Search

Records of element ratios obtained from the Maldives Inner Sea sediments provide a detailed view on how the Indian Monsoon System has varied at high-resolution time scales. Here, we present new records from IODP Site U1471 based on a refined chronology through the past 550,000 years. The record's high resolution and a proper approach to set the chronology allowed us to reconstruct changes in the Indian Monsoon System on a scale of anomalies and to verify their relationships with established records from the East Asian Monsoon System. On the basis of Fe/sum and Fe/Si records, it can be demonstrated that the Asia continental aridity tracks sea-level changes, while the intensity of winter monsoon winds responds to changes in Northern hemisphere summer insolation. Furthermore, the anomalies of continental aridity and intensity of winter monsoon winds at millennial-scale events exhibits power in the precession band, nearly in anti-phase with Northern hemisphere summer insolation. These observations indicate that the insolation drove the anomalies in the Indian Summer Monsoon. The good correspondence between our record and the East Asian monsoon anomaly records suggests the occurrence of anomalous widespread arid events in Asia.

Selective dolomitization of HMC allochems in Neogene carbonates is a common phenomenon. It has been proposed that the higher magnesium concentrations [Mg] in these allochems promotes dolomitization. To directly investigate the effects of [Mg] (reported as mol% MgCO3) in biogenic HMC on dolomitization, high-temperature (200 °C) dolomitization experiments were conducted. Dolomite reaction rate, stoichiometry, and microstructures were tracked during dolomitization for a variety of biogenic HMC reactants, including Goniolithon, Lithothamnion, Lithophyllum, Corallina officinalis, Heterocentrotus mamillatus, and Mellita quinquiesperforata. Solids were characterized using standard powdered X-ray diffraction (XRD) and scanning electron microscopy (SEM). In general, biogenic HMC reactants are progressively replaced by protodolomite products between 2 and 46 hours. In the experiment using Corallina officinalis, no products were detected by XRD after 46 hours. Initial protodolomite products are subsequently replaced by ordered dolomite as the reactions proceed. Dolomitization rate and protodolomite stoichiometry do not correlate with [Mg] of the biogenic HMC reactants. Dolomitized HMC skeletons reliably retain the original microstructure of the HMC reactants, consistent with the microcrystalline mimetic textures observed in nature. These findings collectively suggest that under the conditions investigated, dolomitization is less affected by the concentration of magnesium in the HMC reactants relative to other known factors, such as temperature, reactant mineralogy, organic content, skeletal texture, and fluid chemistry. These results imply that the observed correlation between coralline red algae abundance and global dolomitization events in the Neogene is not driven by the elevated magnesium concentration of the HMC reactants.

The continuous rise in hydrocarbon demand, the production decline in conventional oilfields, and the remarkable improvement in extraction methods have allowed the hydrocarbon industry and subsequently, geoscientists, to turn to studies on both unconventional and mature fields with untapped potential. In such reservoirs, the application of advanced drilling, completion, and production techniques must be preceded by the identification of permeable stratigraphic intervals that favour commercial exploitation. Accordingly, bioturbated deposits can play a key role in providing permeable pathways for enhanced production. Herein, we analyse the effects of bioturbation on the porosity and permeability of the Buda Formation, a highly bioturbated, tight (low-porosity matrix) Upper Cretaceous chalk reservoir from the Texas Gulf Coast Basin, which has been commercially exploited because of the occurrence of natural fractures. Our results show that (in addition to the natural fractures) burrows (and borings) substantially increased the porosity and permeability of this formation, thus, potentially contributing to enhanced hydrocarbon (or groundwater) storage and production. These biogenic structures might also have favoured the development of natural fractures and stylolites in the Buda Formation. However, further studies are required to prove this hypothesis.

Selective dolomitization, where certain carbonate components are preferentially dolomitized over others, can be significant in the overall dynamic context of the global magnesium cycle. Thus, the abundance of these components can modify the Mg balance between the ocean and sediments, thereby disrupting the Mg cycle in certain geological times. Selective dolomitization may be connected to the apparent correlation between global dolomitization events in the Neogene and the synchronous rise in species abundance of coralline red algae (CRA), but the underlying issue remains unclear. In the Caribbean islands, excellent examples of Neogene partially dolomitized carbonates containing coralline red algal facies are described to understand selective dolomitization of different components (grains and matrix) by examining the well-preserved outcrop of partially dolomitized Mio–Pliocene carbonates at the Seru Grandi locality on Bonaire Island, in the Caribbean. The degree and timing of selective dolomitization of various carbonate components are assessed using petrographical and geochemical methods. The micrite matrix is dolomitized first, followed by coralline red algal bioclasts, and subsequently all other grains. Dolomite crystals appear to originate from within and immediately around coralline algal fragments, suggesting that dolomite could have initiated from internally sourced Mg of the CRA’s high-magnesium calcite skeleton. Collectively, these observations suggest that selective dolomitization is controlled primarily by reactive surface area of the carbonate components, but it is less clear as to whether there is a dependency on original mineralogy.

The Neogene carbonate succession on the island of Bonaire (Netherland Antilles) shows complex geometries associated with a sequence of depositional and erosional events which reflects the history of this isolated platform and the interaction between eustasy and tectonics. Three major episodes of carbonate platform deposition are defined which show contrasting depositional styles: 1) aggradational platform (Lower-Middle Miocene) with sediments showing a fining-upward trend from mixed coral rudstone to medium-grained coralgal grain/packstone, partly dolomitized and tilted by tectonic deformation; 2) progradational platform (Upper Miocene-Pliocene) which is formed of several shallowing-upward prograding units mainly composed of reworked red algal grain/packstone, with significant dolomitization, passing upward to shoreline and aeolian deposits formed of cor-algal grain/packstone and large benthic foraminifera grainstone, and 3) flat-topped platform (Pleistocene) with a reefal framework composed of a rich variety of corals in a bioclastic pack/wackestone matrix. These platform episodes exhibit contrasting stacking patterns and are separated by erosional unconformities. Overprinting this depositional succession is a series of Quaternary near-horizontal shoreline erosional terraces and vertical cliffs which have been cut into the island stratigraphy and complicate the stratal field relationships. However, this terrace morphology clearly does not represent depositional episodes, as has been suggested before. The internal architecture of each of the three carbonate platform reflects of the dynamics of sedimentation with allogenic controls. The latter relate to major oceanographic and tectonic events in the region, including changing ocean circulation as a result of the closure of the Panama isthmus, and Caribbean plate dynamics that affected sea-floor and island topography. The Bonaire succession provides a model for understanding and predicting isolated carbonate platform development, as well as architecture, facies and potential diagenetic changes, in an active tectonic setting.

Carbonate clinoforms are often challenging to characterize and model due to their complex geometries and additional heterogeneity introduced by diagenetic processes. Dolomitization can influence petrophysical properties resulting in either an increase or reduction in porosity and permeability of the host rock and forms geobodies of varied shapes depending on pre-dolomitization permeability patterns and dolomitization mechanism. Therefore, in partially or fully dolomitized successions, the prediction of fluid flow behavior is not trivial. This study uses a well-studied outcrop analogue of Mio-Pliocene partially dolomitized clinoforms at Seru Grandi (Bonaire) to better understand fluid flow in different dolomitization scenarios. Clinothems consist of heterogeneous coralline algal facies overlying bioclastic facies, with dolomite geobodies truncated on their upper and lower bounds by clinoform surfaces. Digital outcrop models were used to characterize geometry and spatial relationship of facies and heterogeneity, such as clinoform dip, length, height, and spacing. Multiple realizations of clinoform and dolomite body geometries are modelled using a surface-based modelling (SBM) approach coupled with an unstructured mesh flow simulator (IC-FERST). Two scenarios are considered, in which dolomitization has resulted in either a decrease in porosity and permeability as observed in outcrop, or a relative increase of porosity and permeability values as a potential subsurface scenario. Flow simulation results reveal an exponential relationship between water breakthrough times and flow rates versus dolomite proportions. Additionally, the arrangement of the dolomite bodies (aligned vs. disjoined) exhibits very similar fluid flow behavior across a wide range of dolomite proportions. Sensitivity of flow behavior to the geological models is strongly dependent on dolomite permeability relative to precursor limestone. Dolomite body arrangement is more important for flow behavior at high dolomite proportions for low permeability dolomite, or at low dolomite proportions for high permeability dolomite. This study emphasizes the significance of having a good understanding of the dolomitization mechanism and dolomite body geometries, reducing uncertainty in dolomite distribution, petrophysical properties, and, therefore, fluid flow behavior.

The Cenomanian Buda Limestone is a widespread coccolith-rich carbonate unit deposited on the Comanche Shelf of the Texas Gulf Coast Basin. This formation is a key stratigraphic marker, and its hydrocarbon resources have been exploited since the 1920s. Despite its stratigraphic and economic importance, the depositional environments, and controls on the stratigraphic architecture of the Buda Limestone remain poorly understood. Here, based on the integration of high-resolution sedimentology, mineralogy and stratigraphy, the west Texas Buda Limestone is interpreted to be deposited in inner-neritic waters (likely

We report a study of the magnetic stratigraphy and the anisotropy of isothermal remanent magnetization of Pliocene sediments from International Ocean Discovery Program (IODP) Site U1467 drilled in the Maldives platform (Indian Ocean) during Exp. 359. Magnetic stratigraphy gives a precise record of geomagnetic reversals of the early Pliocene from approximately 5.3 Ma to 3.1 Ma providing a detailed age model in an interval where the biostratigraphic record is scarce. We use the anisotropy of isothermal remanent magnetization (AIRM) to investigate the statistical orientation of fine magnetic particles and provide data on the strength and direction of bottom currents during the early Pliocene. The strength of bottom currents recorded by the AIRM, shows a prominent increase at the top of Chron C3n.1n (about 4.2 Ma), and the current direction (NE - SW) is consistent with that of modern instrumental measurements. Since bottom currents in the Maldives are driven by the monsoon, we speculate that the 4.2 Ma increase of bottom currents could mark the onset of the present-day setting, probably related to the coeval uplift phase of the Himalayan plateau. IODP-Italia University of Urbino (DiSPeA)

This paper reports on the newly discovered occurrence of thick sequences (similar to 100 m) of Late Oligocene and Early Miocene (similar to 24.9 to similar to 20 Ma) interbedded organic-rich sediments (sapropels) and pelagic (organic poor) carbonates at Sites 01466 and U1468 drilled in the Maldives archipelago during the International Ocean Discovery Program (IODP) Expedition 359. This occurrence is unusual in that this sequence is located > 1000 m above the surrounding ocean floor within an inter-atoll basin and not linked to any known global oceanic events. Total organic content reaches as high as 35% in the darker layers, while the interbedded carbonates have concentrations of less than 0.1%. Trace elements characteristic of anoxic waters, such as Mo, V, Cr, U, and Pb, correlate positively with concentrations of organic carbon. Nitrogen isotopic data show no evidence that the intervals of high total organic carbon are related to enhanced productivity driven by upwelling. Instead, high organic carbon is associated with intervals of anoxia. We propose that sea-level fluctuations linked to changes in Antarctic ice volume restricted exchange with the open ocean causing bottom waters of the inter-atoll basin to become anoxic periodically. The architecture of the platform at the end of the Oligocene, combined with the global sea-level highstand, set the stage for orbitally-driven sea-level changes producing cyclic deposition of sapropels. The proposed mechanism may serve as an analogue for other occurrences of organic carbon rich sediments within carbonate platform settings. (C) 2019 Elsevier B.V. All rights reserved. Portuguese National Science and Technology Foundation [SFRH/BPD/96960/2013, UID/Multi/04326/2013] Natural History Museum, London UKIODP [NE/N014049/1] NERCNERC Natural Environment Research Council [3148] IODP U.S. Science Support Program [NSF OCE1450528] Comparative Sedimentology Laboratory JAMSTEC IODP After Cruise Research Program (Exp. 359)

In the original version of this article (Kunkelova et al. 2018), published on 18 December 2018, there was 1 error in the author name of Dr. Yu.

Tem uma correção em http://hdl.handle.net/10400.1/12390 Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth’s orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ18O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition. SFRH/BPD/96960/2013; PTDC/MAR-PRO/3396/2014 info:eu-repo/semantics/publishedVersion

Neogene dolomites are common in island settings, and they have been used to understand the complex processes of dolomitization. The island of Bonaire was one of the first locations where the concept of reflux dolomitization was applied. Given this historical significance, here we re-evaluate the importance and nature of reflux using a previously unstudied set of outcrops in Bonaire. Mio-Pliocene units in Seru Grandi in northwestern Bonaire show well-defined bodies of dolomite that extend along clinoform surfaces beneath a subhorizontal erosional unconformity. The dolomite distribution suggests early dolomitization as a result of fluids moving downwards through a succession of subtidal facies, as expected from the reflux model. However, non-stoichiometric compositions, weak 18O enrichment, low trace element concentrations and the sedimentological context of the dolomites suggest that refluxing fluid was more likely to be mesohaline in composition rather than hypersaline as previously proposed. In addition, our findings suggest that the fluids did not dolomitize the succession uniformly, but rather elongate bodies of dolomite were developed within selected clinoforms through different events. This variability may be due to temporal changes in the flux, chemistry of reactive fluids and textural changes of original sediment, whereas downdip trends may reflect evolution of magnesium exchange efficiency with distance from the brine source and reactivity of the rock.

Sedimentary rocks tend to progressively lose porosity with depth due to mechanical and chemical compaction. In carbonates, this trend is hard to predict since many factors can create porosity in the burial setting. The Oligocene-Miocene Perla Limestone, a giant gas reservoir located in the Gulf of Venezuela Basin, shows a complex porosity system marked by a strong diagenetic control. Despite exhaustive depositional facies modelling carried out in the carbonate reservoir, inconsistencies remained when distributing petrophysical properties with depositional facies. These inconsistencies become more important in areas strongly affected by intense diagenetic processes. After the initial investigation, burial dissolution was identified as the main diagenetic process affecting porosity in this succession. To understand the origin of the burial dissolution process and its distribution along the reservoir, detailed petrographic, mineralogical and isotopic studies were carried out on recovered cores from different exploration wells. Results show a series of diagenetic features which were associated with the evolution of the strata including burial dissolution, dolomitization and compaction as the main processes. After testing several hypotheses, the results support an inorganic-CO2 model as responsible for the burial dissolution process in the Perla Limestone. According to this model, deep-burial dissolution created pervasive microporosity, with subordinated moldic and vuggy pores that enhanced the reservoir quality in localized areas of the carbonate succession. These features are located where the ascent of hydrothermal CO2-rich fluids funneled by discontinuity surfaces (faults, fractures, stylolites, etc.) reached the Perla Limestone.

Based on high-resolution reflection seismic and core data from IODP Expedition 359 we present a new channel-related drift type attached to a carbonate platform slope, which we termed delta drift. Like a river delta, it is comprised of several stacked lobes and connected to a point source. The delta drifts were deposited at the exit of two gateways that connect the Inner Sea of the Maldives carbonate platform with the open ocean. The channels served as conduits focusing and accelerating the water flow; Entrained material was deposited at their mouth where the flows relaxed. The lobe-shaped calcareous sediment drifts must have formed under persistent water through flow. Sediment supply was relatively high and continuous, resulting in an average sedimentation rate of 17 cm ka−1. The two delta drifts occupy 342 and 384 km2, respectively; with a depositional relief of approximately 500 m. They have a sigmoidal clinoform reflection pattern with a particular convex upward bending of the foresets. In the Maldives the drift onset marks the transition from a sea-level controlled to a progressively current dominated depositional regime. This major event occurred in the Serravallian about 13 Ma ago, leading to the partial drowning of the carbonate platform and the creation of shallow seaways. The initial bank-enclosed topography resembles an “empty bucket” geometry which is rapidly filled by the drift sediments that aggrade and prograde into the basin. Thereby the depositional environment of the delta drifts changes from deep water (>500) to shallow-water conditions at their topsets, indicated by the overall coarsening upward trend in grain size and the presence of shallow water large benthic foraminifers at their top.

International Ocean Discovery Program (IODP) Expedition 359 cored sediments from eight borehole locations in the carbonate platform of the Maldives in the Indian Ocean. The expedition set out to unravel the timing of Neogene climate changes, in particular the evolution of the South Asian monsoon and fluctuations of the sea level. The timing of these changes are assessed by dating resultant sedimentary alterations that mark stratigraphic turning points in the Neogene Maldives platform system. The first four turning points during the early and middle Miocene are related to sea-level changes. These are reliably recorded in the stratigraphy of the carbonate sequences in which sequence boundaries provide the ages of the sea-level lowstand. Phases of aggradational platform growth give precise age brackets of long-term sea-level high stands during the early Miocene and the early to middle Miocene Climate Optimum that is dated here between 17 to 15.1 Ma. The subsequent middle Miocene cooling coincident with the eastern Antarctic ice sheet expansion resulted in a long-term lowering of sea level that is reflected by a progradational platform growth. The change in platform architecture from aggradation to progradation marks this turning point at 15.1 Ma.& para;& para;An abrupt change in sedimentation pattern is recognized across the entire archipelago at a sequence boundary dated as 12.9-13 Ma. At this turning point, the platform sedimentation switched to a current-controlled mode when the monsoon-wind-driven circulation started in the Indian Ocean. The similar age of the onset of drift deposition from monsoon-wind-driven circulation across the entire archipelago indicates an abrupt onset of monsoon winds in the Indian Ocean. Ten unconformities dissect the drift sequences, attesting changes in current strength or direction that are likely caused by the combined product of changes in the monsoon-wind intensity and sea level fluctuations in the last 13 Ma. A major shift in the drift packages is dated with 3.8 Ma that coincides with the end of stepwise platform drowning and a reduction of the oxygen minimum zone in the Inner Sea.& para;& para;The strata of the Maldives platform provides a detailed record of the extrinsic controlling factors on carbonate platform growth through time. This potential of carbonate platforms for dating the Neogene climate and current changes has been exploited in other platforms drilled by the Ocean Drilling Program. For example, Great Bahama Bank, the Queensland Plateau, and the platforms on the Marion Plateau show similar histories with sediment architectures driven by sea level in their early history (early to middle Miocene) replaced by current-driven drowning or partial drowning during their later history (Late Miocene). In all three platform systems, the influence of currents on sedimentations is reported between 11 and 13 Ma. German Federal Ministry of Education and Research [03S0405, 03G0236A]; New Zealand institute for Geological and Nuclear Sciences; US National Science Foundation (NSF); Ministry of Earth Sciences (India); European Consortium for Ocean Research Drilling (ECORD); Australian Research Council; Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT); Korea Institute of Geoscience and Mineral Resources; Ministry of Science and Technology (People's Republic of China) info:eu-repo/semantics/publishedVersion

The authors regret the mistake in the drawing of the delta drift architecture in figure 11. The authors would like to apologise for any inconvenience caused. [Figure presented]

The Early Cretaceous Fort Terrett Formation of Mason County, central Texas, is a succession of subtidal to peritidal mud-dominated facies with minor intervals of bioclastic packstone–grainstone, rudist floatstone, and interbedded chert nodules. The strata conformably overlie the Hensel Formation, which was deposited unconformably on Precambrian basement. The Hensel Formation also contains a significant percentage of dolomite, precipitated within a fine-grained clayey matrix. The Hensel and Fort Terrett Formations were deposited during a transgressive episode, which provided the conditions for the extensive shallow-water Comanche carbonate platform. Siliciclastic and carbonate sediments were deposited along the coastal margin in subtidal, intertidal to supratidal areas. Previous dolomitization models have suggested that high permeability layers are required for dolomitizing brines to flow through a carbonate succession. Although, interparticle porosity in muddy tidal-flat successions can be significant, it has a limited flow capacity. However, interconnected fenestral porosity can allow sufficient fluid flow to move dolomitizing fluids more efficiently through the succession. Thus, it is hypothesized that interconnected fenestral porosity could have had a significant impact on permeability within this muddy succession and provided the pathways and conduits for Mg-rich brines. Four types of dolomite are recognized in the Fort Terrett succession. Three of these dolomite types formed largely by replacement and they occur throughout the succession. Features such as crystal size, crystal face geometry and zonation reflect the progressive development and recrystallization of the dolomite types. Only type 4 dolomite formed as a cement in void spaces during a late diagenetic stage. The direction of the dolomitizing fluid movement is difficult to determine, but it was likely downward in this case, controlled by a density-head driving-mechanism generated by dense hypersaline fluids from an evaporating lagoon.

Palmarito strata in the mid-Permian of the Venezuelan Andes show three different types of metre-scale cycle: Type A cycles are mixed clastic-carbonate, shallowing-upward peritidal cycles. The upper boundaries of the cycles are exposure surfaces with calcrete. This kind of cycle shows a significant degree of randomness in its thickness pattern and this is attributed to an autocyclic origin through tidal-flat progradation, and variations in carbonate productivity and clastic input to the depositional area. Type B cycles consist entirely of shallow subtidal facies with a shallowing-upward arrangement and an alternation between heterozoan and photozoan assemblages. Type C cycles were deposited in a middle to outer ramp setting and are characterized by a heterozoan assemblage and shallowing-upward trends that includes spiculitic wackestone–packstone passing up into neomorphic bioclastic wackestone or bioclastic crinoidal–bryozoan wackestone–packstone. All cycles are interpreted as 4th–5th order (104 to 105 years duration) and some can be linked to Milankovitch orbital rhythms, notably short eccentricity (~ 100,000 years). Overall, the origin of the Palmarito cycles was a complex combination of autocyclic and allocyclic controls; however, the evidence suggests that cycles in the lower part of the succession were dominated more by autocyclic processes whereas those in the upper part were more the result of allocyclic controls. Climate-driven processes, such as migration of the intertropical convergence one and the waxing and waning of polar ice-caps, had significant effects on deposition of the Palmarito succession and the cycles therein, controlling the clastic sediment supply, nutrient availability and thus carbonate production, and sea-level change, and these factors determined the vertical stacking pattern of the cycles.

The Late Palaeozoic period was an important time in Earth history, primarily as a result of the formation of Pangea and the Gondwana glaciations that had direct influences in high latitudes and indirect, but no less important, effects in low latitudes. This study documents and interprets the isotopic record for the Early–Middle Permian in northern Gondwana from detailed fieldwork in the Venezuelan Andes. Sr-isotope dating of well-preserved brachiopod shells suggests a Kungurian age from samples located within the middle part of the Palmarito Formation. dC data show a long-term trend through the section towards more positive values, but with some very negative dC values suggesting carbonates affected by pedogenic processes. In the middle part of the succession, major excursions in dC and dO show a strong connection with glacial–deglacial events during the Early–Middle Permian. Overall results presented here fill an important gap in the regional palaeogeography and, therefore, have significant implications for the palaeoclimate and palaeoceanography of this Late Palaeozoic time. The assembly of Pangea during the Permian triggered important geological, oceanographical and climatic events, which had a direct influence on the geological record. Many isotope studies of Permian rocks from the equatorial region of Pangea have been undertaken during the last two decades, primarily focusing on understanding palaeoceanography and palaeoclimate (e.g. Tabor & Montanez 2002; Isbell et al. 2003; Brand 2004; Korte et al. 2006; Montanez et al. 2007; Tabor & Poulsen 2008; Fielding et al. 2008; Peyser & Poulsen 2008). As a result, palaeoclimate models have been developed showing reconstructions of palaeoprecipitation, palaeotemperature and the variation in position of the Intertropical Convergence Zone (ITCZ) during the Permian. However, there is still insufficient information about regions around northern Gondwana, particularly for Central and South America. In northern South America, Upper Palaeozoic strata were deposited extensively over pericratonic areas but in many places they are rarely exposed and so are poorly documented. This is largely the result of extensive weathering and dense vegetation in the tropical Andes, as well as the remoteness of the outcrop areas. However, these strata do have significant information for the palaeogeographical and palaeoclimatic reconstructions, and for the evolution of northern Gondwana, at this critical time in Earth history. The existence of a seaway connecting the Palaeotethys and Panthalassa oceans, which lasted until the late Early Permian, has been suggested by just a few authors (Davydov & Leven 2003; Izart et al. 2003; Vai 2003). This deduction has been based on palaeontological evidence, including Tethyan brachiopod and fusulinid distributions. An east–west seaway across northern Gondwana accounts for the shallow-marine sedimentary succession across western Venezuela during the Permian. These earlier publications have not described the depositional setting of this Venezuelan basin or how it was connected and related to the neighbouring oceans. Figure 1, modified from the map for 280 Ma of Blakey (2007), shows the palaeogeography following the reinterpretations of Laya & Tucker (2012). Permian rocks in Venezuela have previously been described in several studies (Arnold 1966; Garcia 1972; Odreman & Wagner 1979; Bellizia 1992; Viscarret & Laya 2007). The From: Gąsiewicz, A. & Slowakiewicz, M. (eds) Palaeozoic Climate Cycles: Their Evolutionary and Sedimentological Impact. Geological Society, London, Special Publications, 376, http://dx.doi.org/10.1144/SP376.10 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics facies and microfacies of the Palmarito Formation, which crops out throughout the Venezuelan Andes, suggest that there was a seaway connecting central Pangea with basins to the NW, and also a connection to the SW with basins in the Bolivian–Peruvian region (Laya & Tucker 2012). This would have implications for the regional climate in terms of land–sea distribution, supercontinentality, uplift– collapse of the Central Pangean Mountains and the source of moisture. The Palmarito sediments were deposited on a carbonate ramp that dipped basinwards towards the north facing the open ocean. The formation evolved from the underlying fluvial deposits (Sabaneta Formation) through to tidal-flat and to midouter ramp deposits, with all facies recording a well-developed cyclicity. The aims of this study are to present and discuss the stable isotope record in the context of the sedimentology of the Palmarito Formation located in western equatorial Pangea, and to consider these data in terms of climatic and oceanographical regimes in these low latitudes during the Permian. The Permian succession in Venezuela covers a poorly known region between Gondwana and Laurentia, before the final assembly of Pangea. Geological background The Palmarito Formation is part of the Palaeozoic tectonostratigraphical unit in western Venezuela that has been referred to as a supraterrane by Bellizia (1992), with sediments deposited within the Mucuchachi Basin, a name introduced by Arnold (1966). Sedimentation of Permian carbonates seems to have been a widespread phenomenon in NW Venezuela, with likely extensions and correlations through Colombia to the SW, then to Peru and Bolivia farther south, but also northwards to Guatemala, Mexico and to the southern USA (Laya & Tucker 2012). Lithostratigraphy of the Late Palaeozoic in the Venezuelan Andes During the 1950s–1970s, fieldwork and biostratigraphical studies connected with petroleum exploration by Gonzalez De Juana (1951), Pierce et al. (1961), Shell de Venezuela & Creole Petroleum Corporation (1964) and Shagam (1972) resulted in different lithostratigraphical and palaeogeographical interpretations. However, these studies did not provide an accurate chronostratigraphy to establish the age of the strata to the stage level. The Mucuchachi Formation is the oldest unit in the area that has been proposed to date from the Devonian to Lower Pennsylvanian by Gonzalez De Juana (1951), Pierce et al. (1961), Shell de Venezuela & Creole Petroleum Corporation (1964) and Arnold (1966) on the basis of field relationships and regional lithostratigraphical correlations across the area. However, there was no strong biostratigraphical evidence to support this interpretation. Later, Odreman & Useche (1997) proposed that the age is restricted to the Pennsylvanian based on palaeontological evidence. The Mucuchachi Formation consists of slate and fine-grained quartzite that was affected by regional metamorphism, perhaps in the late Pennsylvanian (Laya & Tucker 2012). These rocks form the basement in the region and are overlain by the sedimentary cover of the Sabaneta and Palmarito formations. The Sabaneta Formation (Middle Pennsylvanian) is composed of conglomerates and reddish sandstones with channel structures, and these grade into thinly bedded red mudrocks with palaeosoils of floodplain origin (Arnold 1966; Viscarret 2002). Fig. 1. Mollweide projection for the Early Permian Artinskian stage (280 Ma) modified from Blakey (2007). The red star (black in print version) represents the palaeogeographical location of the Palmarito Formation. J. C. LAYA ET AL.

International Ocean Discovery Program Expedition 359 was designed to address changes in sea level and currents, along with monsoon evolution in the Indian Ocean. Eight drill sites are located in the carbonate edifice of the Republic of Maldives, which bears a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. This tropical marine record is key for better understanding the effects of this global evolution in the Indo-Pacific realm. The bank geometries of the growing carbonate archipelago provide a physical record of changing sea level and ocean currents. The bank growth occurs in pulses of aggradation and progradation that are controlled by sea level fluctuations during the early and middle Miocene, including the mid-Miocene Climate Optimum. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system appears to be directly linked to the evolving Indian monsoon. This phase led to a twofold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and deposition of contourite fans and giant sediment drifts. Expedition 359 cores are intended for reconstructing the changing current system through time that is directly related to the evolution of the Indian monsoon. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives. Expedition 359 had two main focus points. The first was to date precisely the onset of the current system that is potentially in concert with the onset or the intensification of the Indian monsoon and coincides with the onset of the modern current system in the world’s ocean. The second important outcome of Expedition 359 is groundtruthing the hypothesis that the dramatic, pronounced change in style of the sedimentary carbonate sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. These questions were directly addressed by the shipboard scientific data. In addition, Expedition 359 cores will provide a complete Neogene δ13C record of the platform and platform margin sediments and a comparison with pelagic records over the same time period. This comparison will allow assessment of the extent to which platform carbonates record changes in the global carbon cycle and whether changes in the carbon isotopic composition of organic and inorganic components covary and the implications this has on the deep-time record. This determination is important, as such records are the only type that exist in deep time.

The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12.9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system. The German Federal Ministry of Education and Research is thanked for funding the seismic surveys (03S0405, 03G0236A).

Upper Palaeozoic strata in South America were deposited over cratonic areas and in intracratonic basins (e.g. Solimoes, Amazonas, Parana); however in many areas such as Venezuela and Colombia they are rarely exposed through dense vegetation and the nature of the terrain, so that the strata are poorly documented. However, these strata do have significant implications for the palaeogeography of the time. This article reports on a study of the Permian carbonates of the Palmarito Formation, exposed throughout the Venezuelan Andes, and discusses the succession of palaeoenvironments and the palaeogeography resulting from detailed field and lab work. Deposition took place on an extensive ramp which probably dipped gently northwards towards the open ocean. Much of the Palmarito succession shows a general transgressive trend, with a few thinner, more-regressive intervals, likely a response to glaciation–deglaciation cycles. Towards the end of the Permian in the Venezuelan Andes region, a major sea-level fall led to extensive uplift and erosion, resulting in a major disconformity between the Upper Guadalupian carbonates and overlying Jurassic red beds. The early Palmarito tidal-flat facies are noteworthy for their sub-metre-scale mud-to-sand cycles with incipient palaeosoil fabrics. Overlying mid-outer ramp carbonate facies are characterised by thin storm beds and bioclastic lenses, arranged into metre-scale coarsening-upward cycles. Succeeding shallow-marine inner-mid ramp, bioclastic grain–wacke-stones are dominated by an open-marine fauna of fusulinids, calcareous algae, crinoids, bryozoans and brachiopods. Outer-ramp facies are wacke–mud-stones with sponge spicules, radiolarians and brachiopod fragments. There are similarities between the Permian deposits of Venezuela and those recorded from Guatemala and Mexico to the north, and from Colombia and Peru–Bolivia to the west and southwest, where carbonate systems also dominate. These facies were all part of a tropical foreland basin setting, the Mucuchachi Basin, which contrasts with the other Late Palaeozoic intracratonic basins in South America. Evidence provided here demonstrates that a seaway existed between Laurentia and Gondwana from the Early Permian through to the late Early Permian.

We utilize carbonate clumped isotope thermometry to explore the diagenetic and thermal histories of exhumed brachiopods, crinoids, cements, and host rock in the Permian Palmarito Formation, Venezuela, and the Carboniferous Bird Spring Formation, Nevada, USA. Carbonate components in the Palmarito Formation, buried to ∼4 km depth, yield statistically indistinguishable clumped isotope temperatures [ T (Δ47)] ranging from 86 to 122 °C. Clumped isotope temperatures of components in the more deeply buried Bird Spring Formation (>5 km) range from ∼100 to 165 °C and differ by component type, with brachiopods and pore-filling cements yielding the highest T (Δ47) (mean = 153 and 141 °C, respectively) and crinoids and host rock yielding significantly cooler T (Δ47) (mean = 103 and 114 °C). New high-resolution thermal histories are coupled with kinetic models to predict the extent of solid-state C-O bond reordering during burial and exhumation for both sites. Application of these models, termed “THRMs” (thermal history reordering models), suggests that brachiopods in the Palmarito Formation experienced partial bond reordering without complete equilibration of clumped isotopes at maximum burial temperature. In contrast, clumped isotope bonds of brachiopods from the Bird Spring Formation completely equilibrated at maximum burial temperature, and now reflect blocking temperatures achieved during cooling. The 40–50-°C-cooler clumped isotope temperatures measured in Bird Spring Formation crinoids and host rock can be explained by recrystallization and cementation during shallow burial combined with a greater inherent resistance to solid-state reordering than brachiopods.