Formation Lacustrine Research Articles

A Successful Application of the Petroleum System Concept in the Camamu Basin, Offshore Brazil: ABSTRACT

The characterization of a major petroleum system in the Camamu basin, NE Brazil, was undertaken using a multidisciplinary approach involving geochemical, geological, geophysical and microbiostratigraphic research. This approach has greatly enhanced the level of understanding of the petroleum system concept in the area, allowing the identification of a new exploration target. The hydrocarbons sourced by the lowermost Cretaceous lacustrine fresh to brackish water black shales, started migration during the Early Cretaceous times, continuing up to now in some parts of the basin. The hydrocarbons were accumulated in Lower Cretaceous, Rio de Contas Formation lacustrine sandstone reservoirs, structured during the rifting process, and sealed by deep water lacustrine shales, or trapped in the Dom Joao Stage (Jurassic), Sergi Formation, against the footwall of major regional faults. The geochemical parameters indicate that the Camamu basin is basically oil prone. Mapping the geographic extent of the petroleum system emphasizes the association of the oil fields with the proposed pod of active source rocks. The integration of these data with a 2D-geochemical modelling allowed the prediction and characterization, in time and space, of the petroleum pathways from source to trap in the area. Two major petroleum systems were selected, as the most attractive, inmore » the Camamu Basin: the pre-rift Morro do Barro-Sergi (!) and synrift Morro do Barro-Rio de Contas (!). This approach allowed the identification of a new exploration target, in the latter one, which, after drilling, resulted in a 157 M bbl discovery, and brought a new insight for the hydrocarbon exploration in the basin.« less

Magnetostratigraphy of Neogene Sediments in the San Jacinto Fault Zone, Southern California, and Paleomagnetic Evidence for Block Rotation

A suite of oriented paleomagnetic samples from a continuous sedimentary section in the right-lateral San Jacinto fault zone allows the interpretation of magnetic stratigraphy, documentation of the clockwise rotation of crustal blocks, and identification of several potentially adverse effects on the precision of paleomagnetic directions. Accounting for these effects has led to a clearer understanding of the structural evolution and depositional patterns within the fault zone. The 500-m sampled interval includes all of the upper Pleistocene Ocotillo Formation (alluvial sands and interbedded shales) and the upper 25 m of the underlying Borrego Formation (lacustrine deposits). Most samples contain two magnetic components: a low-temperature component that fails the fold test (suggesting its recent acquisition), and a high-temperature component that passes the fold test. The magnetostratigraphy of the sampled interval, calibrated by vertebrate biostratigraphy, implies the base of the Ocotillo Formation is 1.25 million years old. Compared to published ages for the base of this formation towards the southeast, these new data suggest the onset of alluvial deposition was diachronous within the fault zone. Scatter in paleomagnetic directions results from two depositional and two structural effects. Depositional effects include paleocurrent-induced grain orientation and inclination shallowing due to compaction. Structural overprints include shearmore » associated with both faulting and folding that induces rotation of magnetic grains. Removal of samples affected by these factors suggests an average clockwise block rotation of 21{degree}{plus minus}7{degree} over the past 1.3 m.y. and further that rotation has been progressive over this interval.« less

Lacustrine sedimentation in a Permian intermontane basin: The Villé graben (Vosges, France)

The Permian Villé graben, located on a major fault of the Vosges basement, has several stages of fluvial fill interrupted by a period of lacustrine sedimentation. The lacustrine deposits of the Autunian 2 series include various facies: marginal and fan-delta clastics and permanent lacustrine carbonate facies evolving into evaporitic playa facies. Differential subsidence of tectonic blocks controlled the facies patterns from the margin to the centre of the basin. The sedimentation is determined by three components: terrigenous, volcanosedimentary and carbonate. Fan-delta progradation with resedimentation processes provided the clastic material. In the upper part of the lacustrine formation, volcanosedimentary material was deposited. Primary ash-fall sedimentation was followed by sub-aqueous erosion and redeposition. Towards the edge of the basin, the lacustrine facies is thin and was subject to frequent emergence. Sediments were occasionally oxidized and iron was redistributed to give mottled horizons. Cabonate crusts were precipitated and some silicification took place. In the centre of the basin, sapropelic carbonate sedimentation develops into a eutrophic lake with anoxic bottom waters. The sapropels are massive to finely laminated; they include monospecific ostracod faunas, type II to type III kerogens and a total organic carbon content reaching 2.7%. Cyanobacterial and microbial activity in these organic-rich sediments produced early diagenetic carbonate, phosphate and sulfide phases. At the top of the formation, important sedimentological changes follow a lacustrine regression. A restricted and evaporative environment leads to the development of an evaporitic playa lake with stromatolites.

Geochemistry of Organic Matter-Rich Mesozoic Lacustrine Formations of Eastern United States: ABSTRACT

During the initial extension of Laurasia, a series of rift basins formed along the eastern coast of North America. Cyclic lacustrine sedimentary sequences are found in the exposed basins, which extend from Nova Scotia to North Carolina. These lacustrine deposits, collectively known as the Newark Supergroup, consist of transgressive-regressive cycles. Muds (now shales) rich in organic matter were deposited during highstands of the lakes. The authors have conducted a detailed geochemical examination of lacustrine units from the Hartford, Newark, and Culpeper basins in order to determine their depositional environment, hydrocarbon source potential, and thermal history. Correlations between migrated bitumens and produced oils from the Richmond and Sanford basins were also made.

Response spectra of earthquakes on very soft clay

Abstract The response spectra of two strong and two mild earthquakes recorded on the thick lacustrine formation of Mexico City in 1961 and 1962 are presented. The velocity spectra of the two strong ones are compared with studies made independently by Jennings. Discrepancies there-with are explained in terms of wave reflections. A criterion to simplify data reduction and spectrum computations is supported by these comparisons. Velocity and pseudovelocity spectra are practically alike. The period corresponding to the maximum peak and the general shape of these curves agree closely with those predicted applying the one-dimensional theory of multiple wave reflections to the formations in question.

Correspondance entre les couples erosion-sedimentation et pluvial-aride au Sahara nord-occidental

Abstract A climato-sedimentologic cycle is proposed on the basis of Villafranchian deposits in the northwest Sahara. The relationship between the erosion-sedimentation cycle and the pluvial-arid cycle is shown. The stratigraphy and sedimentation of the material composing the terrace deposits show an evolution toward increasing aridity, beginning with gravel deposits of a fluvial character and progressing toward typically arid sediments. The proposed cycle begins with a period of maximum aridity during which massive dunes cover the ancient terraces and hamadas, and debris from gravity erosion accumulates in cones. In the arid-pluvial transition period, humidity gradually increases, causing erosion of the slopes and debris cones. Maximum erosion occurs in the pluvial period. In the pluvial-arid transition period, sedimentation is at first fluvial, involving coarse-grained material, then loamy, and finally eolian. Lacustrine levels, crust formations and secondary rhythms are also recognized and briefly described. This cycle is confirmed by the prehistoric civilizations from the Pebble Culture to the Neolithic.

Le recif miocene du Languedoc

Abstract The Miocene reef of the Languedoc region, France, originated at the edge of the Vindobonian shore following a change from marly to essentially limestone deposition. At present only scattered remnants remain. The fringing nature of the reef is shown by its passage westward into beach conglomerates or brackish and even lacustrine formations.

Niveau a coprolithes de crustaces

Abstract Cites a number of brackish to lacustrine formations, of Liassic, uppermost Jurassic, and Neocomian (Cretaceous) age, which contain crustacean coprolites (mainly in Aquitaine, France, and north Africa).

First Note on the Archaeology of the Mohawk Town of Ossernenon

The grounds of the shrine dedicated to three of the canonized North American Martyrs, in the township of Auriesville, N.Y., have long been believed to embrace the site of the Mohawk town of Ossernenon. The two reasons for such an opinion have been principally: the topography, and the surface finds. To this evidence may be added the sundry post-contact Indian graves found nearby. In order to locate and study the town accurately, excavations were made on the shrine grounds, during the summer of 1952, under the direction of the writer.The site is situated on a terrace, some 400 feet above sea level, on the south side of the Mohawk River, 40 miles up the river from its confluence with the Hudson, and a mile upstream from the juncture of the Schoharie River with the Mohawk. The area is represented on the' Fonda Quadrangle of the U.S. Geological Survey maps, and on the map accompanying the monograph of Brigham (1929, p. 60), who calls this terrace the Schoharie Wash Plain, and identifies it to be a lacustrine formation dating from the closing phase of the last glaciation.

On the Origin of the Mineral Springs of Vichy

In this memoir I wish to put on record a few observations I made last summer at the baths of Vichy, which may serve to connect the issue of the mineral waters of that place with certain geological phaenomena that then fell under my notice. The little town of Vichy is situated on the right bank of the Allier in the southern portion of the Bourbonnais, and about twenty-five miles south of Moulins. Geologically considered, Vichy is near the northern termination of the great lacustrine formation of the Limagne d'Auvergne, the lower parts of which have been considered to be of older tertiary age. Occupying low hills and plateaux on both banks of the Allier, around Vichy, the lacustrine limestones and marls of that age extend to the north of the Sichon by Cusset as far as Billy (in the direction of Moulins), where they stand out in great horizontal masses to the plains of the Bourbonnais and the Orleanais, without any existing traces of the barrier that formerly retained the waters in which they were accumulated. This fact proves that these deposits are of very remote age as respects the present outline of the country, and leads us to suppose that they have since been raised up en masse . The lowest members of this tertiary group are well seen in various sections in different parts of Central France, and consist of granitic arkose, red sandstone, and argillaceous marl, Such strata are not visible in the neighbourhood of Vichy, where

Remarks on the Geology of the Island of Samos

The island is divided into two equal parts by a high mountain running transversely across from the north to the south shore, and attaining a height of 4000 feet. The ancient as well as modern name of this range is Ampeloni. Besides Mount Ampeloni, there are two other conspicuous mountains rising at the two extremes of the island. The western one, Mount Kerki, is the highest point in the island and is 4000 feet above the sea. The eastern mountain is the least in elevation of the three, and does not exceed 1200 feet. Mounts Kerki and Ampeloni are composed of a mass of crystalline limestone overlying mica schists, but whether conformably I had no opportunity of observing; neither can I speak of the amount and direction of the dip of these older rocks; in Mount Kerki however the dip was considerable, whilst in Ampeloni and the eastern mountain it is not great; in the latter indeed the strata are nearly horizontal, so that the schistose rocks do not appear at all. These mountains are connected together by a series of flat-topped hills and ridges from 400 to 800 feet in height. The deposits forming these are all of freshwater origin, and appear by their fossils to be identical with the lacustrine formations on the shores of the Gulf of Smyrna and the island of Scio, which have been described on a former occasion, and are supposed to be of eocene date. The portion of the island of Samos described