Abiogenic aragonite crystal habit – Novel archive of precipitation environment?

Marine calcite cement's crystal habit is often considered a function of the fluid Mg/Ca ratio. In contrast, marine aragonite fabrics are commonly described as acicular (needle) cement with pointed terminations and width-to-length ratios in the order of 1:10. Similarly, botryoidal or spherulitic aragonite cements are well-known from Mesozoic (and older) reefal and slope depositional environments but are less common in Recent depositional environments. Here, we explore a wide range of abiogenic aragonite cement habits (morphologies) in caves and coastal marine depositional environments. We propose that the cement habit represents a novel (and underexplored) archive of diagenetic environment, fluid chemistry and precipitation kinetics. Based on SEM imaging, we find the often-described acicular and fibrous fabrics but also a plethora of less well-known morphotypes such as columnar (often pseudo-hexagonal prisms) and lath, tabular and sheet-like (prismatic single crystals) forms. Twinning of (flat) needle aragonite is observed and might point to precursor phases. Based on the data available, the common needle-type aragonite cement typifies normal marine diagenetic (porewater) environments. Increasingly complex habits (polysynthetic twins, flat needles, pseudo-prismatic and prismatic sheet-like) aragonite crystals) are present under increasing levels of restriction and precipitate from high-salinity porewaters. Intriguingly, pseudo-prismatic aragonite crystals are also present in meteoric, gravity-defying cave carbonates, specifically helictites. Aragonite cement habits are documented and placed into context with their depositional and diagenetic environment, and preliminary interpretations are presented.