CARBONATE ACCUMULATION IN THE NEW HAVEN ARKOSE (NEWARK SUPERGROUP, HARTFORD BASIN)

The New Haven Arkose is the lowermost sedimentary unit in the Hartford Basin (Newark Supergroup). It is interpreted as fluvial sediments consisting of sheet sand and mud complexes deposited in episodic high-energy flows exceeding bankfull capacity. New data from associated paleosols indicate precipitation as high as 123 cm per year. One outcrop, in Meriden, CT, contains decimeter-thick, carbonate-rich mudstone/sandstone contacts. We examine the calcite cement stratigraphy within one contact as well as its sedimentologic relationships to test whether an interpretation of pedogenic calcrete is appropriate. Long vertical tapering features in the overlying sandstone, interpreted as taproots, contain calcite separating fragments of brecciated grains. The uppermost, underlying mudstone contains a decimeter-thick, carbonate-rich brecciated fabric with associated gleyed veins and tubules filled with calcite. Based on similar calcite cements associated with tubules (rhizoliths) in the mudstone and overlying sandstone taproot, we interpret the cements to be of groundwater origin instead. Six generations of calcite cement (G1 – G6) in the mudstone are also observed in the taproot sandstone. The three earliest calcite generations (G1 – G3) explode apart grains in the taproot and separate ‘clods’ of the uppermost mudstone. Although two generations of sparry calcite (G1 and G2) appear to predate it, G3 micrite is also associated with clast fragmentation. In the taproots, sand grains are surrounded by sparry calcite G1 and G2 and float in G3 micrite cement. In sandstone away from the taproot, massive micrite cements with floating grains are pervasive and G1 and G2 are not observed. This G3 cement is cut by rhizoliths, defined by alveolar septal structures, in the taproots and mudstone. G1-G3 are interpreted to form very early from groundwater, just following deposition. Rhizoliths in the mudstone are filled with later sparry calcite (G4) that is entirely non-luminescent. In the sandstone, a very thin G4 cement is non-luminescent with G5 bright orange luminescent cement. These generations are interpreted to have formed later, but prior to burial. Brightly luminescent cement (G6) cuts and replaces former cement generations in the mudstone, replaces some grains in the sandstone, and is interpreted to have formed after lithification.