Root calcrete formation on Quaternary karstic surfaces of Grand Cayman

The rugged karst terrain developed on the dolostones of the Miocene Cayman Formation (Fm) on Grand Cayman includes numerous large cavities that formed through the activity of tree roots. The surfaces of those cavities are coated with laminated calcrete crusts up to 8 cm thick that are formed of an alteration zone, an accretionary zone, and final infill of the cavities. These crusts are formed of various laminae, including dolostone with root traces, alveolar septal structures, peloids, micritic and microsparitic laminae, micrite with bioclasts, and pisoliths. Features such as microborings, spores, needle-fiber calcite and micro-rods are common in all parts of the calcrete crust. Calcrete formation was initiated as the roots and associated microorganisms generated the cavities. Later on trapping and binding processes and organically induced precipitation of carbonate allowed the formation of the accretionary (mostly laminar) part of the calcrete. The last phases of crust formation took place when ponded waters filled the cavities. The calcrete crusts developed on the Cayman Formation dolostones record a very specific setting for calcrete formation and constitute a good example of non-horizontal calcrete crusts

Timanttiporaukset Kaukovainion monitoimitalossa

Opinnäytetyön aiheena oli timanttiporaukset ja sahaukset Kaukovainion monitoimitalossa. Tavoitteena oli kuvata ja havainnollistaa timanttiporausta sekä timanttisahausta ensin teoreettisesti ja sitten käytännön kannalta. Opinnäytetyön teoriaosuudessa käydään läpi erilaiset työmenetelmät sekä työturvallisuus. Käytännön osiossa käydään läpi timanttiporauksen ja -sahauksen työsisältö sekä tehtävän suoritus ja kuvaus. Pääpainotteisesti tutustutaan työmaalla esiintyneisiin ongelmiin. Lähtötilanteena oli, että LVIS-reitityksille oli saatava uudet läpiviennit jo olemassa oleviin rakenteisiin. Työmenetelminä käytettiin timanttisahausta sekä timanttiporausta. Suurimmalta osaltaan työt olivat timanttiporausta. Töiden eteneminen tapahtui eri alojen sekä työnjohdon yhteistyöllä. Työn vaiheet olivat tiivistettynä merkkaus, poraus, tarkastus ja läpiviennin asennus. Olennaisimmat tulokset ja johtopäätökset kohdistuivat työmaalla esiintyneisiin ongelmiin. Niihin saatiin vastauksia sekä ratkaisuja työn edetessä. Merkittävin ongelma oli suunnitelmien puutteellisuus tai niiden puuttuminen. Ratkaisuksi löytyi eri alojen suunnittelijoiden yhteistyön lisääminen ja parantaminen. Muita tärkeitä ja myös hoidettavissa olevia ongelmia olivat tekniset ongelmat sekä hankinnalliset ongelmat. Niiden ratkaisuksi löytyi ammattitaidon lisääminen ja kehittäminen sekä riittävän työmaatekniikan saatavuuden turvaaminen

Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin

The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors onsedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonicallyactive arca, soils were weakly developed in aggrading alluvial fans, dominated by mass flows. reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed: the former were associated with Mg-poor fan sediments whitc: the latter formed on Mg-rich lake clays exposed during minar lake lowstands. The nonh-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream Aood deposits, sourced by carbonate terrains. Floodplain and freshwater lakc deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential developmenl on calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quatemary fans. Which are characterized by climatically induced periods of stability and instability

Root calcrete formation on Quaternary karstic surfaces of Grand Cayman

The rugged karst terrain developed on the dolostones of the Miocene Cayman Formation (Fm) on Grand Cayman includes numerous large cavities that formed through the activity of tree roots. The surfaces of those cavities are coated with laminated calcrete crusts up to 8 cm thick that are formed of an alteration zone, an accretionary zone, and final infill of the cavities. These crusts are formed of various laminae, including dolostone with root traces, alveolar septal structures, peloids, micritic and microsparitic laminae, micrite with bioclasts, and pisoliths. Features such as microborings, spores, needle-fiber calcite and micro-rods are common in all parts of the calcrete crust. Calcrete formation was initiated as the roots and associated microorganisms generated the cavities. Later on trapping and binding processes and organically induced precipitation of carbonate allowed the formation of the accretionary (mostly laminar) part of the calcrete. The last phases of crust formation took place when ponded waters filled the cavities. The calcrete crusts developed on the Cayman Formation dolostones record a very specific setting for calcrete formation and constitute a good example of non-horizontal calcrete crusts

Diagenesis of a drapery speleothem from Castañar Cave: from dissolution to dolomitization

A drapery speleothem (DRA-1) from Castañar Cave in Spain was subjected to a detailed petrographical study in order to identify its primary and diagenetic features. The drapery’s present day characteristics are the result of the combined effects of the primary and diagenetic processes that DRA-1 underwent. Its primary minerals are calcite, aragonite and huntite. Calcite is the main constituent of the speleothem, whereas aragonite forms as frostwork over the calcite. Huntite is the main mineral of moonmilk which covers the tips of aragonite. These primary minerals have undergone a set of diagenetic processes, which include: 1) partial dissolution or corrosion that produces the formation of powdery matt-white coatings on the surface of the speleothem. These are seen under the microscope as dark and highly porous microcrystalline aggregates; 2) total dissolution produces pores of few cm2 in size; 3) calcitization and dolomitization of aragonite result in the thickening and lost of shine of the aragonite fibres. Microscopically, calcitization is seen as rhombohedral crystals which cover and replace aragonite forming mosaics that preserve relics of aragonite precursor. Dolomitization results in the formation of microcrystalline rounded aggregates over aragonite fibres. These aggregates are formed by dolomite crystals of around 1 μm size. The sequence of diagenetic processes follows two main pathways. Pathway 1 is driven by the increase of saturation degree and Mg/Ca ratio of the karstic waters and is visible in the NW side of the drapery. This sequence of processes includes: 1) aragonite and huntite primary precipitation and 2) dolomitization. Pathway 2 is driven by a decrease in the degree of saturation of calcite and aragonite and Mg/Ca ratio of the cave waters, and it is observed in the SE side of the drapery. The diagenetic processes of the second pathway include: 1) calcitization of aragonite; 2) incomplete dissolution (micritization) of both aragonite and calcite; 3) total dissolution. This study highlights the importance of diagenetic processes on speleothems and their complexity. The correct interpretation of these processes is crucial for the understanding of possible changes in the chemistry of waters, temperature, or pCO2 and so is critical to the correct interpretation of the paleoenvironmental significance of speleothems

Reply to the comment on “Mudflat/distal fan and shallow lake sedimentation (upper Vallesian–Turolian) in the Tianshui Basin, Central China: Evidence against the late Miocene eolian loess” by A.M. Alonso-Zarza, Z. Zhao, C.H. Song, J.J. Li, J. Zhang, A. Martín-Pérez, R. Martín-García, X.X. Wang, Y. Zhang and M.H. Zhang

Guo's et al. comments on our paper (Z.T. Guo, J.Y, Ge, G.Q. Xiao, Q.Z. Hao, H.B. Wu, T. Zhan, L. Liu, L. Qin, F.M. Zeng, B.Y. Yuan, Comment on “Mudflat/distal fan and shallow lake sedimentation (upper Vallesian–Turolian) in the Tianshui Basin, Central China: Evidence against the late Miocene eolian loess” by A.M. Alonso-Zarza, Z. Zhao, C.H. Song, J.J. Li, J. Zhang, A. Martín-Pérez, R. Martín-García, X.X. Wang, Y. Zhang and M.H. Zhang [Sedimentary Geology 222 (2009) 42–51], Sedimentary Geology, 2010-this issue) mostly stress their previous data and their model of configuration and evolution of the study area; it is not a real discussion of the sedimentological features we describe. In this reply we will discuss some of the key features of the basin configuration, correlations and sedimentology of the Tinshui basin. Our work has followed the common procedures used in stratigraphy and sedimentology and so we can confirm our interpretation on basin configuration and correlations. In all cases we have taken into account previous papers, including those of Guo's group. In addition the sedimentological model we proposed is new due to the lack of previous sedimentological studies, including facies analysis and petrography, in the studied area. Our model of a continental alluvial-lacustrine basin fits well with other well-known examples over the world and explains clearly the lateral facies transitions across the basin. It is not the aim of this reply to discuss all the previous papers by Guo's group, but to reply to their main comments on our paper. © 201

Caracteristicas petrograficas y datacion U/Th de una calcreta laminar quaternaria: implicaciones de la captura de la cuenca de Guadix-Baza por el rio Guadalquivir

The Guadix topographic depression is a Neogene-Quaternary basin located in the central sector of the Betic Cordillera at the boundary between the South Iberian margin and the Alboran domain. This topographic depression is a plateau with an average elevation of 1000 m in the northern limb of the Sierra Nevada range. The continental deposits infilling the Guadix basin span time from the late Tortonian to the Pleistocene, when a laminar calcrete developed on fine to coarse-grained fluvial and lacustrine deposits. Four coeval subsamples from the top laminae of the calcrete were collected and dated by the U/Th method. The resulting date is 42.6 ± 5.6 ka, which indicates the minimum age for the cessation of active sedimentation in the Guadix basin. We envisage the capture of the Pliocene-Pleistocene endorheic Guadix basin by the Guadalquivir River after 42 ka as the main factor triggering the formation of the present-day eroded landscape. After the capture, the combination of climatic (wet periods), lithological (soft and loose sediments), and topographic (high average altitude) features allowed the development of the present-day entrenched drainage patter

Mudflat/distal fan and shallow lake sedimentation (upper Vallesian–Turolian) in the Tianshui Basin, Central China: Evidence against the late Miocene eolian loess

The Tianshui Basin in central China contains a thick sedimentary sequence (~1400 m) of continental deposits, Aragonian to Villafranchian (Miocene-Pliocene) in age. Intense Himalayan movements around the Paleogene/Miocene boundary triggered the uplift of mountain ranges around the Tianshui Basin, providing the deposition site for continental sediments. The sedimentary infill of the basin consists of four stratigraphic units (I to IV). This paper focuses on Unit II. Most of the accommodation space was occupied by Unit I, so during the sedimentation of Unit II, the morphology of the basin was relatively flat, promoting the development of wide distal fan/mudflat areas and wide shallow lakes. Deposits include: red mudstones, pedogenic and groundwater calcretes, reworked calcrete deposits, sheet-floods, fluvial channels, rippled sandstones/siltstones, ooidal/peloidal packstones, palustrine limestones, bioturbated marls and intraclastic limestones/marls. The characteristics and organization of the deposits indicate the gradual transition from alluvial to lake environments. Within the distal fan/mudflat, the deposition of reworked calcrete clasts as one of the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and red clays. At the lake margins, the presence of ooids and palustrine limestones suggests the possibility of ramplike margins within different energy settings. The origin of some of the deposits of the basin's QA-I section is under discussion, and their consideration as eolian has been recently proposed. However, we believe this possibility is precluded by the characteristics of the deposits. Our proposal has important implications for revising the interpretation of Miocene paleoclimatic conditions in central Asia