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Reconstructing the environmental conditions that supported early life on Earth relies on 32 well-preserved geochemical archives in the rock record. However, many geochemical tracers 33 either lack specificity or they are affected by post-depositional alteration. We present a data 34 set of major and trace element abundances and Cd isotope compositions of dome-shaped 35 and conophyton-type stromatolites of the Late Mesoproterozoic Paranoá Group (Brazil), 36 showing distinct values with unprecedented resolution at the lamina scale. 37 The studied stromatolites consist of dolomite with a high purity and a negligible content of 38 immobile elements (e.g., < 0.66 ppm Zr), indicating that elemental compositions are not 39 influenced by detrital contamination. Even though the carbonates have experienced different 40 extent of recrystallization, the measured elemental and isotopic compositions do not 41 correlate with fluid mobile elements. The stromatolites thus represent prime archives for 42 geochemical proxies to reconstruct paleo-environmental conditions. 43 Two endmember compositions can be distinguished by multiple proxy analysis, reflecting 44 the contrasting depositional environments of the two types of stromatolites: Shale-normalized 45 rare earth elements including yttrium (REY SN) patterns of domal stromatolites show a light 46 REY SN (LREY) enrichment (Yb SN /Pr SN < 0.84), slightly super-chondritic Y/Ho ratios (33.6-47 39.3) and unfractionated Cd isotopes relative to upper continental crust. This indicates that 48 the stromatolites formed in a shallow-water environment that was episodically influenced by 49 seawater. Their REY and Cd compositions are dominated by dissolved elements that were 50 delivered via weathering and erosion processes from the ambient continent. 51 In contrast, REY SN patterns of the conophyta are parallel those of modern seawater with 52 an LREY SN depletion relative to HREY SN (Yb SN /Pr SN = 2.1 to 3.9), positive Gd SN anomalies 53 (1.1 to 1.4) and strong super-chondritic Y/Ho ratios (37.9 to 46.2), suggesting a microbial 54 habitat that was dominated by seawater. Cd isotopes correlate negatively with Cd and U, but 55 positively with Mn and Ce concentrations, reflecting authigenic carbonate formation at 56 different depths within a redox gradient of the ancient microbial mat. ε 112/110 Cd dol values 57 increase from-3.52 at the mat surface to +3.46 in the interior of the mat, due to the effect of 58 kinetic fractionation during Cd-uptake, e.g. by adsorption onto organic matter or by 59 precipitation of sulfides, in addition to incorporation into carbonate minerals. Hence, our 60 multi-proxy approach including Cd isotopes bears a high potential to shed light on 61 environmental conditions in ancient microbial habitats and the activity of microbial life on 62 Early Earth.

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