Solomon Buckman

Tectonic evolution of Palaeozoic terranes in West Junggar, Xinjiang, NW China

Abstract Nine separate Cambrian to Carboniferous terranes are recognized in West Junggar, northwest China. They were amalgamated as part of the Central Asian Orogenic Belt which records accretion of continental, island-arc and oceanic terranes to Archaean-Proterozoic continental nuclei. Tangbale, Kekesayi, Ebinur and Mayila terranes (Cambrian-Silurian) evolved in intra-oceanic settings and docked, along a series of north-dipping subduction zones, on to the Laba terrane to their south. This southern continent was contiguous with lithosphere of the Kulumudi Ocean to the north. Devonian subduction on the northern edge of this ocean resulted in formation of a continental arc (Toli terrane) and accretionary complex (Kulumudi terrane). The Karamay terrane formed as an accretionary complex during the Carboniferous. The ophiolitic Sartuohai terrane was emplaced as mélange between Kulumudi and Karamay terranes during the Late Carboniferous. Subduction migrated southward, continuing beneath these terranes, resulting in the intrusion of I-type granites into the Toli, Kulumudi, Sartuohai and Karamay terranes. These granites are closely associated with epithermal and porphyry-style gold mineralization. Composite terranes either side of the Kulumudi Ocean collided in the Late Carboniferous, marking the final consolidation of Central Asia. Collision was accompanied by anorogenic granite and diabase dyke intrusion, followed by widespread latest Carboniferous to Permian extension, and subsequently the formation of the Junggar Basin. West Junggar has been further disrupted by Cenozoic strike-slip faulting along Junggar and Dalabute faults.

Middle Ordovician (Llandeilan) radiolarians from West Junggar, Xinjiang, China

A distinctive long-spined Inaniguttid dominated radiolarian fauna is present in cherts of the Kekesayi terrane in west Junggar, Xinjiang Province, China. This fauna contains moderately well preserved specimens of Protoceratoikiscum clarksoni on which the presence of caveal ribs and patagial tissue can be observed. Characteristics of the fauna are similar to others of correlative late Middle Ordovician (Llandeilan) age known from Scotland (U.K.) suggesting that Protoceratoikiscum clarksoni may be biostratigraphically useful.

Holocene palaeofire records in a high-level, proximal valley-fill (Wilson Bog), Mount Lofty Ranges, South Australia

An elevated valley-fill peat bog (Wilson Bog) near Mount Lofty, South Australia, failed in November 2005 following a flooding event, and exposed representative sections of the sediment infill. Two distinct units were revealed: 2 m of coarse-grained, siliciclastic sand/gravel, overlain by 2 m of peat. A simple charcoal extraction technique based on floatation and skimming was developed to extract coarse charcoal from coarse-grained gravels to determine the palaeofire record at a proximal site of sedimentation. Optically stimulated luminescence (OSL) dating of basal sediments revealed a minimum age of deposition of 7.02 +0.50 —0.56 ka, while the oldest charcoal peak yielded a radiocarbon age of 6000—5740 cal. yr BP. The lower half of the siliciclastic unit contains three distinct charcoal peaks suggesting there were infrequent but intense fires associated with wetter conditions during the Holocene climatic optimum 8000—5000 years ago. The period from 4000 to 2000 cal. yr BP is characterised by more frequent charcoal peaks and higher background levels of charcoal, which is consistent with more regular but less intense fires during drier, cooler conditions. The sharp transition from siliciclastic sedimentation to peat formation began ~1200 cal. yr BP, which may relate to a return to wetter conditions. However, fire frequency appears to have increased in this time suggesting augmentation by anthropogenic or ENSO-related factors. Charcoal-rich layers in the siliciclastic unit are associated with poorly sorted, bimodal sediments with high proportions of clay, silt and gravel, which supports the hypothesis that there is an association between past fire events and rapid, coarse-grained, post-fire aggradation. By analogy with active colluvial aggradation following recent fires at nearby Mount Bold, it is evident that fire plays a significant role in hillslope destabilization and subsequent sediment movement, leading to rapid valley-fill aggradation — a chain of events to which we apply the term ‘pyrocolluviation’.

Age and origin of alluvial sediments within and flanking the Mt Lofty Ranges, southern South Australia: a Late Quaternary archive of climate and environmental change

Quaternary alluvial sediments occur within and on the flanks of the Mt Lofty Ranges of southern South Australia. Within the ranges they occupy colluvium-filled bedrock depressions, alluvial-fan sequences at hill/plain junctions and river terraces that flank major streamlines in both locations. Sediments ranging in age throughout the Quaternary have been identified, but this paper focuses on those deposits of Late Quaternary age. Luminescence dating has verified a Last Interglacial age (132–118 ka) for the most widespread of the alluvial units, the Pooraka Formation. A younger, Marine Isotope Stage 3, alluvial unit, in places containing bones of the extinct marsupial Diprotodon, has also been identified. Deposition of the alluvial sediments is associated with relatively warmer and wetter conditions, whereas the valleys that they occupy were eroded under drier climatic conditions. A more widespread occurrence of Stage 3 units is expected to be present but has not yet been verified. Cold, arid environments are inferred from the presence of dunes (∼18 ka) deposited during the Last Glacial Maximum when stream valleys were incised. Grey/black mid-Holocene alluvium (Waldeila Formation), forming present-day floodplains and low river terraces, equates with the Holocene Hypsithermal. The sequence of climatic changes revealed by these sediments is correlated with evidence of Late Quaternary climatic change from other Australian locations. The identification of equivalent units in different tectonic settings reveals that sedimentation is largely climatically driven although active tectonism may accelerate the supply of sediments available for transport.

Traces from the past: the Cenozoic regolith and intraplate neotectonic history of the Gun Emplacement, a ferricreted bench on the western margin of the Mt Lofty Ranges, South Australia

The Gun Emplacement is a small but distinctive bench on the Eden–Burnside Fault Escarpment near Anstey Hill, in the northeastern suburbs of Adelaide, South Australia, occurring at an elevation of ∼210–220 m asl. It is underlain by Middle Eocene North Maslin Sand and is capped by resistant, ferricreted colluvium. Paleomagnetic dating of hematitic mottles in the ferricreted colluvium, immediately underlying the emplacement, returned a Pliocene/Early Pleistocene age. This age is equivalent to that obtained for summit surface weathering. Fault scarps and exposures, including slickensides and fault gouge material, suggest that the Eden–Burnside Fault at this location has a strong en échelon pattern developed in response to reverse-sinistral oblique-slip faulting, reflecting continental stress fields. Remnants of ferricrete cappings forming stranded benches on the Eden–Burnside Fault Escarpment at elevations up to 25 m above the Gun Emplacement demonstrate recurrent tectonism of the South Mt Lofty Ranges related to intraplate deformation. There are at least four distinct ferricrete benches preserved on the eastern side of the active fault leading up from the Gun Emplacement surface. These benches demonstrate alternating periods of stability and tectonic activity disrupting and uplifting the ferricreted surfaces. A fresh surface rupture occurs and may be related to a recent seismic event.

Provenance of Paleocene - Eocene red beds from NE Iraq: constraints from framework petrography

The red-bed deposits in northern Iraq are situated in an active foreland basin adjacent to the Zagros Orogenic Belt, bound to the north by the Iranian plate thrust over the edge of the Arabian plate. The red-bed successions are composed of alternating red and brown silty mudstones, purplish red calcareous siltstone, fine- to coarse-grained pebbly sandstone and conglomerate. The red beds in the current study can be divided into four parts showing a trend of upward coarsening with fine-grained deposits at the top. A detailed petrographic study was carried out on the sandstone units. The clastic rocks consist mainly of calcite cemented litharenite with rock fragments (volcanic, metamorphic and sedimentary), quartz and minor feldspar. The petrographic components reflect the tectonic system in the source area, laterally ranging from a mixed orogenic and magmatic arc in Mawat–Chwarta area to recycled orogenic material rich in sedimentary rock fragments in the Qandel area. The Cretaceous–Palaeogene foreland basin of northern Iraq formed to the southwest of the Zagros Suture Zone and the Sanandaj–Sirjan Zone of western Iran. During Palaeogene time deposition of the red beds was caused by renewed shortening in the thrust sheets overlying the Arabian margin with uplift of radiolarites (Qulqula Formation), resulting in an influx of radiolarian debris in addition to continuing ophiolitic detritus. Mixed sources, including metamorphic, volcanic and sedimentary terranes, were present during deposition of the upper part of the red beds.

Lajishankou Ophiolite Complex: Implications for Paleozoic Multiple Accretionary and Collisional Events in the South Qilian Belt

The Lajishan ophiolite complex in the Qilian Orogen is one of several ophiolites situated between the Qaidam and North China blocks that record episodic closure of the Proto-Tethyan Ocean. Detailed field relations and geochemical and geochronological studies are critical to unraveling the tectonic processes responsible for an extensive period of intraoceanic subduction that produced juvenile ophiolite/island arc terranes, which were obducted onto continental margins during ocean closure. The Lajishankou ophiolite complex crops out along the northern margin of the South Qilian belt and was thrust over a Neoproterozoic-Ordovician passive margin sequence that was deposited upon the Proterozoic Central Qilian block. The mafic rocks in Lajishankou ophiolite complex are the most abundant slices and can be categorized into three distinct groups based on petrological, geochemical, and geochronological characteristics: massive island arc tholeiites, 509-Ma back-arc dolerite dykes, and 491-Ma pillow basaltic and dolerite slices that are of seamount origin in a back-arc basin. These results, together with spatial relationships, indicate that the Cambrian island arc rocks, ophiolite complex, and accretionary complex developed between 530 and 480 Ma as a single, intraoceanic arc-basin system as a result of south directed subduction of the Proto-Tethyan Ocean prior to Early Ordovician obduction of this system onto the Central Qilian block. Final continental amalgamation involved continental collision of the Central Qilian block with the Qaidam block during the Late Ordovician. This model solves the long-lasting discussion on the emplacement of the Lajishan ophiolite and contributes to an improved understanding of multiple accretionary and collisional processes in the Qilian Orogen.

Radiocarbon dating of a speleothem record of paleoclimate for Angkor, Cambodia

We report the chronological construction for the top portion of a speleothem, PC1, from southern Cambodia with the aim of reconstructing a continuous high-resolution climate record covering the fluorescence and decline of the medieval Khmer kingdom and its capital at Angkor (~9th–15th centuries AD). Earlier attempts to date PC1 by the standard U-Th method proved unsuccessful. We have therefore dated this speleothem using radiocarbon. Fifty carbonate samples along the growth axis of PC1 were collected for accelerator mass spectrometry (AMS) analysis. Chronological reconstruction for PC1 was achieved using two different approaches described by Hua et al. (2012a) and Lechleitner et al. (2016a). Excellent concordance between the two age-depth models indicates that the top ~47 mm of PC1 grew during the last millennium with a growth hiatus during ~1250–1650 AD, resulting from a large change in measured 14 C values at 34.4–35.2 mm depth. The timing of the growth hiatus covers the period of decades-long droughts during the 14th–16th centuries AD indicated in regional climate records.

Tectono-stratigraphy and structure of the northwestern Zagros collision zone across the Iraq-Iran border

Tectono-stratigraphic units within the Zagros Oroge n in northeast Iraq (foreland) and northwest Iran ( hinterland) are correlated to provide an integrated map along t he collision zone. Access to this part of Iraq duri ng the past four decades has been limited due to geopolitical s ituation. Structural cross-sections across the Zagr os Suture Zone in this area reveal the relationships between the tectonic terranes of various ages and different origins. Terranes of oceanic affinity have accreted onto the Arabian plate during collision-accretion events th at started in the Late Cretaceous. The collision resulted in clos ure of the Neotethys Ocean and the construction of a structurally complex suture zone. Jurassic-Cretaceo us deep ocean radiolarites of the Qulqula-Kermansha h terrane and ophiolitic melange serpentinites were s tructurally accreted against the Arabian passive ma rgin during an ophiolite arc-continent collision event in the L ate Cretaceous. The overthrust radiolarites and oph iolitic melange terranes initiated the development of the f oreland basin overlapping flysch (turbidites) and m olasse assemblages on the now active Arabian margin. Eocene-Oligocene volcano-sedimentary rocks of the WalashNaopurdan-Kamyaran terrane developed as an intra-oceanic island-arc within the intervening Neotethys O cean. They now structurally overlie the older ophiolite m elange and radiolarite terranes as a result of cont inued convergence onto the margin of the Arabian Plate. T hese younger thrust sheets and nappes have been tra nsported over the Miocene molasse unit of the Tertiary Red B eds in the flexural foreland basin and covered the Late Cretaceous accretionary complex terranes and forela nd basin assemblages. The Qulqula-Kermanshah terrane is exposed in a tectonic window in the northeastern pa rt of the mapped area indicating that the Late Cret aceous accreted terranes occur below the Walash-Naopurdan-Kamyaran thrust sheet. A Late Cretaceous ophiolitebearing terrane named the “Upper Allochthon” (i.e. Gemo-Qandil nappe, 97-118 Ma) was emplaced by younger thrust sheets over the Eocene-Oligocene Walash-Naopurdan-Kamyaran terrane by out-of-sequence thrusting. Mesozoic metamorphic rocks from the hinterland, including volcanic and intrusive rocks of the active I ranian continental margin (Sanandaj-Sirjan zone), were emplaced during continent-continent collision and occu r in the youngest nappes and klippes along the Zagros Suture Zone.

Inselbergs and monoliths: a comparative review of two iconic Australian landforms, Uluru (Ayers Rock) and Burringurrah (Mount Augustus)

The concept of ‘monolith’ is considered with reference to two imposing inselbergs in semi-arid Australia, Uluru (Ayers Rock) and Burringurrah (Mount Augustus). Individually each has been described as the ‘largest monolith in Australia’. To assess this comparison we outline the geology, morphology and geomorphic history of each. Both consist of sedimentary rock, but they differ in almost all other aspects including dimensions, lithological variations, geological evolution, tectonics, rock structures, operating processes and ages of both the landforms and the underlying rocks. The term ‘monolith’ has been used to describe such a wide range of features involving so many criteria that we prefer not to use ‘monolith’ as a geomorphic term. In relation to the inselbergs described here, the use of the term ‘monolith’ has led to needless and unhelpful comparisons between these two remarkable landforms.