Detrital Unit Research Articles

The Late Oligocene rodent faunas of Canales (MP28) and Parrales (MP29) from the Loranca Basin, Province of Cuenca, Spain

Two rodent faunas from the Upper Oligocene fluvial sediments of the Upper Detrital Unit of the Loranca Basin are described. The oldest fauna of Canales contains lssiodoromys limognensis and is correlated to MP28; the other, more modern fauna of Parrales contains I. pseudanaema and it is correlated to MP29. The cricetid genera Adelomyarion Hugueney, 1969 and Allocricetodon Freudenthal, 1994 are reviewed and the latter one is considered to be a junior synonym of the former one. The faunas are compared to other Spanish late Oligocene faunas such as Vivel de Río, Hinojosa de Jarque, and Sayaton 1 and 6. The resulting succession is correlated to the most important remaining European late Oligocene localities, and the biochronological subdivision of this period is discussed.

Miocene Rocks Around the Marádah Oasis, Central Sirt Basin, Libya: Facies Development and Implication on Stratigraphy

The Miocene rocks of the Marádah Formation have been stratigraphically investigated from four stratigraphical sections around the Marádah Oasis in the Central Sirt Basin of Libya. The field investigations led to the identification of two members, the lower Qarat Jahannam Member and the upper Ar Ráhlah Member. Fourteen sedimentary facies at the outcrop-scale representing a gradual development of sedimentation from a continental clastic witness in the southwestern outcrops to transitional estuarine, lagoonal, and beaches to the proximal offshore in the northern outcrops, were recognized. The results indicates that the accumulation of the Marádah Formation is transgressive in nature and corresponding to two phases of deposition which have been mentioned in the earlier studies.
 
 The first phase is continental-dominated facies in which cross-bedded sandstones and calcareous sands comprise most of the depositional sequence of the lower Qarat Jahannam Member at the southwestern outcrops. This phase, however, is characterized by extremely bioturbated laminated-shale conquered by Skolithos ichnofacies in the lower part of the upper Ar Ráhlah Member at the northern outcrops. This phase is providing further evidence that the contact between the two members is diachronous everywhere in the study area. The clastic-phase has thought to be deposited in the Lower Miocene (Aquitanian-Burdigalian) since the lower Qarat Jahannam Member rests on an erosional surface of submarine origin in the southwestern outcrops above a 0.5 m. thick of a nummulitic unit of the Oligocene Bu Hashish Formation.
 
 The second phase is marine-dominated facies in which a bioclastic limestone unit rich in thick and disarticulated oysters, including Crassostrea gryphoides (Schlottheim), characterizes the sediments of the Ar Ráhlah Member at the southwestern outcrops. This phase also includes the upper part of the latter member at the northern outcrops in which a detrital limestone unit rich in turritelline gastropods is overlying by thick-bedded calcarenites rich in disarticulated oysters, gastropods, irregular echinoids (notably, Clypeaster and Echinolampas), bryozoans, and celestite corals. The upper part of the Ar Ráhlah Member at the northern outcrops, nevertheless, is terminated by a quite hard dolomitic limestone and by a pretty soft dolomitic marly limestone. Both lithologies, however, are combined with medium-sized oysters, including Ostrea digitalina Fuchs, and pectinid bivalves. The second phase, however, is interpreted to be deposited in the Middle Miocene (Langhian and Serravallian) based on the total-stratigraphic range of the larger benthic foraminifera Borelis melo melo (Fichtel & Moll), which recovered from the studied washed residues, and the associated microfacies.

Molecular biomarkers in the subsurface of the Salar Grande (Atacama, Chile) evaporitic deposits

The Late Miocene–Pliocene aged hyperarid evaporitic system of Salar Grande is a unique, halite-rich sedimentary basin in the Cordillera de la Costa of the Central Andes (Chile) whose bio-sedimentary record is poorly understood. The persistence of hyperacidity over millions of years, the hypersalinity, and the intense UV radiation make it a terrestrial analogue to assess the potential presence of organic matter in the halite deposits found on Mars. We investigated the occurrence and distribution of biomolecules along a 100-m depth drill down to the ~ 9 Ma old detrital deposits topped by La Soledad Formation (ESF). We have identified two well-defined mineralogical and geochemical units by X-ray diffractometry (XRD) and ion chromatography: a nearly pure halite down to 40 m, and a detrital one down to 100 m depth. One-dimensional GC–MS and two-dimensional GC × GC-TOF–MS gas chromatography–mass spectrometry techniques allowed us to detect a variety of lipidic compounds (n-alkanes, n-alkanols, isoprenoids, steroids, and hopanoids), and a relative abundance of functionalized hydrocarbons (n-fatty acids or n-aldehydes), mostly in the upper halite. We also detected biopolymers and microbial markers by fluorescence sandwich-microarray immunoassays. A dominant prokaryotic origin was associated with halophile bacteria and archaea, with minor contributions of lichens, macrophytes, or higher plants. The lipidic record was also imprinted by oxic (high pristane over phytane ratios) and saline (squalane, and mono-methyl n-alkanes) signatures. The vertical abundance and distribution of biomarkers in the Salar Grande was explained by a generalized effect of xeropreservation, combined with salt encapsulation in the upper halite deposits, or with protective organics-mineral interactions in the deeper detrital unit. The results contribute to the interpretation of terrestrial bio-sedimentary records of halite deposits and their association to environmental conditions. The high potential for preservation of biosignatures at Salar Grande suggests that similar evaporitic deposits in Mars should be priority targets for searching for signs of life.

Bacterial and Archaeal Lipids Recovered from Subsurface Evaporites of Dalangtan Playa on the Tibetan Plateau and Their Astrobiological Implications.

Qaidam Basin (Tibetan Plateau) is considered an applicable analogue to Mars with regard to sustained extreme aridity and abundant evaporites. To investigate the possibility of the preservation of microbial lipids under these Mars analog conditions, we conducted a mineralogical and organic geochemistry study on samples collected from two Quaternary sections in Dalangtan Playa, northwestern Qaidam Basin, which will enhance our understanding of the potential preservation of molecular biomarkers on Mars. Two sedimentary units were identified along two profiles: one salt unit characterized by a predominance of gypsum and halite, and one detrital unit with a decrease of gypsum and halite and enrichment in siliciclastic minerals. Bacterial fatty acids and archaeal acyclic diether and tetraether membrane lipids were detected, and they varied throughout the sections in concentration and abundance. Bacterial and archaeal biomolecules indicate a dominance of Gram-positive bacteria and halophilic archaea in this hypersaline ecosystem that is similar to those in other hypersaline environments. Furthermore, the abundance of bacterial lipids decreases with the increase of salinity, whereas archaeal lipids showed a reverse trend. The detection of microbial lipids in hypersaline environments would indicate, for example on Mars, a high potential for the detection of microbial biomarkers in evaporites over geological timescales. Key Words: Dalangtan playa-The Qaidam Basin-Subsurface evaporites-Lipid biomarkers-Mars. Astrobiology 17, 1112-1122.

Rhynchosauroides Footprint Variability in a Muschelkalk Detrital Interval (Late Anisian–Middle Ladinian) from the Catalan Basin (NE Iberian Peninsula)

ABSTRACTThe Middle Triassic successions of coastal and distal alluvial systems are often characterized by the presence of the tetrapod ichnotaxon Rhynchosauroides. Nevertheless, few studies paid attention on the paleoenvironmental implications of this widely distributed ichnogenus. The finding of a new Rhynchosauroides-dominated tracksite opens the window to the use of such footprints in paleoenvironmental studies. The tracksite is located in the active quarry of Pedrera de Can Sallent, at Castellar del Vallès (Catalan Basin, NE Iberian Peninsula). The footprints were recovered from the Middle Muschelkalk detrital unit, composed of a claystone-sandstone-gypsum succession from a sabkha setting of late Anisian-middle Ladinian age. This unit was deposited during a short regression interval within the main Middle Triassic transgression represented by the Muschelkalk facies. The ichnoassociation is composed of Rhynchosauroides isp., and a single, partially preserved, undetermined large footprint. Among Rhynchosauroides specimens, three different preservation states were recognized, corresponding to substrates in (1) subaqueous conditions (surfaces with scarce, deformed, and deeply impressed ichnites), (2) occasionally flooded (mostly trampled surfaces, footprints commonly well preserved), and (3) subaerial exposition (surfaces with few footprints, sometimes corresponding to faint impressions or only preserved by claw marks). The footprint morphological variations of Rhynchosauroides are correlated to substrate rheology and further to the environmental conditions. Rhynchosauroides is a characteristic morphotype that often dominates in the Anisian-Ladinian coastal and distal alluvial settings of several European tracksites. Therefore, these ichnoassociations in such environments, awaiting further detailed analyses, may constitute a distinct ichnocoenosis.

GEOLOGICAL NOTE

Abstract The term “Sukunka Formation” is proposed for a 113 to 169 metre thick mixed siliciclastic and carbonate unit lying between the Middle Devonian Stone and Dunedin Formations in the Rocky Mountain Front Ranges of northeastern British Columbia. The unit is best developed near the headwaters of the Sukunka River, where it outcrops along a series of closely spaced imbricate thrusts. In the type area, it can be divided into three (informal) members: lower, middle and upper. The lower member overlies the Stone Formation unconformably and consists of inter-bedded orthoquartzite, dolostone and sandy dolostone. It is overlain by the middle member that consists predominantly of brick red weathering siltstones interbedded with minor amounts of dolostone. These ‘red beds’ are readily recognizable in the field and can be used elsewhere in the area to identify thrust imbricates. The upper member consists of a series of thick to massive bedded, well cross-bedded and resistant weathering clean quartzose sandstones which gradationally overlie the middle member. The top of the formation is also disconformable. It is transgressed and overlain by the basal calcareous shales and limes of the Dd-1 member of the Dunedin Formation. However, lag deposits from the Sukunka Formation occur within the basal calcareous shales and limes of the Dd-1 member. This condition is thought to reflect progressive transgression of higher stratigraphic levels of the Sukunka Formation to the east by the rising waters that led to accumulation of the Dunedin Formation. Diagnostic fossils have not been recognized in the Sukunka Formation. Presently, it is dated as early Middle Devonian based solely on stratigraphic position. In the subsurface, in the same stratigraphic position between the Stone and Dunedin formations, unnamed argillaceous, sandy and silty carbonates have also been identified. These, further to the east, may be equivalent to the unnamed detrital unit of the Chinchaga Formation.

Oxalate formation under the hyperarid conditions of the Atacama desert as a mineral marker to provide clues to the source of organic carbon on Mars

AbstractIn this study, we report the detection and characterization of the organic minerals weddellite (CaC2O4 · 2H2O) and whewellite (CaC2O4 · H2O) in the hyperarid, Mars‐like conditions of the Salar Grande, Atacama desert, Chile. Weddellite and whewellite are commonly of biological origin on Earth and have great potential for preserving records of carbon geochemistry and possible biological activity on Mars if they are present there. Weddellite and whewellite have been found as secondary minerals occurring inside the lower detrital unit that fills the Salar Grande basin. The extremely low solubility of most oxalate minerals inhibits detection of oxalate by ion chromatography (IC). Crystalline oxalates, including weddellite and whewellite, were detected by X‐ray diffraction (XRD). The association of weddellite with surface biota and its presence among subsurface detrital materials suggest the potential of a biological origin for Salar Grande weddellite and whewellite. In this regard, biological activity is uniquely capable of concentrating oxalates at levels detectable by XRD. The complementary detection of oxalate‐bearing phases through IC in the upper halite‐rich unit suggests the presence of a soluble oxalate phase in the basin that is not detected by XRD. The formation, transport, and concentration of oxalate in the Salar Grande may provide a geochemical analogue for oxalate‐bearing minerals recently suggested to exist on Mars.

Transition from alkaline to calc-alkaline volcanism during evolution of the Paleoproterozoic Francevillian basin of eastern Gabon (Western Central Africa)

We report new geochemical data for the volcanic and subvolcanic rocks associated with the evolution of the Francevillian basin of eastern Gabon during Paleoproterozoic times (c. 2.1–2Ga). Filling of this basin has proceeded through four main sedimentary or volcano-sedimentary episodes, namely FA, FB, FC and FD. Volcanism started during the FB episode being present only in the northern part of the basin (Okondja sub-basin). This volcanism is ultramafic to trachytic in composition and displays a rather constant alkaline geochemical signature. This signature is typical of a within-plate environment, consistent with the rift-setting generally postulated for the Francevillian basin during the FB period. Following FB, the FC unit is 10–20m-thick silicic horizon (jasper) attesting for a massive input of silica in the basin. Following FC, the FD unit is a c. 200–400m-thick volcano-sedimentary sequence including felsic tuffs and epiclastic rocks. The geochemical signatures of these rocks are totally distinct from those of the FB alkaline lavas. High Th/Ta and La/Ta ratios attest for a calc-alkaline signature and slight fractionation between heavy rare-earth suggests melting at a rather low pressure. Such characteristics are comparable to those of felsic lavas associated with the Taupo zone of New Zealand, a modern ensialic back-arc basin. Following FD, the FE detrital unit is defined only in the Okondja region, probably associated with a late-stage collapse of the northern part of the basin.It is suggested that the alkaline to calc-alkaline volcanic transition reflects the evolution of the Francevillian basin from a diverging to a converging setting, in response to the onset of converging movements in the Eburnean Belt of Central Africa.

Quantification of soil erosion rates related to ancient Maya deforestation

We used seismic and sediment core data to quantify soil erosion rates for the past ~6000 yr in the closed catchment of Lake Salpeten, in the tropical lowlands of northern Guatemala. The region was affected by ancient Maya land use from before ca. 1000 B.C. to A.D. 900. This period of human impact coincided with deposition in the lake of a detrital unit (Maya Clay) as much as 7 m thick that contrasts sharply with the relatively organic-rich gyttja deposited both before and after Maya occupation of the watershed. The greatest soil loss, with mean sustained values of ~1000 t/km2yr–1, occurred in the Middle and Late Preclassic Periods (700 B.C. to A.D. 250), associated with relatively low Maya population densities. Soil erosion slowed during the period of maximum population density in the Late Classic Period (A.D. 550–830), indicating a decoupling between human population density and soil erosion rate. The most rapid soil loss occurred early during initial land clearance, suggesting that even low numbers of people can have profound impacts on lowland tropical karst landscapes.

Geological evolution of the Neoproterozoic Corumbágraben system (Brazil). Depositional context of the stratified Fe and Mn ores of the Jacadigo Group

The Corumbáregion is located near the junction of two young (545–480 Ma) Brasiliano provinces: the Chiquitos-Tucavaca aulacogen which cross cuts the Amazon craton-Rio Apa block, and the Paraguay fold belt. Formation of the aulacogen and the Paraguay basin, which is interpreted as a foreland basin, was roughly synchronous with the 590 Ma metamorphism in the neighbouring old Brasiliano Brasilia fold belt. Deformation and metamorphism in the Paraguay belt are bracketed between 545 and 500 Ma, whereas folding in the aulacogen occurred between 500 and 480 Ma ago. The NE–SW-trending, Corumbágraben system is located on the eastern part of the WNW–ESE-trending, Chiquitos-Tucavaca aulacogen. The extensional structures of the Corumbágraben system are attributed to flexure of the Amazon craton along the western border of the Paraguay basin. Stratigraphic successions in the Corumbágraben system resemble those of the adjacent cover rocks of the Amazon craton: a lower detrital unit (Jacadigo Group and Boqui, Puga, and Cadieus formations), partly of glacial origin, and an upper carbonate-rich unit, (CorumbáGroup and Pororó, Cerradinho, Bocaina, and Araras formations) with local preservation of an Ediacara-like fauna. The whole sequence is probably Vendian. In the cover sequence around Cuiabá, the carbonate unit is capped by siliciclastic sediments. In comparison to the cratonic cover rocks, the Jacadigo Group, which is filling the Corumbágraben system, differs on three points: it is thicker, contains chemical manganese and iron sedimentary intercalations and was affected by a diagenetic to epimetamorphic event during which temperatures reached 250–280°C. These features are in good agreement with sedimentation of the Jacadigo Group in an extensional environment where Fe and Mn, of probable hydrothermal origin, would be generated by leaching of hypothetical, hidden intrusive mafic plutons associated with graben formation.

Interpretación paleoambiental de depósitos siliciclásticos en el sector de Esquivias (Cuenca de Madrid)

The occurrence of kerolite-stevensite bearing lithofacies in Neogene Madrid Basin has special outstanding in the Esquivias deposit (Toledo>. In tliis zone Mg elays are bounded at top and bottom by two detrital units. In tliis paper the mineralogical association and sedimentological features of sandy facies related to lower detrital unit (arenas 1), magnesie unit (arenas 2) and upper detrital unit (arenas 3> has been studied. Granulometrie results are: high centile, median values ranging between 0.12 and 0.20 mm. (80ixm % in arenas 2) and good sorting with ranging between 1.58 and 2.07 (up to 4.5 in arenas 2). The sandy facies mineralogy aJways shows feldspars (Ca-Na>K> predominance over quartz and variable content in mica. Heavy mineral assemblages mainly are made up of: biotite, zircon, apatite, tourmaline, garnet and andalusite. Olten these minerals, even apatites, show euhedrail grains, sometimes with unweathered surfaces. Siliciclastie alluvial sedimentation in saline-alkaline lacustrine environment and semiarid climatie conditions are inferred.

Late Jurassic deformation in Honduras. Proposals for a revised regional stratigraphy

The lithostratigraphical subdivision of Mesozoic rocks in Honduras poses problems that are still imperfectly resolved. Observations made by the authors in Honduras between 1988 and 1992, show a clear separation between an older detrital unit, locally known as the Agua Fria Formation which is relatively homogeneous and can be found throughout the so-called Chortis Block, and a younger one composed essentially of cyclic detrital deposition (conglomerates and other molasse type rocks grading into pelites and silstones), usually called red beds (“capas rojas”). The older detrital unit, here called the Honduras Group, is an Early to Middle Jurassic folded and locally metamorphosed unit. The younger unit known as “capas rojas” starts with a molasse type rock which is not metamorphosed and presently have no generic name, and was deposited in extensional basins during a second sedimentary cycle of Early (and younger?) Cretaceous age. Between the two cycles a clear deformation phase took place in the late Jurassic. At La Chacra, near Comayagua in the centre of the country, outcrop conditions and exploration data enabled the observation of a composite section through the lithostratigraphic succession of the two Mesozoic cycles. The following succession was observed from bottom to top: • • Schist and conglomerate of the Agua Fria Formation, turned to a near-vertical position, which was intruded by granite and mineralized veins that are considered to have a late magmatic (Late Jurassic) age. • • A paleo-erosion surface over the Agua Fria Formation, shown by the presence of discordant weathering phenomena and a palaeosol. • • Detrital deposits (calcareous sandstone) and carbonate rocks of the Cretaceous cycle (molasse and red beds of the second cycle), which unconformably overlie the rocks of the first cycle. These observations confirm the existence, in Honduras and throughout the Chortis Block, of two distinct depositional cycles of Mesozoic age that were separated by a major crustal-deformation phase of Late Jurassic age. The same features are known from central Mexico, whence the Chortis Block seems to have come according to generally admitted crustal-block reconstructions of Central America. Early Cretaceous deposits in Honduras fill Cretaceous graben of the central zone. Although superficially resembling the (Triassic-Jurassic) Todos Santos Formation in Mexico and Guatemala, they cannot be compared with this unit because of their different age and origin, and will require better definition and a new name in Honduras.

Early Paleozoic Sedimentation in Reelfoot Rift: ABSTRACT

Analysis of subsurface data from deep tests drilled in the northern Mississippi embayment and southern Mid-Continent suggests that earliest Paleozoic sedimentation was dominated by the tectonic evolution of the Reelfoot rift. Throughout most of the Mid-Continent, the Upper Cambrian Lamotte (Mt. Simon) Sandstone rests nonconformably on Precambrian basement and is overlain by the Bonneterre (Eau Claire) Formation. However, in the area of the Reelfoot rift, both the Lamotte and Bonneterre grade into thick, basinal shales that locally display evidence of episodic deposition of coarse clastics, perhaps on submarine fans. Moreover, two major sedimentary units are present beneath the Lamotte-Bonneterre basinal facies within the Reelfoot rift. Immediately underlying the Lamotte-Bonneterre shale is a carbonate stratum (probably dolomite) that thickens to more than 1,000 ft (300 m) along the axis of the basin in eastern Arkansas. Underlying this carbonate is a detrital unit that grades from arkosic sandstone near the northern terminus of the basin to a basinal shale southward. This basinal shale is at least several hundred feet thick near the axis of the basin. These two strata occupy the stratigraphic position of the Conasauga (Middle Cambrian) and Rome (Lower Cambrian) Formations of the southern Appalachians. The axial and transverse distribution of these strata suggests that the Reelfoot evolved as paired grabens or half grabens during the Early and Middle Cambrian. Subsequently, the Reelfoot remained the axis for more widespread subsidence and sedimentation throughout much of the Paleozoic. End_of_Article - Last_Page 1456------------