Animal-substrate interactions preserved in ancient lagoonal chalk

Area of Science:

• Paleontology
• Sedimentology
• Ichnology

Background:

• Trace fossils are key indicators of benthic paleoenvironmental conditions.
• Previous studies focused on pelagic shelf and deep-sea chalks, neglecting lagoonal chalks.
• Lagoonal environments exhibit dynamic physicochemical parameters influencing benthic life.

Purpose of the Study:

• To conduct the first ichnologic analysis of ancient lagoonal chalk deposits.
• To investigate trace-fossil assemblages in the Upper Cretaceous Buda Formation, Texas.
• To understand the impact of lagoonal circulation on trace-fossil content.

Main Methods:

• Detailed ichnologic analysis of Buda Formation chalk.
• Identification and classification of ichnotaxa.
• Comparison of trace-fossil assemblages with open marine chalks.

Main Results:

• Twenty ichnotaxa identified, dominated by Thalassinoides isp. and Chondrites isp.
• Trace-fossil assemblages show similarities to shallow-water shelf-sea chalks.
• Lagoonal chalk exhibits higher ichnodiversity and ichnodisparity than open marine chalks.

Conclusions:

• Lagoonal chalk trace-fossil content is influenced by variable ocean connectivity and physicochemical fluctuations.
• Dominance of Thalassinoides isp. in both soft and firmgrounds indicates similarities with shallow marine settings.
• Increased ichnodiversity and ichnodisparity in lagoonal chalks result from taphonomic and ecologic factors, including environmental heterogeneity.