Trioctahedral smectite and regularly interstratified chlorite/smectite in strata of the East Berlin Formation of the Connecticut Valley are largely restricted to black shale and gray mudstone deposited in alkaline, perennial lakes. The precursor of the mixed-layer clay appears to have been a smectite. Alkaline lake waters and inherited pore waters rich in magnesium favored the transformation of smectite to mixed-layer chlorite/smectite by fixation of brucitic interlayers into the smectite unit structure. Gray mudstones containing the mixed-layer chlorite/smectite are invariably underlain by magnesium-rich black shale—a possible source of Mg for the clay mineral transformations. The black shale is composed predominantly of Mg-rich trioctahedral smectite of probable authigenic origin.

Zeolites having the structures of phillipsite, merlinoite, and gobbinsite were synthesized from clear solutions at 80°C in the system Na2O-K2O-Al2O3-SiO2-H2O and their morphologies, cell parameters, and compositions determined. At 3.5 M silica concentration, the formation of merlinoite (synthetic zeolite W) is favored over the formation of phillipsite (synthetic zeolite ZK-19) by solution conditions of high pH (> 13.6) and low Na/(Na + K) ratios (<0.5).

Using the information obtained from the synthesis experiments, the presence of merlinoite was predicted in sediments from Searles Lake, a saline, alkaline lake in California with ideal physiochemical conditions for its formation. Merlinoite was subsequently discovered to occur in tuffaceous sediments as part of an authigenic silicate zonation pattern from phillipsite → phillipsite + merlinoite → merlinoite → K-feldspar with increasing depth. Because of the close similarities in the physical properties of phillipsite and merlinoite, merlinoite may be much more common as an authigenic mineral than is currently realized.

We present a continuous, sediment core-based record of paleohydroclimate spanning ~5800 cal yr BP to recent from Lower Pahranagat Lake (LPAH), a shallow, alkaline lake in southern Nevada. We apply stable isotopes (δ18O and δ13C) from fine-fraction authigenic carbonate, which are sensitive recorders of hydroclimatic variability in this highly evaporative region. Additional geochemical proxies (total organic carbon, C/N, and total inorganic carbon) provide supporting information on paleoecological change in and around the lake. Our data suggest progressively wetter conditions starting at the later part of the middle Holocene and extending into the late Holocene (~5500–3350 cal yr BP) followed by a millennial-scale dry period from ~3150 to 1700 cal yr BP. This latter interval encompasses the ‘Late Holocene dry period’ (LHDP) reported by other investigators, and our data help refine the area affected in this episode. Our data also show evidence for a series of century-scale fluctuations in regional hydroclimate, including wet and dry intervals between 2350 and 1600 cal yr BP, and drier conditions over the past few centuries. Paleohydroclimate trends in the LPAH record show correspondence with those from the central Great Basin to the north, suggesting that both areas were subject to similar climatic forcings.