A new macrofaunal limit in the deep biosphere revealed by extreme burrow depths in ancient sediments

Macrofauna is known to inhabit the top few 10s cm of marine sediments, with rare burrows up to two metres below the seabed. Here, we provide evidence from deep-water Permian strata for a previously unrecognised habitat up to at least 8 metres below the sediment-water interface. Infaunal organisms exploited networks of forcibly injected sand below the seabed, forming living traces and reworking sediment. This is the first record that shows sediment injections are responsible for hosting macrofaunal life metres below the contemporaneous seabed. In addition, given the widespread occurrence of thick sandy successions that accumulate in deep-water settings, macrofauna living in the deep biosphere are likely much more prevalent than considered previously. These findings should influence future sampling strategies to better constrain the depth range of infaunal animals living in modern deep-sea sands. One Sentence Summary: The living depth of infaunal macrofauna is shown to reach at least 8 metres in new habitats associated with sand injections

Cyclic phosphate-rich successions in the upper Cretaceous of Colombia

Upper Cretaceous neritic to hemipelagic successions from the eastern Colombian Cordillera display frequent and rhythmic intercalations of phosphate-rich sediment. Their accumulation is attributed to a back-arc setting between the Andean arctrench system and the Guayana cratonic shield. In three examined sections near Tausa, Tunja, and Iza (all north of Bogotá), respectively, the phosphate-rich sediments occur in 1-15 m thick coarsening-upward series ideally consisting - from the base to the top - of porcelanite, organic-rich claystone, siltstone, sandstone, and a condensed and thoroughly burrowed top bed. Phosphatic particles appear either in thin gravity-flow deposits or in pristine, in-situ occurrences near the base of these successions, intercalated in fine-grained biosiliceous or clay-rich sediment, or in the condensed top bed. The major portion of this coarsening-upward series (porcelanite to sandstone) is considered a shallowing-upward succession and the thin condensed phosphatic top bed a deepening-upward succession. These rhythmic successions are interpreted as parasequences resulting from fourth-order relative sea-level changes. Based upon biostratigraphic age estimates, the time span of formation of these parasequences range between approximately 100,000 and 200,00 yr. The allochthonous phosphate intercalations near the base of the parasequences are derived from condensed phosphatic top beds, which may have been exposed at the sediment-water interface in proximal directions. This suggests that the parasequence boundaries, i.e., marine flooding surfaces, are diachronous and become younger in onshore directions. using the vertical stacking patterns of these parasequences, we distinguish between transgressive and highstand-systems tracts (TST and HST). TST's are characterized by the dominance of phosphatic sediment, laminated and organic-rich claystone, and laminated porcelanite. This suite of sediments documents high nutrient fluxes and the presence of an oxygen-minimum zone, both probably induced by coastal upwelling. HST's include laminated to well-bioturbated siliciclastic successions, which may reflect a weakening or basinward shift of upwelling cells and higher levles of bottom-water oxygenation. The dominance of siliciclastics in HST's is indicative of high detrital fluxes, which outpaced sediment-accomodation rates on the shelf. Upper Campanian ammonoids have been found in three levels of the Lower Plaeners Member of the Guadalupe Formation in the section near Tausa - Nostoceras (Nostoceras) liratum sp.n., Exiteloceras jenneyi (Whitfield, 1887), and Libycoceras sp. E. jenneyi is an important zonal marker in the U.S. Western Interior that is also known from the basal Mount Laurel Sand of Delaware, USA. Its occurrence at Tausa is the first record outside the USA and provides an important datum for intercontinental correlation. The type of Libycoceras sp. encountered in Tausa is also known from the upper Campanian of Peru and Angola. Together with the presence of Andalusiella polymorphia (Malloy, 1972), a dinoflagellate cyst, an age range is given for the formation of the Lower Plaeners Member at Tausa (late Campanian to early Maastrichtian). © 1992

Stratigraphy of Palaeocene phosphate pelagic stromatolites (Prebetic Zone, SE Spain)

The hemipelagic domain of the ancient southern continental margin of Iberia is home to a strongly condensed pelagic succession (6–15 cm thick) characterized by the presence of phosphate stromatolites. This succession, probably generated in the slope of the continental margin, records a period of some 9 Ma, corresponding to the latest Maastrichtian to Late Thanetian interval. A microstratigraphical analysis allows for characterizing and biostratigraphically dating six successive developmental stages in the succession, which outline the main environmental evolution of the depositional setting. The Wrst of them determined the generation of a submarine hardground during the latest Maastrichtian to earliest Danian interval. The other Wve are represented by Wve successive microstratigraphical, unconformity-bounded, genetic units, respectively Early– Middle Danian, Late Danian–Early Selandian, intra-Selandian, Late Selandian–Early Thanetian, and Middle–?Late Thanetian in age. The three oldest units are characterized by the accretion of phosphate stromatolites, favoured by very low rates of pelagic sedimentation and by a microbially mediated extra input of phosphate. The two youngest units are dominated by carbonate deposition, which has always taken place at very low rates. Condensed sedimentation was abruptly interrupted at the end of the Palaeocene (?latest Thanetian), when the condensed succession and its hosting substrate were gravitationally slumped and redeposited at the base of the slope in the form of a megadebris Xow that can be now observed in Sierra de Aixorta (Alicante, SE Spain). The Aixorta pelagic phosphatic stromatolites are among the youngest ever described, and their existence suggests that the oceanographic conditions necessary for their development prevailed during most of the Palaeocene, but disappeared during the Late Selandian, never to return