Lacustrine Limestones Research Articles

Groundwater flow modeling to support water management scenarios – the Bekaa Valley, Lebanon

The Italian Ministry of Foreign Affairs funded a project aimed at developing tools for water management in the Bekaa valley, Lebanon. The Lebanese Ministry of Energy and Water implemented the project, supported by the University of Milan Department of Agricultural and Environmental Sciences (DISAA).The geologic framework consists of a Cretaceous-Eocene carbonatic structure, crossed by a fracture system parallel to the anticlines of the Anti-Lebanon and Mount Hermon ranges and to the synclinal constituting the Bekaa valley. The carbonatic structure is overlain by a Neogene-Quaternary sequence of lacustrine limestones, marls and conglomerates outcropping in the lower valley.In the study area, groundwater bodies fed by precipitation along the mountain ridges, give origin to the Orontes river. Surficial and ground water feed the population, agriculture and fish farming and, since 2011, over one million of Syrian refugees.A Decision Support System (DSS) was set up based on WEAP, a software that represents the interaction between water resources and users by simulating flow mechanisms directly or coupled to external models. MODFLOW-2000, one of such models, was used to represent groundwater flow in the carbonatic and in the overlying Quaternary aquifer, which is present in the lower valley.By coupling WEAP with MODFLOW, it is possible to represent physically-based scenarios of water management, with the aim of optimizing both water extraction and distribution. Moreover, the groundwater flow model could support negotiations between Lebanon, Syria and Turkey for the distribution of surface and ground water through joint data and knowledge.

Cenozoic lacustrine stromatolites from the southern margin of the Junggar Basin, NW China and adjacent areas: indicators for palaeoclimatic and tectonic evolution

AbstractLacustrine stromatolites provide high‐resolution and sensitive palaeoenvironmental and palaeoclimatic records of their respective drainage basins and beyond. A well‐developed stromatolite bed was discovered within the clastic deposits of the Early Miocene Taxihe Formation in the southern margin of the Junggar Basin, north of the Tian Shan Mountains. Their sedimentological features indicate a near‐shore stable environment of a shrinking lake. The study of the stable oxygen and carbon isotopes in this stromatolite bed revealed that δ18O V‐PDB values range from −11.3‰ to −5. 6‰ and those of δ13C V‐PDB from −1.8‰ to 1.7‰. Lower values −10. 2‰ and −8. 2‰, respectively, were determined from nearby lacustrine limestones of Oligocene age. The co‐variation and overall increasing trend of the δ18O and δ13C values indicate deposition in a closed basin during a period of aridification. This environmental change can be related to the major uplift of the Tian Shan Mountains, the southern border of the Junggar Basin, during the Early Miocene. Several δ18O and δ13C records of lacustrine stromatolites ranging in age from Oligocene to Middle Miocene were reported: from localities in the Northern Tibetan Plateau and western Qaidam Basin. The similarity of the individual stable isotope records in stromatolites from Northwest China, indicate an underlying regional cause. These stromatolites were deposited during the period of major uplift of the Tibetan Plateau and the Tian Shan Mountains. It is therefore concluded that the stromatolite records provide local snapshots of the effect of this major process on atmospheric precipitation and environmental conditions in Northwest China. Copyright © 2016 John Wiley & Sons, Ltd.

The Acheulean workshop of la Noira (France, 700 ka) in the European technological context

The prehistoric site of la Noira, located in the Cher Valley, a tributary of the Loire River in the center of France, has yielded a lithic assemblage composed of large bifacial tools, cores and flakes. The archaeological level, lying on the Tertiary lacustrine limestone bedrock, was covered and fossilized by a 6 m-thick fluvial sandy formation. The mean age value of ESR dates obtained on bleached fluvial quartz grains sampled in the sandy levels covering the archeological level is 665 ± 55 ka, confirming the antiquity of the archaeological assemblage. ESR dates and the technical characteristics of the assemblage suggest that it is among the oldest sites with bifacial technology in Western Europe.Since 2011, following geological and geochronological studies, the archaeological level has been excavated over a surface of about 100 m2. The aim of this paper is to provide new data on the lithic assemblage and to place the lithic patterns of the site in the European technological framework. La Noira is a workshop site, belonging to a key-period of time with the earliest evidence of the bifacial technology in Europe (as for instance levels P–Q of Arago in France or Notarchirico in Italy) contemporaneous with 800–500 ka sites without bifacial technology, such as Happisburgh, Pakefield in England or Isernia in Italy. This phase predates the wide-scale dissemination of the bifacial technology all over Western Europe from the MIS 12. Technological comparisons between these assemblages and a discussion of the diversity of assemblages and technological features point to early episodic arrivals of new traditions in Europe against a background of earlier traditions.

Rhyolite petrogenesis and meteoric–hydrothermal alteration at the Maghnia volcanic massif, Northwest Algeria

Volcanic rocks from the Maghnia region of northwest Algeria consist of fresh to altered rhyolitic units that were emplaced during late Miocene time. Petrographic observations and geochemical data indicate that rhyolitic rocks were derived from a hybridized peraluminous magma. Petrogenetic modeling, REE contents and oxygen isotope data of quartz and feldspar and spessartine-rich garnet allows the reconstruction of the fractional crystallization between 680 and 780°C and pressure of less than 0.5GPa. Rhyolitic units are partially weathered and form an economic deposit of montmorillonite. Spectroscopic data and stable isotopes (O, H) of glass and montmorillonite indicate that the residual glass was partially hydrated by meteoric water at temperatures between 31 and 54°C. The chemical mass balance indicates that rhyolitic rocks were altered to montmorillonite by meteoric water enriched in Ca, Mg and Sr. The combination of the chemical mass balance and the 87Sr/86Sr initial ratios of rhyolite and montmorillonite indicate that continental water/rock interaction was related to the surrounding Miocene lacustrine limestone.

Geology, mineralogy, geochemistry, and depositional environment of a Late Miocene/Pliocene fluviolacustrine succession, Cappadocian Volcanic Province, central Anatolia, Turkey

This paper investigates the mineralogy, geochemistry, and depositional environment of Late Miocene/Pliocene fluviolacustrine deposits, including multiple ignimbrite levels and andesitic and basaltic lavas, within the Cappadocian Volcanic Province (CVP) of central Anatolia, Turkey. Palaeosols and calcretes formed within these terrestrial sedimentary rocks under near-surface or surface conditions. The palaeosols are composed predominantly of smectite ± illite with feldspar, quartz, calcite, opal-CT, and amphibole, and the calcretes mainly of calcite with minor feldspar, quartz, and accessory smectite ± palygorskite. The palygorskite occurs on and between the calcite crystals in the calcretes and at the edges of smectite flakes within the palaeosols, indicating an in situ formation from evaporated alkaline water rich in Si and Mg and poor in Al under arid or seasonally arid climatic conditions. In the palaeosols and calcretes, negative Ba, Nb, Ce, Sr, and Ti anomalies and an enrichment of light rare earth elements relative to medium rare earth elements and heavy rare earth elements, with a distinct negative Eu anomaly, likely reflect the alteration of feldspars and amphiboles in the ignimbrite. The alteration of the ignimbrites caused the depletion of SiO2, Al2O3+Fe2O3, TiO2, and K2O through the precipitation of smectite ± illite in the palaeosols and CaO in the form of calcite in the calcretes. The delta18O values of the calcretes and limestones range from –8.71‰ to –10.71‰, which are mainly related to the involvement of high-elevation meteoric water, whereas the delta13C values for the same rocks vary between –1.97‰ and 5.71‰. The positive delta13C values for the limestones reflect calcite precipitation in isotopic equilibrium with meteoric water in a lake. The slightly negative delta13C values of the lacustrine limestone carbonates may indicate precipitation from a relatively thick water column and an inflow of surface or groundwater through the ignimbrites with high Ba/Sr values. Conversely, the calcrete delta13C values (3.0‰ to 4.97‰) may suggest a pedogenic origin with low plant respiration rates and a predominance of C4 plants. Based on stable oxygen isotope values from the lake sediments and calcretes, this study suggests that the global warming trend that followed the Late Miocene continued into the Pliocene within the CVP.

The East Africa Oligocene intertrappean beds: Regional distribution, depositional environments and Afro/Arabian mammal dispersals

The East Africa Oligocene intertrappean beds: Regional distribution, depositional environments and Afro/Arabian mammal dispersals

The uppermost deposits of the stratigraphic succession of the Farafra Depression (Western Desert, Egypt): Evolution to a Post-Eocene continental event

This paper gives insight into continental sedimentary deposits that occur at the uppermost part of the stratigraphic succession present in the north-eastern sector of the Farafra Depression (Western Desert, Egypt). Using space imagery to complete the field work, the geology of the area has been mapped and the presence of a N–S oriented fault system is documented. The analysis of the morphotectonic features related to this fault system allows reconstructing the structural and sedimentological evolution of the area. The study indicates that the continental deposits were accumulated in alluvial systems that unconformably overlie shale and evaporitic rocks attributable to the Paleocene–Eocene Esna Formation. The deposits of the Esna Formation show soft-sediment deformation features, which include slump associated to dish and pillar sedimentary structures and provide evidence of syndepositional tectonic activity during the sedimentation of this unit. The outcrops are preserved in two areas on separated fault-bounded blocks. Proximal alluvial fan facies crop out in a dowthrown block close to the depression boundary. The proximal facies are made up mostly by polymictic conglomerates which occasionally contain boulders. The conglomerate clasts are mainly quartz, carbonate, anhydrite satin spar vein, mudrock, ironstone and nummulite fossils. The mid-fan facies consist of trough cross-bedded, rippled and cross-laminated quartzarenites with reworked glauconite grains and carbonate rock fragments, interpreted as deposited by distributary streams. The distal alluvial fan deposits consist of sandy marls that evolve toward the top of the sections into root-bioturbated lacustrine limestone beds that are locally silicified. The limestones are biomicrites containing characea, ostracods and gastropods with fenestral porosity.A number of features, including clast provenance (mainly from marine Paleocene and Eocene rocks), the observed fractural pattern (N–S direction related to the opening of the Red Sea), and the sedimentary relationships, suggests that the continental deposits were accumulated during the Oligocene–Miocene interval.

An overview and interpretation of autocyclic and allocyclic processes and the accumulation of strata during the Pennsylvanian–Permian transition in the central Appalachian Basin, USA

Autocyclic and allocyclic processes controlled the lithostratigraphy of strata that accumulated in the central Appalachian foreland basin during the Pennsylvanian and the transition to the Permian. The transition strata, from bottom to top, include the Late Pennsylvanian Pittsburgh and Uniontown formations of the Monongahela Group, the Waynesburg and Washington formations of the Dunkard Group and the Permian Greene Formation of the Dunkard. Variations in the amount of precipitation were the predominant allocyclic control on stratigraphic variations in terrestrial organic productivity, lacustrine base levels, basin-scale weathering, water table and pedogenesis, sediment supply, and sedimentary geochemistry. Tectonic subsidence controlled accommodation space and basin configuration. Eustasy had little or no effect on the stratigraphy of strata deposited in this continental basin during the Pennsylvanian–Permian transition. Autocyclic processes were the predominant spatial control on architecture of alluvial plain aggradation.Paleosols, delineating regional unconformities, show a gradual upward transition from kaolinitic underclay paleosols indicative of a humid climate in the Late Pennsylvanian Monongahela Group to petrocalcic paleosols indicative of a dry subhumid to semiarid climate during deposition of Dunkard strata. As in the Monongahela Group, the Dunkard Group Waynesburg and Washington Formations contain multi-bedded nonmarine lacustrine limestones with subareal exposure features. These limestones grade laterally into petrocalcic paleo-Vertisols in the up-dip alluvial plain. Subareal exposure features are uncommon in centimeter-scale micritic limestones in the Permian Greene Formation; equivalent up-dip paleosols have been lost to erosion. Coal bed continuity, thickness, and quality, also decrease up-section from the very thick (>m) and laterally continuous Pittsburgh Coal at the base of the Monongahela Group to thin (cm scale) and laterally discontinuous coal beds that unconformably overlie the paleosol/underclay/limestone complexes in the Greene Formation. Lacustrine shales and impure (wacke) fluvio-lacustrine sandstones, commonly with a weak pedogenic overprint, generally overlie coal beds.During accumulation of Monongahela and Dunkard (MDG) strata within the basin center, unconformities at the tops of regional paleosols, overlain by lacustrine strata, suggest allocyclic-induced repeated rise and fall of lacustrine conditions in a lacustrine-fan-delta complex analogous to the Okavango basin and fan in Namibia, southern Africa, and/or the Pantanal in southern Brazil. During maximum lake levels, progradation of fluvio-deltaic systems resulted in laminated shale conformably overlain by dark shale and flat-bottomed distributary mouth bar siltstones and sandstones. Prograding distributaries and/or fluvial channels subsequently incised the flat-bottom mouth bar sands. Where basin margin strata are preserved, south of the basin center, depositional environments consist of aggrading alluvial plain sequences with paleosols, fluvial channel sands, and flood plain deposits. Anastomosing fluvial systems prograded across a low gradient (~1ft/mile; ~20cm/km) alluvial plain into the basin center. A weak pedogenic overprint, marked by ubiquitous root penetrations, occurs throughout most basin-centered fluvial deposits.The subtle but continuous decline in the repetition of cyclic lithostratigraphy up-section in the MDG, particularly in the Greene Formation, appears to be the result of a 10-myr-climate transition from the humid to dry subhumid climate cycles of the Late Pennsylvanian to the equable semiarid to arid climate of the Middle Permian in North America. Cyclothems, common in Pennsylvanian strata, become less distinct up-section in the Dunkard because of decreasing development of underclays, coal, and limestone. This 30-myr period of transition from the humid Pennsylvanian to the arid Permian has been referred to as the Dyassic Period.

The Ostracod Fauna And Environmental Characteristics Of The Volcanosedimentary Yolüstü Formation In The Hınıs Region, Erzurum (Eastern Anatolia), Turkey

The volcanosedimentary Yolustu formation which outcrops in the vicinity of Hinis Town, the southeast of Erzurum City, consists of conglomerate, marl, agglomerate, claystone, tuffite, fragmented travertine limestone with fragments of sand – pebble - plant, lacustrine limestone and tuffaceous – clayey limestone. In this formation, carefully selected 3 measured stratigraphic sections were taken at levels in which the lithology of hard travertine limestones with plant fragments and soft tuffaceous – clayey limestone are present. Washed samples which had been taken from these sections were studied and assessed, and then ostracods reflecting freshwater and brackish water environments were detected. In the unit, 5 genera and 12 species of ostracod and their taxonomies, which are generally peculiar to Ponto – Caspian basin, were defined. Besides; few micro mollusks, and 2 genera and 1 species of gastropod and 1 species of pelecypod (non well preserved) were found from the recrystallized looking tuffaceous, clayey, consolidated, hard limestone levels. In sequence, genera and species types of osracod such as; Leptocythere (Amnicythere) cf. litiva Livental, Tyrrhenocythere bailovi (Suzin), Loxoconcha granulata Sars, L. cf. diligena Kulieva, L. agilis Ruggieri, Candona (Caspiocypris) araxica Freels, C. (Caspiocypris) erzurumensis Freels, C. (Caspiocypris) aff. alta (Zalanyi), C. (Typhlocypris) amblygonica Freels, C. (Candona) parallela pannonica Zalanyi, C. (Candona) burdurensis Freels, C. (Candona) candida (O.F.Muller), C. (Candona) sp. 1 Freels, gastropods like Valvata piscinalis (O.F.Muller), Viviparus sp. and genus and species types of pelecypod like Dreissena polymorpha (Palas) were defined. For the main fossil envrionmtents; Leptocythere and Tyrrhenocythere indicate the brackish water environment, Loxoconcha mesohaline, Candona (Caspiocypris), C. (Typhlocypris) oligohaline, Candona (Candona), Valvata, Viviparus and Dreissena indicate the freshwater environment

Probable aestivation burrows from the Eocene/Oligocene transition in south-eastern France and their palaeoenvironmental implications

Enigmatic biogenic structures are reported from the Palaeogene of south-eastern France in the Castellane-Blieux area (Alpes de Haute-Provence French Department). They occur at the Eocene/Oligocene transition at the top of the Marnes Bleues Formation, which corresponds to a clearly defined regressive sequence, where thick marls are overlain by lacustrine limestones or sandstones. The marls have abundant shallow marine fauna and the upper part of the Formation corresponds to a rapid transition to non-marine deposits. The studied structures exhibit three main morphologies: vertical shafts, furrows, and tunnels. They can also form dense clusters and cross-cut marginal marine crustacean burrows such as Psilonichnus. By comparison with modern and fossil examples, these trace fossils are interpreted as probably aestivation burrows. The possible trace-makers could be lungfish (in particular for the common vertical burrows) or amphibians (for the furrows and tunnels). The occurrence of these different aestivation burrows defines the border of a basin and probably indicates increasing droughts on the coastal plain. This could reflect the well-known development of arid conditions in south-eastern France at the beginning of the Oligocene.

Sedimentology and paleoenvironments of the Las Chacritas carbonate paleolake, Cañadón Asfalto Formation (Jurassic), Patagonia, Argentina

The Las Chacritas Member is the lower part of the Cañadón Asfalto Formation (Jurassic). The unit is a completely continental limestone succession with volcanic contributions that were deposited during the development of the Cañadón Asfalto Rift Basin (Chubut province, Patagonia, Argentina). A detailed sedimentological analysis was performed in the Fossati depocenter to determine the paleoenvironments that developed in the context of this rift. The Las Chacritas Member represents a carbonate paleolake system with ramp-shaped margins associated with wetlands that were eventually affected by subaerial exposure and pedogenesis. This process is represented by three main subenvironments: a) a lacustrine setting sensu stricto (lacustrine limestone facies association), represented by Mudstones/Wackestones containing porifera spicules (F1), Intraclastic packstones (F6) and Tabular stromatolites (F10) in which deposition and diagenesis were entirely subaqueous; b) a palustrine setting (palustrine limestone facies association) containing Microbial Mudstones (F2), Intraclastic sandy packstone with ostracode remains (F3), Oncolitic packstone (F5), Brecciated limestone (F7) and Nodular-Mottled limestone (F8) representing shallow marginal areas affected by groundwater fluctuations and minor subaerial exposure; and c) a pedogenic paleoenvironment (pedogenic limestone facies association) including Intraclastic limestone (F4) and Packstones containing Microcodium (F9) facies displaying the major features of subaerial exposure, pedogenic diagenesis and the development of paleosols. The fluvial–palustrine–lacustrine succession shows a general shallow upward trend in which contraction–expansion cycles are represented (delimited by exposure and surface erosion). The variations in the successive formations reflect the responses to fluctuations in a combination of two major controls, the tectonic and local climatic variables. The predominance of the palustrine facies associations was determined by its accommodation space as well as the local climate conditions. The variations in the lacustrine limestone facies associations reflect differential patterns of subsidence within the sub-basin. The diagnostic features of the palustrine limestone facies associations (organic matter (OM) content, microinvertebrate fauna, abundant mud cracks, brecciation, presence of evaporitic minerals) frame the sub-basin in a climatic context intermediate between arid and subhumid conditions.

Upper Cretaceous paleogeography of the Central Southern Pyrenean Basins (Catalonia, Spain) from microfacies analysis and charophyte biostratigraphy

The most extensive latest Cretaceous deposits of the Pyrenees are non-marine facies traditionally called “Garumnian”, which represent the first continentalization of the Pyrenean Foreland Basins. The age and paleogeography of the basal Garumnian facies in the different parts of the Pyrenean Basin has been a matter of debate. Charophyte biostratigraphy and microfacies analysis suggest that the continentalization was diachronous in the Central Southern Pyrenean basins, i.e., between the Ager and Tremp basins, and the emersion progressed from south to north. In the Ager Basin, to the south, the first Upper Cretaceous non-marine rocks are represented by the La Macana Formation. This unit is mainly formed by freshwater lacustrine limestones organized into hundreds of shallowing-upwards sequences ranging from deeper lacustrine facies, through marginal, well-illuminated environments dominated by characean meadows, and finishing with lakeshores dominated by clavatoracean meadows. The charophyte assemblage from the La Macana Fm is mainly formed by Peckichara cancellata, P. sertulata, Microchara cristata, M. parazensis, Platychara caudata, and Clavator brachycerus, which belong to the Peckichara cancellata charophyte biozone (Late Campanian). In contrast, in the Tremp Basin, located to the north, the beginning of the non-marine sedimentation is organized into a few cycles of the well-known La Posa Fm. These cycles begin with brackish deposits formed by thick marls with euryhaline molluscs at the base, followed by lignite and brackish to freshwater limestones. The brackish facies are dominated by porocharaceans. The charophyte assemblage of the La Posa Formation is formed by Feistiella malladae, Peckichara sertulata, Microchara cristata, and Clavator brachycerus, which belong to the Septorella ultima charophyte biozone (Early Maastrichtian).

Le karst de Casteljaloux (Lot-et-Garonne). Rôle du processus de fantômisation dans la genèse des grottes épikarstiques et du fonctionnement hydrologique

The underground karst of Casteljaloux (Lot-et-Garonne, France) : role of ghost-rock processes on epikarstic cave evolution and hydrological functioning of the springs. The karst of Casteljaloux is located on the left bank of the Garonne river , 80 km southeast of Bordeaux (70-150 m a.s.l.). The epikarstic caves develop a few meters below the surface in Miocene lacustrine limestones of Lower and Upper Aquitanian. The southern part is covered by a quarternary eolian sandy formation (Sables des Landes) covering the Tertiary. The ghost-rock process in limestone was observed in sections of quarries, roads and in caves. In the quarry of Trouyre, there are false galleries showing an evolution with weathered rock, brown clay injection on top and into the altered rock, compaction of the sediments, inwash of quartz gravels (paleo-terrace of Garonne), and finally recent deposits (charcoal). In the subhorizontal cave of Saint-Julien, 3 m below the topographic surface, there is an alteration of the Aquitanian limestone and the marly limestone forming the ceiling, resulting in densely packed sodastraws. The petrographic analysis confirms thaqt porosity is due to alteration. The hydrochemical regime of springs is very specific. The concentration of calcium and bicarbonate increases with flow rate (concentrative effect), opposite to classical karst. This hydrochemical response indicates a very porous karst, directly related to the strong alteration of Aquitanian limestone and the sandy cover which enhances retarded recharge in water.

Cascading carbonate lakes of the Mayran Basin system, northeast Mexico: The interplay of inherited structural geometry, bedrock lithology, and climate

Research Article| May 01, 2012 Cascading carbonate lakes of the Mayrán Basin system, northeast México: The interplay of inherited structural geometry, bedrock lithology, and climate Natalia Amezcua; Natalia Amezcua * 1Basin Studies and Petroleum Geoscience, University of Manchester, Manchester M13 9PL, UK *Present address: Mexican Geological Survey, Avenida España 1331, C.P. 44190, Guadalajara, Jalisco, México; e-mail: namezcua@sgm.gob.mx Search for other works by this author on: GSW Google Scholar Robert Gawthorpe; Robert Gawthorpe 2Department of Earth Science, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway Search for other works by this author on: GSW Google Scholar Joe MacQuaker Joe MacQuaker 3Department of Earth Sciences, Memorial University, St. John's, A1B 3X5 Newfoundland, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Natalia Amezcua * 1Basin Studies and Petroleum Geoscience, University of Manchester, Manchester M13 9PL, UK Robert Gawthorpe 2Department of Earth Science, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway Joe MacQuaker 3Department of Earth Sciences, Memorial University, St. John's, A1B 3X5 Newfoundland, Canada *Present address: Mexican Geological Survey, Avenida España 1331, C.P. 44190, Guadalajara, Jalisco, México; e-mail: namezcua@sgm.gob.mx Publisher: Geological Society of America Received: 31 Aug 2010 Revision Received: 09 Apr 2011 Accepted: 14 Apr 2011 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2012 Geological Society of America GSA Bulletin (2012) 124 (5-6): 975–988. https://doi.org/10.1130/B30403.1 Article history Received: 31 Aug 2010 Revision Received: 09 Apr 2011 Accepted: 14 Apr 2011 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Natalia Amezcua, Robert Gawthorpe, Joe MacQuaker; Cascading carbonate lakes of the Mayrán Basin system, northeast México: The interplay of inherited structural geometry, bedrock lithology, and climate. GSA Bulletin 2012;; 124 (5-6): 975–988. doi: https://doi.org/10.1130/B30403.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We investigated the Mayrán Formation (late Neogene), exposed in northeast México, to determine the ways in which antecedenttopography, climate, sediment input, bedrock geology, and primary production controlled facies architectures in this lacustrine-dominated succession. The succession was deposited in four, broadly coeval lake subbasins (Mayrán Basin system) developed at different elevations. The subbasins are separated by Cretaceous bedrock ridges and infilled by differing proportions of siliciclastic and carbonate deposits. Adjacent subbasins are connected by spillover points. To investigate how these factors controlled overall facies architectures, we generated a structural and stratigraphic framework for each subbasin. In the most proximal subbasin (I), alluvial sediments consisting of nonchannelized and channelized conglomerates, pebblysandstones, and calcareous sandy and siliciclastic mudstones change laterally into horizontally bedded lacustrine limestones, calcareous mudstones, and evaporites. Vertically, these lithofacies are organized into shallowing-upward cycles. The more distal subbasins (II–IV) are predominantly filled by lacustrine limestones. Striking aggradational and progradational tufa topsets and clinoforms are present at the spillover points (waterfalls) between subbasins. These tufas interfinger up- and downdip with the lacustrine limestones.The distribution of clastic facies was mainly controlled by their proximity to the major sediment input in the south, and to the Cretaceous bedrock ridges. Primary production within each subbasin was controlled by a combination of lake level, accommodation availability, and solute inputs. Overall, while autogenic processes likely controlled facies distribution within the basin, climate was the overall driver of large-scale facies variability. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geologic and hydrogeologic factors affecting sinkhole (obruk) development in Central Turkey

Konya region is located near Tuzgolu (salt lake) in the center of Turkey. The surface of the study area which is between Cumra-Karapinar and Aksaray-Sultanhani-Obruk plains in the Konya region is 2,100 km2. Obruk landforms are concentrated in a 100 km2 section of the study area which contains approximately 50 obruks. The climate is typically continental and annual average precipitation varies between 314.2 mm/year in Sultanhani, 298.4 mm/year in Karapinar, and 333 mm/year in Besagil. Evaporation value is 1,444 mm/year. In the study area, agricultural activities are carried out on 5,115 ha of land, which is irrigated from the 109 wells drilled and operated by several soil-water cooperatives. The static water levels in the wells vary between 75–91 m. Even though Karapinar and Sultanhani plains are closed basins, there is groundwater connection between them. Since the groundwater flow in this area is canalized between some lithological and tectonic barriers, the underground formations are eroded by groundwater flow moving between the limestone. Over time, dissolution occurs within the limestone formations and they eventually collapse. Generally speaking, circular obruks are formed in horizontal layers and oval ones are observed in layers with inclination. Some obruks reach the groundwater table. The main composition in the study area is, from the oldest to the youngest, Paleozoic schist–fillit–quartzite–crystallized limestone and Mesozoic ophiolites, Cenozoic limestone with pebble, marl, clay, calcite, silica, dolomites and tufa, marl layers with gypsum and salt, lacustrine limestone with tufa layers and andesite near the volcanites, sediments of clay, sand, pebble, and silt of Plioquaternary and basalt flows. Samples collected from all of the sampling stations were analyzed and hydrochemical graphs were prepared. According to hydrochemical evaluations, pH is between 7.1 and 8.2, EC is between 840 and 1,965 μmho/cm, and hardness varies between 40 and 81 FS°, and the water is classified as C3 S1 category according to US Salinity Laboratory interpretations. With respect to irrigation water criteria, the water is of good quality, but not good as drinking water. In the study, the effects of dissolved CO2 in groundwater on karstification were also investigated. Water from wells drilled at Yarimca, Acikkuyu, and Badirik plains contains large amounts of CO2. As is commonly known, those waters which contain CO2 more than 50 mg/l are considered to be corrosive and can cause dissolution of limestone. Through the preparation of topographical elevation maps of the groundwater, water level maps were drawn and the flow direction of groundwater, recharge area of groundwater, groundwater hydraulic balance and level fluctuations of the groundwater, as well as the locations of possible exploitation sites were determined.

DMP XV: Palaeohydrology and Palaeoenvironment: Initial Results and Report of 2010 and 2011 Fieldwork

AbstractThis paper reports the results of fieldwork conducted in the 2010 and 2011 DMP field seasons and of analysis of samples collected during these and previous years. Research has involved 1) studying palaeolake sediment outcrops, 2) using ground penetrating radar (GPR) to determine their extent under the Dahān Ubārī, and 3) coring palaeolakes in order to determine their palaeoenvironmental records. Research on these samples is continuing but some initial findings are discussed in this paper. The most extensive palaeolake sediments are found within the al-Mahruqah Formation and were deposited by a giant lake system that developed in the Fazzān Basin during past humid periods. Stratigraphic analysis of Lake Megafazzān sediments suggests two different sedimentary successions, a lake margin succession distinctive for its lacustrine and palaeosol carbonates, and a clastic-dominated, intensely rootleted, basin-centre succession which has terrestrial intervals (aeolian and palaeosols) as well as in the upper parts lacustrine limestones. Both basin margin and basin centre successions are underlain by fluvial deposits. Magnetostratigraphy suggests that the formation may be as old as the mid-Pliocene. After the Lake Megafazzān phase, smaller palaeolakes developed within the basin during subsequent humid periods. One of the largest is found in the Wādī al-Hayāt in the area between Jarma and Ubārī. Similar deposits further west along the Wādī at progressively higher altitudes are interpreted as small lakes and marshes fed by springs issuing from aquifers at the base of the escarpment, last replenished during the Holocene humid phase. Dating of sediments suggests that this was betweenc. 11 andc. 8 ka. The Wādī ash-Shāţī palaeolake core also provides a Holocene palaeoclimate record that paints a slightly different picture, indicating lake conditions until around 7 ka, whereupon it started oscillating until around 5.5 ka when sedimentation terminates. The reasons for the differences in these records are discussed.

Sedimentology, diagenesis and ichnology of Cretaceous and Palaeogene calcretes and palustrine carbonates from Uruguay

The Cretaceous (Mercedes Formation) and Paleogene (Queguay Formation) deposits cropping out in W and S Uruguay comprise two terrestrial limestone units that are very rich in trace fossils. The study of these units permits to propose a sedimentological model for palustrine limestones and calcretes in which the distribution of different types of trace fossils is considered. The study units include three main types of deposit: lacustrine limestones, palustrine limestones and calcretes. The lacustrine limestones are relatively homogeneous and contain gastropods, charophytes and ostracods, but no trace fossils. They were deposited in a relatively more perennial lacustrine environment. The palustrine limestones include four different facies: desiccated mudstones, nodular limestones, granular limestones and gravel-sheets. The desiccated mudstones indicate a lesser degree of pedogenic modification and the granular limestones a higher degree. The gravel-sheets are an indication of the reworking of previous limestones deposits during low lakewater levels. Most of the palustrine limestones (except the gravel sheets) contain the same bioclasts as the lacustrine limestones plus a variety of trace fossils such as Rebuffoichnus sciuttoi, Fictovichnus gobiensis and different ichnospecies of Celliforma. The calcretes are either massive (groundwater) or laminar. The massive calcretes are sandy limestones made up of a carbonate matrix and cements. The laminar calcretes (root mats), which contain alveolar septal structures, occur as centimetre-thick layers and can be seen in all types of deposit. They contain the same trace fossil association as the palustrine limestones; the massive calcretes are poorer in such fossils. The distribution of trace fossils in these environments is under strong facies control and provides good evidence of subaerial exposure and semi-arid climates. All the limestones are partially replaced and cemented by opal and quartz, but in all cases the primary structure is preserved. Silicification occurred under groundwater meteoric conditions. Overall, the limestones facies (calcretes, palustrine and lacustrine) and their lateral distribution likely reflect the existence of wetland environments in semiarid to sub-humid climates. These climatic conditions were interrupted by a period of increased precipitations, probably the Early Eocene Climatic Optimum.

Criteria for recognition of localization and timing of multiple events of hydrothermal alteration in sandstones illustrated by petrographic, fluid inclusion, and isotopic analysis of the Tera Group, Northern Spain

Stratigraphic relations, detailed petrography, microthermometry of fluid inclusions, and fine-scale isotopic analysis of diagenetic phases indicate a complex thermal history in Tithonian fluvial sandstones and lacustrine limestones of the Tera Group (North Spain). Two different thermal events have been recognized and characterized, which are likely associated with hydrothermal events that affected the Cameros Basin during the mid-Cretaceous and the Eocene. Multiple stages of quartz cementation were identified using scanning electron microscope cathodoluminescence on sandstones and fracture fills. Primary fluid inclusions reveal homogenization temperatures (Th) from 195 to 350°C in the quartz cements of extensional fracture fillings. The high variability of Th data in each particular fluid inclusion assemblage is related to natural reequilibration of the fluid inclusions, probably due to Cretaceous hydrothermal metamorphism. Some secondary fluid inclusion assemblages show very consistent data (Th = 281–305°C) and are considered not to have reequilibrated. They are likely related to an Eocene hydrothermal event or to a retrograde stage of the Cretaceous hydrothermalism. This approach shows how multiple thermal events can be discriminated. A very steep thermal gradient of 97–214°C/km can be deduced from δ18O values of ferroan calcites (δ18O −14.2/−11.8‰ V-PDB) that postdate quartz cements in fracture fillings. Furthermore, illite crystallinity data (anchizone–epizone boundary) are out of equilibrium with high fluid inclusion Th. These observations are consistent with heat-flux related to short-lived events of hydrothermal alteration focused by permeability contrasts, rather than to regional heat-flux associated with dynamo-thermal metamorphism. These results illustrate how thermal data from fracture systems can yield thermal histories markedly different from host-rock values, a finding indicative of hydrothermal fluid flow.

Natural and induced sinkholes of the Obruk Plateau and Karapınar-Hotamış Plain, Turkey

The number of sinkholes (locally known as obruks) has increased rapidly in recent years near Karapınar, located in the semi-arid Konya Closed Basin in Central Anatolia. Nineteen sinkholes have formed in the last 33 years (1977–2009) as a result of the collapse of cavity roofs in the Neogene lacustrine limestone in the Obruk Plateau and beneath Quaternary lake sediments in the Karapınar-Hotamış Plain. Of these, 13 have formed within the past 4 years (2006–2009). The Obruk Plateau takes its name from the presence of several hundred paleo-sinkholes which formed as a result of natural processes during the Quaternary period. More recently, human activity has induced the formation of new sinkholes, which presents a hazard to life and property. Changing agricultural patterns have led to the opening of thousands of deep wells in recent years, and increased water pumping currently exceeds the sustainable yield of the aquifer. Thus the formation of sinkholes has been triggered by a combination of natural and human causes. The groundwater level has dropped almost 24 m in the vicinity of Karapınar during the last 26 years (1983–2008). Approximately 8 m of this drop occurred within the 4 years prior to the study (2005–2008). Legally-binding precautions must be taken to prevent further water table decline, in order to decrease sinkhole formation within the basin in the years to come.

A reconstruction of the fossil palm Sabalites longirhachis (Unger) J. Kvaček et Herman from the Maastrichtian of Pyrenees

Fragmented leaf laminas were the only organ known of the fossil palms Sabalites longirhachis (Unger) J. Kvaček et Herman. Recently, isolated leaves of S. longirhachis, palm logs and rooting systems have been found associated in Fumanya, a new Maastrichtian locality from the Southern Pyrenees. This has allowed proposing a taphonomy-based hypothesis of the habit and paleoecology of these extinct palms. Fossil leaves are represented by complete laminas bearing petioles attached. Leaves and logs are parautochthonous at the base of the first coal seam of the stratigraphic succession. Rooting systems provide evidence for autochthony in coal layers formed at the top of lacustrine limestones. The tree bearing S. longirhachis leaves is reconstructed as relatively slender, of up to 14 m high, showing a smooth trunk with adventitious roots at the base and a crown keeping the marcescent leaves attached. The rooting system consisted of straight radial rootlets of about 1.5 m in total diameter. Taphonomic and facies analyses carried out in Fumanya suggest that the habitats colonized by this species were small peat mires at the lakeshores of freshwater alkaline lakes.