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Arthropods from the late Campanian (Late Cretaceous) of the Western Interior Seaway produced U-shaped Diplocraterion parallelum in mudstones along two closely spaced surfaces (10 cm apart), one of which corresponds to a maximum transgressive surface. Diplocraterion parallelum are widely distributed across both surfaces, with substantial variations in burrow orientations. Based on a comparison of paleocurrent indicators to burrow orientations, we demonstrate that D. parallelum are preferentially oriented parallel to the prevailing fair-weather wave propagation direction (wave-forced currents) that acted upon the colonized surfaces. There is an apparent maximum (34% above uniformity) preferential orientation of the burrows, attributed to the fact that wave-forced currents represent only one of several factors controlling shrimp burrowing behaviors. Based on this study, we propose that in the absence of paleocurrent data, Diplocraterion and other U-shaped burrows can be used to resolve flow directions, and that preferential burrow orientations ≥ 2% above uniformity are significant. However, it is noted that it is only possible to resolve 2-way flow directions (trend) from U-shaped burrows, as there is no way to determine vector directions.
Conodont apatite from a shallow-marine Middle Devonian transgressive unit has been investigated in five borehole sections representative of the epicontinental Belarussian Basin located in a near-equatorial setting. The transgression is related to the onset of the late Eifelian Kačák Event, an important biotic episode recorded worldwide. The δ18Oapatite data were acquired using the secondary ion mass spectrometry (SHRIMP) technique. The mean corrected values in the studied sections are in the range 19.8 ‰ to 20.2 ‰, significantly exceeding the values measured for late Eifelian low-latitude open marine basins. This can be explained by higher average δ18Oseawater levels related to elevated seawater salinities in the Belarussian epeiric basin, in agreement with the presence of impoverished marine fauna. The intra-specimen δ18O variability, with differences ranging up to 2.6 ‰ in some specimens, can be explained by fluctuating δ18Oseawater and, to a smaller degree, temperature variations in the Belarussian inland sea under a monsoonal climate. The present results demonstrate that local paleoclimate and epeiric paleogeography may considerably obscure the global climatic signature of the conodont apatite isotopic record.
Cassid gastropods are well-known drilling predators of a whole suite of echinoids which are common in both Recent and fossil environments. In many cases, the identification of cassids as possible predators is based on drill hole morphology only. A detailed study of drill hole characteristics is thus imperative for predator recognition and provided here by a thorough descriptive and statistical analysis. Fifty drill holes in the sand dollar Leodia sexiesperforata produced by the predatory gastropod Cassis tuberosa are analyzed for recognizable characters and compared to 174 drill holes in 289 denuded and empty tests from San Salvador, the Bahamas. The drill holes in dead tests are identical to the freshly drilled holes. Drill holes show subcircular to elliptical outlines with irregular margins and can feature notches produced by the predator. The cross-sectional drill hole profile range from concave parabolic to sigmoidal. The collected tests reveal a drilling intensity of 59.5% with only three individuals (1.74%) featuring multiple drill holes. The high drilling intensity and the presence of almost exclusively single drill holes indicate a high drilling success rate for the cassid predator in Caribbean ecosystems. Although the results suggest size selectivity, taphonomic processes and handling effects of the predator might result in a weaker selectivity than that inferred directly from the investigated material. Cassis tuberosa drills predominantly into the oral side of the test (86.3%) particularly in the area below the internal organs (90.9%). Most drill holes occur in the anterior part of the sand dollar's test (66.7%).
The stratigraphic and facies distribution of 20 calcimicrobial genera (including calcified cyanobacteria and associated problematic calcified microfossils) are reported for the entire Ordovician succession in the Tarim Basin in northwestern China based on examination of drill cores and 8500 thin sections from 64 wells from the Tabei, Bachu, Tazhong, and Tadong uplifts. A total of ten calcimicrobial associations are recognized in the Lower to Upper Ordovician based on taxonomic composition and distribution within four paleoenvironment types: reef (marginal and patch reef), open platform/bank (marginal and patch bank), lagoon, and tidal flat. The temporal distribution of the calcimicrobial genera closely follows changes in sedimentary environments; an extensive literature survey reveals similar relationships in much of the Paleozoic and Mesozoic. Based on their paleoenvironmental preferences, calcimicrobes can be classified into five paleohabitat types: (1) reef-adapted (Acuasiphonoria, Razumovskia, Phacelophyton , Gomphosiphon, Epiphyton, Renalcis, and Izhella); (2) open platform/bank-adapted (Subtifloria and Bevocastria); (3) both reef and open platform/bank-adapted (Bija, Apophoretella, Rothpletzella, and Wetheredella); (4) lagoon-adapted (Hedstromia, Cayeuxia, Zonotrichites, Ortonella, and Garwoodia), and (5) not only reef and open platform/bank-adapted but also tolerant of tidal flat conditions (Girvanella and Proaulopora). The occurrences of these calcimicrobes in strata not only can indicate ancient sedimentary facies but also can reveal paleoecological parameters of ancient seas, such as nutrient levels (e.g., N and P), predation pressure, and sea level, especially in strata absence of other well-studied facies fossils.