Basal Marl Research Articles

DID A CATASTROPHIC LAKE SPILLOVER INTEGRATE THE LATE MIOCENE EARLY PLIOCENE COLORADO RIVER AND THE GULF OF CALIFORNIA?: MICROFAUNAL AND STABLE ISOTOPE EVIDENCE FROM BLYTHE BASIN, CALIFORNIA-ARIZONA, USA

Abstract The southern Bouse Formation (late Miocene–early Pliocene) in Blythe basin, CA-AZ, contains a controversial record of the events that preceded the integration of the developing Colorado River with the Gulf of California. High resolution microfaunal and stable isotope (δ18O, δ13C; VPDB) data from a key outcrop of marl and claystone record an abrupt change in water chemistry that we interpret to be the result of a catastrophic sill breach. Basal marl contains a mix of brackish-water ostracodes and marine foraminifers. Ostracode δ18O values are slightly negative and 6‰ higher than the host sediment carbonate precipitated in the upper water column, indicating isotopically stratified hydrologic conditions during deposition. Freshwater ostracodes abruptly appear in the overlying sediments in association with marine foraminifers, in conjunction with an abrupt change in the isotopic composition of ostracode and host sediment carbonate. The δ18O values from brackish and freshwater ostracodes and the host ...

Stratigraphic status, age, and paleobathymetry of the Grey shale Member, Dalmiapuram Formation, Cauvery Basin, India

Grey shale Member of the Dalmiapuram Formation, Ariyalur Group, Cauvery Basin, India was studied for its stratigraphic position, age, and paleobathymetry with a re-look into the lithological relationship and foraminifer assemblages in the deepened limestone mine excavations at M/s Dalmia Cements, Dalmiapuram. Twenty grey shale samples from Kovandankurchchi (pit-4) and Kallakkudi mines yielded diversified calcareous, benthic, and rare index planktic foraminifera. The foraminiferal assemblages suggest a latest Albian age and middle neritic depositional conditions. The abundance of kaolinite and smectite clay minerals relate to warm/humid climate which corroborate with rising relative sea level during grey shale deposition. The grey shale occurs in patches within the marl bedded limestone member which exhibits cyclic deposition of limestone and marl. The limestone mine sections demonstrate that the grey shale forms part of basal marl bedded limestone, directly overlying the coral algal limestone. The present study demonstrates that the grey shale outcrops in Dalmiapuram Formation should be placed stratigraphically as part of marl bedded limestone. The member status for grey shale which is current usage stands discounted.

Review and analysis of the age and origin of the Pliocene Bouse Formation, lower Colorado River Valley, southwestern USA

The lower Pliocene Bouse Formation in the lower Colorado River Valley (southwestern USA) consists of basal marl and dense tufa overlain by siltstone and fine sandstone. It is locally overlain by and interbedded with sands derived from the Colorado River. We briefly review 87 Sr/ 86 Sr analyses of Bouse carbonates and shells and carbonate and gypsum of similar age east of Las Vegas that indicate that all of these strata are isotopically similar to modern Colorado River water. We also review and add new data that are consistent with a step in Bouse Formation maximum elevations from 330 m south of Topock Gorge to 555 m to the north. New geochemical data from glass shards in a volcanic ash bed within the Bouse Formation, and from an ash bed within similar deposits in Bristol Basin west of the Colorado River Valley, indicate correlation of the two ash beds and coeval submergence of both areas. The tuff bed is identified as the 4.83 Ma Lawlor Tuff derived from the San Francisco Bay region. We conclude, as have some others, that the Bouse Formation was deposited in lakes produced by first-arriving Colorado River water that entered closed basins inherited from Basin and Range extension, and estimate that first arrival of river water occurred ca. 4.9 Ma. If this interpretation is correct, addition of Bristol Basin to the Blythe Basin inundation area means that river discharge was sufficient to fill and spill a lake with an area of ∼10,000 km 2 . For spillover to occur, evaporation rates must have been significantly less in early Pliocene time than modern rates of ∼2–4 m/yr, and/or Colorado River discharge was significantly greater than the current ∼15 km 3 /yr. In this lacustrine interpretation, evaporation rates were sufficient to concentrate salts to levels that were hospitable to some marine organisms presumably introduced by birds.

Foraminiferal stratigraphy and palaeoecological implications in turbidite-like deposits from the Early Tortonian (Late Miocene) of Greece

Abstract. The Lower Tortonian Ag. Giannis section, in Gavdos Island, Greece, consists of an outer neritic to upper bathyal, marly hemipelagic sequence which is interrupted by thick turbidite-like sandy deposits. During deposition of the marly intervals, reworking was considerably reduced.This paper contributes to knowledge concerning benthic foraminiferal response to dynamic sedimentary environments. Important palaeoecological information for benthic foraminiferal assemblages was gathered and analyzed in order to create a regionally consistent picture of the palaeoenvironment. Samples were analyzed statistically in order to identify the different palaeoenvironmental settings during turbiditic sedimentation. Undisturbed basal marls of the section are characterized by the predominance of a diversified Uvigerina striatissima assemblage typified by a broad variety of morphotypes with different inferred habitat preferences and feeding strategies, indicating rather well-oxygenated bottom waters. This environmental stability was subsequently disrupted by recurrent deposition of turbidite-like sands. A low-diversity Valvulineria complanata-Globobulimina sp. assemblage is dominant in this part of the succession, as these specialized endobenthic species could keep pace with high-energy sedimentary settings. Just above the turbidites, a “recolonization” fauna (Bolivina alata assemblage), composed entirely of infaunal elements is observed, indicating a nutrient-rich substrate. This oligotypic fauna is later replaced by a more diversified microfauna capable of occupying a wider range of ecological niches.

Chemostratigraphy and diagenetic constraints on Neoproterozoic carbonate successions from the Sierras Bayas Group, Tandilia System, Argentina

Carbon and oxygen isotopic data, combined with a detailed diagenetic study, obtained from undeformed and unmetamorphosed dolomite and limestone from the Neoproterozoic Sierras Bayas Group, Argentina, provide a new record of isotopic stratigraphic variations useful for regional and global correlations. The Sierras Bayas Group is subdivided into the Villa Mónica (sandstones and dolomites), Cerro Largo (siliciclastic rocks) and Loma Negra (limestones) formations, unconformably overlain by the Cerro Negro Formation (siliciclastic rocks with basal marls), and grouped into four depositional sequences bounded by unconformities. The dolomite samples from the Villa Mónica Formation show ranges of δ 13C (PDB) values from − 1.3 to + 2.2‰ and of δ 13C (PDB) values from − 2.1 to − 6.7‰. Elemental data (Mn/Sr, Fe/Sr and Ca/Sr) and stable isotope compositions point to a moderate to significant degree of diagenetic alteration in samples from this formation. The Loma Negra Formation is composed of homogeneous, non-luminescent micritic limestone with δ 13C (PDB) values of samples between + 2.7 and + 4.5‰; δ 13C (PDB) values vary from − 7.1 to − 13.5‰. Selected element ratios using Mn/Sr (< 1.4) and Fe/Sr (< 30) combined with C/O isotope data suggest near to primary carbon isotope signatures in these samples. The Villa Mónica Formation can be broadly constrained between 800 and 900 Ma, based on Rb/Sr radimetric data and stromatolite morphologies. The Loma Negra Formation fits in global δ 13C and 87Sr/ 86Sr trends that suggest an age range of ~ 580 – 590 Ma, which is regionally important as it places constraints on the continuity of Vendian basins in south-western Gondwana. In the same sense, the isotopic signatures of Loma Negra Formation samples along with the preservation of a unique shelly fauna make a direct connection of the Argentinian succession to Vendian intervals in Uruguay (Polanco Formation) and Brazil (Corumbá Group).

An unusual Messinian succession in the Sinis Peninsula, western Sardinia, Italy

Recently completed sedimentological and palaeontological analyses of the Messinian deposits of western Sardinia yielded dating, palaeoenvironmental and new sequence stratigraphic interpretations. The Basal Marls and the Capo San Marco Formation are referred to the Messinian. Both formations were deposited in a ramp setting, whereas the overlaying Sinis Limestone Formation is interpreted as a carbonate platform of wide extent, probably equivalent to part of the Terminal Carbonate Complex. All these deposits are considered to have formed under normal marine conditions. The three formations developed during one and a half cycles of progradation–retrogradation. Compared with other Messinian Mediterranean carbonate platforms, the Sinis Peninsula exhibits several unusual features: (1) The notable absence of scleractinian coral reefs is related to dominantly cool seawater in this area. (2) The Capo San Marco Formation contains widespread microbial–bryozoan–serpulid carbonate buildups, partially associated with upwelling currents. (3) The breccias at the top of the Sinis Limestone Formation are regarded as resulting from a major seismic shock over the whole peninsula.

EARLY STAGES OF LIGNITE FORMATION IN PTOLEMAIS BASIN: A COAL-PETROGRAPHIC APPROACH

With the present study it is intended to assess the depositional palaeoenvironment of the lower part of the Lignite-bearing Sequence in the Ptolemais Basin, and more specifically in the areas of Notio-Field and Tomeas-6 open pits. The sediments under study represent the seam between the Volcanic Tephra Layer and the Basal Marl, which constitute the roof and the floor, respectively. Coal-petrographic results showed that Huminite is the main macerai group (84-96%), while macérais from Liptinite and Inertinite groups display low values (&lt;10%). In bulk lignite samples the main mineral phases are quartz, calcite, clay minerals and feldspars, while in the ashes the main phases are quartz, anhydrite and lime. The palaeoenvironment of the lignite formation was reconstructed using the lithological, coalpetrographic and mineralogical data, as well as coal-facies diagrammes. In Notio-Field Mine, at the early stages of lignite formation the conditions used to be limnotelmatic, while in Tomeas-6 Mine they were telmatic. Upwards the conditions turned to more telmatic in both mine areas. The vegetation was mainly herbaceous with some arboreal elements occurring mostly in Tomeas-6 area. The water influx was generally intense resulting in enhanced inorganic input

The base of the Portsdown Chalk Formation (Chalk Group, White Chalk Subgroup) in the BGS Big Almer Wood Borehole, Dorset, southern England

The mapped boundary between the Spetisbury Chalk Member of the Culver Chalk Formation and the overlying Portsdown Chalk Formation of the White Chalk Subgroup is taken in central Dorset at a pronounced negative feature break. In the absence of any section across the junction, the feature was thought to mark the upward change from marl-free chalk into chalk with numerous marl seams, as in the Isle of Wight. However, in the BGS Big Aimer Wood Borehole, drilled to investigate this boundary, marl seams are largely absent in the lower part of the Portsdown Chalk, and it is the upward change from flinty to flint-free chalk which marks the Spetisbury/Portsdown Chalk boundary. The basal beds are rich in comminuted inoceramid debris. A new member, the Big Aimer Wood Member, is introduced for this basal marl- and flint-free, ‘gritty’ chalk. This paper includes a revised foraminiferal zonal scheme for that part of the Lower Campanian corresponding to the G quadrata macrofossil Zone. In this scheme, the Big Aimer Wood Member is more-or-less co-extensive with the BGS20iv Subzone. New foraminiferal evidence shows that the basal Portsdown Chalk boundary in this part of Dorset lies at about the level of the Scratchell's Marls, i.e. a short distance above the basal boundary marl seam (Portsdown Marl) of the Portsdown Chalk of the Isle of Wight standard successions; i.e. the base of the Portsdown Chalk is slightly diachronous.

Cenomanian–Coniacian transition from siliciclastic to carbonate marine deposition, Giralia Anticline, Southern Carnarvon Platform, Western Australia

Three formations exposed in the Giralia Anticline record the transition from siliciclastic to carbonate-dominated sedimentation on the Southern Carnarvon Platform, a stable shelf on the passive western Australian continental margin. The succession consists of condensed and partly eroded sequences that record maximum marine flooding events and the unconformities between them. The stratigraphic record of the depositional change is evident in four <2-m-thick sections analysed here by outcrop logging and micropalaeontological analysis. The oldest sequence, at 96–94Ma, includes transgressive-phase deposits truncated by an unconformity, but reflecting a maximum water depth of less than 50m in the preserved record. This sequence is represented in the uppermost 0.5m of the Gearle Siltstone in its type area as a dark grey mudstone that belongs to nannofossil Zone CC10a (Middle Cenomanian). The second sequence, dated at 92–91Ma, is evidenced by a very thin (<0.25m thick) unit of yellowish brown to pale yellow marl that belongs to the upper Lower Turonian (based on the overlap of the upper part of nannofossil Zone CC11 and the planktic foraminiferal Helvetoglobotruncana helvetica Zone). A middle neritic (water depth about 100m) depositional setting is suggested by the foraminiferal assemblage. The transgressive base of the third sequence (dated at 88–87Ma) includes the lowest 20cm of the Toolonga Calcilutite that contains abundant nannofossils indicative of zone CC14 (mid Coniacian). The basal marls and calcilutites of this sequence were deposited on a marine erosion surface at water depths of about 50m. There is broad correspondence between the local record of bathymetric change and the eustatic sea-level curve for the mid Cenomanian to mid Coniacian interval. In shallow waters (50–100m deep) relatively close to the shoreline, influx of siliciclastic mud decreased allowing accumulation of nannofossiliferous muds during the Turonian and Coniacian interval. A decrease in the amount of precipitation, erosion and river transport of sediment onto the continental shelf (indicative of climatic change, perhaps to more arid conditions in the hinterland) was probably the main factor that led to the change from marine siliciclastic to carbonate sedimentation that occurred between 96–94Ma and 92–91Ma in the Giralia region.

Petroleum potential of the North Hungarian Oligocene sediments

As part of Eoparatethys, a partly isolated sea existed to the north of the present-day Pannonian Basin during Oligocene time. From Lattorfian times thick shale sequences, rich in organic matter, were deposited. Locally, laminates of euxinic facies formed (Tard Clay Formation) and are the best oil-prone source rocks of the Oligocene sequence. Although oil discoveries were made in the basin in the late 1930s, exploration was prevented by the complicated tectonics. Currently, detailed seismic, geological and geochemical studies have been initiated, the first results of which are summarized in this paper. Rock-Eval pyrolysis data and bituminological analysis show the Tard Clay Formation to be a good source rock. Its thermal maturity has been influenced by subsequent tectonic movements and Neogene heat flux. Migration and accumulation of the generated hydrocarbons is controlled by unconformities and, in particular, by the tectonic elements. Complicated structural and stratigraphical traps are covered by the Pliocene basal marl.

Corry bog, pennsylvania: A case study of the radiocarbon dating of marl

New radiocarbon dates, carbon and oxygen isotope analyses of mollusks and marl, and palynologic analysis have clarified age relationships at the Corry kettle bog in northwestern Pennsylvania. A 4000-yr difference in radiocarbon dates between basal peat and marl top, previously interpreted as caused by the presence of an unconformity, is reinterpreted as due to “hard-water effects” from carbonate bedrock and glacial deposits. A radiocarbon date of 14,000 yr from basal marl, previously used as a minimum age for glacial deposition, is also likely too old; instead a similar age is estimated for the base of the underlying lake clay. Radiocarbon dates on marl should be used with caution and supported by isotopic and pollen analyses.

Surface Exposures of Late Cretaceous Strata at Rayburns Salt Dome, Bienville Parish, Louisiana: ABSTRACT

Surface exposures of Cretaceous strata in Louisiana are restricted to isolated occurrences associated with salt domes in the northwestern part of the state. The best known Cretaceous exposures are associated with the Rayburns salt dome in Bienville Parish. Strata exposed at this structure previously have been correlated with formations exposed in southwestern Arkansas, in particular, the Marlbrook Formation and the Saratoga Chalk. Several distinct Upper Cretaceous lithologic units can be identified at the Rayburns locality. Detailed stratigraphic relationships of these units are obscured by the incomplete nature of the exposures and by dense vegetation. Strata on the west side of the outcrop area include a basal olive-gray marl that is locally glauconitic. This unit is thought to correlate with the Brownstown Marl in Arkansas. The basal marl is overlain in part by a massive glauconitic sandstone at the western end of the outcrop area and by a gray chalky marl at the eastern end. These lithologies are thought to correlate with the Buckrange Sand Lentil or basal Ozan Formation exposed in Arkansas. The sandstone and gray chalky marl units are directly overlain by a hard white chalk. This chalk lithology correlates faunally and lithologically with the upper Ozan and the Annona Chalk in Arkansas. Exposures along the east side of the outcrop area, adjacent to an abandoned quarry, are blue-gray marl and chalk whose fauna and lithology correlate with the Saratoga Chalk in southwest Arkansas. The concretionary clays of the Midway Group, of Paleocene age, lie unconformably on the truncated surface of this Saratoga equivalent. The unconformity is marked by a thin layer of bored, calcareous nodules. The uppermost portions of the Navarro Group, which occur elsewhere between Cretaceous and Paleocene strata, have apparently been eroded at this locality. End_of_Article - Last_Page 1212------------