The Upper Palaeozoic pebbly mudstone facies of peninsular Thailand and western Malaysia - Continental margin deposits of Palaeoeurasia

Die devonische bis unterpermlsche Phuket Group in Thailand und deren Äquivalent in Malaysia, die Singha Formation, gehören zum SE-asiatischen "pebbly mudstone Gürtel", welcher sich vom südlichen Tibet bis Sumatra erstreckt. Diese ca. 3000 m mächtigen klastischen Serien wurden yon MITCHELL et al. (1970) als Kontinentalhang Deposita gedeutet. In neueren Veröffentlichungen wird eine glaziomarine Entstehung dieser Serien vorgeschlagen (BUNOPAS et al. 1978; STAUFFER 1983). Diese Autoren sind der Ansicht, daß Teile SE-Asiens (Shan-Thai Kraton) sich im unteren Karbon von Gondwana losgelöst und nach einer Rotation um 180 Grad in der oberen Trias mit Eurasien kollidiert haben. Die pebbly mudstones werden dabei als Zeugen der Gondwana Vergletscherung (Karbon/Perm) und Beweis für diese Theorie angeführt. Die vorliegende Arbeit diskutiert die sedimentologischen Argumente für und wider eine glaziomarine Entstehung dieser Sedimentserien. Es wird gezeigt, daß diese Mixtite Kontinentalhangablagerungen sind, die am Nordrand der Tethys bzw. am südlichen Kontinentalhang von Euroasien (Shan-Thai Kraton) sedimentiert wurden

The Permo-Carbonigferous Facies Development in Thailand: A plate tectonic discussion

The Permo-Carboniferous sedimentary facies development in Thailand reflects the late Variscan orogeny in S E Asia. During the Carboniferous and Permian, a N -S trending trough separated the " S h a n Thai Craton" and the "Indosinia Craton". In this pelagic basin, deposition of ribbon cherts continued from pre-Asselian to Kubergandian. I n Lower Permian, carbonatic and tuffitic turbidites were transported from the neighbouring platforms into the basin. The Middle Permian flysch sedimentation resulted from a strong orogenic activity. T h e basin was E-vergent, isoclinally folded and pverthrusted. Parts of the basin are metamorphosed into the greenschist facies. I n the eastern marginal parts Kubergandina to Midian; molasse was deposited from the new rising fold belt. The intensity of folding of the molasse decreases towards the east or the younger strata. The total width of the basin was probably not greater than 200 km. T h e pelagic sediments, flysch and molasse represent a thick pile of a coarsening-upwards sequence, typical of subduction related sutures. Folding affected a marginal marine basin and was caused by a westward directed subduction (A-subduction) under the volcanic arc. West of the arc, pebbly mudstones were laid down on the trench slope or the continental margin of Paleoeurasia. T h e deposition of these mixtites continued through the Carboniferous to Lower Permian and came to an end contemporary with the relative uplift of the " S h an Thai Craton" and the onset of the A-subduction under the Petchabun marginal basin. T h e Benioff- subduction must have been located west of the depositional area of the pebbly mudstones and directed towards the east

Structural history of the southwestern corner of the Kaapvaal Craton and the adjacent Namaqua realm: new observations and a reappraisal

The rocks along the southwestern margin of the Kaapvaal Craton were deformed up to 7 times during the Early to Middle Proterozoic. The oldest deformation D1 is recorded in the N-S-trending Uitkoms cataclasite of pre-Makganyene age (>2.24 Ga) on the craton, and interpreted as a bedding-parallel thrust. It is assumed to be a branch rising towards the surface from a blind sole thrust that initiated early N-S-trending F,-folds above it. D2 is represented by mainly N-S but also NE-SW and NW-SE-trending imbricates and recumbent fold zones ranging in size from small gravity slumps to large tectonic decollements in Asbesheuwel BIF and the Koegas Subgroup, and is younger than D1, or equals D1 in age. These age. These structures pre-date the Westerberg dyke-sheet intrusion. D3 south-verging folds and thrusts are the oldest post-Matsap deformations, just less than 2.07-1.88 Ga. D4 are upright to east vergent and N-S-trending folds deforming all previous structures. D4 post-dates the Westerberg dyke-sheet and probably reactivates N-S folds above the earlier sole thrust during renewed E-W compression. D5, producing the main NW-trending Namaqua structures, is only very feebly developed in the Kheis terrain and absent from the cratonic areas overlain by Olifantshoek and older strata, i.e. NE, E and SE of the Marydale High. Very gentle D6 E-W to ENE-WSW folds produce culminations and depressions in all NW-trending older structures. During D7 the NW-SE-trending Doornberg Lineament, an oblique left-lateral wrench, and smaller N-trending faults such as the Westerberg Fault developed. These and similar, but right-lateral faults are the last movements along the rim of the craton and occurred around 1.0 Ga. Multiple folding and thrusting with riebeckite mobilization happened prior to Namaqua events and resulted inter alia in discernable duplication and thickening of the Transvaal Supergroup along the southwestern margin of the Kaapvaal Craton and at least some 130 km into the craton interior. This complicates stratigraphic correlation as well as true thickness estimates of BIF units in Griqualand West, and affects the model for the environmental evolution of the Ghaap Group. A structural model of thin-skin decoupling at the base of the Transvaal Supergroup and starting in the Middle-Early Proterozoic is proposed

Tubular microfossils from ∼2.8 to 2.7Ga-old lacustrine deposits of South Africa: A sign for early origin of eukaryotes?

Unequivocal evidence for Archean eukaryotic life has been long sought for and is a matter of lively debate. In the absence of unambiguous fossils this debate has focused on biogeochemical signatures and molecular phylogenies. Most researchers agree that fossil forms comparable with modern eukaryotic cells can be credibly identified only in Proterozoic (∼1.8–1.6 Ga) and younger rocks. Herein, we report for the first time, Neoarchean mineralized tubular microfossils from ∼2.8 to 2.7 Ga lacustrine deposits of South Africa. The exceptional preservation of these microfossils allows recognition of important morphological details in petrographic thin section and in HF-macerates that links them to modern siphonous (coenocytic) green or yellow-green microalgae (Chlorophyta and Xanthophyta). The microfossil identification is supported by Raman spectroscopic analyses, EPMA, SEM/BSE and SEM/EDS microprobe analytical results, NanoSIMS elemental mapping and micro-tomographic sectioning of the thalli. All results point to indigenous, bona fide eukaryotic microfossils of algal affinity. These Neoarchean microalgae-like remains and their assumingly combined in vivo and early post-mortem precipitated mineral envelopes greatly improve our knowledge of early life and its habitats and may have far-reaching consequences for the studies of the evolution of life

Structural history of the southwestern corner of the Kaapvaal Craton and the adjacent Namaqua realm: new observations and a reappraisal

The rocks along the southwestern margin of the Kaapvaal Craton were deformed up to 7 times during the Early to Middle Proterozoic. The oldest deformation D1 is recorded in the N-S-trending Uitkoms cataclasite of pre-Makganyene age (>2.24 Ga) on the craton, and interpreted as a bedding-parallel thrust. It is assumed to be a branch rising towards the surface from a blind sole thrust that initiated early N-S-trending F,-folds above it. D2 is represented by mainly N-S but also NE-SW and NW-SE-trending imbricates and recumbent fold zones ranging in size from small gravity slumps to large tectonic decollements in Asbesheuwel BIF and the Koegas Subgroup, and is younger than D1, or equals D1 in age. These age. These structures pre-date the Westerberg dyke-sheet intrusion. D3 south-verging folds and thrusts are the oldest post-Matsap deformations, just less than 2.07-1.88 Ga. D4 are upright to east vergent and N-S-trending folds deforming all previous structures. D4 post-dates the Westerberg dyke-sheet and probably reactivates N-S folds above the earlier sole thrust during renewed E-W compression. D5, producing the main NW-trending Namaqua structures, is only very feebly developed in the Kheis terrain and absent from the cratonic areas overlain by Olifantshoek and older strata, i.e. NE, E and SE of the Marydale High. Very gentle D6 E-W to ENE-WSW folds produce culminations and depressions in all NW-trending older structures. During D7 the NW-SE-trending Doornberg Lineament, an oblique left-lateral wrench, and smaller N-trending faults such as the Westerberg Fault developed. These and similar, but right-lateral faults are the last movements along the rim of the craton and occurred around 1.0 Ga. Multiple folding and thrusting with riebeckite mobilization happened prior to Namaqua events and resulted inter alia in discernable duplication and thickening of the Transvaal Supergroup along the southwestern margin of the Kaapvaal Craton and at least some 130 km into the craton interior. This complicates stratigraphic correlation as well as true thickness estimates of BIF units in Griqualand West, and affects the model for the environmental evolution of the Ghaap Group. A structural model of thin-skin decoupling at the base of the Transvaal Supergroup and starting in the Middle-Early Proterozoic is proposed