<i>Shajia</i>, a new genus of polyconitid rudist from the Langshan Formation of the Lhasa Block, Tibet, and its palaeogeographical implications

A new polyconitid rudist Shajia tibetica gen. et sp. nov., of late Aptian to Albian age, is described from the Langshan Formation of Nyima County, northern Lhasa Block, Tibet. Though comparable in size and external morphology with Horiopleura haydeni Douvillé, which is a common endemic species in southwestern Asia, Shajia differs from the latter species in its possession of an inwardly inclined, instead of outwardly facing, posterior myophore in the right valve. In addition, a single specimen from Ladakh, which was previously assigned to Polyconites? sp., on account of a similar myophoral distinction from H. haydeni, is transferred to the new genus. Shajia is considered most likely to have been derived from one of a group of Horiopleura species that lived on the southern margin of the Mediterranean Tethys. The so-called ‘Yasin fauna’ represented by the late Aptian to Albian Horiopleura haydeni/ Auroradiolites gilgitensis rudist association, is considered to be restricted to southwestern Asia, including Afghanistan, Kohistan in northern Pakistan and Ladakh in northern India, though those two species in particular have not so far been recorded from the Lhasa Block of Tibet. Nevertheless, S. tibetica co-occurs with Auroradiolites biconvexus (Yang et al.), which probably evolved directly from A. gilgitensis (Douvillé), and the age of the latter association is in accordance with the generally accepted age of the Yasin fauna as late Aptian to Albian. Hence the S. tibetica and A. biconvexus association can be considered a regional variant of the Yasin fauna, which had evidently already dispersed to the Lhasa Block by the late Aptian. So the Langshan Formation can be considered palaeogeographically linked with other mid-Cretaceous shallow-marine carbonate deposits in adjacent southwestern Asian regions. These findings also provide new evidence that the age of the rudist assemblage of the Lhasa Block is late Aptian to Albian, although a slightly younger age cannot be excluded

Microencrusters from the Upper Jurassic–Lower Cretaceous İnaltı Formation (Central Pontides, Turkey): remarks on the development of reefal/peri-reefal facies

A detailed taxonomical study was carried out for the identification of encrusting micro- organisms. Among these microencrusters, Perturbatacrusta leini, Iberopora bodeuri, Calcistella jachenhausenensis, and Pseudorothpletzella schmidi have been taxonomically revealed for the first time in Turkey. Within the biostratigraphic frame of the I. nalti Formation consisting of Mesoendothyra izjumiana zone ( Kimmeridgian), Calcistella jachenhausenensis zone ( Lower Tithonian- Upper Tithonian) and Protopeneroplis ultragranulata zone ( Upper Tithonian- Berriasian), carbonate sedimentation occurred in five depositional environments comprising slope, fore- reef, reef, back- reef and lagoonal environments. The majority of the reefal deposits of the I. nalti carbonates can be classified as coral- microbial- microencruster boundstones, which frequently occur in association with back- reef and fore- reef deposits within the Kimmeridgian- Berriasian interval. A shallowing and a subsequent deepening of water depth in the Berriasian have been revealed by the examination of stacking patterns and vertical evolution of the microfacies. Based on the observed microfacies and general features of micro- encrusting organisms, it is concluded that I. nalti carbonates share many similarities with the reefal carbonate deposits of Intra- Tethyan domain in terms of microfacies types and microencruster content

Mirdita Zone ophiolites and associated sediments in Albania reveal Neotethys Ocean origin

The Mirdita Ophiolite Zone in Albania is associated with widespread melanges containing components of up to nappe-size. We dated matrix and components of the melange by radiolarians, conodonts, and other taxa. The components consist of radiolarites, pelagic limestones and shallow-water limestones, all of Triassic age, as well as ophiolites. Triassic radiolarite as a primary cover of ophiolite material proves Middle Triassic onset of Mirdita ocean-floor formation. The melange contains a turbiditic radiolarite-rich matrix (''radiolaritic flysch''), dated as Late Bajocian to Early Oxfordian. It formed as a synorogenic sediment during west-directed thrusting of ophiolite and sediment-cover nappes representing ocean floor and underplated fragments of the western continental margin. The tectonic structures formed during these orogenic events (''Younger Kimmeridian or Eohellenic Orogeny'') are sealed by Late Jurassic platform carbonates. The geological history conforms with that of the Inner Dinarides and adjoining areas; we therefore correlate the Mirdita-Pindos Ophiolite Zone with the Vardar Zone and explain its present position by far-distance west-directed thrusting

Oncoid growth and distribution controlled by sea-level fluctuations and climate (Late Oxfordian, Swiss Jura Mountains)

Abundant lagoonal oncoids occur in the Late Oxfordian Hauptmumienbank Member of the Swiss Jura Mountains. Four oncoid types are observed in the studied sections and classified according to the oncoid surface morphology, the structure and composition of the cortex, and the texture and fauna of the encasing sediment. Micrite-dominated oncoids (types 1 and 2) have a smooth surface. Type 1 has a rather homogeneous cortex and occurs in moderate-energy environments. Type 2 presents continuous or discontinuous micritic laminae. It is associated with a low-diversity fauna and occurs in high-energy facies. Bacinella and Lithocodium oncoids (types 3 and 4) display a lobate surface. They are dominated by microencrusters (Bacinella irregularis and Lithocodium aggregatum) and are found in low-energy facies. The stratigraphic and spatial distribution of these oncoid types shows a correlation with the sequence-stratigraphic evolution of the studied interval, and thus with relative sea-level fluctuations. It can be shown that these sea-level fluctuations were controlled by orbital cycles with 100- and 20-kyr periodicities. At the scale of 100- and 20-kyr sequences, types 1 and 2 oncoids are preferentially found around sequence boundaries and in transgressive deposits, while types 3 and 4 oncoids are preferentially found around maximum floodings and in highstand deposits. This implies that changes of water energy and water depth were direct controlling factors. Discrepancies in oncoid distribution point to additional controlling factors. Platform morphology defines the distribution and type of the lagoon where the oncoids flourished. A low accumulation rate is required for oncoid growth. Additionally, humidity changes in the hinterland act on the terrigenous influx, which modifies water transparency and trophic level and thus plays a role in the biotic composition and diversity in the oncoid cortex