Glacial Processes Research Articles

The late Carboniferous basal Grant Group unconformity, Canning Basin, Australia: a complex surface recording glacial tectonic and halotectonic processes

The angular unconformity at the base of the Grant Group forms a distinctive surface evident both at outcrop and in the subsurface on seismic and well logs. Detailed analysis of a 2D seismic dataset, integrated with available well data, suggests a complex suite of processes controlling the formation, deformation and resultant morphology of this surface. They can be subdivided into three categories depending on whether the mechanisms pre-dated, were coeval with, or post-dated deposition of the Grant Group. Pre-Grant faulting during the Devonian–Lower Carboniferous Pillara Extension resulted in development of significant paleotopography that influenced the morphology of the Base Grant Group unconformity. The pre-Grant interval contained thick salt, which was locally removed in the Silurian, with the development of isolated bodies of thickened Worral Formation. Later after deposition of the Grant group, the remainder of the Mallowa salt underwent dissolution/withdrawal, resulting in collapse of the flanks of earlier Worral pods of sediments, forming a ‘sombreros’ structure and folding the Base Grant Group unconformity. The main syn-Grant processes include regional glacial erosion, and extensive development of paleo-tunnel valleys that formed beneath and at the margin of the Permian–Carboniferous ice sheet as it advanced into the Fitzroy Trough. This created significant relief on the Base Grant Group unconformity, with tunnel valleys characterised by steep-sided, often U-shaped valleys up to 525 m deep and 12 km wide. Post Grant deposition, the unconformity surface was subsequently modified during the Triassic–Jurassic Fitzroy Movement, resulting in fault reactivation and development of a series of en-echelon anticlines associated with a regional wrench system.

Reconstruction of Late Pleistocene glaciers on Mount Lovćen, Montenegro

The study of Pleistocene glaciations in the Dinaric Alps began at the end of the 19th century. Since then, the interpretation of glaciation in this area has not seen much study until the beginning of the 21st century, when a few modern geomorphological studies with numerical dating and equilibrium line altitude (ELA) reconstructions were carried out in the SE part of the Dinaric Alps (where Mount Lovćen is situated). The morphology of Mount Lovćen consists of a karst landscape modified by glacial processes. This paper presents geomorphological evidence of glaciations on Mount Lovćen, along with a reconstruction of paleoglacier dimensions and estimations of the paleo-equilibrium line altitude. Mapping of glacial landforms on Mount Lovćen revealed at least two different glacial events. Only limited patches of older glacial deposits were identified, and therefore the reconstruction of glacier dimensions and ELA were only performed for the younger glaciation. This glacier extended over an area of at least 39.9 km2 and reached a maximum thickness of about 290 m. The regional ELA for the Mount Lovćen glaciers was calculated as 1259 m.

Geomorfología de la microcuenca Pastoruri- Cordillera Blanca

RESUMEN El presente estudio geomorfológico de la microcuenca Pastoruri, comprende tanto las características más saltantes de la configuración del relieve, como los aspectos esenciales de los procesomorfodinámicos y morfogenéticos que actúan en modelado glacial y periglacial de la misma. Etrabajo desarrolla tareas de investigación para cumplir con el objetivo de avanzar en el conocimientdel retroceso glaciar, su relación con el cambio climático y de sus efectos en la disponibilidade recursos hídricos. Se trata de una problemática de enorme importancia para la región, cuymagnitud apenas se vislumbra, debido a las crecientes necesidades de la población de mayorey más intensivas formas de ocupación del territorio y con ello, el creciente requerimiento principalmente de recursos hídricos, energía, actividades agrícolas, turísticas, entre otras, de caráctevital para garantizar el desarrollo sostenible de importantes ciudades asentadas en el valle deCallejón de Huaylas y fuera de él, algunas de las cuales resultan vitales para el país.

Possible open-system (hydraulic) pingos in and around the Argyre impact region of Mars

We report the observation of possible (hydraulic) open-system pingos (OSPs) at the mid latitudes (∼37°S) in and around the Argyre impact-basin. OSPs are perennial (water)–ice cored mounds; they originate and evolve in periglacial and pro-glacial landscapes on Earth where intra- or sub-permafrost water under hydraulic/artesian pressure uplifts localised sections of surface or near-surface permafrost that then freezes in-situ. We invoke three lines of evidence in support of our analogue-based interpretation: (1) similarities of shape, size and summit traits between terrestrial OSPs and the Martian mounds; (2) clustered distribution and the slope-side location of the mounds, consistent with terrestrial permafrost-environments where OSPs are found; and, (3) spatially-associated landforms putatively indicative of periglacial and glacial processes on Mars that characterise OSP landscapes on Earth.This article presents five OSP candidate-locations and nests these mound locations within a new geological map of the Argyre impact-basin and margins. It also presents three periglacial hypotheses about the possible origin of the water required to develop the mounds. Alternative (non-periglacial) formation-hypotheses also are considered; however, we show that their robustness is not equal to that of the periglacial ones.

The sediment properties of glacial diamicts from the Jutulsessen area of Gjelsvikfjella, East Antarctica: A reflection of source materials and regional climate

The glacial diamicts deposited in the Jutulsessen area of Gjelsvikfjella, Dronning Maud Land, East Antarctica show the effects of localized meltwater channels and wind processes, as well as of the dominant glacial processes. These glacial sediments are characterized by poor sorting and a variable mean particle size, and the localized meltwater channels have removed silt- and clay-sized sediments, resulting in the relative enrichment of coarser sediments. The X-ray diffraction (XRD) patterns of clay minerals in samples collected across the study area show very similar characteristics. Biotite is the dominant mica mineral in the clay together with chlorite and K-feldspar. The presence of illite, and small amounts of smectite, demonstrates the limited extent of chemical weathering due to the cold and arid conditions. The samples from the glacial fan area contain mixed-layer clays, suggesting the effects of localized meltwater and limited chemical activity which has altered the crystal structure of biotite at lower topographic level. Scanning electron microscopy (SEM) analysis of surface microtextures from representative quartz grains suggest the dominance of glacial and glaciofluvial processes. The low rates of biogenic activity in this area are indicated by the low total organic carbon (TOC) content of the sediments.

A Reconstruction of the Pleistocene Glacial Maximum in the Žijovo Range (Prokletije Mountains, Montenegro)

The Žijovo Range belongs to the Prokletije Mountains of Montenegro and is located in the extreme southeast, on the border with Albania. Glacial processes were intensively active in this range during the Pleistocene. This is indicated by erosive and accumulative glacial features of relief that have been preserved due to the favorable geologic structure. The glacial maximum in the Žijovo Range is characterized by a unique glacier on the entire area of the range. Preglacial relief prevented the formation of a typical icecap glacier. Due to drainage of the central glacial mass in the direction of the preglacial valleys, there was a transection glacier in the central, northern, and northwestern parts, and an icefield glacier in the eastern and southeastern parts of the Žijovo Range. These glaciers covered an area of 180 km during the glacial maximum.

The Pattern of Sediment Dispersion in the Front Sector of the Stenhouse and Ajax Glaciers, Visca Anchorage, King George Island, Antarctica

This study investigated the dispersal pattern of suspended sediment in the areas near the Stenhouse and Ajax glaciers, Visca Anchorage, Martel Inlet, King George Island, Antarctica. This study was conducted using visible band processing of Quickbird high-resolution spatial images obtained in October 2006. The methodology was also based on the collection and interpretation of data obtained from water samples collected in Admiralty Bay in December 2004. The digital processing of satellite images was performed using a classification method based on the reflectance characteristics of water. The classified images improved visual identification of the dispersion pattern of suspended sediments in the study area. These data were related to the interpretation of analyses conducted on suspended particulate matter (SPM) in the water. The sediment dispersal pattern observed may be associated with glacial erosion processes, their input of meltwater from the front of the glaciers into the study area, detritus flow processes and glaciomarine circulation in the region.

Rola procesów glacjalnych w kształtowaniu rzeźby południowego obrzeżenia Kotliny Kolskiej

The article analyses the southern part of the expansion of the Bzura-Ner Spillway (Bzura-Ner Pradolina), called the Koło Basin as well as neighbouring areas of the Łask Upland Plain and the Turek Upland Plain. The purpose of the study was to present the role of Pleistocene glaciations, especially the Warta Glaciation and, in particular, their role in the evolution of land relief in this area. It was noted that morphological activity of continental glaciers depended on morphology, lithology and dynamics of the bedrock. Special attention was paid to effects characteristic of the transgression and disappearance of the Warta ice sheet. A survey of geological and geomorphological literature, analyses of archival data, mainly the accounts of geological drillings as well as results of geomorphological and palaeogeomorphological research constitute the basis for the presented data and views. It was found that successive continental glaciers had reduced height differences of the Pleistocene bedrock without obliterating the main forms in the area. Despite the genetic diversity of forms, postglacial forms and sediments – which emerged during the glaciation of the Warta (the last glaciation in this area) – play a predominant part in the described area. The features of glacial tills and fluvioglacial and limnoglacial sediments which form Wartian mounds, hills, and ridges prove that at the end of the Warta glaciation, during deglaciation (in the Bzura sub-phase), the dynamics of glacial processes was intensified. Accumulation of ice in the lower part of the current Koło Basin was conducive to increased dynamics of the ice lobe through oscillations and, possibly, through glacial surges. However, activity of the ice sheet edge has been blurred as a result of areal deglaciation, which is documented by numerous kames – the most widespread convex glacial forms in the area.

Late Quaternary glacial history and meltwater discharges along the Northeastern Newfoundland Shelf

The geomorphology of the Eastern Canadian margin has been shaped by glacial processes during the Quaternary. Many studies have focused on the ice-sediment pathway through Hudson Strait to reconstruct the dynamics of the Laurentide Ice Sheet, and as a consequence, little is known on its marginal ice domes. Here we reconstruct the dynamics of two trough mouth fans (TMFs) offshore NE Newfoundland using sediment cores and radiocarbon ages supported by very high resolution seismic reflection profiles. These two TMFs, namely Notre Dame and Hawke, are fed by two glacial troughs incised in the bedrock. The TMFs show a complete sedimentary sequence from 30 ka BP to the beginning of the Holocene. The sampled sedimentary record on the upper slope extends back to a thick Heinrich event 3 (H3) deposit that corresponds to the end of the maximum extent of the Newfoundland ice dome. Above H3, a thick succession of turbidite deposits (>10 m) observed in both TMFs is correlated with periods of major meltwater supply from 28–29 to 17 ka BP. Our results show that the Last Glacial Maximum (LGM) period was characterized by major input of meltwater events stemming from the Newfoundland dome. The presence of H1 (∼17 ka BP) coincide with the end of the turbidite activity which is replaced by an open-water environment characterized by hemipelagic sediments rich in ice-rafted debris. The proglacial muddy sediment older than 13.3 ka BP on the shelf shows that ice was not grounded after H1, suggesting a very rapid retreat of the ice on the Newfoundland shelf after 17 ka BP.

Erosion by cooling

The thermal history of thousands of rock samples convincingly confirms the idea that climate cooling accelerates the rate of erosion at Earth's surface — and implicates glaciers in particular. See Letter p.423 Climatic and tectonic changes are thought to influence topography and erosion rates. A prime example of a major climate shift is the Late Cenozoic cooling, but its impact on global erosion remains uncertain. This paper quantifies erosion rates on the basis of inverse modelling and thermochronometric data from around the world and finds an increase in erosion rates at all latitudes, coinciding with enhanced cooling during the Late Cenozoic. In particular, mountain erosion rates have increased in the past 6 million years and most rapidly in the past 2 million years. The increase in erosion is most pronounced in glaciated mountain ranges, suggesting an important influence of glacial processes on erosion.

Worldwide acceleration of mountain erosion under a cooling climate

Climate influences the erosion processes acting at the Earth's surface. However, the effect of cooling during the Late Cenozoic era, including the onset of Pliocene-Pleistocene Northern Hemisphere glaciation (about two to three million years ago), on global erosion rates remains unclear. The uncertainty arises mainly from a lack of consensus on the use of the sedimentary record as a proxy for erosion and the difficulty of isolating the respective contributions of tectonics and climate to erosion. Here we compile 18,000 bedrock thermochronometric ages from around the world and use a formal inversion procedure to estimate temporal and spatial variations in erosion rates. This allows for the quantification of erosion for the source areas that ultimately produce the sediment record on a timescale of millions of years. We find that mountain erosion rates have increased since about six million years ago and most rapidly since two million years ago. The increase of erosion rates is observed at all latitudes, but is most pronounced in glaciated mountain ranges, indicating that glacial processes played an important part. Because mountains represent a considerable fraction of the global production of sediments, our results imply an increase in sediment flux at a global scale that coincides closely with enhanced cooling during the Pliocene and Pleistocene epochs.

Biotic origin for Mima mounds supported by numerical modeling

Mima mounds are ~1-m-high hillocks found on every continent except Antarctica. Despite often numbering in the millions within a single field, their origin has been a mystery, with proposed explanations ranging from glacial processes to seismic shaking. One hypothesis proposes that mounds in North America are built by burrowing mammals to provide refuge from seasonally saturated soils. We test this hypothesis with a numerical model, parameterized with measurements of soil transport by gophers from a California mound field, that couples animal behavior with geomorphic processes. The model successfully simulates the development of the mounds as well as key details such as the creation of vernal pools, small intermound basins that provide habitat for endemic species. Furthermore, we demonstrate that the spatial structure of the modeled mound fields is similar to actual mound fields and provides an example of self-organized topographic features. We conclude that, scaled by body mass, Mima mounds are the largest structures built by nonhuman mammals and may provide a rare example of an evolutionary coupling between landforms and the organisms that create them.

Geomorphological map of the central sector of the Matese Mountains (Southern Italy): an example of complex landscape evolution in a Mediterranean mountain environment

A 1:28,000 scale geomorphological map of the central sector of the Matese Mountains (Southern Italy) is presented in this paper. Geomorphological investigation by means of remote sensing, cartographic analysis and field surveys allowed the identification of the main geomorphic processes and to map the related landforms which are both of monogenetic and polygenetic origin. Most of them are erosional landforms generated by the action of periglacial, glacial and karst processes which often occur under the control of the geological structure. Glacial relics and polygenetic landforms of glaciokarst and fluviokarst origin provide good evidence of the strong influence of variable climatic conditions on landform genesis during the Quaternary. They also highlight the influence of extensive tectonics during the Quaternary which caused progressive uplift, fragmentation and disarticulation of the developing mountainous landscape and its consequent polycyclic evolution. The map illustrates the geomorphologic peculiarities of the Mediterranean mountain landscape that typically characterizes the Apennine chain, and contributes to the understanding of its tectonic evolution and the influence of climate and climatic changes on landscape evolution. It further provides a basic map for land planning policy including the exploitation of the geological heritage and the development of sustainable mountain tourism and geo-tourism.

Suspended sediment and total dissolved solid yield patterns at the headwaters of Urumqi River, northwestern China: a comparison between glacial and non‐glacial catchments

ABSTRACTIn order to understand the differences in the suspended sediment and total dissolved solid (TDS) yield patterns between the glacial and non‐glacial catchments at the headwaters of Urumqi River, northwestern China, water samples were collected from a glacier catchment and an empty cirque catchment within the region, during three melting seasons from 2006 to 2008. These samples were analyzed to estimate suspended sediment and TDS concentrations, fluxes and erosion rates in the two adjoining catchments. There were remarked differences in suspended sediment and TDS yield patterns between the two catchments. Suspended sediment concentrations were controlled mainly by the sediment source, whereas TDS concentrations were primarily related to the hydrologic interaction with soil minerals. Generally, the glacial catchment had much higher suspended sediment and TDS yields, together with higher denudation rates, than the non‐glacial catchment. Overall, glacial catchment was mainly dominated by physical denudation process, whereas the non‐glacial catchment was jointly influenced by physical and chemical denudation processes. The observed differences in material delivery patterns were mainly controlled by the runoff source and the glacial processes. The melting periods of glacier and snow were typically the most important time for the suspended sediment and TDS yields. Meanwhile, episodic precipitation events could generate disproportionately large yields. Subglacial hydrology dynamics, glaciers pluck and grind processes could affect erodibility, and the large quantities of dust stored on the glacier surface provided additional sources for suspended sediment transport in the glacial catchment. These mechanisms imply that, in response to climate change, the catchment behaviour will be modified significantly in this region, in terms of material flux. Copyright © 2013 John Wiley & Sons, Ltd.

Seismic stratigraphic record of the Amundsen Sea Embayment shelf from pre-glacial to recent times: Evidence for a dynamic West Antarctic ice sheet

Studies of the sedimentary architecture and characteristics of the Antarctic continental margin provide clues about past ice sheet advance-retreat cycles and help improve constraints for paleo-ice dynamic models since early glacial periods. A first seismostratigraphic analysis of the Amundsen Sea Embayment shelf and slope of West Antarctica reveals insights into the structural architecture of the continental margin and shows stages of sediment deposition, erosion and transport reflecting the history from pre-glacial times to early glaciation and to the late Pleistocene glacial-interglacial cycles. The shelf geometry consists of a large pre- and syn-rift basin in the middle shelf region between basement cropping out on the inner shelf and buried basement ridge and highs on the outer shelf. A subordinate basin within the large basin on the mid-shelf may be associated with motion along an early West Antarctic Rift System branch. At least 4 km of pre-glacial strata have been eroded from the present inner shelf and coastal hinterland by glacial processes. Six major sedimentary units (ASS-1 to ASS-6) separated by five major erosional unconformities (ASS-u1 to ASS-u5) are distinguished from bottom to top. Unconformity ASS-u4 results from a major truncational event by glacial advance to the middle and outer shelf, which was followed by several episodes of glacial advance and retreat as observed from smaller-scale truncational unconformities within the units above ASS-u4. Some of the eroded sediments were deposited as a progradional wedge that extends the outer shelf by 25 to 65 km oceanward of the pre-glacial shelf-break. We compare the observed seismic characteristics with those of other Antarctic shelf sequences and assign an Early Cretaceous age to bottom sedimentary unit ASS-1, a Late Cretaceous to Oligocene age to unit ASS-2, an Early to Mid-Miocene age to unit ASS-3, a Mid-Miocene age to unit ASS-4, a Late Miocene to Early Pliocene age to unit ASS-5, and a Pliocene to Pleistocene age to the top unit ASS-6. Buried grounding zone wedges in the upper part of unit ASS-5 on the outer shelf suggest pronounced warming phases and ice sheet retreats during the early Pliocene as observed for the Ross Sea shelf and predicted by paleo-ice sheet models. Our data also reveal that on the middle and outer shelf the flow-path of the Pine Island-Thwaites paleo-ice stream system has remained stationary in the central Pine Island Trough since the earliest glacial advances, which is different from the Ross Sea shelf where glacial troughs shifted more dynamically. This study and its stratigraphic constraints will serve as a basis for future drilling operations required for an improved understanding of processes and mechanisms leading to change in the West Antarctic Ice Sheet, such as the contemporary thinning and grounding line retreat in the Amundsen Sea drainage sector.

Characteristics of landslides in western Colorado, USA

Mass movement can be activated by earthquakes, rapid snowmelt, or intense rainstorms in conjunction with gravity. Whereas mass movement plays a major role in the evolution of a hillslope by modifying slope morphology and transporting material from the slope to the valley, it is also a potential natural hazard. Determining the relationships of frequency and magnitude of landslides are fundamental to understanding the role of landslides in the study of landscape evolution, hazard assessment, and determination of the rate of hillslope denudation. We mapped 735 shallow and active landslides in the Paonia to McClure Pass area of western Colorado from aerial photographs and field surveys. The study area covers ∼815 km2. The frequency–magnitude relationships of the landslides illustrate the flux of debris by mass movement in the area. The comparison of the probability density of the landslides with the double Pareto curve, defined by power scaling for negative slope (α), power scaling for positive slope (β), and location of rollover (t), shows that α = 1.1, β = 1.9, and t = 1,600 m2 for areas of landslides and α = 1.15, β = 1.8, and t = 1,900 m3 for volumes of landslides. The total area of landslides is 4.8 × 106 m2 and the total volume of the landslides is 1.4 × 107 m3. The areas (A) and the volumes (V) of landslides are related by V = 0.0254 × A 1.45. The frequency–magnitude analysis shows that landslides with areas ranging in size from 1,600 to 20,000 m2 are the most hazardous landslides in the study area. These landslides are the most frequent and also do a significant amount of geomorphic work. We also developed a conceptual model of hillslope development to upland plateau driven by river incision, shallow landsliding, and deep-seated large landsliding. The gentle slope to flat upland plateau that dominated the Quaternary landscape of the study area was modified to the present steep and rugged topography by the combined action of fluvial incision and glacial processes in response to rock uplift, very-frequent shallow landsliding, and less-frequent deep-seated landsliding.

Lake floor morphology and sediment architecture of lake torneträsk, northern sweden

Here we present datasets from a hydroacoustic survey in uly 2011 at Lake orneträsk, northern weden. Our hydroacoustic data exhibit lake floor morphologies formed by glacial erosion and accumulation processes, insights into lacustrine sediment accumulation since the beginning of deglaciation, and information on seismic activity along the Pärvie Fault. Features of glacial scouring with a high‐energy relief, steep slopes, and relative reliefs of more than 50 m are observed in the large ‐basin. The remainder of the lacustrine subsurface appears to host a broad variety of well preserved formations from glacial accumulation related to the last retreat of the Fennoscandian ice sheet. Deposition of glaciolacustrine and lacustrine sediments is focused in areas situated in proximity to major inlets. Sediment accumulation in distal areas of the lake seldom exceeds 2 m or is not observable. We assume that lack of sediment deposition in the lake is a result of different factors, including low rates of erosion in the catchment, a previously high lake level leading to deposition of sediments in higher elevated paleodeltas, tributaries carrying low suspension loads as a result of sedimentation in upstream lakes, and an overall low productivity in the lake. A clear off‐shore trace of the Pärvie Fault could not be detected from our hydroacoustic data. However, an absence of sediment disturbance in close proximity to the presumed fault trace implies minimal seismic activity since deposition of the glaciolacustrine and lacustrine sediments.

Quantitative geomorphological analysis of drumlins in the peterborough drumlin field, ontario, canada

Drumlins are enigmatic subglacial landforms that have been interpreted to form by a number of processes, including incremental accumulation of till, erosion of previously deposited sediment, catastrophic meltwater floods, and sediment deformation. However, relatively little is known about the controls on drumlin formation, such as spatially variable glacial processes or substrate characteristics, and how these controls may be identified from variations in drumlin morphology within a single drumlin field. This paper explores a computational method that allows identification of drumlins and extraction of their morphological characteristics from existing topographic digital data for a portion of the eterborough drumlin field in ntario, anada. Spatial and non‐spatial analysis of the form and distribution of drumlins across the study area identifies drumlin characteristics such as size, elongation ratio, symmetry and long axis orientation and shows that drumlins are not randomly distributed across the region and their form characteristics have distinct regional trends. Kernel density analysis is used to identify the regional trends in drumlin characteristics. Factors that appear to influence the form and distribution of drumlins in the study area include sediment thickness, length of time beneath the ice, ice velocity and direction of ice movement. The distribution of particularly well developed asymmetric and elongate drumlins coincides with the location of a broad bedrock low and is interpreted to identify the former location of a fast‐flowing ice stream.

Age and evolution of the lower NW flank of the Hecates Tholus volcano, Mars, based on crater size–frequency distribution on CTX images

We present results of crater size–frequency distribution (SFD) analysis of the lower NW flank of the Hecates Tholus volcano, Elysium volcanic province of Mars, by the use of images acquired by the Context (CTX) instrument on board of Mars Reconnaissance Orbiter (6m/pixel in resolution). Previous similar works were focused on the caldera complex of the volcano and some sectors of the lower NW flank. In this study, we analyzed the complete crater population of the main geomorphological units characterizing this sector of the volcano (de Pablo, M.A., Centeno, J.D. [2012]. Journal of Maps 8(3), 208–2014), discarding areas with possible clustering to avoid erroneous results. In total, 16 areas corresponding to 10 geomorphological units were measured and absolute model ages were derived for them. The ages correspond to ages of origin as well as of the end of resurfacing events, depending on the analyzed sector, resulting in some cases in more than one age per area.Our results are in general in agreement with previous works, and establish that the age of the origin of the Hecates Tholus volcano could be at least 3.8Ga, with possible volcanic eruptions occurring until at least 335Ma. Glacial events were also dated at 90Ma, 30Ma, 16Ma, and 6Ma, although it is possible to recognize ages which could also be related to the recent ice ages of Mars, between 2 and 0.4Ma. Our results allowed us to determine that glacial processes could have been active as far back as 1.4Ga, with possible events at intermediate ages. We deduced from the resulting ages and our observations on CTX images and the available geomorphological map of the area, that glacial-related processes played an important role in sculpting this flank of the volcano, and the possible level of the glacial sheet at the edge of the main depression of this flank was also deduced, with altitudes ranging between −2035m and −2490m, in agreement with the presence of smooth outcrops and roche moutonnées in the area. Finally, a possible evolution of this region of the Hecates Tholus volcano is proposed and discussed, establishing the sequence of the most important geological events which occurred in the area and their possible timings.

New ichnospecies of scratching traces from phosphatic nodules (Cenomanian, England)

Surfaces of phosphorite nodules and pebbles from the “Cambridge Green Sand” (Cenomanian, South England) yielded several discernible types of scratches. These originated before the burial of nodules/pebbles as evidenced by fossil epibiotic oysters cemented to cover the scratches. The individual forms of scratches differ in size and shape; therefore, the set of “scratching instruments” also had to be different. The scratches described differ from scratches generated by glacial processes, namely by the regularity of length and intervals, parallel orientation, existence of recurrent forms and placement along the nodule edges. We interpret the scratches as trace fossils of the ichnogenus Machichnus. Three new species, namely M. normani, M. harlandi and M. jeansi, are erected for them herein. The series of scratches originated probably by teeth on a couple of jaws; the makers possibly scraped bacterial or algal film off the surface of nodules that were covered with the phosphate gel. Both homodont and heterodont animals (probably fish) were involved.