sea level controls sedimentation and environments in coastal caves and sinkholes abstract quaternary climate and sea level research in coastal karst basins caves cenotes sinkholes blueholes etc generally focuses on analyzing isotopes in speleothems or associating cave elevations prior sea level highstands the sediments in coastal karst basins represent an overlooked source of climate and sea level information in the coastal zone but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them in this study we hypothesize that coastal karst basins transition through vadose littoral anchialine and finally into submarine environments during sea level rise because groundwater and sea level oscillate in near synchrony in the coastal zone causing each environment to deposit a unique sedimentary facies to test this hypothesis the stratigraphy in twelve sediment cores from a bermudian underwater cave green bay cave was investigated and temporally constrained with twenty radiocarbon dates the results indicate that we recovered the first succession spanning the entire holocene from an underwater cave 13 ka to present the sediments were characterized with x radiography fossil remains bulk organic matter organic geochemistry 13corg c n and grain size analysis four distinct facies represent the four depositional environments i vadose facies 7 7 ka calcite rafts lithofacies ii littoral facies 7 7 to 7 3 ka calcite rafts and mud lithofacies iii anchialine facies 7 3 to 1 6 ka slackwater and diamict lithofacies and iv submarine facies

characterization of seafloor pockmark seepage of hydrocarbons employing fractal a case study from the western continental margin of india here we apply quantitative technique to describe the seafloor seepages based on the multibeam backscatter and bathymetric investigations to characterize the pockmark morphology the variable seafloor backscatter strength for coarser seafloor sediments are related to the diagenesis derived from biodegraded seepages in this regard box counting method is used to estimate fractal dimension for backscatter imagery data of 398 blocks these blocks are further sub grouped into six classes depending on the spread of pockmark related seepages the study area lies 102 km west off marmagao along the central west coast of india which contains pre dominantly 70 gas charged sediments comparison between the estimated self similar fractals reveals that there is approximately 97 correlation between the box dbox and information dinfo dimensions box dimension derived fractal dimension values suggest that the seepages are more along the fault trace in deeper waters in comparison to sparsely distributed shallow water seepages besides this poor seepage is confined within the smooth to moderately rough seafloor it is established that the high backscatter strength along the upper slope of the pockmark region having higher fractal dimensions reflects multifractal behavior of seepage distribution entire area indicates patchy seepage patterns as supported by estimated fractal values showing intermittent fluctuations which emphasizes non linear behavior estimated self organizing criticality soc parameters for six representative blocks reveal that the nature of pockmark fault trace sediment nature coupled with slumping of pockmark s wall sediment movement due to bottom currents are controlling the dynamic balance in the area seepage system further our study emphasizing the multifractal behavior of seepage blocks clearly depicts the drift in the seepage pattern

palaeomagnetism of devonian ring complexes from the bayuda desert sudan new constraints on the apparent polar wander path for gondwanaland summary the approach of gondwana and or microplates derived from its northern margins towards laurentia and the closure of the intervening palaeo tethys is a controlling factor in the geodynamic evolution of the atlantic bordering continents during the early and mid palaeozoic however the currently available palaeomagnetic data for gondwana especially for the geodynamically critical silurian to devonian interval are still rather sparse and are compatible with a number of palaeogeographic scenarios in order to address this issue 114 samples 18 sites have been collected from a series of high level acidic intrusive rocks rhyolitic lavas and tuffs of mid devonian age 377 5 ma rb sr along the southern escarpment of the gilif hills sudan 17 83 n 32 67 e detailed demagnetization experiments revealed the presence of three directionally distinct components of magnetization labelled a b and c the overall mean direction of component a dec 0 9 inc 29 8 95 4 6 k 91 1 n 12 sites is indistinguishable from either the direction of the present field or the geocentric axial dipole field in northern sudan mixed polarities suggest a recent or pleistocene age of this component component b also displays mixed polarities the site mean directions for this component average to 6 5 declination 40 2 inclination with 95 7 0 and k 48 1 based on 10 sites and yield a palaeomagnetic pole at 48 8 s 23 5 e dp 5 1 1 dm 8 4 maghaemite and haematite have been identified to be the predominant magnetic phases in samples which carry component a and or b both a and b are the probable results of low temperature oxidation of magnetite although the age of component b can not be directly determined it is inferred by correlation with published data to reflect a late carboniferous overprint component c identified in 11 sites 39 samples is characterized by a very steep downward magnetization dec 296 2 inc 79 3 95 10 8 k 18 7 n 11 sites which corresponds to a palaeomagnetic pole position in the southwestern corner of libya 25 9 n 11 6 e dp 19 6 dm 20 6 maximum blocking temperatures of component c generally below 580 c are indicative of magnetite as carrier of this remanence the results of thermal remanent magnetization experiments demonstrate that component c is a thermo remanent magnetization probably primary and suggest this component to be representative for the direction of the earth s magnetic field during emplacement of the gilif hills volcanic rocks in mid devonian times the position of the resulting palaeomagnetic pole lends new support to geodynamic scenarios advocating the existence of a wide approx 5000 km pre hercynian ocean during devonian times the simplest reconciliation of component b with the reference apparent polar wander path is achieved by assuming it to be of carboniferous age and by invoking a westward cusp in the carboniferous part of the apparent polar wander path taken at face value the age of this cusp coincides with large scale post orogenic right lateral strike slip movements in hercynian europe and north africa this interpretation does not require the apparent polar wander apw loop and very high rates of plate motion implied by some alternative models however if it is valid it will require reinterpretation of the remanence age of one west african intrusive suite and of some eastern australian palaeozoic rocks

crustal accretion beneath the koyna coastal region india and late cretaceous geodynamics abstract in 1967 a major earthquake in the koyna region attracted attention to the hitherto considered stable indian shield the region is covered by a thick pile of deccan lava flows and characterized by several hidden tectonic features and complex geophysical signatures although deep seismic sounding studies have provided vital information regarding the crustal structure of the koyna region much remains unknown the two available dss profiles in the region have been combined along the trend of bouguer gravity anomalies unified 2 d density modelling of the koyna crust mantle suggests a ca 3 km thick and 40 km wide high velocity high density anomalous layer at the base of the crust along the coastline the thickness of this anomalous layer decreases gradually towards the east and ahead of the koyna gravity low the layer ceases to be visible based on the seismic and gravity data interpretation in the geodynamical rheological boundary conditions the anomalous layer is attributed to igneous crustal accretion at the base of the crust it is suggested that the underplated layer is the imprint of the magmatism caused by the deep mantle plume when the northward migrating indian plate passed over the reunion hotspot

structural highs on the western continental slope of india implications for regional tectonics abstract integrated geological and geophysical explorations over the last two decades along the central western continental margin of india reveal from east to west a terrace like flat shelf an advancing shelf break a nw se oriented wide shelf margin basin the upper slope ridge the prathap ridge and the laccadive ridge the basin on the continental slope extends between the shelf break and the eastern slope of the laccadive ridge and is divided longitudinally into a relatively narrow eastern and a wide western basin by the prominent upper slope ridge detailed multibeam swath mapping now over an area of little more than 20 300 km 2 within the shelf margin basin located on the upper continental slope now reveals the occurrence of several isolated structural highs of variable height four of these highs are located over the upper slope ridge and a similar number on the prathap ridge of these four highs have summit height 1000 m two have heights between 500 and 999 m while the remaining two have heights less than 499 m the digital terrain model developed from the processed multibeam swath bathymetry data offers a three dimensional perspective of these structural highs the tectonic understanding from multibeam bathymetry findings and satellite gravity data supported by other geophysical information suggest that these structural highs are likely to be the peaks of the upper slope ridge and the prathap ridge we discuss the possible origin and mode of emplacement of these structural highs and ridges in the light of regional tectonics and suggest that both the upper slope and prathap ridges may have been formed during the separation of india from madagascar during the middle cretaceous

gravity anomalies and associated tectonic features over the indian peninsular shield and adjoining ocean basins abstract a combined gravity map over the indian peninsular shield ips and adjoining oceans brings out well the inter relationships between the older tectonic features of the continent and the adjoining younger oceanic features the nw se ne sw and n s precambrian trends of the ips are reflected in the structural trends of the arabian sea and the bay of bengal suggesting their probable reactivation the simple bouguer anomaly map shows consistent increase in gravity value from the continent to the deep ocean basins which is attributed to isostatic compensation due to variations in the crustal thickness a crustal density model computed along a profile across this region suggests a thick crust of 35 40 km under the continent which reduces to 22 20 24 km under the bay of bengal with thick sediments of 8 10 km underlain by crustal layers of density 2720 and 2900 2840 kg m3 large crustal thickness and trends of the gravity anomalies may suggest a transitional crust in the bay of bengal up to 150 200 km from the east coast the crustal thickness under the laxmi ridge and east of it in the arabian sea is 20 and 14 km respectively with 5 6 km thick tertiary and mesozoic sediments separated by a thin layer of deccan trap crustal layers of densities 2750 and 2950 kg m3 underlie sediments the crustal density model in this part of the arabian sea east of laxmi ridge and the structural trends similar to the indian peninsular shield suggest a continent ocean transitional crust cotc the cotc may represent down dropped and submerged parts of the indian crust evolved at the time of break up along the west coast of india and passage of reunion hotspot over india during late cretaceous the crustal model under this part also shows an underplated lower crust and a low density upper mantle extending over the continent across the west coast of india which appears to be related to the deccan volcanism the crustal thickness under the western arabian sea west of the laxmi ridge reduces to 8 9 km with crustal layers of densities 2650 and 2870 kg m3 representing an oceanic crust

evidence for seafloor spreading in the laxmi basin northeastern arabian sea abstract marine magnetic anomaly data from the laxmi basin for the first time reveal the presence of fairly correlatable nnw trending magnetic lineations these magnetic lineations are symmetric about a central negative magnetic anomaly and the axis of symmetry coincides with a characteristic short wavelength free air gravity low the anomalies are interpreted as representing a two limbed seafloor spreading sequence which can be equated to the a28 a33 interval of the geomagnetic polarity reversal timescale these results suggest that the laxmi basin is underlain by an oceanic crust evidence of seafloor spreading in this basin possibly implies a pre a27 spreading episode in the evolutionary history of the arabian sea

foraminifera in elevated bermudian caves provide further evidence for 21 m eustatic sea level during marine isotope stage 11 abstract two hypotheses have been proposed to explain the origin of marine isotope stage mis 11 deposits in small bermudian caves at 21 m above modern sea level 1 a 21 m mis 11 eustatic sea level highstand and 2 a mis 11 mega tsunami event importantly the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments after statistically comparing foraminifera in modern bermudian littoral caves and the mis 11 calonectris pocket a 21 m cave to the largest available database of bermudian coastal foraminifera the assemblages found in modern littoral caves and calonectris pocket a cannot be statistically differentiated from lagoons this observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone where typical coastal processes waves storms homogenize and rework lagoonal reefal and occasional planktic taxa fossil protoconchs of the bermudian cave stygobite caecum caverna were also associated with the foraminifera these results indicate that the mis 11 bermudian caves are fossil littoral caves breached flank margin caves where the total mis 11 microfossil assemblage is preserving a signature of coeval sea level at 21 m brackish foraminifera polysaccammina pseudothurammina and anchialine gastropods 95 300 individuals indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase the onset of sea level regression following the 21 m highstand would first lower the ancient brackish ghyben herzberg lens

crustal structure and tectonics of the ninetyeast ridge from seismic and gravity studies seismic reflection and refraction gravity and bathymetric data across and along the central part of the ninetyeast ridge were analyzed to determine the crustal structure of the ridge and to understand its tectonics the ridge in the study area rises to 3 5 km above the seafloor of adjacent ocean basins basement is covered by sediments up to 0 8 km thick but exposed at some locations seismic refraction and gravity models of the ridge show that the crustal thickness is 22 km greater than the average thickness 7 km of oceanic crust estimated in the central indian and wharton basins the ridge is compensated by flexure of layers 2a 2b and 3a to the extent of 2 km and by a 12 km thick deep crustal body layer 3b of underplated material upper crustal velocities layer 2a beneath the ridge are lower up to 3 4 km s 1 than in adjacent basins because of weathering process and hydrothermal circulation of the waters in the tectonized blocks while velocities in deep crustal body layer 3b are higher up to 7 8 km s 1 and seem to be resulted from magmatic rocks accreted within the lithosphere steep down ward faulting of 2 km along the eastern flank of the ninetyeast ridge possibly originated because of compressional and extensional stresses applied along the 89 e fracture zone fz the stresses are interpreted as resulting from multiple ridge jumps of wharton spreading centers during the late cretaceous and middle eocene the velocity depth model suggests that the rocks of layers 2a and 2b and layer 3a are exposed on the eastern flank of the ninetyeast ridge and 90 e fz respectively they are consistent with basalt dolerite and gabbro rocks collected from the fault scarps the central part of the ridge between 1 n and 11 s has uniformly deepened by 0 7 km and is bounded by major sublatitudinal deep seated fractures we interpret that the deepened structural block and associated fractures resulted from the activity of the intense deformation of the central indian ocean

early palaeozoic cooling events peri gondwana and beyond the short lived end ordovician hirnantian glaciation allied to marine mass extinction is variously considered as a short lived event or as the peak of long drawn out climatic cooling through at least late ordovician early silurian times evidence from early palaeozoic facies faunas and stable isotope excursions used to interpret climatic cooling events ranges farther from late mid cambrian to late silurian times glacigenic sediments structures and geomorphology provide direct evidence of glacial episodes cool water carbonate deposition which is particularly widespread during the late ordovician boda event in high latitude peri gondwana gondwana and beyond into mid low palaeolatitudes is interpreted as indicating global cooling not warming as has been proposed such carbonates also characterize mid latitude continents widely at horizons earlier in the ordovician and more locally in the mid silurian in high latitude gondwana cool water carbonate mounds have distinctive facies controlled mound faunas across palaeocontinents other facies evidence for palaeoclimates includes black shale deposition including deglacial organic rich hot shales which indicate transgression in epeiric seas and sea level curves interpreted from facies and faunal successions correlation is shown between facies evidence and positive c isotope excursions from which cyclicities are apparent the possible interface of orbitally controlled rhythms is considered against evolving palaeobiogeography and changes in global sea level and in pco2 facies and faunal evidence from peri gondwanan terranes armorica central europe alborz is assessed with that from gondwana mostly north africa south america and correlatives in avalonia baltica and laurentia to establish a wider picture of early palaeozoic cooling events

early silurian glaciation along the western margin of gondwana peru bolivia and northern argentina palaeogeographic and geodynamic setting the record of the ordovician silurian transition within the southern peru bolivia palaeozoic basin extending across peru bolivia and northern argentina is characterized by a diamictite bearing unit which overlies several different ordovician units and underlies mid silurian shales we review the lithostratigraphy sedimentology and biostratigraphy of this unit revising stratigraphic relationships and several ideas and interpretations previously proposed analysis of facies and lithofacies associations allow for a reinterpretation of sedimentary processes and environments involved during its deposition turbidite and shale interbeds within the diamictites indicate a deep marine environment with interbedded mud flows debris flows slumps and large displaced slabs providing evidence for sediment instability and resedimentation chitinozoan biostratigraphy indicates a llandovery age in contrast with previous proposals of a hirnantian age and suggests the need for more detailed sedimentologic and biostratigraphic studies and a reassessment of this diamictite unit in relation to adjacent regions in south america the resedimented character of the deposit explains some of the ordovician fauna previously described which must be considered as recycled from underlying units in situ fauna needs to be reassessed as it may be endemic diachronic and or indicative of migrations within gondwana glacially faceted and striated clasts as well as large granitoid boulders within the resedimented materials provide evidence for glaciation of the source area and are interpreted as recycled from former glacigenic deposits the evidence found in the central andes indicates a glaciomarine origin for the diamictites and corroborates glaciation of a western source area prior to the late llandovery telychian the precise age of glaciation in this part of gondwana cannot be confirmed do to a lack of true tillites tectonic deformation and the resulting relief are respectively identified as the origin for sediment instability and for local glaciation along the active margin of western gondwana during the late ordovician and early silurian the new data imply that the ordovician silurian boundary was not preserved in some areas of the basin and that an erosional hiatus disconformity with variable regional significance is present between different ordovician units and the diamictite unit late ordovician late caradoc early ashgill euxinic black shales locally present in the central altiplano and eastern cordillera of bolivia may represent the youngest ordovician unit in the region and more research should be focused on them paleogeographic reconstruction of the early silurian peru bolivia basin depicts the extension of the diamictite unit southwards into northern argentina and western paraguay connecting with the parana basin through the asuncion arch to the north it continued into northern peru and ecuador connecting with the silurian record in colombia and venezuela and to the northeast into brazil solimoes and amazonas basins the sedimentary record of glaciation in the peru bolivia basin was due to the development of local ice fields to the west of the basin related with tectonism and resulting reliefs along the active margin of gondwana and probably did not coincide with the development of the north african late ashgillian ice cap

late holocene mangrove development and onset of sedimentation in the yax chen cave system ox bel ha yucatan mexico implications for using cave sediments as a sea level indicator abstract this study examines the relationship between the flooding of cenotes and formation of coastal mangrove with holocene sea level rise and the onset of aquatic sedimentation in yax chen a cave system in quintana roo on mexico s yucatan peninsula sediment depth measurements n 180 were collected along 2 7 km of an underwater cave passage and three cores were radiocarbon dated to examine both the extent and timing of sedimentation in the cave basal radiocarbon ages 4 ka for aquatic sediments in the cave show that holocene sea level rise flooded cenotes creating sunlit open water conditions with associated mangroves on the upper karst surface these conditions initiated abundant and widespread sedimentation in the cave cenote surface area controlled the long term sediment accumulation in the cave passages through primary productivity in the sunlit open water areas of the cenotes this primary productivity was enhanced with mangrove formation which causes funneling of precipitation and nutrient rich waters into the cenotes from the mangroves accumulation histories from the radiocarbon dated sediment cores n 3 were compared with accumulation histories in previously published studies including actun ha mexico and green bay cave gbc bermuda

morphotectonic characteristics distribution and probable genesis of bathymetric highs off southwest coast of india abstract the western continental margin of india and the adjacent deep ocean basins were formed by break up and separation among india seychelles and madagascar since the late cretaceous the initial india madagascar separation and the subsequent india seychelles separation are believed to have been caused by the marion hotspot at 90 ma and the reunion hotspot at 68 5 ma respectively these geodynamic events resulted in the formation of several bathymetric highs that probably represent imprints of these volcanic events in the present study these bathymetric high features were mapped comprehensively to understand their morphotectonic characteristics using a fresh set of multibeam bathymetry sea surface gravity and magnetic anomalies complemented by the available multichannel seismic reflection sections a high resolution bathymetric map of the southwestern continental margin of india and the adjoining deep offshore regions has been generated to decipher detailed morphological configuration and distribution of prominent undersea bathymetric features we also carried out detailed morphometric analysis of these features to deduce the morphological parameters a total of 33 individual bathymetric high features were identified and classified as seamounts hills knolls guyots and plateaus based on the standardization of undersea feature names published by intergovernmental oceanographic commission ioc and international hydrographic organization iho in 2013 multichannel seismic reflection sea surface gravity and magnetic data were used to describe the sub seafloor configuration and qualitative interpretation of the geophysical signatures associated with the bathymetric highs interpretation of the multichannel seismic reflection sections suggest that some of these identified features are extrusive in nature while others are intrusive these features are associated with characteristic gravity highs superimposed over regional negative anomalies and complex negative and positive magnetic anomalies the study results suggest that the genesis of the bathymetric highs mapped in the study area could be attributed to the hotspot volcanism caused by the marion or reunion hotspots we infer that the features in the southwestern continental margin of india closer to the alleppey trivandrum terrace complex might have been created by the marion hotspot volcanism while those in the laccadive basin and eastern sector of the laccadive plateau might have been formed by reunion hotspot volcanism

processes controlling arsenic enrichment along the eastern arabian sea surficial sediments the processes enriching redox sensitive arsenic as was investigated in 111 surficial sediments 27 3679 m water depth overlain by varying levels of dissolved oxygen along the eastern arabian sea under oxygenated conditions diagenetic enrichment of as was noticed at deeper water depths 1200 m while lattice held as dominant at few station from shallow depths 150 m in sediments impinged by oxygen minimum zone omz 150 1200 m as is released from organic matter during sub oxic diagenesis as seems to precipitate as as iron sulfide mineral under intense omz based on a positive correlation between as and s and cd in northeastern part of the study area while as may diffuse to water column under less intense omz evidenced by lack of correlation between as and s and cd in southeastern part several processes can enrich as a careful approach is recommended for its usage in understanding anthropogenic sources transport and paleodepositional environment along eastern arabian sea

madagascar a continental fragment of the paleo super dharwar craton of india the morphological kinship of madagascar to its immediate neighbors on the west african continent and east indian subcontinent during the early and middle cretaceous has been debated for the past two decades on the basis of available geologic tectonic and paleomagnetic information most of the paleoreconstructions of madagascar have shown its attachment to the east african continent we present magnetic satelite and gravity data and morphological geophysical and geotectonic similarities to hypothesize that in the period before the breakup of gondwana madagascar was a continental fragment of the paleo super dharwar craton of india

identification and origin of a subsurface ridge on the continental margin of western india abstract gravity and magnetic studies in the eastern arabian sea reveal the presence of subsurface and exposed ridges on and beyond the continental shelf of western india distinct patterns of geophysical anomalies are associated with the ridges and also reveal the presence of magnetic polarity reversals the portions of negative and positive magnetic anomalies of the ridges indicate that the northern part was formed in normal polarity time and the southern part in reversed polarity time the boundary line of magnetic polarity reversals is marked along 15 10 n further it is conjectured that these ridges probably originated because of the movement of the indian plate over the reunion hotspot during the late cretaceous and early tertiary

morphology of pockmarks along the western continental margin of india employing multibeam bathymetry and backscatter data this study addresses the morphology of pockmarks along the western continental margin of india using multibeam bathymetry and backscatter data here for the first time we have utilized the application of arcgis geographical information system for understanding the morphology of pockmarks from the western continental margin of india the pockmarks observed in water depths of 145 330 m are circular elliptical or elongated in plan view with an average length and width of 157 72 m and 83 19 m respectively the average pockmark relief and perimeter are 1 9 0 9 m and 412 181 m respectively the pockmarks have average areas and volumes of 10 759 m and 15 315 m respectively spatial separation that coincides with 210 m isobath divides the pockmarks into two groups with differing distributions and morphologies these pockmarks originated from seepages of biogenic or thermogenic gas or from pore fluids from deeper sources migrated vertically along the faults besides a possible structural control the pockmark morphologies are also affected by bottom currents and or by submarine slumping the average acoustic backscatter strength from pockmark centre is higher 35 db than the average backscatter of the total area 40 db which suggests their possible linkage to the precipitation of diagenitic minerals from biodegradation of seepage material

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

organic matter sources and lateral sedimentation in a bahamian karst basin sinkhole over the late holocene influence of local vegetation and climate abstract karst basins e g blueholes sinkholes accumulate well preserved sedimentary successions that provide transformative paleoclimatic and paleoenvironmental information however the sedimentary processes within these basins are not yet fully understood here we present stable carbon isotopic values 13corg and c n ratios of bulk organic matter in well dated sediment cores from blackwood sinkhole abaco the bahamas to investigate the changing flux of organic matter into the sinkhole during the late holocene the provenance of preserved organic matter changed through the late holocene between three primary sources as determined by three endmember mixing modeling wetland organic matter from the adjacent epikarst surface authigenic primary productivity in the oligohaline meteoric lens and terrestrial organic matter from the surrounding landscape expansion of wetlands on the adjacent epikarst surface played a critical role by increasing the flux of wetland organic matter to the sinkhole especially during the last 1000 years hurricanes and regional rainfall may have mediated organic matter delivery to the benthos either through hampering wetland development prior to 1000 cal yr bp or by changing dissolved nutrient concentrations available in the basin for primary producers these results demonstrate that organic matter provenance in karst basins is not constant through time and is significantly dependent upon both landscape vegetation on the epikarst surface and changing hydrographic conditions that impacts nutrient availability to primary producers

calcite raft geochemistry as a hydrological proxy for holocene aquifer conditions in hoyo negro and ich balam sac actun cave system quintana roo mexico abstract two cores from calcite rafts deposits located in cenote ich balam and hoyo negro were dated and analyzed for 87sr 86sr 18o 13c sr ca and cl ca the geochemical records show changing aquifer salinity spanning the last 8 5 cal kyrs bp and interrelationships with holocene climate trends wet and dry periods during the wet mid holocene the salinity of the meteoric water mass wm at 7 8 8 3 cal kyrs bp was relatively high at 1 5 2 7 ppt and then became less saline 1 0 1 5 ppt during the last 7000 yrs as climate became progressively drier high salinity of the meteoric wm during the wet mid holocene is attributed to increased turbulent mixing between the meteoric and underlying marine wm increased precipitation in terms of amount frequency and intensity e g hurricanes causes higher flow of meteoric water towards the coast and mixing at the halocline a phenomenon recorded with recent instrumental monitoring of the aquifer conversely during dry periods reduced precipitation and flow in the meteoric wm would result in lower salinity karst properties and holocene sea level rise also seem to have an effect on the aquifer when the regionally extensive network of shallow cave passages 10 12 m water depth are flooded at 8000 cal yrs bp there is a rapid shift in salinity this study demonstrates that calcite raft deposits can be used as paleo environmental recorders documenting the effects of sea level and climate change on aquifer condition

paleozoic and mesozoic geological history of northeastern africa based upon new interpretation of nubian strata 1 the nubia terrain in southern egypt and northern sudan is the type area for strata of mainly cretaceous age because nubian sandstone or nubian formation or similar terms were used for strata in other areas and of other stratigraphic positions the name nubian has become meaningless this paper summarizes results of field work done in egypt and sudan since 1976 reconstruction of the tectonics and paleogeography of northeast africa since the early paleozoic permits division of all strata related broadly to the nubian into three cycles the paleozoic cycle cambrian to early carboniferous is mainly marine this cycle was interrupted by the collision of gondwana with northern continents the resultant karoo cycle representing purely continental sedimentation exte ded from the late cretaceous until the early jurassic the disintegration of pangea led to a third cycle that began in the late jurassic and resulted in the marginal marine to continental strata of the nubian cycle that ranges in age from late jurassic to latest cretaceous

crustal structure along mehmadabad billimora profile in the cambay basin india from deep seismic soundings abstract deep seismic sounding dss investigations were carried out along a 220 km long n s profile from mehmadabad 22 50 n 72 46 e to billimora 20 46 n 72 58 e in the cambay basin india for studying the detailed crustal structure in the region seismic refraction as well as narrow and wide angle reflection travel time data were obtained for various crustal boundaries starting from the sedimentary section down to the moho by continuous profiling analysis of reversed reflection and refraction travel time data has yielded crustal velocity depth functions for the mehmadabad broach and broach navsari sections along the profile which are significantly different from each other the average velocities at depths in the magmadabad broach section have been found to be considerably lower than those in the broach navsari section by about 25 at 5 km 17 at 10 km 7 at 20 km and 2 at the moho depth and even deeper down in the upper mantle the presence of a relatively thicker sedimentary section especially in the jambusar broach area as revealed by the reversed refraction data analysis is responsible for this gross difference in the average velocity functions for the two parts of the profile and the same have therefore been used for obtaining the detailed crustal depth along the profile the cambay basin which is well known to be bounded by step faults on the eastern and western margins is also dissected into seven major crustal blocks in the n s direction from mehmadabad to billimora the various crustal blocks identified are from the north 1 i mehmadabad block 2 ii tarapur block 3 iii petlad katana block 4 iv jambusar broach block 5 v kosamba block 6 vi surat block and 7 vii navsari billimora block these blocks are displaced up or down relative to the adjacent blocks due to movements along the faults bounding them most of the faults have been found to extend quite deep and to affect the moho boundary considerably as is quite evident from the relief of the moho found along the profile further the seismic activity observed in the region during historical as well as modern times suggests that these deep faults may even be currently active the jambusar broach block which is well known as a broad regional syncline with the maximum thickness of cenozoic sediments has been found to be a major graben revealing a maximum crustal thickness of 38 40 km the granitic basement in this graben is also the deepest at 6 0 6 5 km depth towards the north and south of this major graben the moho as well as the granitic basement are found to be at relatively shallower depths in various crustal blocks the boundary velocity at the moho has been found to be 8 1 8 2 km sec whereas at the granitic basement level there seems to be a lateral velocity variation from 5 7 to 6 3 km sec the crustal depth section obtained in the present study reveals a close relationship between the deep and shallow structural features in this region the deccan traps which form the basement of the overlying tertiary sediments over most part of the profile vary in thickness from 1 0 to 1 8 km however the trap surface rises to very shallow depths on the southern part of the profile the boundary velocity in the deccan traps has been found to vary between 4 8 and 5 2 km sec in the anklesvar kosamba area there is also evidence for the presence of a 1 2 km thick layer of mesozoic sediments with a velocity of about 4 0 km sec underlying the 1 1 km thick deccan traps layer

stratigraphy and ages of four early silurian through late devonian early and middle mississippian glaciation events in the parnaiba basin and adjacent areas ne brazil abstract turbidity currents tectonism debris flows glaciation and other geologic processes are considered to be responsible for the generation of silurian mississippian diamictites in northern brazil processes that best account for the features observed in these strata are glaciation deglaciation and sedimentary deformation four main glacial ages are identified to have occurred in the parnaiba basin during the paleozoic glacially influenced deposits are found in the lower silurian upper devonian lower mississippian and middle mississippian strata the parnaiba basin is characterized by outcrops providing robust lithological evidence for three glacial ages identified by lithological features and dated by palynological studies a fourth glaciation as old as tournaisian was recently recognized only in the subsurface of the basin the glacial features were illustrated and the rocks accurately dated with palynomorphs based on very accurate palynological studies additional palynological information derives from outcrops and shallow boreholes drilled by a private company themag and the national state mineral production department departamento nacional de producao mineral dnpm and the brazilian geological survey company companhia de pesquisa de recursos minerais cprm the purpose of this reexamination including many new illustrations interpretations and conclusions is to evaluate primary sedimentological and paleontological data related to the above mentioned glaciations some authors remain skeptical about the record of early to early late paleozoic glaciations in western gondwana especially in brazil mainly because evidence provided in the literature is relatively scanty the parnaiba basin provides special conditions for the study of these glaciations although evidence for each of them varies considerably as discussed in the text

terminal classic drought in the northern maya lowlands inferred from multiple sediment cores in lake chichancanab mexico we present new density records from sediment cores taken along a depth transect in lake chichancanab mexico the data reveal in great detail the climatic events that comprised the terminal classic drought tcd and coincided with the demise of classic maya civilization between ca 750 and 1050 ad in shallow water cores the tcd is marked by a condensed gypsum horizon in deeper water sections it is expanded and represented by numerous interbedded gypsum and organic rich strata the tcd was not a single two century long megadrought but rather consisted of a series of dry events separated by intervening periods of relatively moister conditions we estimate the tcd occurred between ca 770 and 1100 ad and included an early phase ca 770 870 ad and late phase ca 920 1100 ad the intervening 50 year period ca 870 920 ad was relatively moister each dry phase is represented by multiple gypsum density bands interbedded with organic rich sediment that indicate alternating dry and wet conditions spectral analysis revealed significant periods around 213 50 and 27 years despite uncertainty regarding the ages of these events their pattern is robust and generally consistent with other proxy records under the same climate regime such as the marine cariaco basin off northern venezuela science 299 2003 1731

the paleozoic petroleum geology of central arabia exploratory drilling in central saudi arabia has established significant paleozoic petroleum potential in this region in recent discoveries the permian interval of the unayzah formation has been identified as the primary oil and gas reservoir the unayzah formation consists of alluvial and fluvial to shallow marine siliciclastic sandstones and siltstones that were deposited on a major pre unayzah unconformity saudi arabian paleozoic oil is a high gravity 43 53 degrees api crude with low sulfur content usually less than 0 07 that is classified as arabian super light oil gas with condensate has also been discovered in the unayzah formation the identified paleozoic traps are moderate relief fault generated structures with generally 30 100 m of closure unayzah structural traps developed primarily during the triassic to early jurassic however an earlier phase of significant pre unayzah structural development is also indicated between the devonian and late carboniferous and is related to a hercynian structural event post triassic structure in central arabia is mainly regional and results principally from late cretaceous to tertiary development of the central arabian arch the established source rock is the basal qusaiba shale a widespread organic rich shale that was deposited following regional deglaciation in the early silurian migration occurred regionally updip through unayzah formation reservoirs from the underlying qusaiba shale subcrop and or vertically along fault bounded zones on the flanks of structures from the underlying qusaiba shale interbedded upper permian shales and evaporites provide a top seal for the unayzah and form the basal sequence of the overlying transgressive khuff carbonate pre qusaiba reservoir targets include the cambrian ordovician saq sandstone the ordovician qasim formation and upper ordovician to lower silurian periglacial clastics of the zarqa and sarah formations high gravity low sulfur oil has also been discovered in this pre qusaiba clastic section the reservoirs of the pre qusaiba structures are fault bounded and sources laterally by the down faulted qusaiba shale

geochemical characteristics of organic rich shale upper yangtze basin implications for the late ordovician early silurian orogeny in south china abstract the tectonic sedimentary environment of the upper yangtze basin in china underwent significant changes from the late ordovician to early silurian the widely distributed shale formed during this interval has recorded key information about paleo ocean conditions analysis of major trace and rare earth elements was conducted on 135 shale samples collected from five wells in the study area the covariation of the mo u enrichment factors indicates that the upper yangtze basin in the wufeng stage was characterized by sedimentary differentiation the southern basin was dominated by a reducing bottom water environment under euxinic conditions the northern and central basins were dominated by a suboxic anoxic environment up to the early longmaxi stage the upper yangtze basin formed a relatively uniform sedimentary environment with gradually increasing oxygen content in the bottom water the paleoproductivity index indicates that marine organisms flourished in the wufeng to early longmaxi stages making an important contribution to the siliceous content in organic rich shale subsequently terrestrial siliciclastics gradually dominated analysis of paleogeography rare earth elements and weathering indicates that chuanzhong and qianzhong uplifts in the wufeng stage were the provenance area of the upper yangtze basin with a relatively high weathering degree weathering decreased in the beginning of the longmaxi stage and then gradually increased with the xuefeng uplift becoming the main provenance areas after the early longmaxi stage controlled by stress transfer from the continuous syn caledonian kwangsian orogeny in eastern south china the upper yangtze basin and xiangzhong basin were squeezed and pushed up successively the uplift separated the open shallow sea and formed a relatively limited deep water shelf environment resulting in a relatively euxinic bottom water environment which was favorable for organic matter accumulation the tectonic sedimentary evolution of the upper yangtze basin in the late ordovician to early silurian proposed in this study indicates that the formation of organic enriched shale was not only related to glacio eustatic change but also strongly controlled by tectonic activities in south china

seasonal trends in calcite raft precipitation from cenotes rainbow feno and monkey dust quintana roo mexico implications for paleoenvironmental studies abstract calcite raft precipitation was monitored in three yucatan cenotes rainbow feno and monkey dust over a 2 year period site specific variables including water temperature relative humidity water level and salinity were recorded as well as rainfall cozumel calcite raft surface area was monitored through trail cameras that collected photographs every 60 min accumulation rates were recorded using sediment traps that were collected in may and december of each year calcite raft surface area was calculated using an image segmentation procedure that identified the boundary of objects edge detection that share certain pixel characteristics removed non points of interest and measured the sum of the area covered by the raft material results show that large rainfall events have a regional effect on the meteoric water mass i e salinity as well as the precipitation of calcite rafts the large rainfalls and increased inflows cause dilution of the caco3 supersaturated meteoric water mass and cause increased flow hindering calcite raft precipitation for days to weeks after the rainfall raft precipitation gradually returns with deceasing flow after the event and stagnation allows the recurrence of caco3 supersaturation and accumulation of nucleation particles small rainfalls did not seem to have the same effect as slower percolation of rainwater through the epikarst would be more saturated and micro topographic relief may isolate the water pools from the lower flow the sediment trap data shows that calcite rafts accumulate relatively constantly throughout the year in all three sites sedimentation rates from feno and monkey dust responded to seasonal changes in surface water disturbance associated with rainfall wet and dry although rainbow didn t show any seasonality likely due to other site specific factors affecting water disturbance e g bats wind

nature of the crust in the laxmi basin 14 20 n western continental margin of india 1 the nature of the crust in the laxmi basin western margin of india is an uncertain issue more importantly this has implications on paleogeographic reconstructions of the western indian ocean we have analyzed three geophysical data sets and modeled gravity and magnetic anomalies for determining nature of the crust basement of the laxmi basin includes numerous highs which make the basement uneven and shallower compared to the western basin the laxmi basin is characterized by a broad gravity high and a narrower prominent gravity low within it while within the basin the broad anomaly gradually increases toward north the panikkar ridge is associated with the gravity low which is comparable at least in sign to known negative gravity anomaly of the laxmi ridge intrusive structures mapped in the laxmi basin coincide with significant magnetic anomalies which were earlier interpreted as seafloor spreading anomalies model studies reveal that the laxmi basin consists of 14 km thick stretched continental crust in which magmatic bodies have been emplaced whereas the panikkar ridge remains less altered stretched continental crust the crust of the laxmi basin is mostly thinner than crust under the laxmi ridge and continental margin in addition to the rift drift related stretching of the continental margin the laxmi basin possibly has undergone extra stretching in e w direction during the pre tertiary period at 68 ma deccan volcanism on western india may have disrupted the initial conditions that were leading to onset of spreading in the basin subsequently the reunion hot spot had emplaced the volcanic material within the stretched thinned continental crust we interpret the laxmi basin as a failed rift undergone stretching following intraplate kinematics prior to deccan volcanism

periodic deformation of oceanic crust in the central indian ocean new seismic reflection profiles of 5370 km running through the ocean drilling program leg 116 sites and deep sea drilling project sites 215 and 218 were obtained to investigate the spatial extent timing and nature of the tertiary deformation of the equatorial central indian ocean analyses of the data revealed basement and sedimentary structures and structural unconformities that resulted from the release of compressional forces long wavelength 150 300 km anticlinal basement structures with 1 2 km relief and tight folding and high angle faulting 5 20 km long of oceanic basement and overlying sediments exist between the afanasy nikitin seamount and the ninety east ridge the deformation zone extends from 10 s to the north up to 7 n latitude the changes in the regional basement trend along 87 e longitude between latitudes 11 s and 15 n coincide with the significant tectonic events of the first major plate reorganization occurred in the eastern indian ocean at 90 5 ma and changes in the indian plate motion at 65 5 ma the basement deformation at selected places a widespread unconformity of the upper miocene and subsequent younger unconformities lower pliocene and upper pleistocene indicate that the deformation activity might have begun earlier than the generally believed age of 7 5 ma and appears to be periodic the upper miocene and upper pleistocene deformational unconformities are in general observed south of 1 s while the basement deformation and lower pliocene deformational unconformity are mostly present in the area north of 1 s it is surmised that the compressional stresses built up since the hard collision of india with eurasia may have released for a short period prior to the early miocene time and deformed the oceanic basement in the northeastern indian ocean thereafter the stress regime seems to have transferred to the north of the indian shield and caused deformation of the continental lithosphere later the activity reoccurred during the late miocene 7 5 ma early pliocene 4 ma and late pleistocene 0 8 ma with a cyclicity of 3 5 m y and deformed the oceanic crust and sedimentary strata in the central indian ocean

the silurian glaciation in the eastern parnaiba basin brazil paleoenvironment sequence stratigraphy and insights for the evolution and paleogeography of west gondwana abstract glacial strata are excellent stratigraphic markers in paleozoic basins worldwide the eastern parnaiba basin in northern brazil is a highly favorable setting for studying episodes related to the ordovician silurian glaciation previous studies in this region led to the recognition of unequivocally glaciogenic sediments associated with pre and postglacial deposits favoring the understanding of lower paleozoic events that occurred in west gondwana outcrop based facies and stratigraphic analyses of the 170 m thick siliciclastic succession of the serra grande group indicate fluvial glacial and coastal depositional systems seventeen sedimentary facies are grouped into seven facies associations fas fa1 interpreted as intermediary sheet braided plain deposits that consist of tabular cross bedded coarse grained sandstones and conglomerates fa2 fa4 which correspond to subaqueous glacial deposits comprising massive to stratified diamictites cross laminated sandstones diamictites and organic matter rich black shales with dumpstone and dropstone structures fa5 fa6 constituting organic matter rich black shales fine to medium grained sandstones with sigmoidal cross bedding and occurrences of the ichnotaxon arthrophycus interpreted as delta front deposits and fa7 composed of medium to coarse grained pebbly sandstones interpreted as channelized braided plain deposits this interpretation partially confirms the previous paleoenvironmental interpretation discounting the presence of subaerial alluvial fan and outwash plain deposits for this unit the sequence stratigraphy of the serra grande group is refined mainly using the coherent interpretation of the key surfaces and comparing the systems tracts with the global sea level curve providing a more robust third order sequential evolutionary model that includes three depositional sequences the middle ordovician sheet braided deposits are the lowstand sediments of sequence 1 truncated by an extensive unconformity that possibly removed the transgressive and highstand strata this unconformity generated by glacial dynamics represents 23 myr during the late ordovician to early silurian the second sequence started with the advance of ice sheets in marginal areas of the basin causing the deposition of ablation diamicton during the lowstand the postglacial transgression is marked by ice rafted debris from icebergs deposited onto organic matter rich mud in the shoreface offshore zone the maximum flooding during the middle to late silurian was succeeded by the highstand phase marked by the progradation of deltaic deposits biological activity is marked by the presence of polychaetes that reworked the marine seafloor the early devonian featured extensive sea level fall and renewed continental drainage with the formation of a braided plain marking a lowstand phase of sequence 3 these new interpretations allow the global correlation of the serra grande group and provide an improved understanding of the role of ice sheets and postglacial transgressions that affected west gondwana during the ordovician silurian periods

a pre hirnantian late ordovician interval of global cooling the boda event re assessed facies analysis suggests that the early mid ashgill late ordovician boda event of fortey and cocks fortey r a cocks l r m 2005 late ordovician global warming the boda event geology 33 5 405 408 was an episode of global cooling not of warming as they proposed limestones are widely developed at this level from mid latitude to high latitude commonly interrupting thick ordovician successions of fine clastic sediments bryozoan carbonate mud mounds in a laterally extensive cool water carbonate belt along the high palaeolatitude margin of w gondwana are associated with glacial diamictites and grew during glacial lowstand with sea ice prior to the hirnantian glaciation from high to mid palaeolatitudes contemporaneous cool water carbonates with mud mounds including stromatactis both in gondwana and in baltica developed in mid outer ramp settings during regression in the dominantly clastic welsh basin of avalonia phosphatic facies on an iapetus facing carbonate ramp indicate upwelling cold waters down ramp yet up ramp coralliferous algal limestones suggest warm surface waters we propose that the late ordovician cool water carbonates developed in response to global cooling and expansion of gondwanan terrestrial and sea ice that lowered eustatic sea level and on the w gondwanan shelf reduced or shut down fluvial clastic input previously poorly circulated salinity stratified oceans that had restricted benthic dispersal in mid low latitudes were replaced by thermohaline ocean circulation that oxygenated bottom waters and dispersed benthic faunas an earlier caradoc carbonate interval in low mid palaeolatitudes that shares many facies characteristics with the ashgill cool water limestones and correlates with a widely recognised isotope excursion is interpreted as indicating an earlier global cooling episode

extension of structural and tectonic trends from the indian subcontinent into the eastern arabian sea abstract trends of basement highs faults and structural patterns on the india pakistan indus continental shelf and slope and in the deep waters extending to the lakshmi laxmi chagos laccadive ridge complex in the eastern arabian sea are parallel to the ancient precambrian structural and tectonic grain of the indian subcontinent these trends the occurrence of horst graben style features of the basement of the lakshmi ridge and of the region north and east of it both in deep waters and shelf areas and the oceanic nature of the basement west of the ridge suggest that the rifted transitional crust extends as far as the lakshmi chagos laccadive ridge complex the extension of rifted crust with horst graben style tectonic features into deep offshore areas of the arabian sea has implications for future hydrocarbon exploration in the region

reconstructing water level in hoyo negro quintana roo mexico implications for early paleoamerican and faunal access abstract the skeletal remains of a paleoamerican naia hn5 48 and extinct megafauna were found at 40 to 43 mbsl in a submerged dissolution chamber named hoyo negro hn in the sac actun cave system yucatan peninsula mexico the human remains were dated to between 12 and 13 ka making these remains the oldest securely dated in the yucatan twelve sediment cores were used to reconstruct the holocene flooding history of the now phreatic cave passages and cenotes ich balam oasis that connect to hn four facies were found 1 bat guano and seed sf 2 lime mud mf 3 calcite rafts crf and 4 organic matter calcite rafts om crf which were defined by their lithologic characteristics and ostracod foraminifera and testate amoebae content basal radiocarbon ages ams of aquatic sediments sf combined with cave bottom and ceiling height profiles determined the history of flooding in hn and when access was restricted for human and animal entry our results show that the bottom of hn was flooded at least by 9850 cal yr bp but likely earlier we also found that the pit became inaccessible for human and animal entry at 8100 cal yr bp when water reaching the cave ceiling effectively prevented entry water level continued to rise between 6000 and 8100 cal yr bp filling the cave passages and entry points to hn cenotes ich balam and oasis analysis of cave facies revealed that both holocene sea level rise and cave ceiling height determined the configuration of airways and the deposition of floating and bat derived om guano and seeds calcite rafts which form on the water surface are also dependent on the presence of airways but can also form in isolated air domes in the cave ceiling that affect their loci of deposition on the cave bottom these results indicated that aquatic cave sedimentation is transient in time and space necessitating extraction of multiple cores to determine a limit after which flooding occurred

a global compilation of coral sea level benchmarks implications and new challenges i present a quality controlled compilation of sea level data from u th dated corals encompassing 30 studies of 13 locations around the world the compilation contains relative sea level rsl data from each location based on both conventional and open system u th ages i have applied a commonly used age quality control criterion based on the initial 234u 238u activity ratios of corals in order to select reliable ages and to reconstruct sea level histories for the last 150 000 yr this analysis reveals scatter of rsl estimates among coeval coral benchmarks both within individual locations and between locations particularly during marine isotope stage mis 5a and the glacial inception following the last interglacial the character of data scatter during these time intervals imply that uncertainties still exist regarding tectonics glacio isostacy u series dating and or coral position to elucidate robust underlying patterns with confidence limits i performed a monte carlo style statistical analysis of the compiled coral data considering appropriate age and sea level uncertainties by its nature such an analysis has the tendency to smooth obscure millennial scale and finer details that may be important in individual datasets and favour the major underlying patterns that are supported by all datasets this statistical analysis is thus functional to illustrate major trends that are statistically robust what we know trends that are suggested but still are supported by few data what we might know subject to addition of more supporting data and improved corrections and which patterns data are clear outliers unlikely to be realistic given the rest of the global data and possibly needing further adjustments prior to the last glacial maximum and with the possible exception of the 130 120 ka period available coral data generally have insufficient temporal resolution and unexplained scatter which hinders identification of a well defined pattern with usefully narrow confidence limits this analysis thus provides a framework that objectively identifies critical targets for new data collection improved corrections and integration of coral data with independent stratigraphically continuous methods of sea level reconstruction

detrital cave sediments record late quaternary hydrologic and climatic variability in northwestern florida usa abstract detrital sediment in florida s usa submerged cave systems may preserve records of regional climate and hydrologic variability however the basic sedimentology mineralogy stratigraphic variability and emplacement history of the successions in florida s submerged caves remains poorly understood here we present stratigraphic mineralogical and elemental data on sediment cores from two phreatic cave systems in northwestern florida usa on the dougherty karst plain hole in the wall cave hitw and twin cave water flowing through these caves is subsurface flow in the apalachicola river drainage basin and the caves are located just downstream from jackson blue 1st magnitude spring 2 8 m3 s 1 discharge sedimentation in these caves is dominated by three primary sedimentary styles i ferromanganese deposits dominate the basal recovered stratigraphy which pass upsection into ii poorly sorted carbonate sediment and finally into iii fine grained organic matter gyttja deposits resolving the emplacement history of the lower stratigraphic units was hampered by a lack of suitable material for radiocarbon dating but the upper organic rich deposits have a punctuated depositional history beginning in the earliest holocene for example gyttja primarily accumulated in hitw and twin caves from 5500 to 3500 cal yr bp which coincides with regional evidence for water table rise of the upper floridian aquifer associated with relative sea level rise in the gulf of mexico and evidence for invigorated drainage through the apalachicola river drainage basin gyttja sediments were also deposited in one of the caves during the bolling allerod climate oscillation biologically these results indicate that some floridian aquatic cave stygobitic ecosystems presently receive minimal organic matter supply in comparison to prehistoric intervals the pre holocene poorly sorted carbonate sediment contains abundant invertebrate fossils and likely documents a period of enhanced limestone dissolution and cave formation speleogenesis during lower paleo water levels further work is still required to a determine whether precipitation of the ferromanganese deposits is inorganically or biologically mediated b temporally constrain the emplacement history of the primary sedimentary styles and c determine the full geographic extent of these sedimentary signals however these preliminary observations suggest that sedimentation in the inland underwater caves of northwestern florida is related to quaternary scale hydrographic variability in the apalachicola river drainage basin in response to broader ocean and atmospheric forcing

evaluation of reservoir temperatures and local utilization of geothermal waters of the konkan coast india abstract geochemical studies on fifteen geothermal manifestations 38 70 c from the konkan coast geothermal province of india have been used to evaluate the reservoir temperatures activity studies of the minerals and the waters present in the reservoirs suggest that the thermal waters are in equilibrium with montmorillonite kaolinite and quartz at about 100 c reservoir temperatures of these geothermal systems as estimated by geochemical thermometers are 88 to 128 c and thus too low for economic electricity production

cenozoic sedimentation in the mumbai offshore basin implications for tectonic evolution of the western continental margin of india abstract interpretation of multichannel seismic reflection data along the mumbai offshore basin mob revealed the tectonic processes that led to the development of sedimentary basins during cenozoic evolution structural interpretation along three selected mcs profiles from mob revealed seven major sedimentary sequences 3 0 s twt thick and the associated complex fault patterns these stratigraphic sequences are interpreted to host detritus of syn to post rift events during rift drift process the acoustic basement appeared to be faulted with interspaced intrusive bodies the sections also depicted the presence of slumping of sediments subsidence marginal basins rollover anticlines mud diapirs etc accompanied by normal to thrust faults related to recent tectonics presence of upthrusts in the slope region marks the locations of local compression during collision forward gravity modeling constrained with results from seismic and drill results revealed that the crustal structure beneath the mob has undergone an extensional type tectonics intruded with intrusive bodies results from the seismo gravity modeling in association with litholog data from drilled wells from the western continental margin of india wcmi are presented here

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

a 6000 year record of ecological and hydrological changes from laguna de la leche north coastal cuba abstract laguna de la leche north coastal cuba is a shallow 3 m oligohaline 2 0 4 5 coastal lake surrounded by mangroves and cattail stands a 227 cm core was studied using loss on ignition pollen calcareous microfossils and plant macrofossils from 6200 to 4800 cal yr bp the area was an oligohaline lake the period from 4800 to 4200 cal yr bp saw higher water levels and a freshened system these changes are indicated by an increase in the regional pollen rain as well as by the presence of charophyte oogonia and an increase in freshwater gastropods hydrobiidae by 4000 cal yr bp an open mesohaline lagoon had formed an increase in salt tolerant foraminifers suggests that water level increase was driven by relative sea level rise the initiation of laguna de la leche correlates with a shift to wetter conditions as indicated in pollen records from the southeastern united states e g lake tulane this synchronicity suggests that sea level rise caused middle holocene environmental change region wide two other cores sampled from mangrove swamps in the vicinity of laguna de la leche indicate that a major expansion of mangroves was underway by 1700 cal yr bp

yucatan subsurface stratigraphy implications and constraints for the chicxulub impact much of the discussion about the effects of an end of cretaceous impact by a large extraterrestrial body in northwestern yucatan has been done in the context of limited and partly erroneous published data on the mesozoic stratigraphy of that area reexamination of cores and geophysical logs taken in several pemex wells has produced improved lithologic and biostratigraphic correlation of the jurassic to maastrichtian section across the northern yucatan peninsula these data suggest that major disturbance of strata by an impact would have been confined to within about 100 km of the proposed impact center near chicxulub the only unusual lithologic unit is polymict breccia which apparently was penetrated at or near the top of the cretaceous section in all the deep wells of northern yucatan this breccia in pemex wells yucatan 1 2 4 5a and 6 is composed predominantly of detrital dolomite limestone and anhydrite clasts set in dolomitized carbonate mud matrix which contains upper maastrichtian foraminifers these constituents mixed with fragments of altered glass or melt rock shocked quartz and feldspar and basement rock suggest an impact as the most likely origin for the breccia the timing of brecciation is poorly constrained by biostratigraphic data there is some evidence however that the breccia unit is overlain by about 18 m of uppermost maastrichtian marls suggesting an impact before the cretaceous tertiary boundary in addition there may have been more than one episode of breccia deposition

structure and tectonics of the southwestern continental margin of india abstract a nnw sse trending graben in the inner shelf 40 60 m isobaths a mid shelf basement ridge 60 150 m isobaths a shelf margin basin 150 1000 m isobaths and the prathap ridge complex in the slope 1000 2000 m isobaths extend as linear features along the southwestern continental margin of india between 12 20 n and 15 00 n the basic structural framework of the margin seems to be influenced by the pre existing precambrian structural fabric of the continent the mid shelf basement ridge and the prathap ridge complex are interpreted as manifestation of the rift phase volcanism when india separated from madagascar around 84 ma

floating rafts of calcite crystals in cave pools central texas u s a crystal habit vs saturation state abstract calcite precipitation at the air water interface in cave pools in central texas u s a produces floating rafts of interconnected low mg calcite crystals with individual crystal habits that range from equant length to width 1 1 to prismatic 4 1 saturation state for the waters ranges from 0 19 to 1 35 sic log iap k equant crystals precipitate from waters with a lower saturation index sic and form rafts with a fused fabric whereas prismatic crystals precipitate from higher sic waters and form rafts with an interlaced fabric the pools contain low magnesium molal mg ca 0 6 calcium bicarbonate and calcium bicarbonate nitrate type waters with temperatures that range from 13 8 c to 20 7 c and ph readings from 6 7 to 8 4 equant euhedral crystals precipitate from water with saturation states close to equilibrium visible defects in the equant crystals include incomplete edges between faces and nearly circular mean diameter 9 m to angular holes in faces the holes apparently result from crystallite growth around foreign objects on the crystal surface such as gas bubbles prismatic crystals precipitate from supersaturated water faces of these subhedral crystals are smaller in area than the faces of the equant crystals no intrafacial circular holes are seen but trigonal intercrystallite pores are common in the prismatic crystals the variety in crystal habits from equant to prismatic is due to preferential growth along one crystallographic axis thus in these cave pools crystal habit is related to the saturation state of the water

hells bells unique speleothems from the yucatan peninsula mexico generated under highly specific subaquatic conditions abstract we here report on a type of meter sized pendant speleothem growing under water in the submerged el zapote sinkhole cenote west of puerto morelos on the mexican yucatan peninsula these conical mantle shaped downward expanding and diverging calcareous structures here termed as hells bells are yet unreported in the scientific literature they are characterized by bell or trumpet shaped longitudinal and circular elliptical or horse shoe like horizontal cross sections hells bells grow downward based on the downward divergence of the structures and the horizontally laminated internal texture of both blade shaped spar calcite and microspar laminae age dating confirms that hells bells are young

inorganic calcite morphology roles of fluid chemistry and fluid flow abstract evaluation of calcite crystal habits and fabric and their relation to precipitating fluids in spelean environments indicates that habit variations are controlled primarily by degree of supersaturation at less than 6 times supersaturation crystal habits are limited to those with shallow to steep rhombohedral forms i e 1011 4041 with increasing supersaturation scalenohedrons extremely steep rhombohedrons pinacoids and hexagonal prisms are developed slight elongation due to differences in crystal dimensions of these forms may arise i e scalenohedrons versus shallow rhombohedrons at extreme supersaturation 12 times curvature of crystal faces or curved surfaces appear the development of fibrous versus equant fabrics is the result of changes or modification of reactant supply rates and the number of crystallites nuclei present under rapid flow conditions growth rates are accelerated and greater numbers of nuclei are present thus compromise boundaries parallel to c axis and perpendicular to flow and substrate are rapidly attained in the absence of flow fewer crystallites are present and larger well developed crystals or branching forms dictated by saturation conditions arise in the absence of flow at low supersaturation elongate composite crystals and hence fibrous fabrics may result from migration of the fluid crystal interface as a result of changing or oscillating water levels a flow control mechanism can be applied to numerous geological conditions in which transitions from fibrous to equant crystal morphologies are observed

ring of cenotes sinkholes northwest yucatan mexico its hydrogeologic characteristics and possible association with the chicxulub impact crater a 180 km diameter semicircular band of abundant karst sinkholes ring of cenotes in northwest yucatan mexico coincides approximately with a concentric ring of the buried chicxulub structure a circular feature manifested in cretaceous and older rocks that has been identified as the product of the impact of a bolide the ring expressed in tertiary rocks marks a zone of high permeability as shown by 1 the sinkholes themselves 2 breaks in the coastal dune system and high density of springs where the ring intersects the coast and 3 water level transects characterized by a decline in water level toward the ring any direct relation that exists between the ring of cenotes and the chicxulub structure bears on regional hydrogeology if the layer or zone responsible for the ring is deeply buried it may act as a barrier to the movement of ground water across the main flow direction shallower zones of horizontal permeability could result in less complete diversion of ground water through its influence on yucatan aquifer characteristics the ring may provide a link between modern environmental problems and astrogeology possible origins for the ring of cenotes are 1 faulting perhaps reactivated by post eocene mid miocene basin loading 2 permeability in a buried reef complex developed in the shallow paleocene sea around the crater rim or 3 breccia collapse occasioned by consolidation or by solution of evaporite components if the ring developed on ancient faults it may outline hydrothermal systems and mineral deposits produced during paleocene cooling of the chicxulub melt sheet

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

structure and early evolution of the arabian sea and east somali basin summary the laxmi ridge is a large scale basement high buried beneath the sediments of the indus fan the location of the ocean continent transition oct on this margin has previously been proposed at either the southern edge of the laxmi ridge or beyond it towards the india pakistan shelf the former explains the margin parallel laxmi basin as thinned continental crust the latter as a failed rift of earlier seafloor spreading to examine the structure of this margin a reassessment of marine magnetic data has detailed seafloor spreading magnetic anomalies prior to anomaly 24 in both the arabian and east somali basins the previously identified anomaly 28 is not interpreted as a seafloor spreading anomaly but as a magnetized basement feature adjacent to and merging with the ridge the laxmi spur new gravity models across the laxmi ridge and adjacent margin using ship and satellite data corroborate the existence of underplated crust beneath the laxmi ridge and basin and the location of the oct at the southern edge of the ridge the results are not compatible with the existence of a pre anomaly 28 phase of seafloor spreading although large scale intrusions may be the origin of some of the basement features in the laxmi basin the models also identify the laxmi spur as a low density feature with a natural remanent magnetization nrm compatible with serpentinization the laxmi ridge is mapped to the southeast where it appears to terminate at a point coinciding with the appearance of e w magnetic lineations and gravity anomalies at 15 5 n thereafter it becomes indistinct this is interpreted as necessary in the reconstruction to the mascarene plateau to avoid continental overlap

geohistory analysis of bombay high region abstract geohistory diagrams have been constructed for three representative sites in the bombay high region offshore west coast india the model curve for 60 lithospheric injection matches the intitial part of a thermo tectonic curve for one of the sites where a complete tertiary sequence is developed the study suggests that the four paleogene unconformities recognised in this region were caused by eustatic falls a distinct phase of active subsidence occurred during the late middle late miocene probably due to more active spreading at the mid indian ocean ridge

linkages between holocene paleoclimate and paleohydrogeology preserved in a yucatan underwater cave abstract three sediment cores spanning the last 4200 years from aktun ha cave on the yucatan peninsula mexico demonstrate that underwater caves can document changes to regional hydrogeology and climate benthic microfossils testate amoebae foraminifera organic matter geochemistry 13 c 15 n c n and particle size distributions were analyzed however microfossil paleoecology proved the most useful for indicating three salinity phases in the aktun ha sediment cores phase 1 4300 yr bp contains predominantly foraminifera physalidia simplex 78 that indicate the meteoric lens flooding the cave was initially brackish salinity 3 5 g l 1 phase 2 2800 4300 cal yr bp has both freshwater testate amoebae centropyxis spp 40 and p simplex 42 which indicates a slight freshening of the meteoric lens to 1 5 2 g l 1 phase 3 lagenodifflugia vas and difflugia oblonga with a reduction in p simplex 10 this last faunal shift represents the initiation of modern freshwater conditions in the cave 1 5 g l 1 this final freshening is synchronous with a significant reduction in the c n ratio e g core 2 27 to 19 which suggests an expansion of primary productivity in the adjacent cenote the 15 n values ranged from 1 5 to 3 5 with observed cycles likely from intervals of increased terrestrial om input into the cave during high rainfall events e g hurricanes the observed paleoenvironmental shifts in the cave correlate well with regional precipitation patterns aquifer recharge and storm activity caused by southward migration of the intertropical convergence zone therefore regional climate change impacted eastern yucatan groundwater during the mid to late holocene however decelerating holocene sea level rise and aquifer occlusion are likely contributing factors these results demonstrate that underwater cave sediments and microfossils can be useful proxies for aquifer evolution and climate change

an insight into the fifty fathom flat off india s west coast abstract the architecture of the western continental margin of india wcmi is likely to have been influenced in the geological past by several episodes of volcanic eruptions rifting and continental break up the wcmi is characterized by a wide shelf in the north few hundreds of kilometers wide which tapers down to just few kilometers towards the south a detailed multibeam swath bathymetry study was made of a part of the wide flat shelf off mumbai encountered at an approximate depth of 50 fathom about 100 m that holds one of the world s richest offshore petroleum resources the multibeam bathymetry images suggest that the western boundary of the fifty fathom flat fff coincides with the shelf break with a fall much sharper than other places along the west coast this break also coincides with the western extremity of the carbonate platform the stratigraphic succession and petrology of the fff bear strong resemblance to that of the seychelles and mascarene plateau we discuss the tectonic implications of such resemblance and the possible reasons for the remarkably low bathymetric relief of the fff

holocene submarine terraces on the western continental shelf of india implications for sea level changes abstract detailed echosounding side scan sonar and high resolution seismic reflection profiling on the western continental shelf of india have revealed a series of submarine terraces at different depths between the outer fringe of the inner shelf and the shelf break being more common between 11 and 20 n the terraces are prominent between water depths of 50 and 115 m and occur at six distinct levels 1 55 60 m 2 65 70 m 3 75 80 m 4 85 90 m 5 95 100 m and 6 110 115 m they are categorized into 1 wave cut terraces 2 coral algal reef induced terraces and 3 palaeo beach barrier terraces the reef induced terraces occur predominantly in the carbonate rich province 20 13 n while both the wave cut and palaeo beach barrier terraces are discernible in the terrigenous regime which is located north and south of these latitudes despite their genetic differences their evolution is ascribed to reef growth progradation and wave activity during the lowstands of sea level and reflect different phases of stillstands of the late pleistocene to mid holocene age

did lingering ice sheets moderate anoxia in the early palaeozoic of libya the hirnantian glaciation of west gondwana produced a glacially sculpted topography which is draped by organic rich latest ordovician and early silurian hot shales although these are the most important early palaeozoic source rock in north africa organic enrichment is distributed unevenly for example in al kufrah basin libya hot shales are elusive but outcrop analysis at the western basin demonstrates why this is the case the topmost mamuniyat formation of hirnantian age comprises glaciogenic sandstones passing upward into mixed facies of the tanezzuft formation which has a latest ordovician early silurian age the basal tanezzuft formation contains a shelly carbonate cool water deposits accumulated under oxygenating conditions and bioturbated sandstone succession above hummocky cross bedded and graded sandstone intervals are intercalated with shale and siltstone storm influx onto a muddy shelf these are interrupted by several lonestone bearing intervals ice rafted debris a striated pavement of subglacial origin and manganese oxide crusts and concretions the concretions and bioturbation imply oxygenation of the sea floor during transgression these putative glacial deposits were deposited following the main phase of the hirnantian glaciation at the same stratigraphic level as hot shales elsewhere in northern gondwana lingering ice caps may have produced well oxygenated marine waters precluding hot shale deposition

the jebel hadid structure al kufrah basin se libya a possible impact structure and potential hydrocarbon trap abstract the jebel hadid structure that formed in the nubian sandstone of the southern al kufrah basin is a 4 7 km circular feature with a set of multiple concentric annular ridges the age of the structure is probably post early cretaceous to pre pliocene as the prevalent geological processes that usually account for the formation of circular structures magmatism diapirism sand volcanism karst dissolution glacial erosion can be widely excluded in this region we suggest that the jebel hadid structure might represent an eroded complex impact structure in particular the jebel hadid structure bears a strong morphological resemblance to the impact structure of tin bider in algeria general host rock properties may be compared to those at the upheaval dome impact structure usa numerous terrestrial impact structures are hosts to hydrocarbon reservoirs this investigation provides a first prospective approach based on remote sensing discussing the economic potential of a circular structure of suspected impact origin the still underexplored al kufrah basin is considered as a high potential area for future hydrocarbon exploration if we consider a possible impact origin of the jebel hadid structure this feature might provide local secondary pathways and traps for hydrocarbon migration accumulation in the nubian series and thus ought to be considered as a preferential site for oil and gas exploration

the middle rhuddanian lower silurian hot shale of north africa and arabia an atypical hydrocarbon source rock an important hydrocarbon source rock a hot shale has been identified from the middle rhuddanian llandovery lower silurian of a number of localities in north africa and arabia it is unusual in having been deposited during a eustatic fall in sea level evidence for this sea level fall in libya and jordan is manifested in a wide variety of palynological proxy data including reduced acritarch and chitinozoan total abundance reduced acritarch diversity and changes in the relative abundances of various environmentally sensitive acritarch morphogroups and from the presence of a minor positive 13corg excursion at the same stratigraphical level as the hot shale the environment of deposition was anoxic before during and after deposition of the hot shale except for some very brief incursions of more oxygenated water that enabled the development of a very limited burrowing benthos and graptolite preservation as three dimensional pyrite internal moulds these incursions occurred just before and during deposition of the hot shale and are interpreted as resulting from the influx of sediment laden oxygenated currents from shallower water environments enhanced organic matter preservation within the hot shale is attributed to greater productivity resulting from increased nutrient input particularly from wind blown dust more rapid descent through the water column of organic matter in post bloom marine snow macroaggregates development of geochemically sealing microbial mats at the sea floor and more rapid burial of organic material than had occurred earlier in the rhuddanian

lower palaeozoic unconformities in an intracratonic platform setting glacial erosion versus tectonics in the eastern murzuq basin southern libya the stratigraphic record of the eastern murzuq basin has been importantly influenced by deformation resulting in angular and or deeply erosional unconformities though the overall context is intracratonic major transgressive events and the ordovician glaciation are nevertheless documented allowing the delineation of tectonic eustasy or climate driven unconformities lower palaeozoic key events and related unconformities that characterize the north gondwana platform have therefore a signature in the eastern murzuq basin the basement cover unconformity also known as the infra tassilian surface truncates all the deformed and metamorphosed lower cambrian and older rocks above is a middle cambrian to lower ordovician megasequence murizidie and hasawnah fms which is in turn truncated by an intra ordovician angular unconformity this megasequence is unconformably overlain by a middle ordovician hawaz fm to silurian tanzzuft and akakus fms megasequence which includes the upper ordovician glaciogenic unit mamuniyat fm bounded at the base by a polygenic glacial erosion surface showing corrugated glacial lineations tillites and glaciotectonic structures the middle ordovician to silurian megasequence is finally truncated by a base devonian angular unconformity overlain by fluvial sandstones regarding the possibility that those fluvial deposits may be as younger as late devonian in the eastern murzuq basin based on palaeoflora the so called caledonian unconformity might be here a much younger mid eifelian surface and the occurrence of the lower devonian tadrart fm is questioned the upper ordovician glacial erosion surface which is sometimes referred to as the taconic unconformity usually truncates middle ordovician strata in the murzuq basin but reaches significantly deeper stratigraphic levels in places that have been previously involved in the intra ordovician deformation event in the murizidie southeastern murzuq basin the infra tassilian surface the intra ordovician unconformity and the upper ordovician glacial erosion surface amalgamate together here an estimate of the glacial erosion depth cannot be derived from the stratigraphic hiatus beneath the glacial incision the main part of which relate to the intra ordovician tectonic event the upper ordovician climate related glacial erosion surface is not a valid unconformity for a sequence hierarchy framework of the lower palaeozoic although it presents most of the physical attributes of tectonic driven unconformities

tholeiitic dykes in the seychelles and the original spatial extent of the deccan we report geochemical data from c deccan age tholeiitic dykes from praslin island in the seychelles a continental fragment which lay adjacent to the coast of india before sea floor spreading started in the arabian sea at 64 ma the dykes have compositions very similar to the distinctive bushe magma type from the deccan and hence constitute the first traces of deccan activity recognized on the seychelles fitting the seychelles and india back together to reconstruct the original extent of the deccan we find that the present estimate of 1 million km 2 needs to be revised upwards by c 25 to account for the deccan magmatism in the seychelles if dipping reflectors found on seismic lines to the northwest of the seychelles are also deccan age flows this would increase still further the area and volume estimates

evolution of the carlsberg ridge between 60 and 45 ma ridge propagation spreading asymmetry and the deccan reunion hotspot despite the availability of numerous geophysical data no convincing magnetic anomaly identification and structural map of a major part of the arabian and eastern somali basins have been published to date i propose a new interpretation of the available magnetic data based on the identification of tiny wiggles i e singular second order patterns of the magnetic signal only one fracture zone and a set of propagating rifts existed between the owen fracture zone and the chagos laccadive ridge between anomalies 26 and 20 at anomalies 26 25 at least two eastward propagating rifts are identified while at anomalies 24 20 seven westward propagating rifts are confidently recognized the major consequence of this systematic ridge propagation is a tremendous regional asymmetry between anomalies 26 and 25 about 65 of the crust formed at the carlsberg ridge was accreted to the african plate while at anomalies 24 20 more than 75 benefited to the indian plate i suggest that these asymmetries result from the relative position of the carlsberg ridge and the nearby deccan reunion hotspot the ridge tending to remain near the hotspot

low frequency storminess signal at bermuda linked to cooling events in the north atlantic region north atlantic climate archives provide evidence for increased storm activity during the little ice age 150 to 600 calibrated years cal years b p and centered at 1700 and 3000 cal years b p typically in centennial scale sedimentary records meteorological tropical versus extratropical storms and climate forcings of this signal remain poorly understood although variability in the north atlantic oscillation nao or atlantic meridional overturning circulation amoc are frequently hypothesized to be involved here we present records of late holocene storminess and coastal temperature change from a bermudian submarine cave that is hydrographically circulated with the coastal ocean thermal variability in the cave is documented by stable oxygen isotope values of cave benthic foraminifera which document a close linkage between regional temperature change and nao phasing during the late holocene however erosion of terrestrial sediment into the submarine cave provides a storminess signal that correlates with higher latitude storminess archives and broader north atlantic cooling events understanding the driver of this storminess signal will require higher resolution storm records to disentangle the contribution of tropical versus extratropical cyclones and a better understanding of cyclone activity during hemispheric cooling periods most importantly however the signal in bermuda appears more closely correlated with proxy based evidence for subtle amoc reductions than nao phasing

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

trigonal dendritic calcite crystals forming from hot spring waters at waikite north island new zealand amorphous silica and calcite form the deposits in the vent and on the discharge apron of waikite spring 100 ws 100 which is located in the waikite geothermal area on north island new zealand these precipitates formed from spring water that has a temperature of 90 c and a ph of 8 1 8 8 the opaline silica is restricted to areas around the vent where cooling and evaporation of the spring water triggered precipitation the calcite deposits in the spring vent and on the discharge apron are formed of large up to 15 cm long asymmetrical dendrite crystals that are characterized by multiple levels of branching branches grew preferentially from the downflow side of their parent branch all branches have a trigonal transverse cross section except in areas where competition for growth space induced merger of neighboring crystals the primary branches of the dendrite crystals are sub perpendicular to the substrate even in areas where the discharge apron slopes at a high angle up to 80 on the steeper parts of the discharge apron the plate like primary branches form the floors of the small terrace pools whereas their distal edges form the rims of the pools growth of these dendrite crystals is attributed to abiotic processes high levels of saturation with respect to calcite were caused by rapid co2 degassing of the sheets of spring water that flowed down the steep discharge apron calcite crystals with different crystal morphologies characterize other springs near this spring the variation in crystal morphologies from spring to spring is attributed to different levels of saturation that are related to the initial pco2 of the spring water upon discharge and the rate of co2 degassing at each spring

deep seismic sounding studies in the north cambay and sanchor basins india summary deep seismic sounding dss studies have been carried out in the north cambay and sanchor sedimentary basins in western india along three lines covering about 350km seismic refraction and wide angle reflection data pertinent to the sedimentary basin as well as the deep crustal section have been recorded from 41 shot points using a 60 channel dfs v digital recording system with 200 m geophone spacing and 4 ms data sampling extensive modelling and interpretation of a large number of seismic record sections reveal four sub basins in the sedimentary section along these lines maximum depth to the granitic proterozoic basement p wave velocity 5 9 6 0 km s 1 is about 5000 m in the north sanchor and the patan sub basins and about 5600 m in the south sanchor sub basin the deepest part of the sedimentary basin is delineated within the gandhinagar sub basin where the basement depth reaches 7700 m the deccan traps p wave velocity 4 3 4 8 km s 1 form the base of the tertiary sediments almost in the entire study area except the extreme northern part there is also some indication of the presence of sub trappean mesozoic sediments along this profile within the sedimentary basin two horst features one near diyodar the diyodar ridge and the other northwest of mehsana the unhawa ridge are indicated by the seismic data consistent with the tectonics of the region the thickness of the upper crust in this region does not exceed 15 km p wave velocity reaching 6 3km s 1 a prominent low velocity zone velocity 5 5 km s 1 occurs in the depth range from 10 5 to 12 5 km the lower crust consists of two layers of velocities 6 6 6 9 km s 1 and 7 3 7 4 km s 1 the discontinuity between them occurring at 23 25 km depth the moho discontinuity pm velocity 8 0 km s 1 lies at a depth of 31 33 km the high velocity 7 3 7 4 km s 1 lower crustal layer represents underplating of the crust due to mantle upwelling and rifting with large scale extrusion of the deccan volcanics the large thickness of the tertiary sediments in the cambay basin and a relatively thin crust in the region suggest further rifting during the tertiary

carbon and oxygen isotopic composition of silurian brachiopods gotland sweden palaeoceanographic implications abstract one hundred and seventy two non luminescent brachiopod shells from the silurian sequence of gotland were investigated for their carbon and oxygen isotopic composition diagenetic alteration of the shell calcite was excluded by means of petrographic trace element and cathodoluminescence analysis oxygen and carbon isotopic signals vary considerably within the uppermost llandovery to the ludlow average 18o and 13c values of well defined stratigraphic units range from 2 4 to 5 9 and 1 to 8 respectively we observed parallel trends in the carbon and oxygen isotope curves with the most prominent shifts occurring in the lower wenlock upper wenlock and middle ludlow average 18o values 2 4 to 2 9 recorded in the middle ludlow are among the highest 18o values reported for the early palaeozoic the recorded 18o variations cannot solely be explained by changes in sea surface temperature and salinity the variations in the isotopic signals correlate negatively with changes in sea level heavy carbon and oxygen signals coincide with sea level lowstands whereas light signals are recorded during sea level highstands sea level highstands were probably characterized by the formation of warm saline waters on subtropical epicontinental shelves inducing oxygen deficiency in the basins alumshale facies the low 18o values are attributed to 18o depletion in surface waters owing to the storage of 18o enriched saline waters in the basins low 13c values are explained by a low surface water productivity since nutrients were not supplied to the photic zone but rather stored in the deeper ocean during sea level lowstands colder waters that formed in higher latitudes may have represented the main intermediate water source a better ventilation of the basins is documented by the deposition of well aerated sediments whereas the high 18o values are explained by the change in oceanic circulation the high 13c values are attributed to an enhanced primary productivity and possibly to an enhanced burial of corg the model discussed here may provide an attractive scenario for accounting for the recorded short term variations in the isotopic signals without the necessity of introducing an isotopic correction factor for silurian sea water

flexural and stratigraphic development of the west indian continental margin subsidence curves for 27 wells from the western continental margin of india show a characteristic late oligocene to early miocene 24 5 ma rapid increase in subsidence rate superposed on the long lived slow subsidence typical of the thermal subsidence phase of passive continental margins by subtracting a best fit negative exponential subsidence from the observed subsidence curves we obtain an estimate of the distribution and magnitude of the excess subsidence affecting the neogene development of the west indian margin the magnitude of this excess subsidence increases seaward from the coast ranging from a few meters to 2000 m near the shelf edge we examine the following hypotheses to explain the distribution and timing of this excess subsidence 1 modification of basin stratigraphy due to the effects of lithospheric in plane compression 2 creation of accommodation space on the margin by flexural effects associated with indus fan loading and 3 rapid growth of the continental margin and associated flexural effects of the three hypotheses tested the least important mechanism to account for the observed excess subsidence is that of variations of lithospheric in plane force principally because maximum in plane compression within the indo australian plate was only achieved in the late miocene because indus fan sediment deposition began in the late oligocene to early miocene we investigated three dimensional flexural effects associated with fan loading as a cause of the excess subsidence beginning at 24 ma the distribution and magnitude of modeled flexural deflection however are not consistent with the observed excess subsidence interpretation of seismic reflection data indicates that the margin has aggraded and prograded by 100 km basin ward since the oligocene therefore we evaluate the flexural effects of this margin growth by estimating the amount of space infilled by margin progradation and aggradation since 24 ma and computing the resulting deflection this deflection matches the distribution and magnitude of observed excess subsidence along the margin in addition the distribution of the flexural bulge predicted from the combined deflections due to indus fan and margin loading is spatially coincident with the distribution of exposed marine terraces and drainage divides in the saurastra peninsula and the regions surrounding the gulfs of cambay and kutch respectively available gravity seismic reflection refraction and well data are consistent with our prediction of a 4000 to 5000 m thick sediment load developed during the neogene along the outer margin we propose that flexural deformation due to sedimentary loading provides a potential tectonic feedback mechanism that affects coastal and fluvial depositional processes as regions in close proximity to the load are depressed regions farther from the load experience uplift i e the peripheral bulge which is sufficient to cause subaerial exposure of large portions of the shelf and to modify existing drainage networks this feedback represents a mechanism for inducing relative sea level changes without invoking glacial eustasy

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

multistage 8 2 kyr event revealed through high resolution xrf core scanning of cuban sinkhole sediments we use sediments from a flooded sinkhole cenote jennifer in northern cuba to provide new well dated high resolution evidence for the 8 2 kyr event from 7600 to 8700 cal yr b p the sinkhole contained shallow low salinity water which supported a marsh dominated by cattail and grass peaks in cl and br occurring at 8150 8200 and 8250 cal yr b p are attributable to increased evaporation due to regional drying associated with the 8 2 kyr event the three peaks in these elements also closely correspond to the greyscale record from the cariaco basin indicative of increased upwelling in the southern caribbean sea at this time supporting the notion of a multistage 8 2 kyr event our work provides new data that help to clarify the initiation behavior and impacts of the 8 2 kyr event in the northern tropics

early paleozoic paleogeography of the northern gondwana margin new evidence for ordovician silurian glaciation during the early paleozoic transgressions and the distribution of sedimentary facies on the northern gondwana margin were controlled by a regional nnw sse to almost north south striking structural relief in early silurian times a eustatic highstand enabled the sea to reach its maximum southward extent

early tertiary seafloor spreading magnetic anomalies and paleo propagators in the northern arabian sea abstract study of closely spaced new marine magnetic profiles in conjunction with published magnetic data provide an updated identification of linear magnetic anomalies in the northern arabian sea from the owen fracture zone in the west to the laxmi and chagos laccadive ridges in the east for the first time the entire magnetic anomaly sequence 28 through 20 is mapped eastwards from 65 e up to about 70 e further eastward the post anomaly 28 oceanic crust appears to have been overlain by the volcanic material forming the chagos laccadive ridge contrary to earlier interpretations the identified magnetic lineations are observed to have been segmented mainly by oblique offsets representing the pseudofaults associated with 11 major paleo propagating ridges these ridge propagation events commenced around anomaly 28 time 63 ma and continued at least until anomaly 23 time 52 ma and during the process a large amount of crust was transferred from the african plate to the indian plate the pre anomaly 24 period was characterized by ridge reorientation whereas such a phenomenon was not apparent during the post anomaly 24 period almost all these propagating ridges appear to have been propagating westward probably to migrate away from the proximity of the reunion hotspot the accretionary process of the early tertiary oceanic crust in the arabian sea thus appears to have been greatly influenced by the propagating ridges and the nearby hotspot

analyses of multichannel seismic reflection gravity and magnetic data along a regional profile across the central western continental margin of india abstract analyses of multichannel seismic reflection gravity magnetic and bathymetry data along a regional profile across the central western continental margin of india have revealed the depositional pattern of sediments crustal structure and tectonics the four most distinct and varied crustal regions of the margin are palaeo shelf edges shelf margin basin prathap and laccadive ridges and the arabian basin the shelf margin basin is carpeted by 4 5 km maximum thick aggraded and prograded paleocene to holocene sediments six major seismic sequences of the sediments of the margin are identified and their ages are assigned on correlation with drill well results development of the sequence boundaries is attributed to the events of rifting of western india eustatic sea level changes indian and eurasian plate collision and himalayan orogeny tilted fault blocks half grabens located almost equi distance from the igneous construct of the prathap ridge in the shelf margin basin suggest a failed rift associated with stretched continental crust of the basin 2 d model studies of gravity and magnetic anomalies constrained by the seismic results have revealed 6 to 27 km thick crust across the margin the laccadive ridge crust limited by two volcanic intrusives and a steep scarp at its western end is 16 km thick it gradually thins towards offshore and juxtaposed with early tertiary normal oceanic crust 6 km thick of the arabian basin the crustal thickness and velocity and density structure of the ridge are comparable to that of the laxmi ridge a continental sliver the inferences and abrupt change in magnetic and gravity anomaly signatures across the western end of the laccadive ridge mark the zone of transition from continental to oceanic crust

regional response of the coastal aquifer to hurricane ingrid and sedimentation flux in the yax chen cave system ox bel ha yucatan mexico abstract coastal karst aquifers are an important source of potable water which can be affected by external forcing on various temporal and spatial scales e g sea level but there is a lack of long term data to understand their response sediment cores and their proxy records have been used in lakes and oceans to assess past environmental change but haven t been extensively applied to anchialine caves where there is less known about the physical biological and chemical processes affecting sedimentation over fifty sediment traps were placed in yax chen which is part of the ox bel ha cave system near tulum mexico and four water level sensors were placed in two additional cave systems ponderosa sac actun for comparative water table fluctuations data collected over the past three years 2011 2013 captured seasonal and spatial sediment flux including the effect of an intense rainfall associated with hurricane ingrid september 18 2013 the data indicates that sediment deposition was controlled by cenote size and the presence of mangrove areas upstream of cenote gemini had negligible sediment accumulation as there were few cenotes and the terrain is dominated by lowland tropical forest while areas downstream from cenote gemini were dominated by mangrove forests and larger cenotes which resulted in higher sediment accumulation rates 0 014 vs 0 22 mg cm 2 day bi annual sedimentation rates in 2013 2014 were higher in the months after the rainy season 0 2 vs 0 5 mg cm 2 day indicating that cenote productivity was likely controlling sedimentation mangrove areas with their peat accumulations occlude the porous karst causing funneling of nutrient rich rainwater into the sunlit cenotes enhancing primary productivity and sedimentation in downstream areas hurricane ingrid had little effect on the yearly sediment rate even though water table fluctuations were high 0 7 m compared to the yearly values 0 3 m this likely is due to water bypassing the cenotes with little residence time to enhance productivity and sedimentation in downstream areas

the lower silurian qalibah formation of saudi arabia an important hydrocarbon source rock 1 the lower silurian qalibah formation represents a distinct lithostratigraphic time transgressive sequence it is disconformably bounded below by the upper ordovician to possibly lower silurian sarah formation and above by the continental to marginal marine lower devonian and possibly upper silurian tawil sandstone formation this paper redefines the qalibah formation within these boundaries in its reference section near the town of al qalibah in northwest saudi arabia the qalibah is 499 m thick whereas in a subsurface composite section it reaches 955 m the qalibah formation is a coarsening upward progradational sequence consisting of a lower qusaiba shale member and an upper sharawra sandstone member the basal hot shale of the qusaiba is a black euxinic bottomset shale up to 70 m thick which was deposited during the early silurian sea level rise following the deglaciation of gondwana this paleozoic shale is organic rich and the most likely source rock of the low sulfur high gravity oil condensate and gas discovered in recent years in the paleozoic rocks of central and eastern saudi arabia lithologically similar silurian sequences were deposited over most of the broad stable shelf of gondwana from the middle east to the african sahara

evidence for multiphase folding of the central indian ocean lithosphere long wavelength 100 300 km folding in the central indian ocean associated with the diffuse plate boundary separating the indian australian and capricorn plates is earth s most convincing example of organized large scale lithospheric deformation to test the timing and mechanics of this deformation as implied by plate kinematic and deformation models we present a new analysis of the seismic stratigraphy of the bengal fan sediments this analysis shows that the folding of the oceanic lithosphere was multiphase with major events occurring in the miocene 8 0 7 5 ma pliocene 5 0 4 0 ma and pleistocene 0 8 ma the miocene phase was the most intense and involved deformation of an area south of 1 s whereas in the pliocene the activity shifted northward in the final phase pleistocene the activity was focused in the equatorial region no evidence was found for deformation prior to 8 0 7 5 ma the spatial extent of the pleistocene folding event overlaps the pliocene and or miocene folding events and coincides with both the area of most active faulting and the zone of greatest historical seismicity the seismic data show that the timing of reverse faulting and thus more significant shortening of the lithosphere generally coincided with the phases of folding but there are examples of folding of the oceanic lithosphere without associated reverse faulting

the muknal cave near tulum mexico an early holocene funeral site on the yucatan peninsula here we report on an incomplete human skeleton soot patches related to anthropogenic fireplaces and cut marks on the mandible of an extinct peccary from the submerged muknal cave southwest of t

foraminifera and testate amoebae thecamoebians in an anchialine cave surface distributions from aktun ha carwash cave system mexico surface sediment samples from aktun ha carwash cave system mexico were analyzed for microfossils carbonate isotopes and organic matter content saline water flooded the cave during the sangamon interglacial highstand 124 119 kyr hosting a marine assemblage dominated by saline foraminifera bolivina sp 73 and elphidium sp 11 with a mean 13c 25 5 and a mean 18o 22 7 this assemblage was found distal to sinkholes 75 m upstream 150 m downstream and in yellow orange sediment mean total organic carbon toc 3 6 late pleistocene 95 15 kyr sea level fall reestablished vadose conditions in the cave allowing for localized speleothem flowstone to seal in the marine assemblage holocene sea level rise completely reflooded the cave with freshwater by 6 5 kyr providing a suitable habitat for a freshwater assemblage of living testate amoebae centropyxis aculeata 38 arcella vulgaris 10 and the foraminifer ammonia tepida var juvenile 35 with a mean 13c 210 8 and a mean 18o 24 9 on the ostracod cytheridella ilosvayi this assemblage was found proximal to sinkholes 75 m upstream 150 m downstream and in black to brown sediment mean toc 17 5 foraminifera and testate amoebae colonize aquatic cave environments respond to physicochemical conditions in the cave similarly to other coastal settings and thereby provide promise for the application of protists as proxies in flooded caves

early spreading and continental to oceanic basement transition beneath the indus deep sea fan northeastern arabian sea abstract a seismic survey to study the indus deep sea fan penetrated into basement this enabled the mapping of basement structures and a description of the geodynamical evolution of a part of the northeastern arabian sea the main tectonic structure of the basement is an e w graben gop rift with a prominent central e w horst the palitana horst this rift is cut obliquely by several ne sw faults large e w magnetic anomalies are not the continuation of the magnetic anomaly sequence of the oceanic arabian basin however these anomalies are linked to inverse magnetisation in the crust suggesting that the rift is either underlain by stretched continental crust intruded by linear volcanic bodies related to the deccan traps or by oceanic crust older than chron 28 64 ma as proposed in the laxmi basin southeastwards accompanying these structures ne sw faults with a strike slip pattern may have played the role of transform direction during the separation of the laxmi ridge from the indian continent we propose that rifting and oceanic spreading have occurred around a triple junction connecting the oceanic laxmi basin the narmada son lineament and the gop rift this phase preceded oceanic spreading in the arabian basin this interpretation is in agreement with the previously proposed initial separation of india and the seychelles before chron 28 the laxmi ridge could be a part of the seychelles microplate subsequently left attached to india

geologic and environmental aspects of surface cementation north coast yucatan mexico the northernmost part of the fresh water aquifer of yucatan mexico is confined near the coast by a thin flat nearly impermeable calcareous layer the authors think it probable that this confining layer is now developing by a process of sedimentation and precipitation of pore filling cement on and near the surface of older limestone at the landward margin of the swamp that extends virtually continuously along the north yucatan coast it is their interpretation that this caco sub 3 cemented layer which is 0 5 to 1 4 m thick developed in the zone of discharge of the fresh water aquifer the presence of sup 14 c 6 0 plus minus 0 4 modern carbon in a sample of aquitard supports the hypothesis that cementation is an ongoing process further support comes from the remarkable regularity between modern mean sea level and the elevation of the landward boundary between the confining zone and normal karst along 250 km of coast confinement of the aquifer produces an elevation of the piezometric surface to about 0 5 m above mean sea level and a concurrent depression of the fresh water salt water interface to an estimated depth of about 18 m below mean sea level at the coast breaching of the confining layer implicit inmore some development schemes for the region could dramatically decrease the thickness of the fresh water lens a valuable water resource the mixing zone beneath the confined part of the aquifer is a chemically active volume that may be vigorously pumped by tides as evidenced by increased salinity of ground water near the coast thus making this zone a likely place for rock water interaction including perhaps dolomite formation less