Palynostratigraphy of the Mesozoic continental clastics in western and southeastern Libya

Ali Omar Tekbali, University of Texas at El Paso

Abstract

Abundant and diverse terrestrial palynomorphs recovered from 287 samples from 55 wells and outcrop material in the Mesozoic continental sequence of western and southeastern Libya have been used to establish palynological zonations, reconstruct paleogeography and depositional environments, and to delineate regional unconformities.^ Two miospore suites and six palynological assemblage zones include 365 distinct taxa. Thirty-five new palynomorph species and two genera are described and illustrated. Critical palynomorph types are systematically described, compared to other species, and documented stratigraphically.^ Middle Triassic conifer pollen and spores recovered from a cored section of the Al Aziziyah Formation are separated into two discrete suites. On the basis of new appearances of diagnostic species, Suite I is assigned to the early Ladinian, and Suite II is assigned to the late Ladinian.^ Palynological analysis of outcrop material and several boreholes permits the establishment of three palynozones within the Jurassic-Lower Cretaceous sediments of western Libya. Palynomorph assemblages of these biozones range in age from the Callovian (Middle Jurassic) to the Berriasian (Early Cretaceous).^ Spore and pollen assemblages from subsurface Kiklah Formation (Albian) are often associated with dinoflagellates and allow recognition of three distinct assemblage zones. Zone III, which is late Albian in age, is further separated into two subzones on the basis of appearance of characteristic species.^ Paleogeographic distribution of palynomorphs is analysed to assess the previously proposed dates and boundaries, and to interpret the continental to marginal marine depositional system characteristic of the Jurassic-Early Cretaceous sequence in northwestern Libya. The "Nubian Sandstone" facies in the As Sarir region and in the Murzuq Basin, traditionally considered of Jurassic-Cretaceous age, are divided on the basis of pollen and spores into four assemblage zones. Environments of deposition and paleogeography of these facies are interpreted in the light of new findings. Palynomorph assemblages indicate that "Nubian Sandstone" in western Libya was deposited by braided streams, flowing from the southern highlands.^ Application of local biostratigraphy for species-level comparisons with coeval microfloras from other parts of Northern Gondwana, particularly North Africa, Gabon Basin, and Brazil, confirms extension of the West African-South American (WASA) Province into North Africa. Sparse Laurasian palynomorphs may indicate that the West African-South American/Boreal floral boundary crossed into North Africa.^ Developed regional correlations and palynostratigraphy are used to test hypotheses on paleogeography, place and time of origin, and adaptive radiation of the early angiosperms. The new data are used to improve knowledge on the first appearance of specific microfloras and the geographic and geologic conditions of the African craton during the Mesozoic. Palynostratigraphic data support the concept that initial angiosperm evolution took place in semiarid environment of the tropical and subtropical regions before migration poleward. Occurrence of small smooth tricolpate pollen in the Aptian and Albian sediments of Libya and Egypt supports the pseudoanthial theory, and suggests that wind-pollination was well-established, at least, as early as the Aptian. However, coexistence of these psilate species with large coarsely sculptured insect-pollinated pollen add credibility to the idea that angiosperms are polyphyletic in origin. ^

Subject Area

Geology|Palynology

Recommended Citation

Tekbali, Ali Omar, "Palynostratigraphy of the Mesozoic continental clastics in western and southeastern Libya" (1994). ETD Collection for University of Texas, El Paso. AAI9503518.
http://digitalcommons.utep.edu/dissertations/AAI9503518

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