ENVIRONMENT OF DEPOSITION AND CHARACTER OF SHELL HASHES AT TWO SECTIONS IN THE UPPER MOUNT MARION FORMATION (HAMILTON GROUP) IN EASTERN NEW YORK STATE

Mucrospirifer mucronatus is a late Middle Devonian spiriferid brachiopod that makes up the majority of bioclasts in shell hashes in the coarser intervals of the upper part of the Mount Marion Formation (Hamilton Group) in eastern New York. The goal of this project is to a) document the sedimentology of the sections in order to interpret the depositional environment and b) describe changes in the character of shell hashes through the interval to better understand what drove their composition.

We measured and described two sections in Albany County. The eastern section is proximal to the fourth-order sequence boundary in the upper part of the Mount Marion Formation. The section 12.5km to the northwest occurs higher up, near the third order contact with the overlying Panther Mountain Formation. Both sections are composed of a few small-scale shallowing-upward cycles.

Silty mudstone packages (1-5m thick) at both sections are heavily bioturbated with few macrofossils except for rare, 2-6cm thick layers that contain a low diversity brachiopod fauna. Each mudstone package is capped by a 10-15cm thick, bioturbated, silty sandstone bed containing abundant bioclasts. Brachiopod shells are not preferentially oriented in a convex up position, and most are disarticulated. At both sections, Mucrospirifer makes up nearly monospecific accumulations near the base with the addition of bivalves and a higher diversity of brachiopods up-section.

The relatively coarse grain size and intense bioturbation suggest that deposition occurred at shallow depths. Disarticulation of brachiopod shells requires high energy, so depth must have been at least above storm wave base, and a lack of evidence for winnowing may be explained by high sedimentation rates. Herringbone cross-beds found at the western section indicate that deposition was well above fair-weather wave base there.

A low abundance and diversity of the epifaunal benthic fauna in the mudstone packages can be explained by high sedimentation rates, which inhibit opportunities for colonization, or by the presence of inhospitable environmental conditions such as a soft and/or mobile substrate. The sandstone beds, which contain a much higher concentration of bioclasts, may therefore represent lower sedimentation rates or a shift to more favorable environmental conditions, or both.

Session No. 36

T15. Improvements to our Understanding of Past Climate and Environments through the Development of Proxies, the Generation of New Biomarker Records, and the Interpretation of Sedimentary Archives

Tuesday, 19 March 2024: 8:00 AM-12:00 PM

Contoocook Room (Doubletree by Hilton)

Geological Society of America Abstracts with Programs. Vol. 56, No. 1
doi: 10.1130/abs/2024NE-397699

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