Similar Outcrops Research Articles

Paleoecology of a Lower Cretaceous (Barremian) fish community of the Morro do Chaves Formation, Sergipe-Alagoas Basin, NE Brazil

Opportunities to examine the structure of paleocommunities are extremely rare, due to the incompleteness of the fossil record. Regarding the Morro do Chaves Formation, there are many studies about the fauna and flora since 1870. However, paleoecological data are relatively scarce. According to the most recent study, the palynological records of the Morro do Chaves Formation were related to a disturbed paleoenvironment, caused by marine incursions in the northern sector of the Sergipe-Alagoas Basin during Lower Cretaceous. Thus, this paper aims to analyze the paleoecological relationships of the paleocommunity of fishes in the Morro do Chaves Formation, as the possible responses to the paleoenvironmental disturbances. From the basic matrix of abundance data for four fish orders found in 11 pelitic levels, similarity matrices were computed, using the Bray-Curtis distance coefficient. Cluster analysis by the unweighted pair-group method using arithmetic averages (UPGMA) was performed on these matrices, for grouping the levels. The advantages of multivariate analysis in paleoecological studies are also discussed. In addition, the Morro do Chaves Formation is composed of active piscivorous predators, benthophagous and planktiphagous fishes. The aulopiform fishes probably acted as top-down regulators in the paleocommunity, controlling the local fish populations. Mawsonia and “Lepidotes” are usually recorded in similar outcrops and inferred to be associated fauna. While Mawsonia likely possesses a sit-wait strategy, “Lepidotes” would be a relatively more active predator.

The Fractured Model Study of Low-Permeability Reservoir in Xinli Oil Field

With the development of the petroleum industry, the importance of low-permeability reservoirs becomes clear. The fracture, which serves as the notable characteristic of a low-permeability reservoir, controls the flow system of reservoir fluid and restrains the development effect. Finding ways to recognize the fracture by using the normal data and building the fracture 3-D model are the important and difficult points of low-permeability development. According to this problem, the authors use a helpful probe. First, from similar outcrop and drilling core study of the fractured original model, the knowledge base of the fracture was built. Second, based on the analysis of the principle of dual-later log identification fracture, the core calibration was used to make logging, and using dual-later log, the fracture in wells was recognized. Third, based on the analysis of the principle of the fractal kriging method, the inter-well fractures were predicted. Finally, the 3-D model of fracture was built with fractural random simulation. The result shows that the 3-D model is in accordance with the fact of the development. So, the method is correct.

Palaeoentomological study of the lacustrine oil-shales of the lower Miocene San Chils locality (Ribesalbes-Alcora Basin, Castellón province, Spain)

For the first time, the study of the fossil record present in laminated bituminous dolostones from the San Chils locality, lower Miocene in age (ca. 19 Ma), located at the Ribesalbes-Alcora Basin, is addressed. The identification of 11 families and three genera belonging to six insect orders (Orthoptera, Thysanoptera, Hemiptera, Coleoptera, Hymenoptera and Diptera) has been carried out. Furthermore, ephippia of ladoceran crustaceans, one bird feather, vertebrate coprolites and plant remains have been found. The San Chils palaeodiversity has been compared to that of La Rinconada, a similar outcrop in the same basin and depositional unit. Both localities correspond to lacustrine deposits and were mined during the past two centuries. This work has increased the palaeontological richness of the Ribesalbes-Alcora Basin with new fi ndings such as specimens of the subfamily Corixinae (Hemiptera: Corixidae), some ant workers (Hymenoptera: ormicidae), a specimen assigned to the genus Exechia (Diptera: Mycetophilidae), ephippia of Daphnia (Ctenodapnia ) sp. (Branchiopoda: Cladocera), the possible first report of the genus Sciocoris (Hemiptera: Pentatomidae) for the Neogene fossil record and the possible presence of the family Aeolothripidae (Thysanoptera). The current collection of fossil specimens from San Chils is small, but shows that it shared similar palaeoenvironmental conditions to that of La Rinconada, both in the lake waters and in the surroundings.

Lichenometric Dating of Historic Inscriptions on a Rock Outcrop in Coastal Oregon

We estimated the age of inscriptions on a rock outcrop by estimating the ages of lichens that had overgrown the inscriptions. The inscriptions are considered to be historically important, potentially representing some of the earliest European exploration of Neahkahnie Mountain, the highest point along the Pacific coast from Baja California to Strait of Juan de Fuca, Washington. The rock bearing the inscriptions was destroyed by road construction activities in about 1970–1980, but the inscriptions had been photographed with sufficient detail to allow diameter estimates for the lichens on the rock, affording an opportunity for dating based on lichen sizes. Aspicilia and Placopsis are currently the only lichen genera that are common on similar outcrops in the area and form large light-colored discrete individuals with a radial form. We therefore derived a calibration curve for lichen size in relation to age based on Aspicilia and Placopsis sizes on nearby surfaces of known age (road cuts and stone walls), then applied that curve to the diameters of lichens in the photo. Based on the sizes of the lichens on the rock outcrop with inscriptions, the rock face had been available for lichen colonization and growth for > 100 yrs and perhaps shows a pulse of recruitment following extensive wildfires on the immediate coast in the 1840s. Calculated lichen ages are within 25 years of the expected time of US Army exploration of Neahkahnie Mountain under Captain C. C. Augur in the mid-1800s.

Avian and crocodilian eggshells from the upper Barremian site of Vadillos-1 (Lower Cretaceous, Cuenca province, Spain)

The new upper Barremian microfossil site of Vadillos-1 (Lower Cretaceous, Beteta Gorges, Cuenca province, Spain) has yielded a rich fossil assemblage consisting of numerous eggshell fragments along with diverse skeletal remains of fishes, amphibians, turtles, crocodyliforms and dinosaurs. Crocodilian eggshells constitute the main fraction of the eggshell assemblage which includes abundant material belonging to the oofamily Krokolithidae, as well as a new type of crocodilian eggshells (Neokrokolithes trigonalis oogen. et oosp. nov.) characterised by a type of ornamentation and microstructure of the basal knobs not described before. Few fragments of the oospecies cf. Mycomorphoolithus kohringi, attributed to non-eusuchian crocodylomorphs, have been also found in this site thus expanding the record of this oospecies to the upper Barremian. The eggshell assemblage has also yielded the first record of avian eggshells (Tristratioolithus minuta oogen. et oosp. nov.) from the Lower Cretaceous of Europe. Comparisons with Lower Cretaceous avian eggshells suggest its possible attribution to Enantiornithes. The tiny eggshell fragments assemblage found at Vadillos-1 site is representative of a small sized fauna. Besides, the diversity appears strongly biased with >90% of the eggshells belonging to crocodilians and approximately 9% to Aves. As established for similar outcrops, this bias may reflect differences in preservation of eggshell types or represent, at least in part, a wetland ground nesting site.

Expected evolution of a Technosol derived from excavated Callovo-Oxfordian clay material

Raw geological materials excavated then piled on large surface areas are submitted to pedogenetic factors. Knowledge of the evolution of this freshly exposed material is required to predict the newly developed Technosol and the corresponding ecosystem. The pedogenetic evolution of a Technosol developed on excavated Callovo-Oxfordian clay minerals (COx) is assessed from the analysis of natural soils developed on analogous materials. Work was based on the hypothesis that the evolution of raw geological materials could be deduced from that of natural soils on similar outcrops in similar climatic conditions. A comparison was made on the basis of mineralogical and geochemical criteria between the unweathered clays and soil material collected from the horizons of two reference pedons on a COx outcrop in North-Eastern France, used by forest or agriculture, and a 10-year-old Technosol derived from freshly excavated COx material piled under outdoor climatic conditions. Soil profiles were described and each sampled horizon was characterized for mineralogy, and physical and chemical properties. Soil profiles were classified as Vertic Stagnic Hypereutric Cambisol (Forest) and Vertic Stagnic Calcaric Cambisol (Meadow), and compared to the Calcaric Technosol (no vegetation yet). They clearly showed brunification and decarbonatization as the major processes having governed their evolution. Signs of clay leaching were also visible on the forest soil. A fairly good adequacy was observed between soil material sampled in the soil deep horizons (2.5 m), the Technosol deep horizon (1.7 m), and the freshly excavated material. Slight differences were recorded, however, i.e., salt loss (NaCl), sulfide oxidation, and precipitation of gypsum from sulfate and calcium released by decarbonatization, as earlier observed in leaching experiments. Salt loss is a rapid process almost completed to the same extent in the Technosol after 10 years than in the Calcaric Cambisol after centuries. The soil under forest showed signs of stronger pedogenetic evolution than the soil submitted to agriculture (meadow), probably because the latter has been refreshed by man-induced erosion. COx evolution can be predicted from the analysis of soils developed on similar outcrops. The Technosol developed on these carbonated materials would evolve as a result of extremely rapid leaching of the soluble phases, then surface enrichment of organic matter, surface decarbonatization, and progressive brunification of the whole profile as the major processes, and give rise to a Cambisol. Technosol study is an interesting approach for dating the age of pedogenetic processes.

Late Ordovician trilobites from northwest Iran and their biogeographical affinities

ABSTRACTA diverse, previously undescribed trilobite fauna from northwest Iran sheds new light on the Early Palaeozoic geography of the Alborz terrane. The structural history of the Alborz region is well known, though faunal data for the area are sparse, especially for the Ordovician. Trilobites, brachiopods, conodonts, bryozoans and echinoderms occur in a red grainstone/packstone near the village of Tatavrud, 35 km southwest of Bandar-e-Anzali. The fossils indicate a Late Ordovician age, although lithologically similar outcrops in northern Iran have previously been considered Silurian. Trilobite genera occurring include Trinodus, Geragnostus, Illaenus, Panderia, Phorocephala, Ovalocephalus, Dicranopeltis, Symphysops, Cyclopyge, and Sphaerexochus. Similar assemblages have been reported from the Late Ordovician of Ireland, Spain, Poland, Norway, northwest China, Kazakhstan and the Turkistan–Alai Ridge (Uzbekistan–Kyrgyzstan border). Reconstructions of Late Ordovician geography place the Alborz terrane near the eastern margin of Gondwana, but there is doubt as to its precise location. Some workers have considered it part of the margin while others have considered it a separate terrane. Several species present, including Mezzaluna tatavrudensis n. sp. and Phorocephala cf. ulugtana (Petrunina, 1975) are very similar to taxa described from the Turkistan–Alai Ridge. In addition, the isocolid genus Paratiresias has only been reported from Iran, the Turkistan–Alai Ridge and northwest China. The presence of these taxa indicates that the Alborz terrane was in close proximity to the eastern margin of Gondwana at this time.

Degradation of Pedogenic Calcretes in West Texas

Calcretes (petrocalcic horizons) are widespread indurated accumulations of carbonate in arid and semiarid regions of the world. Many studies have detailed the formation of these calcretes; however, litde direct attention has been given to their degradation. The primary objective of this study was to evaluate the continuity of calcrete on the Llano Estacado as a step toward understanding processes of calcrete degradation across the region. The Llano Estacado is a tableland spanning eastern New Mexico and West Texas with a well-developed calcrete, known as the caprock, exposed as an escarpment around most of its perimeter. We excavated several deep pits along a transect between the caprock on the eastern margin of the Llano Estacado and a similar outcrop on a playa slope. We documented degradation features in the calcrete and compared the extent of degradation with a calcrete in a more arid region (Diablo Plateau). Our findings show a lack of continuity of the calcrete on the Llano Estacado even in a relatively short transect (220 m) between the two outcrops. Individual calcrete fragments showed evidence of partial dissolution. These observations were confirmed in road cuts and pits excavated for road material across the area. Geomorphic position and surface slope control water movement across the landscape and apparendy explain both the variation in the presence of degradational features and the distribution of calcrete fragments in the transect. Observations from the more arid Diablo Plateau suggest that calcrete degradation is widespread. The degradation of calcrete on the Llano Estacado makes the caprock unreliable in some areas as a stratigraphic marker in distinguishing the Ogallala and Blackwater Draw Formations.

Degradation of Pedogenic Calcretes in West Texas

Calcretes (petrocalcic horizons) are widespread indurated accumulations of carbonate in arid and semiarid regions of the world. Many studies have detailed the formation of these calcretes; however, little direct attention has been given to their degradation. The primary objective of this study was to evaluate the continuity of calcrete on the Llano Estacado as a step toward understanding processes of calcrete degradation across the region. The Llano Estacado is a tableland spanning eastern New Mexico and West Texas with a well‐developed calcrete, known as the “caprock,” exposed as an escarpment around most of its perimeter. We excavated several deep pits along a transect between the caprock on the eastern margin of the Llano Estacado and a similar outcrop on a playa slope. We documented degradation features in the calcrete and compared the extent of degradation with a calcrete in a more arid region (Diablo Plateau). Our findings show a lack of continuity of the calcrete on the Llano Estacado even in a relatively short transect (220 m) between the two outcrops. Individual calcrete fragments showed evidence of partial dissolution. These observations were confirmed in road cuts and pits excavated for road material across the area. Geomorphic position and surface slope control water movement across the landscape and apparently explain both the variation in the presence of degradational features and the distribution of calcrete fragments in the transect. Observations from the more arid Diablo Plateau suggest that calcrete degradation is widespread. The degradation of calcrete on the Llano Estacado makes the caprock unreliable in some areas as a stratigraphic marker in distinguishing the Ogallala and Blackwater Draw Formations.

Ituzaingó Formation. A key for the interpretation of upper tertiary stratigraphy, Mesopotamia-Chaco Paraná Basin, Argentina

Four years of sedimentological detailled study led me to reinterpretate the Upper Terriry Mesopotamia region stratigraphic squeme. Upon a detailed sedimentary environment analysis of the Mesopotamia – Chaco Paraná basin, I made a different interpretation about previous ideas of the several units present at this morphostructural domain. The Ituzaingo Formation was interpretated as continental (fluvial) in origin by several researchers based on an insecure fossil fauna of invertebrates, always present at the top of the layers. These fossil fauna his a broad and extend biochron over the Cenozoic time. The Paraná Formation infralies the Ituzaingó Formation. The idea of an erosion uncorformity between them was strongly proposed. The Paraná Formation carries marine fossil fauna of invertebrates dated as Middle Miocene. It generally is accepted that Toropí and Yupoí Formations rest over Ituzaingó Formation elsewhere. The structural contact was assumed as an erosional unconformity surface. Paraná Formation was dated by fossil invertebrate fauna as Middle Miocene. Topoí and Yupoí Formations were dated as of Midlle to Upper Pleistocene based on fossil vertebrate fauna. I assumed that the position of these fossils vertebrate fauna of is ofaloctonous for the Toropí and Yupoí muddy formations and I propose that the fossil vertebrate fauna is in Holocene sediments. I carried out detailled studies which include: architectural, granulometric and morphoscopic analysis, petrographic data, paleocurrent measurements, scanning electron microscopy, diffractometric x-ray measurements, detailled sedimentologic profiles, drill hole correlations and remote sensing digital processing image analysis. Architectural analysis me to distinguish the following internal sedimentary structures: hummocky cross stratification, tidal bundles, herringbone cross stratification, lenticular bedding, flaser bedding, bipolar cross stratification and several types of wavy stratifications. These studies led me to realize that the sedimentary environments and specially the relationship between these units are different from previously proposed studies. I propose a common shallow littoral marine origin (intertidal) for all these units in a Middle Miocene age, sincronous with the Paranense Sea ingression (12-14 MA) and an interdigitation between sand and mud lithofacies. A subsurface unit, near Paraná Formation, the Puelches Formatioin, is interpretated as belonging to this sandy-muddy typical shallow marine lithofacies, desoite of a previous work, that accepted a fluvial origin for this unit. An erosion unconformity was also proposed between Paraná and Puelches Formation. The Paraná and Ituzaingó Formations are composed by some 80% friable arenaceous facies and of about 20% of muddy facies. This is a typical heterolithic successioin. A neat but irregular ferricretization forehead is present, specially, in the sandy lithofacies. This physico-chemical phenomena led previous authors to a misinterpretation of the stratigraphic scheme. My results show that the contacts between forehead ferricretization in the sandy lithofacies was assumed as an erosion unconformity, which is not the case. In some place, the ferricretization formed ferrigenous sandstones, which I called ferrigenous duricrust. This is os a very recent age of about Upper Pleistocene-Holocene times. Calcretizatioin is also present in the outcrops. All these secondary processes hid the primary physical structures and chemical composition of the sandy-muddy lithofacies. Paraná, Ituzaingó, Toropí, Yupoí and Puelches Formations are suggested to have the same origin (intertidal) and the same age, Middle Miocene. They constitute a blanket body of about 1500 kilometers in extension at the northeastern portion of Argentina and have approximately 300 meters of thickness. They are composed only by medium, fine to very fine white sands and grey to beige mud lithofacies. When alternation is present (ferricretization), the sediments change its colours to reddish or yellowist, sometimes purple, brown or black. In a few cases the alternation (ferricretization) is very intense, then sands are converted into reddish to black sandstones. In this case, primary sedimentary tractive structures were always recognized. These units, Paraná and Ituzaingó Formations are sincronous and may be correlated with other similar outcrops at Uruguay, Brazil, Paraguay, Bolivia, Perú, Ecuador, Colombia, Venezuela and Guyanas. They were formed during Paranense-Amazon Seas.

Three-Dimensional Facies Architecture of the Salem Limestone (Middle Mississippian), Eastern Margin of Illinois Basin: ABSTRACT

Mapping of sedimentary surfaces in the Middle Mississippian Salem Limestone exposed on sawed quarry walls in south-central Indiana has revealed a hierarchy of depositional units representative of the extremely dynamic hydrographic regime of the upper shoreface zone. The depositional units on the scale of microform and mesoform are represented by the microfacies and the facies respectively. Based on their hierarchy, genetically related depositional units and associated bounding surfaces were grouped together to construct four architectural packages (APs) of the scale of mesoforms. AP-I is dominantly an echinoderm- and bryozoan-rich grainstone and consists of bedforms ranging from small ripples bounded by first-order surfaces to two- and three- dimensional megaripples bounded by the second-order surfaces. It formed as part of a giant ramp (asymmetric wavefield) within the intrashoal channel setting. AP-II, also a skeletal grainstone, is a complex of giant sandwaves that moved into the area under the infulence of a storm and partly filled the basal channel form of AP-I. Large avalanche foresets with tangential toesets prevail. AP-III is a dark-gray spatially discontinuous skeletal grainstone to packstone that laterally grades into a skeletal packstone to wackestone. It locally developed overhangs, rips-ups, and hardground on its upper surface. AP-IV is a skeletalmore » and oolitic grainstone formed of tabular two-dimensional megaripples (planar cross-beds) and three-dimensional oscillatory megaripples (trough cross-beds). These architectural packages based on the bedform architecture and micro-and mesoscale compositional changes can be used to characterize micro-, meso, and macroscale heterogeneities. Models of facies architecture from this and similar outcrop studies can be applied to the subsurface Salem reservoirs in the Illinois Basin using cores.« less

Cheilanthes feei New to Virginia

The Slender Lip Fern, Cheilanthes feei Moore, is a widely distributed species of the western United States which occurs eastward to Arkansas, Missouri, Kentucky, and Illinois (Fernald, 1950; Steyermark, 1963; Cranfill, 1980; Mohlenbrock, 1967). The easternmost station for this fern was along Cedar Creek in Bullitt County, Kentucky, in a region known as The Knobs. This small population, discovered originally by Clyde Reed (Reed, 1952), is thought to be disjunct from the next nearest stations along the Ohio River in southern Illinois (Cranfill, 1980). Cheilanthes feei was discovered in 1979 by Bentley during a routine survey of the plants of Claytor Lake State Park, Pulaski County, Virginia. The actual identity of the plant went unknown until the station was visited by the authors on May 8, 1981, when the first voucher collections were made. This discovery is a remarkable disjunction of approximately 450 km eastward from the Bullitt County, Kentucky station and nearly 650 km from the more contiguous portion of its range from Illinois westward. The preferred habitats of this fern are dry, exposed crevices in limestone or dolomite cliffs (Wherry, 1961; Mohlenbrock, 1967). Extensive exposures of this kind may be found along the New River in Virginia. Claytor Lake is a large impoundment of some 4500 acres formed in 1939 when the Appalachian Power Company built its Claytor Dam on the New River just upstream of Radford, Montgomery County, Virginia. In the southeastern sector of Pulaski County, the New River is deeply entrenched where it has cut through thick beds of limestone of the Rome formation and Elbrook dolomite, both of Cambrian origin. The more resistant dolomite forms nearly vertical cliffs, frequently several hundred feet high. The station for C. feei is a rather small but precipitous cliff, perhaps fifty feet high, which forms a nose-like projection along a westward facing portion of the shoreline. Because of the configuration of the rock, the exposures range from northwestern to southern. During a second visit to the outcrop on May 14, 1981, an estimate of 1200 plants was made. Most of these are extremely small and occupy nearly every minute fracture in the rock. Several hundred larger, mature plants crowd the deeper cracks and more protected, overhanging sites. Several smaller, shaded outcrops in oak woods adjacent to the main cliff support a considerable number of additional plants. Adjacent areas of the lake shore, where similar outcrops and exposures occur, were searched for additional populations of C. feei, but only six other plants were found on a very small ledge at the water level several hundred feet to the north. Since the normal pool elevation is approximately eighty-feet above the former river level, this same outcrop was undoubtedly much more extensive prior to flooding. A much larger population may have existed and, of course, other nearby populations may have been inundated by the lake waters.

Cryogenic Forms in the Orlické Mountains

The relief of the Orlické Mountains, north-east Bohemia, similarly as other parts of the Bohemian Highlands shows cryogenic forms. Most frequent are rock outcrops re-modelled by frost occurring on the summit plateaus, ranges, slopes and valley sides in the form of frost cliffs and abrupt walls, isolated rocks and rocky ridges. They are predominantly composed of crystalline schists (migmatites, orthogneiss, paragneiss, garnetic mica schists, quartzites, a. o.). Due to a different lithological and structural composition of the rock also the selective destruction influenced the development and the modellation of the rocky outcrops. Consequently, only more resisting parts have survived. Frost cliffs are of assymetrical profiles with abrupt foreheads (arranged in grades or overhanging) situated along fissures. Their gradient is usually identical with the gradient of the planes of schistosity. At the foot of the frost cliffs cryoplanes occur with mild gradients of 5-15 ° covered with waste of sharp-edged boulders. On the summit flat range of the Orlické Mountains cryogenic forms are not so frequent as on smaller ridges. Most often they occur in deep river valleys where they are due to the erosion activity of the river as well as to a strong frost splitting. Large rocky outcrops occur in the slopes of the fault gap of the Divoká Orlice above Klášterec n/O. Similar outcrops may be found in the valleys of the rivers and tributaries, such as the Bělá, the Zdobnice, the Říčka, the Tichá Orlice a. o. Even if cryogenic forms are not typical of the relief of the Orlické Mountains, they have been produced in this area by the periglacial climate. Most of them are fossil forms whose recent development is negligible.