Emese M. Bordy

Advanced Early Jurassic Termite (Insecta: Isoptera) Nests: Evidence From the Clarens Formation in the Tuli Basin, Southern Africa

Abstract Sandstone pillars in the Lower Jurassic eolian strata of the Clarens Formation are concentrated in clusters, with up to four pillars within 25 m2 in two localities in the Tuli Basin of northern South Africa and southern Zimbabwe. The pillars are generally vertical, have a preserved height of up to 3.3 m, and are elliptical in plan view. Pillars are grouped into two styles of architecture: those with oriented elliptical shapes and side buttresses, and those less well oriented with a smooth outer wall, internal open spaces, and vertical shafts cutting the pillar. The long axes of the elliptical pillars are generally oriented to the north. Northwards-oriented side buttresses also are associated with some of the pillars. The internal architecture of the pillars is characterized by intense bioturbation with two different burrowing styles. Type 1 burrows are composed of a network of randomly oriented, anastomosing sandstone-filled tubes, 0.3 to 0.8 cm in diameter. Type 2 burrows are rare, north-south oriented, and have a smaller diameter. Other associated features are back-filled tubes, open, vertical shafts, and open spaces between the interior and exterior of the pillars. The pillars are interpreted as fossilized termite nests. Type 1 burrows are interpreted as termite passageways within the nest. Type 2 burrows may be related to invading ants. Back-filled burrows may be a result of either beetle predation on resident termites or backfilling by termites themselves. The strong north-south orientations are comparable with modern-day nest architecture of magnetic termites in northern Australia, where nest-orientation is related to cooling. The orientations and features reported here are interpreted to be modified for the high latitudes proposed for the Lower Jurassic Clarens desert. Complex nest architecture preserved in the Clarens Formation suggests that advanced eusocial behavior and ability to construct large nests had appeared in African termites by the Early Jurassic.

Sedimentology and palaeontology of upper Karoo aeolian strata (Early Jurassic) in the Tuli Basin, South Africa

The Karoo Supergroup in the Tuli Basin (South Africa) consists of a sedimentary sequence composed of four stratigraphic units, namely the Basal, Middle and Upper units, and Clarens Formation. The units were deposited in continental settings from approximately Late Carboniferous to Middle Jurassic. This paper focuses on the Clarens Formation, which was examined in terms of sedimentary facies and palaeo-environments based on evidence provided by primary sedimentary structures, palaeo-flow measurements and palaeontological findings. Two main facies associations have been identified: (i) massive and large-scale planar crossbedded sandstones of aeolian origin; and (ii) horizontally and cross-stratified sandstones of fluvial origin. Most of the sandstone lithofacies of the Clarens Formation were generated as transverse aeolian dunes produced by northwesterly winds in a relatively wet erg milieu. Direct evidence of aquatic subenvironments comes from local small ephemeral stream deposits, whereas palaeontological data provide indirect evidence. Fossils of the Clarens Formation include petrified logs of Agathoxylon sp. wood type and several trace fossils which were produced by insects and vertebrates. The upper part of the Clarens Formation lacks both direct and indirect evidence of aquatic conditions, and this suggests aridification that led to the dominance of dry sand sea conditions. 2002 Elsevier Science Ltd. All rights reserved.

Sedimentology of the upper Karoo fluvial strata in the Tuli Basin, South Africa

Abstract The sedimentary rocks of the Karoo Supergroup in the Tuli Basin (South Africa) may be grouped in four stratigraphic units: the basal, middle and upper units, and the Clarens Formation. This paper presents the findings of the sedimentological investigation of the fluvial terrigenous clastic and chemical deposits of the upper unit. Evidence provided by primary sedimentary structures, palaeontological record, borehole data, palaeo-flow measurements and stratigraphic relations resulted in the palaeo-environmental reconstruction of the upper unit. The dominant facies assemblages are represented by sandstones and finer-grained sediments, which both can be interbedded with subordinate intraformational coarser facies. The facies assemblages of the upper unit are interpreted as deposits of a low-sinuosity, ephemeral stream system with calcretes and silcretes in the dinosaur-inhabited overbank area. During the deposition of the upper unit, the climate was semi-arid with sparse precipitation resulting in high-magnitude, low-frequency devastating flash floods. The current indicators of the palaeo-drainage system suggest flow direction from northwest to southeast, in a dominantly extensional tectonic setting. Based on sedimentologic and biostratigraphic evidence, the upper unit of the Tuli Basin correlates to the Elliot Formation in the main Karoo Basin to the south.

Sedimentology of the lower Karoo Supergroup fluvial strata in the Tuli Basin, South Africa

Abstract The Karoo Supergroup in the Tuli Basin (South Africa) consists of a sedimentary sequence (∼450–500 m) composed of four stratigraphic units, namely the informal Basal, Middle and Upper Units, and the formal Clarens Formation. The units were deposited in continental settings from approximately Late Carboniferous to Middle Jurassic. This paper focuses on the ∼60-m-thick Basal Unit, which was examined in terms of sedimentary facies and palaeo-environments based on evidence provided by primary sedimentary structures, palaeo-flow measurements, palaeontological findings, borehole data (59 core descriptions) and stratigraphic relations. Three main facies associations have been identified: (i) gravelstone (breccias and conglomerate-breccias), (ii) sandstone and (iii) fine-grained sedimentary rocks. The coarser facies are interpreted as colluvial fan deposits, possibly associated with glaciogenic diamictites. The sandstone facies association is mainly attributed to channel fills of low sinuosity, braided fluvial systems. The coal-bearing finer-grained facies are interpreted as overbank and thaw-lake deposits, and represent the lower energy correlatives of the sandy channel fills. Sediment aggradation in this fluvio-lacustrine system took place under cold climatic conditions, with floating lake ice likely associated with lacustrine environments. Palaeo-current indicators suggest that the highly weathered, quartz-vein-rich metamorphic rock source of the Basal Unit was situated east–northeast of the study area. The accumulation of the Basal Unit took place within the back-bulge depozone of the Karoo foreland system. In addition to flexural subsidence, the amount of accommodation in this tectonic setting was also possibly modified by extensional tectonism in the later stages of the basin development. Based on sedimentological and biostratigraphic evidence, the coal-bearing fine-grained facies association displays strong similarities with the Vryheid Formation of the main Karoo Basin to the south. The lowermost non-fossiliferous breccias have been correlated before with the Dwyka Group in the main Karoo, and hence the Basal Unit may be regarded as the distal equivalent of the Dwyka and Ecca groups to the south.

The contact of the Molteno and Elliot formations through the main Karoo Basin, South Africa: a second-order sequence boundary

The Late Triassic to Early Jurassic Molteno, Elliot and Clarens formations of the uppermost part of the Karoo Supergroup in the main Karoo Basin of South Africa form a distinct tectono-sedimentary sequence. A major problem with the modeling of this part of the Karoo basinal fill is that the nature of the Molteno-Elliot contact is poorly understood. Previously the contact has been defined on a mix of lithological and palaeontological criteria, and has been considered to be gradational or transitional in nature, with the Elliot considered the distal equivalent of the upper Molteno Formation. Recent field investigations demonstrate that the boundary can be defined on lithologic changes, including the gross and internal geometries of the sandstone units and contained lithofacies associations, the presence/absence of coal seams and paleosols, and on palaeocurrent patterns, sandstone composition and grain-size variations. This boundary represents a regional unconformity throughout the basin and the recognition of this cryptic second order sequence boundary invalidates previous interpretations of an interfingering stratigraphic relationship between the two formations. Stacking patterns in the upper Karoo Supergroup, and the tectonic framework of their development, suggest that the southern margin of the Kaapvaal Craton acted as a regional control on sequence development during Late Triassic - Early Jurassic times.

Sedimentology of the Beaufort-Molteno Karoo fluvial strata in the Tuli Basin, South Africa

The sedimentary rocks of the Karoo Supergroup in the Tuli Basin (South Africa) may be grouped into four stratigraphic units: the Basal, Middle and Upper units, and the Clarens Formation. This paper presents the findings of the sedimentological investigation of the fluvial clastic deposits of the Middle Unit. The lack of bio- and chronostratigraphic control hampers an unequivocal correlation of the Middle Unit with the formations of the main Karoo Basin. Existing constraints place the Middle Unit in a stratigraphic position older than the Elliot Formation and younger than the Ecca Group. Between these limits, the Middle Unit may correlate with either the Beaufort Group or the Molteno Formation of the main Karoo Basin (Table 1[⇓][1]). The Middle Unit may be subdivided into three parts, based on lithological differences. The lower part includes rudites and arenites (lithofacies Gh, Sp, Sh, and Sm); the middle part is dominated by siltstones and very fine sandstones (lithofacies Fl); and the upper part consists of mudstones (lithofacies Fsm). This succession accumulated in a perennial braided fluvial system, with well developed inter-channel flood plains. The observed lithofacies and architectural elements are partly coeval, with the overall upward-fining profile related to gradual denudation and peneplanation. Petrographic analyses indicate multiple source areas, as well as reworking of the underlying Basal Unit. The accumulation of the Middle Unit in the Tuli Basin corresponds to a distinct stage of tectonic development in the region, when the topographic gradient was consistently dipping from south-east to north-west. In contrast with this, the Basal and Upper units were accumulated on topographic slopes dipping from east-northeast to west-southwest, and from north-northwest to south-southeast respectively. [1]: #T1

A History of Ideas in Ichnology

Abstract Although the concept of ichnology as a single coherent field arose in the nineteenth century, the endeavor of understanding traces is old as civilization and involved cultural areas worldwide. In fact, fossil and recent traces were recognized since prehistoric times and their study emerged from the European Renaissance. This progression, from empirical knowledge toward the modern concepts of ichnology, formed a major research field which developed on a global scale. This report outlines the history of ichnology by (1) exploring the individual cultural areas, (2) tracing a comprehensive bibliographic database, and (3) analyzing the evolution of ichnology semiquantitatively and in a graphical form (“tree of ichnology”). The results form a review and synthesis of the history of ichnology, establishing the individual and integrated importance of the different ichnological schools in the world.