Firmness Profiles Associated with Tidal-Creek Deposits: The Temporal Significance of Glossifungites Assemblages

Abstract

Indentation tests are used to detail firmness profiles from intertidal creek deposits and wave-exhumed substrates at Willapa Bay. Both of these sedimentological settings are characterized by occurrences of modern Glossifungites assemblages. Firm substrates associated with the intertidal-creek deposits are derived from dewatered modern sediments, whereas firmgrounds associated with wave erosion consist of dewatered and compacted Pleistocene strata. The Pleistocene firmgrounds are notably firmer than those derived from modern deposits. A strong correlation between sediment firmness and burrowing behavior is evident in these deposits.In tidal-creek systems, the comparatively firm cutbank is characterized by unlined, large-diameter, open burrows that form a Glossifungites assemblage. Intertidal point-bar deposits contain a softground suite consisting of mucous-lined, small-diameter, dominantly vertical traces. Finally, a softground suite of robust, mucous-or mud-lined, vertical and horizontal traces are observed in intertidal-flat deposits. In contrast, Pleistocene firmgrounds generally contain large-and small-diameter traces, with dominantly vertical architectures (Thalassinoides-, Gastrochaenolites-, Diplocraterion-, or Arenicolites-like burrows), depending upon the firmness of the substrate.Glossifungites occurrences on modern firmgrounds are temporally insignificant, whereas similar occurrences in Pleistocene substrates are temporally significant. Contrasting these two databases suggests that the stratigraphic significance of a Glossifungites-demarcated discontinuity can be assessed in the rock record. Several criteria that are useful for identifying temporally significant surfaces are suggested, including: absence of compaction of the Glossifungites assemblage; presence of well-preserved burrow sculptings; and planar to gently undulatory erosional surfaces as opposed to surfaces with notable topographic relief. Conceptual models demonstrate that muddy substrates potentially require several millennia to compact and dewater. Sandy deposits, on the other hand, have indeterminate significance.

The transgressive infill of an inherited-valley system: The Springhill Formation (lower Cretaceous) in southern Austral Basin, Argentina

“…The lower boundary of this facies association is usually demarcated by Thalassinoides burrows, which are penetrating the fine-grained underlying (host) sediments and are filled with coarse sand and skeletal fragments. These passively-filled burrows, typically presented as subspherical sections of horizontal and inclined tubes, are attributed to a Glossifungites ichnofacies (Gingras et al, 2000). This facies association is solely present in the northern region where it lies above central-estuary deposits (association B3) and it is invariably overlain by open-marine deposits (facies associations C2 and C3).…”

“…These outer-estuary complexes could have partially enclosed the estuary mouth, favouring the development of low-energy conditions in the central portion of some estuarine systems (facies association B3). The lower boundary of these deposits, commonly demarcated by a Glossifungites ichnofacies in several wells across the study area, suggests the development of a regional erosional event (Gingras et al, 2000). 5.2.5.…”

“…Although Glossifungites-demarcated discontinuities could be the product of autocyclic process (e.g. at the base of tidal creeks, Gingras et al, 2000), the regional distribution of the surface and its stratigraphic position suggest that erosion in this case was associated with tidal and wave activity during the transgression of the estuarine system (MacEachern et al, 2007b).…”

A Field Method for Determining the Firmness of Colonized Sediment Substrates

“…It is somewhat intuitive that the degree of firmground induration affects the burrow architecture used to colonize a substrate (Frey and Seilacher 1980;Pemberton and Frey 1985). This has been illustrated in the modern (Pemberton and Frey 1985;Gingras et al 2000) but has not been related to the rock record; a situation attributable to the small database of modern studies and an absence of reported (comparable) firmness measurements.…”

“…Also, antecedent topography due to the erosion of surfaces characterized by the patchy distribution of firmgrounds (Huang 1993) affects sediment distribution patterns on many scales (Sanford and Halka 1993). Finally, bioturbation itself alters the overall cohesiveness of the substrate (Cadée 1998;Gingras et al 2000).…”