Vermiform Burrows and Rate of Sedimentation in the Lower Greensand

Middlemiss, F. A.

doi:10.1017/s0016756800057101

Cited by 20 publications

(4 citation statements)

References 4 publications

(2 reference statements)

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“…These (in turn) pass upward into the large, well-constructed and clay-®lled branching burrow networks associated with the fossiliferous and cemented beds capping each cycle. This succession of burrow fabrics, and their implications for sedimentation rates, were described from this section by Middlemiss (1962a). The trace fossil genera observed through each cycle of the Ferruginous Sands Formation are somewhat diverse (Fig.…”

Section: Ichnofaunamentioning

confidence: 71%

Firmgrounds – key surfaces in the recognition of parasequences in the Aptian Lower Greensand Group, Isle of Wight (southern England)

Ruffell

Wach²

1998

Sedimentology

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Aptian Lower Greensand Group exposures in the cliffs of the Isle of Wight (southern England) display a consistent coarsening‐up cyclicity on the scale of centimetres to tens of metres that reflects the bed, bed‐set, parasequence, parasequence set and sequence hierarchy. These coarsening‐up cycles are most commonly recognized at the scale of parasequences (20 cm to 10 m thick), genetically related groups of which form parasequence sets. Both parasequences and parasequence sets contain the succession of biofacies that culminate in firmground development. Numerous episodes of erosion, deposition and colonization are recorded, reflecting multiple erosion/bypass events. The increase in mean grain‐size through each cycle is reflected by changes in physical sedimentary structures; ichnofauna or bioturbational fabric; fossil fauna and diagenesis. Interbedded mudstones, siltstones and sandstones in the lower beds of each cycle display a variety of structures ranging from low‐angle, hummocky, or tabular cross‐strata, sandstone‐filled erosional gutters and planar lamination. The cleaner sandstones found in the upper parts to each cycle are often completely bioturbated with only rare stratification and pebble/plant debris‐filled scours preserved. Bioturbational fabrics change upward through each cycle from small, subhorizontal, mud‐ or sandstone‐filled burrows to large, branching, clay‐filled or cemented burrow systems. The top surface of each cycle is marked by a fossil epifauna indicative of firm to hard substrate conditions. Concentrations of bivalves, brachiopods, bryozoa, crinoids and corals are preferentially cemented by iron oxide, carbonate or phosphate. Such cements were early and thus utilized by firm or hard substrate dwellers. This fossiliferous, cemented sandstone is overlain by a flooding surface marked by the mudstone and silt‐rich sandstones at the base of the next cycle. Together, the fauna and ichnofauna in each cycle represent the gradual development of firm substrate conditions, culminating in the diverse firmground fauna preserved at the top of each cycle. The fauna and changing substrate conditions reflect the hiatuses developed during successive episodes of marine flooding. High species diversity is matched by complex patterns of taphonomic feedback in the mature firmground faunas that mark major flooding surfaces. Increasing faunal maturity allows recognition of a hierarchy of hiatuses. This hierarchy is analogous to the parasequence–parasequence set division. The stratigraphic condensation of firmgrounds can be used to empirically define the condensed section, the thickness of sediment between firmgrounds being a function of sediment supply and water depth (accommodation space).

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Section: Ichnofaunamentioning

confidence: 71%

Firmgrounds – key surfaces in the recognition of parasequences in the Aptian Lower Greensand Group, Isle of Wight (southern England)

Ruffell

Wach²

1998

Sedimentology

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“…Macaronichnus-Ophiomorpha ichnofabric associated with primary lamination (Fig. 4) This ichnofabric is based on observations of sections in the Woburn Sands (Lower Greensand, Aptian, Lower Cretaceous) of the Leighton Buzzard area, southern England (Buck 1987), though it was figured first by Middlemiss (1962).…”

Section: Lchnofabrics Containing Ophiomorphamentioning

confidence: 99%

Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretation

Pollard

Goldring

Buck³

1993

JGS

181

116

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In an attempt to interpret Ophiomorpha ichnofabrics observed in core, three ichnofabrics are described from outcrops where O. nodosa is a conspicuous element. These ichnofabrics enable sandy shoreline sedimentary environments to be characterized and differentiated: (1) shoreface with mottledOphiomorpha-Planolites ichnofabric generally without primary lamination; (2) offshore tidal shelf sand wave facies with Macaronichnus-Ophiomorpha ichnofabric associated with primary, mainly crosslaminated or cross-bedded sands; (3) estuarine facies with Ophiomorpha ichnofabric associated with primary lamination and, commonly, heterolithic sands and mudstones. Distinctions between the ichnofabrics are attributed to differences in primary stratification, the total ichnocoenoses, morphological features (such as burrow attitude, shaft restriction, pellet wall lining), to the nature of the substrate and, particularly, to the time available for colonization (larval settlement or relocation) and burrow construction, referred to here as the colonization window• The analysis is applied to an interval of core (Upper Jurassic, Central Graben, North Sea) and a sequence in Eocene sediments in southern England.Ophiomorpha nodosa Lundgren is one of the most widely quoted and widely known trace fossils. It is also a well-established and conspicuous trace fossil in shallow-marine sandy facies from the Mesozoic onwards. The principal account of its morphology and facies significance is by Frey et al. (1978).This pellet-lined burrow (Fig. 1) is today found over a range of~ nearshore environments, including lagoon and estuary floors, wherever the substrate consists mainly of sand grade sediment.

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“…Such environmentally induced asymmetry has been widely described in articulate brachiopods (e.g. Asgaard 1968;Atkins 1960;Fischer & Oehlert 1892;Lee 1978a, b;Middlemiss 1962). In contrast, there exists a kind of asymmetry which appears to include a genetic component in its determination.…”

Section: Streptis Altosinuata Holtedahlmentioning

confidence: 92%

Commissural asymmetry in brachiopods

Fürsich¹,

Palmer²

1984

Lethaia

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Tim 1984 10 15: Commissural asymmetry in brachiopods. Lethaia. Vol. 17, Consistent asymmetric folding of the commissure is a characteristic feature of a small but significant number of brachiopod species. The feature may be obligate or facultative and is almost entirely confined to rhynchonellids, most of which are Mesozoic. The detailed nature of the asymmetry is very variable, but does not extend to internal hard parts such as crura. Taken as a whole, asymmetric brachiopod species show no preference for any particular environment or geographic region, and in no circumstances seem to have been markedly more or less successful than symmetric species. We are thus led to suggest that asymmetry was a genetically based condition which cropped up periodically in brachiopod evolution, and which possibly was selected neither particularly for nor against. 0 Brachiopoda, asymmetry, functional morphology, mode of life.

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Vermiform Burrows and Rate of Sedimentation in the Lower Greensand

Cited by 20 publications

References 4 publications

Firmgrounds – key surfaces in the recognition of parasequences in the Aptian Lower Greensand Group, Isle of Wight (southern England)

Firmgrounds – key surfaces in the recognition of parasequences in the Aptian Lower Greensand Group, Isle of Wight (southern England)

Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretation

Commissural asymmetry in brachiopods

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