Platform-derived Sediment Research Articles

Tectono-sedimentary evolution of a fossil ocean-continent transition: Tasna nappe, central Alps (SE Switzerland)

AbstractMagma-poor ocean-continent transitions at distal rifted margins record complex stratigraphic interactions engendered by extreme crustal thinning and mantle exhumation. The Tasna ocean-continent transition, exposed in the Middle Penninic Tasna nappe in eastern Switzerland, is so far the only known example where the lateral transition from continental crust to exhumed serpentinized mantle lithosphere is exposed and not overprinted by later Alpine deformation. This paper presents sedimentological, structural, and petrographical observations and detrital zircon provenance data to document: (1) the processes controlling continental hyperextension and mantle exhumation; and (2) the facies, depositional systems, sediment sources, delivery pathways, and depositional stacking patterns associated with magma-poor ocean-continent transitions. Our results show that the basement units of the Tasna ocean-continent transition are composed of prerift upper and lower crust and subcontinental mantle rocks juxtaposed as part of the continental crustal thinning process. The absence of pervasive, synrift deformation in the lower-crustal rocks indicates that the thinning was likely achieved by deformation along localized shear zones before being exhumed at the seafloor by brittle, late extensional detachment faulting and not by any form of lower-crustal flow.The age of the first sediments deposited on the continental crust and exhumed mantle, the so-called Tonschiefer Formation, is considered to be Late Jurassic. A key observation is that the restored morpho-tectonic and sedimentary evolution of the Tasna ocean-continent transition shows the intercalation of downdip, transported platform-derived sediments and along-axis–derived siliciclastic sediments originating from the recycling of prerift sediments, local basement, and/or extra-Alpine sources.

The palaeoceanographic crisis of the Early Aptian (OAE 1a) in the Vocontian Basin (SE France)

The Vocontian Basin (SE France) which presents lower Aptian expanded successions characterized by major lithological changes, is particularly suitable to determine palaeoenvironmental changes occurring across the OAE 1a. A multidisciplinary study (sedimentology, CaCO3, TOC, carbon and oxygen stable isotopes, micropalaeontology, cyclostratigraphy) was carried out in the Notre-Dame-de-Rosans section in order to establish a detailed chronological framework of these changes. The OAE 1a corresponds to carbon isotope segments C3–C6, and it lasted for 1.2 Myr. A first drop in the carbonate production occurs 500 kyr before the OAE 1a (upper part of the carbon isotope segment C2), and could result from both onset of “Urgonian” carbonate platform demise and associated reducing export of platform-derived sediments into the basin, and nannoconid crisis. A second drastic drop (crash) in the carbonate production is recorded within the lower part of the OAE 1a (latter part of segment C3 to C5) and is explained by a strong dissolution. This study then shows that the onset of the major carbonate crisis, that occurs before the OAE 1a, could be due to both rise in sea-level and in marine surface water fertility, whereas its “acme” that occurs within the OAE 1a, could be related to CO2-induced ocean acidification. Black shales of the “Niveau Goguel” occur in the upper part of the OAE 1a and represent the lower part of segment C6. Surface-waters primary producers are principally represented by cyanobacteria, whereas nannofossil primary productivity is reduced, and deep-water anoxia prevailed during the deposition of “the Niveau Goguel”. The last 300 kyr of the OAE 1a are characterized by a partial recovery of both nannofossil primary productivity and pelagic carbonate production, which sharply increase just after the end of the event. This study also shows that organic-rich layers associated to the OAE 1a are diachronous in the Tethyan realm.

Carbonate slope morphology revealing sediment transfer from bank-to-slope (Little Bahama Bank, Bahamas)

New high-quality multibeam and high-resolution seismic data reveal new observations on sediment transfer and distribution and margin morphometrics in the uppermost slope of Northeastern Little Bahama Bank between 20 and 300 m water depth. The echofacies/backscatter facies show an alongslope sediment distribution forming successive strips. The upper part of the uppermost slope corresponds to the alternation of several submerged coral terraces and escarpments that could be related to Late Quaternary sea-level variations. The terraces could either be related to periods of stagnating sea-level or slow-down in sea-level change and therefore increased erosion by waves, or periods of accelerated sea-level rise since the Last Glacial Maximum. Terraces could therefore be related to coral construction and drowing. The medium part corresponds to the marginal escarpment, a steep cemented area. The lower part of the uppermost slope shows a discontinuous Holocene sediment wedge with varying thickness between 0 and 35 m. It is separated from the upper part by a zone of well-cemented seafloor associated with the marginal escarpment. Passing cold fronts result in sediment export caused by density cascading. The associated sediment fall-out and convective sedimentation can generate density currents that form this wedge and eventually flow through linear structures on the upper slope. The survey reveals the presence of recently active channels that extend over the entire uppermost slope and interrupt the wedge. The channels connect shallow tidal channels to submarine valleys connected to the proximal part of canyons. They directly feed the canyons with platform-derived sediment forming low-density turbidity currents and could supply the deepest part of the system with coarse-grained sediment directly exported from the carbonate platform.

Discovery of the Late Triassic (Middle Carnian–Rhaetian) radiolarians in the volcano-sedimentary sequences of the Kocali Complex, SE Turkey: Correlation with the other Tauride units

The Kocali Complex in SE Turkey includes pelagic sediments (pelagic limestones, cherts, etc.), basic volcanic rocks of oceanic crust origin together with platform-derived sediments. Its depositional age was previously assigned as Late Jurassic–Early Cretaceous. In order to study the radiolarian contents of volcano-sedimentary sequences in this complex, six stratigraphic sections have been measured mainly at the NE and NW Adiyaman city. Radiolarian faunas from these stratigraphic sections reveal that the age of these sequences ranges from middle Carnian to Rhaetian. Based on these data, the depositional age of the complex is older than the previously assigned. Lithological characteristics (widespread Triassic basic volcanic rocks associated with pelagic sediments) and radiolarian contents of these sequences have close similarities with the sequences of the Alakircay Nappe of the Antalya Nappes in western and central Taurides. Based on taxonomic studies, 99 taxa have been determined of which one genus ( Adiyamanium) and four species ( Monocapnuchosphaera kocaliensis, Paronaella speciosa, Ferresium okuyucui and Adiyamanium crassum) are described as new.

The effect of syndepositional deformation within the Upper Permian Capitan Platform on the speleogenesis and geomorphology of the Guadalupe Mountains, New Mexico, USA

The Guadalupe Mountains in New Mexico and Texas are home to more than 300 caves. Caves have been formed within the Upper Permian Capitan carbonate platform and are oriented along two structural trends, one of which is parallel to the platform margin and the other of which is roughly perpendicular to it. Our recent studies of the Capitan Platform have identified syndepositional faults associated with growth monoclines and synclines in Slaughter Canyon, New Mexico, and these are also parallel to the platform margin. In this study, we demonstrate that syndepositional faults and folds are also present in Rattlesnake and Walnut Canyons, as much as 19 km along strike, and that they have exerted control on karstification of the Guadalupe Mountains from the Upper Permian until present. Three distinctive episodes of karst formation have been recognised in outcrops on the basis of karst-filling deposits and crosscutting relationships. The syndepositional “Phase 1 karst” was formed along syndepositional faults and fractures and is filled by platform-derived sediments. The burial “Phase 2 karst” is filled by post-Permian siliciclastics and is limited to the youngest syndepositional faults and fractures that penetrate the platform in the proximity of its terminal margin. Connectivity of these youngest faults and fractures to the platform top and the overlying stratigraphy is inferred to have controlled the distribution of the Phase 2 karst. The “Phase 3 karst” includes the present cave systems, which were mainly formed by sulphuric acid produced by mixing of fossil and fresh underground waters in conjunction with the uplift of the Guadalupe Mountains in the Late Tertiary, and have since been modified by vadose karst processes. The Phase 3 karst caves are not solely developed along syndepositional faults and fractures as the earlier karst palaeocaverns are, but also follow another, uplift-related, structural trend. Syndepositional folds, faults, and fractures in the Capitan Platform have influenced the shaping of the modern surface geomorphology of the Guadalupe Mountains by controlling drainage and, hence, erosion. Trellis drainage parallel to the platform margin is developed where syndepositional folds, faults, and fractures occur. The morphology of the trellis drainage varies systematically across the range in response to the character of the deformation structures and karst features along which the drainage channels have developed.

Heterogeneity in Fill and Properties of Karst-Modified Syndepositional Faults and Fractures: Upper Permian Capitan Platform, New Mexico, U.S.A.

Abstract This study examines the heterogeneity in properties of syndepositional faults and fractures found in the Upper Permian Capitan carbonate platform, Guadalupe Mountains, New Mexico. Syndepositional faults and fractures grew incrementally, and were repeatedly exploited by early karst as the platform developed. Primary fault and fracture rocks were preferentially dissolved to form structure-controlled paleocaverns, which were subsequently filled with platform-derived sediments. These are divided here into three groups: (i) carbonate-dominated, (ii) siliciclastic-dominated, and (iii) mixed carbonate-siliciclastic lithologies. The affinity of the paleocavern-filling deposits to platform strata permits linking of the different fill types to different stages of sea-level cycle. Consequently, periods of dissolution and deposition within paleocaverns can be tied to the platform's sequence stratigraphy. Paleocavern-filling sediments have a distinct vertical stratigraphy, and are observed to vary with distance from the platform margin over a distance of 2.6 km. Their distribution is thus to some extent predictable. Vertical and lateral variability in paleocavern fill is chiefly related to siliciclastic-filled karstic chimneys that narrow downwards and tend to become more frequent and laterally extensive upwards. This is because upper structural levels of fault and fracture zones were more frequently opened by early karst, and also because siliciclastics are not prone to dissolution, whereas carbonates are. Across platform, karst-modified faults and fractures located close to the platform margin are dominated by carbonate lithologies. The proportion and vertical penetration of siliciclastics increases with distance from platform margin. These patterns appear to reflect variations in the frequency and duration of subaerial exposure events across the basinward-inclined Capitan platform. The results of this study have implications for understanding properties of early faults and fractures in carbonate strata. Faults and fractures presented here are heterogeneous, and the heterogeneity is related principally to distribution of sedimentary rocks within paleocaverns developed along them. As a consequence, their properties are not related to dimensions or throw, as is the case for faults and fractures within siliciclastic rocks. Data and interpretations presented here have implications for Capitan hydrocarbon reservoirs, and can be applied to characterization of faults and fractures in other carbonate platforms subjected to early deformation.

Bypass Margins, Basin-Restricted Wedges, and Platform-to-Basin Correlation, Upper Devonian, Canadian Rocky Mountains: Implications for Sequence Stratigraphy of Carbonate Platform Systems

ABSTRACT Carbonate platforms can commonly keep up with relative sea-level rise because of high rates of sediment accumulation and platform aggradation. Surrounding basinal environments are commonly starved but can receive variable extrabasinal siliciclastic input and episodically deposited carbonate sediment. If accumulation rates in basinal settings lag behind those of the platform, a bypass or erosional margin can develop. Under these circumstances platform and basin depositional sequences become physically detached and direct correlation of basinal and platform sequences is hindered. We report here the results of high-resolution stratigraphic analyses of two Upper Devonian isolated carbonate platforms in western Alberta that provide insight into the sequence stratigraphy of bypass margins and criteria for accurate correlation of platform and basinal sequences. The slope and basin sequences surrounding the Miette and Ancient Wall platforms consist of basin-restricted, onlapping wedges of fine-grained background sediment deposited dominantly from suspension and coarse-grained platform-derived sediment redeposited by a variety of gravity-flow mechanisms. Sequence boundaries are identified within the redeposited carbonate intervals. Identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal facies was based on the geometry, mineralogy, and clast content of redeposited carbonate units. Highstand carbonates contain sheet-like debris flows and turbidites with abundant slope-derived clasts and background facies with high total carbonate content. Lowstand carbonates contain sheet-like and channelized debris flows and turbidites with abundant platform-derived clasts and background facies with low carbonate content and locally high amounts of organic carbon. Transgressive facies are dominated by initially carbonate-poor and organic-rich background sediments that display a progressive increase in carbonate content and decrease in organic carbon content. These patterns are interpreted to record abundant background carbonate sedimentation during late transgression and highstand when the carbonate factory was robust. Highstand redeposited carbonates record slope erosion due to oversteepening and slope readjustment processes. Lowstand redeposited carbonates indicate platform and platform-margin erosion and low background carbonate sedimentation when the platform was either exposed or under very shallow peritidal conditions. High siliciclastic and organic contents during lowstand and early transgression may partly be the result of reciprocal sedimentation but alternatively may represent continuous siliciclastic supply during times with little dilution by fine-grained carbonate sediment. Successive stages of platform development at Miette and Ancient Wall were controlled by accommodation changes driven by relative sea-level fluctuations. Backstripping analyses of strata from both platforms confirm that significant differential subsidence was a major control on variations in platform thickness and patterns of slope development. Greater subsidence at Ancient Wall fostered the development of a steeper bypass margin and different slope evolution compared to Miette. Slope oversteepening also initiated a process of slope readjustment that eventually reduced the platform-to-basin gradient and facilitated regressive platform progradation. In conventional siliciclastic sequence stratigraphy, basin-restricted wedges are interpreted as lowstand deposits on the basis of their geometry and position relative to an updip margin. Wedge-shaped basinal units along the Miette and Ancient Wall bypass margins contain both highstand and lowstand facies that straddle sequence boundaries. The results of this study provide objective criteria for differentiating systems tracts in carbonate slope and basin environments through mineralogic and compositional analyses providing more accurate correlation of detached platform and basin sequences. Interpretation of carbonate basin-restricted wedges as purely highstand or lowstand deposits may lead to erroneous conclusions regarding sequence stratigraphy, platform-to-basin correlation, and the volumetric partitioning of sediments deposited in different systems tracts.

Deep-Water Stromatolites, Canning Basin, Northwestern Australia

Deep-water stromatolites are a conspicuous facies in the fore-reef successions of the Upper Devonian reef complexes of the northern Canning Basin. Stratigraphic analysis shows that the stromatolites are present in a diverse range of sedimentological associations which precludes using their distribution to indicate only transgressive or only regressive conditions during reef evolution. All the stromatolites grew at localities where little or no platform-derived sediment could be deposited, either because no sediment was being supplied from the platform or the stromatolites grew at sites protected from sediment gravity-flow deposition. The latter enabled some stromatolites to grow during times of high productivity on the platform (i.e., during high-stands). For example, bioherms developed on downslope sides of allochthonous blocks, near-vertical eroded platform margins, eroded pinnacles, and basement topographic highs, until buried by fore-reef sediment. Other bioherms and biostromes grew on open slopes when little platform-derived sediment was being deposited during times of lowered relative sea level (i.e., lowstand and transgressive systems tracts). These stromatolites record depositional breaks during carbonate or siliciclastic sedimentation, and are typically accompanied by other facies indicative of very slow sedimentation or slope reworking (i.e., bioturbated limestones and intraclastic breccias). Water depths and growth rates remain poorly constrained; however, consideration of stromatolite accumulation within a sequence-stratigraphic framework suggests rates of at least 50-100 microns/year. Although this is a minimum rate, it represents a substantial increase on previous estimates of a few microns/year.

Controls on Early Cretaceous Carbonate Platform Margin Development: Northeastern Gulf of Mexico: ABSTRACT

A seismic stratigraphic analysis of approximately 3000 km of multifold reflection data correlated to available geologic information documents the development of an Early Cretaceous carbonate platform margin in the De Soto Canyon area of the northeastern Gulf of Mexico. During the Jurassic(.), inferred oceanic and thin transitional crust underlying the Gulf subsided and formed a flexure zone on which the Early Cretaceous margin developed. By the late Aptian to late Albian, two types of margin morphologies evolved in response to different paleogeographic settings. Northwest of De Soto Canyon, a gently dipping accretionary slope morphology formed as a result of its proximity to a terrigenous clastic province. Seawater turbidity and chemistry probably inhibited buildup formation on this leeward margin, thus allowing both carbonate and siliciclastic sediments to be transported from the platform interior to the adjacent slope. Southeast of De Soto Canyon, the carbonate province was cleaner and a steeply dipping bypass slope morphology formed due to the development of robust buildups that probably limited downslope deposition of platform-derived sediments, thereby gradually starving the adjacent basin. Total tectonic subsidence profiles across both types of margin morphologies show steeper gradients associated with the bypass slope morphology, suggesting that differential subsidence rates contributedmore » to the development of the margin's morphology and may reflect the margin's proximity to the oceanic-continental crust boundary. In the late Albian, the platform interior drowned in response to a pronounced fluctuation in short-term eustatic sea level superimposed on a long-term rise. Buildups continued to form at the margin, however, until they drowned in the middle Cenomanian due to another big change in short-term eustatic sea level combined with down-to-basin faulting and the continuing long-term rise.« less

Influence of Platform-Derived Sediment on Facies, Diagenesis, and Deformation in Slope and Basinal Deposits, Tongue of The Ocean, Bahamas: ABSTRACT

Influence of Platform-Derived Sediment on Facies, Diagenesis, and Deformation in Slope and Basinal Deposits, Tongue of The Ocean, Bahamas: ABSTRACT

Distribution and Geologic Significance of Microboring Organisms Within Sediments of the Arlington Reef Complex, Australia

Surface sediments from 120 locations surrounding the Arlington Reef Complex of the Great Barrier Reef of Australia were examined to determine the types and relative abundances of microborers present, to describe the morphology of their excavations, and to plot and interpret their distributional patterns. The most widespread and abundant microborings found within carbonate particles were those produced by fungi, which appear to be among the first endolithic organisms to attack skeletal debris. A characteristic branching red(?) alga was found to be most abundant at depths in excess of 60 ft (18 m), although it was not restricted to these depths. However, a distinctive endolithic sponge was found only at depths below 60 ft (18 m) and may prove valuable as a paleoecologic guide. An 8- to 10-μ green alga actively infests carbonate particles of the interior reef platform to depths as great as 100 ft (30 m), although it is generally more abundant at shallower depths. This endolithic alga serves both as a photic zone indicator and sediment tracer within the study area. Its distribution within sediments indicates that net transport is landward from the interior reef platform with little or no sediment being carried seaward. Southward movement of platform-derived sediment along the back-reef axial channel is also suggested. Endolithic organisms were observed to infest preferentially molluscan fragments, thereby selectively removing them from the carbonate fraction. The distribution and spatial relationships of endolithic organisms within Arlington Reef Complex sediments suggest that microborers may be useful as relative depth indicators in recent, and possibly ancient, carbonates.