Littoral Lacustrine Research Articles

The Miocene lacustrine carbonate factory of the Ñirihuau Formation, Ñirihuau Basin, North Patagonian Andes, Argentina

AbstractFacies, microfacies and stable isotope analyses of limestone beds in the northernmost Ñirihuau Basin, North Patagonian Andes, Argentina, document and constrain the past hydrological, sedimentological and climate conditions that prevailed during the deposition of a lacustrine system between ca 15 and 13 Ma. This palaeoenvironment is recorded in the middle section of the Ñirihuau Formation, which holds significance because: (1) It was deposited during a transition from an extensional to a compressional tectonic regime; (2) it spans the Middle Miocene Climatic Optimum and the beginning of the Middle Miocene Climatic Transition; and (3) it contains limestone beds interbedded within a 600 m thick interval of mudstones and siltstones, along with intercalated sandstone and volcaniclastic bodies. Two detailed sedimentary logs were surveyed along the Arroyo Las Bayas, at the western and eastern flank of the David Syncline. Limestones from both stratigraphic sections were sampled as well as isolated limestone beds from two other sites. One facies association was defined and interpreted as a perennial lake associated with a deltaic system and dominated by detrital clastic material. It comprises Facies 1 (Marginal lacustrine) and Facies 2 (Lower delta plain); in both, the presence of grainstones and calcimudstones stands out. Through petrography and cathodoluminescence studies of these continental carbonates, nine microfacies were identified: (a) Intraclastic grainstone, (b) Homogeneous calcimudstone, (c) Silty grainstone, (d) Disrupted micrite, (e) Birds eye micrite, (f) Bioclastic mudstone, (g) Calcimudstone with sparse detrital grains, (h) Fenestral micrite, (i) Stromatolitic boundstone. These indicate mainly bio‐induced subaqueous carbonate precipitation and subordinate deposition by tractive flows with short‐distance transport on a littoral lacustrine environment. Most of these microfacies exhibit very early diagenesis (eogenesis) effects. These features, and the geochemistry results, indicate that they were deposited in a palaeolake system under temperate to warm and humid conditions.

Holocene East African monsoonal variations recorded in wave-dominated clastic paleo-shorelines of Lake Abhe, Central Afar region (Ethiopia & Djibouti)

In tropical Africa, Late Pleistocene-Holocene climatic fluctuations heavily impacted the continental hydro-systems. The timing and magnitude of ‘African Humid Period’ hydrological dynamics (AHP; ~14.8 to ~5.5 ka BP) are not yet fully understood due to the extreme variability in African geomorphic patterns and the complex network of past air convergence boundary shifts. The investigation of the functioning of specific hydro-sedimentary basins is needed to improve our knowledge on the AHP spatial and chronological patterns over the continent. In this paper we present a revised Holocene lake level curve of Lake Abhe: an endorheic basin situated in the Afar Depression at the northern extremity of the East African Rift System (EARS). Located at the boundary of the Red Sea and the Indian and Atlantic Oceans' air moisture mass fluxes, the Lake Abhe watershed represents a system sensitive to changes in Northeast African hydro-climate. Based on numerous littoral lacustrine geomorphic features and 53 related radiocarbon ages on stromatolites and nearshore deposits, we have defined the main Holocene lake highstands proposing a detailed paleo-shoreline record. The first rise in water level is dated to ~11.1 ka cal. BP, while the Maximal Holocene Highstand Shoreline (~420 m a.s.l.) was rapidly reached around ~10 ka cal. BP. Evidence of the impact of the 8.2 ka North Atlantic cooling event is recognized with slow lake level regression until ~8.3 ka cal. BP and with an abrupt drop at ~8 ka cal. BP. The resurgence of humid conditions was recorded from ~7.7 ka cal. BP to ~4.6 ka cal. BP. Radiocarbon ages on littoral materials allow us to propose a Holocene subsidence rate of the Abhe basin axial valley. Furthermore, multiphase sill overflow incisions towards the downstream Hanle basin and transient fluvial connectivity with the upstream Ziway-Shala basin, indicate strong geomorphic controls on lake highstand elevations. In summary, Lake Abhe Holocene fluctuations are the result of combined hydro-climatic, tectonic and local geomorphic controls. However, the confrontation with others East African basins allows us to discuss the transport of moisture masses dynamics into the northern EARS during the Holocene.

Piacenzian–Gelasian non‐marine ostracods from the Dunarobba Fossil Forest (Tiberino Basin, Umbria, central Italy)

AbstractThe taxonomy of some non‐marine ostracod assemblages from the Dunarobba Fossil Forest area (south Tiberino Basin, Umbria, Italy) is discussed, adding to the scientific understanding of Piacenzian–Gelasian non‐marine ostracods in central Italy and providing a palaeoenvironmental reconstruction of the shallow coastal lacustrine environments of the Palaeolake Tiberino. The ostracod assemblages include Darwinula stevensoni, Vestalenula cylindrica, Candona (Candona) improvisa, Candona (Neglecandona) neglecta, Candona (Neglecandona) angulata, Candona (Neglecandona) paludinica, Caspiocypris basilicii, Caspiocypris tiberina, Candonopsis kingsleii, Cyclocypris ovum, Ilyocypris bradyi, Ilyocypris decipiens, Cypris mandelstami, Zonocypris membranae quadricella, Potamocypris fulva, Cyprideis crotonensis, Cyprideis rectangularis and two new species: Hemicypris lomastroi sp. nov. and Paralimnocythere turgida sp. nov. In addition to widespread European species, the ostracod assemblages contain some rare species that were previously known from the Pliocene Paludinian Beds of Serbia. A cluster analysis applied to the ostracod frequency matrix has lead to the identification of four separate assemblages that can be attributed to several ecological niches, including emerged hydrosols, ephemeral coastal pools and a littoral lacustrine margin, which suggest a complex coastal environment.

A late Miocene ostracod record from the northeastern Tibetan Plateau

Lake Qinghai, the largest inland brackish lake in China, is located on the northeastern margin of the Tibetan Plateau and is affected by both the Asian Monsoon and Westerlies climate systems. It is very sensitive to climate and environmental changes. Moreover, its sediments accumulated over the Cenozoic Era and contain abundant information about past tectonics and environmental changes. Here we present a record of late Miocene ostracods from Lake Qinghai sediment cores. A taxonomic analysis of the ostracods yielded 7 families, 14 genera, and 31 species. Six distinct sediment facies were recognized and their corresponding paleolimnological and paleoenvironmental changes were inferred from the ostracod assemblages. The first appearance of ostracod shells at about 7.60 Ma reflects a switch from an eolian sedimentation facies (ca. 8.10–7.60 Ma) to a shallow lacustrine environment (ca. 7.60–5.85 Ma). Ostracod shells were absent from ca. 5.85 to 4.64 Ma in eolian sediments. A transition to a deep lacustrine facies began at ca. 4.64 Ma, and ended at ca. 3.58 Ma. Thus, Lake Qinghai existed in the late Miocene and became larger and deeper in the early Pliocene (ca. 4.64 Ma). During the time interval ca. 3.58–0.70 Ma, littoral lacustrine sedimentation occurred at the core sites. After ca. 0.70 Ma, there were alternating shallow lacustrine and lakeshore environments at the sites, until ca. 0.12 Ma. Changes in ostracod assemblages and their abundance during the intervals ca. 4.64–3.56 Ma and ca. 0.70–0.12 Ma indicate that the sedimentary environment fluctuated over short time scales. Given Lake Qinghai’s sensitivity to environmental and tectonic changes, related to its special location, we concluded that changes in the relative and absolute abundances of ostracods reflect the evolution of the Asian monsoon-arid environment and Plateau growth, as well as global climate changes.

Highly Seasonal and Perennial Fluvial Facies: Implications For Climatic Control On the Douglas Creek and Parachute Creek Members, Green River Formation, Southeastern Uinta Basin, Utah, U.S.A.

Abstract: The early to middle Eocene Green River Formation consists of continental strata deposited in Laramide ponded basins in Utah, Colorado, and Wyoming. This study (1) documents fluvial and lacustrine strata from the Douglas Creek and Parachute Creek members of the middle Green River Formation, southeastern Uinta Basin, Utah, and (2) uses new interpretations of the link between climate and fluvial sedimentary expression to interpret the terrestrial evolution of early Eocene climate. The stratigraphy was analyzed via outcrops along a 10 km transect in Main Canyon on the Tavaputs Plateau, and is divided into three distinct, stratigraphically separated depositional settings: (1) the lowermost Interval 1 is dominated by amalgamated sandstone channels that contain 70–100% upper-flow-regime sedimentary structures. The channels are interpreted to represent fluvial deposits controlled by a highly seasonal climate, where most deposition was limited to seasonal flooding events. (2) Interval 2 is dominated by alternating siliciclastic and carbonate lacustrine deposits, interpreted as local pulsed fluvial siliciclastic input into shallow Lake Uinta, and periods of fluvial quiescence represented by littoral carbonate deposition. (3) The uppermost Interval 3 is dominated by erosionally-based, trough cross bedded sandstone channels interbedded with littoral lacustrine and deltaic deposits. The Interval 3 sandstone channels are interpreted as perennial fluvial deposits with relatively little variation in annual discharge, akin to modern humid-temperate fluvial systems. The stratigraphic transition from seasonally controlled (Interval 1) to perennial (Interval 3) fluvial deposits is interpreted to represent a fundamental shift in Eocene climate, from the peak hyperthermal regime of the Early Eocene Climatic Optimum (EECO) to a more stable post-EECO climate.

The Upper Jurassic Stanleyville Group of the eastern Congo Basin: An example of perennial lacustrine system

The intracratonic Congo Basin, located in the Democratic Republic of Congo (DRC), is the largest sedimentary basin of Africa. The Jurassic strata outcrop along its eastern margin, south of Kisangani (formerly Stanleyville). In the last century, the Upper Jurassic Stanleyville Group was described as a lacustrine series containing a thin basal marine limestone designed as the “Lime Fine” beds. Since the proposal of this early model, the depositional environment of the Stanleyville Group, and especially the possible marine incursion, has been debated, but without re-examining the existing cores, outcrop samples and historical fossils from the type location near Kisangani that are available at the Royal Museum for Central Africa (MRAC/KMMA, Tervuren, Belgium). In order to refine the former sedimentology, a series of nine exploration cores drilled in the Kisangani sub-basin have been described. This study aims at integrating sedimentary facies in existing sedimentary models and to discuss the hypothesis of the presence of Kimmeridgian marine deposits along the Congo River near Kisangani, a region which lies in the middle of the African continent. Eight facies have been identified, which permit a reinterpretation of the depositional environment and paleogeography of the Stanleyville Group. The base of the Stanleyville Group is interpreted to represent a conglomeratic fluvial succession, which filled an inherited Triassic paleotopography. Above these conglomerates, a transition to a typically lacustrine system is interpreted, which includes: (1) a basal profundal, sublittoral (brown to dark fine-grained siltstones with microbial carbonates, i.e., the “Lime Fine” beds) and littoral lacustrine series; covered by (2) a sublittoral to profundal interval (brown to dark organic-rich, fine-grained siltstones), which corresponds to the maximum extent of the paleo-lake; and, finally (3) a shallow lacustrine series (greenish calcareous siltstones and sandstones with red siltstones). Unlike what has been proposed, the “Lime Fine” beds are interpreted herein to be of lacustrine origin, rather than representing a Kimmeridgian marine transgression. We conclude that a Jurassic marine transgression did not, in fact, occur in the eastern region of the Congo Basin.

Changing lake dynamics and sequence stratigraphy of synrift lacustrine strata in a half‐graben: an example from the Triassic Ischigualasto–Villa Unión Basin, Argentina

AbstractWell‐exposed Triassic rift strata from the Ischigualasto–Villa Unión Basin (NW Argentina) include a 80 to ca 515 m thick lacustrine‐dominated package that can be correlated across a half‐graben using key stratigraphic surfaces (sequence boundaries, lacustrine flooding surfaces and forced regressive surfaces). The characteristics of the synrift lacustrine fill in different parts of the half‐graben have been examined and the mechanisms controlling sedimentation inferred. A variety of sedimentary environments are recognized including; volcaniclastic floodplain, mildly saline lake and playa lake, offshore lacustrine, delta front to fluvial‐dominated and wave‐dominated deltas, distributary and fluvial channel, and interdistributary bay. The succession can be divided into four stratigraphic sequences (SS1 to SS4), the oldest of which (SS1) contains volcaniclastic, fluvial and saline lake deposits; it is thickest close to the western border fault zone, reflecting more rapid subsidence here. Accommodation exceeded sediment and water input during SS1. The second and third sequences (SS2 and SS3) mark the onset of widespread lacustrine sedimentation, reflecting a balance between accommodation creation and water and sediment fluxes. Sequences SS2 and SS3 are represented by offshore meromictic lacustrine and deltaic deposits, the latter mostly sourced from the flexural and southern axial margins of the half‐graben. The presence of stacked parasequences bound by lacustrine flooding surfaces is related to climatically induced lake‐level fluctuations superimposed on variable rates of subsidence on the controlling rift border fault zone. The youngest sequence (SS4) is represented by the deposits of littoral lacustrine and shallow shelf deltas distinguished by a change in lithofacies, palaeocurrents and sandstone composition, suggesting a switch in sediment supply to the footwall margin to the NW. The change in the sediment source is related to reduced footwall uplift, the possible presence of a relay ramp and/or supply from a captured antecedent drainage network. During SS4, the rate of creation of accommodation was exceeded by the sediment and water discharge. The stratigraphic evolution of lacustrine strata in the half‐graben was mainly controlled by tectonic processes, including subsidence rate and the growth and evolution of the border fault zone, but changing climate (inducing changes in water balance and lake level) and autocyclic processes (delta lobe switching) were also important.

Sedimentology of tufa facies and continental microbialites from the Palaeogene of Mallorca Island (Spain)

The Middle Eocene and Oligocene basins in northwestern half of Mallorca are filled by detrital rocks (conglomerates, calcarenites and lutites) and carbonates deposited in alluvial, fluvial, palustrine and lacustrine settings. The sediment supplied to these continental basins was transported by alkaline, bicarbonate-rich waters. As a consequence, these non-marine carbonate deposits display extensive developments of diverse kinds of organosedimentary facies. The sedimentary record from three localities (Peguera, Alaró and Sineu) enabled one to characterize well-preserved Eocene tufa deposits as well as Eocene and Oligocene stromatolites and oncolites. A total of ten carbonate facies are described and interpreted. The facies related to tufa deposits are diverse types of boundstones, rudstones and packstones of bryophytes, in situ stems s.l., phytoclasts, etc. and associated oncolite rudstones and bioclastic mudstones-to-packstones. These facies deposited in littoral lacustrine and fluvio-lacustrine environments. Oncolites and stromatolites present a great variety of shapes and sizes (oncolites from centimetres to several meters in diameter) that somehow were conditioned by environmental conditions within shallow lacustrine and fluvial settings. Three types of lamination apparently dependent on the type of microorganisms responsible for calcite precipitation are distinguished (fan-shaped and bush-shaped grouped filaments and isolated to loosely grouped filaments). The δ 13C and δ 18O composition of these deposits agrees with carbonate precipitation in freshwater, hydrologically open systems with similar carbon sources throughout the Eocene and Oligocene. However, Eocene and Oligocene samples are set apart by the δ 18O. Oligocene facies present lower δ 18O values, which might indicate deposition from isotopically less evolved waters, perhaps under slightly greater precipitation/evaporation conditions. Tufa facies have the highest δ 13C composition and show some positive covariation of δ 13C and δ 18O, primarily reflecting the effects of physical and biological CO 2 outgassing, and maybe also minor evaporation.

Depositional environments of Quaternary lacustrine travertines and stromatolites from high-altitude Andean lakes, northwestern Argentina

Four distinctive depositional subenvironments of fossil travertines and stromatolites are identified in three high-altitude (3500–4000 m above sea level) lacustrine basins: El Peinado, San Francisco (Las Coladas Salar subbasin), and Las Peladas (southern Andean Altiplano, northwestern Argentina). These late Quaternary occurrences are characterized using geomorphological, sedimentological, petrographic, and stable isotopic data. Stromatolites of cyanobacterial origin only develop in shallow lacustrine margins of El Peinado basin. In the same basin, macrophytic travertines occur both near thermal spring seepage areas along the lake margin as in situ facies and in littoral lacustrine environments up to water depths of several metres as phytoclastic travertine facies. The stromatolites and macrophytic travertines have relatively heavy δ18O compositions, suggesting initial16O-depleted waters and (or) evaporation effects through time. Their high δ13C compositions are interpreted as a reflection of intense CO2evasion from the thermal groundwaters feeding the lakes. Similar laminated travertine facies, with no petrographic evidence for biotic origin, occur in both Las Coladas and Las Peladas basins. Neither petrographic nor isotopic data alone can differentiate between these two cases. Besides, diagenetic overprint in Las Peladas facies precludes the use of isotopic values as original isotopic signatures. However, the depositional environmental conditions defined by the geomorphological and sedimentological features are different. Laminated aragonitic crusts in Las Coladas basin formed in a shallow, saline lake and are associated with shoreline and terrace deposits cemented by aragonite. These travertine crusts represent periods of spring,16O-rich discharge to the lake, as suggested by the lighter oxygen isotopic compositions. In contrast, travertines from Las Peladas occur as laminated calcitic and aragonitic units intercalated at the top of fining-upward sequences composed of conglomerates, sandstones, and intraclastic limestones. Sedimentological data suggest that these travertines originated in fluvial-influenced lake margins during low lake-level episodes.

Isotope signature of the Younger Dryas and two minor oscillations at Gerzensee (Switzerland): palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates

Oxygen- and carbon-isotope ratios in the carbonate of benthic ostracodes ( Pseudocandona marchica) and molluscs ( Pisidium ssp.) were measured across the transitions bordering the Younger Dryas chronozone in littoral lacustrine cores from Gerzensee (Switzerland). The specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk-carbonate oxygen-isotope record ( δ 18O Cc). If corrected for their vital offsets, oxygen-isotope ratios of Pisidium and juvenile P. marchica, both formed in summer, are almost identical to δ 18O Cc. This bulk carbonate is mainly composed of encrustations of benthic macrophythes ( Chara ssp.), also mainly produced during summer. Adult P. marchica, which calcify in winter, show consistently higher δ 18O, larger shifts across both transitions, and short positive excursions compared with the summer forms, especially during early Preboreal. Despite such complexity, the δ 18O of adult P. marchica probably reflects more accurately the variations of the δ 18O of former lake water because, during winter, calcification temperatures are less variable and the water column isotopically uniform. The difference between normalised δ 18O of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures. In general, the results indicate warmer summers during the late Allerød and early Preboreal compared with the Younger Dryas. Altogether, the isotopic composition of lake water ( δ 18O L) and of the dissolved inorganic carbonate ( δ 13C DIC) reconstructed from adult Pseudocandona marchica, as well as the seasonal water temperature contrasts, indicate that the major shifts in the δ 18O of local precipitation at Gerzensee were augmented by changes of the lake's water balance, with relatively higher evaporative loss occurring during the Allerød compared with the Younger Dryas. It is possible that during the early Preboreal the lake might even have been hydrologically closed for a short period. We speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts.

Response of metallothionein concentrations in a freshwater bivalve (Anodonta grandis) along an environmental cadmium gradient

Surficial (oxic) sediments, overlying water, and specimens of the freshwater bivalve Anodonta grandis were collected by divers at 11 littoral lacustrine sites located along a geochemical gradient of pH, [Cd], [Cu], and [Zn] in an area influenced by mining and smelting activities. The molluscs were dissected (gills; hepatopancreas; remaining tissues) and analyzed for Cd, Cu, Zn, and metallothioneins (MT). Tissue concentrations of MT in A. grandis varied between 100 and 440 nmol metal binding sites (g dry wt)−1. Metallothionein levels in the gills, the remaining tissues, and the whole organism were significantly correlated (P < 0.01) with tissue Cd concentrations. In contrast, correlations between [MT] and tissue levels of Cu or Zn were weak or nonexistent. The intersite variations in MT concentrations were best related, not to total dissolved metal concentrations at the time of sampling, nor to extractable metal concentrations in the sediments, but to the free Cd2+ concentration at the sediment‐water interface, as estimated from sediment‐water sorptive equilibria. These observations suggest that Cd2+ activity is the key environmental factor to which metallothionein levels in A. grandis are responding in the studied lakes. The mollusc condition indices (C.I. = 1,000 × total dry wt of flesh of the animals/total intervalval volume) deteriorated as Cd concentrations in the tissues increased.

Oligocene-Miocene lacustrine rudite-dominated alluvial-fan delta, southwest Montana, U.S.A.

Facies continuum and facies profiles from outcrops aud drili cores in die Tertiar>' Medicine Lodge beds were analyzed in the Medicine Lodge and Horse Prairie basins in Southwest Montana, U.S.A. These betAs consist of interbedded conglomerates. sandstones, siltstones, mudstones, limestones, carbonaceous sitales, antA coals that malce up coarsening- and fining-upward megasequences. Tite study indicates titat die Medicine Lodge beds were deposited in freshwater lake alluvial-fan delta antA sitort-headed stream delta environments. The lake, whicit probabi>' occurred in an asymmetrical protobasin formed during Laramide deformation and ancestral to tite Medicine antA Horse Prairie basins, was initiali>' infilled by coal-forming, short-headed stream deltas antA littoral lacustrine carbonate platfonns alqng its steeply dipping margin. Ihis early stage of infilling was characterized by rapid basin subsidence, witich was accompanied by lake expansion, antA by subdued provenance tectonism developed west-soudiwest of tite protobasin. Ibe late stage of lake infilhing continued along tite steeply dipping margin of the protobasin where east-northeast flowing alluvial-fan delta complex formed an aggrading, subaerial alluvial fan antA a prograding, subaqueous delta front. Tite alluvialfan delta complex was bounded tu tite south by a lacustrine coastal plain that was drainedby coal-forming, short-headed streams deltas antA tu the immediate nortit by lacustrine littoral carbonate platforms that supported stromatolite Cuadernos de Geologia Iberica N.0 15, 241-278. Madrid, 1991. Edit. Universidad Complutense. R. Al. Flores & J. W. M'Gonigle 242 bioitenns. Titis stage of lake-basin infilling was marked by intense provenance uplifts and was accompanied by moderate basin subsidence antA local lake expansion with marked lake-level fluctuations. Climate did not significantly influence fluctuations of the lake level since tite lake remained fresitwater and open throughout infilling. However, microclimate (e.g., ram sitadows) may have controlled coal distribution in the Medicine Lodge basin part of tite protobasin. Humid-temperate climate is indicated by common presence of debris flows on the alluvial fan, which were triggered it>' intense rainfali. Titus, tite lake protobasin is a microcosm of clastic, carbonate and organic environments, itydrodynamics, provenance tectonism, climate, and basin subsidence titat greati>' influenced facies variations.