Plate tectonic control on the formation and tectonic migration of Cenozoic basins in northern margin of the South China Sea

The tectonic evolution history of the South China Sea(SCS) is important for understanding the interaction between the Pacific Tectonic Domain and the Tethyan Tectonic Domain,as well as the regional tectonics and geodynamics during the multi-plate convergence in the Cenozoic.Several Cenozoic basins formed in the northern margin of the SCS,which preserve the sedimentary tectonic records of the opening of the SCS.Due to the spatial non-uniformity among different basins,a systematic study on the various basins in the northern margin of the SCS constituting the Northern Cenozoic Basin Group(NCBG) is essential.Here we present results from a detailed evaluation of the spatial-temporal migration of the boundary faults and primary unconformities to unravel the mechanism of formation of the NCBG.The NCBG is composed of the Beibu Gulf Basin(BBGB),Qiongdongnan Basin(QDNB),Pearl River Mouth Basin(PRMB) and Taixinan Basin(TXNB).Based on seismic profiles and gravity-magnetic anomalies,we confirm that the NE-striking onshore boundary faults propagated into the northern margin of the SCS.Combining the fault slip rate,fault combination and a comparison of the unconformities in different basins,we identify NE-striking rift composed of two-stage rifting events in the NCBG:an early-stage rifting(from the Paleocene to the Early Oligocene) and a late-stage rifting(from the Late Eocene to the beginning of the Miocene).Spatially only the late-stage faults occurs in the western part of the NCBG(the BBGB,the QDNB and the western PRMB),but the early-stage rifting is distributed in the whole NCBG.Temporally,the early-stage rifting can be subdivided into three phases which show an eastward migration,resulting in the same trend of the primary unconformities and peak faulting within the NCBG.The late-stage rifting is subdivided into two phases,which took place simultaneously in different basins.The first and second phase of the early-stage rifting is related to back-arc extension of the Pacific subduction retreat system.The third phase of the earlystage rifting resulted from the joint effect of slab-pull force due to southward subduction of the proto-SCS and the back-arc extension of the Pacific subduction retreat system.In addition,the first phase of the late-stage faulting corresponds with the combined effect of the post-collision extension along the Red River Fault and slab-pull force of the proto-SCS subduction.The second phase of the late-stage faulting fits well with the sinistral faulting of the Red River Fault in response to the Indochina Block escape tectonics and the slab-pull force of the proto-SCS.

Origin and evolution of the genera Lonsdaleia and Actinocyathus:Insights for the Mississippian palaeogeography from the western Palaeotethys

Representatives of the subfamily Lonsdaleiinae Chapman,1893 are common in the Mississippian of the western Palaeotethys.A general analysis of the origin,distribution and evolution of that subfamily has been undertaken.The most probable hypothesis for the origin of the genus Lonsdaleia McCoy,1849 is to acquire colonialism via the genus Axophyllum Milne Edwards and Haime,1851.Actinocyathus d'Orbigny,1849 would be a descendant of Lonsdaleia by increasing integration in the colonies.The first occurrences of Lonsdaleia have been recorded in the lower Visean from northern Britain and northern Tianshan Mountains of northwestern China,but the diversification and migration to the whole Palaeotethys only happened in the late Visean.Three hypotheses are proposed on that matter.The Serpukhovian was also a period of migrations and diversification for these genera.Both Lonsdaleia and Actinocyathus have been recorded in Bashkirian refuges,the Sverdrup Basin in northern Laurasia and the Tindouf Basin in northern Africa,respectively.The division of the western Palaeotethys into six subprovinces based on the distribution of corals is proposed.

A revised Mississippian lithostratigraphy of County Galway(western Ireland) with an analysis of carbonate lithofacies, biostratigraphy, depositional environments and palaeogeographic reconstructions utilising new borehole data

An integrated study of borehole data and outcrop of Mississippian （late Tournaisian to late Visean） rocks in Co. （County） Galway, western Ireland has enabled a more detailed geological map and lithostratigraphy to be constructed for the region. Several carbonate formations have been distinguished by microfacies analysis and their precise ages established by micropalaeontological investigations using foraminifers and calcareous algae. In addition, palaeogeographic maps have been constructed for the late Tournaisian, and early to late Visoan intervals in the region. The oldest marine Mississippian （late Tournaisian） deposits are recorded in the south of the study region from the Loughrea/Tynagh area and further south in the Gort Borehole; they belong to the Limerick Province. They comprise the Lower Limestone Shale Group succeeded by the Ballysteen Group, Waulsortian Limestone and Kilbryan Limestone Formations. These rocks were deposited in increasing water depth associated with a transgression that moved northwards across Co. Galway. In the northwest and north of the region, marginal marine and non-marine Tournaisian rocks are developed, with a shoreline located NW of Galway City （Galway High）. The central region of Co. Galway has a standard Visdan marine succession that can be directly correlated with the Carrick-on- Shannon succession in counties Leitrim and Roscommon to the northeast and east as far as the River Shannon. It is dominated by shallow-water limestones （Oakport, Ballymore and Croghan Limestone Formations） that formed the Galway-Roscommon Shelf. This facies is lat- erally equivalent to the Tubber Formation to the south which developed on the Clare-Galway Shelf. In the southeast, basinal facies of the Lucan Formation accumulated in the Athenry Basin throughout much of the Visean. This basin formed during a phase of extensional tectonics in the early Visean and was probably connected to the Tynagh Basin to the east. In the late Visean, shallow-water limestones of the Burren Formation extend across much of the southern part of the region. They are characterized by the presence of rich concentrations of large brachiopod shells and colonial coral horizons which developed in predominantly high-energy conditions. These limestones also exhibit palaeokarstic surfaces and palaeosols which formed during regressive conditions of glacio-eustatically controlled cyclicity. Locally, slightly deeper water, lower energy conditions developed on the shelf with the formation of rare bryozoan-rich mud-mounds. Deep-water basinal facies were maintained in the central and southeastern parts of the region between the two shelves with the persistence of the Lucan Formation. Ac- tive syn-sedimentary faulting influenced deposition in the Visean and interfingering of basinal sediments with slumps and shallow-water shelf carbonates are recognized.

Tribute to Prof.Zeng-Zhao Feng

It is with great sadness that I heard today of the passing of Prof.Feng whom I had known personally for over a decade.He was a kind and generous man who took a great interest in everyone he met and dealt with.He will be remembered for his immense contribution to the Chinese Geoscience community for his many published articles and books.

Linkage between reactivation of the sinistral strike-slip faults and 28 September 2018 Mw7.5 Palu earthquake, Indonesia

On September 28, 2018, a Mw7.5 earthquake occurred near Sulawesi, Indonesia as a result of strike-slip faulting at shallow depth within the interior of the Molucca Sea Microplate that forms a part of the broader Sunda Plate. Focal mechanism solutions and distribution for the earthquakes indicate rupture occurred on a left-lateral NNW-SSE-to N-S-striking fault. This region has been characterized by complex tectonics in which motions of numerous small microplates are accommodating large-scale convergence between the Australia, Sunda, Pacific and Philippine Sea plates. In this paper, the Coulomb stress calculation verified the WNW-, nearly E-W-trending sinistral strike slip receiver fault in Sulawesi, which is consistent with the giant sinisterly strike-slip fault system across New Guinea, Pacific Tectonic System and the Tethys Tectonic System caused by the oblique convergence. The result has been reconciled within the modern GPS velocity field.

Palaeobiogeographical constraints on the distribution of foraminifers and rugose corals in the Carboniferous Tindouf Basin,South Morocco

The northern flank of the Tindouf Syncline in southern Morocco exhibits a continuous, well exposed Carboniferous succession with limestones of Late Asbian to Early Bashkirian age containing rich and diverse foraminiferal and rugose coral assemblages. Analysis of these assemblages provides new data on the relatively poorly known Saharan basins. The palaeobiogeographical relationship of the Tindouf Basin with other Palaeotethyan basins is complex. Although there is a predominance of cosmopolitan taxa for the Palaeotethys, it is recognized that there was an influence of basins from NW Europe, such as the UK and Ireland. Some taxa are recorded in both NW Europe and Tindouf without any characteristic contributions from intermediate basins in northern Morocco. The neighbouring Béchar Basin in Algeria presents distinct assemblages. The bulk of the data analyzed suggest that this sector of the western Palaeotethys can be subdivided into four palaeobiogeographical subprovinces: the Atlantic Subprovince (UK, Ireland, N France and Belgium), the Mediterranean Subprovince (Pyrenees, Montagne Noire, Betic Cordillera, Rif (N Morocco) and Balearic Islands), and the Saharan Subprovince (Béchar, Reggan, Ahnet-Mouydir and Tindouf). In between, mobile belts of mixed faunal assemblage characteristics are observed (e.g., SW Spain and Central Meseta) forming the West peri-Gondwanan Subprovince.Analysis of the Tindouf Basin faunas shows that, as in other Saharan basins, there is a high diversity and abundance of foraminiferal taxa, with a higher proportion of survivors and longer stratigraphic ranges; these features also are mirrored by rugose corals. This emphasizes the longevity of the carbonate platform in a tropical setting, where periodic transgressions introduced new assemblages, and oceanic currents are interpreted as one of the main controlling factors for the distribution of the taxa in these subprovinces. Moreover, not only were water temperatures on the platform higher, but also tectonic stability greater. It is considered that the effects of the first phases of the Gond-wanan glaciation were minimal on the Tindouf faunas.

A new early Visean coral assemblage from Azrou-Khenifra Basin,central Morocco and palaeobiogeographic implications

A new early Visean coral assemblage has been recorded from turbidite facies in the southern part of the AzrouKhenifra Basin,northwest of Khenifra,central Morocco.The newly discovered Ba Moussa West(BMW)coral fauna includes Siphonophyllia khenifrense sp.nov.,Sychnoelasma urbanowitschi,Cravenia lamellata,Cravenia tela,Cravenia rhytoides,Turnacipora megastoma and Pleurosiphonella crustosa.The early Visean age of the coral assemblage is supported by foraminiferal and conodont data,with the recognition of the basal Visean MFZ9 Zone.This confirms that the first transgression in the Azrou-Khenifra Basin was during the earliest Visean.The allochthonous coral assemblage was recovered from coarse-grained proximal limestone debris flow and turbidite beds within a faultbounded unit,lying to the west of a thrust syncline containing upper Visean limestones.No evidence exists of the former early Visean shallow-water platform from which the corals were derived.All other in situ platform carbonate rocks around the southern margin of the Azrou-Khenifra Basin are probably of late Visean(Asbian–Brigantian)age.The early Visean Ba Moussa West coral fauna can be compared with that at Tafilalt in eastern Morocco,as well as in other Saharian basins of Algeria.Many of the genera and species in the Ba Moussa West assemblage are identical to those in NW Europe,with which it must have had marine connections.The new rugose species described,Siphonophyllia khenifrense,is probably endemic to North Africa.Its ecological niche in NW Europe was occupied by S.cylindrica or S.aff.garwoodi.