The ups and downs ofDiplocraterionin the Glen Rose Formation (Lower Cretaceous), Dinosaur Valley State Park, Texas (USA)

Abstract

Diplocraterion, a U-shaped burrow attributed to infaunal invertebrates, is normally a shallow-marine trace fossil and not part of a continental vertebrate ichnoassemblage. Hence, the Glen Rose Formation (Aptian-Albian) of Texas (USA) presents an opportunity to study Diplocraterion associated with a world-class dinosaur tracksite. Most Diplocraterion are in a bioclastic wackestone-packstone bed just above the Taylor Tracklayer, a significant dinosaur track horizon. Diplocraterion are consistently sized, but with variable depths; most have protrusive spreiten and northeast-southwest trends. Smaller Arenicolites co-occur with Diplocraterion, and other trace fossils include Rhizocorallium and a large theropod trackway. Based on our analysis, a sea-level rise buried the Taylor Tracklayer, with a shallow-marine carbonate mud colonised by Diplocraterion and Arenicolites tracemakers. Protrusive Diplocraterion, eroded burrow tops, Rhizocorallium, and other criteria point towards firming and net erosion of the bed caused by a stillstand. The depositional environment of the Diplocraterion bed was possibly a subtidal lagoon that covered shoreward sediments impacted by large theropods. Burrow orientations suggest bidirectional currents consistent with trends of theropod trackways, implying each were controlled by a shoreline. The results of our study demonstrate how marine invertebrate and continental vertebrate trace fossils can be used together to define fine-scale changes in former carbonate shorelines.

Unconformity generation and the shift from storm‐dominated to tide‐dominated processes in a Jurassic retroarc foreland basin: Insights from ichnology

“…At Glendo and Alcova, the Pine Butte Member represents a tide‐dominated, deltaic system as demonstrated by its more heterolithic, rhythmically bedded deposits and ichnofossil suites that are dominated by Diplocraterion and other traces typical of tidal environments (Figure 3; see Cornish, 1986; Higgs & Higgs, 2015; Mángano & Buatois, 2015; Martin et al, 2015). This transitions upwards into the ripple‐laminated to massive‐bedded Hulett and Lak members, both of which were deposited in physicochemically stressed sabkhas and lagoons with limited ichnological diversity aside from bivalve resting traces ( Lockeia ) and limited, surface traces such as Gyrochorte (see Johnson, 1992).…”