Late Cretaceous Series Research Articles

Paleoclimate and paleoenvironment reconstruction of paleosols spanning the Lower to Upper Cretaceous from the Rukwa Rift Basin, Tanzania

The Cretaceous Period is considered the archetypical greenhouse interval, yet there is mounting evidence for intermittent cooler climatic phases throughout this geologic span. Few continental climate histories exist for the Cretaceous south of the paleoequator, and fewer still for Africa during this time. The Cretaceous Galula Formation is one of the few exposed fossiliferous continental sedimentary successions from what is now subequatorial Africa that also contains paleosols and spans both the Early and Late Cretaceous series. Bulk sediment and pedogenic carbonate nodules were sampled from paleosols located throughout ~500 m of the Galula Formation stratotype section, including four from the lower Mtuka Member (Aptian-Cenomanian) and four from the upper Namba Member (Cenomanian-Campanian), to reconstruct the paleoclimate and paleoenvironment of the Rukwa Rift Basin. The Mtuka paleosols developed on channel fill deposits in a semi-arid climate amidst well-defined wet and dry seasons that predominantly generated vertic Calcisols. Geochemical and morphological climofunctions determined that mean annual precipitation (MAP) increased up-section from 454 to 860 mm/yr, whereas the δ18O values of pedogenic carbonates and Bt horizon major-element paleothermometry estimated mean annual temperature (MAT) remained relatively steady, ranging between 12.9 and 13.9 °C throughout the Mtuka Member. The paleosols of the overlying Namba Member formed on channel fill and overbank deposits proximal to the main channels, in a semi-arid to sub-humid climate with little seasonality, forming mostly calcic Argillisols. The Namba paleosols formed under slightly wetter and cooler conditions, recording MAP values between 602 and 987 mm/yr, and MAT estimates between 10.3 and 12.5 °C. These data are consistent with the Mtuka paleosols corresponding to the cool greenhouse period that spanned the Aptian-Albian, with the Namba paleosols corresponding to Late Cretaceous cooling following the Cretaceous Thermal Maximum. This work demonstrates that temperate conditions prevailed in the Rukwa Rift Basin during the mid-Late Cretaceous.

Geology, mineralogy and fluid inclusion study of Oued Jebs Pb–Zn–Sr deposit; comparison with the Bou Grine deposit (diapirs zone, Tunisian atlas)

The Oued Jebs Pb–Zn–Sr deposit is situated on the south edge of the Mourra Triassic diapir, in the Diapir Zone of the Tunisian Atlas. Tow orebody-type are recognized: (1) lens-chapped orebodies hosted in the Dolomitic cap rock that marks the transition zone between the Triassic gypsum cap rock and the overlaying Late Cretaceous series. Mineralization is composed of epigenetic celestite and minor Pb–Zn sulfides. (2) Vein-type and massive-type orebodies crosscutting the Late Cenomanian and Turonian limestone. Mineralization is composed of high-grade ore ranging from 10 to 25 % combined Pb–Zn. Fluid inclusion data for celestite indicate that deposition took place between 70 and 100 °C, or more cooler conditions as indicated by the presence of single-phase inclusions, from mixed NaCl–CaCl2-bearing brines (12–19 wt% NaCl equiv). For the vein-type and massive-type fluid inclusion, data recorded in sphalerite indicate that sulfide deposition took place between 125 and 130 °C mixed NaCl–CaCl2-bearing brines (10–15 wt% NaCl equiv). At least three dilution and cooling trends are also observed that indicate the involvement of more than one fluid in the Oued Jebs hydrothermal system. The epigenetic character of the ores, the host rock nature and the fluid inclusion together permitted to include the Oued Jebs deposit in the large class of MVT deposits and preciously in the sub-class of MVTs associated with salt diapirs environment. The new discovered Oued Jebs deposit is similar in many aspects to the economic Bou Grine deposit. This may point to significant other potential for economic Pb–Zn concentrations that may be located at depth alongside or above many other unexplored Triassic diapirs in the Diapirs zone of the Tunisian Atlas.

The relationships between tectonics and sedimentation in the Late Cretaceous series of the eastern Atlasic Domain (Algeria)

Our study of the Late Cretaceous series in the eastern Atlasic Domain of Algeria is intended to show the geometry of the sedimentary deposits and the sequential palaeogeographic evolution of the region’s basins. The Late Cretaceous series consist of four transgressive–regressive sedimentary megasequences corresponding to 2nd order cycles, noted as I–IV. Each megasequence is made up of three or four sequences that have been correlated with 3rd order cycles. The beginning of megasequences I and II mark a rapid tectonic deepening concomitant with an acceleration of sea-level rise which allowed the deposition of pelagic sediments at their initiation, during the latest Albian and early Turonian times. This tectonism reflects the reactivation of basement faults resulting in extension and block-tilting. The succeeding sequences, showing alternating marls and carbonate beds with benthic facies were deposited in a homoclinal ramp and are indicative of a gradual development of shallow marine conditions. In the megasequences III (Coniacian to Santonian) and IV (Campanian to Maastrichtian) the sequences were wholly deposited on a homoclinal ramp. The major basement faults are NE-SW trending transtensional strike-slip faults, which delimit the margins of the basins, and WNW-ESE and NW-SE trending normal faults that led to block tilting during the Late Cretaceous. Both types of faults strongly influenced palaeogeography and sedimentation. The evolution of the subsidence through the Late Cretaceous shows a progressive sagging of these basins, interrupted by short phases of extension highlighted by accelerations on the subsidence curves. These phases constitute, after the Jurassic extension, a new extensional episode occurring during the latest Albian and Early Turonian, which led to a tilting of basement blocks. The Late Cretaceous extension phases reflect reorientations of the stress in the African plate, during its northeastwardly directed drift, and rifting processes on its northeastern margin. A first compressive phase, which was relatively localized, is registered at the end of the Maastrichtian, leading to palaeogeographic reorganization of the Atlasic basins.

Sedimentary and tectonic evolution of the arc zone of Southwestern Ecuador during Late Cretaceous and early Tertiary times

The eastern part of the “Celica basin” of southwesternmost Ecuador exhibits Late Cretaceous to Tertiary sediments which belong to the magmatic arc paleogeographic zone. Important N-S to NE-trending faults separate a western, mainly Late Cretaceous series (Río Playas) from an eastern succession (Catamayo-Gonzanamá) of (?) Late Cretaceous to early Tertiary age. The analysis of these sediments indicates a complex geologic history, which recorded the main stages of the early tectonic evolution of the Andes. In the Río Playas area, a submarine andesitic volcanic pile (Celica Fm) represents the products of a volcanic arc of probably Albian age. It is apparently overlain by a thick, early Late Cretaceous series of volcanic flows and coarse-grained volcaniclastic high-density turbiditic beds (Alamor Fm), the deposition of which might result from the Mochica phase (late Albian-early Cenomanian) Deformation, uplift and erosion (early Peruvian phase) are followed by the sedimentation of unconformable marls and greywackes of marine open shelf to deltaic environment. These comprise Santonian and/or Campanian fine- to mediumgrained deposits (Naranjo Fm), abruptly overlain (late Peruvian phase ?) by fan-delta coarse-grained marine deposits of latest Cretaceous age (Casanga Fm) They are locally capped by undated, partly volcaniclastic red beds, indicating an important regression/uplift of latest Cretaceous-early Tertiary age. In the Catamayo-Gonzanamá area, thick subaerial andesitic volcanic rocks (Sacapalca Fm) are intruded by Paleocene to early Eocene plutons and are overlain by undated fluvial red beds. They express uplift movements of latest Cretaceous-early Tertiary age. To the South, these are capped by slumped lacustrine black shales and greywackes of possible Maastrichtian-Paleocene age (Gonzanamá Fm) Farther north, the Sacapalca volcanics and red beds are overlain by variegated shales, sandstones and conglomerates, dated as latest Oligocene-early Miocene (Catamayo Fm) They are eroded by an angular unconformity and capped by early Miocene volcanics and sediments, which express an early Miocene deformation phase. The apparent sedimentary hiatus including most of Eocene-Oligocene times is interpreted as a result of the late Paleocene and late Eocene Incaic tectonic phases.

Relations between Tectonic Zones of the Albanides on the Basis of Results of Geophysical Studies

The Ablanides are located between the Dinarides of Yugoslavia and the Hellenides of Greece, which together form the southern branch of the Mediterranean Alpine Belt. Our analysis of the Albanides and their extension into the Adriatic Sea integrates surface geological observations, well data, and results of seismological, reflection-seismic, gravity, magnetic, and geoelectric surveys. Evolution of the Albandies began with the Triassic subsidence of their Hercynian substratum under a tensional regime, culminating in crustal separation and opening of the Hellenic-Dinaride oceanic basin. The internal Albanides (IA) formed part of the oceanic Hellenic-Dinaride Basin, whereas the external Albanides (EA) developed out of the westward adjacent passive margin and continental shelf of the Adriatic plate. This was accompanied by the development of a synorogenic foredeep basin. During the tectonic, tarditectonic, and neotectonic phases, progressive westward shift of the foredeep basin axis to its present location in the Adriatic. The EA evolved out of a shelf and continental margin sedimentary prism and a superimposed foredeep wedge, which together form the Alpine-deformed hydrocarbon-bearing Albanian Sedimentary Basin. Reflection-seismic and gravity surveys done in the EA and the Adriatic Sea define distinct structural belts related to different tectonic zones of the Albanian Sedimentary Basin. The most importantmore » oil and gas accumulations are found in the Jonian zone and in the Periadriatic depression. The carbonate-dominated Late Triassic to Late Cretaceous series of the lonian, Kruja, and Krasta-Cukali zones contains several rich source rock intervals. In the lonian zone, Late Cretaceous, Paleocene, and Eocene carbonates and oligocene-Miocene flysch-type sandstones form the reservoirs of the main oil and gas accumulations. The Tortonian-Pliocene Molasse-type clastics of the Periadriatic depression also contain source rocks and stratigraphically trapped gas accumulations.« less