Elizabeth Gierlowski-Kordesch

Carbonate deposition in an ephemeral siliciclastic alluvial system: Jurassic Shuttle Meadow Formation, Newark Supergroup, Hartford Basin, USA

Abstract Nonmarine carbonate accumulation, from a sedimentologic perspective, has multiple possible origins: clastic load, springs, groundwater discharge, soil development, biochemical seasonal changes, cave speleothems, and eolian influx. Many of these carbonates contain diagnostic textures from which origin is easy to ascertain. However, differentiating between clastic and spring/groundwater carbonates, especially in depositional systems dominated by siliciclastics, is not always simple; here criteria for recognition are developed. Subsurface hydrology and tectonic origin of the depositional basin, source rocks surrounding the basin, sedimentologic packaging and extent of the carbonates in question, as well as their sedimentary structures and fossil content, and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution. The present study focuses on a nonmarine carbonate deposit found within the Jurassic Shuttle Meadow Formation of the Hartford Basin, one of many rift basins which formed as a result of the opening of the North Atlantic Ocean during the Late Triassic to Early Jurassic. The upper 50 m of the formation at Plainville, Connecticut, is interpreted as continental in origin and is composed of five facies: red ripple cross-laminated muddy siltstones to sandstones (Fr, Sr), massive red siliciclastic mudstones (Fm), buff fine- to medium-grained horizontally laminated sandstones (Sh), red to white disrupted calcareous shales (Fl3), and rare micritic carbonates (Pm). Facies Fr, Sr, Sh, and Fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism, similar to the Channel Country drainage system of central Australia. In addition, preservation of lateral accretion sandstone sheets (accretionary benches) indicate that the Shuttle Meadow alluvial system was rapidly accreting. The anomalous existence of carbonate beds (in Facies Fl3 and Pm) in the SMF bedload-dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin; no direct evidence for a spring/groundwater input is apparent. The shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment. The intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration, desiccation cracks, and burrowing.

Ichnology of an ephemeral lacustrine/alluvial plain system: Jurassic East Berlin Formation, Hartford Basin, USA

A trace fossil assemblage from the Lower Jurassic East Berlin Formation of the Newark Supergroup, Hartford Basin, New England, USA, includes: Scoyenia gracilis, Skolithos ichnosp., Palaeophycus striatus, Planolites montanus, Fuersichnus ichnosp., fusiform burrows, pelleted material, an escape structure, and large burrows. This assemblage is assigned to the Scoyenia ichnofacies. Specific lebensspuren are not limited to specific lithofacies; instead, their initial distribution seems to have been influenced principally by water availability within an ephemeral lacustrine/alluvial plain system. Other factors in distribution may have included amounts of organic matter, patterns of sedimentation, sediment grain size, biotic factors (settling from invertebrate drift, competition), and additional abiotic factors (wind deflation, waves, currents, desiccation, soft‐sediment deformation, evaporite formation, pedoturbation). Extreme environmental conditions within the original depositional setting strongly influenced...

Chapter 1 Lacustrine Carbonates

Abstract Lacustrine carbonates accumulate in all climates and in any tectonic situation. Their depositional patterns are assessed through a database involving literature representing over 250 lakes and lake basins worldwide. Carbonates and calcium-rich rocks (i.e., basalt or carbonatite) need to be available for weathering in the catchment and subsurface in order to produce carbonate sediments in lakes in the first place. Tectonics and climate control the distribution of carbonates through (1) the input and output of ions and minerals through surface water, groundwater, rainfall, and wind; (2) the morphometry of the lake; and (3) the temperature ranges and seasonality of the catchment location. Carbonate deposition proceeds through (1) biogenic mediation, including high productivity of micro- and picoplankton, macrofauna shell formation, and encrustations on any substrate, (2) concentration through evaporation, (3) eolian input, and (4) water-borne clastic input. Five general facies types are recognized for lacustrine carbonates: (1) laminated carbonates, (2) massive carbonates, (3) microbial carbonates, (4) marginal carbonates, and (5) open-water carbonates. Important fauna and flora associated with carbonates include diatoms, charophytes, insects, bivalves, gastropods, and ostracodes. Facies distribution is dependent on the input mode of calcium-rich waters and carbonate clasts in addition to lake circulation patterns and stratification. The use of stable isotopes of oxygen, carbon, and strontium as well as the recognition of diagenetic alternation in lacustrine carbonates aids in the reconstruction of climate, hydrology, and lake evolution. Dominantly carbonate lakes contain carbonate sediments from the littoral to profundal zone; the source areas for these lakes are composed of a significant percentage of carbonate rocks (more than 60–70% of provenance). Partially carbonate lakes contain carbonate sediments in some areas of the lakes with 40–60% of carbonate-rich provenance. Sparsely carbonate lakes show less significant carbonate accumulation within lakes because of minor carbonate-source rocks (

Impact of Grassland Radiation on the Nonmarine Silica Cycle and Miocene Diatomite

Abstract The Early Miocene rise of the grass-dominated ecosystem is a plausible trigger for a sharp Miocene increase in accumulation of nonmarine diatomaceous sediment as well as diversification of nonmarine diatoms. This grassland radiation introduced a biogeochemical mechanism for enhancing widespread and sustained mobilization of usable silica and other nutrients. Volcanism was probably responsible for episodic nonmarine diatomaceous sediments from the advent of the oldest known nonmarine diatoms in the Late Cretaceous through the Oligocene. Although prolific Miocene volcanism was undoubtedly still important in the development of many diatomites, feedback from grassland colonization of volcanic soils may explain why diatomaceous sedimentation surged in the Miocene following a more sparse pre-Miocene record. The initial rise of the grass-dominated ecosystem, increased nonmarine diatomite accumulation, and Early Miocene evolutionary radiations of nonmarine diatom taxa are at least approximately coeval. Although the earliest known grass is Paleocene, multiple lines of evidence, including mollic-epipedon paleosols, fossil occurrences of hypsodontic ungulate grazers, and fossil phytoliths, suggest that the grass-dominated ecosystem did not expand significantly until Early Miocene. The grassland radiation apparently was delayed until Middle Miocene in parts of Eurasia, Africa, and Australia. If that delay is real, the diatom/diatomite record in those regions should coincide with it. The onset of increased Miocene diatomite accumulation is as yet imprecisely dated, but coincidence with the rise of the grass-dominated ecosystem is predicted herein. Early Miocene diversifications of Actinocyclus and Thalassiosira diatoms are consistent temporally with grassland expansion where it is Early Miocene. Subsequent adjustments in the silica cycle also may be attributed to grasslands. Nonmarine diatom radiations in the Late Miocene and Pliocene coincide with sharp regressions that may have released nutrients and soluble phytolith opal stored in Miocene soils and paleosols as well as dissolved silica in soil pore waters. Regressional erosive pulses of phytoliths provide a new explanation for low Ge/ Si ratios in marine diatoms during Pleistocene glacial intervals. Nonmarine diatoms from regressive intervals should record lower Ge/Si ratios than before and after those regressions because of phytolith contributions with low Ge/Si ratios. Late Miocene radiations of C4 and moist tall-grass ecosystems may have mobilized even more silica than the short, dry-climate Early Miocene grasses. Abundance of diatomite may have fluctuated in concert with changes in degree of volcanism, even after grassland expansion, but at substantially higher levels than before this new terrestrial ecosystem arose.

Watershed reconstruction of a Paleocene–Eocene lake basin using Sr isotopes in carbonate rocks

Provenance studies have used Sr isotopes ( 87 Sr/ 86 Sr) of silicate source rocks as a link to their eroded basinal equivalents. This technique, however, cannot identify the proportional inputs from different watersheds or define more precisely sedimentation events due to tectonic or climatic change. Erosion of carbonate rocks dominates the Sr input within basin drainage and potentially can be used through 87 Sr/ 86 Sr ratios to reconstruct paleohydrology of the entire basin and trace watershed inputs and depositional patterns in continental basins. The Sr isotopic ratios from waters of the source area, allowing for the mixing of shallow groundwater and surface water along the transport path, are homogenized in the basinal carbonate sediments. Mineralogy and diagenesis of carbonate rocks generally do not affect the Sr isotopic signal in a near-surface system lacking external influence by volcanism, eolian dust, or deep geothermal waters. The 87 Sr/ 86 Sr ratios from the source area are directly comparable to those in the receiving continental basin. The Sr isotopic signal of the Paleocene–Eocene Flagstaff Formation (central Utah), a carbonate lake deposit in a foreland basin, is compared to that of projected source waters draining its thrust front, the Sevier fold-thrust belt. Freshwater carbonates compose a large portion of the lowermost Ferron Mountain and uppermost Musinia Peak Members of the formation, whereas gypsum and carbonates predominate in the middle Cove Mountain Member. Previous research had attributed gypsum deposition to the deposition of the middle Cove Mountain Member to either climatic change or unroofing of diapirs of Jurassic gypsiferous carbonates. To examine more closely the influence of climate versus tectonics on Flagstaff sedimentation as well as the efficacy of provenance studies using carbonates, we collected rock samples from the three members of the formation on the Wasatch Plateau of central Utah in addition to sampling stream water associated with Pennsylvanian–Permian and Jurassic carbonate terrains from the nearby thrust front. The 87 Sr/ 86 Sr ratios in carbonates and gyprock belonging to the Flagstaff Formation remained unchanged during deposition, the average Sr isotope composition of the Flagstaff rocks being identical to that of sampled waters draining the projected provenance area. There was little change in source rock weathering as the thrust front evolved. Deposition of gypsum occurred in the basinal lake only during the deposition of the middle Cove Mountain Member, despite its constant exposure in the drainage area, suggesting a changing balance of tectonic and climatic controls during lake sedimentation. The 87 Sr/ 86 Sr isotopic studies targeting carbonate rocks and their presumed source waters are a simple but accurate method for reconstructing the paleohydrology of lake basins.

Pennsylvanian continental cyclothem development: no evidence of direct climatic control in the Upper Freeport Formation (Allegheny Group) of Pennsylvania (northern Appalachian Basin)

Abstract The occurrence of lacustrine carbonates in the Allegheny Group (upper Middle Pennsylvanian) continental cyclothems of the northern Appalachian Basin has been attributed to climatic alternation of wet (coal deposition) and dry (carbonate deposition) periods. However, we present evidence from facies associations, coal and carbonate petrography, and carbonate stable isotope geochemistry for a uniformly wet climate throughout deposition of one of the earliest continental cyclothems, the Upper Freeport Formation (UFF). We propose a depositional model comprising a large wetland complex drained by an anastomosed fluvial system containing a mosaic of channels, freshwater siliciclastic and carbonate lakes, and peat bogs/swamps on a siliciclastic floodplain. Carbonate phases represent bio-induced precipitates modified by lake dynamics, and not evaporative deposits. Absence of covariant isotopic trends between δ18O and δ13C and a relatively small range of δ18O values (−1.9 to −6.4% PDB), that are close to or lighter than predicted paleoprecipitation for the Pennsylvanian equatorial regions, indicate hydrologically open, short residence time lake systems, in support of our sedimentary model. Combined sedimentologic and isotopic data do not indicate reduced effective moisture (precipitation-evaporation) during intervals of limestone deposition. The UFF lakes developed in a relatively wet climate zone without significant episodic closure due to climatically induced water deficit. Lithologic patterns within the UFF cyclothem are primarily attributed to the evolution of anastomosed fluvial systems controlled by subsidence in an active foreland basin rather than to short-term climatic change or eustacy.

Comparing Species Diversity in the Modern and Fossil Record of Lakes

Lake faunal diversity has been the focus of many modern studies; however, there have been few studies comparing the lacustrine diversity in the modern and fossil record. Whether or not this comparison is possible is dependent on preservation. By comparing the exceptional preservation of the Konservat Lagerstätten of the Eocene Green River Formation with its various modern analogs in East Africa, unique factors controlling diversity within a lake system can be determined. Such factors would include lake surface area, lake longevity, productivity, and lake type. In order to effectively compare lake diversity in the modern and fossil record, we first estimated the potential preservational bias of the fauna from modern Lake Tanganyika and determined that, at maximum, approximately 43.8% of species, 59.3% of genera, and 65.8% of families would be identifiable. With this taphonomic filter in place, we compared fish species diversity versus lake area; no strong relationship was found. Faunal species diversity versus lake longevity was shown to correlate in long‐lived lakes both in a modern and geologic context. When including modern lakes into this comparison, the correlation is not as strong, possibly because of the limited life span of these lakes. Lake Tanganyika was comparable to lakes in the geologic record, after the taphonomic filter was applied. Finally, to test the relationship between species and lake type and productivity, the underfilled, balanced‐filled, and overfilled lake basin model of Carroll, Bohacs, and coworkers was used as a basis for comparison between the fauna found in lake deposits within the Green River Formation and modern lakes from East Africa.

Lacustrine carbonate deposition in Middle Pennsylvanian cyclothems — the Upper Freeport Formation, Appalachian Basin, USA

The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest non-marine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analyses of 25 cores from the Upper Freeport Limestone in western Pennsylvania (Armstrong and Indiana Counties) identified four facies associations containing thirteen separate facies: rudstone-limestone (Association A), rudstone-laminated limestone (Association B), laminated limestone (Association C), and coal — siliciclastics (Association D). We interpreted them, respectively, as shallow, high energy lacustrine margin (A); littoral to sublittoral lacustrine (B); offshore lake (C); and vegetated swamp and marsh (D). The depositional environment is envisaged as an anastomosed channel system surrounded by extensive wetlands containing adjacent densely vegetated swamp and marsh areas and freshwater, carbonate-producing lakes.Lakes developed in the topographic lows of the alluvial plain, protected and filtered from siliciclastic deposition by vegetated swamps. These lakes were small in size (several square km), shallow, and stratified, as indicated by the abundance of laminated facies. They were hydrologically open, and interconnected by surface and ground waters. Carbonate production in this lacustrine system was not triggered by evaporative concentration but by biogenic algal production. Carbonates were continually being recycled, both physicochemically and biologically, within the depositional system. Various early diagenetic processes, including brecciation, pedogenesis and recrystallization, masked original evidence for transport mode. The Upper Freeport Limestone contains numerous features of palustrine carbonates, and provides a case study for one end-member of freshwater carbonate models, characterized by a very short period of subaerial exposure. Small-scale climatic changes or autocyclic processes such as small topographic differences, changes in local drainage patterns, and fluvial dynamics may have controlled Upper Freeport lake level changes.Facies analysis does not support a climate forcing as a control for cyclothem development of non-marine sequences during the Pennsylvanian. Tectonic and autocyclic processes better explain the evolution of these wetland (lacustrine/alluvial) systems with its associated coal formation.

Limnogeology, news in brief

We’ve invited Michael R. Rosen, water quality specialist within the USGS Water Science Field Team in Carson City and Elizabeth Gierlowski-Kordesch, professor of geology at Ohio University, to take a look at the intriguing new developments that are emerging in limnogeologic studies. These studies are increasing our understanding of how climate and movements of the Earth’s surface influence terrestrial environments, as well as how contaminants are distributed and retained in the environment. They present a selection of recent significant research on sediments, rock, and biota that have been preserved in modern and ancient lake basins.