Late Neogene nannofossil biostratigraphy and paleoceanography of the northeastern Gulf of Mexico and adjacent areas

Two 305 m cored sections from the northwest Florida continental shelf contain a nearly complete record of late Neogene hemipelagic sedimentation. One of the sites, south and east of De Soto Canyon, is isolated from terrigenous sediment except for sediment transported in suspension. This site contains a continuous record from the late Miocene to the Recent. The second site, on the western rim of De Soto Canyon, is more expanded and continuous from the late Pliocene to the Recent. A hiatus separates the late Pliocene from the middle Miocene. Six prominent nannofossil biohorizons were recognized within the Pleistocene, seven within the Pliocene, and three within the Miocene; in addition one biohorizon marks the base of the Pleistocene and another the base of the Pliocene.Nearly all carbonate in the sediment is pelagic. Terrigenous detrital sedimentation was controlled by glacioeustatic sea level fluctuations during the Pleistocene, and sea level changes are probably responsible for fluctuations in the ratio of pelagic carbonate to clayey detritus in pre-Pleistocene sediments also. Carbonate content, coarse fraction percent, and relative abundances of environmentally sensitive nannoplankton species suggest important paleoceanographic changes in the northeastern Gulf of Mexico and adjacent areas. Fluctuations in the relative abundance of the solution-resistant coccoliths of the genusCyclococcolithus indicate that waters at a depth of 600–1000 m were more corrosive during the late Miocene than they are today. The decrease in carbonate dissolution during the late Miocene probably was a response to gradual constriction of the Central American passage and the consequent restriction of flow of corrosive water from the Pacific. Short term fluctuations in dissolution during the Pliocene and Pleistocene are related to climatic cycles.Productivity variations in the surface waters, recorded mainly by the relative abundance of small and large morphotypes of closely related coccolith species, indicate that productivity increased during the Pliocene, but the most dramatic change — a major oceanwide increase in productivity — occurred during the Pleistocene, during and just prior to the Jaramillo magnetic event about 0.9 m.y. ago. Surprisingly the late Miocene Messinian event did not leave a significant imprint in the northeastern Gulf of Mexico.     

Late neogene biostratigraphy and paleoceanography of DSDP site 310 Central North Pacific and correlation with the Southwest Pacific

Late Neogene planktonic foraminifera have been examined at Site 310 in the Central North Pacific and their stratigraphic ranges and frequencies are presented here. Blow's (1969) zonation developed for tropical regions has been applied where applicable. Where tropical index taxa are rare or absent in this temperate region, Globorotalia crassaformis, and the evolutionary bioseries G. conoidea — G. conomiozea and G. puncticula — G. inflata have been found useful for zonal subdivisions. A correlation between stratigraphic ranges and frequency distributions of these species at Site 310 in the Central North Pacific, and Site 284 in the Southwest Pacific indicates that these species are relatively consistent biostratigraphic markers in temperate regions of both the North and South Pacific Oceans. An informal zonation for temperate latitudes of the Southwest Pacific has been established by Kennett (1973) and a similar zonal subdivision can be made at Site 310.Paleoclimatic/paleoceanographic interpretations based on coiling ratios, percent abundance, and phenotypic variations of Neogloboquadrina pachyderma indicate four major cold events during early, middle, and late Pliocene, and early Pleistocene. Faunal correlations of these events with similar events elsewhere in the Northeast and Southwest Pacific which have been paleomagnetically dated indicate the following approximate ages for these cold events: 4.7 Ma, 3.0 Ma, 2.6–1.8 Ma. and 1.2 Ma. Faunal assemblages have been divided into three groups representing cool, intermediate, and warmer water assemblages. Cool water assemblages are dominated by >60% N. pachyderma; intermediate temperature faunas are dominated by species of Globigerina and Globigerinita and contain between 20% and 30% N. pachyderma. Warmer water assemblages are dominated by species of Globorotalia and contain <10% N. pachyderma. Frequency oscillations within these groups, in addition to paleotemperature parameters evident in N. pachyderma, afford refined paleoclimatic/paleoceanographic interpretations.     

Late eocene—early oligocene integrated isotope stratigraphy and biostratigraphy for paleoshelf sequences in southern Australia: paleoceanographic implications

A late Eocene—early Oligocene planktonic foraminiferal oxygen-isotope stratigraphy derived for two overlapping sections (Browns Creek and Castle Cove) through paleoshelf sequences in southern Victoria, Australia, contains a pronounced late Eocene depletion (warm) peak (1.2%PDB) centred at about 41 Ma, followed by a two-stage enrichment (cooling) pattern, the later one coinciding with the well known Terminal Eocene Event (37 Ma), exhibiting 1.0%PDB) erinchment. The early Oligocene isotope stratigraphy shows fluctuations of about 1.0%PDB, with prominent depletion peak immediately following the terminal Eocene δ¹⁸O enrichment. The start of the terminal Eocene δ¹⁸O enrichment coincides with the LAD of the nannofossil indicator of the Eo-Oligocene boundary, Discoaster saipanensis (early NP21 Zone). On this basis the traditional southern Australia planktonic foraminiferal Eocene-Oligocene boudary markers (LAD Globigerapsis index, LAD Subbotina linaperta Subbotina linaperta) locally survived into Zone NP22, well into the early Oligocene.

Sea-surface paleotemperature estimates derived from the δ¹⁸O data assuming a δW value of −1.2%PDB, show that the late Eocene ingression of the tropical planktonic foraminiferal genus Hankenina coincided with peak surface-water tempertures of 24°C. The temperature decline in the southern Australia shelf waters associated with the Terminal Eocene Event may have been as much as 7°C, reaching a minimum value of 13°C. The later survival of G. index and S. linaperta coincides with a rapid recovery of water temperatures over the south Australian shelf following the Terminal Eocene Event. This is attributed to the local warming of waters in shallow broad embayments where circulation patterns were decoupled from the developing Circum-Antartic Current to the south.     

Late Quaternary biostratigraphy and paleotemperatures of the Red Sea and the Gulf of Aden based on planktonic foraminifera and pteropods

The quantitative distributions of planktonic foraminifera and pteropods were analyzed in seven Red Sea cores and two deep-sea cores from the Gulf of Aden and off Sokotra Island. Biostratigraphic intervals were distin-guished corresponding to oxygen-isotope stages 1–5 in the Red Sea and stages 1–3 in the Gulf of Aden.The faunal assemblages demonstrate that in the Red Sea hydrological conditions changed significantly during the Late Quaternary — especially at the last Glacial maximum, when water exchange at the Bab-el-Mandeb Straits was at a minimum and at the Pleistocene/Holocene boundary. At the end of deglaciation, water-exchange renewal and pluvial conditions resulted in surface salinity decrease and stable stratification, which was followed by a rise in planktonic fauna abundance and stagnation of bottom waters. The more constant composition of rather cold-water (subtropical) faunal assemblages in the Gulf of Aden during the last 40,000–50,000 yrs. points to more stable hydrological parameters and to local upwelling or influx of Arabian upwelling waters.During the last Stadial, mean annual sea-surface temperatures fell by at least 5°C compared to the present in the central part of the Red Sea and by 3.5°C in the western Gulf of Aden.     

An enigmatic heteronemertean from the Gulf of Mexico

The effects of acid (HNO3) on drift and survival of benthic invertebrate communities were assessed in stream microcosms over a 7-day exposure period. Communities were obtained from the Cache la Poudre River, Colorado, using artificial substrates colonized in the stream for 30 days and then transferred to stream microcosms. Streams receiving the highest acid concentration (pH 4.0) contained significantly fewer individuals ( F = 378.42, p < 0.0001) and taxa ( F = 7.8, p = 0.0123) at the end of the experiment compared to the other two treatments (pH 5.5, 6.5) and the control (pH 7.4). Reduced macroinvertebrate abundance resulted primarily from reduced abundance of mayflies (Ephemeroptera) which were particularly sensitive. Comparisons of Plecoptera, Trichoptera, and Diptera abundances showed no statistically significant differences among treatments. Analysis of invertebrate drift samples, collected after 2, 6, 18, and 42 h exposure, revealed that percent drift in the most acidic streams was nine times that of control streams. Ephemeroptera was the only aquatic insect order to exhibit a significant drift response, and timing and magnitude of responses varied among mayfly taxa. Differences in sensitivity to acid among aquatic insect orders observed in our experimental streams were similar to those reported from field studies in other regions. Effects of acid on drift and survival of benthic invertebrate communities were also similar to effects of heavy metals, one of the primary water quality concerns in the Rocky Mountain region. These results suggest a general pattern of responses to chemical stressors in benthic communities from Rocky Mountain streams. This revised version was published online in July 2006 with corrections to the Cover Date.     

An enigmatic heteronemertean from the Gulf of Mexico

Heteroenopleus enigmaticus gen. nov., sp. nov. isdescribed from the northwestern Gulf of Mexico. Itoccurs both in the nearshore Gulf and in high salinityestuarine areas. Body wall musculature conforms tothe general plan of heteronemerteans, i.e. outerlongitudinal, middle circular and inner longitudinalmuscle layers. The head bears a pair of horizontallateral slits, characteristic of the lineids. Theproboscis musculature is of the heteronemerteanpalaeotype with two muscle layers, outer circularand inner longitudinal. Other morphologicalcharacters agree with those of heteronemerteans withone major exception: the proboscis is armed with tworows of structures, herein named parastylets. Thisarmature has no morphological similarity to either themicrovillar proboscideal spines of heteronemerteans orto the stylets of mono- or polystiliferans. A newsubfamily Heteroenopleinae is erected to contain theapomorphic character of an armed proboscis.     

Late Devonian carbon isotope stratigraphy and sea level fluctuations, Canning Basin, Western Australia

The Upper Devonian reef complexes of the Canning Basin contain some of the world’s best exposed, continuous stratigraphic sections through the Frasnian-Famennian boundary. The facies distribution and composition of these reef complexes record interactions among sea level changes, sediment supply, ocean chemistry, and paleoecology. Changes in relative sea level produced spatial shifts in reef platform development and regional changes in sediment supply that can be correlated across facies boundaries using a combination of sequence stratigraphy, biostratigraphy, and carbon isotope stratigraphy. During the lowstand interval below the Frasnian-Famennian boundary, the reef margin advanced down the reef slope in shallow-water environments, and siliciclastics locally dominated in the marginal slope environment. Compilation of a broad late Frasnian to early Famennian sequence stratigraphic framework for the Canning Basin demonstrates that transgressive intervals correlate to positive carbon isotopic excursions within the basin. These isotopic shifts also can be correlated to time-equivalent positive carbon isotopic excursions reported from transgressive intervals in Europe. Thus, the late Frasnian transgressions in the Canning Basin were primarily eustatic rather than tectonic in origin, and positive carbon isotopic signatures of the Kellwasser horizons are globally correlative.     

Late Ordovician carbon isotope trend in Estonia, its significance in stratigraphy and environmental analysis

Carbon isotope changes during most of Late Ordovician time (from the mid-Caradoc Kinnekulle K-bentonite until the beginning of the Silurian) were investigated. As the corresponding sequence of rocks is stratigraphically nearly complete in Estonia, an attempt was made to use it to elaborate the general pattern of carbon isotope changes in the Late Ordovician. Complications were caused by several local or regional hiatuses in the middle and late Caradoc and Hirnantian. A total of 385 whole rock samples were studied from eight drill cores in northern and central Estonia. The following positive carbon isotope events were observed: (1) the mid-Caradoc excursion (peak δ¹³C value 2.2‰) in the uppermost part of the Keila Stage, also known in Sweden; (2) the first late Caradoc excursion (1.9‰) in the lower part of the Rakvere Stage; (3) the second late Caradoc excursion (2.4‰) in the upper part of the Nabala Stage; (4) the early Ashgill excursion (2.5‰) in the lowermost part of the Pirgu Stage; (5) the widely known large Hirnantian excursion (in Estonia the peak value reaches 6.7‰) in the Porkuni Stage. The study interval comprises a long (10 Ma) period characterized by low-magnitude carbon isotope changes and a following brief (2 Ma) interval with large changes. No obvious lithological preference for hosting the positive shifts was recorded. In principle, the δ¹³C values exceeding the background values may occur in all types of rocks present in a sedimentary basin. Several δ¹³C positive excursions (values 1.5‰ to 3‰) in the Mohawkian of North America are evidence that the minor Caradoc and early Ashgill δ¹³C positive shifts in Baltoscandia may have counterparts in Laurentia. If correctly correlated, these shifts may have global significance. The Hirnantian excursion is usually linked to a major glacial event, even if some carbon cycling mechanisms are not completely understood. The environmental causes suggested for the earlier minor shifts range from global climatic and glacial events to very local changes in basin regime and sea level. Our study supports the primary role of climatic or climatically triggered oceanic processes.     

Phylogeny of Marine Bacillus Isolates from the Gulf of Mexico

The phylogeny of 11 pigmented, aerobic, spore-forming isolates from marine sources was studied. Forty-two biochemical characteristics were examined, and a 16S rDNA sequence was obtained for each isolate. In a phylogenetic tree based on 16S sequencing, four isolates (NRRL B-14850, NRRL B-14904, NRRL B-14907, and NRRL B-14908) clustered with B. subtilis and related organisms; NRRL B-14907 was closely related to B. amyloliquefaciens. NRRL B-14907 and NRRL B-14908 were phenotypically similar to B. amyloliquefaciens and B. pumilus, respectively. Three strains (NRRL B-14906, NRRL B-14910, and NRRL B-14911) clustered in a clade that included B. firmus, B. lentus, and B. megaterium. NRRL B-14910 was closely related phenotypically and phylogenetically to B. megaterium. NRRL B-14905 clustered with the mesophilic round spore-producing species, B. fusiformis and B. sphaericus; the isolate was more closely related to B. fusiformis. NRRL B-14905 displayed characteristics typical of the B. sphaericus-like organisms. NRRL B-14909 and NRRL B-14912 clustered with the Paenibacillus species and displayed characteristics typical of the genus. Only NRRL B-14851, an unusually thin rod that forms very small spores, may represent a new Bacillus species. Received: 8 December 1999 / Accepted: 14 February 2000     

Diatom biostratigraphy and comparative core correlation within a small lake basin

A number of short cores from Lough Augher, Co. Tyrone, N. Ireland, with water depths ranging from 3–12 m, were independently correlated using various parameters: diatom biostratigraphy, magnetic mineral stratigraphy (, SIRM, S-Ratio) and loss-on-ignition (LOI). Correlating between deep and shallow water sites using LOI proved problematical, although this was possible with both bio- and magneto-stratigraphy. Agreement between these techniques was generally good, but decreased with increasing sediment depth. Although correlation errors are considerably less than those derived from dating, they do suggest that exclusive use of unsubstantiated correlations based on magnetic parameters may lead to erroneous estimates of dry mass or micro fossil accumulation rates, particularly when a whole basin approach is taken.     

Structural and chemical defenses of echinoderms from the northern Gulf of Mexico

The feeding deterrent effects of echinoderm body-wall tissues and ethanolic extracts containing mid-polarity compounds were evaluated utilizing generalist fish and crabs as model predators. The body-wall tissues of the echinoderms examined ranged 10-fold from 0.9–9.4 mm in thickness, and four and a half-fold in level of mineralization (17.8–82.7% ash content). Holothuroids had the thickest body-wall tissues and contained the lowest levels of mineralization in their body-walls. Crinoids and ophiuroids had high levels of mineralization in their arms. Asteroid body-wall tissues varied the most in thickness and ash content (0.9–3.9 mm in thickness and 29.2–55.5% in ash content). Body-wall tissues of 19 species of echinoderms were tested for their feeding deterrent properties against the marine fishes Lagodon rhomboides (Linnaeus) and Cyprinodon variegatus (Lacepede), as well as the decapod crustacean Libinia emarginata (Leach). Equivalent sized pieces of fresh body-wall tissue of 16 species of echinoderms caused observable feeding deterrence responses in at least two of the three model predators. There was no significant correlation between body-wall thickness or percent ash and its palatability to any of the three model predators. Agar pellets containing ethanolic body-wall extracts of 12 of 18 echinoderm species caused observable feeding deterrence responses in the fish L. rhomboides. In similar experiments with the arrow crab Stenorhyncus seticornis (Herbst), using carrageenan fish-meal blocks as food models, no differences in consumption of control fish-meal and experimental body-wall extract blocks were detected. Our findings indicate that invertebrate and vertebrate predators may respond quite differently to echinoderm body-wall extracts.     

Crustaceans from antipatharians on banks of the northwestern Gulf of Mexico

The stalked barnacle Oxynaspis gracilis, the chirostylid squat lobster Uroptychus sp., and the caridean shrimps Periclimenes cf. antipathophilus and Pseudopontonides principis have been collected at 68–124 m by a remotely operated vehicle (ROV) on banks in the northern Gulf of Mexico. These species inhabited six species of antipatharian hosts. Pseudopontonides principis, Oxynaspis gracilis, and Uroptychus sp. were not confined to a single host species. Except for Oxynaspis gracilis, collected by ROV in 2004–2005, these species have not been reported previously in the northwestern Gulf of Mexico.     

Behaviour of a sharptail mola in the Gulf of Mexico

A sharptail mola Masturus lanceolatus was tagged and released with a pop-up satellite archival tag in the Gulf of Mexico and tracked for 61 days. The fish travelled a horizontal distance of 594 km while generally staying in water <200 m depth and >20° C. Occasionally the sharptail mola dived to depths >700 m and experienced water colder than 6° C.     

Echinoids (Echinodermata: Echinoidea) from the Gulf of Mexico

The echinoid fauna of the Gulf of Mexico collected during three research cruises (20-1260 m depth) was surveyed from samples were taken at 43 stations. A total of 190 individuals were identified (eight orders, 11 families, 15 genera and 18 species). Six species are new records for the Gulf of Mexico: Stylocidaris lineata, Phormosoma placenta placenta, Plesiodiadema antillarum, Plethotaenia spatangoides, Brissopsis atlantica and Hypselaster limicolus. This adds to the little information available on the echinoid fauna of Tamaulipas, Veracruz, Tabasco, Campeche and Yucatan states in Mexico.     

Echinoderms (Echinodermata) from the Gulf of California, Mexico

A systematic list of the echinoderms of the Gulf of California, based on museum specimens of the Colección Nacional de Equinodermos, Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autónoma de México and the National Museum of Natural History, Smithsonian Institution, Washington, D.C. is presented. A total of 193 echinoderm species is recorded, distributed in 108 genera, 51 families and 19 orders. 12 new records for the Gulf of California are presented: Asteroidea (four), Ophiuroidea (three) and Holothuroidea (five).     

Lower Emsian biostratigraphy and event stratigraphy of Ha Giang Province,northern Vietnam

A new species of rugose coral, Sanidophyllum dubium n. sp., and the typical Emsian (Early Devonian) rugose coral Xystriphylloides nobilis are described from the Mia Le Formation in northern Vietnam. The lower Emsian index conodonts ranging from the Polygnathus excavatus zone to the P. nothoperbonus zone are illustrated. The biostratigraphic correlation between northern Vietnam and South China shows that the Mia Le Formation in northern Vietnam is early Emsian in age, and its upper part can be correlated with the lower part of the Shizhou Member of the Yukiang Formation in Liujing, Guangxi and its equivalents in South China. Based on the study of the lower Emsian biostratigraphic sequence, the disappearance of Xystriphylloides nobilis fauna in the overlying bed of the uppermost Mia Le Formation and the extinction of the “tonkinensis fauna” (sensu lato) in the interval between the basal Si Phai Formation and the uppermost Mia Le Formation demonstrate the influence of the Yujiang Event in northern Vietnam.     

Foraminiferal biostratigraphy and sequence stratigraphy across the mid-Carboniferous boundary in the Central Taurides,Turkey

The Aladağ Unit is one of the main tectonic units in the Tauride Belt, located in southern Turkey. It includes a continuous Paleozoic carbonate sequence encompassing the mid-Carboniferous boundary, with outcrops being especially well exposed in the Hadim region. The boundary succession lithology is mainly composed of carbonates with intercalated quartz arenitic sandstone layers. Based on foraminifers, four biostratigraphic zones have been defined in the interval from the Upper Serpukhovian to the Lower Bashkirian. These zones are, in ascending order: the Eostaffella ex gr. ikensis—E. postmosquensis Zone (Zapaltyubinsky Horizon, Upper Serpukhovian); the Plectostaffella jakhensis—P. bogdanovkensis Zone, and the Millerella marblensis Zone (Bogdanovsky Horizon, lower Bashkirian); and the Semistaffella sp. Zone (Syuransky Horizon, lower Bashkirian). The mid-Carboniferous boundary occurs between the Eostaffella ex gr. ikensis—E. postmosquensis Zone and the Plectostaffella jakhensis—P. bogdanovkensis Zone. Boundary beds are characterized by eight, repeatedly occurring microfacies types, namely: (1) coated crinoidal packstone; (2) coated bioclastic grainstone; (3) oolitic grainstone; (4) oolitic packstone-grainstone; (5) intraclastic grainstone; (6) mudstone-wackestone; (7) quartz-peloidal packstone; and 8) quartz arenitic sandstone. Based on microfacies stacking patterns, various types of shallowing-upward cycles have been recognized. Depositional sequences and sequence boundaries are correlatable with those described from North America and Russia and Carboniferous global sea-level curves. The duration of cycles has been estimated as 100 ky, suggesting that cycle periodicities correspond to the Milankovitch eccentricity band.     

Belemnite ecology and the environment of the Nusplingen Plattenkalk (Late Jurassic,southern Germany): evidence from stable isotope data

The late Kimmeridgian Nusplingen Plattenkalk (palaeolatitude ~30°N) is one of the well‐known European Plattenkalk konservatlagerstätten. The laminated limestones of this lagerstätte have been deposited in a shallow lagoon, surrounded by sponge‐microbial mounds, some of which formed small islands. Plattenkalk sediments are often thought to have been deposited below a halocline, which was induced by high evaporation rates. By measuring the stable isotope composition of belemnite rostra (n = 27) of the species Hibolithes semisulcatus, the depositional environment of the Nusplingen Plattenkalk has been investigated. Cathodoluminescence‐microscopy and trace element analysis have been applied to check for diagenetic alteration of the studied rostra. The mean δ¹³C of the well‐preserved rostra is +0.03 ± 0.27‰, the mean δ¹⁸O ?0.68 ± 0.3‰. A narrow range of stable isotope data acquired from an accumulation of rostra, regurgitated by a fish or reptile, supports the notion that belemnite calcite reflects environmental conditions. The palaeontological and sedimentological findings suggest that H. semisulcatus was autochthonous to the Nusplingen Plattenkalk. Anoxic conditions prevailed in the sediments and temporarily in the water‐column above the sediment/bottom water interface. A nektobenthic life style can be excluded for the Nusplingen belemnites; a demersal life style seems unlikely. Comparison with δ¹⁸O_bel data from other latitudes indicates that a latitudinal gradient played a role in the δ¹⁸O composition of seawater. A pelagic, inner shelf setting is therefore suggested for the Plattenkalk, an interpretation that is supported by palaeontological evidence. It is here proposed that the formation of the Nusplingen Plattenkalk was not caused by salinity stratification. It is further suggested that the belemnites were not restricted to deep‐water settings, but also occurred in shallow waters and higher in the water‐column.     

The core seafloor microbiome in the Gulf of Mexico is remarkably consistent and shows evidence of recovery from disturbance caused by major oil spills

The microbial ecology of oligotrophic deep ocean sediments is understudied relative to their shallow counterparts, and this lack of understanding hampers our ability to predict responses to current and future perturbations. The Gulf of Mexico has experienced two of the largest accidental marine oil spills, the 1979 Ixtoc-1 blowout and the 2010 Deepwater Horizon (DWH) discharge. Here, microbial communities were characterized for 29 sites across multiple years in > 700 samples. The composition of the seafloor microbiome was broadly consistent across the region and was well approximated by the overlying water depth and depth within the sediment column, while geographic distance played a limited role. Biogeographical distributions were employed to generate predictive models for over 4000 OTU that leverage easy-to-obtain geospatial variables which are linked to measured sedimentary oxygen profiles. Depth stratification and putative niche diversification are evidenced by the distribution of taxa that mediate the microbial nitrogen cycle. Furthermore, these results demonstrate that sediments impacted by the DWH spill had returned to near baseline conditions after 2 years. The distributions of benthic microorganisms in the Gulf can be constrained, and moreover, deviations from these predictions may pinpoint impacted sites and aid in future response efforts or long-term stability studies.