45 research outputs found
Palaeoenvironment of Eocene prodelta in Spitsbergen recorded by the trace fossil Phycosiphon incertum
Ichnological, sedimentological and geochemical analyses were conducted on the Eocene Frysjaodden Formation in order to interpret palaeoenvironment prodelta sediments in the Central Basin of Spitsbergen. Phycosiphon incertum is the exclusive ichnotaxon showing differences in size, distribution, abundance and density, and relation to laminated/bioturbated intervals. Large P. incertum mainly occur dispersed, isolated and randomly distributed throughout the weakly laminated/non-laminated intervals. Small P. incertum occur occasionally in patches of several burrows within laminated intervals or as densely packed burrows in thin horizons in laminated intervals or constituting fully bioturbated intervals that are several centimetres thick. Ichnological changes are mainly controlled by oxygenation, although the availability of benthic food cannot be discarded. Changes in oxygenation and rate of sedimentation can be correlated with the registered variations in the Bouma sequence of the distal turbiditic beds within prodeltal shelf sediments.Funding for this research was provided by Project CGL2012-33281 (Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain), Project RYC-2009-04316 (Ramón y Cajal Programme) and Projects RNM-3715 and RNM-7408 and Research Group RNM-178 (Junta de Andalucía). The authors benefited from a bilateral agreement between the universities of Granada and Oslo, supported by the University of Granada
True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces
Abstract: Rock outcrops of the sedimentary–stratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sediment–water or sediment–air interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. Some true substrates are notable for their sedimentary, palaeontological and ichnological signatures that provide windows into key intervals of Earth history, but countless others occur routinely throughout the sedimentary–stratigraphic record. They frequently reveal patterns that are strikingly familiar from modern sedimentary environments, such as ripple marks, animal trackways, raindrop impressions or mudcracks: all phenomena that are apparently ephemeral in modern settings, and which form on recognizably human timescales. This paper sets out to explain why these short‐term, transient, small‐scale features are counter‐intuitively abundant within a 3.8 billion year‐long sedimentary–stratigraphic record that is known to be inherently time‐incomplete. True substrates are fundamentally related to a state of stasis in ancient sedimentation systems, and distinguishable from other types of bedding surfaces that formed from a dominance of states of deposition or erosion. Stasis is shown to play a key role in both their formation and preservation, rendering them faithful and valuable archives of palaeoenvironmental and temporal information. Further, the intersection between the time–length scale of their formative processes and outcrop expressions can be used to explain why they are so frequently encountered in outcrop investigations. Explaining true substrates as inevitable and unexceptional by‐products of the accrual of the sedimentary–stratigraphic record should shift perspectives on what can be understood about Earth history from field studies of the sedimentary–stratigraphic record. They should be recognized as providing high‐definition information about the mundane day to day operation of ancient environments, and critically assuage the argument that the incomplete sedimentary–stratigraphic record is unrepresentative of the geological past
Ichnofabric analysis of a shallow marine deposit, Chenque Formation, Lower Miocene, Punta Delgada, Patagonia, Argentina
Microbially induced pseudotraces from a Pantanal soda lake, Brazil: Alternative interpretations for Ediacaran simple trails and their limits
Sedimentary dynamics and evolutionary history of a Late Carboniferous Gondwanic lake in north-western Argentina
Permian macroburrows as microhabitats for meiofauna organisms: an ancient behaviour common in extant organisms
Variable style of transition between Palaeogene fluvial fan and lacustrine systems, southern Pyrenean foreland, NE Spain
Two Palaeogene fluvial fan systems linked to the south-Pyrenean margin are
recognized in the eastern Ebro Basin: the Cardona–Su´ ria and Solsona–Sanau¨ ja
fans. These had radii of 40 and 35 km and were 800 and 600 km2 in area
respectively. During the Priabonian to the Middle Rupelian, the fluvial fans
built into a hydrologically closed foreland basin, and shallow lacustrine
systems persisted in the basin centre. In the studied area, both fans are part of
the same upward-coarsening megasequence (up to 800 m thick), driven by
hinterland drainage expansion and foreland propagation of Pyrenean thrusts.
Fourteen sedimentary facies have been grouped into seven facies associations
corresponding to medial fluvial fan, channelized terminal lobe, nonchannelized
terminal lobe, mudflat, deltaic, evaporitic playa-lake and
carbonate-rich, shallow lacustrine environments. Lateral correlations define
two styles of alluvial-lacustrine transition. During low lake-level stages,
terminal lobes developed, whereas during lake highstands, fluvial-dominated
deltas and interdistributary bays were formed. Terminal lobe deposits are
characterized by extensive (100–600 m wide) sheet-like fine sandstone beds
formed by sub-aqueous, quasi-steady, hyperpycnal turbidity currents.
Sedimentary structures and trace fossils indicate rapid desiccation and subaerial
exposure of the lobe deposits. These deposits are arranged in
coarsening–fining sequences (metres to tens of metres in thickness)
controlled by a combination of tectonics, climatic oscillations and autocyclic
sedimentary processes. The presence of anomalously deeply incised
distributary channels associated with distal terminal lobe or mudflat
deposits indicates rapid lake-level falls. Deltaic deposits form progradational
coarsening-upward sequences (several metres thick) characterized by channel
and friction-dominated mouth-bar facies overlying white-grey offshore
lacustrine facies. Deltaic bar deposits are less extensive (50–300 m wide)
than the terminal lobes and were also deposited by hyperpycnal currents,
although they lack evidence of emergence. Sandy deltaic deposits
accumulated locally at the mouths of main feeder distal fan streams and
were separated by muddy interdistributary bays; whereas the terminal lobe
sheets expand from a series of mid-fan intersection points and coalesced to
form a more continuous sandy fan fringe