LATERAL CONTINUITY OF STROMATOLITE LAMINAE: IMPLICATIONS FOR ASSESSING THE DOMINANT SCALES OF CONTROL

Stromatolites are attached, laminated, lithified sedimentary growth structures, and are commonly regarded as Earth’s earliest macroscopic fossils. However, the detailed mechanisms that govern the formation and lithification of stromatolite laminae and overall morphology in the rock record remain obscure. It is relatively common for processes local to the stromatolite to receive the most attention with respect to stromatolite morphogenesis. For example, the involvement of microbes and local conditions that might affect microbial processes (layered microbial communities, nutrient availability, sunlight, currents, substrate, carbonate saturation state, etc.) are most commonly considered important during stromatolite morphogenesis. However, the focus on the local processes may overlook the imprint of larger-scale processes recorded during stromatolite growth. Here, we present a multi-scale approach that can highlight local versus regional (and perhaps even global) scales of control, increasing the utility of stromatolites as environmental indicators and helping to understand the scale of processes responsible for stromatolite morphogenesis.

Building upon the traditional mega-, meso-, and micro-scale analyses (e.g., Shapiro, 2000), we expand the scale of investigation by employing a lateral continuity assessment of fine- to large-scale textures that may allow us to identify the scale of the dominant process(es) that contributed to the morphogenesis of the stromatolites in question. As examples, we investigate Miocene lacustrine stromatolites from the Barstow Formation, and marginal marine stromatolites from the upper Triassic of the southwestern United Kingdom. We focus on laminated and banded examples as they are (1) most representative of deposits found throughout most of Earth history and (2) deposits that are increasingly difficult to reproduce in the laboratory and rarely found lithifying in modern environments, warranting alternate complementary methods of investigation. The addition of the lateral continuity approach demonstrates that certain features are indeed primarily locally controlled, whereas others occur across the depositional system and are therefore responding to larger-scale processes (e.g, climate, environmental change, etc).