous nannofossil and foraminifer) abundances and diversities in the biogenic reef carbonates of core NK-1. Based on the assemblages of the calcareous microfossils, seven biostratigraphic datums are recognized from the sequence of core NK-1, revealing a general continuous succession of the earliest Miocene to Pleistocene age. By combining with the magnetostratigraphic data, the development and evolution of carbonate platform in Nansha Islands are reconstructed. The bottom age of the biogenic reef sequence of NK-1 is estimated for 23.03 ± 1.06 Ma, close to the Oligocene/Miocene boundary. The new chronology highlights three short hiatuses of 3.6–2.4 Ma, 11.1–10.0 Ma, and 13.5–11.9 Ma, which are well correlated with the prominent exposed surfaces at 210.3 m, 464.6 m and 561.6 m, respectively. It reveals remarkably similar evolution history of carbonate platforms in the SCS since Neogene by comparing with records of stratigraphy and growth rate from deep drilling cores on isolated coral reefs in Nansha and Xisha Islands. The results showed that the SCS carbonate platform developments, which go through Late Oligocene / Early Miocene initiation phase, Early-Middle Miocene rapid growth phase, Middle-Late Miocene erosion phase, Miocene-Pliocene stable development phase and Quaternary growth phase, are mainly influenced by global sea level changes, environmental factors and regional tectonism such as the SCS basin spreading, Sabah Orogeny Movement and Dongsha Movement.

Magnesium isotopic compositions and origin of Neogene dolomites in Xisha Islands, South China Sea

A common consideration of dolomite-based records for paleoseawater geochemistry reconstruction is the process of dolomite precipitation, which is closely related to the source of relevant elements. “Island dolomite” has been proposed as having great potential for recording paleoseawater geochemical characteristics, however, dolomitization should be strictly constrained in advance. As a major element in dolomites, magnesium (Mg) and its isotopes are critically involved in dolomitization, which may serve as a tool for providing direct insights into this process. Here, we report the Mg isotopic compositions of reef dolomites from the well Xike−1 reef core in Xisha Islands, South China Sea. The geochemical and mineralogical characteristics suggest that these reef dolomites experienced limited diagenetic alteration, and retained primary geochemical characteristics after dolomitization was complete. These reef dolomites reached chemical equilibrium with contemporaneous seawater during dolomitization, which were buffered by coeval seawater. Our results suggest that the development of carbonate platform and the formation of reef dolomites in Xisha Islands were related to tectonic subsidence. These reef dolomites were deposited during periods of decreasing tectonic subsidence rate. Then, dolomitization model for these reef dolomites was established, which provides an effective basis for reconstructing the chemical characteristics of paleoseawater. The occurrence of near-invariant seawater δ26Mg value during the past ∼23 Myr was subsequently verified via cross-checks provided by different seawater δ26Mg archives in this and previous studies. Our results highlight the great potential of seawater-buffered dolomites with limited postdepositional diagenetic alteration for constructing paleoseawater geochemistry though the geological history.

The Cretaceous carbonate platforms of the Americas and their rudist bivalves

Abstract Following the break-up of Pangaea, many rifted margins of the Americas became carbonate platforms. During the Cretaceous, these platforms, as well as those associated with volcanic arcs, were populated by rudist bivalves that underwent a major radiation from the Early to Late Cretaceous. Carbonate platform development was episodic with major platforms represented by the Hauterivian to early Aptian, the early to late Albian and the Campanian to Maastrichtian. Different rudist bivalves characterized different phases of platform development. The Hauterivian to Aptian saw the rise of the Rethinae and Caprinidae, and was terminated by Oceanic Anoxic Event 1a (OAE1a). The Albian saw the rise of the Caprinuloideina and Youngicaprininae together with the first radiolitids. The Cenomanian is poorly understood in term of rudist bivalve development and the effects of the Cenomanian–Turonian boundary event (CTBE or OAE2) are not well documented in the Americas. The Turonian to Maastrichtian saw a major radiation at the genus level of the rudists – hippuritids were initially represented by cosmopolitan genera, but through the late Santonian to early Campanian these were replaced by endemic genera. The radiolitids and antillocaprinids also underwent major radiations at this time, and numerous new endemic taxa characterized the carbonate platforms of the Americas. The Cretaceous–Paleogene boundary event decimated the carbonate platforms of the Americas and wiped out the rudist bivalves. Two new radiolitid genera are described: Vermuntia and Thiadensia .

Evolution of Cenozoic sedimentary architecture in Central and Southern South China Sea basins

The Central and Southern South China Sea (CSSCS) has a complex tectonic dynamic background and abundant oil and gas resources, which has always been a hot topic of academic and industrial attention. However, systematic analyses are still lacking regarding its sediment filling structure and evolution, mostly due to limited borehole penetration and poor quality of seismic reflection data for deeply buried sequences. No consensus has been reached yet on the sedimentary infilling processes, which impeded the reconstruction of the palaeogeography of Southeast Asia and the oil-and-gas exploration undertakings. Here, we illustrate the Cenozoic sedimentary evolution of the CSSCS region by synthesizing relevant data from previous literature and our own observations and displaying the evolution of depositional systems in sequential reconstructions. Besides, the controlling factors of preferred sedimentary scenarios in the CSSCS incorporate the latest interpretations of the spreading of South China Sea (SCS) as well as the demise of the hypothetical Proto-South China Sea (PSCS). The results show that there are three types of sedimentary basins in the CSSCS (foreland, strike-slip, and rift basins) with different sedimentary filling structures. The foreland basins formed a depositional pattern of ‘transition from deep water to shallow water environments’, dominated by deep-water depositional systems which were formed before the Early Oligocene with submarine fans developed. Later, the foreland basins were gradually dominated by shallow-water depositional systems with deltas and shallow marine facies. The strike-slip basins showed the depositional architecture of ‘transition from lake to marine environments’, i.e. the basins were dominated by lacustrine deposits during the Eocene and evolved into the marine depositional environment since Oligocene with delta developed in the western part of the basin. The depositional evolution of rift basins illustrated the characteristics of ‘transition from clastic to carbonate deposits’, i.e., the rift basins were dominated by Eocene–Oligocene shallow marine clastic depositional systems, while carbonate platforms started to develop since the Early Oligocene from east to west. The above-mentioned differences of depositional architecture in the CSSCS were controlled by the scissor-style closure of the PSCS and the progressive-style expansion of the SCS. Specifically, the early-period deep-water sedimentary environment of CSSCS basins was controlled by the distribution of PSCS in the Eocene. As the scissor-style closure of PSCS progressed from west to east during the Oligocene to Early Miocene, the northwest of Borneo continued to rise, providing a great number of clastic materials to the basins and gradually developing large-scale deltas from west to east. The distribution of early-period lacustrine sedimentation of strike-slip basins was affected by paleo uplift, and the basins transgressed from the northeast and gradually evolved into marine sedimentary environment due to the expansion of SCS. The expansion of SCS also controlled the sedimentary filling evolution of the rift basins, which broke away from the South China continent and drifted southward. Thus, the rift basins lacked the supply of terrigenous clastic sediments which hindered the development of large-scale deltas and formed a clear water environment conducive to the development of carbonate platforms from east to west.

Microfacies analysis and paleoenvironmental interpretation of the late Aptian–Albian (Early Cretaceous) carbonates of the Riachuelo Formation in the Sergipe Sub-basin, northeastern Brazil

The beginning of the drift phase, in the Aptian–Albian transition, marked the development of marine conditions in the South Atlantic Ocean, characterized by the deposition of evaporites, followed by the development of carbonate platforms. The carbonate rocks of this interval were deposited in a passive margin context as part of the Riachuelo Formation in the Sergipe-Alagoas Basin, northeastern Brazil. The objective of present study was to analyze the microfacies of the Aptian–Albian interval in the northern portion of Sergipe State, near the city of Pacatuba. The mainly carbonates of two cores were investigated and five carbonate microfacies were identified: oncoidal rudstone, bioclastic rudstone, oncoidal packstone, peloidal packstone/wackestone, and mudstone with planktonic bioelements that suggest the paleoenvironments were relatively shallow marine. The microfacies were dominated by oncoids in almost every sample, which occurred in association with stromatolites. The biostratigraphic results were based on palynomorphs and calcareous nannofossils. The palynomorphs assemblages indicated a late Aptian age. Paleoecological results of these fossil groups show paleoenvironmental conditions of the shallow waters with proximal characteristics, with the predominance of pollens and spores associated with rare dinoflagellates and ascidians. A striking feature was the presence of authigenic glauconite which filled skeletal cavities and partially replaced the oncoids and their nuclei, mostly in the oncoidal packstone facies. Together, these findings suggest that the samples formed at the basal portion of the Riachuelo Formation in a transgressive systems tract, corresponding to the first depositional stage of the Riachuelo Formation.

Tropical ocean temperatures and changes in terrigenous flux during the Paleocene-Eocene Thermal Maximum in southern Tibet

The Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma) was an extreme climate warming event of the early Cenozoic. The development and ecology of carbonate platforms are highly sensitive to changes in SSTs, sea level and terrestrial detrital input. However, no record of SST changes during the PETM has yet been reported from a shallow marine carbonate platform. Here, we reconstruct SSTs for two shallow marine carbonate PETM sections in present-day southern Tibet from the distribution of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGT). Our dataset demonstrates that the temperature of the tropical eastern Tethys likely increased 3 to 5 °C during the PETM (depending on the TEX86 calibration used), and it supports a reduction of 2 °C in the meridional gradient between middle and low latitudes. Elemental data and quartz content imply an increase in terrigenous flux prior to the onset of the CIE, possibly linked to initial PETM warming. However, inconsistent changes in terrigenous flux at other PETM sections in the eastern Tethys suggest a variable response modulated by sea-level change and hinterland weathering, erosion and sediment delivery.

The Role of Cyanobacteria In the Microfabric Heterogeneity of Cambrian Leiolite, North China

ABSTRACT Based on their mesostructures, carbonate microbialites are divided into four major groups: laminated stromatolite, clotted thrombolites, structureless leiolites, and dendritic dendrolite. Among the various types of microbialites, leiolites, also known as “cryptomicrobial deposits,” are uncommon in the stratigraphic records. This is exacerbated by leiolites relatively structureless and aphanitic structure, making their identification and characterization more challenging. Previous studies have revealed that leiolites have contrasting fabrics at different scale, heterogeneous microscopic fabrics and structureless mesoscopic to macroscopic fabrics. While it is widely assumed that cyanobacteria play a significant role in the formation of carbonate microbialites in marine environments, the origin and controlling mechanisms of variations in leiolites microstructures and macrostructures remain enigmatic. In the central part of the North China Platform, two excellent exposures of massive, structureless Cambrian bioherms (Furongian) dominated by leiolites were observed (Qijayu section). The Qijayu-section leiolites offer a unique opportunity to investigate the role of cyanobacterial input in governing the formation and textural heterogeneities of such microbialites. In addition, the significance of the Furongian leiolites stems from their association with a period of global development of microbial-dominated carbonate platforms. Our findings suggest that these Furongian leiolites developed during the forced-regressive systems tract. At the microscopic level, these Furongian leiolites exhibit a high degree of heterogeneity which is controlled by the presence of various types of cyanobacteria (Hedstroemia, Subtifioria, Girvanella), sponge mummy, and benthic ooids. The Hedstroemia, Subtifioria and Girvanella excreted extracellular polymeric substances that form multiple biofilms in cyanobacterial microbial mats where Furongian leiolites grew. The role of cyanobacteria in the microscale heterogeneity of Cambrian leiolites is evident, and this provides new insights into the development of microbial-dominated carbonate platforms in similar settings elsewhere. As a result, this study provides not only a reference example for global correlation but also some solid clues for further understanding the growth style of leiolites in the geologic record.

Educational Potential of Geoheritage: Textbook Localities from the Zagros and the Greater Caucasus

Geoheritage requires proper conservation and has significant importance for geoscience education at universities. Furthermore, its related potential needs to be evaluated. This study focuses on two textbook localities (these are parts of larger geosites) from the Cenozoic orogenic belts, namely the Zagros and the Greater Caucasus. The novel, tentatively proposed approach aims at general geological characteristics of the localities, identification of the principal teaching topics and teaching opportunities, and semi-quantitative evaluation of the educational potential on the basis of several objective criteria. The Abmorghan anticline (Zagros, Iran) is suitable for learning about the regional Paleogene stratigraphy, carbonate platform evolution, and karst. The locality of the Skala monocline (Greater Caucasus, Russia) allows the deposition in past tropical conditions and monocline structures to be explained. Both localities can be used for training student skills and challenging their geological thinking. The semi-quantitative evaluation shows that the geoeducational potential of the Abmorghan anticline is advanced and that of the Skala monocline is moderate. The established potential can be exploited by universities, although this requires focusing attention on the other geoheritage sites and special marketing efforts.

Global Geodynamic Control on Phanerozoic Marine Carbonates Sedimentary Systems

AbstractThis pilot study is founded on an exhaustive investigation of representative and well-documented cases (120) of carbonate systems during the Phanerozoic. We investigated the coupling between geodynamic settings and geometry, physiography, and stratigraphic architecture of carbonate platforms. The objective is to identify and quantify the impact of geodynamic controls on carbonate platforms and possible global trends during the Phanerozoic. Carbonate platforms are characterized in terms of geometry, stratigraphic architecture, time duration, preservation rate, progradation and rates of progradation, platform type, and thickness. Geodynamic parameters are characterized in terms of basin physiography, basement depth and type, tectonic setting, and subsidence origin. Relationships between carbonate parameters and geodynamic characteristics are investigated, leading to nine models of Geodynamic Carbonate Platforms. Passive margin is the most favorable geodynamic setting for the development of carbonate platforms in three dimensions. The continental crust hosts most of the carbonate platforms independently of time and geodynamic settings. Carbonate platforms developed above the exhumed mantle or oceanic crust (volcano) are the exception or very small and isolated. Global trends during the Phanerozoic of carbonate platform lateral extend, progradation, or thickness are tentatively interpreted in relation to geodynamic and eustatic parameters. The concept of spatial intersection between geodynamic and climatic windows favorable to carbonate platforms is introduced with its possible retroaction to the global carbon cycle.

Reconstruction of Tournaisian-Viséan tectonic and climatically induced event histories of the Mobarak carbonate platform along depositional strike in the northeastern margin of Gondwana: Constraints from high-resolution cycle and sequence stratigraphy

Cyclic successions are one of the most important types of deposits in the carbonate platform of the Mississippian (Tournaisian-Viséan) in Gondwanan and Laurussian margins. The importance of climatically induced events impact on the amplitudes and frequencies of sea-level fluctuations in Mississippian of Iran is significant because the beginning, extent, duration, and significance of periods of climatically induced events in northern margin of Gondwana are not well recognized. A high-resolution sequence architecture in integration with paleoenvironmental reconstruction and foraminiferal biozonation from the Tournaisian-early Visean carbonate successions of the Mobarak Formation in Alborz basin along depositional strike (E-W- a distance of c. 340 km) suggests a mosaic-like pattern of deposition and compartmentalization of the depositional settings (homocline ramp to distally steepened ramp). According to the recognized facies, the stacking pattern of high-frequency cycles across the platform, and major accommodation events recognized on the correlated Fischer plots, six 3rd-order sequences (DS1–DS6) were identified. Detailed analysis on high-frequency cycles representing a highly variable number of shallowing-upward cycles, types, thicknesses, and facies heterogeneity along depositional strike. A combination of the episodic tectonic events along faults interacting with autocyclic processes, and inherited topographic irregularities are suggested as the driving mechanism for the cycle development. Six stages of Mobarak carbonate platform evolution based on understand the interplay of autocyclic and allocyclic controls are recognized in a hierarchical 3rd-order sequence stratigraphic framework and a chronological order: (1) early Hastarian corresponds to post-glacial transgressive episode with progressive backstepping of facies belts of early TST of DS1 throughout the region; (2) middle to late Hastarian corresponds to a major transgressional phase of DS1 following global temperature rise superimposed on different subsidence/uplift rates with the deformation of the platform along depositional strike; (3) Hastarian–Ivorian boundary corresponds to TST of DS2 with facies heterogeneity along depositional strike related to continuation of different subsidence/uplift rates. The absence of any systematic changes in the amplitude and period of cyclicity or lowstand deposits and subaerial surfaces during this phase shows the lack of influence of mid-Tournaisian glaciation and concurrent eustatic regression in northern margin of Gondwana. (4) early to middle Ivorian coincides with the RST of DS2 and TST of DS3 showing by remarkable topographic irregularities in the basin physiography and change in the position of the depocenter axis from a E–W trend to the center; (5) late Ivorian-early Moliniacian coincides with the RST of DS3 and DS4 showing by the Late Tournaisian thermal period and eustatic rise superimposed on uplift and subaerial exposure of the western part and subsidence in the central and eastern parts of the basin; (6) Moliniacian coincides with DS5-DS6 sequences showing by change from fault-related topography to major tilted fault-block topography accompanied by eustatic sea-level fall caused indirectly by the Viséan and Serpukhovian glaciations phases.

Controls on evaporite facies distribution during the early phases of the Zechstein Basin development (Zechstein 1, Upper Permian): Implications from the marginal part of the basin in SW Poland

Amongst the least understood issues in the giant evaporite basin evolution is their early development. Here, we use a unique set of archival data from the Fore-Sudetic Homocline in SW Poland to investigate the controls on evaporite facies distribution in the marginal part of the Zechstein Basin after the Zechstein Sea transgression (Upper Permian, Z1 cycle). Based on integrated data from boreholes, subsurface mining survey and seismic profiling we constructed a 3D structural model, which showed that the carbonate, sulphate and chloride facies boundaries originally extended W–E, irrespective of the fault patterns in the basement. The thickness distribution for the Zechstein Limestone (Ca1), Lower Anhydrite (A1d) and Upper Anhydrite (A1g) evidences carbonate and sulphate platform development in respective evaporitic phases. Although the sea bathymetry and progressive seawater evaporation were the main factors responsible for the northward progradation of the evaporite facies, the relief over the sulphate platforms implies a significant influence of sea currents on the sulphate deposition. The channelised circulation of variably saturated seawater decreased the overall accumulation rate in the channels and promoted the high-and-trough topography development over the platforms. The Upper Anhydrite (A1d) top relief was evened by the Oldest Halite (Na1) rocksalt deposition. Prior to the Zechstein Limestone (Ca1) deposition, the distribution of clastic facies was mostly restrained by the dune relief inherited after the aeolian sedimentation in the Rotliegend. This old relief partly influenced also the Zechstein Limestone (Ca1) carbonate thickness and subfacies distribution and was eventually buried by the Lower Anhydrite (A1d) sulphates. There is no evidence on tectonic controls on evaporite depositional patterns throughout the Z1 cycle in the studied area.