%0 Journal Article %J Palaeogeography, Palaeoclimatology, Palaeoecology %D 2011 %T Mudrock Sequence Stratigraphy: A Multi-proxy (Sedimentological, Paleobiological, Geochemical) Approach, Devonian Appalachian Basin %A C. A. Ver Straeten %A C. Brett %A Sageman, B. B. %K Acadian Orogeny %K Appalachian Basin %K Devonian %K Geochemical proxies %K Mudrocks %K sequence stratigraphy %X

Delineation of stratigraphic sequences and their component systems tracts in mudrock-dominated facies is generally difficult due to the relatively homogenous, fine-grained nature of the strata. In this study, we apply a multi-proxy analytical approach to a thick Devonian mudrock-dominated succession through detailed analysis of sedimentologic, paleobiologic, and geochemical data through 600 m of mudrock-rich facies. Varied combinations of proxies prove to be most useful in delineating sequence development in anoxic-, dysoxic-, and oxic-dominated mudrock settings, and in mixed mudrock–carbonate and mixed mudrock–sandstone successions. These interpretations are tested against an established sequence stratigraphic framework for 11 Middle to Upper Devonian (mid-Eifelian to lower Famennian) sequences in the Appalachian Basin. The sequences presented here further detail and refine global Devonian T–R cycles Id to IIe of the well known Johnson, Sandberg and Klapper sea-level curve.

The usefulness of proxies in delineating depositional sequences and systems tracts varies dependent on depositional, paleoceanographic, paleoecologic, and early diagenetic conditions. Those proxies that show a range of variations in specific settings, such as grain size, degree of bioturbation, and concentrations of TOC and elements/elemental ratios (e.g., CaCO3, Al, Ti, Mg, Sc, Si, Mo, Ni, V; Si/Al and Ti/Al) may help delineate depositional dynamics related to redox conditions, condensation, dilution, and clastic, biologic, and/or authigenic sediment sources.

In fine-grained, anoxic-dominated facies, interpreted to represent basinal settings, sequences and systems tracts are best delineated by anoxic-related proxies TOC and Mo. In intermediate, dysoxic-dominated settings, TOC, Mo, bioturbation, and Al remain effective indicators of sequence development. In relatively oxygenated, mudrock-rich and carbonate poor sequences, bioturbation may function as the most effective proxy for recognizing systems tracts.

For mixed fine-grained siliciclastic–carbonate successions, concentration and type of CaCO3 (e.g., benthic macroskeletal, pelagic styliolinid/dacryoconarid, and micritic/calcisilt) are useful in identifying position within cycles. In more proximal, carbonate-poor successions, fine- and coarse-grained fractions become increasingly differentiated; these can be distinguished by relatively high Si/Al ratios (Si/Al ≥ ca. 5).

Elemental ratios indicative of coarser clastic input (e.g., Si/Al, Zr/Al and Ti/Al) are applicable to identifying position with a sequence, but they may also be affected by input from eolian, volcanogenic, or biogenic sources. In addition, fluxes of siliciclastic, carbonate, and TOC sediment types may dilute the concentration of the others. Multiple lines of evidence should be examined in interpreting relative depth and position within a sequence.

%B Palaeogeography, Palaeoclimatology, Palaeoecology %V 304 %P 54-73 %G eng %U http://dx.doi.org/10.1016/j.palaeo.2010.10.010 %R 10.1016/j.palaeo.2010.10.010 %0 Journal Article %J Geological Society of America Bulletin %D 2004 %T K-bentonites, Volcanic Ash Preservation, and Implications for Lower to Middle Devonian Volcanism in the Acadian Orogen, Eastern North America %A C. A. Ver Straeten %K Acadian Orogeny %K Devonian %K K-bentonites %K marine processes %K Preservation %X

Lower to Middle Devonian marine strata in the Appalachian foreland basin feature up to 80 or more thin K-bentonites that represent ancient volcanic ashes. The time vs. space distribution of K-bentonites through the Lochkovian to Eifelian Stages (representing ∼30 m.y.) shows a distinct pattern of clustered multiple beds, several scattered beds, and thick intervals with no K-bentonites. Four clusters of 7 to 15 individual, closely spaced layers occur in the middle Lochkovian (Bald Hill K-bentonites, Kalkberg–New Scotland Formations), late Pragian or early Emsian (Sprout Brook K-bentonites, Esopus Formation) and early Eifelian (two clusters, the Tioga middle coarse zone and Tioga A–G K-bentonites, Onondaga Formation).

Detailed examination of these Devonian K-bentonites shows that in many cases they do not represent a single eruption. Multilayered beds, fossil layers within beds, authigenic minerals (e.g., glauconite and phosphate nodules), subjacent hardgrounds, and an irregular distribution of beds through space and time raise questions about the depositional history and preservation potential of volcanic ash in marine environments and the degree to which the beds represent a primary record of volcanism. These and other lines of evidence indicate that postdepositional physical, biological, and geochemical processes (e.g., sedimentation rate, event, and background physical processes, burrowing) have modified the primary record of these water-laid ash-fall events. These factors may lead to preservation of primary ash deposits or to their resedimentation and/or partial to complete mixing with background sediments.

The preservation potential, and resulting distribution, of the Devonian K-bentonites can be analyzed across a spectrum of preservational magnafacies. In this paper I present a model of ash preservation; the model incorporates environmentally related physical, biological, and chemical processes active in epicontinental seas and marine foreland basins. Conclusions based on the model indicate that the middle Lochkovian, early Emsian, and early Eifelian were times of peak volcanic activity in eastern North America, related to times of increased tectonism in the Acadian orogen.

%B Geological Society of America Bulletin %V 116 %P 474-489 %G eng %U http://gsabulletin.gsapubs.org/content/116/3-4/474.short %R 10.1130/B25244.1