Anatomy and origin of authochthonous late Pleistocene forced regression deposits, east Coromandel inner shelf, New Zealand: implications for the development and definition of the regressive systems tract

High-resolution seismic reflection data from the east Coromandel coast, New Zealand, provide details of the sequence stratigraphy beneath an autochthonous, wave dominated inner shelf margin during the late Quaternary (0-140 ka). Since c. 1 Ma, the shelf has experienced limited subsidence and fluvial sediment input, producing a depositional regime characterised by extensive reworking of coastal and shelf sediments during glacio-eustatic sea-level fluctuations. It appears that only one complete fifth-order (c. 100 000 yr) depositional sequence is preserved beneath the inner shelf, the late Pleistocene Waihi Sequence, suggesting any earlier Quaternary sequences were mainly cannibalised into successively younger sequences. The predominantly Holocene-age Whangamata Sequence is also evident in seismic data and modern coastal deposits, and represents an incomplete depositional sequence in its early stages of formation. A prominent aspect of the sequence stratigraphy off parts of the east Coromandel coast is the presence of forced regressive deposits (FRDs) within the regressive systems tract (RST) of the late Pleistocene Waihi Sequence. The FRDs are interpreted to represent regressive barrier-shoreface sands that were sourced from erosion and onshore reworking of underlying Pleistocene sediments during the period of slow falling sea level from isotope stages 5 to 2 (c. 112-18 ka). The RST is volumetrically the most significant depositional component of the Waihi Sequence; the regressive deposits form a 15-20 m thick, sharp-based, tabular seismic unit that downsteps and progrades continuously across the inner shelf. The sequence boundary for the Waihi Sequence is placed at the most prominent, regionally correlative, and chronostratigraphically significant surface, namely an erosional unconformity characterised in many areas by large incised valleys that was generated above the RST. This unconformity is interpreted as a surface of maximum subaerial erosion generated during the last glacial lowstand (c. 18 ka). Although the base of the RST is associated with a prominent regressive surface of erosion, this is not used as the sequence boundary as it is highly diachronous and difficult to identify and correlate where FRDs are not developed. The previous highstand deposits are limited to subaerial barrier deposits preserved behind several modern Holocene barriers along the coast, while the transgressive systems tract is preserved locally as incised-valley fill deposits beneath the regressive surface of erosion at the base of the RST. Many documented late Pleistocene RSTs have been actively sourced from fluvial systems feeding the shelf and building basinward-thickening, often stacked wedges of FRDs, for which the name allochthonous FRDs is suggested. The Waihi Sequence RST is unusual in that it appears to have been sourced predominantly from reworking of underlying shelf sediments, and thus represents an autochthonous FRD. Autochthonous FRDs are also present on the Forster-Tuncurry shelf in southeast Australia, and may be a common feature in other shelf settings with low subsidence and low sediment supply rates, provided shelf gradients are not too steep, and an underlying source of unconsolidated shelf sediments is available to source FRDs. The preservation potential of such autochthonous FRDs in ancient deposits is probably low given that they are likely to be cannibalised during subsequent sea-level falls

Formation of Mangala Valles outflow channel, Mars: morphological development and water discharge and duration estimates.

The morphology of features on the floor of the Mangala Valles suggests that the channel system was not bank‐full for most of the duration of its formation by water being released from its source, the Mangala Fossa graben. For an estimated typical 50 m water depth, local slopes of sin α = ∼0.002 imply a discharge of ∼1 × 107 m3 s−1, a water flow speed of ∼9 m s−1, and a subcritical Froude number of ∼0.7–0.8. For a range of published estimates of the volume of material eroded from the channel system this implies a duration of ∼17 days if the sediment carrying capacity of the ∼15,000 km3 of water involved had been 40% by volume. If the sediment load had been 20% by volume, the duration would have been ∼46 days and the water volume required would have been ∼40,000 km3. Implied bed erosion rates lie in the range ∼1 to ∼12 m/day. If the system had been bank‐full during the early stages of channel development the discharge could have been up to ∼108 m3 s−1, with flow speeds of ∼15 m s−1 and a subcritical Froude number of ∼0.4–0.5

Formation of Mangala Fossa, the source of the Mangala Valles, Mars : Morphological development as a result of volcano-cryosphere interactions.

The morphology of the Mangala Fossa graben forming the source of the Mangala Valles implies that two episodes of graben subsidence took place, each induced by lateral dike intrusion from Arsia Mons. Quantitative modeling suggests that graben boundary faults breaching the cryosphere provided pathways for water release from an underlying aquifer at a peak rate of ∼107 m3 s−1. In the first event, the graben subsided by ∼200 m, and water carrying a thin ice layer filled the graben, overflowing after ∼2.5 hours, mainly at a low point on the north rim. This captured the water flux, eroding a gap in the north wall which, with an erosion rate of ∼100 μm s−1 and a duration of ∼1 month, was ∼250 m deep by the end of water release. Erosion of the graben floor also took place, at ∼20 μm s−1, lowering it by ∼50 m. Subsequently, heat from the cooling dike melted cryosphere ice, causing a further ∼150 m of subsidence on compaction. In the second event, with a similar duration and peak discharge, the graben again subsided by ∼200 m and filled with ice‐covered water until overflow through the gap began at a water depth of ∼350 m. The gap was eroded down by a further ∼400 m, and the floor was eroded by a further ∼50 m. Finally, heat from the second dike sublimed cryosphere ice, lowering the floor by ∼100 m. In places, combined erosion and subsidence of the graben floor exposed ∼200 m of the first dike

Gathering pipeline methane emissions in Fayetteville shale pipelines and scoping guidelines for future pipeline measurement campaigns

Gathering pipelines, which transport gas from well pads to downstream processing, are a sector of the natural gas supply chain for which little measured methane emissions data are available. This study performed leak detection and measurement on 96 km of gathering pipeline and the associated 56 pigging facilities and 39 block valves. The study found one underground leak accounting for 83% (4.0 kg CH4/hr) of total measured emissions. Methane emissions for the 4684 km of gathering pipeline in the study area were estimated at 402 kg CH4/hr [95 to 1065 kg CH4/hr, 95% CI], or 1% [0.2% to 2.6%] of all methane emissions measured during a prior aircraft study of the same area. Emissions estimated by this study fall within the uncertainty range of emissions estimated using emission factors from EPA’s 2015 Greenhouse Inventory and study activity estimates. While EPA’s current inventory is based upon emission factors from distribution mains measured in the 1990s, this study indicates that using emission factors from more recent distribution studies could significantly underestimate emissions from gathering pipelines. To guide broader studies of pipeline emissions, we also estimate the fraction of the pipeline length within a basin that must be measured to constrain uncertainty of pipeline emissions estimates to within 1% of total basin emissions. The study provides both substantial insight into the mix of emission sources and guidance for future gathering pipeline studies, but since measurements were made in a single basin, the results are not sufficiently representative to provide methane emission factors at the regional or national level

Dataset associated with "Temporal variability largely explains difference in top-down and bottom-up estimates of methane emissions from a natural gas production region"

This dataset includes input and output data used in the bottom-up model described in the associated manuscript and accompanying Supplemental Information Appendix. Additionally, the input dataset includes a ReadMe.txt describing it, and each of the output datasets includes a ReadMe.txt and a FileListing.txt describing their contents.This study is the first to spatially and temporally align top-down and bottom-up methane emission estimates for a natural gas production basin, using multi-scale emission measurements and detailed activity data reporting. We show that episodic venting from manual liquid unloadings, which occur at a small fraction of natural gas well pads, drives a factor-of-two temporal variation in the basin-scale emission rate of a US dry shale gas play. The mid-afternoon peak emission rate aligns with the sampling time of all regional aircraft emission studies, which target well-mixed boundary layer conditions present in the afternoon. A mechanistic understanding of emission estimates derived from various methods is critical for unbiased emission verification and effective GHG emission mitigation. Our results demonstrate that direct comparison of emission estimates from methods covering widely different time scales can be misleading

Reply to the comments of W. Helland-Hansen on “Towards the standardization of sequence stratigraphy” by Catuneanu et al. [\u3ci\u3eEarth-Sciences Review\u3c/i\u3e 92 (2009), pp. 1–33]

We thank William Helland-Hansen for his compliments and feedback on our paper. We aimed to establish a consensus in sequence stratigraphy by using a neutral approach that focused on model-independent, fundamental concepts, because these are the ones common to various approaches. This search for common ground is what we meant by “standardization,” not the imposition of a strict, inflexible set of rules for the placement of sequence- stratigraphic surfaces. Our work is meant to eliminate the present state of methodological and nomenclatural confusion within sequence stratigraphy, which is largely the result of uncoordinated effort in the development of the method and the proliferation of terminology that is unnecessarily complex. [...] The flexibility afforded by a “standard” model-independent workflow that lays emphasis on stratal stacking patterns (genetic units) and bounding surfaces in the rock record, rather than on the selection of any particular boundary-dependent model, eliminates the need for any predefined templates. As such, the practitioner should no longer feel the need to fulfill the predictions of any particular model. Each case study is different, and the sequence stratigraphic organization of the rock record varies greatly with the tectonic and depositional setting. The types of data available for analysis, as well as the scale of observation, also make a difference to what can be interpreted from the rock record. This immense variability underlines the value of defining a model-independent workflow. In spite of this variability, however, there are common elements between all stratigraphic sequences in the rock record, no matter how they are defined: they are all the product of changes in accommodation (whether fluvial or marine) or sediment supply and they all consist of a combination of the same basic “building blocks” (i.e., “conventional” or “unconventional” systems tracts). The identification of these “building blocks,” without any expectations in terms of model predictions and templates, provides the key to the universal application of sequence stratigraphy