Jurassic-Lower Cretaceous Research Articles

Stratigraphic and Structural Distribution of Reservoirs in Romania.

In Romania, there are reservoirs at different levels of the whole Cambrian-Pliocene interval, but only some of these levels have the favorable structural conditions to accumulate hydrocarbons in commercial quantities. These levels are the Devonian, Triassic, Middle Jurassic, Lower Cretaceous (locally including the uppermost Jurassic), Eocene, Oligocene-lower Miocene, middle and upper Miocene, and Pliocene. The productive reservoirs are represented either by carbonate rocks (in Devonian, Middle Triassic and uppermost Jurassic-Lower Cretaceous) or by detrital rocks (in Lower and Upper Triassic, Middle Jurassic, Eocene, Oligocene, Miocene, and Pliocene). From the structural point of view, the Romanian territory is characterized by the coexistence both of platforms (East European, Scythian, and Moesian platforms) and of the strongly tectonized orogenes (North Dobrogea and Carpathian orogenes). Each importance crust shortening was followed by the accumulation of post-tectonic covers, some of them being folded during subsequently tectonic movements. The youngest post-tectonic cover is common both for the platforms (foreland) and Carpathian orogene, representing the Carpathian foredeep. Producing reservoirs are present in the East European and Moesian platforms, in the outer Carpathian units (Tarcau and Marginal folds nappes) and in certain post-tectonic covers which fill the Carpathian foredeep and the Transylvanian and Pannonian basins. In the platforms,more » hydrocarbons accumulated both in calcareous and detrital reservoirs, whereas in the Carpathian units and in their reservoirs, whereas in the Carpathian units and in their post-tectonic covers, hydrocarbons accumulated only in detrital reservoirs.« less

Sedimentary Basins and Petroleum Occurrences, Mongolia

Mongolia is situated on the southern margin of the Siberian craton. Successive tectonostratigraphic terrain accreted to the Laurasian, Siberian craton during the proto-Tethys, paleo-Tethys, and neo-Tethys. These terrains have been described as micro-plates made up of continental, ocean basin and volcanic-arc fragments docking onto the Siberian craton. Extensive, post-accretionary rifting developed during extensional periods of opening and closing of paleo-Tethys and neo-Tethys. Rift and graben deformation was initiated in the Upper Jurassic. Rift-fill included conglomerates, breccias, and volcanics. During the Lower Cretaceous, continental deposits with lacustrine clastics continued as the rift-fill sequence. The Upper Cretaceous continental sediments are related to the wrench-rifting, compressive phase. Geophysical data (gravity, magnetics, and seismic) are used with surface, regional geology, and subsurface well data to illustrate the Mesozoic rift basins' geometry, the thickness of sediments, and the existing type of hydrocarbon traps. The Upper Jurassic-Lower Cretaceous shale-sandstone sequence contains the known source rocks and reservoir rocks in the southeastern and eastern part of Mongolia. These rocks are described and their structural and stratigraphic relationship are illustrated. The known oil occurrences are surface oil seeps, impregnated outcrops, oil shows in core holes and in samples, and cores in exploration wells. The two oil fields thatmore » have been discovered in Southeastern Mongolia, Tsagaan-Els and Zuunbayan, are described.« less

STRATIGRAPHY AND PETROLEUM POTENTIAL OF THE ONSHORE CARPENTARIA BASIN, QUEENSLAND

Over the past four years Comalco in joint venture with Bridge Oil have undertaken extensive exploration within the Carpentaria Basin. Over 3000 km of multifold reflection seismic data has been acquired and four petroleum exploration wells were drilled. In addition, the Queensland Department of Mines (GSQ) has drilled four cored full-section stratigraphic wells in the deeper parts of the basin.Analysis of the work to date indicates that the basin is not as structurally simple as first thought. Four sub- basins are recognised based on the composition and timing of Mesozoic sedimentary fill. These are the Weipa, Western Gulf, Staaten and Boomarra sub-basins. The Boomarra Sub-basin contains a Middle Triassic red-bed sequence which is 250 m thick in drill hole GSQ Dobbyn- 1. Thick, Middle Jurassic-Lower Cretaceous, basal fluvial and marine sandstone sequences are restricted to the Weipa and Staaten sub-basins, where they are confined principally to the palaeotopographic valleys. The Western Gulf Sub-basin is believed to contain minimal basal Mesozoic sandstone.Although sedimentary depositional environments exhibit widespread continuity throughout the Carpentaria Basin, variations in lithology and provenance as well as diachronism can be demonstrated between the various sub-basins. Most notably the late Neocomian marine transgression began earlier at Weipa than in the southern sub-basins. A basin-wide stratigraphy has been developed from deep drill hole correlations and mapping of outcrop sections around the margin of the basin in the Olive River, Gregory Range and Melish Park areas thus enabling the petroleum reservoir character of the basin to be determined.

Depositional trends in the Upper Jurassic-Lower Cretaceous of the northern margin of the Wessex Basin

In the exposed Upper Jurassic and Lower Cretaceous sediments along the northern margin of the Wessex Basin (Buckinghamshire to Wiltshire), structural and minor depositional basin orientations are often aligned NW to SE. Local depocentres in the late Jurassic and earliest Cretaceous rarely coincide with those of the mid-Cretaceous Lower Greensand. The “inversion” of these sub-basins is commonly across major NW-SE orientated faults; this change in the position of basins subsidiary to the Wessex Basin occurred in the time gap now represented by the base Lower Greensand unconformity (?Berriasian-mid-Aptian). It was during this time that subtle (or long term) shifts in basement structure became amplified. In this case sub-basin inversion is adequately explained by a long sedimentary hiatus rather than short lived active tectonism.

Sedimentology and Sandstone Diagenesis of Hibernia Formation in Hibernia Oil Field, Grand Banks of Newfoundland

The Hibernia oil field is the largest discovery off the east coast of North America. The most important reservoir unit in the field is the Jurassic-Lower Cretaceous Hibernia formation, which averages 200 m in thickness and occurs at depths between 3,475 and 4,200 m. On the basis of sedimentological descriptions of cores and downhole log responses, five lithofacies have been defined, and the formation has been subdivided into two lithostratigraphic units. The Main Hibernia zone is dominated by thick medium to very coarse-grained quartzarenites, interpreted as distributary channel deposits of a deltaic plain environment. The Upper Hibernia zone consists of relatively thin very fine to medium-grained quartzarenites interbedded with mudstones and siltstones. This zo e is interpreted as deposits of a shallow marine delta-front environment. Porosities observed in thin section and provided by core analysis in the Hibernia sandstones range from 1 to 22%. Many sandstones with high porosities show evidence of dissolution of carbonate cement and some framework grains. This late enhancement of porosity by decarbonatization preceded main hydrocarbon migration and is a major factor in both the accumulation of large reserves and the potential producibility of the field. Lower porosities are associated mainly with well-compacted sandstones or those retaining abundant unleached carbonate cements. Time-temperature index modeling constrains the interpreted time and depth of hydrocarbon generation and accumulation in the sandstone reservoirs.

Paleomagnetism of Permo-Triassic Redbeds from the Asturias and Cantabric Chain (northern Spain): evidence for strong lower Tertiary remagnetizations

The paleomagnetic analysis of the Permo-Triassic redbeds outcropping in the western part of the Cantabric Chain and the small Mesozoic basin from the Asturias shows that these formations have a history of complex magnetization. Only a few sites did not experience the remagnetization processes and retained original directions. The most reliable results yield a paleomagnetic pole located at: lat. 49° N, long. 217° E ( n = 11, α 95 = 3.7°), which is suggested as reliable Permo-Triassic data for the Iberian plate. Two remagnetization phases are recognized: a moderate phase predating the folding gave rise to a first overprinting. It is connected with the distension which occurred in the Pyreneo-Cantabrian region during the upper Jurassic-lower Cretaceous. The main remagnetization phase which occurred after the folding is dated from the lower Tertiary, and can be related to the compression induced on the northern boundary of Iberia from upper Cretaceous onwards. In some cases this phase led to a complete replacement of the primary magnetization. Previously published data, which were at the time interpreted as being European-like in direction, are attributed to this phase. Hence, our results do not support the hypothesis of a micro-plate called “le Danois block”, which was suggested in order to explain these results. We believe that there is no paleomagnetic evidence supporting the existence of a complicated boundary between Europe and Iberia during the mid-Cretaceous opening of the Bay of Biscay.

The iron ores and associated sediments of the Chichali formation (Oxfordian to Valanginian) of the Trans-Indus Salt Range, Pakistan

A distinctive and widespread belemnite-bearing shale of the Tethyan region is well exposed in the Trans-Indus Salt Range as the Chichali Formation, where it contains two workable ironstone seams. Facies analysis indicates a pronounced deepening in the Upper Oxfordian and Kimmeridgian followed by two regressive cycles marked by a transition from glauconitic–phosphatic shales to glauconitic silts and sands and finally to winnowed and oxidized glauconitic sandy ironstones. The first cycle ends in Berriasian belemnite-rich beds; the second cycle, which has few belemnites, extends into the Valanginian, and is followed by deltaic sediments of the Lumshiwal Formation. Comparison with other areas indicates that the source area for the clastic components was the Indian Shield to the east and south. The increased clastic supply in the Upper Jurassic–Lower Cretaceous is thought to result from tectonic uplift in this source area rather than from climatic change. The ironstone beds are distinctive in being pelletal glauconites compared with the oolitic chamosite and goethite so typical of the Jurassic elsewhere. Enrichment of the glauconite to commercial grade was by winnowing and oxidation on the seafloor. The absence of oolitic chamosite and goethite could be related to generally deeper water and an overall Eh in the environment too high to allow iron to migrate in appreciable quantities as Fe 2+ .

Watznaueria manivitae Bukry taxonomic problems and distribution in the Jurassic-Lower Cretaceous sediments of Israel and other Tethyan areas.

<i>Watznaueria manivitae</i> Bukry taxonomic problems and distribution in the Jurassic-Lower Cretaceous sediments of Israel and other Tethyan areas.

Lower Jurassic-Lower Cretaceous belemnite biogeography and the development of the Mesozoic Boreal Realm

The distribution of Lower Jurassic-Lower Cretaceous belemnites is reviewed in the light of recent taxonomic and biogeographic studies and it is seen that belemnite provinciality developed in the late Lower Jurassic, when distinct Arctic taxa are first recognised. In the Middle Jurassic, Boreal and Tethyan belemnite realms are apparent, the Boreal Realm being divisable into informal Boreal-Atlantic and Arctic provinces, which can be recognised up into the Lower Cretaceous. In the Upper Jurassic and Lower Cretaceous distinct Arctic belemnites are found in association with Tethyan ammonites in California, and it is this factor, in association with an observed increase in belemnite diversity northwards from the Boreal-Atlantic to the Arctic provinces that suggests that latitudinal temperature gradients were not the overall control influencing the development of Boreal and Tethyan belemnite realms. Instead, the hostile environment of the Boreal-Atlantic area (the European Archipelago) is seen as an effective barrier to the migration of Tethyan belemnites to the Arctic, and vice versa. However, high sea level stands may have helped blur these distinctions, as in the late Valanginian-Hauterivian, when Arctic taxa invaded Europe, and Tethyan taxa the periphery of the Arctic basin.

関東山地西部の浜平層群 ジュラ系‐下部白亜系付加体の発達過程

関東山地西部の浜平層群 ジュラ系‐下部白亜系付加体の発達過程

Productive Continental Block-Fault Deposits of a Mesozoic Back-Arc Basin: ABSTRACT

Continental sediments filling major extensional block-faulted basins in the rock record traditionally are ascribed to plate margin rifting. The Triassic Cuyo basin of central Argentina is such a continental sedimentary basin, which contains over 3,600 m of interbedded fluvial, lacustrine, and volcanic deposits and which produces about 98,000 BOPD. It, however, formed within a back-arc tectonic setting as a reentrant into the Pampean craton prior to the onset of compressional deformation. The southern half of this basin (about 9,000 km2) was studied using logs and cutting descriptions from 101 exploratory wells. The basin began as a series of subparallel fault blocks and accumulated at least 2,750 m of fining-upward detritus in its first cycle of sedimentation. Initial deposits were oxidized lithic conglomeratic units confined by elongated grabens. As faulting waned, high-gradient fluvial sandstones became prevalent (41%), derived primarily from reworking of interbedded felsic tuffs (29%). The end of tensional faulting is marked by widespread bituminous lacustrine shales that form the source beds for oil production. Broad basin subsidence, probably associated with lithospheric cooling, initiated a second episode of basin sedimentation in which tuffs and sediments containing fluvial sandstones (48%) markedly overlap the original basin boundaries. Sandy lag conglomerates of an intermontane brai ed-stream system cap the interval. These deposits were temporarily interrupted by valley basalt flows (Upper Jurassic-Lower Cretaceous), which are similar in composition to diabase dikes of the underlying strata. End_of_Article - Last_Page 1449------------

Erosional History and Possible Passive Uplift of Paris-Willard Thrust Allochthon, Wyoming-Idaho-Utah Thrust Belt: ABSTRACT

Stratigraphic distribution of clast lithologies in Sevier foreland basin synorogenic conglomerates in the southwestern Wyoming-southeastern Idaho-northeastern Utah thrust belt provides evidence of the erosional history of the Paris-Willard thrust allochthon. Conglomerates of the Upper Jurassic-Lower Cretaceous Gannett Group were deposited in response to initial movement along the Paris-Willard thrust system and are comprised of cobbles and pebbles of Ordovician through Jurassic strata, with upper Paleozoic and lower Mesozoic clasts most common. Thus, by conclusion of initial Paris-Willard thrust movement, the allochthon had been affected by widespread erosion of lower Paleozoic through lower Mesozoic strata. Evidence for subsequent erosion to deeper stratigraphic levels is contained in the basal Hams Fork Conglomerate Member of the Upper Cretaceous-Paleocene Evanston Formation. This unit contains abundant Precambrian quartzite cobbles, which must have been derived from the Paris-Willard allochthon, the only thrust sheet that contains Precambrian quartzite units. Genesis of the Hams Fork Conglomerate has been related to latest Cretaceous major movement along the Absaroka thrust. Thus, either the Paris-Willard thrust was fortuitously reactivated at the same time as major Absaroka thrust movement or uplift associated with movement along the Absaroka thrust resulted in coeval uplift of the Paris-Willard allochthon. One mechanism that could elevate the older Paris-Willard allochthon and allow for erosion to deep stratigraphic levels during major displacement along the Absaroka thrust would involve antiformal arching of the Paris-Willard allochthon as it was carried passively over a major footwall ramp of the Absaroka thrust. Folding and uplift of older passive thrusts carried piggyback by younger active thrusts might be an important mechanism in formation of source terranes for synorogenic foreland basin clastics. End_of_Article - Last_Page 865------------

Jurassic and Cretaceous black shales of the Janusfjellet Formation, Svalbard, Norway

The Upper Jurassic-Lower Cretaceous Janusfjellet Formation, a ca. 400 m thick shaly unit, divisible into the Agardhfjellet and Rurikfjellet Members, has been studied in the field and by petrographical and geochemical means. The Bathonian-Kimmeridgian Agardhfjellet Member was deposited in an open shelf environment during a transgressive phase, and is characterized by more stagnant conditions than the Berriasian-Hauterivian Rurikfjellet Member. Total organic carbon values range from 1 to 4%, exhibiting a maximum of 12% in the Callovian paper shales. The Rurikfjellet Member, slightly enriched in volcanogenic components compared to the Agardhfjellet Member, displays regressive shelf sedimentation, ending in prodeltaic to deltafront depositional environments. Based on the sedimentpetrographical analyses, each member is divided into minor regressive and transgressive phases, probably reflecting tectonic activity and/or eustatic sea-level variations.

Facies History of the Upper Jurassic-Lower Cretaceous Great Valley Sequence: Response to Structural Development of an Outer-Arc Basin

ABSTRACT The facies history of the Great Valley sequence is closely linked to structural events in an arc-trench system. Upper Jurassic-Lower Cretaceous marine rocks, as much as 8,500 m thick along the western margin of the Sacramento Valley, northern California, were deposited on slopes and submarine fans that extended over an unstable basement floored by ophiolitic rocks. Paleocurrent and paleoslope analyses indicate that eastward subduction, initiated as early as Kimmeridgian, created an outer-arc ridge which bounded the west side of the basin. Debris was shed dominantly from the north and east, but significant contributions were ridge-derived. Sediment fabrics, structures, and bedding styles indicate that earliest deposition on basin plains and on eastward facing slopes was followed, at le st until the Valanginian, by a stable sedimentological framework of prograding and avulsing submarine fans characterized by broad, shallow midfan channels, depositional lobes, and abundant, thick deposits of interchannel mud. The Great Valley rocks are transected by northwest-trending faults that produced strike separation of the east-dipping strata. Smooth facies transitions, but with abrupt thickness variations across faults, suggest that faulting with some normal component of motion was contemporaneous with deposition during latest Jurassic and earliest Cretaceous. Later movement, either strike-slip or reverse, brought coarse, inner-fan facies that were deposited on Klamath basement into fault contact with basin-plain facies that were deposited on ophiolitic basement.

Stratigraphy of Upper Jurassic Morrison and Lower Cretaceous Cloverly Formations of Big Horn Basin, Northern Wyoming: ABSTRACT

The Morrison and Cloverly Formations in the Big Horn basin of northern Wyoming and southern Montana are part of a distal edge of a westward-thickening clastic wedge of sediments deposited in an elongate intracontinental basin in the western North American craton. These formations reflect orogenic and volcanic activity in the western Cordillera during Late Jurassic and the subsequent eastward migration of volcanic centers during Early Cretaceous. The Morrison Formation (Upper Jurassic) conformably overlies the Jurassic marine Sundance Formation and consists of light olive-green, lenticular, calcareous siltstones and mudstones interbedded with white to buff or yellowish green, massive and cross laminated, calcareous quartzarenites. The olive-green mudstones in the upper portion of the formation alternate with red-brown calcareous mudstones or shales producing red banding. A lenticular bed of siliceous accretionary lapilli is present in the upper portion of the formation along the west flank of Sheep Mountain anticline, north of Greybull, suggesting a closer proximity to volcanic vents than previously hypothesized. The Cloverly Formation (Lower Cretaceous) consists of three members: the Pryor Conglomerate, the Little Sheep Mudstone, and the Himes; it overlies the Morrison Formation both conformably and unconformably. Its basal contact is sometimes marked by a lenticular, cross-bedded, conglomeratic quartzarenite or a pebble conglomerate consisting of clasts of black chert (Pryor Conglomerate) derived from uplifted Paleozoic deposits to the west and deposited as channel lag. The Little Sheep Mudstone Member is composed of variegated mudstones which are generally noncalcareous bentonitic, and laced with abundant chalcedony and barite concretions and veinlets. The Himes Member also contains a stacked sequence of devitrified tuffs interbedded with bentonitic mudstones, which locally may be several m ters thick. The individual tuffs, however, are generally less than 1 m (3 ft) thick and are very fine grained, buff to white, and massive. Also, relatively thin lenticular lithic wackes occur in the Himes Member. These are anomalous to the quartzarenites of the rest of the Morrison and Cloverly. A thick lenticular, trough-cross-bedded, quartzarenite caps the formation. Both the Morrison and Cloverly Formations are characterized by high ratios of overbank fines relative to coarse channel sands. It has been assumed, but not documented by detailed sedimentologic study, that the deposits were part of an aggrading alluvial flood plain complex dotted by seasonal lakes and swamps and crossed by braided rivers. This model deviates from most modern braided systems which are characterized by rapid lateral mobility and the lack of fine-grained overbank material. The large ratio of fine-grained siltstones and mudstones to coarser grained sandstones can be explained by a number of processes, the most probable being rapid overbank aggradation as a result of a large influx of wind-blown volcanic material from vents to the west. However, this ratio could also be ob ained in a rapidly subsiding basin whose river systems are characterized by long periods between avulsion, which is common in an arid to semiarid environment. End_of_Article - Last_Page 1346------------

Petrofacies and Provenance of Late Mesozoic Forearc Basin, Northern and Central California

Data from the Great Valley Group (sequence) represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc. This information is useful in documenting tectonic and magmatic events within the arc and related terranes, and forms the basis for the establishment of petrostratigraphic units for mapping and correlation. Sandstone and conglomerate compositions are controlled by changes in provenance, many of which were basinwide and synchronous. Clay-mineral composition is controlled primarily by burial metamorphism. Careful attention to sample collection, sample preparation, and petrographic techniques is essential for uniform results. Seven petrographic parameters (P/F, Lv/L, M, Qp/Q, Q, F, and L--listed in decreasing importance to petrofacies discrimination) define eight petrofacies (Stony Creek, Platina, Lodoga, Grabast, Boxer, Cortina, Los Gatos and Rumsey--listed in approximate order of decreasing age). The Upper Jurassic-Lower Cretaceous petrofacies (Stony Creek, Platina, and Lodoga) contain higher lithic contents (supracrustal sources), whereas the Upper Cretaceous petrofacies (especially the Rumsey) contain higher proportions of plutoniclastic components (quartz, feldspar, and micas). The proportion of potassium-feldspar increases from near zero in the Upper Jurassic to nearly 50% of all feldspars in the uppermost Cretaceous. The lower part of the Great Valley Group (Upper Jurassic and Lower Cretaceous) contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes (tectonic highlands) formed by the arc-arc collision (Nevadan orogeny) that occurred prior to initiation of the Franciscan-Great Valley-Sierra Nevada arc-trench system. The Klamath Mountains area provided a major proportion of this detritus. Ophiolite and serpentinite detritus was deposited locally near the base of the Great Valley Group as a result of deformation along the east side of the growing Franciscan subduction complex. Volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the Sierra Nevada area during the Cretaceous. As the volcanic cover was stripped off, plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin. Crustal components were more continental in the southern Sierra Nevada and more oceanic in the northern Sierra Nevada, as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south. By the middle of the Late Cretaceous, extensive batholithic terranes provided potassium-feldspar-rich arkosic detritus to the entire forearc basin. By the Paleogene, arc magmatism had migrated eastward sufficiently that deeper levels of the California part of the arc were exposed by erosion, tectonic activity decreased in the forearc basin, and the basin was filled to sea leve in most parts.

Development and Hydrocarbon Potential, Carbonate Platforms Offshore Northeastern America: ABSTRACT

The Jurassic-Lower Cretaceous carbonate platforms and banks form a discontinuous belt extending from the Grand Banks to the Bahamas (over 6,000 km). The thickness of the carbonate buildups progressively increases southward along the margin, attaining a thickness of more than 5 km on the Bahamas. The platforms also become younger southward, which has been interpreted as an indication of a northward motion of the North American plate. Six types of carbonate buildups recognized document variability of depositional, paleo-oceanographic, and tectonic processes along the margin. The composition of the buildups closely resembles the recent deposits of the western Great Bahama Bank, since oolitic shoals were present near the shelf edge and skeletal, peloid wackestones and biomicr tes were deposited in the inner part of the platform. Coral-hydrozoan, sponge and algal stromatolite bioherms and reefs are important constituents of the Late Jurassic-Early Cretaceous shelf edge. The hydrocarbon prospectivity of the carbonate front differs for the individual carbonate platform types which prevents construction of a single model for evaluation of their hydrocarbon potential. Porosity has locally developed as a result of secondary dolomitization in a mixing zone. Hydrocarbons were at least locally generated and migrated through the porous carbonate rocks. The major critical factor is presence of a rich source rock. The latest deep sea drilling on the northwestern African and eastern North American margins, together with the interpretation of the Mesozoic paleogeography of the shelf, allows the elucidation of this important factor in a time and space framework of margin development. End_of_Article - Last_Page 585------------

Initiation of Salt Flow, East Texas Basin: ABSTRACT

Salt structures constitute five domains subparallel to the basin margin and the Louann Salt updip limit: (1) thin ( 760 m thick); (4) pre-Gilmer salt diapirs (Oakwood and, possibly, Grand Saline); and (5) post-Gilmer salt diapirs in the basin center. This inward increase in shape maturity results from increasing salt thickness and distribution of post-Louann sedimentary facies. The Louann Salt (Middle Jurassic) was deposited in a broad continental basin on a post-rift unconformity surface. Domain 1 suggests that a critical salt thickness (~500 m) was necessary to initiate flow. In the Late Jurassic, an aggrading carbonate wedge uniformly loaded the underlying salt and formed the salt pillows of domain 2. Salt flow in the basin center had not begun by Gilmer time, probably due to a thinner overburden of basinal carbonate facies there. The Upper Jurassic-Lower Cretaceous Schuler-Hosston regressive terrigenous clastics prograded rapidly across the carbonate platform as coalescing fan deltas, filling the central basin. Salt anticlines of domain 3 grew by serial amplification of pre-Gilmer pillows to form ridges normal to dip direction fronting depocenters. Salt iapirs subsequently evolved from the distal anticlines. Salt anticlines have trapped 80% of petroleum produced from the west-center of the basin. Marine pre-Gilmer source rocks, early initiation of folding, and the large size of the anticlines have all contributed to petroleum accumulation. End_of_Article - Last_Page 585------------

Some Pteridophytes from the Jabalpur Formation

In this paper, some pteridophytes are described from the Jurassic-Lower Cretaceous rocks of Satpura Basin and Jabalpur, Madhya Pradesh. These are ?Equisetum, Todites indicus (Olah. &amp; Morr.) Bose &amp; Sah, Gleichenites sp., Hausmannia dichotoma Dunker, Cladophlebis medlicottiana (Oldh.) Pascoe, Sphenopteris anderssonii Halle, Sphenopteris sp. cf. S. otagoensis Arber and 2 species of Sphenopteris.

Cycadophytic leaves from Jurassic - Lower Cretaceous rocks of India

Under Cycadophytic leaves, various Indian species of Taeniopteris Brongniart, Morrisia Bose, Cycadites Brongniart, Anomozamites Schimper, and Pterophyllum Brongniart have been described here. The study is based on specimens described or figured since 1850 and a large number of specimens collected during the last two decades from the Jurassic-Lower Cretaceous rocks of India.&#x0D; It has been observed that the genera mentioned above are most abundant in some of the localities of the Rajmahal Hills. They are completely missing in most of the undoubted Lower Cretaceous beds of India. So far only a single species, viz., Pterophyllum princeps Oldham &amp; Morris is known from the Lower Cretaceous beds of Than, Gujarat.