Cessation of Grand Cycle Deposition in the Framework of Passive Margin Evolution: Controlling Mechanisms and Effects on Carbonate Deposition and Diagenesis, Cambrian Maynardville Formation, Southern Appalachians

The Middle and Upper Cambrian deposits of the southern Appalachians reveal the existence of a broad carbonate platform that was facing the Iapetus Ocean to the east and was separated from the exposed craton to the west by the Conasauga intrashelf basin. This study focuses on the Maynardville Formation, which was deposited during the early Late Cambrian along the western carbonate platform margin. As the uppermost carbonate unit of the alternating shale and carbonate units or Grand Cycles of the Conasauga Group (Middle to Upper Cambrian), the Maynardville marks a change in style of passive-margin deposition reflected in the cessation of Grand Cycle deposition. The Maynardville is a transitional interval between the largely subtidal carbonate and siliciclastic deposits of the Conasauga Group, and the peritidal carbonate deposits of the overlying Knox Group (Upper Cambrian to Lower Ordovician). The Maynardville consists of a lower subtidal package, underlain by the Nolichucky Shale, and an upper peritidal package, overlain by the Copper Ridge Dolomite. Mixed carbonate/siliciclastic deposition took place in a deep ramp (upper Nolichucky) to shallow-ramp and lagoonal (subtidal Maynardville) setting. To the east was a broad, semi-arid carbonate tidal flat with a variety of peritidal environments (upper Maynardville/Copper Ridge). The Nolichucky represents a retrogradational depositional package that formed in response to an increase in the rate of relative sea-level rise. Deposition of a shallowing-upward succession of the Maynardville reflects carbonate platform aggradation and progradation favored by a subsequent decrease in the rate of relative sea-level rise. Stacking patterns of the Maynardville are a result of the interplay between intrinsic factors of carbonate depositional systems, the mechanisms related to the history of the adjacent siliciclastic basin, and possible eustatic sea-level changes. The cessation of Grand Cycle deposition is a consequence of passive-margin evolution. The abrupt change from carbonate to shale deposition in the Grand Cycles may have been caused by short-term, episodic, non-thermal tectonic subsidence related to active extension and vertical readjustments, enhanced by sediment and water loading, during the immature stage of passive-margin development. These processes were superimposed on eustatic sea-level changes and thermal post-rift subsidence. The transition from an immature to a mature passive-margin setting occurred during deposition of the Maynardville Formation. The mature margin was characterized by the cessation of tectonic activity in the area. Decreased rates of thermal subsidence and the complete infilling of the Conasauga basin favored shallow-water deposition and carbonate platform progradation. The Maynardville grades conformably into the Copper Ridge Dolomite. This conformable interval is interpreted as a sequence boundary zone correlative to the Dresbachian/Franconian (Sauk II!Sauk III) unconformity. This boundary separates a third-order sequence (terminal Grand Cycle), composed of the Upper Shale Member of the Nolichucky and the Maynardville, from the thick peritidal carbonate deposits of the Knox Group, which reflect the final passive-margin stabilization. The transition from the Conasauga into the Knox Group is characterized by a shift in diagenetic patterns. The distribution of early diagenetic phases within the Maynardville was controlled by changes in the depositional setting from a subtidal to a semi-arid tidal flat. The infilling of the Conasauga basin and carbonate platform progradation at the end of Grand Cycle deposition influenced the regional facies distribution, which consequently affected the burial diagenesis of this transitional interval. The subtidal deposits of the Maynardville contain a variety of calcite cements that represent marine, meteoric and burial diagenetic environments. Dolomite is not abundant within these deposits, and it primarily occurs associated with argillaceous layers. The subtidal deposits contain rare ferroan saddle dolomite cement associated with Mississippi Valley Type (MVT) minerals. Pressure dissolution, diagenetic alteration of clay minerals, and pore fluids expelled from interbedded shale, provided a local source for the formation of ferroan dolomite during burial. The presence of MVT minerals suggests the involvement of externally derived diagenetic fluids. The peritidal deposits have been extensively dolomitized. Fine-crystalline penecontemporaneous dolomite formed under sabkha-like conditions. Coarser-crystalline replacement dolomite formed from recrystallization of early dolomite and from dolomitization of limestone during burial. Fenestrae, desiccation and evaporite dissolution voids are occluded with dolomite cement, which is often complexly zoned. Zoned dolomite cement precipitated from modified marine, mixed meteoric/marine, and burial fluids. Saddle dolomite cement in pore-centers, tectonic fractures, and dissolutional voids formed during late burial from warm, basinal fluids associated with the migration of MVT mineralizing brines, and from fluids provided locally by pressure solution. The formation and preservation of Upper Cambrian microbial deposits were controlled by the conditions within the environments of deposition, but were also biotically influenced. Digitate stromatolites and thrombolites formed by calcification of cyanobacteria in lower intertidal and upper subtidal environments, which were not primary sites for dolomitization. Early diagenetic calcification of cyanobacteria reduced the susceptibility of these deposits to dolomitization. Laterally linked hemispheroidal (LLH), vertically stacked hemispheroidal (SH), and columnar stromatolites, as well as most stratiform stromatolite laminae formed by the trapping of sediment in supratidal and intertidal environments on semi-arid tidal flats. Extensive dolomitization altered these peritidal carbonate deposits early in their diagenetic history. The Maynardville Formation records an increase in the 13C/12C ratio of Late Cambrian sea water. Comparison with studies of time-equivalent deposits elsewhere suggests that this positive carbon-isotope excursion is secular in scope. Petrgraphic and geochemical analyses were used to evaluate the extent of variations related to the depositional and diagenetic environments, which are superimposed on the secular marine carbon-isotope trend. This approach enables carbon-isotope variations to be used as a stratigraphic tool, and as an indicator of the global cycling of carbon. The excursion is related to changes in the rate of organic-carbon burial, which can be linked to changes in ocean stratification, climate, sea-level, and paleoproductivity rate. The excursion started during deposition of the Nolichucky Shale, and ended during the deposition of the Copper Ridge Dolomite. The maximum δ13C values (4 to 5 0/00 PDB) are associated with the sequence boundary zone at the Maynardville/Cooper Ridge Dolomite transition. Elsewhere, the excursion started at the base of the Pterocephaliid Biomere (near the base of the Aphelaspis zone). The excursion ended prior to the end of the Pterocephaliid Biomere, with the maximum excursion at the Sauk II/Sauk III unconformity.This supports the correlation between the Late Steptoean (Dresbachian/Franconian) sea-level fall and the sequence boundary at the end of the Grand Cycle deposition, and demonstrates the application of carbon-isotope stratigraphy to successions with poorly constrained biostratigraph

Paleoenvironmental Reconstruction of the Middle Eocene Trieste-Pazin Basin (Croatia) from Benthic Foraminiferal Assemblages

Foraminiferal assemblages from four stratigraphic sections of the Trieste-Pazin basin in central Istria, Croatia (southwestern Tethyan realm) were investigated to reconstruct paleoenvironmental conditions and to determine the age of these deposits. The following five Middle Eocene planktonic foraminiferal zones were identified from the range and frequency of foraminiferal species: Globigerinatheka kugleri/Morozovella aragonensis Zone (E9), Acarinina topilensis Zone (E10), Morozovelloides lehneri Zone (E11), Orbulinoides beckmanni Zone (E12), and Morozovelloides crassatus Zone (E13). A data set of benthic foraminifera relative frequency has been subjected to R- and Q-mode cluster analyses to demonstrate the linkage between taxa distribution and paleoenvironmental gradients. Benthic foraminiferal biofacies indicate that the environment evolved from an initially mesotrophic upper bathyal slope setting towards a deeper, more oligotrophic, middle bathyal setting influenced by turbidity currents. The oligotrophy was a result of the deepening processes, and a consequential decrease in organic flux. The documented short-term periods of eutrophic to mesotrophic conditions within the deeper oligotrophic regime might represent a paleoceanographic influence of water-masses from an adjacent basin to the northwest, thus recording its paleogeographic connection with the Trieste-Pazin basin during the Middle Eocene (Lutetian)

Documentation of Extensive Root Systems of \u3ci\u3eThalassia\u3c/i\u3e Seagrass Along the Banks of Pigeon Creek, San Salvador Island, Bahamas

Reprinted from: Bosiljka Glumac & Michael Savarese (eds.), Proceedings of the 16th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Gerace Research Cente

Stable isotope analysis of Upper Tithonian limestones with dinosaur footprints from Kirmenjak quarry (Istria, Croatia)

The Kirmenjak locality of western Istria, Croatia, represents the oldest evidence of a dinosaur presence on the Adriatic- Dinaridic Carbonate Platform (ADCP). In a quarry at this locality, almost a thousand sauropod footprints are recognized in one distinctive trackbearing horizon within the Upper Tithonian limestones. The stable isotopes of oxygen and carbon, in conjunction with microfacies analysis of carbonate rocks exposed in this quarry, unravel details about the marginal marine or coastal environments in which sauropods left their footprints. Rocks from the trackbearing horizon, and laterally adjacent area, represent intertidal fenestral mudstones that form the top of a shallowing- upward succession, capped with a thin peloidal packstone/grainstone layer and overlain by subtidal mudstone. The formation and preservation of footprints was favoured by short-duration exposure of muddy sediment and its rapid burial beneath more mud. The isotopic composition of the sample from the trackbearing horizon is not substantially different from those of an adjacent area without footprints and from the overlying mudstone. Stable isotope analysis supports petrographic observations that the conditions on the carbonate tidal fl at during formation of rocks with dinosaur footprints were not unique. Documented variations in stable isotope compositions refl ect minor differences in the depositional and diagenetic history of the Kirmenjak quarry succession

New Advances in Long-Term Monitoring of Storm-Deposited Boulder Ridges Along Rocky Shorelines of San Salvador Island, Bahamas

Beginning in January 2012, we have monitored two boulder ridges on San Salvador: Singer Bar Point (SBP, length ~790 m) along the reef- and lagoon-protected northern coast and The Gulf (TG, length ~460 m) on the island’s high-energy southern coast. This long-term monitoring aims at documenting changes in ridge morphology and distribution, and the direction and amount of movement of individual boulders to gain insights into the intensity and effects of storms on these coastal areas. In the initial stage of our investigations, the largest boulders from each site were photographed, GPS-located, measured, and characterized by composition and morphology. Boulders at SBP are generally smaller (15 total; ~150-4000 kg; with most \u3c1500 kg) than those at TG (12 original; ~700-6500 kg; most \u3e1000 kg). Our monitoring surveys from January 2013, 2016, and 2017, after Hurricanes Sandy (October 2012), Joaquin (October 2015), and Matthew (October 2016), respectively, indicated only modest modifications at SBP, and major changes to TG, where we were unable to relocate 2 boulders post- Sandy, and 5 of the 10 remaining original boulders after Joaquin. Two TG boulders, weighing ~1 and 3 tons, were transported inland to the NNW by 20 and 26 meters, respectively during Hurricane Joaquin, and there was significant movement inland of the entire boulder ridge. Even though documentation of boulder movement allows calculation of minimum flow velocity needed to initiate transport, our experience indicated that lack of adequate tagging made it challenging or impossible to relocate individual boulders after major storms. This problem was addressed by the application of RFID (radio frequency identification) tagging in June 2019. With a larger cohort of boulders now tagged, our monitoring program is well established to continue into the future, as passive tags are inductively charged by the reader and can remain operational for decades. Drilling to insert small tags (23 and 32 mm long, and \u3c4 mm in diameter) is minimally destructive and also allows tagging of pebbles and cobbles. This is especially important for monitoring at SBP where large boulders are not moved often or much by waves, but smaller-sized sediment movement is significant during storms

Holocene Tufa-Coated Serpulid Mounds From the Dominican Republic: Depositional and Diagenetic History, With Comparison to Modern Serpulid Aggregates From Baffin Bay, Texas

Ronald D. Lewis and Bruce C. Panuska (eds.) Proceedings of the 11th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Gerace Research Cente

Sphenothallus-Like Fossils from the Martinsburg Formation (Upper Ordovician), Tennessee, USA

Tubular fossils, up to 2 mm in diameter and 60 mm in length, occur rarely in the upper Martinsburg Formation (Upper Ordovician), northeastern Tennessee Appalachians, U.S.A. The fossils are unbranched, straight or slightly bent, occasionally twisted and wrinkled, and not significantly tapered. Orientation of the fossils within shallow-marine tempestites suggests that they represent remains of organisms that were broken, transported, and deposited by storm waves and currents. The fossils are morphologically similar to many of the previously identified species belonging to the genus Sphenothallus, a relatively rare tube-dwelling Paleozoic marine invertebrate. Owing to the limited evidence for distal widening of the tubes, lack of holdfasts, and carbonaceous rather than phosphatic composition, the affinity of these fossils remains uncertain, and we refer to them as Sphenothallus-like

Cenomanian–Turonian Oceanic Anoxic Event (OAE2) Imprint on the Northwestern part of the Adriatic Carbonate Platform and a Coeval Intra-Platform Basin (Istria and Premuda Island, Croatia)

The Cenomanian–Turonian boundary (CTB) on the intra-Tethyan Adriatic Carbonate Platform (AdCP) is generally characterised by a transition between microbially laminated and/or bioclastic limestones to calcisphere-rich massive limestone with bioturbated intervals, organic-rich interbeds, firmgrounds, as well as neptunian dikes, carbonate turbidites, tempestites and slumped structures. Compilation of the results from two study sites in the northwestern part of the AdCP and from previous research (on Istria Peninsula and islands in the Adriatic Sea in Croatia) provides a more complete overview of geological events and paleoenvironmental conditions that transformed the formerly contiguous shallow-marine environments during this time period. For the first time, a comparison between protected inner-platform area (Barban section) and a coeval intra-platform basin (Premuda Island section) during the CTB was made. This study utilized a combination of litho-, bio-, and microfacies studies with SEM, EDS, TOC, δ13C and δ18O stable isotope analyses. The stratigraphic successions start with shallow-marine carbonate deposits of the Milna Formation that is conformably overlain by the drowned-platform deposits of the Sveti Duh Formation on the platform and by the Veli Rat Formation in the contemporaneously developed intraplatform basin. These deposits are in turn overlain by the Gornji Humac Formation, which represents re-establishment of shallow-marine depositional systems on the AdCP, whereas the deeper water environment persisted in the intra-platform basin until the Santonian. Despite diagenetic modifications of shallow-marine carbonate deposits, the results of TOC and stable isotope analyses indicate the influence of global Oceanic Anoxic Event 2 (OAE2). Combination of local and regional synsedimentary tectonics and global Late Cretaceous sea-level changes accompanied by anoxic and hypoxic conditions, extinction of numerous benthic foraminifera, diversification and expansion of planktonic foraminifera and calcareous dinoflagellates, provide new insights into the character of the CTB interval in this part of the Tethyan realm

Climatic Cycles Recorded in the Middle Eocene Hemipelagites from a Dinaric Foreland Basin of Istria (Croatia)

Middle Eocene hemipelagic marls from the Pazin-Trieste Basin, a foreland basin of the Croatian Dinarides, display repetitive alternations of two types of marls with different resistance to weathering. This study focuses on the chemical composition, stable isotopes, and palynomorph content of these marls in order to better understand the nature of their cyclic deposition and to identify possible paleoenvironmental drivers responsible for their formation. The less resistant marls (LRM) have consistently lower carbonate content, lower δ18O and δ13C values, and more abundant dinoflagellate cysts than the more resistant marls (MRM). We interpret these differences between the two marl types to be a result of climatic variations, likely related to Milankovitch oscillations. Periods with wetter climate, associated with increased continental runoff, detrital and nutrient influx produced the LRM. Higher nutrient supply sparked higher dinoflagellate productivity during these times, while reduced salinity and stratification of the water column may have hampered the productivity of calcareous nannoplankton and/or planktonic foraminifera. In contrast, the MRM formed during dryer periods which favoured higher carbonate accumulation rates. This study provides new information about the sedimentary record of short-scale climate variations reflected in wet-dry cycles during an overall warm, greenhouse Earth

Cylindrical Mega-Voids in Quaternary Aeolianites, Little Exuma Island, The Bahamas: Georadar Response

In addition to karst features, tropical carbonates contain a wide range of smaller cylindrical voids (“pipes”) attributed to bioturbation, tree molds, or dissolution, among others. During geophysical investigation of the Little Exuma Island, The Bahamas, several sites with enigmatic voids were investigated using a high-frequency ground-penetrating radar (GPR) imaging. The aim of the paper is to assess the feasibility of GPR to detect voids within lithified Holocene calcarenites of the Hannah Bay Membe