Non-marine Environments Research Articles

The Eemian stage in the Netherlands: history, character and new research

Abstract A historical outline of the Eemian research in the Netherlands is presented as an introduction to recent research in the type area. At the end of the 19th and during the first part of the 20th century, Eemian sediments were recognized because of the presence of lusitanian and mediterranean mollusc species. From 1930 onwards, pollen analysis made it possible to identify also non-shell-bearing deposits and to equate them with the Eemian. At the same time this technique proved a valuable tool for understanding the vegetation development during this interglacial. Pollen zonation offered a unique possibility for the correlation of terrestrial sequences in North-West Europe. The type area of the Eemian, near Amersfoort, was described by Harting in 1874 and was comprehensively restudied by Zagwijn (1961). A pollen zonation was introduced as a standard for the Netherlands, allowing the correlation of pollen records from both marine and non-marine depositional environments. This enabled a more detailed temporal resolution, resulting in a better understanding of the distribution of the various environments in the type area. In the northern and central parts of the Netherlands, the identification of the marine sequence was, apart from the occurrence of the specific mollusc fauna, facilitated by the presence of a till of Saalian age underlying the Eemian deposits. The presence of deep glacial basins in these areas enabled the deposition and preservation of a complete Eemian record in a marine setting. Sediment accumulation in the basins began immediately following deglaciation at the end of the Saalian. The Eemian type sections at Amersfoort are situated near the margin of one of these basins. Recent research of the Eemian focused on the integration of lithostratigraphic evidence and information on the sedimentary environment as derived from diatoms, dinoflagellates, foraminifers, molluscs and pollen.

サハリン（樺太）島の地質と地形 サハリンの新第三紀有孔虫化石層序と古環境変遷

Based on foraminiferal biostratigraphy of the Neogene sedimentary sequences of Shmidta Peninsula at the northern tip and the Makarov region in southeastern Sakhalin, Russian Far East, paleoenvironment and ages are discussed. In the Makarov region, the history of environmental changes is roughly delineated, as follows: warm non-marine environment in late Early Miocene, transgression around early Middle Miocene, abrupt deepening into bathyal depth in Middle Miocene, and regression during Late Miocene and Pliocene. This succession is quite similar to those in Hokkaido and the northern Honshu in Japan. In the Pil'vo section at the west coast of Shmidta Peninsula, the similar bathymetric changes are recognized at the same time as in the Makarov region, although this section is regarded as being in the bathyal depths throughout Early to Middle Miocene.The occurrences of some temperate-water species give evidence of the influence of warm-surface water during the Miocene period. Ammonia spp. survived in early Middle Miocene (the transition period between the MNCO and the following cooler stage in early Middle Miocene) in the Makarov region. A planktonic foraminifer, Globorotalia cf. miozea conoidea was found in the middle part of the Pili Formation (early Middle Miocene) of the Pil'vo section. This is the first discovery of keeled Globorotalia in Sakhalin, and is important for the consideration of the geohistory of the Northwest Pacific, in particular the first appearance of subarctic climate and cold Oyashio water.

Recognition and distinction of normal and forced regression in cyclothemic strata: a Plio-Pleistocene case study from eastern North Island, New Zealand

Abstract The Tangoio block of eastern North Island, New Zealand contains an exceptionally well exposed, 550 m thick sequence of Plio-Pleistocene cyclothemic sedimentary rocks, the Petane Group, that were deposited along the western margin of a shallow (<200 m) pericontinental seaway. The cyclicity that characterizes the Petane Group in this area was generated through recurring 40 ka (sixth-order) sea-level changes of c. 75–150 m. Data from more than 100 sections indicates that the strata consist of five distinct cyclothems, each consisting of a lower formation of mudstone deposited in midshelf environments (highstand system tract, HST), and an upper formation dominated by coarse-grained facies deposited in shallow marine and occasionally non-marine environments. Western exposures of HST mudstones in the lower portion of the Petane Group shoal up into shallow marine siliciclastic sandstones, fluvial gravels and siltstones. The transition is gradational and is consistent with progradation of a siliciclastic shoreline during late sea-level highstand. The shoaling upward siliciclastic sandstone interval represents a regressive system tract (RST) whereas the fluvial beds represent a lowstand system tract (LST). LST gravel beds are sharply overlain by a transgressive surface of erosion and fining-upward siliciclastic sandstone facies of a transgressive systems tract (TST). Carbonate sediments replaced siliciclastic sandstones as the dominant coarse-grained lithology in the upper Petane Group, probably due to bypass of siliciclastic sediment during sea-level fall. Transitions from HST mudstone into carbonate sand and bioclastic limestone (coquina) are generally sharp everywhere except the downdip eastern portions of the Tangoio block. The contacts represent regressive surfaces of erosion produced during falling stages of sea-level and/or ravinement surfaces formed during rising phases of sealevel (transgressive surfaces of erosion). Carbonate facies atop these erosional surfaces are generally interpreted as TST deposits, except for the uppermost limestones in the Petane Group that occur below a sequence boundary and therefore represent a forced regression systems tract (FRST). Stratal position is the only distinguishing characteristic of FRST limestones in the Petane Group, otherwise they are identical to TST deposits. In eastern portions of the Tangoio block, HST mudstones pass gradationally into RST calcareous sandstones and LST limestones. Systems tracts here are bounded by correlative conformities rather than erosive surfaces indicating continuous sedimentation during sea-level fall and lowstand. Differences in sedimentation and subsidence rates between carbonate and siliciclastic sedimentary systems, are responsible for the different stratal architecture of systems tracts in the Petane Group.

Evolution and sulphide mineral occurrences of an incipient nonmarine sedimentary basin, New Zealand

Abstract River sediments at Macraes Flat, east Otago have formed in a tectonically active depression in the Otago Schist basement adjacent to an active northeast striking fault. The depression is the most juvenile of a series of nonmarine basins currently forming during tectonic convergence. The sediments were derived from rapid erosion of the rising fault scarp, with long-term average sedimentation rates between 0.15 and 0.18 mm/year. The Hyde–Macraes Shear Zone crosses the depression, and this shear zone hosts the Macraes gold mine. The shear zone contains sulphide minerals, mainly pyrite and arsenopyrite. Sulphide minerals were eroded and deposited in the Macraes Flat river sediments at least 28,000 years ago. The sulphide minerals have not suffered any detectable decomposition in the sediments, even though some oxygenated water incursion has occurred. This sulphide longevity is due to general water saturation in the basin floor, despite possible occasional drying. Some sands have remained unaffected by oxygenated waters, and authigenic pyrite deposition has occurred. The pore waters in recently-exposed outcrops of organic sands with authigenic pyrite are too oxidised to be in equilibrium with pyrite. The Macraes Flat example demonstrates that sulphide minerals can remain stable for tens of thousands of years, and authigenic sulphides can form locally, within only 5 metres of the surface in an oxygenated atmosphere and only sporadic water saturation in a tectonically active nonmarine environment.

Occurrence of authigenic siderites in the Early Holocene coastal deposit in the west coast of Korea: an indicator of depositional environment

The macrotidal muddy deposits around Youngjong Island in the west coast of Korea with a radiocarbon dating of ca. 8000 yr BP contain micro-scale (ca. 150 μm) siderite concretions. The authigenic siderites exhibit the aggregated spherulitic textures with well-developed rhombs on the grain surfaces, which reflects good preservation. Geochemical analyses indicate that the concentrations of Mg (mean 2.6 mol%) and Ca (mean 9.4 mol%) are low whereas those of Fe (mean 70.4 mol%) and Mn (mean 17.6 mol%) are relatively high. The chemical composition suggests that the authigenic siderites might have precipitated in a non-marine environment. The occurrence of such siderites in the early Holocene sediments, considering the stratigraphic level with respect to the well-established sea-level curve helps recognize the non-marine depositional environment existed before the formation of modern tidal flats along the west coast of Korea.

The sequence stratigraphic concept and the Precambrian rock record: an example from the 2.7–2.1 Ga Transvaal Supergroup, Kaapvaal craton

Sequence stratigraphic concepts are applied to the 2.7–2.1 Ga Transvaal Supergroup, which constitutes the sedimentary floor to the Bushveld igneous complex. The Transvaal succeeds the foreland-fill of the Witwatersrand Supergroup and, in its lowermost portions, is partly synchronous with the Ventersdorp Supergroup lavas that followed upon the Witwatersrand sediments in the stratigraphic record. The unconformable contacts at the base and the top of the Transvaal Supergroup mark significant changes in the overall tectonic setting, which qualifies them as first-order sequence boundaries. Sedimentation within the Transvaal basin was controlled by cycles of extensional and/or thermal subsidence resulting in the accumulation of sequences, separated by stages of base-level fall generating sequence-bounding subaerial unconformities. The Transvaal first-order sequence is subdivided into five second-order unconformity-bounded depositional sequences, i.e. the Protobasinal, Black Reef, Chuniespoort, Rooihoogte–Timeball Hill and Boshoek–Houtenbek sequences. The span of time of these second-order sequences, averaging 130 Ma, is much longer than the duration of the second-order Phanerozoic cycles, which is explained by the less evolved and thus slower plate tectonic processes that dominated the Late Archaean–Early Proterozoic times. Each Transvaal second-order sequence preserves a variable number of systems tracts, mainly as a function of the strength of the erosional processes associated with the ravinement surfaces and subaerial unconformities. In a complete succession, a sequence would include a basal lowstand systems tract (LST), followed by transgressive (TST), highstand (HST) and falling stage (FSST) systems tracts. The Protobasinal and Rooihoogte–Timeball Hill sequences only preserve the LST and TST, due to the strong post-depositional erosion. The Black Reef sequence is composed of LST, TST and HST. The Chuniespoort sequence preserves the TST, HST and FSST, but lacks the LST due to ravinement erosion. The Boshoek–Houtenbek sequence develops the complete succession of systems tracts. Common features may be emphasized between the same types of systems tract developed within different sequences. The LST includes high-energy coarse prograding facies, such as alluvial fans and fan–delta systems, that fill the irregularities of the pre-existing topography and lead to the peneplanation of the depositional areas. The TST may be recognized from retrogradational stacking patterns that are associated with the transgression of marine environments. The HST marks the normal regression of the previous marine environments, which assumes coeval aggradation of fluvial and basinal facies within an overall progradational framework. The FSST would normally include only basinal facies age-equivalent with the correlative subaerial unconformities. In our case study, the stages of base-level fall resulted invariably in fully nonmarine environments within the Transvaal area, generally leading to the development of subaerial unconformities. In particular circumstances, the nonmarine environment may still accumulate and preserve fluvial, alluvial fan or lacustrine sediments as a function of the relative position between topography and local equilibrium profiles and base-levels. The interpretations of base-level rise and fall resulting from the application of the sequence stratigraphic concept to the 2.7–2.1 Ga Transvaal Supergroup enable estimation of sea level changes during deposition of this succession. With an understanding of local tectonic conditions on the Kaapvaal craton and of coeval sedimentation elsewhere in Africa, eustatic and relative sea level changes and variation in continental freeboard conditions may be suggested for the Transvaal Supergroup.

Weald Clay (Lower Cretaceous) palaeoenvironments in south-east England: molluscan evidence

The contribution of molluscan studies to the interpretation of Weald Clay nonmarine environments in the Weald Sub-basin of the Wessex-Weald Basin is summarized. Sedimentological signatures of Weald Clay shell beds reflect a range of lagoonal, lacustrine and alluvial environments and show that the low-diversity molluscan assemblages were subjected to varying degrees of post-mortem modification. These faunas indicate freshwater and fluctuating brackish-water conditions, ranging into the brachyhaline field. Combined palaeontological and sedimentological evidence suggests both Boreal and Tethyan marine influences during the most saline episodes.

Walvis Ridge barrier: its influence on palaeoenvironments and source rock generation deduced from ostracod distributions in the early South Atlantic Ocean

Abstract The early South Atlantic was subdivided latitudinally by the proto-Walvis Ridge, which separated early Cretaceous open marine conditions in the south from non-marine environments to the north. Changes in the palaeogeography, which can be monitored by the distribution of ostracod assemblages, determined the establishment of a wide variety of depositional environments, including evaporitic and total organic carbon-rich facies. Limited northward marine influxes across the barrier are postulated for mid-Aptian time, while largescale southward migrations of marine ostracods from the northern sector occurred in early Cenomanian and/or Turonian times. The latter established cosmopolitan faunas in the southern Atlantic and effectively marked the breakdown of the Walvis Ridge as a physical barrier to north-south migrations, although possible oceanographic factors militated against longitudinal faunal movements. Variations in the composition of ostracod assemblages during so called ‘oceanic anoxic events’ and the production of potential source rocks is briefly reviewed.

Structural and Stratigraphical Setting of the Faiyah Range, Northwestern Oman Mountain Front, United Arab Emirates

ABSTRACTThe Faiyah Range belongs to a group of regional ridges that formed by post-obduction folding of the Upper Cretaceous-Tertiary sedimentary rocks exposed along the western margin of the Northern Oman Mountains. The Faiyah Anticline, generally trends north-northeast to south-southwest with thrust faults striking parallel to the fold axis. The anticlinal hinge was later displaced by a dextral strike-slip fault, named here as the Faiyah Fault, into two segments. The northeastern segment includes Jebels Rumaylah, Faiyah and Mulayhah, and the southwestern segment includes Jebels Buhays and Aqabah. The anticline is interpreted to result from northeast-southwest compression during the Tertiary.In the Faiyah Range the neoautochthonous sedimentary rocks are the Maastrichtian Qahlah and Simsima formations, and the Eocene Dammam Formation. Stratigraphic evidence shows that the lower part of the Qahlah was deposited in a non-marine environment while the upper part was deposited during a marine transgression. The Simsima was deposited in a shallow-marine environment. These units unconformably overlap the allochthonous Semail Ophiolite. The microfaunal content of the so-called Muthaymimah Formation (?Tertiary), of earlier authors, indicates that it is of Maastrichtian age in the Faiyah Range. This sequence is also conformable to the Simsima and therefore it is considered to be the upper member of the Simsima in this area.

The ichnologic record of the continental invertebrate invasion; evolutionary trends in environmental expansion, ecospace utilization, and behavioral complexity

The combined study of continental trace fossils and associated sedimentary facies provides valuable evidence of colonization trends and events throughout the Phanerozoic. Colonization of continental environments was linked to the exploitation of empty or under-utilized ecospace. Although the nonmarine trace fossil record probably begins during the Late Ordovician, significant invasion of nonmarine biotopes began close to the Silurian-Devonian transition with the establishment of a mobile arthropod epifauna (Diplichnites ichnoguild) in coastal marine to alluvial plain settings. Additionally, the presence of vertical burrows in Devonian high-energy fluvial deposits reflects the establishment of a stationary, deep suspension-feeding infauna of the Skolithos ichnoguild. The earliest evidence of plant-arthropod interaction occurred close to the Silurian-Devonian boundary, but widespread and varied feeding patterns are known from the Carboniferous. During the Carboniferous, permanent subaqueous lacustrine settings were colonized by a diverse, mobile detritus-feeding epifauna of the Mermia ichnoguild, which reflects a significant paleoenvironmental expansion of trace fossils. Paleozoic ichnologic evidence supports direct routes to the land from marginal marine environments, and migration to lakes from land settings. All nonmarine sedimentary environments were colonized by the Carboniferous, and subsequent patterns indicate an increase in ecospace utilization within already colonized depositional settings. During the Permian, back-filled traces of the Scoyenia ichnoguild record the establishment of a mobile, intermediate-depth, deposit-feeding infauna in alluvial and transitional alluvial-lacustrine sediments. Diversification of land plants and the establishment of ecologically diverse plant communities through time provided new niches to be exploited by arthropods. Nevertheless, most of the evolutionary feeding innovations took place relatively early, during the Late Paleozoic or early Mesozoic. A stationary deep infauna, the Camborygma ichnoguild, was developed in Triassic transitional alluvial-lacustrine deposits. Terrestrial environments hosted the rise of complex social behavioral patterns, as suggested by the probable presence of hymenopteran and isopteran nests in Triassic paleosols. An increase in diversity of trace fossils is detected in Triassic-Jurassic eolian deposits, where the ichnofauna displays more varied behavioral patterns than their Paleozoic counterparts. Also, a mobile, intermediate-depth, deposit-feeding infauna, the Vagorichnus ichnoguild, was established in deep lake environments during the Jurassic. In contrast to Paleozoic permanent subaqueous assemblages typified by surface trails, Jurassic ichnocoenoses are dominated by infaunal burrows. High density of infaunal deposit-feeding traces of the Planolites ichnoguild caused major disruption of lacustrine sedimentary fabrics during the Cretaceous. Most insect mouthpart classes, functional feeding groups, and dietary guilds were established by the end of the Cretaceous. Diversification of modern insects is recorded by the abundance and complexity of structures produced by wasps, bees, dung-beetles, and termites in Cretaceous-Tertiary paleosols. The increase in bioturbation migrated from fluvial and lake-margin settings to permanent subaqueous lacustrine environments through time.

Environmental controls on perennial and ephemeral carbonate lakes: the central palaeo-Andean Basin of Bolivia during Late Cretaceous to early Tertiary times

In the central palaeo-Andean Basin (Potosí Basin) of Bolivia, the up to 450-m-thick El Molino Formation (Campanian-Maastrichtian to early Tertiary) includes two main carbonate lacustrine episodes each of different extent and duration. These episodes are separated by an extensive development of alluvial facies (floodplain deposits) and limestones deposited in playa lakes or isolated ponds. The El Molino Formation has been investigated in six different areas of the Potosí Basin and affords the opportunity to document climatic and tectonic controls on the development of perennial and ephemeral carbonate lacustrine systems. The first lacustrine episode originated predominantly in perennial lakes with wave-dominated low-gradient ‘ramp’-type margins. Outer marginal lacustrine facies include winnowed oolitic grainstones, ostracod packstones and microbialite bioherms. More agitated areas were characterized by nearshore oolitic bars with associated thrombolite mounds. The fossil content, and the lack of significant precipitation of evaporites, indicate that the lake waters were of low salinity (probably oligohaline) during most of this period. After the first lacustrine episode, the widespread development of terrigenous alluvial facies (floodplain deposits), with interspersed playa lakes or isolated ponds in depressions on the floodplain, may indicate a change in the net water budget. The second lacustrine episode is dominated by dark micritic limestones and, to a lesser extent, microbialite bioherms which developed under semiarid climatic conditions. This episode includes the deposits of ephemeral saline, locally alkaline, shallow lakes which were characterized by low-energy, low-gradient ‘ramp’-type margins. The stable isotopic analysis of 163 carbonate samples covering the different facies and depositional settings displays a wide range of values ( −14.2 < δ 18 O < +2.8‰ and −12.9 < δ 13 C < +2.8‰ ) that is typical of nonmarine environments. The distribution of the values indicates that, during the deposition of the El Molino Formation, the basin was hydrologically closed and experienced no strong hydrogeographical changes, except for variations in the palaeolake level related to fluctuations in the regional P/E ratio. These are recorded by two main isotopic trends related to changes between perennial and ephemeral lacustrine conditions. Lacustrine sedimentation was controlled predominantly by climatically driven hydrological changes with repeated oscillations of the water level (expansion and contraction) and subsequent fluctuations in the width of lacustrine-facies belts.

New internally structured decapod microcoprolites from Germany (Late Triassic/Early Miocene), Southern Spain (Early/Middle Jurassic) and Portugal (Late Jurassic): Taxonomy, palaeoecology and evolutionary implications

Fossil faecal pellets with internal structures are described from non-marine environments for the first time. In the Late Triassic Lehrberg Beds (Middle Keuper, Carnian) of Germany, the oldest stratigraphic record of the form genusHelicerina Bronnimann &Masse,Helicerina keuperina Seegis n. sp., occurs.Favreina kalankyra Ebli from the Norian Hauptdolomit Formation is also attributed to this genus. Another new speciesof Helicerina, H. ruttei Schweigert n. sp., is described from the Early Miocene calcareous freshwater tufas of Southern Germany. It is attributed to the brachyuran freshwater crabProballaya quenstedti (Zittel) which occurs abundantly at the same locality. Hence, the coprolite genusHelicerina is the product of brachyuran decapods or their Triassic ancestors, and not of anomuran decapods as thought before.

Dichloromyristic Acid, a Major Component of Organochlorine Load in Lobster Digestive Gland

It is well established that PCBs and chlorinated pesticides account for only some 15% of extractable organically-bound chlorine (EOCl) in samples from marine and non-marine environments. Work by other investigators on marine sediments and lipids from highly contaminated fish, collected near kraft pulp mills, has shown that chlorinated alkanoic acids contribute significantly to the EOCl. The present investigation extends this work to lipids from lobsters (Homarus americanus) captured in an industrial harbor well removed from any pulp mill effluent. The relatively low chlorine content of these lipids (30−100 μg g-1) necessitated development of fractionation and analysis procedures more discriminating and sensitive than those used previously. Neutron activation analysis for total chlorine was used to monitor the extraction, cleanup, transesterification, and selective EOCl enrichment of the lipids. Fractionation on a Sephadex LH-20 column then concentrated the EOCl into fractions separated from the bulk of the lipid. Mass spectrometric detection using dis sociative electron capture, monitoring only chloride ions, identified those GC peaks containing chlorine. Conventional negative ion mass spectrometry provided mass spectra for peaks of interest and enabled identification of a dichloromyristic acid as a lipid component accounting for ca. 20% of the EOCl on a semi-quantitative basis.

Chapter 19 Jurassic-Cretaceous history

Jurassic-Cretaceous follows Triassic history with minor change. It was an interval dominated by deposition of marine muds, silts and sands, with occasional non-marine environments on advancing deltas (Parker 1967; Harland 1973a; Kelly 1988). Subdued topography contrasted with Triassic and Paleogene terrains. But there was also Late Jurassic and Early Cretaceous intrusion of basic sills and volcanism in eastern Svalbard. Figure 19.1 shows the distribution of Jurassic and Cretaceous deposits in Svalbard. The two periods (208-65 Ma) span 143 million years but the stratal record for this interval totals only 1700 m of which more than half was deposited in Albian time. The Jurassic-Cretaceous rocks of the eastern platform, presently cropping out on some islands, represent a relict of a once continuous sheet of strata, which is still preserved extensively across much of the Barents Shelf. The Triassic-Jurassic boundary is marked by seemingly continuous facies from Rhaetian to Toarcian; but then follows a contrast between the main Spitsbergen Basin (which hardly subsided) and the Eastern Platform. The contrasting areas of east and west Svalbard were divided by the continuing activity along the Billefjorden lineament. To the east, subsidence permitted a complex and variable sequence resulting from deltas from the east (marine and non-marine) through Liassic to mid-Bathonian time. To the west there was little evident subsidence and only condensed deposits of the uppermost Wilhelmoya Formation were washed by shallow seas. This part of the story concluded the history of the Kapp Toscana Group. A Late Bathonian marine transgression transformed east and

Mesozoic palynomorphs from the North West Shelf, offshore Western Australia

Abstract This paper discusses the results of a palynological examination of thirty‐three dredge samples from sediments exposed on the sea floor, offshore Western Australia. The samples are dated as latest Triassic to Early Cretaceous, and represent marine to coastal nonmarine environments. They are integrated with the geological framework of the Rowley Terrace, Wombat and Exmouth plateaus, and Carnarvon Terrace, on the basis of palynological evidence derived from regional petroleum exploration wells and deep sea (ODP) drilling. Biostratigraphic affinity of the dredge samples is given in terms of zonal schemes for spores, pollen grains, and dinoflagellate cysts, currently in use for the Mesozoic of the Australian region. The ages of certain zonations are reviewed on the basis of fresh evidence from ammonites, conodonts, ostracodes, foraminifera, and nannofossils. Details are given of the distribution of species, and several species are described and discussed. New spore‐pollen species Clavifera deformans a...

Systematics of myliobatoid elasmobranchs: with emphasis on the phylogeny and historical biogeography of neotropical freshwater stingrays (Potamotrygonidae: Rajiformes)

The neotropical freshwater family Potamotrygonidae appears to be the only stingray group that has radiated in a non-marine environment. To assess the affinities of potamotrygonids to other rays, a phylogenetic analysis was undertaken using 39 morphological characters from 18 stingray groups. The single tree produced (CI = 0·80, RI = 0·88) suggests that neotropical freshwater rays are a monophyletic group, and that within Potamotrygonidae,Paratrygonis basal to a clade composed ofPlesiotrygonandPotamotrygon. The sister group to potamotrygonids was determined to be amphi-AmericanHimantura— these taxa share synapomorphies of the ventral mandibular musculature and the hyomandibular/mandibular articulation. The topology suggests that potamotrygonids are derived from a freshwater-invading ancestor that was distributed along the northern coast of South America (Pacific and Caribbean) prior to the emergence of the isthmus of Panama. This hypothesis conflicts with parasite-based biogeographic scenarios of a strictly Pacific origin for potamotrygonids. General systematic results concerning urolophids, dasyatids, and pelagic myliobatoid stingrays are also discussed.

Metabolism of methylated osmolytes by aerobic bacteria from Mono Lake, a moderately hypersaline, alkaline environment

Three strains of aerobic bacteria were isolated from water and sediment samples of Mono Lake, a moderately hypersaline (90 ppt), alkaline (pH 9.7) lake in California. The organisms, Gram-negative rods, grew fastest at about pH 9.7 with no growth or much slower growth at pH 7.0. All three isolates grew on glycine betaine (GB) and respirometric experiments indicated that catabolism was by sequential demethylation with dimethyl glycine and sarcosine as intermediates. Two of the isolates also grew on dimethylsulfoniopropionate (DMSP), one with cleavage of the DMSP to yield dimethyl sulfide (DMS) and acrylate, and the other by demethylation with 3-methiolpropionate (MMPA) as an intermediate and the production of methanethiol from MMPA. The methylated osmolytes supported growth at salinities similar to those in Mono Lake, but, at higher salinities, catabolism was suppressed and GB and DMSP functioned as osmolytes. GB and DMSP probably originate from cyanobacteria and/or phytoplankton in Mono Lake and this report is the first indication of both the DMS and demethylation/methanethiol-producing pathways for DMSP degradation in a nonmarine environment.

Metabolism of methylated osmolytes by aerobic bacteria from Mono Lake, a moderately hypersaline, alkaline environment

Three strains of aerobic bacteria were isolated from water and sediment samples of Mono Lake, a moderately hypersaline (90 ppt), alkaline (pH 9.7) lake in California. The organisms, Gram-negative rods, grew fastest at about pH 9.7 with no growth or much slower growth at pH 7.0. All three isolates grew on glycine betaine (GB) and respirometric experiments indicated that catabolism was by sequential demethylation with dimethyl glycine and sarcosine as intermediates. Two of the isolates also grew on dimethylsulfoniopropionate (DMSP), one with cleavage of the DMSP to yield dimethyl sulfide (DMS) and acrylate, and the other by demethylation with 3-methiolpropionate (MMPA) as an intermediate and the production of methanethiol from MMPA. The methylated osmolytes supported growth at salinities similar to those in Mono Lake, but, at higher salinities, catabolism was suppressed and GB and DMSP functioned as osmolytes. GB and DMSP probably originate from cyanobacteria and/or phytoplankton in Mono Lake and this report is the first indication of both the DMS and demethylation/methanethiol-producing pathways for DMSP degradation in a nonmarine environment.

Early diagenetic siderite as an indicator of depositional environment in the Triassic Rewan Group, southern Bowen Basin, eastern Australia

ABSTRACTEarly concretionary and non‐concretionary siderites are common in subsurface Triassic sandstones and mudrocks of the Rewan Group, southern Bowen Basin. A detailed petrological and stable isotopic study was carried out on these siderites in order to provide information on the depositional environment of the host rocks. The siderites are extremely pure, containing 85–97 mol% FeCO3, and are commonly enriched in manganese. δ13C (PDB) values are highly variable, ranging from ‐ 18·4 to +2·9‰, whereas δ18O (PDB) values are very consistent, ranging from ‐ 14·0 to ‐ 10·2‰ (mean= ‐ 11·9 ± 1·0‰). The elemental and oxygen isotopic composition of the siderites indicates that only meteoric porewaters were involved in siderite formation, implying that host rocks accumulated in totally non‐marine environments. The carbon isotopic composition of the siderites is interpreted to reflect mixing of bicarbonate/carbon dioxide generated by methane oxidation and methanogenesis. Very low δ13C values demonstrate that, contrary to current views, highly 13C‐depleted siderite can be produced at shallow burial depths in anoxic non‐marine sediments.

Nitrile hydrolysis by Rhodococcus erythropolis BL1, an acetonitrile-tolerant strain isolated from a marine sediment.

A number of physiologically different nitrile-hydrolysing bacteria were isolated from coastal marine sediments in Denmark by enrichment culture. One strain, BL1, identified as Rhodococcus erythropolis, grew on acetonitrile as sole carbon and nitrogen source in a defined medium. Growth occurred between 0 and 8% NaCl with an optimum around 2%, thus reflecting the marine origin of the isolate. Intact cells of R. erythropolis BL1 could hydrolyse a large variety of saturated and unsaturated aliphatic nitriles to their corresponding acids. Benzonitrile and benzylcyanide were not hydrolysed, whereas some aromatic compounds containing a -CN group attached to a C3 or C4 aliphatic side chain were accepted as substrates. The substrate spectrum of R. erythropolis BL1 was thus markedly different from those of other Grampositive nitrile-hydrolysing bacteria isolated from non-marine environments. Nitrile hydrolysis during growth and in resting cell suspensions usually occurred without intermediate accumulation of amide outside the cells. Detailed studies, however, showed that nitrile hydrolysis by strain BL1 was due to a nitrile hydratase/amidase enzyme system. Nitrile hydratase activity was found to be inducible whereas amidase activity was constitutive. The amidase activity of cells could, however, be enhanced manyfold by growth in media containing acetamide or acetonitrile. In most cases amides were hydrolysed at a much higher rate than the corresponding nitriles, which explained why amides were rarely detected in the surrounding medium during nitrile hydrolysis. R. erythropolis BL1 exhibited the highest tolerance towards acetonitrile ever reported for a nitrile-hydrolysing bacterium, as demonstrated by its ability to grow exponentially in the presence of 900 mM acetonitrile.