Early Neoproterozoic Origin of the Metazoan Clade Recorded in Carbonate Rock Texture: REPLY

We (Neuweiler et al., 2009) used scanning electron microscopic, fluorescence spectroscopic, fluorescence microscopic, and thin-section analytical work from modern, Cretaceous, Silurian, and early Neoproterozoic reefal material to make a geological case for an early Neoproterozoic origin of animals. In a modern analogue for ancient petrographic textures, degradative calcification of the extracellular collagenous matrix (ECM) of a modern siliceous sponge can be directly observed (Neuweiler et al., 2007)

Dynamische Sedimentationsvorgänge, Diagenese und Biofazies unterkretazischer Plattformränder (Apt-Alb; Soba-region, Prov. Cantabria, N-Spanien)

Am Westrand des Basko-Kantabrischen Beckens (Soba-Region, Prov. Cantabria, Nordspanien) sind die Plattform/Becken-Übergangszonen des Apt und Alb in nahezu ungestörtem Verband erhalten. Entlang dieser Randzonen befinden sich großdimensionierte Mud Mound-Strukturen mit einer Basisbreite bis 150 m und einer Höhe bis zu 70 m. Diese Arbeit zielt auf die Erarbeitung der Prozesse, die die Bildung der Mounds begleiten, beeinflussen oder steuern. Das Intervall Oberapt (Clansay) bis Mittelaib besteht aus sechs sedimentär-diagenetischen Zyklen (asymmetrische Trans-, Regressionszyklen), die in Kombination mit Markerhorizonten eine stratigraphische Kontrolle über den Plattform/Becken-Transekt ermöglichen. Meeresspiegelschwankungen (Paläokarst) sind im Apt/Alb-Grenzintervall und hohen Unteralb (Ammonitenzone: Douvilleiceras mammilatum) nachweisbar. Die Vorkommen der Mud Mounds sind an transgressive Faziesdiskontinuitäten gebunden. Ihre Position entspricht dem zu Strömungen exponierten Hang und dem oberen Plattformrand. Die Biofazies reicht von einer aphotischen Gemeinschaft aus “Lithistida“, Hexactinellida, krustosen Foraminiferen, Polychaeten, Thecideen und Acanthochaeteten zu der photischen Biofazies mit Scleractinia, Lithophyllum und Bacinella/Lithocodium. Die Strukturbildung erfolgt durch eine autochthone Mikritproduktion (Automikrit). Akkretionäre Automikrite bilden Stromatolithe, Thrombolithe und massive Gefügetypen. Container-Automikrit befindet sich in geschützten und geschlossen Räumen. Kieselschwamm Container-Automikrite sind aphanitisch, peloidal und peloidal-bakterioform. Unabhängig von Kieselschwämmen treten Container-Automikrite in Kleinhöhlen, Taschen und im Interpartikelvolumen auf. Sie bestehen aus in-situ Peloiden und in-situ Ooiden mit massivem und/oder stromatolithischem Gefüge. Die verschiedenen Automikrittypen besetzen zwischen 50 und 80 Vol.-% der Mud Mounds. Anbohrungen durch lithophage Bivalven und Aka sowie die ausschließliche Produktion angularer Mound-Lithoklasten belegen eine Lithifizierung in statu nascendi. Die Primärmineralogie der Automikrite ist Hoch-Mg-Calcit; die Residualgehalte an MgCOa liegen zwischen 1 ,2 und 3,6 Mol-%. Die Zusammensetzung der stabilen Isotope S13C und S18O (vs PDB) ist analog zu anorganisch gebildeten, marinen Zementen (513C von 2,9 bis 3,8 und S18O von -1,5 bis -4). Die vergleichende Aminosäuren-Analyse ergibt ein relatives Maximum bei Glu und Asp, Pyruvaten und Glycin, resp. Tyrosin. Das Spektrum ist analog zu den Literaturdaten von modernen Automikriten aus Riffhöhlen von Lizard Island (GBR) und unterscheidet sich grundlegend von den strukturgebundenen Skelett-Automikriten von Bacinella/Lithocodium. Die Biomarker-Analyse akkretionärer Automikrite ergab ein spezifisches n-Alkan Muster, ebenfalls vergleichbar mit Spektren rezenter Thrombolithe (Lizard Island) und Beispielen der oberjurassischen Spongiolith-Fazies. Die Grundvoraussetzung der Mud Mound-Genese ist daher die Bereitstellung saurer Makromoleküle (Organomikrit) und eine anhaltend ungestörte Wechselwirkung mit dem umgebenden Medium. Die chemische Randbedingung ist eine erhöhte Karbonatalkalinität. Nach mikrofaziellen Kriterien ist Organomikrit ein faziesbrechendes Element der unterkretazischen Plattformränder. Beispiele reichen von karbonatischen Barrensanden mit Organomikrit-Rindenkörnern, über deltaische Sandsteine (Organomikrit um Quarz) bis zu Kondensationshorizonten auf Paläokarst sowie Drowning-Sequenzen auf Korallenpflastern (Sclercatinia zu Kalkalgen zu Thrombolith). Die Bildung der Mud Mounds (Organomikrit-Riffe) der Soba-Region ist korreliert mit einer regional extrem herabgesetzten Karbonatproduktion. Diese durch terrigenen Input und mögliche Eutrophierungen verursachten Produktionskrisen setzten die relativ uneffektive Organomikritproduktion in Vorteil gegenüber den stenoöken Gemeinschaften der euphotischen Zone. Die erhöhte Karbonatalkalinität kann von der Zufuhr der Verwitterungslösungen (regional) und dem Abau organischer Substanzen abgeleitet werden (lokal, Sulfatreduktion). Möglicherweise bestand ein Zusammenhang mit der Auslaugung von Keuperdiapiren.At the western margin of the Vasco-Cantabrian Basin (Soba-Region, Prov. Cantabria, N-Spain) the primary facies architecture of the Aptian-Albian platform/basin transition is well preserved. Along these zones large-scaled mud mounds reach 70 meters in height with a basal diameter of up to 150 meters. Aim of this work is to point out processes that are limited to coexistance and such that influence or even control mud mound formation. The Upper Aptian (Clansayesian) to Middle Albian interval consists of six sedimentary-diagenetic cycles that represent asymmetric transgressive/regressive facies sequences. In combination with marker horizons these cycles provide a stratigraphic control across the platform/basin transition. Sea-level changes recorded as paleokarst are documented in the Aptian/Albian boundary interval and within the upper parts of the Lower Albian (ammonite zone: Douvilleiceras mammilatum). Mud Mounds follow transgressive discontinuities of facies. These structures are both located at slopes facing wave-induced current systems and at the upper platform margin. The involved biofacies include an aphotic community with lithistid demosponges, hexactinellids, encrusting foraminifera, polychaetes, thecidean brachiopods and acanthochaetetids as well as a photic community with scleractinian corals, calcareous algae such as Lithophyllum and the problematic structure of Bacinella/ Lithocodium. Mud mounds are constructed by autochthonous production of micrite (automicrite). Accretionary automicrites form stromatolites and thrombolites as well as massive fabrics. Container-automicrite is restricted to protected and closed spaces. Container-automicrites of siliceous sponges reveal aphanic, peloidal and peloidal-bacterioform microfabrics. However, container-automicrite may also occur within minicaves, pockets and the interstitial space of rudstones lacking any sponge evidence. These automicrites consist of in-situ peloids and in-situ ooids forming massive and/or stromatolitic microfabrics. All automicrites, variously developed, hold 50 to 80 % of the total mud mound volume. Borings by lithopagous bivalves and sponges (Aka) and additionally the exclusive occurrence of angular mound lithoclasts provide evidence for lithification in statu nascendi. The primary mineralogy of the automicrites is high Mg-calcite with residual MgCOa-contents between 1.2 and 3.6 mole-%. The composition of stable isotopes (S13C and S18O vs. PDB) goes along with inorganically precipitated marine cements (813C: 2.9 to 3.8, S18O: -1,5 to -4). The comparative analysis of amino acid quantity reveals relative maxima of glutamin and asparagin, pyruvates and glycin as well as tyrosin. The relative amounts of amino acids are very similar to those obtained from modern automicrites of Lizard Island reef caves (GBR) and are clearly seperated from skeletal automicrites of Bacinella/ Lithocodium. In addition, biomarker analysis of accretionary automicrites resulted in a specific n-alkane pattern comparable to literature data of modern marine thrombolites (Lizard Island) and Upper Jurassic spongiolites. According to these results, the basic neccessity for mud mound genesis is the occurrence of acidic macromolecules producing a specific automicrite (organomicrite) and their persistent interaction with thesurrounding medium. Chemically, an increased carbonate alkalinity is required. Thin section analysis provides evidence that organomicrite is a widespread element of Lower Cretaceous platform margins overlapping different facies zones. These include carbonate shoal sediments with organomicrite-coated grains and deltaic sandstones with organomicrite-coated quartz grains. Further examples are intervals of stratigraphic condensation overlaying paleokarst or drowning sequences following a succession from scleractinian corals towards calcareous algae and thrombolites. On the regional scale mud mounds (organomicrite reefs) of the Soba-Region correlate with times of drastically reduced carbonate production. This, potentially caused by terrigenous input and episodes of eutrophism, leads to a dominance of the relatively ineffective production of organomicrite over the highly productive stenotopic (euphotic) communities. An increase of carbonate alkalinity can be deduced from regional scale continental weathering and from sulfate reduction on local scale. Possibly, a correlation between brines of subsoluted diapirs (Keuper) and the formation of automicrites might have existed.thesisDFG, SUB Göttinge

Karbonatbänke mit Lithocodium aggregatum Elliott, Bacinella irregularis Radoicic ; Paläobathymetrie, Paläoökologie und stratigraphisches Äquivalent zu thrombolithischen Mud Mounds

Aus dem Unter-/Mittelalb von Nordspanien wird ein Profil mit bis zu 8 m mächtigen Lithocodium/ Bacinella Boundstones vorgesteUt. Die mikrofaziell-sedimentologische Analyse des Profils crgibt für die Lithocodium/ Bacinella Bänke eine bathymetrische Position vom tieferen Subtidal bis flachsten Subtidal/lntertidal. Die maximale Tiefenposition ist an die photische Zone gebunden, die wiederum durch das Ausmaß toniger Suspensionen beeinflußt wird. Die bathymetrische Obergrenze ist mechanisch kontrolliert (z.B. WeUenenergie, Tidenströme). Lithocodium/Bacinella ist zusammen mit anderen Algen/Mikroben ein charakteristischer Bestandteil thrombolithischer Mud Mounds (z.B. Gandara Mound). Die funktionelle Rolle von Lithocodium/Bacinella bei der Mud Mound Genese umfaßt Baffling und Binding, AutomikritProduktion durch Kalzifizierung innerhalb organischer Schleimhüllen und eine Mikritproduktion über intensive Bohraktivitäten an eingelagerten karbonatischen Hartteilen. Das massenhafte Auftreten von Lithocodillm/ Bacinella und diversen Algen/Mikroben kann mit einer längerfristigen Eutrophierung des Lebensraumes oder mit Schwankungen der Karbonat-Alkalinät des Meerwassers erklärt werden.A section including Lithocodium/ Bacinella boundstones with a thickness of up to 8 m is reported from the Lower /Middle Albian of northern Spain. According to microfacies and sedimentological analyses the bathymetric position of the Lithocodium/ Bacinella banks ranges from deeper subtidal to shaUowest subtidal/intertidal conditions. The maximum depth is related to the photic zone, which ,itself is controled by the amount of muddy suspension. The upper bathymetric limit is mechanically defin'ed and corresponds to increased depositional energy (i.e. waves and tidal currents). Together with other algae and microbes Lithocodium/ Bacinella is a major constituent of thrombolitic mud mounds (Gandara mound). In the context of mud mound genesis the functional role of Lithocodium/ Bacinella includes baffling and binding, the production of micrite via the calcification inside of mucilagenous sheaths, and via intensive boring activities upon and inside of skeletal hardparts. The mass occurrence of Lithocodium/ Bacinella with associated algae and microbes may be explained by a longer ranging eutrophism of the environment or by shifts in seawater carbonate alkalinity

Controlling factors and environmental significance of organomicrite production and buildup development

researc

Microbial carbonate crusts - a key to the environmental analysis of fossil spongiolites?

Morphological and geochemical comparisons between modern cryptic microbialites from Lizard Island/Great Barrier Reef and fossil counterparts in the Upper Jurassic (Southern Germany, Dobrogea/Romania) and late Lower Cretaceous (Aptian/ Albian from Cantabria/Spain) spongiolitic environments show that there are common factors controlling the crust formations mostly independent of light despite of diverging (paleo-) oceanographic positions as well as relationships of competitors. Factors such as increased alkalinity ,oligotrophy, and reduced allochthonous deposition are of major importance. Thrombolitic microbialites are interpreted as biologically induced and therefore calcified in isotopic equilibrium with the surrounding sea water. Corresponding with shallowing upward cycles, microbial mats which produce stromatolitic peloidal crusts become more important. Different biomarkers are introduced for the first time extracted and analyzed from spongiolitic limes tones ofLower Kimmeridgian age from Southern Germany

IGCP 380 field workshop October 24 - November 1,1999

excursionguid

Keratose sponges in ancient carbonates – A problem of interpretation

peer reviewedReports of diverse vermiform and peloidal structures in Neoproterozoic to Mesozoic open marine to peritidal carbonates include cases interpreted to be keratose sponges. However, living keratose sponges have elaborate, highly elastic skeletons of spongin (a mesoscopic end-member of a hierarchical assemblage of collagenous structures) lacking spicules, thus have poor preservation potential in contrast to the more easily fossilized spiculebearing sponges. Such interpreted fossil keratose sponges comprise diverse layered, network, amalgamated, granular and variegated microfabrics of narrow curved, branching, vesicular–cellular to irregular areas of calcite cement, thought to represent former spongin, embedded in microcrystalline to peloidal carbonate. Interpreted keratose sponges are presented in publications almost entirely in two-dimensional (thin section) studies, usually displayed normal to bedding, lacking mesoscopic three-dimensional views in support of a sponge body fossil. For these structures to be keratose sponges critically requires conversion of the spongin skeleton into the calcite cement component, under shallow-burial conditions and this must have occurred prior to compaction. However, there is no robust petrographic–geochemical evidence that the fine-grained carbonate component originated from sponge mummification (automicritic body fossils via calcification of structural tissue components) because in the majority of cases the fine-grained component is homogenous and thus likely to be deposited sediment. Thus, despite numerous studies, verification of fossil keratose sponges is lacking. Although some may be sponges, all can be otherwise explained. Alternatives include: (i) meiofaunal activity; (ii) layered microbial (spongiostromate) accretion; (iii) sedimentary peloidal to clotted micrites; (iv) fluid escape and capture resulting in bird’s eye to vuggy porosities; and (v) moulds of siliceous sponge spicules. Uncertainty of keratose sponge identification is fundamental and far-reaching for understanding: (i) microfacies and diagenesis where (ii) fossil assemblages; and (iii) wider aspects of origins of animal clades, sponge ecology, evolution and the systemic recovery from mass extinctions. Thus, alternative explanations must be considered