Humid Climatic Regime Research Articles

Diversity of Micro-algae and Cyanobacteria on Building Facades and Monuments in India

Fifty seven taxa of Cyanobacteria and 15 taxa of Chlorophyta were recorded from the exterior of buildings and rock surfaces of monuments in different regions in India. Four cyanobacteria, e.g. Chroococcidiopsis kashayi, Pseudophormidium indicum, Plectonema puteale and Scytonema geitleri, and the green alga Trentepholia abietina var. tenue occur on the sub-aerial habitats throughout the year. In addition, five other green algae: Chlorococcum infusionum, Scenedesmus arcuatus, Trentepholia aurea, Gloeocystis polydermatica and Printzina effusa, and 18 other cyanobacteria taxa of the genera Chroococcus (5), Asterocapsa (1), Cyanosarcina (2), Gloeocapsa (7), Gloeothece (2) and Scytonema (1) occur on the sub-aerial surfaces enduring extreme temperature and desiccation during summer months of the tropics. During the rainy season, the warm and humid climatic regime coupled with availability of moisture supported an additional ten green algae and 29 cyanobacteria in eight and 17 genera, respectively. The green algal genera Klebsormidium, Stichococcus and Trebouxia, which are dominant in temperate regions, did not occur on the sub-aerial habitats in India, however, species of Gloeocapsa, Chroococcus, Chroococcidiopsis, Phormidium, Leptolyngbya, Nostoc, Scytonema, Chlorella and Trentepholia showed global occurrence in similar habitats.

Late Pleistocene to recent climate change in Córdoba Province, Argentina: Geomorphological evidence

Abstract Repeated episodes of climate change affected the Cordoba Plains during the Late Pleistocene and Holocene. Many of the geomorphologic features of Cordoba Province were developed in response to climatic oscillations, and their development can be correlated to changes in precipitation and hydrologic regimes. Alternating periods marked by dry climate and high evapotranspiration rates were interspersed with more humid intervals, and can be correlated using stratigraphic and geomorphic evidence at the regional level. The initial phase of the Late Pleistocene was characterized by significant loess deposition and the formation of large alluvial fans. These sediments and landforms are representative of a dry climate. The transition to the Late Pleistocene was marked by the initiation of a humid climate regime, giving rise to enhanced fluvial activity and sedimentation, expansion and integration of drainage networks, and development of paludal areas and successions. Pedogenesis occurred in the interbasin areas, involving precipitation of silica and sesquioxides. During Latest Pleistocene–Early Holocene time, coinciding in part with the ‘Last Glacial Maximum’, a dry and cool climate resulted in widespread aeolian sand and loess deposition. The Early to Mid-Holocene was characterized by humid subtropical conditions which became established throughout the region, accompanied by pedogenic development of profiles with prominent Bt horizons, and further modification of drainage networks. During the Mid to Late Holocene, these warm and humid conditions were replaced by a semiarid climate, resulting in widespread aeolian deposition. Wind action formed deflation hollows and dune fields in several areas. The climate reverted to subhumid and temperate conditions during the latter part of the Late Holocene, and small areas of wetlands developed. The Little Ice Age was marked by climatic deterioration, and the deposition of a thin layer of aeolian sediment. The current climate of Cordoba is subhumid and temperate.

Early Carboniferous (Mississippian) Paleosols from Southwest Britain: Influence of Climatic Change on Soil Development

ABSTRACT The Clifton Down Mudstone, a mixed peritidal-fluvial sequence of Arundian (late Osagean-early Meramecian) age from southwest Britain, contains a suite of varied, cumulative paleosols. Temporal changes in soil-type within this paleosol suite provide evidence for a shift in the climatic regime during Arundian times. Calcic Vertisols, in the lower part of the sequence, developed on floodplains and are equated to a seasonally semi-arid climate in which wetter periods induced Vertisol development and promoted leaching. In contrast, a ferric Podzol and thionic Gleysols characterize the upper part of the succession and are associated with a thick fluvial sandstone interval. The ferric Podzol probably developed either in a humid-tropical or temperate climate and indicates that there was a shift to a more humid climatic regime during late Arundian times. Thionic Gleysols with dolocrete horizons represent brackish, hydromorphic marsh soils associated with marine incursions, and overprint earlier paleosols.

Reservoir geology of the Sirikit oilfield, Thailand: lacustrine deltaic sedimentation in a Tertiary intermontane basin

Summary The Sirikit oilfield, situated some 400 km N of Bangkok, Thailand, is a fault-bounded structure within a major half-graben basin, comprising a relatively undeformed eastern sector and a western area characterized by a complex pattern of isolated fault blocks. The 8 km thick basin-fill succession includes alluvial fan-fluvial deposits overlain by the fluvio-deltaic Lan Krabu Formation, which contains two main oil reservoirs. A reservoir geological model has been produced based on cores and wireline log suites from some 45 wells. The geology is characterized by cycles of regressive coarsening-upward sequences, up to 15 m thick, which reflect cyclic progradation of fluvial-dominated deltas into a large relatively shallow lake in a humid tropical climatic regime. The cycles are commonly topped by subaerial flood-plain claystones. Distributary channel sandstones show evidence of stage fluctuation and intermittent abandonment. Individual mouth-bar reservoir sandstones range in thickness from 1 to 5 m and form complex sheet-like bodies of lateral extent up to 20 km 2 . Thus the Sirikit deltas have little inferred geometrical similarity with contemporary bar-finger models postulated for river-dominated lacustrine deltas. The sheet-delta geometry may be due to a combination of high frictional forces related to similar river and lake water densities, shallow lake depth and a large but variable fluvial sediment load. This combination of factors resulted in rapid dumping of sediment, the plugging of channel mouths and subsequent channel bifurcation.

Holocene development of parabolic dunes in the central St. Lawrence Lowland, Québec

Stabilized parabolic dunes in the central St. Lawrence Lowland are oriented NE-SW, in the postulated direction of dune-building winds coming from anticyclonic air circulation induced by the retreating Laurentide Ice Sheet about 10,000 yr ago. The eolian chronology reconstructed from several sections in mixed dune-peatland environments indicates that postglacial plant colonization, characterized by a fortuitous assemblage of arctic-subarctic and boreal elements, preceded dune formation during Champlain Sea regression around 10,000 yr B.P. Confined peatlands and small forests were buried by eolian sands between 10,000 and 7500 yr B.P. under dry and temperate conditions. This eolian episode lasted about 2500 14C yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the Laurentide Ice Sheet over Hudson Bay and peripheral areas. Dune stabilization, through paludification of well-drained eolian sands about 7500 yr B.P., suggests a major shift in climate toward wetter conditions that have been characteristic during most of the Holocene in eastern North America. Minor eolian erosion induced by wildfire was recorded during late Holocene time (about 1250 yr B.P.). Anthropogenic perturbation (logging and agriculture practice) was also responsible for recent very local eolian activity.

Ein Hochdruckphasenübergang in Cordierit

environment probably reflect small-scale oscillations in the rainfall and soil-moisture budget and/or changes in soil type [21]. Thus either during or just after the Arundian stage a climatic change occurred bringing in an essentially humid climatic regime, which continued into the Upper Carboniferous. A problem in recognizing such changes is to separate changes in palaeosol type caused by true climatic from those caused by local geomorphic changes. The absence of petrocalcic horizon bearing palaeosols above the Arundian as well as the occurrence of coal-bearing palaeosols and large-scale palaeokarstic surfaces indicates a significant change in climate. Also during the Arundian there was a fluctuation to a humid climate, lasting several thousand years followed by a lengthy period of aridity. A better idea of the complexity of Lower Carboniferous climates will only be achieved by further studies of palaeosol and palaeokarst distribution, but the Arundian seems to have been a period of significant climatic change, the implications of this for other aspects of geology, particularly palaeobotany are far reaching.

Middle and Upper Ordovician Paleogeography of Region Bordering Transcontinental Arch: ABSTRACT

Following a period of Whiterockian erosion, Middle Ordovician seas transgressed into the North American continental interior, and a diachronous sheet of clastic sediments (St. Peter, McLish, Winnipeg) lapped onto the margins of the Transcontinental arch. The arch served as a major clastic source region during subsequent deposition (especially Decorah). Middle Ordovician clastic sediments adjacent to the Transcontinental arch and in the Williston basin were probably deposited in a humid climatic regime, and carbonate deposition predominated in an arid belt that included Wisconsin, southeastern Iowa, Missouri, and Illinois, where carbonate oolites and evaporites are noted. Clastic source areas on the Transcontinental arch were inundated, as the marine transgression continue , and a continuous sheet of carbonate sediments (Galena, Viola, Red River, Bighorn) spread across most of the continental interior by the close of the Edenian. Migration of North America across latitudinally-related climatic belts brought the Williston basin area into an arid climatic regime by middle-Late Ordovician as evidenced by the deposition of upper Red River evaporites. Widespread carbonate deposition was replaced by Dubuque-Maquoketa and Stony Mountain carbonate-clastic deposition as source regions emerged on the Transcontinental arch and Ozark uplift. The lower Maquoketa is conformable with the underlying Dubuque over most of the eastern Mid-Continent, and the joint occurrence of organic-rich shales and phosphorites is attributed to a low-oxygen, phosphate-rich water mass in the Maquoketa sea. The Ordovician closed with red clastic deposition, intermixed with carbonates and/or ironstones, adjacent to the arch. End_of_Article - Last_Page 805------------

Coorong Model for Penecontemporaneous Dolomite Formation in Middle Proterozoic McArthur Group, Northern Territory, Australia: ABSTRACT

Many types of penecontemporaneous dolomites have been explained in the literature by involving the well-known sabkha model. The various carbonates now precipitating in the ephemeral lakes of the South Australian Coorong Lagoon are the products of a more humid climatic and hydrologic regime. The distribution of carbonate rocks in the Coorong region is largely controlled by the hydrology of the depositional environment. Both primary and early diagenetic mineralogy can be related to regional hydrology as it has varied throughout the Quaternary. Characteristic sedimentary structures (including stromatolites) are formed in specific parts of the Coorong system, and these can be confidently identified in an ancient analogue, the 1,600-m.y.-old Yalco Formation of the McArthur Gro p of Australia. The resemblance between the ancient and modern environments, in terms of both sedimentary structures and mineralogy, is striking. The following conclusions can be drawn from the comparison: 1. All penecontemporaneous dolomites are not necessarily formed in an arid sabkha environment; a significant number may be formed in a more humid environment analogous to that of the Coorong, in which distinct climatic and seasonal factors prevail. 2. The lack of evaporite minerals or evaporitic casts in an ancient dolomite sequence does not mean that concentrated brines were never present. In the modern Coorong system, minor evaporite minerals are precipitated in the dolomite lakes during dry summer months, but are flushed out during winter by a reflux mechanism. End_of_Article - Last_Page 500------------

Mineralogical changes associated with deep weathering of gabbro in Aberdeenshire

AbstractThe distribution, profile morphology and mineralogy of deeply weathered gabbroic rocks in the basic igneous masses of Insch and Bogancloch, Aberdeenshire, have been studied. The saprolite is characterized by granular disintegration and spheroidal weathering with a relatively low degree of secondary mineral development. The upper part of the profile often shows evidence of mass movement and incorporation into overlying drift but below this zone the degree of alteration is generally uniform with depth. Feldspar and hornblende are largely unaffected, except by disintegration, but pyroxenes show varying degrees of weathering from the incipient development of amorphous iron oxides to replacement by reticulate networks or complete pseudomorphs of trioctahedral vermiculite. Biotite weathers to hydrobiotite and vermiculite, giving rise also, under certain conditions, to kaolinite-gibbsite vermiforms. The correspondence between occurrences of deep weathering and coarser textured biotite-bearing rocks can be related to the instability of this mineral. Consideration of the mineralogical changes found and the morphology of the profile of weathering suggest their formation under a warm, humid climatic regime, probably during the mid Tertiary times.