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

Palaeoenvironmental control on distribution of crinoids in the Bathonian (Middle Jurassic) of England and France

Bulk sampling of a number of different marine and marginal marine lithofacies in the British Bathonian has allowed us to assess the palaeoenvironmental distribution of crinoids for the first time. Although remains are largely fragmentary, many species have been identified by comparison with articulated specimens from elsewhere, whilst the large and unbiased sample sizes allowed assessment of relative proportions of different taxa. Results indicate that distribution of crinoids well corresponds to particular facies. Ossicles of Chariocrinus and Balanocrinus dominate in deeper-water and lower-energy facies,with the former extending further into shallower-water facies than the latter. Isocrinus dominates in shallower water carbonate facies, accompanied by rarer comatulids, and was also present in the more marine parts of lagoons. Pentacrinites remains are abundant in very high-energy oolite shoal lithofacies. The presence of millericrinids within one, partly allochthonous lithofacies suggests the presence of an otherwise unknown hard substrate from which they have been transported. These results are compared to crinoid assemblages from other Mesozoic localities, and it is evident that the same morphological ad-aptations are present within crinoids from similar lithofacies throughout the Jurassic and Early Cretaceous

A New Triassic Brachiopod Fauna from Hokkaido, Japan

A new brachiopod fauna is described from loose material in central Hokkaido, Japan. Three of the forms present are attributed to the genera Canadospira, Robinsonella and Piarorhynchia. A Carnian age is provisionally suggested, though no faunas of this age are known elsewhere in Japan. The biogeography of the forms is briefly discussed

New early Mesozoic Brachiopods from southern Turkey

New Late Triassic and Early Jurassic brachiopod faunas are described from the Taurus Mountains in Southern Turkey. They include the distinctive Norian rhynchonellid Halorella amphitoma (not previously recorded from Turkey), the aberrant Upper Norian rhynchonellid Carapezzia (only previously recorded from Austria and Sicily) and Sinemurian or Pliensbachian faunas. The significance of these typically North European faunas in a Tethyan realm is discusse

Brachiopod palaeobiogeography in the western Tethys during the Early Jurassic diversity maximum: introduction of a Pontic Province

The biogeography of Pliensbachian (Early Jurassic) brachiopods in western Tethys is investigated using complementary multivariate tools including metric and non-metric ordination, additive cluster and bootstrapped spanning network analyses, as well as one-way analysis of similarity and similarity percentage analysis. All analyses were conducted using the Dice and Simpson similarity indices for presence/absence data on occurrence datasets involving 24 assemblages homogenized at the species level, including (403 taxa) or excluding (210 taxa) species found in only one assemblage. The analyses present a highly consistent biogeographical picture involving three main clusters: the Euro-Boreal, Mediterranean and Pontic biochores. The brachiopod species typical of the newly defined Pontic biochore are illustrated. The three assemblages from the Atlas area are interpreted as a fourth biochore, compositionally intermediate between those of the Euro-Boreal and Mediterranean. The Mediterranean biochore can be further divided into an intra- and a peri-Mediterranean group. These five, palaeogeographically well-constrained biochores show moderate to high degrees of species endemicity, ranging from 20% (Atlas) to 58% (Euro-Boreal). Based on available evidence, and after a reasonable cutback of the customary scale of ranks, the following biogeographical categories and names are suggested for the western Tethyan Pliensbachian brachiopod biochores: Euro-Boreal Province, Mediterranean Province (including an intra-Mediterranean and a peri-Mediterranean Subprovince), Pontic Province and Atlas Subprovince. In addition, a still poorly documented brachiopod biochore occurs on the Gondwana margin as a possible precursor of the extensive Middle to Late Jurassic Ethiopian Province