Trypanites and associated bivalve borings in an Upper Albian hardground from the Eastern Saharan Atlas (Algeria)

Abundant Trypanites isp. associated with Gastrochaenolites isp. and Petroxestes pera are evidenced in the first found hardground of the late Albian marine transgressive series, overlying the Continental Intercalaire in the Ouled Nail Range, eastern Saharan Atlas. This hardground is encrusted by oyster shells belonging to Ostrea falco Coquand. The studied hardground developed in warm environment and displays a lateral extension of at least 6 km. It is interpreted as an erosional transgressive surface. The ichnogenus Petroxestes is reported for the first time from Africa. This ichnoassemblage is attributed to the Trypanites ichnofacies.     

Macrobioerosion and Microbioerosion in Marine Molluscan Shells from Holocene and Modern Beaches (39°−40°S, South of Buenos Aires Province, Argentina)

The marine sediments of the area of Verde Peninsula-Jabali Island(39°28′S/62°19′W-40°28′S/62°11′W) Holocene in age(3-2 ky),and modern beaches contain a significant amount of bioeroded mollusc shells.Fifteen sites were analyzed,in which 20.11%of the mollusc shells(2168 valves) presented bioerosion traces,in 54 species(30 bivalves and 24 gastropods).Fourteen ichnogenera were reported:Entobia,Maeandropoiydora,Iramena,Caulostrepsis,Pennatichnus,Pinaceocladichnus,Trypanites,and Gastrochaenolites(Domichnia),Gnathichnus and Radulichnus(Pascichnia),Finichnus and Centrichnus(Fixichnia),Oichnus(Praedicnia)(macrobioerosion),y Semidendrina(microbioerosion),the latter is first reported in mollusc shells in Argentina.Eleven ichnospecies were identified Finichnus peristroma,Maeandropoiydora sulcans,Gnathichnus pentax,Pinaceocladichnus onubensis,Caulostrepsis taeniola,Centrichnus eccentricus,Radulichnus inopinatus,Oichnus simplex,Oichnus paraboloides,Oichnus gradatus,and Gastrochaenolites torpedo(lithic remains).The dominant ichnogenera in the Holocene deposits are Iramena,Entobia and Oichnus.The same ichnogenera are constant with different abundance in the modern beaches,and increasing representation of Pinaceocladichnus and Pennatichnus.The dominant ichnofacies in the Holocene deposits is Trypanites,revealing a benthonic marine community composed of cheilostome bryzoans,clionaid sponges,predator gastropods,regular echinoids,polychaete annelids,bivalves,thallophytas and fungi.Generally,the area was described as a sublittoral,low-energy,stable environment with high rate of oxygenation,and sandy bottoms,with rocky bottoms at Villalonga locality.     

Taphonomic differentiation of Acropora palmata facies in cores from Campeche Bank Reefs, Gulf of México

A common assumption in the geological analysis of modern reefs is that coral community zonation seen on the surface should also be found in cores from the reef interior. Such assumptions not only underestimate the impact of tropical storms on reef facies development, but have been difficult to test because of restrictions imposed by narrow‐diameter cores and poor recovery. That assumption is tested here using large‐diameter cores recovered from a range of common zones across three Campeche Bank reefs. It is found that cores from the reef‐front, crest, flat and rubble‐cay zones are similar in texture and coral composition, making it impossible to recognize coral assemblages that reflect the surface zonation. Taphonomic signatures imparted by variations in encrustation, bioerosion and cementation, however, produce distinct facies and delineate a clear depth zonation. Cores from the reef‐front zone (2–10 m depth) are characterized by sections of Acropora palmata cobble gravel interspersed with sections of in‐place (but truncated) A. palmata stumps. Upper surfaces of truncated colonies are intensely bioeroded by traces of Entobia isp. and Gastrochaenolites isp. and encrusted by mm‐thick crustose corallines before colony regeneration and, therefore, indicate punctuated growth resulting from a hurricane‐induced cycle of destruction and regeneration. Cores from the reef crest/flat (0–2 m depth) are also characterized by sections of hurricane‐derived A. palmata cobble‐gravels as well as in‐place A. palmata colonies. In contrast to the reef front, however, these cobble gravels are encrusted by cm‐thick crusts of intergrown coralline algae, low‐relief Homotrema and vermetids, bored by traces of Entobia isp. and Trypanites isp. and coated by a dense, peloidal, micrite cement. Cores from the inter‐ to supratidal rubble‐cay zone (+0–5 m) are only composed of A. palmata cobble gravels and, although clasts show evidence of subtidal encrustation and bioerosion, these always represent processes that occurred before deposition on the cay. Instead, these gravels are distinguished on the basis of their limited bioerosion and marine cements, which exhibit fabrics formed in the intertidal zone. These results confirm that hurricanes have a major influence on facies development in Campeche Bank reefs. Instead of reflecting the surface coral zonation, each facies records a distinctive, depth‐related set of taphonomic processes, which reflect colonization, alteration and stabilization following the production of new substrates by hurricanes.     

Gastrochaenolites ornatus Kelly and Bromley and other trace fossils on a Middle Miocene omission surface from the Aures Massif,Algeria

Trace fossils provide detailed palaeoenvironmental and palaeoecological information of both ancient and modern sedimentary systems. During middle Miocene times the Aures Massif located in the northeastern part of Algeria, was affected by, at least, one marine transgression. The latter led to the installation of a carbonate platform, which is placed, for the first time, in a Mediterranean context. In the Rhassira basin, the Middle Miocene marine succession is characterised by carbonate platform deposits dominated by rhodolith beds, typical of those known throughout the Mediterranean area. This succession can be divided into many units separated by discontinuities interpreted here as omission surfaces. The Djebel Arhane section shows two omission surfaces characterised by a pre-omission suite (firmground) represented by Balanoglossites burrows for the first surface and Gastrochaenolites ornatus burrows/borings for the second one, and an omission suite (hardground) as evidenced by the bioerosive structures Trypanites and Caulostrepsis, in both surfaces, respectively. Gastrochaenolites ornatus traces were formed and preserved in firm, compact, semi-lithified and fine-grained substrates (firm- to hardground), indicating the Glossifungites ichnofacies. They show bioglyphs which have been formed during contraction of the posterior adductor muscles. These suggest that their tracemakers were represented by suspension-feeding bivalves, most probably Pholadidae or Mytilidae, which rotated during penetration. The fill of these traces is composed of marine deposits related to a transgressive lag. The omission suite is divided into two ichnocoenoses: (i) pre-lithification burrows/borings, and (ii) post-lithification borings. This is the first report of the ichnotaxon G. ornatus from Algeria.     

Integrated ichnological and sedimentological studies of the Parahio Formation (Cambrian) of the Zanskar region (Zanskar-Spiti Basin), Northwest Himalaya

Lower-Middle Cambrian (Lungwangmiaoan-Hsuchuangian stage) Parahio Formation (Kunzam La Formation) exposed at Purni Village, Niri-Tsarap Chu Valley of Zanskar region of Tethyan Himalaya has yielded a high diversity and abundant ichnofossils with myriapod trackways. It includes Cruziana isp., Phycodes palmatum, Diplocraterion isp., Diplichnites isp., Dimorphichnus isp., Tapherhelminthopsis cf. circularis, Teichichnus isp., Monomorphicnus isp., Lockeia isp., Skolithos isp., Planolites isp., Palaeophycus isp., Isopodichnus isp., and arthropod appendage marks. Integration of ichnological and sedimentological studies for measured part of the Parahio Formation (Cambrian) reveals that alternating energy conditions due to recurring storm events were superimposed on low energy fair-weather sediments. The post-depositional Arenicolites ichnofacies, preserved within the high-energy storm beds of shoreface deposits, commonly overlies the fair-weather assemblage of pre-depositional Cruziana ichnofacies of relatively more offshore deposits, which contains more diverse and varied behavioral signatures of various deposit feeders. The traces of the Cruziana ichnofacies are abruptly replaced by traces of Arenicolites ichnofacies and show reiteration throughout the measured part of the Parahio Formation. The ichnofabric indices in these deposits range from ii3–ii5. No discrete sets of tiers are observed; perhaps there were two coeval communities. Ichnologically, an idealized wave-dominated progradational cycle in the Parahio Formation is characterized, from base to top, by a Cruziana ichnofacies (lower-upper offshore to offshore transition) and storm related Arenicolites ichnofacies (shoreface). Each progradational cycle reflects a progressive increase in sand content, degree of oxygenation, hydrodynamic energy and dearth of food. These environmental factors controlled the vertical distribution of trace fossils in Parahio Formation. The occurrence of Cruziana ichnoassociation much below the Middle Cambrian trilobite horizon in the Parahio Formation restricts the age of this part of the formation to the pre-Middle Cambrian, probably series 2 of Cambrian system.     

Bioerosion in the middle Eocene larger foraminifer Nummulites in the Fayum depression,Egypt

The present paper focuses for the first time on the trace fossils present in carbonate tests of the famous Egyptian middle Eocene larger foraminifer Nummulites gizehensis group. Bioerosion is represented by a unique diversified assemblage of seven ichnospecies belonging to four ichnogenera. Diagnostic drilling holes of the ichnogenus Oichnus are represented by the three ichnospecies O. simplex, O. paraboloides and O. asperus. Rare spiral galleries of Trypanites helicus and sinuous tunnels of Maeandropolydora sulcans were identified. Simple U-shaped borings of Caulostrepsis taeniola and Caulostrepsis isp. were also recognized within the studied nummulites. The reported drilling holes are attributed essentially to the predation of gastropods, whereas the other recognized galleries are assigned mainly to boring activities of the polychaete worms. Well-preserved tests with rare bioerosion and encrustation indicate deposition under a high rate of sedimentation and no prolonged transportation. Conversely, taphonomic characteristics of the bioeroded and encrusted nummulites can be used as good palaeoecological indictors of a deposition under low to fair rate of sedimentation. Coexistence of non-bioeroded and bioeroded/encrusted tests, common thick-bedded nummulite wackestone and packestone, predominated larger and flat Nummulites spp., and non-preferred imbrications are taken altogether with the reported ichnological assemblage to suggest that the nummulites were accumulated in situ and/or under weak influence of physical processes (storm and waves) in a shallow-marine environment, possibly middle to inner carbonate ramps.     

Lithofacies,palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria

Integrated sedimentologic, macrofossil, trace fossil, and palynofacies data from Paleocene-Middle Eocene outcrops document a comprehensive sequence stratigraphy in the Anambra Basin/Afikpo Syncline complex of southeastern Nigeria. Four lithofacies associations occur: (1) lithofacies association I is characterized by fluvial channel and/or tidally influenced fluvial channel sediments; (2) lithofacies association II (Glossifungites and Skolithos ichnofacies) is estuarine and/or proximal lagoonal in origin; (3) lithofacies association III (Skolithos and Cruziana ichnofacies) is from the distal lagoon to shallow shelf; and (4) shoreface and foreshore sediments (Skolithos ichnofacies) comprise lithofacies association IV. Five depositional sequences, one in the Upper Nsukka Formation (Paleocene), two in the Imo Formation (Paleocene), and one each in the Ameki Group and Ogwashi-Asaba Formation (Eocene), are identified. Each sequence is bounded by a type-1 sequence boundary, and contains a basal fluvio-marine portion representing the transgressive systems tract, which is succeeded by shoreface and foreshore deposits of the highstand systems tract. In the study area, the outcropping Ogwashi-Asaba Formation is composed of non-marine/coastal aggradational deposits representing the early transgressive systems tract. The occurrence of the estuarine cycles in the Palaeogene succession is interpreted as evidence of significant relative sea level fluctuations, and the presence of type-1 sequence boundaries may well be the stratigraphic signature of major drops in relative sea level during the Paleocene and Eocene. Sequence architecture appears to have been tectono-eustatically controlled.     

Sea level changes in the upper Aptian-lower/middle(?) Turonian sequence of Cauvery Basin,India – An ichnological perspective

Cauvery Basin, a pericratonic rift basin along the Eastern Continental Margin of India, evolved during the breakup of the Eastern Gondwanaland. It exposes both syn-rift and later post-rift passive margin deposits ranging from Barremian to Miocene. The Karai Formation, upper Aptian-lower/middle (?) Turonian represents the oldest passive margin in the Cauvery Basin. It is bounded at both contacts by major sequence boundaries viz. the break-up unconformity and the Turonian tilt event. The present communication deals with the ichnology of the Karai Formation and its integration with sedimentary facies and biostratigraphy to interpret the sea level changes during deposition. A traverse between the villages Karai and Kulakkalnattam was studied in detail for this purpose. Based on the lithological position, characters and internal grain size trends, the Karai Formation is sub-divided into four informal lithologic units; the lower three units, constitute a lithostratigraphic unit known in literature as the Gypsiferous Clay Member, while the uppermost, corresponds to the Sandy Clay Member. At the base, clays of the Karai Formation unconformably onlap onto the Precambrian basement or the fluvial syn-rift deposits across the break-up unconformity. Upper Aptian to middle Cenomanian, units I and II showing the distal Cruziana ichnofacies, deepening of the basin and a retrogradational stacking pattern represent a transgressive system tract (TST). This long phase of transgression is attributed to continuous accommodation created by the post-breakup thermal subsidence. The upper part of unit II (middle Cenomanian) shows condensation, with its top representing the maximum flooding surface (MFS). Upper Cenomanian to lower/middle (?) Turonian, units III and IV characterised by a shift from the distal Cruziana to the Skolithos ichnofacies, an initial aggradational and later deltaic, progradational stacking pattern resulting from a fall in the relative sea level and filling up of accommodation space represent the highstand system tract (HST). A further fall in the relative sea level led to the exposure, incision and erosion of the Karai Formation over which the younger transgressive sequence of the Trichinopoly Group was deposited with an angular unconformity.     

Pliocene trace fossils from oyster substrates in the Nijar Basin,Betic Cordillera,southern Spain

The Almería-Níjar Basin is a Neogene, intermontane depression marginal to the Mediterranean in southern Spain in the vicinity of El Argamasón, Andalucia. The Pliocene Cuevas Formation rests unconformably on the Upper Messinian rock succession in the Carboneras Fault Zone. The Cuevas Formation is a coarse-grained, bioclastic-rich, calcarenite to calcirudite shoreface deposit. Oysters, namely Saccostrea cucullata (Born), are locally common and preserve a moderate diversity of borings: Caulostrepsis taeniola Clarke; Entobia isp.; Gastrochaenolites isp. aff. G. lapidicus Kelly and Bromley; Maeandropolydora isp. cf. M. sulcans Voigt; Oichnus paraboloides Bromley; and Talpina isp. aff. T. hirsuta Voigt. All represent domiciles except for the predatory O. paraboloides trace. This suite of ichnotaxa is assigned to the Entobia ichnofacies sensu Bromley and Asgaard; they are comparable, particularly, with the Boulder Assemblage of the Pliocene of Rhodes, Greece. Physical disturbance is an important parameter in favouring this pattern of infestation, whether the bored clasts are boulders or oyster valves.     

An insight into the Eocene tide-dominated estuarine system: implications for palaeoenvironmental and sequence stratigraphic interpretations

This article describes a complete sedimentary succession of an ancient macrotidal tide-dominated estuarine system based on the detailed outcrop study. The Eocene siliciclastic sedimentary facies of Ameki Group in the south-eastern Nigeria provides a record of the sedimentary response to an initial regression, followed by marine incursion (transgression) into the Niger Delta Basin. These sedimentary successions are analogues to the subsurface petrolific Niger Delta lithostratigraphic units. Seven facies associations (FA 1 to FA 7) are documented in the study area and the sediments are interpreted as fluvial channel, tidally influenced fluvial channel, tidal channel, tidal flats, supratidal, tidal sand bar and estuarine embayment (open estuarine) deposits. The occurrence of low diversity ichnofaunal assemblages and/or localised high-density monospecific ichnofossil assemblages indicates brackish-water condition typical of estuarine settings. The suites of assemblages include Scoyenia, Skolithos, Cruziana, mixed Skolithos-Cruziana, Glossifungites, Psilonichnus and Teredolites ichnofacies. A complete depositional sequence is encountered in the Eocene Ameki Group which consists of the lowstand, transgressive, highstand and falling stage systems tracts. This depositional succession was most probably controlled by relative sea level changes, sediment supply, accommodation and regional tectonics which affected the development of Niger Delta Basin.     

塔里木盆地下志留统塔塔埃尔塔格组痕迹化石与海进期沉积及海进体系域

在层序地层学研究中,海进（transgrssion）常被认为是快速形成的,序列简单,并以少量沉积为特征。对塔里木盆地下志留统塔塔埃尔塔格组痕迹化石及沉积特征研究表明,海进期沉积及海进体系域比人们想象的要复杂,由三类沉积组成:（1）与海进侵蚀有关,包括海进滞留沉积,发育固底控制Glossifungites痕迹相;（2）与海进初期的海面缓慢上升或总体海进过程中的静止期有关,包括前滨和临滨砂泥岩,发育Skolithos痕迹相和近端Gruziana痕迹相;（3）与海面快速上升有关,包括滨外泥岩,发育远端Gruziana痕迹相。     

Preservation of a heavily bored belemnite rostrum from the upper Maastrichtian of north-east Belgium

The robust calcite rostra (or guards) of belemnites were attractive substrates for some boring organisms in the Mesozoic. The rostra of belemnitellid coleoids are common at certain levels within the Gulpen and Maastricht formations of the extended type area of the Maastrichtian Stage (Upper Cretaceous) in the south-east Netherlands and north-east Belgium. A range of episkeletozoans have been reported from these substrates hitherto. A new specimen preserved as a natural mould in flint from the province of Liège, north-east Belgium, is distinctive, preserving a dense three-dimensional infestation of long, slender, unbranched and unsculptured borings of constant diameter, Trypanites? isp. These may be the spoor of polychaetes. Variations in diameter between borings suggests that the traces in this specimen may represent four separate infestations.     

The Faraoni event (latest Hauterivian) in ichnological record: The Río Argos section of southern Spain

The Early Cretaceous (latest Hauterivian) Faraoni Oceanic Anoxic Event (F-OAE) in the Río Argos section (Caravaca region, southern Spain), the candidate for the Global Boundary Stratotype Section and Point (GSSP) of the Hauterivian–Barremian transition, has been studied. Its ichnological bed-by-bed analysis allows for interpretation of oxygenation changes through the Faraoni Level interval and improvement upon previous characterization of oxygen conditions prior, during and after the F-OAE. The trace fossil assemblage belongs to the Zoophycos ichnofacies and it includes Chondrites intricatus, Chondrites targionii, Halimedides isp., Palaeophycus isp., ?Patagonichnus isp., Planolites isp., Rhizocorallium isp., Taenidium isp., Thalassinoides isp., Trichichnus linearis, Zavitokichnus fusiformis, and Zoophycos isp. Their diversity in particular beds fluctuates. Beds with four to six ichnotaxa reflect a multi-tiered macrobenthic trace maker assemblage living in good oxic and trophic conditions. In one bed below and one bed above the Faraoni Level (both marls without primary lamination), there are only two or three, mostly opportunistic ichnotaxa (Trichichnus, Chondrites, Planolites). They record dysoxic conditions. At the base of the Faraoni Level, one thicker and two thinner beds of marly mudstones (21.2 and 3.5 cm thick, respectively) are characterized by primary lamination. At the top and in the basal part of the thicker bed and in the thinner beds some trace fossils are present. These beds were deposited under anoxic conditions and later colonized by trace makers either from overlying beds deposited under oxic conditions or from the level of a greenish lamina in the lower part of the thicker bed, recording short episodes of dysoxic conditions. The thinner anoxic beds are separated by marls deposited under dysoxic conditions.     

Paleoenvironmental reconstruction of the coastal Monte Léon and Santa Cruz formations (Early Miocene) at Rincón del Buque,Southern Patagonia: A revisited locality

Sedimentological, ichnological and paleontological analyses of the Early Miocene uppermost Monte León Formation and the lower part of the Santa Cruz Formation were carried out in Rincón del Buque (RDB), a fossiliferous locality north of Río Coyle in Santa Cruz Province, Patagonia, Argentina. This locality is of special importance because it contains the basal contact between the Monte Léon (MLF) and the Santa Cruz (SCF) formations and because it preserves a rich fossil assemblage of marine invertebrates and marine trace fossils, and terrestrial vertebrates and plants, which has not been extensively studied. A ∼90 m-thick section of the MLF and the SCF that crops out at RDB was selected for this study. Eleven facies associations (FA) are described, which are, from base to top: subtidal–intertidal deposits with Crassotrea orbignyi and bioturbation of the Skolithos-Cruziana ichnofacies (FA1); tidal creek deposits with terrestrial fossil mammals and Ophiomorpha isp. burrows (FA2); tidal flat deposits with Glossifungites ichnofacies (FA3); deposits of tidal channels (FA4) and tidal sand flats (FA5) both with and impoverish Skolithos ichnofacies associated; marsh deposits (FA6); tidal point bar deposits recording a depauperate mixture of both the Skolithos and Cruziana ichnofacies (FA7); fluvial channel deposits (FA8); fluvial point bar deposits (FA9); floodplain deposits (FA10); and pyroclastic and volcaniclastic deposits of the floodplain where terrestrial fossil mammal remains occur (FA11).The transition of the MLF–SCF at RDB reflects a changing depositional environment from the outer part of an estuary (FA1) through the central (FA2–6) to inner part of a tide-dominated estuary (FA7). Finally a fluvial system occurs with single channels of relatively low energy and low sinuosity enclosed by a broad, low-energy floodplain dominated by partially edaphized ash-fall, sheet-flood, and overbank deposits (FA8–11). Pyroclastic and volcaniclastic materials throughout the succession must have been deposited as ash-fall distal facies in a fluvial setting and also were carried by fluvial streams and redeposited in both estuarine and fluvial settings. These materials preserve most of the analyzed terrestrial fossil mammals that characterize the Santacrucian age of the RDB's succession. Episodic sedimentation under volcanic influence, high sedimentation rates and a relatively warm and seasonal climate are inferred for the MLF and SCF section.Lateral continuity of the marker horizons at RDB serve for correlation with other coastal localities such as the lower part of the coastal SCF south of Río Coyle (∼17.6–17.4 Ma) belonging to the Estancia La Costa Member of the SCF.     

Bioerosion and encrustation rates in recent mollusk death assemblages on a supratidal siliciclastic setting,Playa Norte,Veracruz State,Mexico

This study presents both qualitative and quantitative data regarding marine mollusk (gastropods and bivalves) shell bioerosion and encrustation based on death assemblages obtained from a recent supratidal environment in Playa Norte, Veracruz State. The objectives of this study were to assess the nature of bioerosion and encrustation processes and to investigate the role of these taphonomic features contributing to the deterioration of natural shell accumulations within a tropical siliciclastic tidal environment. The assemblage comprises 31 species: 13 gastropods and 18 bivalves. The bioerosion and encrustation degrees were low to moderate for both types. The most abundant traces were predatory gastropod structures (Oichnus paraboloides and O. simplex), whereas sponge borings (Entobia isp.), polychaete dwellings (Caulostrepsis taeniola), and echinoid raspings (Gnatichnus isp.) were less frequent. The encrusting organisms include polychaete serpulids, bryozoans, and rare foraminifers (Homotrema rubrum). Because of the low bioerosion and encrustation degrees occurring in this area, accumulation is expected to predominate over biotic destruction. As deposition conditions (richly fossiliferous carbonate sandstone beds) were similar to those prevailing in the Tuxpan Formation during the Miocene (Langhian), it is suggested that this study provides an equivalent reference to interpret mollusk fossil assemblages located in this site.     

Ichnofauna from the Harbans Bed of the Badhaura Formation (Sterlitmakian), Rajasthan,India

In the first ever systematic study of trace fossils from the Badhaura Formation, the authors described a nesting burrow, which they ascribed to a stomatopod. The purpose of this paper is two-fold: primarily, to document ichnofauna from (post-glacial marine late Palaeozoic rocks of peninsular India) the Badhaura Formation (Sterlitmakian) representing marine rocks deposited following the Late Palaeozoic glaciation and secondly to contribute to the data on post-glacial ichnofauna from constituent continents of the Gondwanaland. Trace fossils described here are from the Harbans Bed, the topmost lithounit of the Badhaura Formation. The ichnofauna includes Arenicolites tenuis, Beaconites isp., Curvolithus isp., Cylindrichnus concentricus, Didymaulichnus lyelli, Ophiomorpha isp., Palaeophycus tubularis, Planolites beverleyensis, P. montanus, Rosselia chonoides, R. socialis, Skolithos linearis, Taenidium cameronensis, Thalassinoides paradoxicus, Thalassinoides isp. and a flask-shaped brood chamber assigned to a stomatopod crustacean. This mixed assemblage is assigned to distal Skolithos ichnofacies and is suggestive of a period of relatively quiet, shallow water conditions of deposition. The ichnofauna, when viewed in context of peri-gondwanic ichnofaunas, mainly consisting of simple tracks and trails, from late Palaeozoic post-glacial deposits of other Gondwanan continents, is interesting due to dominance of domichnia. Profusion of brood chambers along with Thalassinoides in the Badhaura Formation validates the concept of pre-Mesozoic Thalassinoides being non-decapod in origin and suggestive of adaptive convergence.     

Cambrian trace fossils of the Cruziana ichnofacies from the Bikaner-Nagaur Basin,north western Indian Craton

The Marwar Supergroup of the Bikaner-Nagaur Basin is composed of sediments deposited from the late Neoproterozoic (Ediacaran) to Upper Cambrian. The Nagaur Sandstone Formation of the Nagaur Group (uppermost division of the Marwar Supergroup) preserves trace fossils significant for establishing Early Cambrian biostratigraphic zones and depositional facies. Fifteen ichnospecies (and eight ichnogenera) identified in the Nagaur Sandstone Formation include “Treptichnus” pedum, Cruziana cf. tenella, Cruziana isp., Diplichnites ispp. A, B, and C, Gyrophyllites isp., Lockeia isp., Merostomichnites isp., Monomorphichnus gregarius isp. nov., Monomorphichnus isp., Planolites isp., Psammichnites isp., Rusophycus bikanerus isp. nov., Rusophycus cf. carbonarius, Rusophycus isp. and radial trace fossils.These trace fossils belong to ethological categories pascichnia, repichnia, cubichnia, and fodinichnia and represent arthropod and worm-like burrowing biota. The assemblage and a regional comparison with contemporaneous trace fossils in the eastern Gondwanan realm suggest that the sequence in the study area belongs to the Cruziana tenella Ichnozone and to Stage 2 (upper part of Terreneuvian), however the Middle Cambrian is not excluded. The trace fossil assemblage belongs to the archetypal Cruziana ichnofacies. Cross bedded sandstone, mud cracks and rainprints in the ichniferous strata of the Nagaur Sandstone Formation indicate deposition in an intertidal sand flat with channels that was exposed episodically.     

Two bioerosion ichnofacies produced by early and late burial associated with sea-level change

In bioerosion, as in trace fossils as a whole, deeply emplaced structures have greater survival value than shallow structures. That is to say, tiering (the relative depth to which rasping, etching and boring organisms penetrate their substrate) is of paramount importance for the preservation potential of individual trace fossils. An Entobia ichnofacies is established for trace fossil assemblages dominated by deep tier borings and arising from long-term bioerosion, such as occurs on sediment-free submarine cliffs or hardgrounds. A Gnathichnus ichnofacies comprises assemblages containing all tiers, including superficial sculptures produced by radulation that have very little preservation potential. Such assemblages occur in short-term bioerosion situations as on shell surfaces and hardgrounds buried early by sedimentation. Correspondence to: R. G. Bromley     

Ichnology of the Goradongar Formation,Goradongar hill range,Patcham island,Kachchh, Western India

The middle Jurassic Goradongar Formation exposed in Goradongar hill represents a mixed siliciclasticcarbonate succession with shales and limestones. They contain a large number of well preserved trace fossils. Total 44 ichnospecies of 31 ichnogenera; representing diverse ethology, were grouped in five ichnoassemblages (Planolites, Palaeophycus, Gyrochorte, Rhizocorallium and Arenicolites assemblage). These recurring ichnoassemblages represent the Cruziana ichnofacies and occasionally a mixed Skolithos-Cruziana ichnofacies. Patterns of diversity and density of the trace fossils reveal changes in bathymetry, oxygen level, trophic level and the sub-strate conditions at the time of deposition. These paleoenvironment and palaeo-oceanography changes are co-relatable to world-wide Bathonian-Callovian (middle Jurassic) deposits.     

Sedimentological and ichnological implications of rapid Holocene flooding of a gently sloping mud‐dominated incised valley – an example from the Red River (Gulf of Tonkin)

The Gulf of Tonkin coastline migrated at an average rate of ca 60 m year^?1 landward during Holocene sea‐level rise (20 to 8 ka). Due to a combination of rapid coastline migration and undersupply of sand, neither coastal barriers nor tidal sand bars developed at the mouth of the Red River incised valley. Only a 30 to 80 cm thick sandy interval formed at the base of full‐marine deposits. Thus, the river mouth represented a mud‐dominated open funnel‐shaped estuary during transgression. At the base of the valley fill, a thin fluvial lag deposit marks a period of lowered sea‐level when the river did not reach geomorphic equilibrium and was thus prone to erosion. The onset of base‐level rise is documented by non‐bioturbated to sparsely bioturbated mud that occasionally contains pyrite indicating short‐term seawater incursions. Siderite in overlying deposits points to low‐salinity estuarine conditions. The open funnel‐shaped river mouth favoured upstream incursion of seawater that varied inversely to the seasonal strongly fluctuating discharge: several centimetres to a few tens of centimetres thick intervals showing marine or freshwater dominance alternate, as indicated by bioturbational and physical sedimentary structures, and by the presence of Fe sulphides or siderite, respectively. Recurrent short‐term seawater incursions stressed the burrowing fauna. The degree of bioturbation increases upward corresponding to increasing marine influence. The uppermost estuarine sediments are completely bioturbated. The estuarine deposits aggraded on average rapidly, up to several metres kyr^?1. Siphonichnidal burrows produced by bivalves, however, document recurrent episodes of enhanced deposition (>0·5 m) and pronounced erosion (<1 m) that are otherwise not recorded. The slope of the incised valley affected the sedimentary facies. In steep valley segments, the marine transgressive surface (equivalent to the onset of full‐marine conditions) is accentuated by the Glossifungites ichnofacies, whereas in gently sloped valley segments the marine transgressive surface is gradational and bioturbated. Marine deposits are completely bioturbated.