Pluvial Climate Research Articles

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.

Effect of Drought and Pluvial Climates on the Production and Stability of Different Types of Peanut Cultivars in Guangdong, China

The production and breeding of peanuts was restricted by the frequently extreme climatic conditions in Guangdong province, China. To understand the influence of drought and pluvial climates on peanut traits and yield, a phenotypic investigation of seventy peanut cultivars was conducted from 2018 to 2022; comprehensive field meteorological data collection, and typical drought (2021) and pluvial (2022) climates were recorded. The results revealed that the cultivars achieved the highest single plant pod weight (SPPW) and single plant seed weight (SPSW) of 61.03 g and 45.84 g, respectively, in drought conditions, followed by the control, and finally the pluvial. The SPPW, SPSW and eight agronomy traits exhibited significant differences across the different climatic conditions. Correlation analysis revealed the yield traits and key yield-related traits were positively or negatively correlated with soil water content (SWC), total global radiation (TGR), total precipitation (TP) and total net radiation (TNR). The intermediate and Spanish type cultivars were more stable and productive than the other botanical types of cultivars, commercial varieties exhibited better performance than landraces, and seven cultivars were identified with good production potential, under drought and pluvial conditions. Our study showed that pluvial climate was detrimental to peanut yield, and the SPPW and SPSW were significantly influenced by climates with genotype differences.

The Carboniferous Langness Conglomerate Formation, Isle of Man; an alluvial fan rift-phase deposit

Re-examination of the Langness Conglomerate Formation (LCF) on the coast near Dreswick Harbour, Isle of Man, has established that it is over 65 m thick, twice previous estimates. It formed as a small stream-dominated fan deposit during syndepositional faulting which controlled thickness and facies variations. The sub-Carboniferous surface shows considerable relief, perhaps as much as 10 m and is intricately brecciated and channelled just beneath the base of the conglomerate indicating a pluvial climate even prior to deposition of the LCF. Palaeocurrent data shows that sediment was derived from the NNW. Low in the LCF the sediment is all local in origin, but more exotic material is present higher up. The succession matures texturally (sorting and rounding improve) and mineralogically (lithic sand decreases) upwards and the succession fines upwards. The finer, upper part onlaps northwards across the older Manx Group extending for over 4 km inland thinning to 8 metres. This is consistent with the view that the Isle of Man formed a regional high during the Lower Carboniferous. The LCF resulted from the initial fault movements that led to inundation of the Isle of Man High in the late Chadian to early Arundian.

Exposed columns in the Valles Caldera ignimbrites as records of hydrothermal cooling, Jemez Mountains, New Mexico, USA

Columnar structures have been exposed by preferential weathering in non-welded, non-vapor-phase-altered zones of the 1.2 to 1.8 Ma Bandelier Tuff ignimbrites around Valles Caldera, New Mexico. These long, largely vertical cylindrical features are similar in composition and texture to the host ignimbrite but represent areas that underwent alteration to make them more resistant to erosion. Analyses show that the column ignimbrite was altered by the addition of the zeolite mordenite as a mineral cement into pore spaces. This, and the presence of illite and, to a lesser extent, chlorite, suggests alteration at ~120–125°C. We map column geometry, spacing, stratigraphic location, and spatial distribution. Columns are mostly vertical, there is a correlation between the diameters and spacing, and they exist in linear to rounded clusters of a few to 30 columns. Based on the location within the ignimbrites, the shape and form of column groups, and the temperature of formation of the columns, we propose that slumping of over-steepened valley walls exposed friable, warm, unaltered ignimbrite that enabled ponded meteoritic water to permeate into the deposit, which allowed localized convective chimney cells to form. We develop an analytical model to show that infiltrating water is convectively unstable, and, for reasonable permeabilities, we can explain the observed column spacing and alteration temperature. This model permits columns to form within parts of the deposits perched in ignimbrite deposited against pre-existing valley walls. An abundant supply of water from high precipitation is implied, reflecting a syn-glacial, pluvial climate in the southwestern United States at that time (1–2 Ma ago).

Groundwater recharge timing based on 14C and 2H within Indian Wells Valley, California, USA

A large carbon-14 dataset for groundwater in Indian Wells Valley, California, is used to identify groundwater recharged during the pluvial climate of the previous glacial period, more than 12,000 years before present. Additional data collected in 2019, including measurements of 13C and 14C in the recharge areas and dissolved organic carbon isotopes, substantiated the unusually heavy-isotope-enriched 13C and relatively low 14C compositions in the Sierra Nevada canyons on the northwestern margin of the basin. The carbon isotopic characteristics in this area may be due to aeolian deposits of sodium carbonate minerals from dried lake beds along the ancient Owens River, or dissolution of metasediments within the Sierra Nevada batholith, or geothermally sourced CO2 gas, or a combination of these. Recognizing these isotope characteristics is essential for correcting apparent 14C groundwater ages. Additional complications arise from sulfate reduction and related conversion of 14C-dead sedimentary organic material to dissolved inorganic carbon with a light 13C composition. The lacustrine deposits of pluvial China Lake and organic-rich spring deposits along the Sierra Nevada range front offer reducing environments across much of the valley. A similarly large 2H dataset provides an independent marker for recharge in a previous climate, facilitated by exhaustive regional studies of 2H content of precipitation, springs, and groundwater (Smith et al., 2002). The 14C data support an association of δ2H values less than −100‰ with pluvial-climate groundwater and δ2H values greater than −96‰ with groundwater recharged under current climatic conditions. Groundwaters with δ2H between these values cannot be assigned with certainty to either group. Evaporation is also evident for a small set of groundwater samples, rendering 2H unreliable as a climate indicator for them. Using 14C and 2H in combination, much of Indian Wells Valley is found to contain groundwater consistent with recharge during current climatic conditions, with ages generally less than 6000 years. Groundwater with pluvial characteristics occurs primarily in the far end of the flow system, in the eastern part of the valley near the evapotranspiration discharge area. The footprint of this older water is more extensive in the deeper parts of the flow system and the vertical distribution of ages indicates it moves upward from the deeper parts of the flow system to the shallow zone to discharge. Estimates of groundwater travel time from a numerical flow model of the basin are generally consistent with the isotopic interpretations.

Regional view of a Trans-African Drainage System

Despite the arid to hyperarid climate of the Great Sahara of North Africa, pluvial climates dominated the region. Radar data shed some light on the postulated Trans-African Drainage System and its relationship to active and inactive tributaries of the Nile basin. Interpretations of recent elevation data confirm a source of the river water from the Red Sea highlands did not connect the Atlantic Ocean across Tushka basin, highlands of Uwinate and Darfur, and Chad basin, but northward to the ancestral Nile Delta. Elements of topography and climate were considered. They show that the former segments of the Nile closely mirror present-day tributaries of the Nile basin in drainage geometry, landscape, and climate. A rainfall data interpolation scenario revealed that this basin received concurrent runoff from both flanks such as Gabgaba-Allaqi to the east and Tushka basin to the west, similar to present-day Sobat and White Nile tributaries, respectively. Overall the western tributaries such as those of Tushka basin and Howar lead to the Nile, which was (and still is) the biggest river system in Africa.

The role of climate in the accumulation of lithium-rich brine in the Central Andes

Lithium-rich brine within the sub-surface of the Salar del Hombre Muerto (SHM) salt pan in the Andes of northwestern Argentina has a chemical and isotopic composition which is consistent with Li derived from several sources: the modern halite saturated lagoon, Li-rich salts and brines formed recently, and dissolution of halite which precipitated from ancient saline lakes. SHM lies in the closed basin that includes part of the massive Cerro Galán caldera which is drained by the Río los Patos, which is responsible for 90% of surface runoff into the salar. The low Li isotope composition, +3.4‰, of this river is consistent with significant contributions of geothermal spring water. As water drains through the volcaniclastic deposits which cover a large proportion of the basin, Li removal, as indicated by decreasing Li/Na, occurs but without significant isotope fractionation. This indicates a mechanism of surface sorption onto smectite or ferrihydrite rather than Li incorporation into octahedral structural sites of clays. These observations suggest that conditions in this high altitude desert have limited the dilution of hydrothermal spring water as well as the formation of clay minerals, which jointly have allowed the Li resource to accumulate rapidly. Changes in climate on a multi-millennial time scale, specifically in the hydrologic budget, have resulted in solute accumulation rates that have been variable through time, and decoupled Li and Na fluxes. Inflow to the salar under modern conditions has high Li/Na (7.9×10−3 by wt) with δ7Li indistinguishable from basement rocks (−0.3‰ to +6.4‰), while under pluvial climate conditions the Li/Na of the saline lake was 40 times lower than the modern lagoon (0.1–0.3×10−3 compared to 10.6–13.4×10−3) with slightly higher δ7Li, +6.9‰ to +12.3‰, reflecting the uptake of 6Li into secondary minerals which formed under a wetter climate.

Spatially variable sedimentary responses to orbitally driven pluvial climate during Marine Oxygen Isotope Stage 5.1, Dakhla Oasis region, Egypt

Pleistocene basinal sediments (PBS) in the Dakhla region of Egypt's hyperarid Western Desert comprise four facies: (A) fluvio-lacustrine, (B) mixed lacustrine/pluvio-eolian, (C) pluvio-eolian, and (D) mixed eolian/pluvio-eolian. Contiguity of basins containing each facies, and their stratigraphic position between two bajada gravel formations, P/B-II and P/B-III, confirm their equivalence. Facies A and B, with lacustrine components, are attributed to orbitally forced poleward incursion of the Intertropical Convergence Zone (ITCZ), resulting in increased summer insolation/temperature/precipitation. Facies C and D, comprising pluvio-eolian and eolian sediments, reflect geologic/topographic influences overprinted on regional 'pluvial' conditions, eliminating lacustrine response. A Th/U age of ∼ 62 ka on lacustrine marl within Facies B is minimal, and an OSL age of 110 ± 18 ka on sediments immediately below Facies B is maximal. Since bajada gravels P/B-III are the youngest Pleistocene formation, they must represent the final strong incursion of the ITCZ into the Dakhla region at MIS 5.1, ∼ 80 ka. Because PBS Facies A pass rapidly up into P/B-III bajada gravels, PBS are assigned to the rising limb of the MIS 5.1 insolation/temperature/precipitation curve, slightly younger than 80 ka.

Erosional modification and gully formation at Meteor Crater, Arizona: Insights into crater degradation processes on Mars

Hydrogeological modification of Meteor Crater produced a spectacular set of gullies throughout the interior wall in response to rainwater precipitation, snow melting, and possible groundwater discharge. The crater wall has an exceptionally well-developed centripetal drainage pattern consisting of individual alcoves, channels, and fans. Some of the gullies originate from the rim crest and others from the middle crater wall where a lithologic transition occurs; broad gullies occur along the crater corner radial faults. Deeply incised alcoves are well developed on the soft Coconino Sandstone exposed on the middle crater wall, beneath overlying dolomite. In general, the gully locations are along crater wall radial fractures and faults, which are favorable locales of erosion due to preferential rock breakup from faulting, and groundwater flow/discharge; these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow, causing erosion and crater degradation. Channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor. Caves exposed on the lower crater level point to percolation of surface runoff and selective discharge through fractures on the crater wall. In addition, lake sediments on the crater floor provide significant evidence of a past pluvial climate, when the water table was higher, and groundwater may have seeped from springs on the crater wall. Although these hydrological processes continue at Meteor Crater today, conditions at the crater are much more arid than they were soon after impact, reflecting a climatic shift. This climate shift and the hydrological modifications observed at Meteor Crater provide insights for landscape sculpturing on Mars during various parts of its history.

The Middle Carnian Wet Intermezzo of the Stuttgart Formation (Schilfsandstein), Germanic Basin

The Middle Carnian Wet Intermezzo (MCWI) of the Stuttgart Formation (Schilfsandstein) and age-equivalent strata of the northwestern Tethys occurred entirely within equivalents of the upper subzone of the Austrotrachyceras austriacum ammonoid zone of the late Julian. Its duration is estimated to be only about 0.7–0.8 myr. In both the Germanic Basin and the northwestern Tethys, the warm climate during the MCWI was characterized by a rate of precipitation that exceeded somewhat the evaporation but was not so great as to be pluvial. The MCWI was related to the atmospheric circulation of a megamonsoonal system that was characterized by strong, moisture-laden, northwesterly flowing trade winds that rose as they reached the estimated 2000–3000 m high eastern shoulder uplift of a huge rift causing them to drop an extraordinary amount of rain. This eastern shoulder uplift lay within the Caledonides of modern day western Scandinavia. This region only, between 30 and 50°N palaeolatitude, had a truly pluvial climate, and the huge amounts of fresh water dropped there transported large amounts of siliciclastics from this rift-shoulder uplift southward into the Germanic Basin. Before deposition of the siliciclastics an early Julian eustatic sea-level fall caused widespread erosion in the Germanic Basin. In the later part of late Julian, a transgression from the eastern gates with the concurrent strong fresh water influx from the north flooded the centre of the northern Germanic Basin with a shallow brackish sea in which the Osterhagen Horizon (Basisschichten) of the lower Stuttgart Formation was deposited. In the upper Osterhagen Horizon the salinity rapidly decreased from mesohaline through mio- and oligohaline to fresh water levels. In southern Germany the Basisschichten formed entirely within fresh water or very low salinity brackish environments . Later, a slight subsidence of the southwestern Germanic Basin shifted the main outflow of fresh water toward the southwestern end of the basin, creating local brackish conditions in the northern marginal part of the northwestern Tethys (e.g. in the Lunz Beds). During this time interval, tidal influence also can be found in the Stuttgart Formation deposited in palaeoestuaries of the southwestern Germanic Basin adjacent to the Tethys. The very strong fresh water influx from the north, however, prevented these estuaries from developing a strongly elevated salt content, so that only fresh water to oligohaline brackish faunas are found there such as the Eberstadt bivalve–conchostracan fauna. At the base of the Tuvalian, the megamonsoonal system either disintegrated or else the trade winds shifted their principal flow direction. This caused the climate within the Germanic Basin and in the nearby northwestern Tethys Sea to become arid again as it had been before the deposition of the Stuttgart Formation. These changes in the atmospheric circulation patterns also terminated the pluvial climatic regime to the north along the Scandinavian eastern rift-shoulder uplift. This in turn ended the transport of huge amounts of siliciclastics from this region southward into the Germanic Basin and ended the deposition of the Schilfsandstein. After this, the hypersaline sabkha and playa sedimentation of the Weser Formation began, which was accompanied by some minor marine ingressions in the southwestern Germanic Basin.

Modern and palaeogeographic trends in the salinisation of the Western Australian Wheatbelt

The Western Australian Wheatbelt has been essentially geologically stable since the late Permian although the Archaean basement sustained some movement during the break-up of Gondwanaland and the northward drift of Australia from Antarctica. During the Early Cretaceous, Eocene and more recently, the Wheatbelt region?s weathered mantle has been eroded by rivers. The palaeo-valleys have been infilled with terrestrial and marine sediments, and been subject to ongoing deep weathering. During the Pliocene and Quaternary the region experienced alternating arid and pluvial climates. These cyclic episodes shaped the regolith and impacted on vegetation species and catchment water balances and also promoted the accumulation of massive volumes of salt. In more recent times, this stored salt has interacted with vegetation, soils, surface waterbodies and groundwater systems and left a distinctive and pervasive legacy in the landscape. Salinisation was manifest in the Wheatbelt of WA from as long ago as 2.8 Ma, concentrating in valley floors as arid and pluvial cycles prevailed and whilst the continent migrated northwards. Today, as agricultural development has altered the water balance on 20 M ha of cleared farmland, salinity is again on the move, further degrading the 300,000 ha of variably saline land that existed before the arrival of Europeans, and spreading across an additional 1.1 M ha of formerly non-saline land. Unchecked by reduced rainfall or human induced changes to the water balance, salinity may expand even further, potentially affecting 1.7-3.4 M ha of the Wheatbelt?s agricultural land and its unique and indigenous resources. This paper reviews the palaeogeography and palaeoclimates of the region and its hydrogeology and examines the nature of its susceptibility to salinisation. It poses questions about the relationship between palaeo-salinity and contemporary salinity, seeking geomorphic evidence to determine whether salinity is likely to expand beyond extant palaeo-salinity markers. Finally, it considers the likely timeframes involved in the recovery of systems from primary salinity and whether clearing-induced salinity will follow patterns similar to those observed from past saline episodes in the region.

Holocene Depositional History of the Burdekin River Delta of Northeastern Australia: A Model for a Low-Accommodation, Highstand Delta

Abstract The Burdekin River of northeastern Australia has constructed a substantial delta during the Holocene (delta plain area 1260 km2). The vertical succession through this delta comprises (1) a basal, coarse-grained transgressive lag overlying a continental omission surface, overlain by (2) a mud interval deposited as the coastal region was inundated by the postglacially rising sea, in turn overlain by (3) a generally sharp-based sand unit deposited principally in channel and mouth-bar environments with lesser volumes of floodplain and coastal facies. The Holocene Burdekin Delta was constructed as a series of at least thirteen discrete delta lobes, formed as the river avulsed. Each lobe consists of a composite sand body typically 5–8 m thick. The oldest lobes, formed during the latter stages of the postglacial sea-level rise (10–5.5 kyr BP), are larger than those formed during the highstand (5.5–3 kyr BP), which are in turn larger than those formed during the most recent slight sea-level lowering and stillstand (3–0 kyr BP). Radiocarbon ages and other stratigraphic data indicate that inter-avulsion period has decreased through time coincident with the decrease in delta lobe area. The primary control on Holocene delta architecture appears to have been a change from a pluvial climate known to characterize the region 12–4 kyr BP to the present drier, ENSO-dominated climate. In addition to decreasing the sediment supply via lower rates of chemical weathering, this change may have contributed to the shorter avulsion period by facilitating extreme variability of discharge. More frequent avulsion may also have been facilitated by the lengthening of the delta-plain channels as the system prograded seaward.

Extraction of Martian valley networks from digital topography

We have developed a novel method for delineating valley networks on Mars. The valleys are inferred from digital topography by an autonomous computer algorithm as drainage networks, instead of being manually mapped from images. Individual drainage basins are precisely defined and reconstructed to restore flow continuity disrupted by craters. Drainage networks are extracted from their underlying basins using the contributing area threshold method. We demonstrate that such drainage networks coincide with mapped valley networks verifying that valley networks are indeed drainage systems. Our procedure is capable of delineating and analyzing valley networks with unparalleled speed and consistency. We have applied this method to 28 Noachian locations on Mars exhibiting prominent valley networks. All extracted networks have a planar morphology similar to that of terrestrial river networks. They are characterized by a drainage density of ∼0.1 km−1, low in comparison to the drainage density of terrestrial river networks. Slopes of “streams” in Martian valley networks decrease downstream at a slower rate than slopes of streams in terrestrial river networks. This analysis, based on a sizable data set of valley networks, reveals that although valley networks have some features pointing to their origin by precipitation‐fed runoff erosion, their quantitative characteristics suggest that precipitation intensity and/or longevity of past pluvial climate were inadequate to develop mature drainage basins on Mars.

Constraints on Pleistocene pluvial climates through stable-isotope analysis of fossil-spring tufas and associated gastropods, Kharga Oasis, Egypt

Stable-isotope analyses of fossil-spring carbonates (tufas) and freshwater gastropods ( Melanoides tuberculata) from the currently hyperarid Western Desert of Egypt indicate that this region received enough precipitation to support a small perennial lake during the height of the oxygen-isotope stage 6/5e pluvial event, and a substantial volume of spring discharge during prior pluvial phases. Tufa and gastropod oxygen-isotope ratios are generally low relative to modern precipitation in the region, confirming that the majority of Pleistocene pluvial precipitation came from an Atlantic source, as determined by previous workers. Mean tufa δ 13C (−2‰ PDB) suggests a significant proportion of C4 vegetation in the recharge area of the tufa-depositing springs, while the paucity of tufas with δ 13C greater than 0‰ suggests that equilibrium between spring water and atmospheric CO 2 represented an endpoint for the evolution of spring water carbon. Though spring carbonate deposition requires a substantial increase in humidity in central Egypt relative to modern conditions, high variation in tufa δ 18O (up to 4‰ within individual stratigraphic units), as well as positive covariance between tufa carbon- and oxygen-isotope ratios, reflect significant effects of evaporation on spring water during tufa formation. Similarity in δ 18O and δ 13C values of tufas from different stratigraphic units indicates that climatic conditions did not vary significantly among pluvial phases recorded by spring-carbonate deposition. The lack of substantial carbonate formation at tufa localities during the Holocene pluvial phase, however, suggests that tufa deposition represents substantially wetter conditions than have existed during Holocene time.

Sequence Stratigraphy in Lacustrine Basins: A Model for Part of the Green River Formation (Eocene), Southwest Uinta Basin, Utah, U.S.A.

ABSTRACT In the middle Green River Formation of central Nine Mile Canyon, Uinta Basin, Utah, several lacustrine-dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence. Maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences. These lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences. Two types of sequence boundary are identified. Type A sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or, rarely, parallel unconformity, and they typically juxtapose amalgamated braided fluvial channel sandstone (late lowstand systems tract) onto the profundal oil shale. They also bound depositional sequences that show a distinct asymmetry, being dominated by transgressive systems tracts 5-80 m thick. Highstand systems tracts are less than 4 m thick and may be removed completely, by erosion on overlying sequence boundaries. Other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type B sequence boundaries. Type A sequence boundaries mark pronounced base-level falls following times when the Uinta Lake had merged with a lake in an adjacent basin to form a much deeper lake. Such merging permitted the establishment of a new threshold at higher elevation following lake-level balancing. Type B sequence boundaries are interpreted as marking base-level falls from a barely merged lake or a lake that had an outflow. Over a 200 m stratigraphic thickness, type A sequence boundaries are more common upsection, indicating that, with time, a pluvial climate became more pronounced or that the adjacent lake was more easily filled. Type A sequence boundaries also become angular rather than parallel unconformities upsection, suggesting increased tilting of the basin margin over time.

Systematic and stratigraphic palynology of Late Jurassic-earliest Cretaceous strata of the Eromanga Basin, Queensland, Australia: Part Two

This second and concluding part of a comprehensive account of the Late Jurassic-earliest Cretaceous palynofloras of the Eromanga Basin includes systematic documentation of the trilete-zonate spores not included in Part One, together with monolete and hilate spores, pollen grains, and a few simple microphytoplankton cysts (which are minor constituents of a few samples). The 62 spore-pollen species described and illustrated herein are variously assignable among 36 genera. The following new species are instituted: Interulobites distogranulatus, Velosporites rugulatus, and Perinopollenites mckellarii. Three previously defined, stratigraphically successive Australian palynozones are recognizable through the interval examined. In ascending stratigraphic order, these are: Murospora florida Oppel Zone (signified mainly by the introductory presence of the eponymous species), middle Callovian to late Oxfordian; Retitriletes watherooensis Oppel Zone (also recognizable principally from the presence of its eponym), late Oxfordian to middle Tithonian; and Ruffordiaspora (Cicatricosisporites) australiensis Interval Zone (from the presence of its eponym), middle Tithonian to basal Valanginian. Notwithstanding some regional differences, the palynofloral sequence in the Upper Jurassic of the Eromanga Basin is very similar to that reported from the palynologically well documented Perth Basin sequence (specifically, Yarragadee Formation) in Western Australia.The Westbourne palynoflora is suggestive of a varied parental vegetation of mainly coniferophytes, pteridosperms (seed ferns), ferns, and bryophytes, as has been inferred previously from coeval palynofloras elsewhere in Australia. A warm, pluvial climate during the Late Jurassic-earliest Cretaceous is implied by the palaeofloristic evidence.

A lithostratigraphic revision and palaeoenvironmental assessment of the Cretaceous System exposed in the onshore Cauvery Basin, southern India

The exposed Cretaceous shelf succession of the Cauvery Basin, southeastern India, has provided a world-class record of mid and Late Cretaceous invertebrates, documented in a substantial literature. However, the lithostratigraphy of the succession has been little studied and previously subject to a range of nomenclature. It is revised here, on the basis of intensive regional mapping, to stabilize the definition and nomenclature of lithostratigraphic units. The Uttattur Group is restricted in outcrop to the Ariyalur district and divided into the Arogypapurum Formation (new; Albian), Dalmiapuram Formation (late Albian), and Karai Formation (late Albian–early Turonian) for which the Odiyam and Kunnam Members are recognized. The Trichinopoly Group follows unconformably and is also restricted in outcrop to the Ariyalur district. It is divided into the Kulakkalnattam Formation (Turonian) and Anaipadi Formation (late Turonian–Coniacian). The Ariyalur Group is more widely distributed. In the Ariyalur district, the Sillikkudi Formation (Santonian–Campanian) and its Kilpaluvari Member, the Kallakurichchi Formation (early Maastrichtian), the Kallamedu Formation (mid and Late Maastrichtian) and the Niniyur Formation (Danian) are recognized. The sequence in the Vriddhachalam area consists of the Parur and Patti formations (Campanian), Mattur Formation (late Campanian–earliest Maastrichtian) and Aladi Formation (Maastrichtian). For the Pondicherry district, the Valudavur and Mettuveli formations (Maastrichtian) and Kasur and Manaveli formations (Paleocene) comprise the succession. The interpreted depositional environments for the succession in the Ariyalur district indicate four eustatic cycles in the mid and Late Cretaceous and earliest Tertiary: late Albian–early Turonian, late Turonian–Santonian, Campanian, Maastrichtian, and Paleocene. Overall the Cauvery Basin sequence is arenaceous and relatively labile in terms of framework grain composition, and contrasts with the pelitic assemblage developed on the west Australian margin from which eastern India separated in the Early Cretaceous (Valanginian). The difference is ascribed to palaeoclimate as controlled by palaeolatitude. For the Late Cretaceous, the Cauvery Basin drifted north on the Indian plate from 40 to 30°S. This zone is inferred to constitute Southern Hemisphere horse latitudes for Late Cretaceous time, characterized by an arid climate, physical weathering and the production of labile sands. By contrast, the west Australian margin of matching tectonic history remained in a high palaeolatitude (>40°S) throughout the Late Cretaceous, experiencing a pluvial climate, the dominance of chemical weathering and the production of clays.

U/Th isotopic study of speleothems from the Wadi Sannur Cavern, Eastern Desert of Egypt

The Wadi Sannur Cavern was discovered in 1991 beneath an “Egyptian alabaster” (travertine) quarry, active since pharaonic times. It is the only extensively speleothem-decorated cavern that has been described in Egypt. Nine small stalagmites, 5–10 cm in diameter, were sectioned and sampled according to coloration bands a few cm thick. Of 32 individual samples several exhibited230Th/234U activity ratios greater than unity, indicative of open-system leaching of uranium, and several others had anomalous234U/238U activity ratios. The modal apparent age of the 17 “dateable” samples is close to 200,000 years, but because of leaching indications must be considered only a maximum age for the time of deposition of secondary carbonates in the cave. Both the initial formation of speleothems and subsequent leaching are consistent with what is known about pluvial climates in the Eastern Desert of Egypt.

Luminescence dating of mojave desert sands

Infra-red stimulated luminescence has been used to date periods of sand deposition in the Mojave Desert, California. Dates from the Cronese Basins, Kelso Dunes and Silver Lake are compared with published IRSL ages to provide evidence for discrete pulses of sand accretion during the late Pleistocene and Holocene, linked to both arid and pluvial climates. A critical factor in aeolian deposition throughout this area is shown to be the availability of sand from existing source areas.

Le désert du Namib central

The middle Namib desert. On both sides of the Kuiseb Valley, the Namib coastal desert, which is less known than the chiloperuvian desert, shows a strong contrast between the southern erg which is made up of three dune systems (barchan, linear and star dunes), the age of which, while increasing eastwards, is regarded as Pleistocene, and a northern reg the coarse débris of which suffer active salt weathering and eolian corrasion. This desert, which could be the oldest in the world, presents a great number of typical processes, formations and forms under a « humid » and non- pluvial climate which is more dependent of the structure of the maritime Trades than of the Benguela cold current.