Paper No. 50-7
Presentation Time: 8:00 AM-12:00 PM
PHOTOGRAMETRIC ANALYSES OF: (1) CROSS-CUTTING RELATIONSHIPS BETWEEN EUBRONTES TRACKS AND BEDDING, AND (2) MORPHOLOGIES OF UNIDENTIFIED TRACE FOSSILS AT DINOSAUR STATE PARK, CT
We report ongoing analyses of mm-resolution 3D point-cloud models and associated representations (height maps, DEM’s, orthoimagery) of trace fossils at Dinosaur State Park in Rocky Hill, CT. All models were produced using digital photogrammetry (primarily Agisoft Photoscan) based on dozens-to-hundreds of overlapping full-frame images that include ≈10-30 laser-surveyed ground control points. We consider two puzzling aspects of the well-known DSP tracksite. First, we examine cross-cutting relationships between selected Eubrontes tracks on 3 vertically adjacent fine to coarse-grained sandstone beds that contain >500 Eubrontes tracks. Deepest and oldest bed 0, exposed in the northern third of the tracksite, contains numerous symmetrical ripples. Overlying bed 1, accounting for ≈60% of the tracksite, is finer-grained, lacks ripples, but contains sedimentary evidence of desiccation. Remnants of uppermost bed 2 are present as discontinuous slabs of sandstone with ripples that fill depressions in bed 1. We extract point-cloud models for trackways made by individual dinosaurs that traversed all 3 bedding surfaces as well more detailed models of isolated tracks that cross-cut 2 or more bedding surfaces. While distinguishing whether a track formed before, during, or after a bed was deposited is complex, our models and field observations indicate that some trackways have tracks that clearly disrupt (i.e. cross-cut) ripples on one bedding surface, deform but do not disrupt bedding on lower beds, and/or contain sedimentary drape structures within overlying beds. We are assessing whether these observations enable us to determine the bed upon which trackways were made so as to estimate trackmaker populations. Secondly, we use point cloud data to describe geometric characteristics of 2 sets of trace fossils that have not been described previously at DSP. This includes: (a) aligned segmented traces ≈2.5 m long of alternating curved depressions (≈6-15 cm long, 3-7 cm wide, up to 5 cm deep) with raised rims that are of unknown origin, and (b) 6 occurrences of 0.5 to 2 m long curved indentations, often with double impressions, that may be tail drag traces, but have unusual geometric characteristics that are difficult to explain. We present models and hypotheses for the origin of these traces for discussion.